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Author name code: veronig
ADS astronomy entries on 2022-09-14
author:"Veronig, Astrid M."

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Title: Plasma Heating and Nanoflare Caused by Slow-mode Wave in a
    Coronal Loop
Authors: Xia, Fanxiaoyu; Wang, Tongjiang; Su, Yang; Zhao, Jie; Zhang,
   Qingmin; Veronig, Astrid M.; Gan, Weiqun
2022ApJ...936L..13X    Altcode: 2022arXiv220810029X
  We present a detailed analysis of a reflecting intensity perturbation in
  a large coronal loop that appeared as a sloshing oscillation and lasted
  for at least one and a half periods. The perturbation is initiated by
  a microflare at one footpoint of the loop, propagates along the loop,
  and is eventually reflected at the remote footpoint where significant
  brightenings are observed in all of the Atmospheric Imaging Assembly
  extreme-ultraviolet channels. This unique observation provides
  us with the opportunity to better understand not only the thermal
  properties and damping mechanisms of the sloshing oscillation but also
  the energy transfer at the remote footpoint. Based on differential
  emission measures analysis and the technique of coronal seismology,
  we find that (1) the calculated local sound speed is consistent
  with the observed propagation speed of the perturbation during the
  oscillation, which is suggestive of a slow magnetoacoustic wave;
  (2) thermal conduction is the major damping mechanism of the wave
  but an additional damping mechanism such as anomalous enhancement of
  compressive viscosity or wave leakage is also required to account
  for the rapid decay of the observed waves; (3) the wave produced
  a nanoflare at the remote footpoint, with a peak thermal energy of
  ~10<SUP>24</SUP>-10<SUP>25</SUP> erg. This work provides a consistent
  picture of the magnetoacoustic wave propagation and reflection in a
  coronal loop, and reports the first solid evidence of a wave-induced
  nanoflare. The results reveal new clues for further simulation studies
  and may help with solving the coronal heating problem.

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Title: Detecting stellar CMEs through post-flare coronal dimmings
Authors: Veronig, Astrid; Hudson, Hugh S.; Odert, Petra; Leitzinger,
   Martin; Dissauer, Karin; Fleck, Nikolaus
2022cosp...44.1379V    Altcode:
  Coronal dimmings are sudden decreases of the solar EUV and X-ray
  emission caused by coronal mass ejections (CMEs). Dimming regions map to
  the bipolar ends of closed magnetic field lines that become stretched
  or temporarily opened during an eruption, and are a result of the
  depletion of coronal plasma caused by the expansion and mass loss due
  to the CME. Recently available multi-point imagery from satellites at
  different locations in the heliosphere provided us with unprecedented
  observations of the three-dimensional evolution of solar CMEs and their
  coronal dimmings. These studies showed distinct correlations between CME
  mass and speed with key parameters of the associated coronal dimmings
  such as their spatial extent and intensity drop. While CMEs from our
  Sun are regularly imaged by white-light coronagraphs, and their speeds
  and masses are derived from these observations, for stars such direct
  imaging is not possible. Here, we present a new approach to detect
  stellar mass ejections through post-flare coronal dimmings. To this
  aim, we study Sun-as-a-star broad-band EUV light curves derived from
  SDO's Extreme ultraviolet Variability Experiment (EVE) as a testbed
  to investigate whether coronal dimmings can be also observed on stars
  and used for stellar CME detection. We demonstrate that large eruptive
  flares are with a high probability associated with a post-flare coronal
  dimming, with intensity drops in the 15-25 nm full-Sun light curves
  up to 5%. Searching for similar patterns of post-flare dimmings in
  the X-ray and EUV light curves of solar-like and late-type stars,
  we identify 21 stellar CME candidates. The derived intensity drops
  are an order of magnitude larger than for the Sun, suggesting that a
  substantial part of the stellar corona gets ejected by the CME. This
  study is published in: A.M. Veronig, P. Odert, M. Leitzinger,
  K. Dissauer, N. Fleck, H.S. Hudson, Indications of stellar coronal
  mass ejections through coronal dimmings, Nature Astronomy 5, 697-706
  (2021). https://www.nature.com/articles/s41550-021-01345-9

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Title: First analyses of SEP events with PSP &amp; Solar Orbiter
Authors: Dresing, Nina; Droege, Wolfgang; Warmuth, Alexander; Cohen,
   Christina; Lario, David; Kartavykh, Yulia; Klassen, Andreas; Krupar,
   Vratislav; Kouloumvakos, Athanasios; Kilpua, Emilia; Lee, Christina
   O.; Gieseler, Jan; Gomez-Herrero, Raul; Podladchikova, Tatiana;
   Heber, Bernd; Pomoell, Jens; Mason, Glenn M.; Veronig, Astrid;
   Wimmer-Schweingruber, Robert; Vainio, Rami; Rodriguez-Pacheco, Javier;
   Pacheco, Daniel; Asvestari, Eleanna; Wijsen, Nicolas; Sanchez-Cano,
   Beatriz; Jebaraj, Immanuel; Oleynik, Philipp; Carcaboso, Fernando;
   Xu, Zigong; Rodríguez-García, Laura; Palmroos, Christian; Balmaceda,
   Laura
2022cosp...44.1519D    Altcode:
  Since the launch of Parker Solar Probe (PSP) and Solar Orbiter
  (SolO) during the recent solar minimum, the Sun has woken up and
  has delivered numerous interesting solar energetic particle (SEP)
  events. In combination with close-to-Earth observatories, STEREO-A,
  BepiColombo, and MAVEN, we possess not only novel and state-of-the-art
  particle measurements but also unprecedented multi-spacecraft
  constellations providing new opportunities to study SEP events. Well
  separated spacecraft that cover a large range in heliolongitudes
  and radial distances provide excellent observations of widespread
  SEP events, such as the 17 April 2021 event, allowing us to tackle
  the long-standing problem of disentangling source and transport
  effects. Other constellations such as radial or Parker spiral magnetic
  field alignments, or closely spaced observers help us to understand
  local effects and how the interplanetary medium influences particle
  transport. We present an overview of recent SEP analyses that employ
  PSP and SolO with a focus on the power of multi-spacecraft studies. We
  discuss open issues such as the role of CME-driven shocks and the
  interplanetary medium in shaping the SEP observations, as well as the
  synergy of SEP transport modeling with multipoint measurements. This
  research has received funding from the European Union's Horizon 2020
  research and innovation programme under grant agreement No 101004159
  (SERPENTINE).

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Title: Hard X-ray solar flare observed by Solar Orbiter/STIX
    associated with escaping electron beams
Authors: Battaglia, Andrea Francesco; Warmuth, Alexander; Krucker,
   Samuel; Gary, Dale; Veronig, Astrid; Purkhart, Stefan; Saqri, Jonas;
   Collier, Hannah; Wang, Wen
2022cosp...44.1542B    Altcode:
  Dramatic changes of the magnetic field configuration in the solar
  corona may reduce the magnetic energy in favor of the kinetic energy
  of high-energy particles. Such a phenomenon, known as magnetic
  reconnection, can lead to solar eruptions in the form of flares and
  coronal mass ejections. On the one hand, the accelerated particles heat
  the ambient plasma to temperatures of the order of tens of MK, while,
  on the other hand, particles can escape along open magnetic field lines
  into the heliosphere. Combining remote sensing and in-situ observations
  closer to the Sun, Solar Orbiter is able to study the acceleration
  region, the escape and the transport of solar energetic particles into
  the heliosphere. We analyze images obtained with remote-sensing hard
  X-ray observations by Solar Orbiter/STIX (Spectrometer/Telescope
  for Imaging X-rays) to investigate the acceleration region and
  escape of electron beams detected with in-situ measurements in the
  heliosphere. The prompt electron events show temporal correlation
  with the hard X-ray nonthermal emissions observed by STIX, favoring
  the idea of eruptive solar flares at the origin of the beams under
  investigation. For the SOL2021-08-26 event, the presence of accelerated
  electrons is further confirmed by the synchrotron emission measured
  by the EOVSA (Expanded Owens Valley Solar Array), which originate from
  electrons being accelerated along magnetic field lines.

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Title: Coronal dimmings as indicators of the CME evolution close to
    the Sun
Authors: Chikunova, Galina; Podladchikova, Tatiana; Veronig, Astrid;
   Dissauer, Karin
2022cosp...44.1141C    Altcode:
  Coronal dimmings are regions in the solar corona that represent a sudden
  decrease of the coronal EUV and SXR emission, which is interpreted
  as a density depletion caused by the evacuation of plasma due to the
  CME eruption. Distinct relations have been established between coronal
  dimming (intensity, area, magnetic flux) and key characteristics (mass,
  speed) of the associated CMEs by combining coronal and coronagraphic
  observations from different viewpoints in the heliosphere (Dissauer et
  al. 2019, Chikunova et al. 2020). In this contribution, we study whether
  coronal dimmings can be used to indicate possible deflections of CMEs
  close to the Sun and to identify their propagation direction. We present
  a set of detailed case studies where, by using simultaneous observations
  from the SDO and STEREO satellites, we track both the evolution of
  the coronal dimmings and the CME properties with respect to their
  directions. Our findings suggest that the direction of growth of the
  coronal dimming region and the evolution of the dimming intensity are
  related to the initial direction of the CME and also reflect various
  changes in its evolution, indicating deflection and/or interaction
  with surrounding active regions. These findings are important in
  better constraining CME evolution and direction close to the Sun and
  its further connection toward interplanetary space.

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Title: Magnetic helicity and energy budget around large confined
    and eruptive solar flares
Authors: Gupta, Manu; Veronig, Astrid; Thalmann, Julia K.
2022cosp...44.2424G    Altcode:
  In order to better understand the underlying process and prerequisites
  for solar activity, it is essential to study the time evolution of
  the coronal magnetic field of solar active regions (ARs), which is
  associated to flare activity and leads to large coronal mass ejections
  (CMEs). We investigate the coronal magnetic energy and helicity budgets
  of ten solar ARs around the times of large flares. In particular,
  we are interested in a possible relation of the derived quantities
  to the particular type of flares that the AR produces, i.e., whether
  they are associated with a CME or are confined. Using an optimization
  approach, we employed time series of 3D nonlinear force-free magnetic
  field models for each target AR, covering a time span of several hours
  around the time of occurrence of large solar flares (GOES class M1.0
  and larger). We subsequently computed the 3D magnetic vector potentials
  associated to the model 3D coronal magnetic field using a finite-volume
  method. This allows us to correspondingly compute the coronal magnetic
  energy and helicity budgets (so-called extensive quantities), as well as
  related intensive proxies, such as the relative contribution of free
  magnetic energy (the energy ratio), the fraction of non-potential
  (current-carrying) helicity, and the normalized current-carrying
  helicity. The extensive quantities of flare-productive ARs cover a
  broad range of magnitudes, with no apparent relation to the potential
  of an AR to produce a CME-associated flare. In contrast, we find
  the intensive proxies (the energy ratio, the helicity ratio, and
  the normalized current-carrying helicity) to be distinctly different
  for ARs that produce CME-associated large flares compared to those
  which produce confined flares. Thus, for the majority of ARs in our
  sample, characteristic pre-flare levels of the intensive proxies allow
  statements regarding the likelihood of subsequent CME-productivity.

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Title: Determination of CME orientation and consequences for their
    propagation
Authors: Martinic, Karmen; Vrsnak, Bojan; Veronig, Astrid; Dumbovic,
   Mateja; Temmer, Manuela
2022cosp...44.2441M    Altcode:
  The configuration of the interplanetary magnetic field and features
  of the related ambient solar wind in the ecliptic and meridional
  plane are different. Therefore, one can expect that the orientation
  of the flux rope axis of a coronal mass ejection (CME) influences
  the propagation of the CME itself. However, the determination of the
  CME's orientation remains a challenging task to perform. This study
  aims to provide a reference to different CME orientation determination
  methods in the near-Sun environment. Also, it aims to investigate the
  non-radial flow in the sheath region of the interplanetary CME (ICME)
  in order to provide the first proxy to relate the ICME orientation
  with its propagation. We investigated 22 isolated CME-ICME events
  in the period 2008-2015. We first determined the CME orientation in
  the near-Sun environment using a 3D reconstruction of the CME with
  the graduated cylindrical shell (GCS) model applied to coronagraphic
  images provided by the STEREO and SOHO missions. The CME orientation
  in the near-Sun environment was determined using an ellipse fitting
  technique to the CME outer front as determined from the SOHO/LASCO
  coronagraph. In the near-Earth environment, we obtained the orientation
  of the corresponding ICME using in-situ plasma and field data and also
  investigated the non-radial flow in its sheath region. The ability of
  GCS and ellipse fitting to determine the CME orientation is found to be
  limited to reliably distinguish only between the high or low inclination
  of the events. Most of the CME-ICME pairs under investigation were
  found to be characterized by a low inclination. The majority of
  CME-ICME pairs have a consistent estimation of tilt from remote and
  in situ data. The observed non-radial flows in the sheath region show
  a greater y-direction to z-direction flow ratio for high-inclination
  events indicating that CME orientation could have an impact to the
  CME propagation.

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Title: Development and evaluation of Drag-Based Ensemble Model (DBEM)
Authors: Čalogović, Jaša; Vrsnak, Bojan; Veronig, Astrid; Dumbovic,
   Mateja; Temmer, Manuela
2022cosp...44.3443C    Altcode:
  The Drag-based Model (DBM) is a well-known 2D analytical model for
  simulating the heliospheric propagation of Coronal Mass Ejections
  (CMEs). Main output is the prediction of the CME arrival time and
  speed at Earth or any other given target in the solar system. Due to a
  very short computational time of DBM (&lt; 0.01s), the probabilistic
  Drag-Based Ensemble Model (DBEM) was developed by making an ensemble
  of n different input parameters to account for possible variability
  (uncertainties) in the input parameters. Using such an approach
  to obtain the distribution and significance of the DBM results,
  the DBEM determines the CME hit chance, most probable arrival times
  and speeds, quantifies the prediction uncertainties and calculates
  the confidence intervals. As an important tool for space weather
  forecasters, the fully operational DBM/DBEM web application is
  integrated as one of the ESA Space Situational Awareness portal services
  (https://swe.ssa.esa.int/current-space-weather). In the last few years,
  DBM/DBEM has been constantly improved with various new features such as
  Graduated Cylindrical Shell (GCS) option for the CME geometry input,
  the CME propagation visualizations as well as a new DBEM version
  employing the variable solar wind speeds. The model development,
  new features and the corresponding model evaluations will be presented.

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Title: Energy and impulsive CME dynamics in an eruptive B9 flare
Authors: Saqri, Jonas; Warmuth, Alexander; Podladchikova, Tatiana;
   Veronig, Astrid; Krucker, Samuel; Dickson, Ewan; Battaglia, Andrea
   Francesco; Dissauer, Karin
2022cosp...44.1509S    Altcode:
  Solar flares are the impulsive release of magnetic energy giving rise
  to a wide range of phenomena that influence the heliosphere and in some
  cases even conditions of earth. Part of this liberated energy is used
  for particle acceleration and to heat up the solar plasma. The heated
  solar plasma rising up into the corona is usually observed in soft
  (&lt;10keV) X-rays and EUV, while the flare accelerated particles
  hitting the lower atmosphere produce signatures in the hard X-ray
  band. On April 17th, 2021, the Spectrometer Telescope for Imaging
  X-rays (STIX) onboard the Solar Orbiter spacecraft observed a flare
  that was partially occulted from Earth view. The flare was estimated
  to be of GOES class B9 and shows several episodes of nonthermal hard
  X-ray bursts over a total duration of about an hour. This event was
  also associated with a fast CME and is particularly interesting due to
  spacecraft positions on April 17th. For Solar Orbiter and STEREO-A,
  the flare occurred on disc, enabling us to study the response of the
  lower solar atmosphere to the flare particle acceleration and energy
  deposition using STIX X-ray imaging, spectral fitting and EUV images
  from STEREO EUVI. For earth-orbiting spacecraft like SDO which were
  separated by 98 degrees from Solar Orbiter, the flare occurred just
  behind the eastern limb. With the bright flare footpoints occulted,
  this allows us to study the flare related changes in the corona from
  a side on view and to put them into context of the STIX and STEREO on
  disc observations. We find several instances of plasma motions such
  as detaching plasmoids, flare-related reconnection outflows and super
  arcade downflows observed by SDO AIA. Some of these plasma flows occur
  simultaneously with individual HXR bursts observed by STIX. The most
  distinct instance is the ejection of a hot plasmoid at the beginning
  of the impulsive flare phase where the acceleration coincides with
  a peak in the HXR lightcurve. We analyze the dynamics and thermal
  properties of the flare-related plasma flows and the flaring arcade,
  the energy releases and particle acceleration as diagnosed by STIX
  as well as the relation of the ejected plasmoid to the associated
  CME. Combining different vantage points and instruments allows us to
  perform a detailed study of the flare and the related eruption over
  a wide range of atmospheric heights.

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Title: The restructuring of a solar magnetic flux rope during a
    coronal mass ejection
Authors: Gou, Tingyu; Wang, Yuming; Liu, Rui; Veronig, Astrid;
   Zhuang, Bin
2022cosp...44.2411G    Altcode:
  Solar eruptions are magnificent and energetic explosions in the
  heliosphere, among which the magnetic flux rope is a fundamental
  structure. In the standard model, a magnetic flux rope builds up into
  a CME through magnetic reconnection that continually converts the
  overlying, untwisted magnetic flux into twisted flux enveloping the
  pre-existent rope. However, only about one third of in-situ detected
  CMEs have the flux-rope configuration, which casts doubt on the
  universality of such a well-organized enveloping process. Here we
  present observations of the complete restructuring of a pre-forming
  flux rope during its eruption. The formation process is featured by
  the growth of a hot seed and simultaneous expansion of its footpoint
  into being enclosed by a trapezoid-shaped ribbon. During the subsequent
  eruption, the flux rope's feet migrate to new places, which suggests a
  complete replacement of magnetic fluxes in the original flux rope. Our
  study signifies the three-dimensional reconnection between the flux
  rope and the surrounding field as well as within the rope and provides
  new clues for the development of the CME.

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Title: Prediction of solar cycle amplitude with the maximal growth
    rate in ascending phase
Authors: Jain, Shantanu; Podladchikova, Tatiana; Clette, Fr; Veronig,
   Astrid; Dumbovic, Mateja; Pötzi, Werner; Sutyrina, Olga
2022cosp...44.3230J    Altcode:
  Forecasting the amplitude of the 11-year solar cycle is highly
  important for many space weather applications. We demonstrate a
  steady relationship between the maximal growth rate of sunspot
  activity in the ascending phase of a cycle and the subsequent
  cycle peak on the basis of four data sets of solar activity
  indices: total sunspot numbers, hemispheric sunspot numbers
  from the new catalogue from 1874 onwards (Veronig et al. 2021,
  http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56) total and
  hemispheric sunspot areas. In all cases, a linear regression
  based on the maximal growth rate precursor shows a significant
  correlation. Furthermore, we demonstrated that the sum of maximal
  growth rate indicators determined separately for the North and the
  South hemispheric sunspot numbers provides more accurate forecast
  than that using total sunspot numbers: The rms error of predictions
  is smaller by 27%, the correlation coefficient r is higher by 11%
  on average reaching values in the range r = 0.8-0.9 depending of the
  smoothing window of the monthly mean data. The superior performance is
  also confirmed with the hemispheric sunspot areas with respect to total
  sunspot areas. These results provide a strong foundation for supporting
  regular monitoring, recording, and predictions of solar activity with
  the hemispheric sunspot data, which capture the asymmetric behavior
  of the solar activity and solar magnetic field.

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Title: Stellar CME search using large datasets: Balmer line
    asymmetries in optical SDSS spectra
Authors: Koller, Florian; Odert, Petra; Leitzinger, Martin; Veronig,
   Astrid; Temmer, Manuela; Beck, Paul G.
2022cosp...44.1386K    Altcode:
  On the Sun, a strong correlation between highly energetic flares
  and coronal mass ejections (CMEs) has been well established. Highly
  energetic flares have also been frequently detected on all late-type
  stars. However, the association with CMEs proved to be difficult in the
  stellar case. Large datasets are a necessity to increase the probability
  of detecting these sparse events. In order to find stellar flares
  and associated CMEs, we used optical spectra provided by the Sloan
  Digital Sky Survey (SDSS) data release 14. The sample consisted of F,
  G, K, and M main-sequence type stars, resulting in available spectra
  for more than 630 000 stars. We made use of the individual spectral
  exposures provided by the SDSS. Flares were detected by searching for
  significant amplitude changes in the Hα and Hβ spectral lines. We
  searched for CMEs by identifying asymmetries in the Balmer lines
  caused by the Dopplereffect, which indicate plasma motions in the line
  of sight. We detected 281 flares on late-type stars (spectral types
  K3 - M9) and calculated their Hα flare energies. Six possible CME
  candidates were identified that show excess flux in Balmer line wings,
  five of which show red wing enhancements. Our mass estimates for the
  CME candidates range from 6×10$ ^{16}$ -‑ 6×10$ ^{18}$g, and the
  highest projected velocities are 300 -‑ 700km s$ ^{‑1}$. Our low
  detection rate of CMEs agrees with previous studies.

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Title: Variation in solar differential rotation and activity in the
    period 1964-2016 determined by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Jurkić, T.;
   Brajša, R.; Skokić, I.; Sudar, D.; Ruždjak, D.; Hržina, D.;
   Pötzi, W.; Hanslmeier, A.; Veronig, A. M.
2022A&A...663A..24P    Altcode: 2022arXiv220407396P
  <BR /> Aims: Theoretical calculations predict an increased equatorial
  rotation and more pronounced differential rotation (DR) during
  the minimum of solar magnetic activity. However, the results of
  observational studies vary, some showing less and some more pronounced
  DR during the minimum of solar magnetic activity. Our study aims to gain
  more insight into these discrepancies. <BR /> Methods: We determined
  the DR parameters A and B (corresponding to the equatorial rotation
  velocity and the gradient of the solar DR, respectively) by tracing
  sunspot groups in sunspot drawings of the Kanzelhöhe Observatory
  for Solar and Environmental Research (KSO; 1964-2008, for solar
  cycles 20-23) and KSO white-light images (2009-2016, for solar cycle
  24). We used different statistical methods and approaches to analyse
  variations in DR parameters related to the cycle and to the phase of
  the solar cycle, together with long-term related variations. <BR />
  Results: The comparison of the DR parameters for individual cycles
  obtained from the KSO and from other sources yield statistically
  insignificant differences for the years after 1980, meaning that the
  KSO sunspot group data set is well suited for long-term cycle to cycle
  studies. The DR parameters A and B show statistically significant
  periodic variability. The periodicity corresponds to the solar cycle
  and is correlated with the solar activity. The changes in A related
  to solar cycle phase are in accordance with previously reported
  theoretical and experimental results (higher A during solar minimum,
  lower A during the maximum of activity), while changes in B differ
  from the theoretical predictions as we observe more negative values
  of B, that is, a more pronounced differential rotation during activity
  maximum. The main result of this paper for the long-term variations in
  A is the detection of a phase shift between the activity flip (in the
  1970s) and the equatorial rotation velocity flip (in the early 1990s),
  during which both A and activity show a secular decreasing trend. This
  indicates that the two quantities are correlated in between 1970 and
  1990. Therefore, the theoretical model fails in the phase-shift time
  period that occurs after the modern Gleissberg maximum, while in the
  time period thereafter (after the 1990s), theoretical and experimental
  results are consistent. The long-term variations in B in general yield
  an anticorrelation of B and activity, as a rise of B is observed during
  the entire time period (1964-2016) we analysed, during which activity
  decreased, with the exception of the end of solar cycle 22 and the
  beginning of solar cycle 23. <BR /> Conclusions: We study for the first
  time the variation in solar DR and activity based on 53 years of KSO
  data. Our results agree well with the results related to the solar cycle
  phase from corona observations. The disagreement of the observational
  results for B and theoretical studies may be due to the fact that we
  analysed the period immediately after the modern Gleissberg maximum,
  where for the phase-shift period, A versus activity also entails a
  result that differs from theoretical predictions. Therefore, studies
  of rotation versus activity with data sets encompassing the Gleissberg
  extremes should include separate analyses of the parts of the data set
  in between different flips (e.g., before the activity flip, between
  the activity and the rotation flip, and after the rotation flip).

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Title: Medium-term predictions of F10.7 and F30 cm solar radio flux
    with RESONANCE
Authors: Podladchikova, Tatiana; Flohrer, Tim; Veronig, Astrid;
   Bastida Virgili, Benjamin; Lemmens, Stijn; Petrova, Elena
2022cosp...44.3235P    Altcode:
  The solar radio flux at F10.7 and F30 cm is required by most models
  characterizing the state of the Earth's upper atmosphere, such as the
  thermosphere and ionosphere, to specify satellite orbits, re-entry
  services, collision avoidance maneuvers, and modeling of the evolution
  of space debris. We develop a method called RESONANCE (Radio Emissions
  from the Sun: ONline ANalytical Computer-aided Estimator) for the
  prediction of the 13-month smoothed monthly mean F10.7 and F30 indices
  1-24 months ahead. The prediction algorithm has three steps. First, we
  apply a 13-month optimized running mean technique to effectively reduce
  the noise in the radio flux data. Second, we provide initial predictions
  of the F10.7 and F30 indices using the McNish-Lincoln method. Finally,
  we improve these initial predictions by developing an adaptive Kalman
  filter with identification of the error statistics. The rms error of
  predictions with lead times from 1 to 24 months is 5-27 solar flux units
  (sfu) for the F10.7 index and 3-16 sfu for F30, which statistically
  outperforms current algorithms in use. The proposed approach based
  on the Kalman filter is universal and can be applied to improve the
  initial predictions of a process under study provided by any other
  forecasting method. Furthermore, we present a systematic evaluation
  of re-entry forecast as an application to test the performance of
  F10.7 predictions on past ESA re-entry campaigns for payloads, rocket
  bodies, and space debris that re-entered from 2006 to 2019 June. The
  test results demonstrate that the predictions obtained by RESONANCE in
  general also lead to improvements in the forecasts of re-entry epochs.

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Title: Maximal growth rate of the ascending phase of a sunspot cycle
    for predicting its amplitude
Authors: Podladchikova, Tatiana; Jain, Shantanu; Veronig, Astrid M.;
   Sutyrina, Olga; Dumbović, Mateja; Clette, Frédéric; Pötzi, Werner
2022A&A...663A..88P    Altcode: 2022arXiv220612606P
  Context. Forecasting the solar cycle amplitude is important for a
  better understanding of the solar dynamo as well as for many space
  weather applications. Different empirical relations of solar cycle
  parameters with the peak amplitude of the upcoming solar cycle have
  been established and used for solar cycle forecasts, as, for instance,
  the Waldmeier rule relating the cycle rise time with its amplitude,
  the polar fields at previous minimum, and so on. Recently, a separate
  consideration of the evolution of the two hemispheres revealed even
  tighter relations. <BR /> Aims: We aim to introduce the maximal growth
  rate of sunspot activity in the ascending phase of a cycle as a new
  and reliable precursor of a subsequent solar cycle amplitude. We also
  intend to investigate whether the suggested precursor provides benefits
  for the prediction of the solar cycle amplitude when using the sunspot
  indices (sunspot numbers, sunspot areas) derived separately for the
  two hemispheres compared to the total sunspot indices describing the
  entire solar disc. <BR /> Methods: We investigated the relationship
  between the maximal growth rate of sunspot activity in the ascending
  phase of a cycle and the subsequent cycle amplitude on the basis
  of four data sets of solar activity indices: total sunspot numbers,
  hemispheric sunspot numbers from the new catalogue from 1874 onwards,
  total sunspot areas, and hemispheric sunspot areas. <BR /> Results:
  For all the data sets, a linear regression based on the maximal
  growth rate precursor shows a significant correlation. Validation of
  predictions for cycles 1-24 shows high correlations between the true
  and predicted cycle amplitudes reaching r = 0.93 for the total sunspot
  numbers. The lead time of the predictions varies from 2 to 49 months,
  with a mean value of 21 months. Furthermore, we demonstrated that the
  sum of maximal growth rate indicators determined separately for the
  north and the south hemispheric sunspot numbers provides more accurate
  predictions than that using total sunspot numbers. The advantages reach
  27% and 11% on average in terms of rms and correlation coefficient,
  respectively. The superior performance is also confirmed with
  hemispheric sunspot areas with respect to total sunspot areas. <BR
  /> Conclusions: The maximal growth rate of sunspot activity in the
  ascending phase of a solar cycle serves as a reliable precursor of
  the subsequent cycle amplitude. Furthermore, our findings provide
  a strong foundation for supporting regular monitoring, recording,
  and predictions of solar activity with hemispheric sunspot data,
  which capture the asymmetric behaviour of the solar activity and solar
  magnetic field and enhance solar cycle prediction methods.

---------------------------------------------------------
Title: Probing the coronal magnetic field with physics informed
    neural networks
Authors: Jarolim, Robert; Podladchikova, Tatiana; Veronig, Astrid;
   Thalmann, Julia K.
2022cosp...44.2463J    Altcode:
  While the photospheric magnetic field of our Sun is routinely
  measured, its extent into the upper solar atmosphere (the corona)
  remains elusive. In this study, we present a novel approach for coronal
  magnetic field extrapolation using physics informed neural networks. The
  neural network is optimized to match observations of the photospheric
  magnetic field vector at the bottom-boundary, while simultaneously
  satisfying the force-free and divergence-free equations in the entire
  simulation volume. We demonstrate that our method can account for
  noisy data and deviates from the physical model where the force-free
  magnetic field assumption cannot be satisfied. We utilize meta-learning
  concepts to simulate the evolution of the active region 11158. Our
  simulation of 5 days of observations at full cadence, requires less
  than 13 hours of total computation time. The derived evolution of the
  free magnetic energy and helicity in the active region, shows that
  our model captures flare signatures, and that the depletion of free
  magnetic energy spatially aligns with the observed EUV emission. Our
  method provides the ability to perform magnetic field extrapolations
  in quasi real-time, which can be used for space weather monitoring,
  studying pre-eruptive structures and as initial condition for MHD
  simulations. The flexibility in terms of data and the possibility of
  extending the underlying physical model, offers great potential for
  the field of magnetic field simulations.

---------------------------------------------------------
Title: The effect of spatial sampling on magnetic field modeling
    and helicity computation
Authors: Thalmann, J. K.; Gupta, M.; Veronig, A. M.
2022A&A...662A...3T    Altcode: 2022arXiv220409267T
  Context. Nonlinear force-free (NLFF) modeling is regularly used to
  indirectly infer the 3D geometry of the coronal magnetic field,
  which is not otherwise accessible on a regular basis by means of
  direct measurements. <BR /> Aims: We study the effect of binning in
  time-series NLFF modeling of individual active regions (ARs) in order to
  quantify the effect of a different underlying spatial sampling on the
  quality of modeling as well as on the derived physical parameters. <BR
  /> Methods: We apply an optimization method to sequences of Solar
  Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) vector
  magnetogram data at three different plate scales for three solar active
  regions to obtain nine NLFF model time series. From the NLFF models,
  we deduce active-region magnetic fluxes, electric currents, magnetic
  energies, and relative helicities, and analyze those with respect
  to the underlying spatial sampling. We calculate various metrics to
  quantify the quality of the derived NLFF models and apply a Helmholtz
  decomposition to characterize solenoidal errors. <BR /> Results: At
  a given spatial sampling, the quality of NLFF modeling is different
  for different ARs, and the quality varies along the individual model
  time series. For a given AR, modeling at a certain spatial sampling is
  not necessarily of superior quality compared to that performed with a
  different plate scale. Generally, the NLFF model quality tends to be
  higher for larger pixel sizes with the solenoidal quality being the
  ultimate cause for systematic variations in model-deduced physical
  quantities. <BR /> Conclusions: Optimization-based modeling using
  SDO/HMI vector data binned to larger pixel sizes yields variations
  in magnetic energy and helicity estimates of ≲30% on overall,
  given that concise checks ensure the physical plausibility and high
  solenoidal quality of the tested model. Spatial-sampling-induced
  differences are relatively small compared to those arising from other
  sources of uncertainty, including the effects of applying different
  data calibration methods, those of using vector data from different
  instruments, or those arising from application of different NLFF
  methods to identical input data.

---------------------------------------------------------
Title: The Solar Activity Monitor Network - SAMNet
Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang,
   Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.;
   Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša,
   Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez,
   Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.;
   Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu,
   Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer,
   James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen,
   Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz,
   Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili,
   Teimuraz; Zuccarello, Francesca
2022JSWSC..12....2E    Altcode:
  The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a
  future UK-led international network of ground-based solar telescope
  stations. SAMNet, at its full capacity, will continuously monitor
  the Sun's intensity, magnetic, and Doppler velocity fields at
  multiple heights in the solar atmosphere (from photosphere to upper
  chromosphere). Each SAMM sentinel will be equipped with a cluster of
  identical telescopes each with a different magneto-optical filter (MOFs)
  to take observations in K I, Na D, and Ca I spectral bands. A subset
  of SAMM stations will have white-light coronagraphs and emission line
  coronal spectropolarimeters. The objectives of SAMNet are to provide
  observational data for space weather research and forecast. The goal
  is to achieve an operationally sufficient lead time of e.g., flare
  warning of 2-8 h and provide many sought-after continuous synoptic
  maps (e.g., LoS magnetic and velocity fields, intensity) of the lower
  solar atmosphere with a spatial resolution limited only by seeing or
  diffraction limit, and with a cadence of 10 min. The individual SAMM
  sentinels will be connected to their master HQ hub where data received
  from all the slave stations will be automatically processed and flare
  warning issued up to 26 h in advance.

---------------------------------------------------------
Title: Nanoflare distributions over solar cycle 24 based on SDO/AIA
    differential emission measure observations
Authors: Purkhart, Stefan; Veronig, Astrid M.
2022A&A...661A.149P    Altcode: 2022arXiv220311625P
  <BR /> Aims: Nanoflares in quiet-Sun regions during solar cycle 24
  are studied with the best available plasma diagnostics to derive their
  energy distribution and contribution to coronal heating during different
  levels of solar activity. <BR /> Methods: Extreme ultraviolet filters
  of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics
  Observatory (SDO) were used. We analyzed 30 AIA/SDO image series
  between 2011 and 2018, each covering a 400″ × 400″ quiet-Sun
  field-of-view of over two hours with a 12-s cadence. Differential
  emission measure (DEM) analysis was used to derive the emission measure
  (EM) and temperature evolution for each pixel. We detected nanoflares
  as EM enhancements using a threshold-based algorithm and derived their
  thermal energy from the DEM observations. <BR /> Results: Nanoflare
  energy distributions follow power laws that show slight variations
  in steepness (α = 2.02-2.47), but no correlation to the solar
  activity level. The combined nanoflare distribution of all data sets
  covers five orders of magnitude in event energies (10<SUP>24</SUP>
  − 10<SUP>29</SUP> erg) with a power-law index α = 2.28 ±
  0.03. The derived mean energy flux of (3.7 ± 1.6)×10<SUP>4</SUP>
  erg cm<SUP>−2</SUP> s<SUP>−1</SUP> is one order of magnitude
  smaller than the coronal heating requirement. We found no correlation
  between the derived energy flux and solar activity. Analysis of the
  spatial distribution reveals clusters of high energy flux (up to 3
  × 10<SUP>5</SUP> erg cm<SUP>−2</SUP> s<SUP>−1</SUP>) surrounded
  by extended regions with lower activity. Comparisons with magnetograms
  from the Helioseismic and Magnetic Imager demonstrate that high-activity
  clusters are preferentially located in the magnetic network and above
  regions of enhanced magnetic flux density. <BR /> Conclusions: The
  steep power-law slope (α &gt; 2) suggests that the total energy in
  the flare energy distribution is dominated by the smallest events,
  that is to say nanoflares. We demonstrate that in the quiet-Sun, the
  nanoflare distributions and their contribution to coronal heating does
  not vary over the solar cycle.

---------------------------------------------------------
Title: Determination of coronal mass ejection orientation and
    consequences for their propagation
Authors: Martinić, K.; Dumbović, M.; Temmer, M.; Veronig, A.;
   Vršnak, B.
2022A&A...661A.155M    Altcode: 2022arXiv220410112M
  Context. The configuration of the interplanetary magnetic field
  and features of the related ambient solar wind in the ecliptic
  and meridional plane are different. Therefore, one can expect that
  the orientation of the flux-rope axis of a coronal mass ejection
  (CME) influences the propagation of the CME itself. However, the
  determination of the CME orientation, especially from image data,
  remains a challenging task to perform. Aim. This study aims to provide
  a reference to different CME orientation determination methods in
  the near-Sun environment. Also, it aims to investigate the non-radial
  flow in the sheath region of the interplanetary CME (ICME) in order
  to provide the first proxy to relate the ICME orientation with its
  propagation. <BR /> Methods: We investigated 22 isolated CME-ICME
  events in the period 2008-2015. We determined the CME orientation in
  the near-Sun environment using the following: (1) a 3D reconstruction
  of the CME with the graduated cylindrical shell (GCS) model applied
  to coronagraphic images provided by the STEREO and SOHO missions;
  and (2) an ellipse fitting applied to single spacecraft data from
  SOHO/LASCO C2 and C3 coronagraphs. In the near-Earth environment,
  we obtained the orientation of the corresponding ICME using in situ
  plasma and field data and also investigated the non-radial flow in
  its sheath region. <BR /> Results: The ability of GCS and ellipse
  fitting to determine the CME orientation is found to be limited to
  reliably distinguish only between the high or low inclination of the
  events. Most of the CME-ICME pairs under investigation were found to
  be characterized by a low inclination. For the majority of CME-ICME
  pairs, we obtain consistent estimations of the tilt from remote and
  in situ data. The observed non-radial flows in the sheath region show
  a greater y direction to z direction flow ratio for high-inclination
  events, indicating that the CME orientation could have an impact on
  the CME propagation.

---------------------------------------------------------
Title: Detailed Thermal and Nonthermal Processes in an A-class
    Microflare
Authors: Li, Zhentong; Su, Yang; Veronig, Astrid M.; Kong, Shuting;
   Gan, Weiqun; Chen, Wei
2022ApJ...930..147L    Altcode:
  How microflares behave and differ from large flares is an important
  question in flare studies. Although they have been extensively
  investigated, microflares are not fully understood in terms of
  their detailed energy release processes and the role of energetic
  electrons. A recent study on an A-class microflare suggests the
  existence of a nonthermal component down to 6.5 keV, indicating
  that accelerated electrons play an important role in microflares,
  as in large flares. Here, we revisit this event, and present a
  comprehensive, quantitative analysis of the energy release and plasma
  heating processes. Using careful differential emission measure (DEM)
  analysis, we calculate the thermal X-ray fluxes. By subtracting this
  multithermal component from the observed data, we confirm the existence
  of the remaining nonthermal component. In addition, we analyze the
  clear evaporation process and report the first imaging evidence for a
  low-energy cutoff of energetic electrons in EM maps of &gt;10 MK plasma,
  which first appeared as two coronal sources significantly above the
  chromospheric footpoints. Detailed calculations of electron transport,
  based on the electron parameters and the evolution of loop dynamics,
  provide strong evidence of a beam-driven plasma heating process
  with a low-energy cutoff consistent with that derived independently
  from DEM analysis. This study reveals the important role of electron
  thermalization and low-energy cutoffs in the physical processes of
  microflares.

---------------------------------------------------------
Title: The Coupling of an EUV Coronal Wave and Ion Acceleration in
    a Fermi-LAT Behind-the-Limb Solar Flare
Authors: Pesce-Rollins, Melissa; Omodei, Nicola; Krucker, Säm; Di
   Lalla, Niccolò; Wang, Wen; Battaglia, Andrea F.; Warmuth, Alexander;
   Veronig, Astrid M.; Baldini, Luca
2022ApJ...929..172P    Altcode: 2022arXiv220504760P
  We present the Fermi-LAT observations of the behind-the-limb (BTL)
  flare of 2021 July 17 and the joint detection of this flare by STIX
  on board the Solar Orbiter. The separation between Earth and the
  Solar Orbiter was 99.°2 at 05:00 UT, allowing STIX to have a front
  view of the flare. The location of the flare was S20E140 in Stonyhurst
  heliographic coordinates, making this the most distant behind-the-limb
  flare ever detected in &gt;100 MeV gamma-rays. The LAT detection lasted
  for ~16 minutes, the peak flux was 3.6 ± 0.8 (10<SUP>-5</SUP>) ph
  cm<SUP>-2</SUP> s<SUP>-1</SUP> with a significance &gt;15σ. A coronal
  wave was observed from both STEREO-A and SDO in extreme ultraviolet
  (EUV), with an onset on the visible disk in coincidence with the LAT
  onset. A complex type II radio burst was observed by GLOSS also in
  coincidence with the onset of the LAT emission, indicating the presence
  of a shock wave. We discuss the relation between the time derivative
  of the EUV wave intensity profile at 193 Å as observed by STEREO-A
  and the LAT flux to show that the appearance of the coronal wave at the
  visible disk and the acceleration of protons as traced by the observed
  &gt;100 MeV gamma-ray emission are coupled. We also report how this
  coupling is present in the data from three other BTL flares detected by
  Fermi-LAT, suggesting that the protons driving the gamma-ray emission
  of BTL solar flares and the coronal wave share a common origin.

---------------------------------------------------------
Title: How the area of solar coronal holes affects the properties
of high-speed solar wind streams near Earth: An analytical model
Authors: Hofmeister, Stefan J.; Asvestari, Eleanna; Guo, Jingnan;
   Heidrich-Meisner, Verena; Heinemann, Stephan G.; Magdalenic, Jasmina;
   Poedts, Stefaan; Samara, Evangelia; Temmer, Manuela; Vennerstrom,
   Susanne; Veronig, Astrid; Vršnak, Bojan; Wimmer-Schweingruber, Robert
2022A&A...659A.190H    Altcode: 2022arXiv220315689H
  Since the 1970s it has been empirically known that the area of
  solar coronal holes affects the properties of high-speed solar wind
  streams (HSSs) at Earth. We derive a simple analytical model for the
  propagation of HSSs from the Sun to Earth and thereby show how the
  area of coronal holes and the size of their boundary regions affect
  the HSS velocity, temperature, and density near Earth. We assume that
  velocity, temperature, and density profiles form across the HSS cross
  section close to the Sun and that these spatial profiles translate
  into corresponding temporal profiles in a given radial direction due
  to the solar rotation. These temporal distributions drive the stream
  interface to the preceding slow solar wind plasma and disperse with
  distance from the Sun. The HSS properties at 1 AU are then given by
  all HSS plasma parcels launched from the Sun that did not run into
  the stream interface at Earth distance. We show that the velocity
  plateau region of HSSs as seen at 1 AU, if apparent, originates from
  the center region of the HSS close to the Sun, whereas the velocity
  tail at 1 AU originates from the trailing boundary region. Small
  HSSs can be described to entirely consist of boundary region plasma,
  which intrinsically results in smaller peak velocities. The peak
  velocity of HSSs at Earth further depends on the longitudinal width
  of the HSS close to the Sun. The shorter the longitudinal width of
  an HSS close to the Sun, the more of its "fastest" HSS plasma parcels
  from the HSS core and trailing boundary region have impinged upon the
  stream interface with the preceding slow solar wind, and the smaller
  is the peak velocity of the HSS at Earth. As the longitudinal width
  is statistically correlated to the area of coronal holes, this also
  explains the well-known empirical relationship between coronal hole
  areas and HSS peak velocities. Further, the temperature and density
  of HSS plasma parcels at Earth depend on their radial expansion from
  the Sun to Earth. The radial expansion is determined by the velocity
  gradient across the HSS boundary region close to the Sun and gives
  the velocity-temperature and density-temperature relationships at
  Earth their specific shape. When considering a large number of HSSs,
  the assumed correlation between the HSS velocities and temperatures
  close to the Sun degrades only slightly up to 1 AU, but the correlation
  between the velocities and densities is strongly disrupted up to 1
  AU due to the radial expansion. Finally, we show how the number of
  particles of the piled-up slow solar wind in the stream interaction
  region depends on the velocities and densities of the HSS and preceding
  slow solar wind plasma.

---------------------------------------------------------
Title: Multi-instrument STIX microflare study
Authors: Saqri, Jonas; Veronig, Astrid M.; Warmuth, Alexander; Dickson,
   Ewan C. M.; Battaglia, Andrea Francesco; Podladchikova, Tatiana;
   Xiao, Hualin; Battaglia, Marina; Hurford, Gordon J.; Krucker, Säm
2022A&A...659A..52S    Altcode: 2022arXiv220100712S
  Context. During its commissioning phase in 2020, the
  Spectrometer/Telescope for Imaging X-rays (STIX) on board the Solar
  Orbiter spacecraft observed 69 microflares. The two most significant
  events from this set (of GOES class B2 and B6) were observed on-disk
  from the spacecraft as well as from Earth and analysed in terms of
  the spatial, temporal, and spectral characteristics. <BR /> Aims:
  We complement the observations from the STIX instrument with EUV
  imagery from SDO/AIA and GOES soft X-ray data by adding imaging
  and plasma diagnostics over different temperature ranges for a
  detailed microflare case study that is focussed on energy release
  and transport. <BR /> Methods: We used data from the GOES for SXR
  plasma diagnostics and SDO/AIA for carrying out high-cadence EUV
  imaging and reconstruction of differential emission measure (DEM)
  maps of the thermal flare plasma. The reconstructed DEM profiles were
  used to study the temporal evolution of thermal flare plasma in the
  kernels and loops independently. We derived the time evolution of the
  flare plasma parameters (EM, T) and thermal energy from STIX, GOES,
  and AIA observations. In particular, we studied the STIX spectra to
  determine the nonthermal emission from accelerated electrons. <BR />
  Results: A spectral fitting of the STIX data shows clear nonthermal
  emission for both microflares studied here. For both events, the
  plasma temperature and EM derived from STIX and GOES as well as
  the reconstructed DEM maps differ in absolute values and timing,
  with AIA (which is sensitive to lower plasma temperatures) lagging
  behind. The deduced plasma parameters from either method roughly
  agree with the values in the literature for microflares as do the
  nonthermal fit parameters from STIX. This finding is corroborated
  by the Neupert effect exhibited between the time derivative of the
  GOES SXR emission and the STIX HXR profiles. For the B6 event, for
  which such an analysis was possible, the non-thermal energy deduced
  from STIX roughly coincides with the lower estimates of the thermal
  energy requirement deduced from the SXR and EUV emissions. <BR />
  Conclusions: The observed Neupert effects and impulsive and gradual
  phases indicate that both events covered in this study are consistent
  with the standard chromospheric evaporation flare scenario. For the
  B6 event on 7 June 2020, this interpretation is further supported by
  the temporal evolution seen in the DEM profiles of the flare ribbons
  and loops. For this event, we also find that accelerated electrons
  can roughly account for the required thermal energy. The 6 June 2020
  event demonstrates that STIX can detect nonthermal emission for GOES
  class B2 events that is nonetheless smaller than the background rate
  level. We demonstrate for the first time how detailed multi-instrument
  studies of solar flares can be performed with STIX.

---------------------------------------------------------
Title: Multiwavelength Signatures of Episodic Nullpoint Reconnection
    in a Quadrupolar Magnetic Configuration and the Cause of Failed Flux
    Rope Eruption
Authors: Mitra, Prabir K.; Joshi, Bhuwan; Veronig, Astrid M.;
   Wiegelmann, Thomas
2022ApJ...926..143M    Altcode: 2021arXiv211214412M
  In this paper, we present multiwavelength observations of the
  triggering of a failed-eruptive M-class flare from active region
  NOAA 11302 and investigate the possible reasons for the associated
  failed eruption. Photospheric observations and nonlinear force-free
  field extrapolated coronal magnetic field revealed that the flaring
  region had a complex quadrupolar configuration with a preexisting
  coronal nullpoint situated above the core field. Prior to the onset
  of the M-class flare, we observed multiple periods of small-scale
  flux enhancements in GOES and RHESSI soft X-ray observations from the
  location of the nullpoint. The preflare configuration and evolution
  reported here are similar to the configurations presented in the
  breakout model, but at much lower coronal heights. The core of the
  flaring region was characterized by the presence of two flux ropes in a
  double-decker configuration. During the impulsive phase of the flare,
  one of the two flux ropes initially started erupting, but resulted in
  a failed eruption. Calculation of the magnetic decay index revealed a
  saddle-like profile where the decay index initially increased to the
  torus-unstable limits within the heights of the flux ropes, but then
  decreased rapidly and reached negative values, which was most likely
  responsible for the failed eruption of the initially torus-unstable
  flux rope.

---------------------------------------------------------
Title: Correction to: Kanzelhöhe Observatory: Instruments, Data
    Processing and Data Products
Authors: Pötzi, Werner; Veronig, Astrid; Jarolim, Robert; Rodríguez
   Gómez, Jenny Marcela; Podladchikova, Tatiana; Baumgartner, Dietmar;
   Freislich, Heinrich; Strutzmann, Heinz
2022SoPh..297....1P    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Observational Signatures of Tearing Instability in the Current
    Sheet of a Solar Flare
Authors: Lu, Lei; Feng, Li; Warmuth, Alexander; Veronig, Astrid M.;
   Huang, Jing; Liu, Siming; Gan, Weiqun; Ning, Zongjun; Ying, Beili;
   Gao, Guannan
2022ApJ...924L...7L    Altcode: 2021arXiv211207857L
  Magnetic reconnection is a fundamental physical process converting
  magnetic energy into not only plasma energy but also particle energy
  in various astrophysical phenomena. In this Letter, we show a unique
  data set of a solar flare where various plasmoids were formed by a
  continually stretched current sheet. Extreme ultraviolet images captured
  reconnection inflows, outflows, and particularly the recurring plasma
  blobs (plasmoids). X-ray images reveal nonthermal emission sources at
  the lower end of the current sheet, presumably as large plasmoids with
  a sufficiently amount of energetic electrons trapped in them. In the
  radio domain, an upward, slowly drifting pulsation structure, followed
  by a rare pair of oppositely drifting structures, was observed. These
  structures are supposed to map the evolution of the primary and
  the secondary plasmoids formed in the current sheet. Our results on
  plasmoids at different locations and scales shed important light on
  the dynamics, plasma heating, particle acceleration, and transport
  processes in the turbulent current sheet and provide observational
  evidence for the cascading magnetic reconnection process.

---------------------------------------------------------
Title: The 2019 International Women's Day Event: A Two-step Solar
    Flare with Multiple Eruptive Signatures and Low Earth Impact
Authors: Dumbovic, Mateja; Veronig, Astrid; Podladchikova, Tatiana;
   Thalmann, Julia; Chikunova, Galina; Dissauer, Karin; Magdalenic,
   Jasmina; Temmer, Manuela; Guo, Jingnan; Samara, Evangelia
2021AGUFMSH32A..08D    Altcode:
  We present a detailed analysis of an eruptive event that occurred on
  early 2019 March 8 in active region AR 12734, to which we refer as the
  International Women's day event. The event under study is intriguing in
  several aspects: 1) low-coronal eruptive signatures come in ”pairs” (a
  double-peak flare, two coronal dimmings, and two EUV waves); 2) although
  the event is characterized by a complete chain of eruptive signatures,
  the corresponding coronagraphic signatures are weak; 3) although
  the source region of the eruption is located close to the center of
  the solar disc and the eruption is thus presumably Earth-directed,
  heliospheric signatures are very weak with little Earth-impact. We
  analyze a number of multi-spacecraft and multi-instrument (both
  remote-sensing and in situ) observations, including Soft X-ray,
  (extreme-) ultraviolet (E)UV), radio and white-light emission, as well
  as plasma, magnetic field and particle measurements. We employ 3D NLFF
  modeling to investigate the coronal magnetic field configuration in and
  around the active region, the GCS model to make a 3D reconstruction of
  the CME geometry and the 3D MHD numerical model EUHFORIA to model the
  background state of the heliosphere. Our results indicate two subsequent
  eruptions of two systems of sheared and twisted magnetic fields,
  which merge already in the upper corona and start to evolve further
  out as a single entity. The large-scale magnetic field significantly
  influences both, the early and the interplanetary evolution of the
  structure. During the first eruption the stability of the overlying
  field was disrupted which enabled the second eruption. We find that
  during the propagation in the interplanetary space the large-scale
  magnetic field, i.e. , the location of heliospheric current sheet
  between the AR and the Earth likely influences propagation and the
  evolution of the erupted structure(s).

---------------------------------------------------------
Title: Instrument-to-Instrument translation: A deep learning framework
    for data set restoration of solar observations
Authors: Jarolim, Robert; Veronig, Astrid; Potzi, Werner;
   Podladchikova, Tatiana
2021AGUFMNG45B0556J    Altcode:
  The constant improvement of astronomical instrumentation provides the
  foundation for scientific discoveries. In general, these improvements
  have only implications forward in time, while previous observations do
  not profit from this trend. In solar physics, the study of long-term
  evolution typically exceeds the lifetime of single instruments and
  data driven approaches are strongly limited in terms of coherent
  long-term data samples. We demonstrate that the available data sets
  can directly profit from the most recent instrumental improvements
  and provide a so far unused resource to foster novel research
  and accelerate data driven studies. Here we provide a general deep
  learning framework that translates between image domains of different
  instruments (Instrument-to-Instrument translation; ITI), in order to
  enhance physically relevant features which are otherwise beyond the
  diffraction limit of the telescope, inter-calibrate data sets, mitigate
  atmospheric degradation effects and can estimate observables that are
  not directly covered by the instrument. Our method is independent of
  any temporal or spatial overlap between the considered instruments,
  which makes it applicable to a variety of different domains. We
  show that our method can provide unified long-term data sets at
  the highest quality and demonstrate its versatility by applying
  it to four different applications of ground- and space-based solar
  observations. Our model results are assessed by comparison with real
  high-quality observations. We provide 1) a homogenous data series of
  24 years of space-based observations of the solar corona by enhancing
  observations from SOHO/EIT+MDI and STEREO/EUVI to SDO/AIA+HMI quality,
  2) solar full-disk observations with unprecedented spatial resolution
  by enhancing SDO/HMI continuum observations to Hinode/SOT quality, 3)
  a uniform series of ground-based H observations starting from 1973,
  that unifies solar observations recorded on photographic film and CCD
  at Kanzelhohe Observatory, 4) magnetic field estimates from the solar
  far-side based on multi-band EUV imagery of STEREO/EUVI. Our method
  can provide data sets required for more reliable long-term studies,
  accelerate the development of automated algorithms, and can easily be
  extended to new instruments.

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Title: The Observational Uncertainty of Coronal Hole Boundaries in
    Automated Detection Schemes
Authors: Reiss, Martin; Muglach, Karin; Moestl, Christian; Arge,
   Charles; Bailey, Rachel; Delouille, Veronique; Garton, Tadhg; Hamada,
   Amr; Hofmeister, Stefan; Illarionov, Egor; Jarolim, Robert; Kirk,
   Michael; Kosovichev, Alexander; Krista, Larisza; Lee, Sangwoo; Lowder,
   Chris; MacNeice, Peter; Veronig, Astrid
2021AGUFMSH15G2083R    Altcode:
  Solar coronal holes are the observational manifestation of the solar
  magnetic field open to the heliosphere and are of pivotal importance
  for understanding the origin and acceleration of the solar wind. Space
  missions such as the Solar Dynamics Observatory now allow us to observe
  coronal holes in unprecedented detail. Instrumental effects and other
  factors, however, pose a challenge to automated detection of coronal
  holes in solar imagery. The science community addresses these challenges
  with a variety of detection schemes. Until now, scant attention has
  been paid to assessing the disagreement between these schemes. Here
  we present the first comprehensive comparison of widely-applied
  automated detection schemes in solar and space science. By tying
  together scientific expertise worldwide, we study a coronal hole
  observed by the Atmospheric Imaging Assembly instrument on 2018 May
  30. We find that the choice of detection scheme significantly affects
  the location of the coronal hole boundary. Depending on the detection
  scheme, the physical properties of the coronal hole including the area,
  mean intensity, and mean magnetic field strength vary by a factor of
  up to 4.5 between the maximum and minimum values. This presentation
  discusses the implications of these findings for coronal hole research
  from the past decade. We also outline future strategies on how to use
  our results to diagnose and improve coronal magnetic field models.

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Title: Detection of stellar CMEs through post-flare coronal dimmings
Authors: Veronig, Astrid; Odert, Petra; Leitzinger, Martin; Dissauer,
   Karin; Fleck, Nikolaus; Hudson, Hugh
2021AGUFM.U43B..07V    Altcode:
  Coronal mass ejections (CMEs) from our Sun are regularly imaged by
  white-light coronagraphs, and their speeds and masses are derived
  from these observations. However, for stars such direct imaging is
  not possible, and so far, only a few candidates for stellar CMEs
  have been reported. Here, we present a new approach to detect stellar
  mass ejections through post-flare coronal dimmings. Coronal dimmings
  are sudden decreases of the solar EUV and X-ray emission caused by
  CMEs. Dimming regions map to the bipolar ends of closed magnetic field
  lines that become stretched or temporarily opened during an eruption,
  and are a result of the depletion of coronal plasma caused by the
  expansion and mass loss due to the CME. Recently available multi-point
  imagery from satellites at different locations in the heliosphere
  provided us with unprecedented observations of the three-dimensional
  evolution of solar CMEs and their coronal dimmings. These studies showed
  distinct correlations between CME mass and speed with key parameters
  of the associated coronal dimmings such as their spatial extent
  and intensity drop. In this contribution, we present Sun-as-a-star
  broad-band EUV light curves derived from SDOs Extreme ultraviolet
  Variability Experiment (EVE) as a testbed to study whether coronal
  dimmings can be also observed on stars and used for stellar CME
  detection. We demonstrate that large flares associated with CMEs have
  a high probability to show a post-flare coronal dimming, with intensity
  drops in the 15-25 nm full-Sun light curves of up to 5%. Searching for
  similar patterns of post-flare dimmings in the X-ray and EUV light
  curves of solar-like and late-type stars, we identify 21 stellar
  CME candidates, which is more than all previous reports of stellar
  CMEs. The derived intensity drops are an order of magnitude larger than
  for the Sun, suggesting that a substantial part of the stellar corona
  gets ejected by the CME. This study paves the way for comprehensive
  detections and characterizations of CMEs on stars, which are important
  factors in planetary habitability and stellar evolution. This
  study is published in: A.M. Veronig, P. Odert, M. Leitzinger,
  K. Dissauer, N. Fleck, H.S. Hudson, Indications of stellar coronal
  mass ejections through coronal dimmings, Nature Astronomy 5, 697-706
  (2021). https://www.nature.com/articles/s41550-021-01345-9

---------------------------------------------------------
Title: STIX X-ray microflare observations during the Solar Orbiter
    commissioning phase
Authors: Battaglia, Andrea Francesco; Saqri, Jonas; Massa, Paolo;
   Perracchione, Emma; Dickson, Ewan C. M.; Xiao, Hualin; Veronig,
   Astrid M.; Warmuth, Alexander; Battaglia, Marina; Hurford, Gordon J.;
   Meuris, Aline; Limousin, Olivier; Etesi, László; Maloney, Shane A.;
   Schwartz, Richard A.; Kuhar, Matej; Schuller, Frederic; Senthamizh
   Pavai, Valliappan; Musset, Sophie; Ryan, Daniel F.; Kleint, Lucia;
   Piana, Michele; Massone, Anna Maria; Benvenuto, Federico; Sylwester,
   Janusz; Litwicka, Michalina; Stȩślicki, Marek; Mrozek, Tomasz;
   Vilmer, Nicole; Fárník, František; Kašparová, Jana; Mann,
   Gottfried; Gallagher, Peter T.; Dennis, Brian R.; Csillaghy, André;
   Benz, Arnold O.; Krucker, Säm
2021A&A...656A...4B    Altcode: 2021arXiv210610058B
  Context. The Spectrometer/Telescope for Imaging X-rays (STIX) is the
  hard X-ray instrument onboard Solar Orbiter designed to observe solar
  flares over a broad range of flare sizes. <BR /> Aims: We report
  the first STIX observations of solar microflares recorded during
  the instrument commissioning phase in order to investigate the STIX
  performance at its detection limit. <BR /> Methods: STIX uses hard
  X-ray imaging spectroscopy in the range between 4-150 keV to diagnose
  the hottest flare plasma and related nonthermal electrons. This first
  result paper focuses on the temporal and spectral evolution of STIX
  microflares occuring in the Active Region (AR) AR12765 in June 2020,
  and compares the STIX measurements with Earth-orbiting observatories
  such as the X-ray Sensor of the Geostationary Operational Environmental
  Satellite (GOES/XRS), the Atmospheric Imaging Assembly of the Solar
  Dynamics Observatory, and the X-ray Telescope of the Hinode mission. <BR
  /> Results: For the observed microflares of the GOES A and B class, the
  STIX peak time at lowest energies is located in the impulsive phase of
  the flares, well before the GOES peak time. Such a behavior can either
  be explained by the higher sensitivity of STIX to higher temperatures
  compared to GOES, or due to the existence of a nonthermal component
  reaching down to low energies. The interpretation is inconclusive
  due to limited counting statistics for all but the largest flare
  in our sample. For this largest flare, the low-energy peak time is
  clearly due to thermal emission, and the nonthermal component seen at
  higher energies occurs even earlier. This suggests that the classic
  thermal explanation might also be favored for the majority of the
  smaller flares. In combination with EUV and soft X-ray observations,
  STIX corroborates earlier findings that an isothermal assumption
  is of limited validity. Future diagnostic efforts should focus on
  multi-wavelength studies to derive differential emission measure
  distributions over a wide range of temperatures to accurately describe
  the energetics of solar flares. <BR /> Conclusions: Commissioning
  observations confirm that STIX is working as designed. As a rule of
  thumb, STIX detects flares as small as the GOES A class. For flares
  above the GOES B class, detailed spectral and imaging analyses can
  be performed.

---------------------------------------------------------
Title: Searching for flares and associated CMEs on cool stars using
    Balmer lines in SDSS spectra
Authors: Koller, Florian; Leitzinger, Martin; Temmer, Manuela; Odert,
   Petra; Beck, Paul; Veronig, Astrid
2021AGUFM.U43B..04K    Altcode:
  Flares and coronal mass ejections (CMEs) shape the environment of stars
  and can severely affect the atmospheres and therefore the habitability
  of exoplanets. In the case of our Sun, we find that highly energetic
  flares and CMEs are strongly correlated. While we find frequent
  and highly energetic flares on all late-type stars, determining
  the association with stellar CMEs proves to be more difficult. To
  further constrain the activity of late-type main-sequence stars, we
  aimed to detect and classify stellar flares and potential stellar CME
  signatures. For that, we used optical spectra provided by the Sloan
  Digital Sky Survey (SDSS) data release 14. The sample was constrained
  to all F, G, K, and M main-sequence type stars, which resulted in
  available spectra for more than 630 000 stars. We made use of the
  individual spectral exposures provided by the SDSS. To automatically
  detect flares, we searched for significant amplitude changes in the
  $H\alpha$ and $H\beta$ spectral lines after a Gaussian profile was fit
  to each line core. We searched for CMEs by identifying asymmetries in
  the Balmer lines caused by the Dopplereffect, which indicate plasma
  motions in the line of sight. We report 281 flares on late-type stars
  (spectral types K3 M9). Six possible CME candidates were identified
  that show excess flux in Balmer line wings. We calculated $H\alpha$
  Flare energies and estimated the masses of the CME candidates. The
  $H\alpha$ flare energies we derived range from $3 \times 10^{28}
  - 2 \times 10^{33}$ erg. We find that the $H\alpha$ flare energy
  increases with earlier types, while the fraction of flaring times
  increases with later types. Our mass estimates for the CME candidates
  range from $6 \times 10^{16} - 6 \times 10^{18}$ g, and the highest
  projected velocities are $\sim 300 - 700$ km s$^{-1}$. We conclude
  that our low detection rate of CMEs agrees with previous studies,
  suggesting that the CME occurrence rate that can be detected with
  optical spectroscopy is low for late-type main-sequence stars.

---------------------------------------------------------
Title: Kanzelhöhe Observatory: Instruments, Data Processing and
    Data Products
Authors: Pötzi, Werner; Veronig, Astrid; Jarolim, Robert; Rodríguez
   Gómez, Jenny Marcela; Podlachikova, Tatiana; Baumgartner, Dietmar;
   Freislich, Heinrich; Strutzmann, Heinz
2021SoPh..296..164P    Altcode: 2021arXiv211103176P
  Kanzelhöhe Observatory for Solar and Environmental Research (KSO) of
  the University of Graz (Austria) is in continuous operation since its
  foundation in 1943. Since the beginning, its main task was the regular
  observation of the Sun in full disc. In this long time span covering
  almost seven solar cycles, a substantial amount of data was collected,
  which is made available online. In this article we describe the
  separate processing steps from data acquisition to high level products
  for different observing wavelengths. First of all we present in detail
  the quality classification, which is important for further processing
  of the raw images. We show how we construct centre-to-limb variation
  (CLV) profiles and how we remove large scale intensity variations
  produced by the telescope optics in order to get images with uniform
  intensity and contrast. Another important point is an overview of the
  different data products from raw images to high contrast images with
  heliographic grids overlaid. As the data products are accessible via
  different sources, we also present how to get information about the
  availability and how to obtain these data. Finally, in an appendix,
  we describe in detail the information in the FITS headers, the file
  naming and the data hierarchy.

---------------------------------------------------------
Title: The high-energy Sun - probing the origins of particle
    acceleration on our nearest star
Authors: Matthews, S. A.; Reid, H. A. S.; Baker, D.; Bloomfield, D. S.;
   Browning, P. K.; Calcines, A.; Del Zanna, G.; Erdelyi, R.; Fletcher,
   L.; Hannah, I. G.; Jeffrey, N.; Klein, L.; Krucker, S.; Kontar, E.;
   Long, D. M.; MacKinnon, A.; Mann, G.; Mathioudakis, M.; Milligan,
   R.; Nakariakov, V. M.; Pesce-Rollins, M.; Shih, A. Y.; Smith, D.;
   Veronig, A.; Vilmer, N.
2021ExA...tmp..135M    Altcode:
  As a frequent and energetic particle accelerator, our Sun provides
  us with an excellent astrophysical laboratory for understanding
  the fundamental process of particle acceleration. The exploitation
  of radiative diagnostics from electrons has shown that acceleration
  operates on sub-second time scales in a complex magnetic environment,
  where direct electric fields, wave turbulence, and shock waves all
  must contribute, although precise details are severely lacking. Ions
  were assumed to be accelerated in a similar manner to electrons, but
  γ-ray imaging confirmed that emission sources are spatially separated
  from X-ray sources, suggesting distinctly different acceleration
  mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic
  understanding of accelerated particle spectra and the total energy
  budgets are therefore poorly constrained. Additionally, the recent
  detection of relativistic ion signatures lasting many hours, without
  an electron counterpart, is an enigma. We propose a single platform
  to directly measure the physical conditions present in the energy
  release sites and the environment in which the particles propagate and
  deposit their energy. To address this fundamental issue, we set out
  a suite of dedicated instruments that will probe both electrons and
  ions simultaneously to observe; high (seconds) temporal resolution
  photon spectra (4 keV - 150 MeV) with simultaneous imaging (1 keV -
  30 MeV), polarization measurements (5-1000 keV) and high spatial and
  temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray)
  regimes. These instruments will observe the broad range of radiative
  signatures produced in the solar atmosphere by accelerated particles.

---------------------------------------------------------
Title: Magnetic helicity and energy budget around large confined
    and eruptive solar flares
Authors: Gupta, M.; Thalmann, J. K.; Veronig, A. M.
2021A&A...653A..69G    Altcode: 2021arXiv210608781G
  Context. In order to better understand the underlying processes
  and prerequisites for solar activity, it is essential to study the
  time evolution of the coronal magnetic field of solar active regions
  (ARs) associated with flare activity. <BR /> Aims: We investigate the
  coronal magnetic energy and helicity budgets of ten solar ARs around
  the times of large flares. In particular, we are interested in a
  possible relation of the derived quantities to the particular type of
  the flares that the AR produces, namely, whether they are associated
  with a CME or whether they are confined (i.e., not accompanied by a
  CME). <BR /> Methods: Using an optimization approach, we employed time
  series of 3D nonlinear force-free magnetic field models of ten ARs,
  covering a time span of several hours around the time of occurrence
  of large solar flares (GOES class M1.0 and larger). We subsequently
  computed the 3D magnetic vector potentials associated to the model 3D
  coronal magnetic field using a finite-volume method. This allows us
  to correspondingly compute the coronal magnetic energy and helicity
  budgets, as well as related (intensive) quantities such as the
  relative contribution of free magnetic energy, E<SUB>F</SUB>/E (energy
  ratio), the fraction of non-potential (current-carrying) helicity,
  |H<SUB>J</SUB>|/|H<SUB>V</SUB>| (helicity ratio), and the normalized
  current-carrying helicity, |H<SUB>J</SUB>|/ϕ'<SUP>2</SUP>. <BR />
  Results: The total energy and helicity budgets of flare-productive
  ARs (extensive parameters) cover a broad range of magnitudes, with
  no obvious relation to the eruptive potential of the individual
  ARs, that is, whether or not a CME is produced in association with
  the flare. The intensive eruptivity proxies, E<SUB>F</SUB>/E and
  |H<SUB>J</SUB>|/|H<SUB>V</SUB>|, and |H<SUB>J</SUB>|/ϕ'<SUP>2</SUP>,
  however, seem to be distinctly different for ARs that produce
  CME-associated large flares compared to those which produce confined
  flares. For the majority of ARs in our sample, we are able to identify
  characteristic pre-flare magnitudes of the intensive quantities
  that are clearly associated with subsequent CME-productivity. <BR />
  Conclusions: If the corona of an AR exhibits characteristic values of
  ⟨|H<SUB>J</SUB>|/|H<SUB>V</SUB>|⟩ &gt; 0.1, ⟨E<SUB>F</SUB>/E⟩
  &gt; 0.2, and ⟨|H<SUB>J</SUB>|/ϕ'<SUP>2</SUP>⟩ &gt; 0.005, then
  the AR is likely to produce large CME-associated flares. Conversely,
  confined large flares tend to originate from ARs that exhibit
  coronal values of ⟨|H<SUB>J</SUB>|/|H<SUB>V</SUB>|⟩ ≲ 0.1,
  ⟨E<SUB>F</SUB>/E⟩ ≲ 0.1, and ⟨|H<SUB>J</SUB>|/ϕ'<SUP>2</SUP>⟩
  ≲ 0.002.

---------------------------------------------------------
Title: Magnetic field measurements in a limb solar flare by hydrogen,
    helium and ionized calcium lines
Authors: Yakovkin, I. I.; Veronig, A. M.; Lozitsky, V. G.
2021AdSpR..68.1507Y    Altcode:
  We present simultaneous magnetic field measurements for the limb solar
  flare of 1981 July 17 using of the Ca II K, Hδ, He I 4471.5 Å and Hβ
  lines. For two moments during the flare, which differ in time by 16 min,
  we analyzed Stokes I ± V profiles of these lines from observations
  made on the Echelle spectrograph of the horizontal solar telescope of
  the Astronomical Observatory of Taras Shevchenko National University of
  Kiev. At the time step that was close to the peak phase of the flare,
  all the spectral lines under study showed very wide emissions, with a
  full width at half maximum (FWHM) of 3.5-4 Å. An interesting feature
  was observed in the blue wings of these lines, namely, narrow emission
  peaks with a FWHM of only 0.25-0.35 Å. For heights of 10-18 Mm above
  the level of the photosphere, we found that (a) very strong kG magnetic
  fields (up to about 3 kG) existed at both moments of the flare, (b)
  the locations with strongest fields, in general, do not coincide for
  different spectral lines, (c) the polarities of the magnetic field for
  different spectral lines are in most cases identical, but sometimes they
  do not coincide. The data obtained indicate a significant inhomogeneity
  of the magnetic field in the flaring corona and the probable presence
  of the conditions necessary for magnetic reconnection of field lines.

---------------------------------------------------------
Title: Multi-channel coronal hole detection with convolutional
    neural networks
Authors: Jarolim, R.; Veronig, A. M.; Hofmeister, S.; Heinemann,
   S. G.; Temmer, M.; Podladchikova, T.; Dissauer, K.
2021A&A...652A..13J    Altcode: 2021arXiv210414313J
  Context. A precise detection of the coronal hole boundary is of
  primary interest for a better understanding of the physics of coronal
  holes, their role in the solar cycle evolution, and space weather
  forecasting. <BR /> Aims: We develop a reliable, fully automatic
  method for the detection of coronal holes that provides consistent
  full-disk segmentation maps over the full solar cycle and can perform
  in real-time. <BR /> Methods: We use a convolutional neural network
  to identify the boundaries of coronal holes from the seven extreme
  ultraviolet (EUV) channels of the Atmospheric Imaging Assembly (AIA)
  and from the line-of-sight magnetograms provided by the Helioseismic
  and Magnetic Imager (HMI) on board the Solar Dynamics Observatory
  (SDO). For our primary model (Coronal Hole RecOgnition Neural Network
  Over multi-Spectral-data; CHRONNOS) we use a progressively growing
  network approach that allows for efficient training, provides detailed
  segmentation maps, and takes into account relations across the full
  solar disk. <BR /> Results: We provide a thorough evaluation for
  performance, reliability, and consistency by comparing the model
  results to an independent manually curated test set. Our model shows
  good agreement to the manual labels with an intersection-over-union
  (IoU) of 0.63. From the total of 261 coronal holes with an area
  &gt; 1.5 × 10<SUP>10</SUP> km<SUP>2</SUP> identified during
  the time-period from November 2010 to December 2016, 98.1% were
  correctly detected by our model. The evaluation over almost the full
  solar cycle no. 24 shows that our model provides reliable coronal
  hole detections independent of the level of solar activity. From a
  direct comparison over short timescales of days to weeks, we find
  that our model exceeds human performance in terms of consistency
  and reliability. In addition, we train our model to identify coronal
  holes from each channel separately and show that the neural network
  provides the best performance with the combined channel information,
  but that coronal hole segmentation maps can also be obtained from
  line-of-sight magnetograms alone. <BR /> Conclusions: The proposed
  neural network provides a reliable data set for the study of solar-cycle
  dependencies and coronal-hole parameters. Given the fast and robust
  coronal hole segmentation, the algorithm is also highly suitable for
  real-time space weather applications. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202140640/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Magnetic Flux and Magnetic Nonpotentiality of Active Regions
    in Eruptive and Confined Solar Flares
Authors: Li, Ting; Chen, Anqin; Hou, Yijun; Veronig, Astrid M.; Yang,
   Shuhong; Zhang, Jun
2021ApJ...917L..29L    Altcode: 2021arXiv210801299L
  With the aim of understanding how the magnetic properties of active
  regions (ARs) control the eruptive character of solar flares, we analyze
  719 flares of Geostationary Operational Environmental Satellite (GOES)
  class ≥C5.0 during 2010-2019. We carry out the first statistical study
  that investigates the flare-coronal mass ejection (CME) association
  rate as a function of the flare intensity and the AR characteristics
  that produce the flare, in terms of its total unsigned magnetic flux
  (Φ<SUB>AR</SUB>). Our results show that the slope of the flare-CME
  association rate with flare intensity reveals a steep monotonic decrease
  with Φ<SUB>AR</SUB>. This means that flares of the same GOES class but
  originating from an AR of larger Φ<SUB>AR</SUB>, are much more likely
  to be confined. Based on an AR flux as high as 1.0 × 10<SUP>24</SUP>
  Mx for solar-type stars, we estimate that the CME association rate in
  X100-class "superflares" is no more than 50%. For a sample of 132 flares
  ≥M2.0 class, we measure three nonpotential parameters including the
  length of steep gradient polarity-inversion line (L<SUB>SGPIL</SUB>),
  the total photospheric free magnetic energy (E<SUB>free</SUB>),
  and the area with large shear angle (A<SUB>Ψ</SUB>). We find that
  confined flares tend to have larger values of L<SUB>SGPIL</SUB>,
  E<SUB>free</SUB>, and A<SUB>Ψ</SUB> compared to eruptive flares. Each
  nonpotential parameter shows a moderate positive correlation with
  Φ<SUB>AR</SUB>. Our results imply that Φ<SUB>AR</SUB> is a decisive
  quantity describing the eruptive character of a flare, as it provides
  a global parameter relating to the strength of the background field
  confinement.

---------------------------------------------------------
Title: 2019 International Women's Day event. Two-step solar flare
    with multiple eruptive signatures and low Earth impact
Authors: Dumbović, M.; Veronig, A. M.; Podladchikova, T.; Thalmann,
   J. K.; Chikunova, G.; Dissauer, K.; Magdalenić, J.; Temmer, M.; Guo,
   J.; Samara, E.
2021A&A...652A.159D    Altcode: 2021arXiv210615417D
  Context. We present a detailed analysis of an eruptive event that
  occurred on 2019 March 8 in the active region AR 12734, which we
  refer as the International Women's Day event. The event under study
  is intriguing based on several aspects: (1) low-coronal eruptive
  signatures come in `pairs', namely, there is a double-peaked flare,
  two coronal dimmings, and two extreme ultraviolet (EUV) waves; (2)
  although the event is characterized by a complete chain of eruptive
  signatures, the corresponding coronagraphic signatures are weak;
  and (3) although the source region of the eruption is located close
  to the center of the solar disc and the eruption is thus presumably
  Earth-directed, heliospheric signatures are very weak with very weak
  Earth impact. <BR /> Aims: In order to understand the initiation and
  evolution of this particular event, we performed a comprehensive
  analysis using a combined observational-modeling approach. <BR />
  Methods: We analyzed a number of multi-spacecraft and multi-instrument
  (both remote-sensing and in situ) observations, including soft X-ray,
  EUV, radio and white-light emission, as well as plasma, magnetic field,
  and particle measurements. We employed 3D nonlinear force-free modeling
  to investigate the coronal magnetic field configuration in and around
  the active region, the graduated cylindrical shell model to make a 3D
  reconstruction of the CME geometry, and the 3D magnetohydrodynamical
  numerical model EUropean Heliospheric FORecasting Information Asset
  to model the background state of the heliosphere. <BR /> Results:
  Our results reveal a two-stage C1.3 flare, associated with two
  EUV waves that occur in close succession and two-stage coronal
  dimmings that evolve co-temporally with the flare and type II and
  III radio bursts. Despite its small GOES class, a clear drop in
  magnetic free energy and helicity is observed during the flare. White
  light observations do not unambiguously indicate two separate CMEs,
  but rather a single entity most likely composed of two sheared and
  twisted structures corresponding to the two eruptions observed in the
  low corona. The corresponding interplanetary signatures are that of
  a small flux rope swith indications of strong interactions with the
  ambient plasma, which result in a negligible geomagnetic impact. <BR
  /> Conclusions: Our results indicate two subsequent eruptions of
  two systems of sheared and twisted magnetic fields, which already
  begin to merge in the upper corona and start to evolve further out
  as a single entity. The large-scale magnetic field significantly
  influences both the early and the interplanetary evolution of the
  structure. During the first eruption, the stability of the overlying
  field was disrupted, enabling the second eruption. We find that during
  the propagation in the interplanetary space the large-scale magnetic
  field, that is, the location of heliospheric current sheet between the
  AR and the Earth, is likely to influence propagation, along with the
  evolution of the erupted structure(s). <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202140752/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Hemispheric sunspot numbers 1874-2020
Authors: Veronig, Astrid M.; Jain, Shantanu; Podladchikova, Tatiana;
   Pötzi, Werner; Clette, Frederic
2021A&A...652A..56V    Altcode: 2021arXiv210700553V
  Context. Previous studies show significant north-south asymmetries
  for various features and indicators of solar activity. These findings
  suggest some decoupling between the two hemispheres over the solar
  cycle evolution, which is in agreement with dynamo theories. For the
  most important solar activity index, the sunspot numbers, so far only
  limited data are available for the two hemispheres independently. <BR
  /> Aims: The aim of this study is to create a continuous series of
  daily and monthly hemispheric sunspot numbers (HSNs) from 1874 to
  2020, which will be continuously expanded in the future with the
  HSNs provided by SILSO. <BR /> Methods: Based on the available daily
  measurements of hemispheric sunspot areas from 1874 to 2016 from
  Greenwich Royal Observatory and National Oceanic and Atmospheric
  Administration, we derive the relative fractions of the northern and
  southern activity. These fractions are applied to the international
  sunspot number (ISN) to derive the HSNs. This method and obtained
  data are validated against published HSNs for the period 1945-2004
  and those provided by SILSO for 1992 to 2016. <BR /> Results: We
  provide a continuous data series and catalogue of daily, monthly
  mean, and 13-month smoothed monthly mean HSNs for the time range
  1874-2020 -fully covering solar cycles 12 to 24- that are consistent
  with the newly calibrated ISN (Clette et al., 2014). Validation of the
  reconstructed HSNs against the direct data available since 1945 reveals
  a high level of consistency, with Pearson correlation coefficients
  of r = 0.94 (0.97) for the daily (monthly mean) data. The cumulative
  hemispheric asymmetries for cycles 12-24 give a mean value of 16%,
  with no obvious pattern in north-south predominance over the cycle
  evolution. The strongest asymmetry occurs for cycle no. 19, in which
  the northern hemisphere shows a cumulated predominance of 42%. The
  phase shift between the peaks of solar activity in the two hemispheres
  may be up to 28 months, with a mean absolute value over cycles 12-24
  of 16.8 months. The phase shifts reveal an overall asymmetry of the
  northern hemisphere reaching its cycle maximum earlier (in 10 out of
  13 cases), with a mean signed phase shift of −7.6 months. Relating
  the ISN and HSN peak growth rates during the cycle rise phase with
  the cycle amplitude reveals higher correlations when considering the
  two hemispheres individually, with r ≈ 0.9. <BR /> Conclusions:
  Our findings provide further evidence that to some degree the solar
  cycle evolves independently in the two hemispheres, and demonstrate
  that empirical solar cycle prediction methods can be improved by
  investigating the solar cycle dynamics in terms of the HSN evolution. <P
  />The catalogue is only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56</A>

---------------------------------------------------------
Title: Probabilistic Drag-Based Ensemble Model (DBEM) Evaluation
    for Heliospheric Propagation of CMEs
Authors: Čalogović, Jaša; Dumbović, Mateja; Sudar, Davor; Vršnak,
   Bojan; Martinić, Karmen; Temmer, Manuela; Veronig, Astrid M.
2021SoPh..296..114C    Altcode: 2021arXiv210706684C
  The Drag-based Model (DBM) is a 2D analytical model for heliospheric
  propagation of Coronal Mass Ejections (CMEs) in ecliptic plane
  predicting the CME arrival time and speed at Earth or any other given
  target in the solar system. It is based on the equation of motion and
  depends on initial CME parameters, background solar wind speed, w and
  the drag parameter γ . A very short computational time of DBM (&lt;
  0.01 s) allowed us to develop the Drag-Based Ensemble Model (DBEM)
  that takes into account the variability of model input parameters
  by making an ensemble of n different input parameters to calculate
  the distribution and significance of the DBM results. Thus the DBEM
  is able to calculate the most likely CME arrival times and speeds,
  quantify the prediction uncertainties and determine the confidence
  intervals. A new DBEMv3 version is described in detail and evaluated
  for the first time determining the DBEMv3 performance and errors by
  using various CME-ICME lists and it is compared with previous DBEM
  versions, ICME being a short-hand for interplanetary CME. The analysis
  to find the optimal drag parameter γ and ambient solar wind speed
  w showed that somewhat higher values (γ ≈0.3 ×10<SUP>−7</SUP>
  km<SUP>−1</SUP>, w ≈ 425 km s<SUP>−1</SUP>) for both of these DBEM
  input parameters should be used for the evaluation than the previously
  employed ones. Based on the evaluation performed for 146 CME-ICME pairs,
  the DBEMv3 performance with mean error (ME) of −11.3 h, mean absolute
  error (MAE) of 17.3 h was obtained. There is a clear bias towards
  the negative prediction errors where the fast CMEs are predicted to
  arrive too early, probably due to the model physical limitations and
  input errors (e.g. CME launch speed). This can be partially reduced by
  using larger values for γ resulting in smaller prediction errors (ME
  =−3.9 h, MAE = 14.5 h) but at the cost of larger prediction errors
  for single fast CMEs as well as larger CME arrival speed prediction
  errors. DBEMv3 showed also slight improvement in the performance for
  all calculated output parameters compared to the previous DBEM versions.

---------------------------------------------------------
Title: A journey of exploration to the polar regions of a star:
    probing the solar poles and the heliosphere from high helio-latitude
Authors: Harra, Louise; Andretta, Vincenzo; Appourchaux, Thierry;
   Baudin, Frédéric; Bellot-Rubio, Luis; Birch, Aaron C.; Boumier,
   Patrick; Cameron, Robert H.; Carlsson, Matts; Corbard, Thierry;
   Davies, Jackie; Fazakerley, Andrew; Fineschi, Silvano; Finsterle,
   Wolfgang; Gizon, Laurent; Harrison, Richard; Hassler, Donald M.;
   Leibacher, John; Liewer, Paulett; Macdonald, Malcolm; Maksimovic,
   Milan; Murphy, Neil; Naletto, Giampiero; Nigro, Giuseppina; Owen,
   Christopher; Martínez-Pillet, Valentín; Rochus, Pierre; Romoli,
   Marco; Sekii, Takashi; Spadaro, Daniele; Veronig, Astrid; Schmutz, W.
2021ExA...tmp...93H    Altcode: 2021arXiv210410876H
  A mission to view the solar poles from high helio-latitudes (above 60°)
  will build on the experience of Solar Orbiter as well as a long heritage
  of successful solar missions and instrumentation (e.g. SOHO Domingo et
  al. (Solar Phys. 162(1-2), 1-37 1995), STEREO Howard et al. (Space
  Sci. Rev. 136(1-4), 67-115 2008), Hinode Kosugi et al. (Solar
  Phys. 243(1), 3-17 2007), Pesnell et al. Solar Phys. 275(1-2),
  3-15 2012), but will focus for the first time on the solar poles,
  enabling scientific investigations that cannot be done by any other
  mission. One of the major mysteries of the Sun is the solar cycle. The
  activity cycle of the Sun drives the structure and behaviour of the
  heliosphere and of course, the driver of space weather. In addition,
  solar activity and variability provides fluctuating input into the
  Earth climate models, and these same physical processes are applicable
  to stellar systems hosting exoplanets. One of the main obstructions
  to understanding the solar cycle, and hence all solar activity,
  is our current lack of understanding of the polar regions. In this
  White Paper, submitted to the European Space Agency in response to the
  Voyage 2050 call, we describe a mission concept that aims to address
  this fundamental issue. In parallel, we recognise that viewing the Sun
  from above the polar regions enables further scientific advantages,
  beyond those related to the solar cycle, such as unique and powerful
  studies of coronal mass ejection processes, from a global perspective,
  and studies of coronal structure and activity in polar regions. Not
  only will these provide important scientific advances for fundamental
  stellar physics research, they will feed into our understanding of
  impacts on the Earth and other planets' space environment.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers
    1874-2020 (Veronig+, 2021)
Authors: Veronig, A. M.; Jain, S.; Podladchikova, T.; Poetzi, W.;
   Clette, F.
2021yCat..36520056V    Altcode:
  We provide a catalogue that contains hemispheric sunspot numbers (HSN)
  from 1874 until 2020. Catalogue A contains the daily data. Catalogue
  B contains the monthly mean and 13-month smoothed monthly data. This
  series will be continuously expanded in the future with the HSN
  provided by the SILSO World Data Center (http://www.sidc.be/silso/). The
  long-term HSN catalogue provided here was created using the available
  daily measurements of hemispheric sunspot areas from 1874-2016 from
  Greenwich Royal Observatory and NOAA, from which we derived the
  relative fractions of the Northern and Southern activity. These
  fractions were subsequently applied to the International Sunspot
  Numbers (ISN) to derive the HSN. This method and obtained data have
  been validated against the HSN available for the period 1945-2004
  from Temmer et al. (2006A&amp;A...447..735T, Cat. J/A+A/447/735)
  and 1992-2020 by SILSO. The 13-month smoothed data presented in the
  catalogue uses the optimized smoothing method described in Podladchikova
  et al. (2017ApJ...850...81P). <P />(2 data files).

---------------------------------------------------------
Title: Drag-based model (DBM) tools for forecast of coronal mass
    ejection arrival time and speed
Authors: Dumbović, Mateja; Čalogović, Jaša; Martinić, Karmen;
   Vršnak, Bojan; Sudar, Davor; Temmer, Manuela; Veronig, Astrid
2021FrASS...8...58D    Altcode: 2021arXiv210314292D
  Forecasting the arrival time of coronal mass ejections (CMEs) and
  their associated shocks is one of the key aspects of space weather
  research and predictions. One of the commonly used models is, due
  to its simplicity and calculation speed, the analytical drag-based
  model (DBM) for heliospheric propagation of CMEs. DBM relies on
  the observational fact that slow CMEs accelerate whereas fast CMEs
  decelerate, and is based on the concept of MHD drag, which acts to
  adjust the CME speed to the ambient solar wind. Although physically
  DBM is applicable only to the CME magnetic structure, it is often used
  as a proxy for the shock arrival. In recent years, the DBM equation
  has been used in many studies to describe the propagation of CMEs
  and shocks with different geometries and assumptions. Here we give
  an overview of the five DBM versions currently available and their
  respective tools, developed at Hvar Observatory and frequently used
  by researchers and forecasters. These include: 1) basic 1D DBM, a 1D
  model describing the propagation of a single point (i.e. the apex of
  the CME) or concentric arc (where all points propagate identically); 2)
  advanced 2D self-similar cone DBM, a 2D model which combines basic DBM
  and cone geometry describing the propagation of the CME leading edge
  which evolves self-similarly; 3) 2D flattening cone DBM, a 2D model
  which combines basic DBM and cone geometry describing the propagation
  of the CME leading edge which does not evolve self-similarly; 4)
  DBEMv1, an ensemble version of the 2D flattening cone DBM which uses
  CME ensembles as an input and 5) DBEMv3, an ensemble version of the
  2D flattening cone DBM which creates CME ensembles based on the input
  uncertainties. All five versions have been tested and published in
  recent years and are available online or upon request. We provide an
  overview of these five tools, of their similarities and differences,
  as well as discuss and demonstrate their application.

---------------------------------------------------------
Title: The Observational Uncertainty of Coronal Hole Boundaries in
    Automated Detection Schemes
Authors: Reiss, Martin A.; Muglach, Karin; Möstl, Christian; Arge,
   Charles N.; Bailey, Rachel; Delouille, Véronique; Garton, Tadhg M.;
   Hamada, Amr; Hofmeister, Stefan; Illarionov, Egor; Jarolim, Robert;
   Kirk, Michael S. F.; Kosovichev, Alexander; Krista, Larisza; Lee,
   Sangwoo; Lowder, Chris; MacNeice, Peter J.; Veronig, Astrid; Cospar
   Iswat Coronal Hole Boundary Working Team
2021ApJ...913...28R    Altcode: 2021arXiv210314403R
  Coronal holes are the observational manifestation of the solar
  magnetic field open to the heliosphere and are of pivotal importance
  for our understanding of the origin and acceleration of the solar
  wind. Observations from space missions such as the Solar Dynamics
  Observatory now allow us to study coronal holes in unprecedented
  detail. Instrumental effects and other factors, however, pose a
  challenge to automatically detect coronal holes in solar imagery. The
  science community addresses these challenges with different detection
  schemes. Until now, little attention has been paid to assessing the
  disagreement between these schemes. In this COSPAR ISWAT initiative,
  we present a comparison of nine automated detection schemes widely
  applied in solar and space science. We study, specifically, a prevailing
  coronal hole observed by the Atmospheric Imaging Assembly instrument
  on 2018 May 30. Our results indicate that the choice of detection
  scheme has a significant effect on the location of the coronal hole
  boundary. Physical properties in coronal holes such as the area, mean
  intensity, and mean magnetic field strength vary by a factor of up
  to 4.5 between the maximum and minimum values. We conclude that our
  findings are relevant for coronal hole research from the past decade,
  and are therefore of interest to the solar and space research community.

---------------------------------------------------------
Title: Medium-term Predictions of F10.7 and F30 cm Solar Radio Flux
    with the Adaptive Kalman Filter
Authors: Petrova, Elena; Podladchikova, Tatiana; Veronig, Astrid M.;
   Lemmens, Stijn; Bastida Virgili, Benjamin; Flohrer, Tim
2021ApJS..254....9P    Altcode: 2021arXiv210308059P
  The solar radio flux at F10.7 and F30 cm is required by most models
  characterizing the state of the Earth's upper atmosphere, such as the
  thermosphere and ionosphere, to specify satellite orbits, re-entry
  services, collision avoidance maneuvers, and modeling of the evolution
  of space debris. We develop a method called RESONANCE (Radio Emissions
  from the Sun: ONline ANalytical Computer-aided Estimator) for the
  prediction of the 13-month smoothed monthly mean F10.7 and F30 indices
  1-24 months ahead. The prediction algorithm has three steps. First, we
  apply a 13-month optimized running mean technique to effectively reduce
  the noise in the radio flux data. Second, we provide initial predictions
  of the F10.7 and F30 indices using the McNish-Lincoln method. Finally,
  we improve these initial predictions by developing an adaptive Kalman
  filter with identification of the error statistics. The rms error of
  predictions with lead times from 1 to 24 months is 5-27 solar flux units
  (sfu) for the F10.7 index and 3-16 sfu for F30, which statistically
  outperforms current algorithms in use. The proposed approach based
  on the Kalman filter is universal and can be applied to improve the
  initial predictions of a process under study provided by any other
  forecasting method. Furthermore, we present a systematic evaluation
  of re-entry forecast as an application to test the performance of
  F10.7 predictions on past ESA re-entry campaigns for payloads, rocket
  bodies, and space debris that re-entered from 2006 to 2019 June. The
  test results demonstrate that the predictions obtained by RESONANCE in
  general also lead to improvements in the forecasts of re-entry epochs.

---------------------------------------------------------
Title: Plasma Diagnostics of Microflares observed by STIX and AIA
Authors: Saqri, Jonas; Veronig, Astrid; Dickson, Ewan; Krucker, Säm;
   Battaglia, Andrea Francesco; Battaglia, Marina; Xiao, Hualin; Warmuth,
   Alexander; the STIX Team
2021EGUGA..23.7966S    Altcode:
  Solar flares are generally thought to be the impulsive release
  of magnetic energy giving rise to a wide range of solar phenomena
  that influence the heliosphere and in some cases even conditions of
  earth. Part of this liberated energy is used for particle acceleration
  and to heat up the solar plasma. The Spectrometer/Telescope for Imaging
  X-rays (STIX) instrument onboard the Solar Orbiter mission launched
  on February 10th 2020 promises advances in the study of solar flares
  of various sizes. It is capable of measuring X-ray spectra from 4
  to 150 keV with 1 keV resolution binned into 32 energy bins before
  downlinking. With this energy range and sensitivity, STIX is capable
  of sampling thermal plasma with temperatures of≳10 MK, and to
  diagnose the nonthermal bremsstrahlung emission of flare-accelerated
  electrons. During the spacecraft commissioning phase in the first
  half of the year 2020, STIX observed 68 microflares. Of this set, 26
  events could clearly be identified in at least two energy channels,
  all of which originated in an active region that was also visible from
  earth. These events provided a great opportunity to combine the STIX
  observations with the multi-band EUV imagery from the Atmospheric
  Imaging Assembly (AIA) instrument on board the earth orbiting
  Solar Dynamics Observatory (SDO). For the microflares that could be
  identified in two STIX science energy bands, it was possible to derive
  the temperature and emission measure (EM) of the flaring plasma assuming
  an isothermal source. For larger events where more detailed spectra
  could be derived, a more accurate analysis was performed by fitting
  the spectra assuming various thermal and nonthermal sources. These
  results are compared to the diagnostics derived from AIA images. To
  this aim, the Differential EmissionMeasure (DEM) was reconstructed from
  AIA observations to infer plasma temperatures and EM in the flaring
  regions. Combined with the the relative timing between the emission
  seen by STIX and AIA, this allows us to get deeper insight into the
  flare energy release and transport processes.

---------------------------------------------------------
Title: Statistical study of CMEs, lateral overexpansion and SEP events
Authors: Adamis, Alexandros; Veronig, Astrid; Podladchikova, Tatiana;
   Dissauer, Karin; Miteva, Rositsa; Guo, Jingnan; Haberle, Veronika;
   Dumbovic, Mateja; Temmer, Manuela; Kozarev, Kamen; Magdalenic, Jasmina;
   Kay, Christina
2021EGUGA..23.3216A    Altcode:
  We present a statistical study on the early evolution of coronal mass
  ejections (CMEs), to better understand the effect of CME (over)-
  expansion and how it relates to the production of Solar Energetic
  Particle (SEP) events. We study the kinematic CME characteristics
  in terms of their radial and lateral expansion, from their early
  evolution in the Sun"s atmosphere as observed in EUV imagers and
  coronagraphs. The data covers 72 CMEs that occurred in the time range of
  July 2010 to September 2012, where the twin STEREO spacecraft where in
  quasiquadrature to the Sun-Earth line. From the STEREO point-of-view,
  the CMEs under study were observed close to the limb. We calculated
  the radial and lateral height (width) versus time profiles and
  derived the corresponding peak and mean velocities, accelerations,
  and angular expansion rates, with particular emphasis on the role
  of potential lateral overexpansion in the early CME evolution. We
  find high correlations between the radial and lateral CME velocities
  and accelerations. CMEs that are associated tend to be located at
  the high-value end of the distributions of velocities, widths, and
  expansion rates compared to nonSEP associated events.

---------------------------------------------------------
Title: Multi-Channel Coronal Hole Detection with Convolutional
    Neural Networks
Authors: Jarolim, Robert; Veronig, Astrid; Hofmeister, Stefan;
   Heinemann, Stephan; Temmer, Manuela; Podladchikova, Tatiana; Dissauer,
   Karin
2021EGUGA..23.1490J    Altcode:
  Being the source region of fast solar wind streams, coronal holes are
  one of the key components which impact space weather. The precise
  detection of the coronal hole boundary is an important criterion
  for forecasting and solar wind modeling, but also challenges our
  current understanding of the magnetic structure of the Sun. We use
  deep-learning to provide new methods for the detection of coronal holes,
  based on the multi-band EUV filtergrams and LOS magnetogram from the
  AIA and HMI instruments onboard the Solar Dynamics Observatory. The
  proposed neural network is capable to simultaneously identify full-disk
  correlations as well as small-scale structures and efficiently combines
  the multi-channel information into a single detection. From the
  comparison with an independent manually curated test set, the model
  provides a more stable extraction of coronal holes than the samples
  considered for training. Our method operates in real-time and provides
  reliable coronal hole extractions throughout the solar cycle, without
  any additional adjustments. We further investigate the importance of
  the individual channels and show that our neural network can identify
  coronal holes solely from magnetic field data.

---------------------------------------------------------
Title: Clustering of Fast Coronal Mass Ejections during Solar Cycles
    23 and 24 and Implications for CME-CME Interactions
Authors: Rodriguez Gomez, Jenny Marcela; Podlachikova, Tatiana;
   Veronig, Astrid; Ruzmaikin, Alexander; Feynman, Joan; Petrukovich,
   Anatoly
2021EGUGA..23.3990R    Altcode:
  Coronal Mass Ejections (CMEs) and their interplanetary counterparts
  (ICMEs) are the major sources for strong space weather disturbances. We
  present a study of statistical properties of fast CMEs (v≥1000
  km/s) that occurred during solar cycles 23 and 24. We apply the Max
  Spectrum and the declustering threshold time methods. The Max Spectrum
  can detect the predominant clusters, and the declustering threshold
  time method provides details on the typical clustering properties
  and timescales. Our analysis shows that during the different phases
  of solar cycles 23 and 24, fast CMEs preferentially occur as isolated
  events and in clusters with, on average, two members. However, clusters
  with more members appear, particularly during the maximum phases of
  the solar cycles. During different solar cycle phases, the typical
  declustering timescales of fast CMEs are τc =28-32 hrs, irrespective
  of the very different occurrence frequencies of CMEs during a solar
  minimum and maximum. These findings suggest that τc for extreme events
  may reflect the characteristic energy build-up time for large flare and
  CME-prolific active regions. Statistically associating the clustering
  properties of fast CMEs with the disturbance storm time index at Earth
  suggests that fast CMEs occurring in clusters tend to produce larger
  geomagnetic storms than isolated fast CMEs. Our results highlight the
  importance of CME-CME interaction and their impact on Space Weather.

---------------------------------------------------------
Title: First results of the STIX hard X-ray telescope onboard
    Solar Orbiter
Authors: Battaglia, Andrea Francesco; Saqri, Jonas; Dickson, Ewan;
   Xiao, Hualin; Veronig, Astrid; Warmuth, Alexander; Battaglia, Marina;
   Krucker, Säm
2021EGUGA..23.4390B    Altcode:
  With the launch and commissioning of Solar Orbiter, the
  Spectrometer/Telescope for Imaging X-rays (STIX) is the latest hard
  X-ray telescope to study solar flares over a large range of flare
  sizes. STIX uses hard X-ray imaging spectroscopy in the range from 4 to
  150 keV to diagnose the hottest temperature of solar flare plasma and
  the related nonthermal accelerated electrons. The unique orbit away
  from the Earth-Sun line in combination with the opportunity of joint
  observations with other Solar Orbiter instruments, STIX will provide
  new inputs into understanding the magnetic energy release and particle
  acceleration in solar flares. Commissioning observations showed that
  STIX is working as designed and therefore we report on the first solar
  microflare observations recorded on June 2020, when the spacecraft
  was at 0.52 AU from the Sun. STIX"s measurements are compared with
  Earth-orbiting observatories, such as GOES and SDO/AIA, for which
  we investigate and interpret the different temporal evolution. The
  detected early peak of the STIX profiles relative to GOES is due either
  by nonthermal X-ray emission of accelerated particles interacting
  with the dense chromosphere or the higher sensitivity of STIX toward
  hotter plasma.

---------------------------------------------------------
Title: Deriving CME volume and density from remote sensing data
Authors: Temmer, Manuela; Holzknecht, Lukas; Dumbovic, Mateja;
   Vrsnak, Bojan; Sachdeva, Nishtha; Heinemann, Stephan G.; Dissauer,
   Karin; Scolini, Camilla; Asvestari, Eleanna; Veronig, Astrid M.;
   Hofmeister, Stefan
2021EGUGA..23.2535T    Altcode:
  Using combined STEREO-SOHO white-light data, we present a method to
  determine the volume and density of a coronal mass ejection (CME) by
  applying the graduated cylindrical shell model (GCS) and deprojected
  mass derivation. Under the assumption that the CME mass is roughly
  equally distributed within a specific volume, we expand the CME
  self-similarly and calculate the CME density for distances close to the
  Sun (15-30 Rs) and at 1 AU. The procedure is applied on a sample of 29
  well-observed CMEs and compared to their interplanetary counterparts
  (ICMEs). Specific trends are derived comparing calculated and in-situ
  measured proton densities at 1 AU, though large uncertainties are
  revealed due to the unknown mass and geometry evolution: i) a moderate
  correlation for the magnetic structure having a mass that stays
  rather constant and ii) a weak correlation for the sheath density by
  assuming the sheath region is an extra mass - as expected for a mass
  pile-up process - that is in its amount comparable to the initial
  CME deprojected mass. High correlations are derived between in-situ
  measured sheath density and the solar wind density and solar wind speed
  as measured 24 hours ahead of the arrival of the disturbance. This
  gives additional confirmation that the sheath-plasma indeed stems from
  piled-up solar wind material. While the CME interplanetary propagation
  speed is not related to the sheath density, the size of the CME may
  play some role in how much material is piled up.

---------------------------------------------------------
Title: Coronal dimmings associated with coronal mass ejections on
    the solar limb
Authors: Chikunova, Galina; Dissauer, Karin; Podladchikova, Tatiana;
   Veronig, Astrid
2021EGUGA..23.3134C    Altcode:
  We studied 43 coronal dimming events associated with Earth-directed
  coronal mass ejections (CMEs) that were observed in quasi-quadrature
  by the SDO and STEREO satellites. We derived the properties of the
  dimmings as observed above the limb by STEREO EUVI, and compared them
  with the mass and speed of the associated CMEs. The unique satellite
  constellation allowed us to compare our findings with the results from
  Dissauer et al. (2018, 2019), who studied these events observed against
  the solar disk by SDO AIA. Such statistics is done for the first time
  and confirms the close relation between characteristic dimming and
  CME parameters for the off-limb viewpoint. We find that the dimming
  areas are typically larger for off-limb observations (mean value of
  1.24±1.23×1011 km2 against 3.51±0.71×1010 km2 for on-disk), while
  the decrease in the total extreme ultraviolet intensity is similar
  (c=0.60±0.14). The off-limb dimming areas and brightnesses are
  strongly correlated with the CME mass (c=0.82±0.06 and 0.75±0.08),
  whereas the dimming area and brightness change rate correlate with
  the CME speed (c∼0.6). Our findings suggest that coronal dimmings
  have the potential to provide early estimates of the Earth-directed
  CMEs parameters, relevant for space weather forecasts, for satellite
  locations at both L1 and L5.

---------------------------------------------------------
Title: Validation of Global EUV Wave MHD Simulations and Observational
    Techniques
Authors: Downs, Cooper; Warmuth, Alexander; Long, David M.; Bloomfield,
   D. Shaun; Kwon, Ryun-Young; Veronig, Astrid M.; Vourlidas, Angelos;
   Vršnak, Bojan
2021ApJ...911..118D    Altcode:
  Global EUV waves remain a controversial phenomenon more than 20 yr
  after their discovery by SOHO/EIT. Although consensus is growing in the
  community that they are most likely large-amplitude waves or shocks,
  the wide variety of observations and techniques used to identify
  and analyze them have led to disagreements regarding their physical
  properties and interpretation. Here, we use a 3D magnetohydrodynamic
  (MHD) model of the solar corona to simulate an EUV wave event on 2009
  February 13 to enable a detailed validation of the various commonly used
  detection and analysis techniques of global EUV waves. The simulated
  event exhibits comparable behavior to that of a real EUV wave event,
  with similar kinematic behavior and plasma parameter evolution. The
  kinematics of the wave are estimated via visual identification and
  profile analysis, with both approaches providing comparable results. We
  find that projection effects can affect the derived kinematics of the
  wave, due to the variation in fast-mode wave speed with height in the
  corona. Coronal seismology techniques typically used for estimates
  of the coronal magnetic field are also tested and found to estimate
  fast-mode speeds comparable to those of the model. Plasma density
  and temperature variations of the wave front are also derived using
  a regularized inversion approach and found to be consistent with
  observed wave events. These results indicate that global waves are
  best interpreted as large-amplitude waves and that they can be used
  to probe the coronal medium using well-defined analysis techniques.

---------------------------------------------------------
Title: Search for flares and associated CMEs on late-type
    main-sequence stars in optical SDSS spectra
Authors: Koller, Florian; Leitzinger, Martin; Temmer, Manuela; Odert,
   Petra; Beck, Paul G.; Veronig, Astrid
2021A&A...646A..34K    Altcode: 2020arXiv201200786K
  <BR /> Aims: This work aims to detect and classify stellar flares and
  potential stellar coronal mass ejection (CME) signatures in optical
  spectra provided by the Sloan Digital Sky Survey (SDSS) data release
  14. The sample is constrained to all F, G, K, and M main-sequence
  type stars, resulting in more than 630 000 stars. This work makes
  use of the individual spectral exposures provided by the SDSS. <BR
  /> Methods: An automatic flare search was performed by detecting
  significant amplitude changes in the Hα and Hβ spectral lines after
  a Gaussian profile was fit to the line core. CMEs were searched for
  by identifying asymmetries in the Balmer lines caused by the Doppler
  effect of plasma motions in the line of sight. <BR /> Results: We
  identified 281 flares on late-type stars (spectral types K3 - M9). We
  identified six possible CME candidates showing excess flux in Balmer
  line wings. Flare energies in Hα were calculated and masses of the
  CME candidates were estimated. The derived Hα flare energies range
  from 3 × 10<SUP>28</SUP> - 2 × 10<SUP>33</SUP> erg. The Hα flare
  energy increases with earlier types, while the fraction of flaring times
  increases with later types. Mass estimates for the CME candidates are
  in the range of 6 × 10<SUP>16</SUP> - 6 × 10<SUP>18</SUP> g, and the
  highest projected velocities are ~300-700 km s<SUP>-1</SUP>. <BR />
  Conclusions: The low detection rate of CMEs we obtained agrees with
  previous studies, suggesting that for late-type main-sequence stars the
  CME occurrence rate that can be detected with optical spectroscopy is
  low. <P />Table C.1 is only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A34">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A34</A>

---------------------------------------------------------
Title: Statistical Approach on Differential Emission Measure of
    Coronal Holes using the CATCH Catalog
Authors: Heinemann, Stephan G.; Saqri, Jonas; Veronig, Astrid M.;
   Hofmeister, Stefan J.; Temmer, Manuela
2021SoPh..296...18H    Altcode: 2021arXiv210213396H
  Coronal holes are large-scale structures in the solar atmosphere
  that feature a reduced temperature and density in comparison to the
  surrounding quiet Sun and are usually associated with open magnetic
  fields. We perform a differential emission measure analysis on the
  707 non-polar coronal holes in the Collection of Analysis Tools for
  Coronal Holes (CATCH) catalog to derive and statistically analyze
  their plasma properties (i.e. temperature, electron density, and
  emission measure). We use intensity filtergrams of the six coronal EUV
  filters from the Atmospheric Imaging Assembly onboard the Solar Dynamics
  Observatory, which cover a temperature range from ≈10<SUP>5.5</SUP> to
  10<SUP>7.5</SUP>K. Correcting the data for stray and scattered light, we
  find that all coronal holes have very similar plasma properties with an
  average temperature of 0.94 ±0.18 MK, a mean electron density of (2.4
  ±0.7 )×10<SUP>8</SUP>cm−<SUP>3</SUP>, and a mean emission measure
  of (2.8 ±1.6 )×10<SUP>26</SUP>cm−<SUP>5</SUP>. The temperature
  distribution within the coronal holes was found to be largely uniform,
  whereas the electron density shows a 30 to 40% linear decrease from the
  boundary towards the inside of the coronal hole. At distances greater
  than 20″ (≈15 Mm) from the nearest coronal hole boundary, the
  density also becomes statistically uniform. The coronal hole temperature
  may show a weak solar-cycle dependency, but no statistically significant
  correlation of plasma properties with solar-cycle variations could be
  determined throughout the observed period between 2010 and 2019.

---------------------------------------------------------
Title: CME-CME interactions as sources of CME helio-effectiveness:
    the early September 2017 events
Authors: Scolini, Camilla; Rodriguez, Luciano; Poedts, Stefaan; Kilpua,
   Emilia; Guo, Jingnan; Pomoell, Jens; Dissauer, Karin; Veronig, Astrid;
   Dumbovic, Mateja; Chané, Emmanuel; Palmerio, Erika
2021cosp...43E1030S    Altcode:
  Coronal Mass Ejections (CMEs) are the primary source of strong
  space weather disturbances at Earth and other locations in the
  heliosphere. Understanding the physical processes involved in their
  formation at the Sun, propagation in the heliosphere, and impact
  on planetary bodies is therefore critical to improve current space
  weather predictions throughout the heliosphere. It is known that
  the capability of individual CMEs to drive strong space weather
  disturbances at Earth (known as "geo-effectiveness") and other
  locations in the heliosphere (here referred to as "helio-effectiveness")
  primarily depends on their dynamic pressure, internal magnetic field
  strength, and magnetic field orientation at the impact location. At
  the same time, observational and modelling studies also established
  that CME-CME interactions can significantly alter the properties of
  individual CMEs, in such a way that their geo-effectiveness is often
  dramatically amplified. However, the actual quantification of this
  amplification has been rarely investigated, mostly via observational
  studies of individual events, or via explorative studies performed using
  idealized simulations of CME events, for which no truthful comparison
  with observations is possible. Additionally, the amplification effect
  of CME-CME interactions has been traditionally quantified only for the
  near-Earth region of space, without considering its full space-time
  evolution as the CMEs propagate to the Earth and beyond. In this work,
  we present a comprehensive study on the role of CME-CME interactions
  as sources of CME helio-effectiveness by performing simulations of
  complex CME events with the EUHFORIA heliospheric model. As a case
  study, we consider the sequence of CMEs observed during the unusually
  active week of 4-10 September 2017. As their source region rotated on
  the solar disk, CMEs were launched over a wide range of longitudes,
  interacting with each other and paving the way for the propagation of
  the following ones. CME signatures were observed at Mars and Earth,
  where an intense geomagnetic storm triggered by CME-CME interactions
  was recorded. Using input parameters derived from remote-sensing
  multi-spacecraft observations of the CMEs and their source region,
  we perform global simulations of magnetised CMEs with EUHFORIA. We
  investigate how their interactions affected the propagation and
  internal properties of individual CME structures, and their in-situ
  signatures at Earth and Mars. Taking advantage of 3D simulation
  outputs, we quantify the amplification of the helio-effectiveness of
  the individual CMEs involved, as a function of the interaction phase
  and of the location within the CME structure. Additionally, we also
  explore the possibility of the existence of a "helio-effectiveness
  amplification zone", i.e. a characteristic heliocentric distance at
  which CME-CME interactions have the highest probability to develop into
  highly helio-effective events. Results from this study benchmark our
  current prediction capabilities in the case of complex CME events,
  and provide insights on their large-scale evolution and potential
  impact throughout the heliosphere.

---------------------------------------------------------
Title: Deriving CME Density From Remote Sensing Data and Comparison
    to In Situ Measurements
Authors: Temmer, M.; Holzknecht, L.; Dumbović, M.; Vršnak, B.;
   Sachdeva, N.; Heinemann, S. G.; Dissauer, K.; Scolini, C.; Asvestari,
   E.; Veronig, A. M.; Hofmeister, S. J.
2021JGRA..12628380T    Altcode: 2020arXiv201106880T
  We determine the three dimensional geometry and deprojected mass of 29
  well observed coronal mass ejections (CMEs) and their interplanetary
  counterparts (ICMEs) using combined Solar Terrestrial Relations
  Observatory Solar and Heliospheric Observatory white light data. From
  the geometry parameters, we calculate the volume of the CME for the
  magnetic ejecta (flux rope type geometry) and sheath structure (shell
  like geometry resembling the (I)CME frontal rim). Working under the
  assumption that the CME mass is roughly equally distributed within a
  specific volume, we expand the CME self similarly and calculate the CME
  density for distances close to the Sun (15-30 Rs) and at 1 AU. Specific
  trends are derived comparing calculated and in situ measured proton
  densities at 1 AU, though large uncertainties are revealed due to the
  unknown mass and geometry evolution: (1) a moderate correlation for
  the magnetic structure having a mass that stays rather constant (cc
  ≈ 0.56 - 0.59), and (2) a weak correlation for the sheath density (cc
  ≈ 0.26) by assuming the sheath region is an extra mass—as expected
  for a mass pile up process—that is in its amount comparable to the
  initial CME deprojected mass. High correlations are derived between in
  situ measured sheath density and the solar wind density (cc ≈ -0.73)
  and solar wind speed (cc ≈ 0.56) as measured 24 h ahead of the arrival
  of the disturbance. This gives additional confirmation that the sheath
  plasma indeed stems from piled up solar wind material. While the CME
  interplanetary propagation speed is not related to the sheath density,
  the size of the CME may play some role in how much material could be
  piled up.

---------------------------------------------------------
Title: Interpretable Solar Flare Forecasting with Deep Learning
Authors: Jarolim, Robert; Podladchikova, Tatiana; Veronig, Astrid;
   Thalmann, Julia K.; Hofinger, -Markus; Narnhofer, -Dominik; Pock,
   -Thomas; Schopper, Tobias
2021cosp...43E1036J    Altcode:
  Solar flares and coronal mass ejections (CMEs) are the main drivers
  for severe space weather disturbances on Earth and other planets. While
  the geo-effects of CMEs give us a lead time of about 1 to 4 days, the
  effects of flare induced enhanced radiation and flare-accelerated solar
  energetic particles (SEPs) are very immediate, approximately 8 and 20
  minutes, respectively. Thus, predictions of solar flare occurrence at
  least several hours ahead are of high importance for the mitigation
  of severe space weather effects. Observations and simulations of solar
  flares suggest that the structure and evolution of the active region's
  magnetic field is a key component for energetic eruptions. However,
  the main changes are assumed to happen in the coronal fields, whereas
  current measurements are mostly restricted to the photospheric magnetic
  field. We present an automatic flare prediction deep learning algorithm
  based on the HMI photospheric line-of-sight magnetic field and its
  temporal evolution together with the coronal evolution as observed by
  multi-wavelengths EUV filtergrams from the AIA instrument onboard the
  Solar Dynamics Observatory. As input to our deep learning model we use
  the magnetograms and EUV filtergrams with a cadence of 10 minutes over
  a 40 minutes time interval from pre-identified active regions. The
  neural network predicts X, M and C class flares up to 3 hours ahead,
  hereby the network assigns probabilities for the flare occurrence to
  consecutive time frames of 20 minutes. From this setup the network
  learns independently to identify features in the imaging data based
  on the dynamic evolution of the coronal structure and the photospheric
  magnetic field evolution, which may hint at flare occurrence in the near
  future. In order to overcome the "black box problem" of machine-learning
  algorithms, and thus to allow for physical interpretation of the network
  findings, we employ an attention mechanism at multiple resolution
  scales, which enables the network to focus on relevant regions within
  the spatio-temporal domain. This allows us to extract the emphasized
  regions, which reveal the neural network interpretation of the flare
  onset conditions. Our novel approach combines the performance of neural
  network predictions with the benefit of a direct interpretation of
  the relevant physical features.

---------------------------------------------------------
Title: The Origin and Early Dynamics of Solar Eruptive Flux Ropes
Authors: Gou, Tingyu; Wang, Yuming; Liu, Rui; Veronig, Astrid;
   Zhuang, Bin
2021cosp...43E.998G    Altcode:
  Solar eruptions are explosive events originated from the solar
  atmosphere and can cause a large amount of energy release within a
  short time. Among them, the helical magnetic flux rope is considered as
  a fundamental structure. However, the flux rope's origin still remains
  elusive. We present observations of how stellar-sized solar eruptions
  evolve continuously from a small-scale structure, i.e., a seed. The
  seed forms prior to the eruption and then grows into a typical flux rope
  probably by magnetic reconnection of the sheared arcade. The flux rope
  rises impulsively and it finally produces a large-scale coronal mass
  ejection (CME), accompanied by intense energy release in the form of
  plasma heating and particle acceleration. The small-scale seed plays
  an important role in the origin of large-scale solar eruptions.

---------------------------------------------------------
Title: Forecasting the arrival time of coronal mass ejections
Authors: Dumbovic, Mateja; Mays, M. Leila; Riley, Pete; Mierla,
   Marilena; Kay, Christina; Vrsnak, Bojan; Veronig, Astrid; Cremades,
   Hebe; Čalogović, Jaša; Verbeke, Christine; Temmer, Manuela; Sudar,
   Davor; Scolini, Camilla; Hinterreiter, Jürgen; Paouris, Evangelos;
   Palmerio, Erika; Balmaceda, Laura
2021cosp...43E1038D    Altcode:
  Forecasting the arrival time of coronal mass ejections (CMEs) and their
  associated shocks is one of the key aspects of space weather. In recent
  years many models have been developed by various research groups aiming
  to forecast CME arrival time. The models differ based on the input,
  approach, assumptions and complexity ranging from simple empirical and
  analytical to complex numerical and machine learning models. One of the
  commonly used models is, due to its simplicity and calculation speed,
  the analytical drag-based (ensemble) model [DB(E)M] for heliospheric
  propagation of CMEs. DB(E)M relies on the observational fact that
  slow CMEs accelerate whereas fast CMEs decelerate, and is based on
  the concept of MHD drag, which acts to adjust the CME speed to the
  ambient solar wind. However, regardless of the model, forecasting CME
  arrival time has proven to be exceedingly challenging. One of the major
  setbacks is the uncertainty of the CME observational input, which
  is still substantial despite state-of-the-art remote observational
  capacities such as high-resolution EUV imagers and stereoscopic
  observations. Another major setback is the uncertainty in the CME
  propagation itself, due to e.g. unrealistic background solar wind
  and/or complex interactions. These limits will be discussed in the
  scope of DB(E)M and the CME input analysis performed by the ISSI Bern
  team on the "Understanding Our Capabilities In Observing And Modeling
  Coronal Mass Ejections".

---------------------------------------------------------
Title: Estimating the magnetic flux within an eruptive flux rope
Authors: Temmer, Manuela; Rodriguez, Luciano; Dissauer, Karin; Veronig,
   Astrid; Tschernitz, Johannes; Thalmann, Julia K.; Hinterreiter, Jürgen
2021cosp...43E1741T    Altcode:
  Erupting magnetic flux ropes develop into coronal mass ejections (CMEs)
  as they evolve and finally propagate into interplanetary space. Those
  large scale eruptions are observed to be frequently related to dynamic
  surface phenomena such as coronal waves and dimming regions. The better
  we are able to estimate initial CME parameters such as kinematics,
  geometry, and magnetic properties, the more precisely we can feed
  state-of-the-art CME propagation models and with that improve CME
  forecasting. In that respect, we report on a well-observed flare-CME
  event from 1 October 2011 focusing on the dynamic evolution of the
  CME and its embedded magnetic field. Using combined STEREO and SDO
  observations together with nonlinear force-free (NLFF) modeling we
  derive separately the flare reconnection and dimming flux. We find
  that already before the start of the impulsive flare phase magnetic
  reconnection was ongoing, that added magnetic flux to the flux rope
  before its final eruption. As the dimming evolves over a longer time
  span than the flaring phase, we find that the dimming flux increases by
  more than 25% after the end of the flare. This indicates that magnetic
  flux is still added to the flux rope after eruption and that the derived
  flare reconnection flux is most probably a lower limit for estimating
  the magnetic flux within the flux rope.

---------------------------------------------------------
Title: Lorentz force evolution reveals the energy build-up processes
    during recurrent eruptive solar flares
Authors: Srivastava, Nandita; Veronig, Astrid; Sarkar, Ranadeep
2021cosp...43E1773S    Altcode:
  The energy release and build-up processes in the solar corona
  have significant implications in particular for the case of large
  recurrent flares in the same active region (AR), which pose challenging
  questions about the conditions that lead to the episodic energy release
  processes. It is not yet clear whether these events occur due to the
  continuous supply of free magnetic energy to the solar corona or because
  not all of the available free magnetic energy is released during a
  single major flaring event. In order to address this question, we report
  on the evolution of photospheric magnetic field and the associated net
  Lorentz force changes in ARs 11261 and 11283, each of which gave rise
  to recurrent eruptive M- and X-class flares. Our study reveals that
  after the abrupt downward changes during each flare, the net Lorentz
  force increases significantly between the successive flares. This
  distinct rebuild-up of net Lorentz forces is the first observational
  evidence found in the evolution of any nonpotential parameter of solar
  ARs, which suggests that new energy was supplied to the ARs in order
  to produce the recurrent large flares. The rebuild-up of magnetic
  free energy of the ARs is further confirmed by the observations of
  continuous shearing motion of moving magnetic features of opposite
  polarities near the polarity inversion line. The evolutionary pattern
  of the net Lorentz force changes reported in this study has significant
  implications, in particular, for the forecasting of recurrent large
  eruptive flares from the same AR and hence the chances of interaction
  between the associated CMEs.

---------------------------------------------------------
Title: Indications of stellar coronal mass ejections through coronal
    dimmings
Authors: Veronig, Astrid M.; Odert, Petra; Leitzinger, Martin;
   Dissauer, Karin; Fleck, Nikolaus C.; Hudson, Hugh S.
2021NatAs...5..697V    Altcode: 2021arXiv211012029V; 2021NatAs.tmp...72V
  Coronal mass ejections (CMEs) are huge expulsions of magnetized matter
  from the Sun and stars, traversing space with speeds of millions
  of kilometres per hour. Solar CMEs can cause severe space weather
  disturbances and consumer power outages on Earth, whereas stellar CMEs
  may even pose a hazard to the habitability of exoplanets. Although CMEs
  ejected by our Sun can be directly imaged by white-light coronagraphs,
  for stars this is not possible. So far, only a few candidates for
  stellar CME detections have been reported. Here we demonstrate a
  different approach that is based on sudden dimmings in the extreme
  ultraviolet and X-ray emission caused by the CME mass loss. We report
  dimming detections associated with flares on cool stars, indicative
  of stellar CMEs, and which are benchmarked by Sun-as-a-star extreme
  ultraviolet measurements. This study paves the way for comprehensive
  detections and characterizations of CMEs on stars, which are important
  factors in planetary habitability and stellar evolution.

---------------------------------------------------------
Title: Diagnosing CME/Shock wave association using the radio
    triangulation technique
Authors: Jebaraj, Immanuel; Poedts, Stefaan; Krupar, Vratislav; Kilpua,
   Emilia; Magdalenic, Jasmina; Podladchikova, Tatiana; Pomoell, Jens;
   Dissauer, Karin; Veronig, Astrid; Scolini, Camilla
2021cosp...43E1000J    Altcode:
  Eruptive events such as Coronal mass ejections (CMEs) and flares can
  accelerate particles and generate shock waves. Tracking of shock waves
  and predicting their arrival at the Earth is an important scientific
  goal. Space based radio observations provide us the unique opportunity
  to track shock waves in the inner heliosphere. We present study of
  the CME/flare event on September 27/28, 2012. The GOES C3.7 flare
  that originated from NOAA AR 1577 was associated with a full-halo CME
  (first seen in the SOHO/LASCO C2 field of view at 23:47 UT) and white
  light shock wave observed by all three spacecraft STEREO A, STEREO B,
  and SOHO. The associated radio event shows a group of type III bursts
  and two somewhat unusual type II bursts with significantly different
  starting frequencies. To understand the origin of the two shock waves we
  performed multi-wavelength and radio triangulation study. For the radio
  triangulation we used direction-finding measurements from STEREO/WAVES
  and WIND/WAVES instruments. We reconstructed the shock wave propagation
  and compared results with the CME propagation using the data-driven
  EUHFORIA cone model (EUropean Heliospheric FORecasting Information
  Asset). Results of the study indicate that the interaction of the
  shock wave and the nearby streamer, situated close to the southern
  polar coronal hole, is the most probable source of the observed low
  frequency type II burst. Furthermore, we also demonstrate the importance
  of radio triangulation studies in understanding the projection effects
  when interpreting radio observations.

---------------------------------------------------------
Title: SunCET: The Sun Coronal Ejection Tracker Concept
Authors: Mason, James Paul; Chamberlin, Phillip C.; Seaton, Daniel;
   Burkepile, Joan; Colaninno, Robin; Dissauer, Karin; Eparvier, Francis
   G.; Fan, Yuhong; Gibson, Sarah; Jones, Andrew R.; Kay, Christina; Kirk,
   Michael; Kohnert, Richard; Pesnell, W. Dean; Thompson, Barbara J.;
   Veronig, Astrid M.; West, Matthew J.; Windt, David; Woods, Thomas N.
2021JSWSC..11...20M    Altcode: 2021arXiv210109215M
  The Sun Coronal Ejection Tracker (SunCET) is an extreme ultraviolet
  imager and spectrograph instrument concept for tracking coronal mass
  ejections through the region where they experience the majority
  of their acceleration: the difficult-to-observe middle corona. It
  contains a wide field of view (0-4 R<SUB>⊙</SUB>) imager and a 1 Å
  spectral-resolution-irradiance spectrograph spanning 170-340 Å. It
  leverages new detector technology to read out different areas of the
  detector with different integration times, resulting in what we call
  "simultaneous high dynamic range", as opposed to the traditional high
  dynamic range camera technique of subsequent full-frame images that
  are then combined in post-processing. This allows us to image the
  bright solar disk with short integration time, the middle corona
  with a long integration time, and the spectra with their own,
  independent integration time. Thus, SunCET does not require the use
  of an opaque or filtered occulter. SunCET is also compact - ~15 × 15
  × 10 cm in volume - making it an ideal instrument for a CubeSat or a
  small, complementary addition to a larger mission. Indeed, SunCET is
  presently in a NASA-funded, competitive Phase A as a CubeSat and has
  also been proposed to NASA as an instrument onboard a 184 kg Mission
  of Opportunity.

---------------------------------------------------------
Title: CME evolution and the corresponding Forbush decrease: modelling
    vs multi-spacecraft observation
Authors: Dumbovic, Mateja; Moestl, Christian; Podladchikova, Tatiana;
   Guo, Jingnan; Heber, Bernd; Vrsnak, Bojan; Dissauer, Karin; Veronig,
   Astrid; Amerstorfer, Tanja; Temmer, Manuela; Carcaboso, Fernando;
   Kirin, Anamarija
2021cosp...43E1747D    Altcode:
  One of the very common in-situ signatures of interplanetary coronal
  mass ejections (ICMEs), as well as other interplanetary transients are
  Forbush decreases (FDs), i.e. short-term reductions in the galactic
  cosmic ray (GCR) flux. FD phenomena are caused by the interaction
  of GCRs with a magnetic structure, therefore it is expected that
  different types of interplanetary substructures cause different types
  of GCR time profiles, allowing us to distinguish between shock/sheath,
  flux rope and SIR-type of FDs. Moreover, since the interaction of
  GCRs and CME magnetic structure (i.e. flux rope) occurs all the
  way from Sun to Earth, FDs reflect the evolutionary properties of
  CMEs. We apply modelling to different ICME regions in order to obtain
  a generic FD profile. We model the shock/sheath-related FD using the
  propagating diffusive barrier (PDB) model, the flux-rope-related FD
  using the diffusion model for the expanding flux rope (ForbMod),
  and the exponential time profile approximates the recovery after
  the event. The modeled generic FD profile qualitatively agrees with
  our current observation-based understanding of FDs. In addition, we
  test ForbMod against a set of multi-spacecraft observations of the
  same ICME. We find a reasonable agreement of the ForbMod model with
  multi-spacecraft measurements, indicating that modelled FDs reflect
  well the flux rope evolution.

---------------------------------------------------------
Title: Evolution of coronal mass ejections and the corresponding
Forbush decreases: modelling vs. multi-spacecraft observations
Authors: Dumbovic, M.; Vrsnak, B.; Guo, J.; Heber, B.; Dissauer, K.;
   Carcaboso-Morales, F.; Temmer, M.; Veronig, A.; Podladchikova, T.;
   Moestl, C.; Amerstorfer, T.; Kirin, A.
2020AGUFMSH046..08D    Altcode:
  One of the very common in situ signatures of interplanetary coronal
  mass ejections (ICMEs), as well as other interplanetary transients,
  are Forbush decreases (FDs), i.e. short-term reductions in the galactic
  cosmic ray (GCR) flux. A two-step FD is often regarded as a textbook
  example, which presumably owes its specific morphology to the fact that
  the measuring instrument passed through the ICME head-on, encountering
  first the shock front (if developed), then the sheath and finally the
  CME magnetic structure. The interaction of GCRs and the shock/sheath
  region, as well as the CME magnetic structure, occurs all the way from
  Sun to Earth, therefore, FDs are expected to reflect the evolutionary
  properties of CMEs and their sheaths. We apply modelling to different
  ICME regions in order to obtain a generic two-step FD profile, which
  qualitatively agrees with our current observation-based understanding of
  FDs. We next adapt the models for energy dependence to enable comparison
  with different GCR measurement instruments (as they measure in different
  particle energy ranges). We test these modelling efforts against a
  set of multi-spacecraft observations of the same event, using the
  Forbush decrease model for the expanding flux rope (ForbMod). We find
  a reasonable agreement of the ForbMod model for the GCR depression
  in the CME magnetic structure with multi-spacecraft measurements,
  indicating that modelled FDs reflect well the CME evolution.

---------------------------------------------------------
Title: CME-CME Interactions as Sources of CME Helio-Effectiveness:
    the Early September 2017 Events
Authors: Scolini, C.; Chané, E.; Temmer, M.; Pomoell, J.; Kilpua,
   K. E. J.; Dissauer, K.; Veronig, A.; Palmerio, E.; Dumbovic, M.; Guo,
   J.; Rodriguez, L.; Poedts, S.
2020AGUFMSH0440017S    Altcode:
  Coronal Mass Ejections (CMEs) are the main source of intense space
  weather disturbances in the heliosphere. It is known that the
  capability of individual CMEs to drive strong space weather events
  at Earth (called "geo-effectiveness") and other locations (here
  referred to as "helio-effectiveness") primarily depends on their
  speed, density, and magnetic field strength and orientation at the
  impact location. Moreover, previous studies established that CME--CME
  interactions can significantly alter the properties of individual
  CMEs, in such a way that their geo-effectiveness is often dramatically
  amplified. However, the actual quantification of this amplification has
  been rarely investigated, and previous studies have mostly focused on
  the near-Earth region only, i.e. without considering its full space-time
  evolution as the CMEs propagate to 1 AU and beyond. <P />Here, we
  present a study on the role of CME--CME interactions as sources of CME
  helio-effectiveness by performing simulations of complex CME events
  with the EUHFORIA heliospheric model. As a case study, we consider
  a sequence of CMEs observed in early September 2017. As their source
  region rotated on the solar disk, CMEs were launched over a wide range
  of longitudes, interacting with each other and paving the way for the
  propagation of the following ones. At Earth, their interaction resulted
  in an intense geomagnetic storm. Using initial parameters derived
  from remote-sensing observations, we perform global simulations of
  magnetised CMEs with EUHFORIA, investigating how their interactions
  affected the propagation and internal properties of individual CME
  structures. Taking advantage of 3D simulation outputs, we quantify
  the amplification of the helio-effectiveness of the individual CMEs
  involved, as a function of the interaction phase and of the location
  within the CME structure. Additionally, we explore the possibility of
  the existence of a "helio-effectiveness amplification zone", i.e. a
  characteristic heliocentric distance at which CME--CME interactions have
  the highest probability to develop into helio-effective events. Results
  from this study benchmark our current prediction capabilities in
  the case of complex CME events, and provide new insights on their
  large-scale evolution and potential impact throughout the heliosphere.

---------------------------------------------------------
Title: A Journey of Exploration to the Polar Regions of a Star:
    Probing the Solar Poles and the Heliosphere from High Helio-Latitude
Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.;
   Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.;
   Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi,
   S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.;
   Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.;
   Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli,
   M.; Sekii, T.; Spadaro, D.; Veronig, A.
2020AGUFMSH0110005F    Altcode:
  A mission to view the solar poles from high helio-latitudes (above
  60°) will build on the experience of Solar Orbiter as well as a long
  heritage of successful solar missions and instrumentation (e.g. SOHO,
  STEREO, Hinode, SDO), but will focus for the first time on the solar
  poles, enabling scientific investigations that cannot be done by
  any other mission. One of the major mysteries of the Sun is the solar
  cycle. The activity cycle of the Sun drives the structure and behaviour
  of the heliosphere and is, of course, the driver of space weather. In
  addition, solar activity and variability provides fluctuating input
  into the Earth climate models, and these same physical processes
  are applicable to stellar systems hosting exoplanets. One of the
  main obstructions to understanding the solar cycle, and hence all
  solar activity, is our current lack of understanding of the polar
  regions. We describe a mission concept that aims to address this
  fundamental issue. In parallel, we recognise that viewing the Sun
  from above the polar regions enables further scientific advantages,
  beyond those related to the solar cycle, such as unique and powerful
  studies of coronal mass ejection processes, from a global perspective,
  and studies of coronal structure and activity in polar regions. Not
  only will these provide important scientific advances for fundamental
  stellar physics research, they will feed into our understanding of
  impacts on the Earth and other planets' space environment.

---------------------------------------------------------
Title: SunCET: A CubeSat Mission Dedicated to the Middle Corona
Authors: Mason, J. P.; Seaton, D. B.; Chamberlin, P. C.; Burkepile,
   J.; Colaninno, R. C.; Dissauer, K.; Eparvier, F. G.; Fan, Y.; Gibson,
   S. E.; Jones, A. R.; Kay, C.; Kirk, M. S.; Kohnert, R.; Thompson,
   B. J.; Veronig, A.; West, M. J.; Woods, T. N.
2020AGUFMSH0300006M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Magnetohydrodynamic Simulation of Magnetic Null-point
    Reconnections and Coronal Dimmings during the X2.1 Flare in NOAA
    AR 11283
Authors: Prasad, Avijeet; Dissauer, Karin; Hu, Qiang; Bhattacharyya,
   R.; Veronig, Astrid M.; Kumar, Sanjay; Joshi, Bhuwan
2020ApJ...903..129P    Altcode: 2020arXiv200911109P
  The magnetohydrodynamics of active region NOAA 11283 is simulated
  using an initial non-force-free magnetic field extrapolated from its
  photospheric vector magnetogram. We focus on the magnetic reconnections
  at a magnetic null point that participated in the X2.1 flare on 2011
  September 6 around 22:21 UT (SOL2011-09-06T22:21X2.1) followed by the
  appearance of circular flare ribbons and coronal dimmings. The initial
  magnetic field from extrapolation displays a three-dimensional (3D)
  null topology overlying a sheared arcade. Prior to the flare, magnetic
  loops rise due to the initial Lorentz force, and reconnect at the 3D
  null, leading to expansion and loss of confined plasma that produce the
  observed pre-flare coronal dimmings. Further, the simulated dynamics
  documents the transfer of twist from the arcade to the overlying
  loops through reconnections, developing a flux rope. The nonparallel
  field lines comprising the rope and lower-lying arcades form an X-type
  geometry. Importantly, the simultaneous reconnections at the 3D null
  and the X-type geometry can explain the observed circular and parallel
  flare ribbons. Reconnections at the 3D null transform closed inner spine
  field lines into open field lines of the outer spine. The footpoints
  of these open field lines correspond to a ring-shaped coronal dimming
  region, tracing the dome. Further, the flux rope bifurcates because
  of these reconnections, which also results in the generation of open
  magnetic field lines. The plasma loss along the open field lines can
  potentially explain the observed coronal dimming.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Search for flares and CMEs in
    SDSS data (Koller+, 2021)
Authors: Koller, F.; Leitzinger, M.; Temmer, M.; Odert, P.; Beck,
   P. G.; Veronig, A.
2020yCat..36460034K    Altcode:
  This file contains the complete list of flares found by this work
  and their most important derived or collected parameters. The
  in-depth description of the derivation of these parameters is given
  in the article. <P />The optical spectra by SDSSS data release 14
  (2018ApJS..235...42A) that we used in this work consist of several
  single spectra, which are combined to a final coadded spectrum for each
  observed object. We used the single spectra to find temporal changes
  in Balmer lines, indicating flaring events. With the latest GAIA data
  release (2018A&amp;A...616A...1G), we were able to derive energy and
  luminosity values for the flares. We focused on the Halpha Balmer line
  due to the better S/N. Our methods were based on line fitting algorithms
  to detect changes from one observation to another. <P />Similar to
  the work by Hilton et al. (2010, Cat. J/AJ/140/1402) we give stellar
  coordinates as RAdeg and DEdeg as the first parameters to distinguish
  between the objects. In addition to that, the Plate-MJD-Fiber number
  serves as a unique identifier for the flaring SDSS spectrum. The stellar
  position is not enough because objects can be observed multiple times
  at different surveys by SDSS, resulting in different sets of single
  spectra. The method and the categorization of the S/N bins are defined
  in the article. <P />The spectral type classified by SDSS and by
  other literature is given. The distance and the source for the value
  is given when possible. The defined quiet flag and the consideration
  flag give insight on the reliability of the derived values. Whether a
  flare was also detected in Hilton et al. (2010, Cat. J/AJ/140/1402) is
  given in a separate column. The flare energy, the luminosity, and the
  associated errors were derived using the SDSS spectra as is described
  in the article (see Sect.4.2.2) and given here in units of W and W/s
  (J). <P />The peak spectrum and the spectrum used in the calculation as
  the reference are given. Their number refer to the chronological order
  of the single spectra. The number of available single spectra (in the
  optical red domain containing Halpha) and the number of single spectra
  in a flaring state are given. The overall time of these flaring spectra
  is summed and given in units of minutes. <P />Additional comments made
  during the visual inspection of all flaring spectra are added. <P />(1
  data file).

---------------------------------------------------------
Title: Image-quality assessment for full-disk solar observations
    with generative adversarial networks
Authors: Jarolim, R.; Veronig, A. M.; Pötzi, W.; Podladchikova, T.
2020A&A...643A..72J    Altcode: 2020arXiv200812030J
  Context. In recent decades, solar physics has entered the era of big
  data and the amount of data being constantly produced from ground-
  and space-based observatories can no longer be purely analyzed by
  human observers. <BR /> Aims: In order to assure a stable series of
  recorded images of sufficient quality for further scientific analysis,
  an objective image-quality measure is required. Especially when dealing
  with ground-based observations, which are subject to varying seeing
  conditions and clouds, the quality assessment has to take multiple
  effects into account and provide information about the affected
  regions. The automatic and robust identification of quality-degrading
  effects is critical for maximizing the scientific return from the
  observations and to allow for event detections in real time. In this
  study, we develop a deep-learning method that is suited to identify
  anomalies and provide an image-quality assessment of solar full-disk Hα
  filtergrams. The approach is based on the structural appearance and the
  true image distribution of high-quality observations. <BR /> Methods: We
  employ a neural network with an encoder-decoder architecture to perform
  an identity transformation of selected high-quality observations. The
  encoder network is used to achieve a compressed representation of the
  input data, which is reconstructed to the original by the decoder. We
  use adversarial training to recover truncated information based on
  the high-quality image distribution. When images of reduced quality
  are transformed, the reconstruction of unknown features (e.g.,
  clouds, contrails, partial occultation) shows deviations from the
  original. This difference is used to quantify the quality of the
  observations and to identify the affected regions. In addition, we
  present an extension of this architecture that also uses low-quality
  samples in the training step. This approach takes characteristics
  of both quality domains into account, and improves the sensitivity
  for minor image-quality degradation. <BR /> Results: We apply our
  method to full-disk Hα filtergrams from the Kanzelhöhe Observatory
  recorded during 2012-2019 and demonstrate its capability to perform a
  reliable image-quality assessment for various atmospheric conditions and
  instrumental effects. Our quality metric achieves an accuracy of 98.5%
  in distinguishing observations with quality-degrading effects from
  clear observations and provides a continuous quality measure which is
  in good agreement with the human perception. <BR /> Conclusions: The
  developed method is capable of providing a reliable image-quality
  assessment in real time, without the requirement of reference
  observations. Our approach has the potential for further application
  to similar astrophysical observations and requires only coarse
  manual labeling of a small data set. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202038691/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: The Spectrometer/Telescope for Imaging X-rays (STIX)
Authors: Krucker, Säm; Hurford, G. J.; Grimm, O.; Kögl, S.;
   Gröbelbauer, H. -P.; Etesi, L.; Casadei, D.; Csillaghy, A.; Benz,
   A. O.; Arnold, N. G.; Molendini, F.; Orleanski, P.; Schori, D.; Xiao,
   H.; Kuhar, M.; Hochmuth, N.; Felix, S.; Schramka, F.; Marcin, S.;
   Kobler, S.; Iseli, L.; Dreier, M.; Wiehl, H. J.; Kleint, L.; Battaglia,
   M.; Lastufka, E.; Sathiapal, H.; Lapadula, K.; Bednarzik, M.; Birrer,
   G.; Stutz, St.; Wild, Ch.; Marone, F.; Skup, K. R.; Cichocki, A.; Ber,
   K.; Rutkowski, K.; Bujwan, W.; Juchnikowski, G.; Winkler, M.; Darmetko,
   M.; Michalska, M.; Seweryn, K.; Białek, A.; Osica, P.; Sylwester, J.;
   Kowalinski, M.; Ścisłowski, D.; Siarkowski, M.; Stęślicki, M.;
   Mrozek, T.; Podgórski, P.; Meuris, A.; Limousin, O.; Gevin, O.; Le
   Mer, I.; Brun, S.; Strugarek, A.; Vilmer, N.; Musset, S.; Maksimović,
   M.; Fárník, F.; Kozáček, Z.; Kašparová, J.; Mann, G.; Önel,
   H.; Warmuth, A.; Rendtel, J.; Anderson, J.; Bauer, S.; Dionies, F.;
   Paschke, J.; Plüschke, D.; Woche, M.; Schuller, F.; Veronig, A. M.;
   Dickson, E. C. M.; Gallagher, P. T.; Maloney, S. A.; Bloomfield, D. S.;
   Piana, M.; Massone, A. M.; Benvenuto, F.; Massa, P.; Schwartz, R. A.;
   Dennis, B. R.; van Beek, H. F.; Rodríguez-Pacheco, J.; Lin, R. P.
2020A&A...642A..15K    Altcode:
  <BR /> Aims: The Spectrometer Telescope for Imaging X-rays (STIX)
  on Solar Orbiter is a hard X-ray imaging spectrometer, which
  covers the energy range from 4 to 150 keV. STIX observes hard X-ray
  bremsstrahlung emissions from solar flares and therefore provides
  diagnostics of the hottest (⪆10 MK) flare plasma while quantifying
  the location, spectrum, and energy content of flare-accelerated
  nonthermal electrons. <BR /> Methods: To accomplish this, STIX applies
  an indirect bigrid Fourier imaging technique using a set of tungsten
  grids (at pitches from 0.038 to 1 mm) in front of 32 coarsely pixelated
  CdTe detectors to provide information on angular scales from 7 to 180
  arcsec with 1 keV energy resolution (at 6 keV). The imaging concept of
  STIX has intrinsically low telemetry and it is therefore well-suited
  to the limited resources available to the Solar Orbiter payload. To
  further reduce the downlinked data volume, STIX data are binned on
  board into 32 selectable energy bins and dynamically-adjusted time
  bins with a typical duration of 1 s during flares. <BR /> Results:
  Through hard X-ray diagnostics, STIX provides critical information
  for understanding the acceleration of electrons at the Sun and their
  transport into interplanetary space and for determining the magnetic
  connection of Solar Orbiter back to the Sun. In this way, STIX serves
  to link Solar Orbiter's remote and in-situ measurements.

---------------------------------------------------------
Title: CME Acceleration as a Probe of the Coronal Magnetic Field
Authors: Mason, James Paul; Chamberlin, Phillip C.; Woods, Thomas N.;
   Jones, Andrew; Veronig, Astrid M.; Dissauer, Karin; Kirk, Michael;
   SunCET Team
2020arXiv200905625M    Altcode:
  By 2050, we expect that CME models will accurately describe, and
  ideally predict, observed solar eruptions and the propagation of the
  CMEs through the corona. We describe some of the present known unknowns
  in observations and models that would need to be addressed in order
  to reach this goal. We also describe how we might prepare for some of
  the unknown unknowns that will surely become challenges.

---------------------------------------------------------
Title: Eruptive-Impulsive Homologous M-class Flares Associated with
    Double-decker Flux Rope Configuration in Minisigmoid of NOAA 12673
Authors: Mitra, Prabir K.; Joshi, Bhuwan; Veronig, Astrid M.; Chandra,
   Ramesh; Dissauer, K.; Wiegelmann, Thomas
2020ApJ...900...23M    Altcode: 2020arXiv200711810M
  We present a multiwavelength analysis of two homologous, short-lived,
  impulsive flares of GOES class M1.4 and M7.3 that occurred from a very
  localized minisigmoid region within the active region NOAA 12673 on
  2017 September 7. Both flares were associated with initial jetlike
  plasma ejection that for a brief amount of time moved toward the east
  in a collimated manner before drastically changing direction toward
  the southwest. Nonlinear force-free field extrapolation reveals the
  presence of a compact double-decker flux rope configuration in the
  minisigmoid region prior to the flares. A set of open field lines
  originating near the active region that were most likely responsible
  for the anomalous dynamics of the erupted plasma gave the earliest
  indication of an emerging coronal hole near the active region. The
  horizontal field distribution suggests a rapid decay of the field
  above the active region, implying high proneness of the flux rope
  system toward eruption. In view of the low coronal double-decker flux
  ropes and compact extreme ultraviolet brightening beneath the filament,
  along with associated photospheric magnetic field changes, our analysis
  supports the combination of initial tether-cutting reconnection and
  subsequent torus instability for driving the eruption.

---------------------------------------------------------
Title: Magnetic Flux of Active Regions Determining the Eruptive
    Character of Large Solar Flares
Authors: Li, Ting; Hou, Yijun; Yang, Shuhong; Zhang, Jun; Liu, Lijuan;
   Veronig, Astrid M.
2020ApJ...900..128L    Altcode: 2020arXiv200708127L
  We establish the largest eruptive/confined flare database to date
  and analyze 322 flares of Geostationary Operational Environmental
  Satellite class M1.0 and larger that occurred during 2010-2019, i.e.,
  almost spanning all of solar cycle 24. We find that the total unsigned
  magnetic flux ( ${{\rm{\Phi }}}_{\mathrm{AR}}$ ) of active regions
  (ARs) is a key parameter governing the eruptive character of large
  flares, with the proportion of eruptive flares exhibiting a strong
  anticorrelation with ${{\rm{\Phi }}}_{\mathrm{AR}}$ . This means that
  an AR containing a large magnetic flux has a lower probability that the
  large flares it produces will be associated with a coronal mass ejection
  (CME). This finding is supported by the high positive correlation
  we obtained between the critical decay index height and ${{\rm{\Phi
  }}}_{\mathrm{AR}}$ , implying that ARs with a larger ${{\rm{\Phi
  }}}_{\mathrm{AR}}$ have a stronger magnetic confinement. Moreover, the
  confined flares originating from ARs larger than $1.0\times {10}^{23}$
  Mx have several characteristics in common: stable filament, slipping
  magnetic reconnection, and strongly sheared post-flare loops. Our
  findings reveal new relations between the magnetic flux of ARs and
  the occurrence of CMEs in association with large flares. The relations
  obtained here provide quantitative criteria for forecasting CMEs and
  adverse space weather, and have important implications for "superflares"
  on solar-type stars and stellar CMEs.

---------------------------------------------------------
Title: Clustering of Fast Coronal Mass Ejections during Solar Cycles
    23 and 24 and the Implications for CME-CME Interactions
Authors: Rodríguez Gómez, Jenny M.; Podladchikova, Tatiana; Veronig,
   Astrid; Ruzmaikin, Alexander; Feynman, Joan; Petrukovich, Anatoly
2020ApJ...899...47R    Altcode: 2020arXiv200610404R
  We study the clustering properties of fast coronal mass ejections
  (CMEs) that occurred during solar cycles 23 and 24. We apply two
  methods: the Max Spectrum method can detect the predominant clusters,
  and the declustering threshold time method provides details on the
  typical clustering properties and timescales. Our analysis shows that
  during the different phases of solar cycles 23 and 24, CMEs with speeds
  ≥1000 km s<SUP>-1</SUP> preferentially occur as isolated events and
  in clusters with, on average, two members. However, clusters with more
  members appear, particularly during the maximum phases of the solar
  cycles. Over the total period and in the maximum phases of solar cycles
  23 and 24, about 50% are isolated events, 18% (12%) occur in clusters
  with two (three) members, and another 20% in larger clusters ≥4,
  whereas in a solar minimum, fast CMEs tend to occur more frequently as
  isolated events (62%). During different solar cycle phases, the typical
  declustering timescales of fast CMEs are τ<SUB>c</SUB> = 28-32 hr,
  irrespective of the very different occurrence frequencies of CMEs during
  a solar minimum and maximum. These findings suggest that τ<SUB>c</SUB>
  for extreme events may reflect the characteristic energy build-up
  time for large flare and CME-prolific active regions. Statistically
  associating the clustering properties of fast CMEs with the disturbance
  storm time index at Earth suggests that fast CMEs occurring in clusters
  tend to produce larger geomagnetic storms than isolated fast CMEs. This
  may be related to CME-CME interaction producing a more complex and
  stronger interaction with Earth's magnetosphere.

---------------------------------------------------------
Title: Solar Flare-CME Coupling throughout Two Acceleration Phases
    of a Fast CME
Authors: Gou, Tingyu; Veronig, Astrid M.; Liu, Rui; Zhuang, Bin;
   Dumbović, Mateja; Podladchikova, Tatiana; Reid, Hamish A. S.; Temmer,
   Manuela; Dissauer, Karin; Vršnak, Bojan; Wang, Yuming
2020ApJ...897L..36G    Altcode: 2020arXiv200611707G
  Solar flares and coronal mass ejections (CMEs) are closely coupled
  through magnetic reconnection. CMEs are usually accelerated impulsively
  within the low solar corona, synchronized with the impulsive flare
  energy release. We investigate the dynamic evolution of a fast CME and
  its associated X2.8 flare occurring on 2013 May 13. The CME experiences
  two distinct phases of enhanced acceleration, an impulsive one with a
  peak value of ∼5 km s<SUP>-2</SUP>, followed by an extended phase with
  accelerations up to 0.7 km s<SUP>-2</SUP>. The two-phase CME dynamics
  is associated with a two-episode flare energy release. While the first
  episode is consistent with the "standard" eruption of a magnetic flux
  rope, the second episode of flare energy release is initiated by the
  reconnection of a large-scale loop in the aftermath of the eruption
  and produces stronger nonthermal emission up to γ-rays. In addition,
  this long-duration flare reveals clear signs of ongoing magnetic
  reconnection during the decay phase, evidenced by extended hard X-ray
  bursts with energies up to 100-300 keV and intermittent downflows
  of reconnected loops for &gt;4 hr. The observations reveal that the
  two-step flare reconnection substantially contributes to the two-phase
  CME acceleration, and the impulsive CME acceleration precedes the most
  intense flare energy release. The implications of this non-standard
  flare/CME observation are discussed.

---------------------------------------------------------
Title: Can we predict solar flares?
Authors: Veronig, Astrid M.
2020Sci...369..504V    Altcode:
  Flares from the Sun are the strongest explosions in our Solar
  System. They can cause severe space weather disturbances, posing a
  hazard to astronauts and technological systems in space and on the
  ground. Solar flares have an immediate impact in the form of enhanced
  radiation and energetic particles in as little as 8 min after the
  start of the event. Reliable prediction methods for flares are needed
  to provide longer warning times. However, pinning down the flare onset
  conditions is necessary for reliable predictions and is still a struggle
  (1). On page 587 of this issue, Kusano et al. (2) introduce a method
  to predict and successfully test for large imminent flares.

---------------------------------------------------------
Title: Hard X-Ray Emission from an Activated Flux Rope and Subsequent
    Evolution of an Eruptive Long-duration Solar Flare
Authors: Sahu, Suraj; Joshi, Bhuwan; Mitra, Prabir K.; Veronig,
   Astrid M.; Yurchyshyn, V.
2020ApJ...897..157S    Altcode: 2020arXiv200506221S
  In this paper, we present a comprehensive study of the evolutionary
  phases of a major M6.6 long duration event with special emphasize on
  its pre-flare phase. The event occurred in NOAA 12371 on 2015 June
  22. A remarkable aspect of the event was an active pre-flare phase
  lasting for about an hour during which a hot EUV coronal channel
  was in the build-up stage and displayed cospatial hard X-ray (HXR)
  emission up to energies of 25 keV. This is the first evidence of the
  HXR coronal channel. The coronal magnetic field configuration based
  on nonlinear-force-free-field modeling clearly exhibited a magnetic
  flux rope (MFR) oriented along the polarity inversion line (PIL) and
  cospatial with the coronal channel. We observed significant changes
  in the AR's photospheric magnetic field during an extended period of
  ≍42 hr in the form of rotation of sunspots, moving magnetic features,
  and flux cancellation along the PIL. Prior to the flare onset, the MFR
  underwent a slow rise phase (≍14 km s<SUP>-1</SUP>) for ≍12 minutes,
  which we attribute to the faster build-up and activation of the MFR
  by tether-cutting reconnection occurring at multiple locations along
  the MFR itself. The sudden transition in the kinematic evolution of
  the MFR from the phase of slow to fast rise (≍109 km s<SUP>-1</SUP>
  with acceleration ≍110 m s<SUP>-2</SUP>) precisely divides the
  pre-flare and impulsive phase of the flare, which points toward the
  feedback process between the early dynamics of the eruption and the
  strength of the flare magnetic reconnection.

---------------------------------------------------------
Title: Using radio triangulation to understand the origin of two
    subsequent type II radio bursts
Authors: Jebaraj, I. C.; Magdalenić, J.; Podladchikova, T.; Scolini,
   C.; Pomoell, J.; Veronig, A. M.; Dissauer, K.; Krupar, V.; Kilpua,
   E. K. J.; Poedts, S.
2020A&A...639A..56J    Altcode: 2020arXiv200604586J
  Context. Eruptive events such as coronal mass ejections (CMEs)
  and flares accelerate particles and generate shock waves which can
  arrive at Earth and can disturb the magnetosphere. Understanding the
  association between CMEs and CME-driven shocks is therefore highly
  important for space weather studies. <BR /> Aims: We present a study
  of the CME/flare event associated with two type II bursts observed
  on September 27, 2012. The aim of the study is to understand the
  relationship between the observed CME and the two distinct shock
  wave signatures. <BR /> Methods: The multiwavelength study of the
  eruptive event (CME/flare) was complemented with radio triangulation
  of the associated radio emission and modelling of the CME and the
  shock wave employing MHD simulations. <BR /> Results: We found that,
  although temporal association between the type II bursts and the CME is
  good, the low-frequency type II (LF-type II) burst occurs significantly
  higher in the corona than the CME and its relationship to the CME is not
  straightforward. The analysis of the EIT wave (coronal bright front)
  shows the fastest wave component to be in the southeast quadrant of
  the Sun. This is also the quadrant in which the source positions
  of the LF-type II were found to be located, probably resulting
  from the interaction between the shock wave and a streamer. <BR />
  Conclusions: The relationship between the CME/flare event and the
  shock wave signatures is discussed using the temporal association,
  as well as the spatial information of the radio emission. Further,
  we discuss the importance and possible effects of the frequently
  non-radial propagation of the shock wave.

---------------------------------------------------------
Title: Evolution of Coronal Mass Ejections and the Corresponding
Forbush Decreases: Modeling vs. Multi-Spacecraft Observations
Authors: Dumbović, Mateja; Vršnak, Bojan; Guo, Jingnan; Heber,
   Bernd; Dissauer, Karin; Carcaboso, Fernando; Temmer, Manuela; Veronig,
   Astrid; Podladchikova, Tatiana; Möstl, Christian; Amerstorfer, Tanja;
   Kirin, Anamarija
2020SoPh..295..104D    Altcode: 2020arXiv200602253D
  One of the very common in situ signatures of interplanetary coronal
  mass ejections (ICMEs), as well as other interplanetary transients,
  are Forbush decreases (FDs), i.e. short-term reductions in the galactic
  cosmic ray (GCR) flux. A two-step FD is often regarded as a textbook
  example, which presumably owes its specific morphology to the fact that
  the measuring instrument passed through the ICME head on, encountering
  first the shock front (if developed), then the sheath, and finally the
  CME magnetic structure. The interaction of GCRs and the shock/sheath
  region, as well as the CME magnetic structure, occurs all the way from
  Sun to Earth, therefore, FDs are expected to reflect the evolutionary
  properties of CMEs and their sheaths. We apply modeling to different
  ICME regions in order to obtain a generic two-step FD profile, which
  qualitatively agrees with our current observation-based understanding
  of FDs. We next adapt the models for energy dependence to enable
  comparison with different GCR measurement instruments (as they measure
  in different particle energy ranges). We test these modeling efforts
  against a set of multi-spacecraft observations of the same event, using
  the Forbush decrease model for the expanding flux rope (ForbMod). We
  find a reasonable agreement of the ForbMod model for the GCR depression
  in the CME magnetic structure with multi-spacecraft measurements,
  indicating that modeled FDs reflect well the CME evolution.

---------------------------------------------------------
Title: Sun-to-Earth Observations and Characteristics of Isolated
    Earth-Impacting Interplanetary Coronal Mass Ejections During 2008
    - 2014
Authors: Maričić, D.; Vršnak, B.; Veronig, A. M.; Dumbović, M.;
   Šterc, F.; Roša, D.; Karlica, M.; Hržina, D.; Romštajn, I.
2020SoPh..295...91M    Altcode: 2020arXiv200810265M
  A sample of isolated Earth-impacting interplanetary coronal mass
  ejections (ICMEs) that occurred in the period January 2008 to August
  2014 is analyzed to study in detail the ICME in situ signatures, with
  respect to the type of filament eruption related to the corresponding
  CME. Observations from different vantage points provided by the
  Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial
  Relations Observatory Ahead and Behind (STEREO-A and B) are used to
  determine whether each CME under study is Earth directed or not. For
  Earth-directed CMEs, a kinematical study was performed using the
  STEREO-A and B COR1 and COR2 coronagraphs and the Heliospheric Imagers
  (HI1), to estimate the CME arrival time at 1 AU and to link the CMEs
  with the corresponding in situ solar wind counterparts. Based on the
  extrapolated CME kinematics, we identified interacting CMEs, which
  were excluded from further analysis. Applying this approach, a set
  of 31 isolated Earth-impacting CMEs was unambiguously identified and
  related to the in situ measurements recorded by the Wind spacecraft. We
  classified the events into subsets with respect to the CME source
  location, as well as with respect to the type of the associated filament
  eruption. Hence, the events are divided into three subsamples: active
  region (AR) CMEs, disappearing filament (DSF) CMEs, and stealthy
  CMEs. The related three groups of ICMEs were further divided into
  two subsets: magnetic obstacle (MO) events (out of which four were
  stealthy), covering ICMEs that at least partly showed characteristics of
  flux ropes, and ejecta (EJ) events, not showing such characteristics. In
  this way, 14 MO-ICMEs and 17 EJ-ICMES were identified. The solar
  source regions of the non-stealthy MO-ICMEs are found to be located
  predominantly (9/10, 90%) within ±30<SUP>∘</SUP> from the solar
  central meridian, whereas EJ-ICMEs originate predominantly (16/17, 94%)
  from source regions that are outside ±30<SUP>∘</SUP>. In the next
  step, MO-events were analyzed in more detail, considering the magnetic
  field strength and the plasma characteristics in three different
  segments, defined as the turbulent sheath (TS), the frontal region
  (FR), and the MO itself. The analysis revealed various well-defined
  correlations for AR, DSF, and stealthy ICMEs, which we interpreted
  considering basic physical concepts. Our results support the hypothesis
  that ICMEs show different signatures depending on the in situ spacecraft
  trajectory, in terms of apex versus flank hits.

---------------------------------------------------------
Title: On the Dependency between the Peak Velocity of High-speed
    Solar Wind Streams near Earth and the Area of Their Solar Source
    Coronal Holes
Authors: Hofmeister, Stefan J.; Veronig, Astrid M.; Poedts, Stefaan;
   Samara, Evangelia; Magdalenic, Jasmina
2020ApJ...897L..17H    Altcode: 2020arXiv200702625H
  The relationship between the peak velocities of high-speed solar
  wind streams near Earth and the areas of their solar source regions,
  I.e., coronal holes, has been known since the 1970s, but it is still
  physically not well understood. We perform 3D magnetohydrodynamic (MHD)
  simulations using the European Heliospheric Forecasting Information
  Asset (EUHFORIA) code to show that this empirical relationship
  forms during the propagation phase of high-speed streams from the
  Sun to Earth. For this purpose, we neglect the acceleration phase of
  high-speed streams, and project the areas of coronal holes to a sphere
  at 0.1 au. We then vary only the areas and latitudes of the coronal
  holes. The velocity, temperature, and density in the cross section of
  the corresponding high-speed streams at 0.1 au are set to constant,
  homogeneous values. Finally, we propagate the associated high-speed
  streams through the inner heliosphere using the EUHFORIA code. The
  simulated high-speed stream peak velocities at Earth reveal a linear
  dependence on the area of their source coronal holes. The slopes of
  the relationship decrease with increasing latitudes of the coronal
  holes, and the peak velocities saturate at a value of about 730 km
  s<SUP>-1</SUP>, similar to the observations. These findings imply
  that the empirical relationship between the coronal hole areas and
  high-speed stream peak velocities does not describe the acceleration
  phase of high-speed streams, but is a result of the high-speed stream
  propagation from the Sun to Earth.

---------------------------------------------------------
Title: Coronal Dimmings Associated with Coronal Mass Ejections on
    the Solar Limb
Authors: Chikunova, Galina; Dissauer, Karin; Podladchikova, Tatiana;
   Veronig, Astrid M.
2020ApJ...896...17C    Altcode: 2020arXiv200503348C
  We present a statistical analysis of 43 coronal dimming events
  associated with Earth-directed coronal mass ejections (CMEs) that
  occurred during the period of quasi-quadrature of the Solar Dynamics
  Observatory (SDO) and Solar Terrestrial Relations Observatory (STEREO)
  satellites. We studied coronal dimmings that were observed above the
  limb by STEREO Extreme Ultraviolet Imager and compared their properties
  with the mass and speed of the associated CMEs. The unique position
  of the satellites allowed us to compare our findings with the results
  from Dissauer et al., who studied the same events observed against the
  solar disk by the SDO Atmospheric Imaging Assembly. Such statistics is
  done for the first time and confirms the relation of coronal dimmings
  and CME parameters for the off-limb viewpoint. The observations of
  dimming regions from different lines of sight reveal a similar decrease
  in the total extreme ultraviolet intensity (c = 0.60 ± 0.14). We
  find that the (projected) dimming areas are typically larger for
  off-limb observations (mean value of 1.24 ± 1.23 × 10<SUP>11</SUP>
  km<SUP>2</SUP> against 3.51 ± 0.71 × 10<SUP>10</SUP> km<SUP>2</SUP>
  for on-disk), with a correlation of c = 0.63 ± 0.10. This systematic
  difference can be explained by the (weaker) contributions to the dimming
  regions higher up in the corona that cannot be detected in the on-disk
  observations. The off-limb dimming areas and brightnesses show very
  strong correlations with the CME mass (c = 0.82 ± 0.06 and 0.75 ±
  0.08), whereas the dimming area and brightness change rate correlate
  with the CME speed (c ∼ 0.6). Our findings suggest that coronal
  dimmings have the potential to provide early estimates of the mass and
  speed of Earth-directed CMEs, relevant for space weather forecasts,
  for satellite locations at both L1 and L5.

---------------------------------------------------------
Title: A statistical study of the long-term evolution of coronal
    hole properties as observed by SDO
Authors: Heinemann, S. G.; Jerčić, V.; Temmer, M.; Hofmeister,
   S. J.; Dumbović, M.; Vennerstrom, S.; Verbanac, G.; Veronig, A. M.
2020A&A...638A..68H    Altcode: 2019arXiv190702795H; 2019arXiv190702795J
  Context. Understanding the evolution of coronal holes is especially
  important when studying the high-speed solar wind streams that emanate
  from them. Slow- and high-speed stream interaction regions may deliver
  large amounts of energy into the Earth's magnetosphere-ionosphere
  system, cause geomagnetic storms, and shape interplanetary space. <BR
  /> Aims: By statistically investigating the long-term evolution of
  well-observed coronal holes we aim to reveal processes that drive
  the observed changes in the coronal hole parameters. By analyzing 16
  long-living coronal holes observed by the Solar Dynamic Observatory,
  we focus on coronal, morphological, and underlying photospheric magnetic
  field characteristics, and investigate the evolution of the associated
  high-speed streams. <BR /> Methods: We use the Collection of Analysis
  Tools for Coronal Holes to extract and analyze coronal holes using
  193 Å EUV observations taken by the Atmospheric Imaging Assembly as
  well as line-of-sight magnetograms observed by the Helioseismic and
  Magnetic Imager. We derive changes in the coronal hole properties and
  look for correlations with coronal hole evolution. Further, we analyze
  the properties of the high-speed stream signatures near 1AU from OMNI
  data by manually extracting the peak bulk velocity of the solar wind
  plasma. <BR /> Results: We find that the area evolution of coronal
  holes shows a general trend of growing to a maximum followed by a
  decay. We did not find any correlation between the area evolution
  and the evolution of the signed magnetic flux or signed magnetic
  flux density enclosed in the projected coronal hole area. From this
  we conclude that the magnetic flux within the extracted coronal
  hole boundaries is not the main cause for its area evolution. We
  derive coronal hole area change rates (growth and decay) of (14.2
  ± 15.0)×10<SUP>8</SUP> km<SUP>2</SUP> per day showing a reasonable
  anti-correlation (cc<SUB>Pearson</SUB> = -0.48) to the solar activity,
  approximated by the sunspot number. The change rates of the signed mean
  magnetic flux density (27.3 ± 32.2 mG day<SUP>-1</SUP>) and the signed
  magnetic flux (30.3 ± 31.5 10<SUP>18</SUP> Mx day<SUP>-1</SUP>) were
  also found to be dependent on solar activity (cc<SUB>Pearson</SUB> =
  0.50 and cc<SUB>Pearson</SUB> = 0.69 respectively) rather than on the
  individual coronal hole evolutions. Further we find that the relation
  between coronal hole area and high-speed stream peak velocity is
  valid for each coronal hole over its evolution, but we see significant
  variations in the slopes of the regression lines.

---------------------------------------------------------
Title: Development of a Confined Circular-Cum-Parallel Ribbon Flare
    and Associated Pre-Flare Activity
Authors: Devi, Pooja; Joshi, Bhuwan; Chandra, Ramesh; Mitra, Prabir
   K.; Veronig, Astrid M.; Joshi, Reetika
2020SoPh..295...75D    Altcode: 2020arXiv200509586D
  We study a complex GOES M1.1 circular ribbon flare and related pre-flare
  activity on 26 January 2015 [SOL2015-01-26T16:53] in the solar active
  region NOAA 12268. This flare activity was observed by the Atmospheric
  Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and
  the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The
  examination of photospheric magnetograms during the extended period,
  prior to the event, suggests the successive development of a so-called
  "anemone" type magnetic configuration. The Nonlinear Force Free Field
  (NLFFF) extrapolation reveals a fan-spine magnetic configuration with
  the presence of a coronal null-point. We found that the pre-flare
  activity in the active region starts ≈15 min prior to the main flare
  in the form of localized bright patches at two locations. A comparison
  of locations and spatial structures of the pre-flare activity with
  magnetic configuration of the corresponding region suggests onset of
  magnetic reconnection at the null-point along with the low-atmosphere
  magnetic reconnection caused by the emergence and the cancellation of
  the magnetic flux. The main flare of M1.1 class is characterized by the
  formation of a well-developed circular ribbon along with a region of
  remote brightening. Remarkably, a set of relatively compact parallel
  ribbons formed inside the periphery of the circular ribbon which
  developed lateral to the brightest part of the circular ribbon. During
  the peak phase of the flare, a coronal jet is observed at the north-east
  edge of the circular ribbon, which suggests interchange reconnection
  between large-scale field lines and low-lying closed field lines. Our
  investigation suggests a combination of two distinct processes in which
  ongoing pre-flare null-point reconnection gets further intensified as
  the confined eruption along with jet activity proceeded from within
  the circular ribbon region which results to the formation of inner
  parallel ribbons and corresponding post-reconnection arcade.

---------------------------------------------------------
Title: Magnetic Flux Emergence in a Coronal Hole
Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova,
   Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma,
   Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván;
   Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea;
   Kontogiannis, Ioannis; Cid, Consuelo
2020SoPh..295...64P    Altcode: 2020arXiv200611779P
  A joint campaign of various space-borne and ground-based observatories,
  comprising the Japanese Hinode mission (Hinode Observing Plan 338,
  20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum
  Tower Telescope (VTT), investigated numerous targets such as pores,
  sunspots, and coronal holes. In this study, we focus on the coronal
  hole region target. On 24 September 2017, a very extended non-polar
  coronal hole developed patches of flux emergence, which contributed
  to the decrease of the overall area of the coronal hole. These flux
  emergence patches erode the coronal hole and transform the area into a
  more quiet-Sun-like area, whereby bipolar magnetic structures play an
  important role. Conversely, flux cancellation leads to the reduction
  of opposite-polarity magnetic fields and to an increase in the area
  of the coronal hole.

---------------------------------------------------------
Title: Using Forbush decreases at Earth and Mars to measure the
    radial evolution of ICMEs
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
   Robert F.; Dumbović, Mateja; Janvier, Miho; Démoulin, Pascal;
   Veronig, Astrid; Temmer, Manuela; Papaioannou, Athanasios; Dasso,
   Sergio; Hassler, Donald M.; Zeitlin, Cary J.
2020EGUGA..22.7838V    Altcode:
  Interplanetary coronal mass ejections (ICMEs), large clouds of plasma
  and magnetic field regularly expelled from the Sun, are one of the
  main drivers of space weather effects in the solar system. While
  the prediction of their arrival time at Earth and other locations
  in the heliosphere is still a complex task, it is also necessary to
  further understand the time evolution of their geometric and magnetic
  structure, which is even more challenging considering the limited number
  of available observation points.Forbush decreases (FDs), short-term
  drops in the flux of galactic cosmic rays (GCR), can be caused by the
  shielding from strong and/or turbulent magnetic structures in the solar
  wind, such as ICMEs and their associated shock/sheath regions. In the
  past, FD observations have often been used to determine the arrival
  times of ICMEs at different locations in the solar system, especially
  where sufficient solar wind plasma and magnetic field measurements are
  not (or not always) available. One of these locations is Mars, where the
  Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory
  (MSL) mission's Curiosity rover has been continuously measuring GCRs and
  FDs on the surface for more than 7 years.In this work, we investigate
  whether FD data can be used to derive additional information about the
  ICME properties than just the arrival time by performing a statistical
  study based on catalogs of FDs observed at Earth or Mars. In particular,
  we find that the linear correlation between the FD amplitude and the
  maximum steepness, which was already seen at Earth by previous authors
  (Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars,
  but with a different proprtionality factor.By consulting physics-based
  analytical models of FDs, we find that this quantity is not expected to
  be influenced by the different energy ranges of GCR particles observed
  by the instruments at Earth and Mars. Instead, we suggest that the
  difference in FD characteristics at the two planets is caused by the
  radial enlargement of the ICMEs, and particularly their sheath regions,
  as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening
  factor derived from our analysis extends observations for the evolution
  closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger
  heliocentric distances and is consistent with these results.

---------------------------------------------------------
Title: Observation-based modelling of magnetised CMEs in the inner
    heliosphere with EUHFORIA
Authors: Scolini, Camilla; Pomoell, Jens; Chané, Emmanuel; Poedts,
   Stefaan; Rodriguez, Luciano; Kilpua, Emilia; Temmer, Manuela;
   Verbeke, Christine; Dissauer, Karin; Veronig, Astrid; Palmerio, Erika;
   Dumbović, Mateja
2020EGUGA..22.1777S    Altcode:
  Coronal Mass Ejections (CMEs) are the primary source of strong
  space weather disturbances at Earth and other locations in the
  heliosphere. Understanding the physical processes involved in their
  formation at the Sun, propagation in the heliosphere, and impact
  on planetary bodies is therefore critical to improve current space
  weather predictions throughout the heliosphere. The capability of CMEs
  to drive strong space weather disturbances at Earth and other planetary
  and spacecraft locations primarily depends on their dynamic pressure,
  internal magnetic field strength, and magnetic field orientation at
  the impact location. In addition, phenomena such as the interaction
  with the solar wind and other solar transients along the way, or
  the pre-conditioning of interplanetary space due to the passage of
  previous CMEs, can significantly modify the properties of individual
  CMEs and alter their ultimate space weather impact. Investigating
  and modeling such phenomena via advanced physics-based heliospheric
  models is therefore crucial to improve the space weather prediction
  capabilities in relation to both single and complex CME events. In this
  talk, we present our progress in developing novel methods to model CMEs
  in the inner heliosphere using the EUHFORIA MHD model in combination
  with remote-sensing solar observations. We discuss the various
  observational techniques that can be used to constrain the initial
  CME parameters for EUHFORIA simulations. We present current efforts
  in developing more realistic magnetised CME models aimed at describing
  their internal magnetic structure in a more realistic fashion. We show
  how the combination of these two approaches allows the investigation of
  CME propagation and evolution throughout the heliosphere to a higher
  level of detail, and results in significantly improved predictions of
  CME impact at Earth and other locations in the heliosphere. Finally,
  we discuss current limitations and future improvements in the context
  of studying space weather events throughout the heliosphere.

---------------------------------------------------------
Title: CME evolution and the corresponding Forbush decrease: modelling
    vs multi-spacecraft observation
Authors: Dumbovic, Mateja; Vrsnak, Bojan; Guo, Jingnan; Heber, Bernd;
   Dissauer, Karin; Carcaboso-Morales, Fernando; Temmer, Manuela; Veronig,
   Astrid; Podladchikova, Tatiana; Möstl, Christian; Amerstorfer, Tanja;
   Kirin, Anamarija
2020EGUGA..2210446D    Altcode:
  One of the very common in-situ signatures of ICMEs, as well as other
  interplanetary transients are Forbush decreases (FDs), i.e. short-term
  reductions in the galactic cosmic ray (GCR) flux. A two-step FD is
  often regarded as a textbook example, which presumably owns its specific
  morphology to the fact that the measuring instrument passed through the
  ICME head-on, encountering first the shock front (if developed), then
  the sheath and finally the magnetic structure. The interaction of GCRs
  and the shock/sheath region as well as CME magnetic structure occurs all
  the way from Sun to Earth, therefore, FDs are expected to reflect the
  evolutionary properties of CMEs and their sheaths. We apply modelling
  to different ICME regions in order to obtain a generic two-step FD
  profile, which qualitatively agrees with our current observation-based
  understanding of FDs. We next adapt the models for energy dependence
  to enable comparison with different GCR measurement instruments
  (as they measure in different particle energy ranges). We test these
  modelling efforts against a set of multi-spacecraft observations of
  the same event.

---------------------------------------------------------
Title: Relating CME density derived from remote sensing data to CME
    sheath solar wind plasma pile up as measured in-situ
Authors: Temmer, Manuela; Holzknecht, Lukas; Dumbovic, Mateja; Vrsnak,
   Bojan; Sachdeva, Nishtha; Heinemann, Stephan; Dissauer, Karin; Scolini,
   Camilla; Asvestari, Eleanna; Veronig, Astrid; Hofmeister, Stefan
2020EGUGA..22.3341T    Altcode:
  For better estimating the drag force acting on coronal mass ejections
  (CMEs) in interplanetary space and ram-pressure at planets, improved
  knowledge of the evolution of CME density/mass is highly valuable. We
  investigate a sample of 29 well observed CME-ICME events, for which
  we determine the de-projected 3D mass (STEREO-A and -B data), and the
  CME volume using GCS modeling (STEREO, SoHO). Expanding the volume to
  1AU distance, we derive the density and compare the results to in-situ
  proton density measurements separately for the ICME sheath and magnetic
  structure. A fair agreement between calculated and measured density is
  derived for the magnetic structure as well for the sheath if taking
  into account mass pile up of solar wind plasma. We give evidence and
  observational assessment that during the interplanetary propagation
  of a CME 1) the magnetic structure has rather constant mass and 2)
  the sheath region at the front of the driver is formed from piled-up
  mass that is rather depending on the solar wind density ahead of the
  CME, than on the CME speed.

---------------------------------------------------------
Title: Mitigating flicker noise in high-precision
    photometry. I. Characterization of the noise structure, impact on the
    inferred transit parameters, and predictions for CHEOPS observations
Authors: Sulis, S.; Lendl, M.; Hofmeister, S.; Veronig, A.; Fossati,
   L.; Cubillos, P.; Van Grootel, V.
2020A&A...636A..70S    Altcode: 2020arXiv200307707S
  Context. In photometry, the short-timescale stellar variability
  ("flicker"), such as that caused by granulation and solar-like
  oscillations, can reach amplitudes comparable to the transit depth
  of Earth-sized planets and is correlated over the typical transit
  timescales. It can introduce systematic errors on the inferred planetary
  parameters when a small number of transits are observed. <BR />
  Aims: The objective of this paper is to characterize the statistical
  properties of the flicker noise and quantify its impact on the
  inferred transit parameters. <BR /> Methods: We used the extensive
  solar observations obtained with SoHO/VIRGO to characterize flicker
  noise. We simulated realistic transits across the solar disk using
  SDO/HMI data and used these to obtain transit light curves, which
  we used to estimate the errors made on the transit parameters due to
  the presence of real solar noise. We make these light curves publicly
  available. To extend the study to a wider parameter range, we derived
  the properties of flicker noise using Kepler observations and studied
  their dependence on stellar parameters. Finally, we predicted the
  limiting stellar apparent magnitude for which the properties of the
  flicker noise can be extracted using high-precision CHEOPS and PLATO
  observations. <BR /> Results: Stellar granulation is a stochastic
  colored noise, and is stationary with respect to the stellar magnetic
  cycle. Both the flicker correlation timescales and amplitudes increase
  with the stellar mass and radius. If these correlations are not taken
  into account when fitting for the parameters of transiting exoplanets,
  this can bias the inferred parameters. In particular, we find errors
  of up to 10% on the ratio between the planetary and stellar radius
  (R<SUB>p</SUB>/R<SUB>s</SUB>) for an Earth-sized planet orbiting a
  Sun-like star. <BR /> Conclusions: Flicker will significantly affect
  the inferred parameters of transits observed at high precision with
  CHEOPS and PLATO for F and G stars. Dedicated modeling strategies
  need to be developed to accurately characterize both the star and the
  transiting exoplanets.

---------------------------------------------------------
Title: Comparing the Properties of ICME-Induced Forbush Decreases
    at Earth and Mars
Authors: Freiherr von Forstner, Johan L.; Guo, Jingnan;
   Wimmer-Schweingruber, Robert F.; Dumbović, Mateja; Janvier, Miho;
   Démoulin, Pascal; Veronig, Astrid; Temmer, Manuela; Papaioannou,
   Athanasios; Dasso, Sergio; Hassler, Donald M.; Zeitlin, Cary J.
2020JGRA..12527662F    Altcode: 2020arXiv200303157V
  Forbush decreases (FDs), which are short-term drops in the flux
  of galactic cosmic rays, are caused by the shielding from strong
  and/or turbulent magnetic structures in the solar wind, especially
  interplanetary coronal mass ejections (ICMEs) and their associated
  shocks, as well as corotating interaction regions. Such events can be
  observed at Earth, for example, using neutron monitors, and also at
  many other locations in the solar system, such as on the surface of
  Mars with the Radiation Assessment Detector instrument onboard Mars
  Science Laboratory. They are often used as a proxy for detecting the
  arrival of ICMEs or corotating interaction regions, especially when
  sufficient in situ solar wind measurements are not available. We
  compare the properties of FDs observed at Earth and Mars, focusing
  on events produced by ICMEs. We find that FDs at both locations show
  a correlation between their total amplitude and the maximum hourly
  decrease, but with different proportionality factors. We explain this
  difference using theoretical modeling approaches and suggest that it is
  related to the size increase of ICMEs, and in particular their sheath
  regions, en route from Earth to Mars. From the FD data, we can derive
  the sheath broadening factor to be between about 1.5 and 1.9, agreeing
  with our theoretical considerations. This factor is also in line with
  previous measurements of the sheath evolution closer to the Sun.

---------------------------------------------------------
Title: CME-CME Interactions as Sources of CME Geoeffectiveness:
    The Formation of the Complex Ejecta and Intense Geomagnetic Storm
    in 2017 Early September
Authors: Scolini, Camilla; Chané, Emmanuel; Temmer, Manuela; Kilpua,
   Emilia K. J.; Dissauer, Karin; Veronig, Astrid M.; Palmerio, Erika;
   Pomoell, Jens; Dumbović, Mateja; Guo, Jingnan; Rodriguez, Luciano;
   Poedts, Stefaan
2020ApJS..247...21S    Altcode: 2019arXiv191110817S
  Coronal mass ejections (CMEs) are the primary sources of intense
  disturbances at Earth, where their geoeffectiveness is largely
  determined by their dynamic pressure and internal magnetic field,
  which can be significantly altered during interactions with other
  CMEs in interplanetary space. We analyze three successive CMEs that
  erupted from the Sun during 2017 September 4-6, investigating the
  role of CME-CME interactions as a source of the associated intense
  geomagnetic storm (Dst_{min}=-142 nT on September 7). To quantify
  the impact of interactions on the (geo)effectiveness of individual
  CMEs, we perform global heliospheric simulations with the European
  Heliospheric Forecasting Information Asset (EUHFORIA) model, using
  observation-based initial parameters with the additional purpose of
  validating the predictive capabilities of the model for complex CME
  events. The simulations show that around 0.45 au, the shock driven by
  the September 6 CME started compressing a preceding magnetic ejecta
  formed by the merging of two CMEs launched on September 4, significantly
  amplifying its B<SUB>z</SUB> until a maximum factor of 2.8 around 0.9
  au. The following gradual conversion of magnetic energy into kinetic
  and thermal components reduced the B<SUB>z</SUB> amplification until
  its almost complete disappearance around 1.8 au. We conclude that a
  key factor at the origin of the intense storm triggered by the 2017
  September 4-6 CMEs was their arrival at Earth during the phase of
  maximum B<SUB>z</SUB> amplification. Our analysis highlights how the
  amplification of the magnetic field of individual CMEs in spacetime due
  to interaction processes can be characterized by a growth, a maximum,
  and a decay phase, suggesting that the time interval between the CME
  eruptions and their relative speeds are critical factors in determining
  the resulting impact of complex CMEs at various heliocentric distances
  (helioeffectiveness).

---------------------------------------------------------
Title: Comprehensive Characterization of Solar Eruptions with Remote
and In-Situ Observations, and Modeling: The Major Solar Events on
    4 November 2015
Authors: Cairns, Iver H.; Kozarev, Kamen A.; Nitta, Nariaki V.;
   Agueda, Neus; Battarbee, Markus; Carley, Eoin P.; Dresing, Nina;
   Gómez-Herrero, Raúl; Klein, Karl-Ludwig; Lario, David; Pomoell,
   Jens; Salas-Matamoros, Carolina; Veronig, Astrid M.; Li, Bo; McCauley,
   Patrick
2020SoPh..295...32C    Altcode: 2019arXiv191003319C
  Solar energetic particles (SEPs) are an important product of solar
  activity. They are connected to solar active regions and flares,
  coronal mass ejections (CMEs), EUV waves, shocks, Type II and III
  radio emissions, and X-ray bursts. These phenomena are major probes
  of the partition of energy in solar eruptions, as well as for the
  organization, dynamics, and relaxation of coronal and interplanetary
  magnetic fields. Many of these phenomena cause terrestrial space
  weather, posing multiple hazards for humans and their technology
  from space to the ground. Since particular flares, shocks, CMEs,
  and EUV waves produce SEP events but others do not, since propagation
  effects from the low corona to 1 AU appear important for some events
  but not others, and since Type II and III radio emissions and X-ray
  bursts are sometimes produced by energetic particles leaving these
  acceleration sites, it is necessary to study the whole system with
  a multi-frequency and multi-instrument perspective that combines
  both in-situ and remote observations with detailed modeling of
  phenomena. This article demonstrates this comprehensive approach
  and shows its necessity by analyzing a trio of unusual and striking
  solar eruptions, radio and X-ray bursts, and SEP events that occurred
  on 4 November 2015. These events show both strong similarities and
  differences from standard events and each other, despite having
  very similar interplanetary conditions and only two flare sites and
  CME genesis regions. They are therefore major targets for further
  in-depth observational studies, and for testing both existing and
  new theories and models. We present the complete suite of relevant
  observations, complement them with initial modeling results for the
  SEPs and interplanetary magnetic connectivity, and develop a plausible
  scenario for the eruptions. Perhaps controversially, the SEPs appear to
  be reasonably modelled and evidence points to significant non-Parker
  magnetic fields. Based on the very limited modeling available, we
  identify the aspects that are and are not understood, and we discuss
  ideas that may lead to improved understanding of the SEP, radio,
  and space-weather events.

---------------------------------------------------------
Title: Differential Emission Measure Plasma Diagnostics of a
    Long-Lived Coronal Hole
Authors: Saqri, Jonas; Veronig, Astrid M.; Heinemann, Stephan G.;
   Hofmeister, Stefan J.; Temmer, Manuela; Dissauer, Karin; Su, Yang
2020SoPh..295....6S    Altcode: 2020arXiv200102259S
  We use Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly
  (AIA) data to reconstruct the plasma properties from differential
  emission measure (DEM) analysis for a previously studied long-lived,
  low-latitude coronal hole (CH) over its lifetime of ten solar
  rotations. We initially obtain a non-isothermal DEM distribution with
  a dominant component centered around 0.9 MK and a secondary smaller
  component at 1.5 - 2.0 MK. We find that deconvolving the data with
  the instrument point spread function (PSF) to account for long-range
  scattered light reduces the secondary hot component. Using the 2012
  Venus transit and a 2013 lunar eclipse to test the efficiency of this
  deconvolution, significant amounts of residual stray light are found
  for the occulted areas. Accounting for this stray light in the error
  budget of the different AIA filters further reduces the secondary hot
  emission, yielding CH DEM distributions that are close to isothermal
  with the main contribution centered around 0.9 MK. Based on these DEMs,
  we analyze the evolution of the emission measure (EM), density, and
  averaged temperature during the CH's lifetime. We find that once the CH
  is clearly observed in EUV images, the bulk of the CH plasma reveals
  a quite constant state, i.e. temperature and density reveal no major
  changes, whereas the total CH area and the photospheric magnetic fine
  structure inside the CH show a distinct evolutionary pattern. These
  findings suggest that CH plasma properties are mostly "set" at the CH
  formation or/and that all CHs have similar plasma properties.

---------------------------------------------------------
Title: Comparing the Properties of ICME-Induced Forbush Decreases
    at Earth and Mars
Authors: Freiherr von Forstner, J. L.; Guo, J.; Wimmer-Schweingruber,
   R. F.; Dumbovic, M.; Janvier, M.; Demoulin, P.; Veronig, A.; Temmer,
   M.; Hassler, D.; Zeitlin, C.
2019AGUFMSH41D3339F    Altcode:
  Forbush decreases (FDs), short-term drops in the flux of galactic
  cosmic rays (GCR), can be caused by the shielding from strong and/or
  turbulent magnetic structures in the solar wind, i.e. interplanetary
  coronal mass ejections (ICMEs) and their associated shocks as well
  as corotating interaction regions (CIRs). FDs are often used as a
  proxy for detecting the arrival of ICMEs or CIRs at locations where
  sufficient in situ solar wind measurements are not or not always
  available, such as at Mars. The Radiation Assessment Detector (RAD)
  onboard the Mars Science Laboratory (MSL) mission's Curiosity rover
  has been continuously measuring the GCR environment on the surface
  of Mars for more than 7 years since its landing in August 2012 and is
  thus an excellent source for measurements of FDs at Mars (see e.g. <A
  href="https://doi.org/10.1051/0004-6361/201732087">Guo et al. 2018,
  A&amp;A</A>). <P />Based on the large catalog of FDs at Mars compiled
  by <A href="https://doi.org/10.1007/s11207-019-1454-2">Papaioannou et
  al. (2019, Solar Physics)</A> as well as results from our previous
  work (<A href="https://doi.org/10.1029/2018SW002138">Freiherr von
  Forstner et al., 2019, Space Weather</A>), we study the parameters
  of FDs at Mars and their relations, focusing on events produced by
  ICMEs. We then compare these data with catalogs of terrestrial FDs,
  investigating whether and to what extent the differences of certain FD
  characteristics between the two planets, at two different heliospheric
  distances, are related to the evolution of ICMEs between Earth and
  Mars. <P />Our results show that there is a linear correlation between
  the FD amplitude (drop percentage) and the maximum hourly GCR decrease
  during the FD, which was already found at Earth by previous authors (<A
  href="https://doi.org/10.1017/S1743921309029676">Belov et al., 2008</A>,
  <A href="https://doi.org/10.1134/S0016793212030024">Abunin et al.,
  2012</A>). However, this correlation has a different proprtionality
  factor at Mars than at Earth, especially for ICME-induced events. As
  we do not find a clear dependence of this relationship on the observed
  GCR energy range, we suggest that this difference is probably caused by
  the expansion of the ICME sheath region as it propagates outward from
  1 AU to ∼1.5 AU. The expansion factor derived from our analysis is in
  line with expansion factors of ICME sheaths within the inner heliosphere
  observed by &lt;a href="https://doi.org/10.1029/2018JA025949&gt;Janvier
  et al. (2019, JGR Space Physics).

---------------------------------------------------------
Title: A study of the role of CME-CME interactions on CME
    geo-effectiveness with EUHFORIA
Authors: Scolini, C.; Poedts, S.; Rodriguez, L.; Temmer, M.; Dumbovic,
   M.; Guo, J.; Veronig, A.; Dissauer, K.; Palmerio, E.; Kilpua, K. E. J.;
   Pomoell, J.
2019AGUFMSH43D3368S    Altcode:
  Coronal Mass Ejections (CMEs) are the main source of strong space
  weather disturbances at Earth and other locations in the solar
  system. While their impact is largely determined by their dynamic
  pressure and magnetic field, interactions with other CMEs can
  significantly alter their individual characteristics and enhance their
  (geo-)effectiveness. As observations in the heliosphere are limited,
  investigating such phenomena via physics-based models is therefore
  crucial to advance our understanding of complex CME events, and to
  assess the prediction capabilities at various locations. <P />Here we
  present a comprehensive study of the role of CME-CME interactions on
  their (geo-)effectiveness, by performing simulations of complex CME
  events with the EUHFORIA heliospheric solar wind and CME propagation
  model. As a case study, we consider a sequence of 6 CMEs observed during
  the unusually active week of 4-10 September 2017. As their source region
  moved on the solar disk due to the rotation, CMEs were launched over
  a wide range of longitudes, interacting with each other while paving
  the way for the propagation of the following ones. CME signatures were
  observed at Mars and at Earth, where intense disturbances and space
  weather events were triggered by CME-CME interactions. Using input
  parameters derived from multi-spacecraft remote-sensing observations
  of CMEs and their source region, we perform global simulations of the
  event using the spheromak CME model in EUHFORIA, and we investigate how
  their interactions affected the evolution of single CME structures and
  the in-situ properties at Earth and Mars. <P />Results from this case
  study are complemented by a parametric study of CME-CME interactions,
  performed by running a set of simulations varying the initial CME
  parameters (e.g. speed, waiting time, magnetic field properties,
  density…), with the aim of quantifying the effect of such changes on
  their propagation and interaction. Results will benchmark our current
  prediction capabilities in the case of complex CME events and provide
  insights on their large-scale evolution in the heliosphere.

---------------------------------------------------------
Title: Genesis and impulsive evolution of the fast CME associated
    with the X8.2 flare on 2017 September 10
Authors: Veronig, A.; Podladchikova, T.; Dissauer, K.; Temmer, M.;
   Seaton, D. B.; Long, D.; Guo, J.; Vrsnak, B.; Harra, L. K.; Kliem, B.
2019AGUFMSH13A..02V    Altcode:
  The X8.2 event of 2017 September 10 provides unique observations to
  study the genesis, magnetic morphology, impulsive dynamics and shock
  formation in a very fast coronal mass ejection (CME). As will be
  discussed in this presentation, fundamental insight in the processes
  of magnetic reconnection, CME acceleration and shock formation are
  provided through EUV observations of the middle corona. <P />Combining
  the large field-of-view and high-cadence imagery from GOES-16/SUVI
  and SDO/AIA EUV, respectively, we identify a hot (T ≈ 10-15 MK)
  bright rim around a quickly expanding cavity, embedded inside a much
  larger CME shell (T ≈ 1-2 MK). The CME shell develops from a dense
  set of large AR loops (&gt;0.5Rs) and seamlessly evolves into the
  CME front observed in LASCO C2. The strong lateral overexpansion
  of the CME shell acts as a piston initiating the fast and globally
  propagating EUV shock wave. The hot cavity rim is demonstrated to be
  a manifestation of the dominantly poloidal flux and frozen-in plasma
  added to the rising flux rope by magnetic reconnection in the current
  sheet beneath. The same structure is later observed as the core of the
  white-light CME, challenging the traditional interpretation of the CME
  three-part morphology (Veronig et al. 2018). <P />The large amount of
  added magnetic flux suggested by these observations can explain the
  extreme accelerations of the radial and lateral expansion of the CME
  shell and cavity, all reaching values up to 5-10 km s<SUP>-2</SUP>. The
  acceleration peaks occur simultaneously with the first RHESSI 100-300
  keV hard X-ray burst of the associated flare, further underlining the
  importance of the reconnection process for the impulsive CME evolution
  in the low and middle corona.

---------------------------------------------------------
Title: Understanding the magnetic topology and reconfiguration of
    the early stages of solar eruptions by investigating coronal dimmings
Authors: Dissauer, K.; Prasad, A.; Veronig, A.
2019AGUFMSH32A..04D    Altcode:
  Coronal dimmings are temporary regions of strongly reduced coronal
  emission in extreme-ultraviolet (EUV) and soft X-rays that form in the
  wake of coronal mass ejections (CMEs). In general, their formation is
  interpreted as density depletion due to the expansion and evacuation
  of plasma during the early CME evolution. Recently, strong statistical
  relationships between decisive dimming parameters and CME and flare
  quantities were derived (Dissauer et al. 2018b, 2019). Using a newly
  developed detection algorithm, so far not resolved fine structure within
  the dimming region could be identified for the first time (Dissauer
  et al. 2018a). Both aspects verify the importance of coronal dimmings
  in the early diagnostics of solar eruptions. In order to exploit this
  potential further, we analyze the X2.1 flare/CME event on September
  6, 2011 by combining EUV observations of coronal dimmings in SDO/AIA
  with non-force-free magnetic field modeling. The pre- and post-eruptive
  magnetic field configurations at the observed coronal dimming locations
  are investigated, with respect to the coronal dimming fine structure
  and its intensity distribution. The dynamics of the dimming evolution
  is studied in the form of timing maps, which code when each pixel of
  the dimming region is detected for the first time. These timing maps
  are used to investigate the initiation of the eruption and to identify
  which flux systems are involved. Coronal dimming locations are also
  compared with squashing factor Q maps, indicating locations in favor of
  magnetic reconnection, in order to check whether preferential locations
  for the formation of coronal dimmings exist prior to the eruption.

---------------------------------------------------------
Title: Data assimilation with an adaptive Kalman filter for short-term
    forecasts of the F30 and F10.7 cm radio flux
Authors: Podladchikova, T.; Podladchikova, O.; Veronig, A.
2019AGUFMSH34B..03P    Altcode:
  Solar activity indices such as the F30 and F10.7 cm radio flux are
  required by most models characterizing the state of the upper Earth
  atmosphere, such as the thermosphere and ionosphere, in order to specify
  satellite orbits, re-entry services, collision avoidance maneuvers and
  modeling of space debris evolution. With the aim of advancing current
  forecasting capabilities, we develop a novel prediction method of the
  F30 and F10.7 solar indices 1 to 3 day-ahead using an adaptive Kalman
  filter. Traditional approaches to the solar radio flux forecasting are
  based on linear regression models. However, one of the major concerns
  with such data assimilation scheme is that the evolution of the solar
  radio flux is a strongly non-stationary process, and thus the use of
  constant regression coefficients cannot be an optimal selection. The
  Kalman filter technique removes this disadvantage by adjusting the
  regression coefficients in real-time during the observation period,
  thereby increasing the forecasting accuracy. <P />Testing the developed
  prediction technique over the period 2004-2016, we obtain a correlation
  coefficient between the predicted and observed values of about 0.99
  (1 day) and 0.98 (3 day ahead) for the F30 index and 0.99 (1-day
  ahead) and 0.96 (3-day ahead) for the F10.7 index. We compared our
  forecasts with the results provided by the few currently operating
  models for various periods of the solar cycle (minimum, ascending,
  maximum and declining phases). The RMS errors of the predictions
  are reduced by 3-14% in comparison with the predictions of F30 index
  based on neural networks (CLS) and the F10.7 index provided by the
  SIDC manual analysis. Additionally, the developed technique produces
  non-biased predictions, which is a strong advantage compared to the CLS
  forecast (overestimation) and SIDC forecast (underestimation). Thus,
  the proposed adaptive Kalman filter method significantly improves the
  quality of the F30 and F10.7 cm solar radio flux predictions and can
  be recommended for space weather applications.

---------------------------------------------------------
Title: The Role of Small-Scale Seed in the Origin of Large-Scale
    Solar Eruptions
Authors: Gou, T.; Liu, R.; Veronig, A.; Wang, Y.
2019AGUFMSH33B3395G    Altcode:
  Solar eruptions are explosive events originated from the solar
  atmosphere and can cause a large amount of energy release within a short
  time. Among them, the helical magnetic flux rope is considered as the
  fundamental structure. However, the flux rope's origin still remains
  elusive. Here we present observations of how stellar-sized eruptions
  initiate from a small-scale seed, which plays an important role in
  the flux rope formation. The seed forms prior to the eruption and is
  associated with processes that occur in different layers in the solar
  atmosphere. After that it grows larger and rises impulsively, finally
  producing a large-scale coronal mass ejection (CME), accompanied by
  intense energy release. This study unravels the origin and illuminates
  a complete evolution of solar eruptions.

---------------------------------------------------------
Title: Interstellar Probe - To Touch Interstellar Space
Authors: Wimmer-Schweingruber, R. F.; McNutt, R. L., Jr.; Brandt,
   P. C.; Veronig, A.; Lallement, R.; Lavraud, B.; Galli, A.; Wahlund,
   J. E.; Sorriso-Valvo, L.; Scherer, K.; Vainio, R. O.; Zong, Q.; Wurz,
   P.; Izmodenov, V.; Ip, W. H.; Horbury, T. S.; Bertaux, J. L.; Cairns,
   I. H.
2019AGUFMSH54A..01W    Altcode:
  After the exciting in-situ observations of the termination shock and
  the entry of the Voyager spacecraft into the inner and possibly outer
  heliosheath, there is a growing awareness of the significance of the
  physics of the outer heliosphere. Its understanding helps to clarify
  the structure of our immediate interstellar neighborhood, contributes
  to the clarification of fundamental astrophysical processes like
  the acceleration of charged particles at a stellar wind termination
  shock and beyond, and also sheds light on the question to what extent
  interstellar-terrestrial relations are important for the environment of
  and on the Earth and of exoplanets. In order to explore the boundary
  region of the heliosphere, it is necessary to send a spacecraft to
  perform advanced in-situ measurements particularly in the heliosheath,
  i.e. the region between the solar wind termination shock, and the
  heliopause, as well as in the (very) local interstellar medium. Solar
  activity is decreasing to 'normal values' below those of the Grand
  Solar Maximum which was typical of the space age so far. This is
  likely to reduce the size of the heliosphere and allows us to study a
  'normal' heliosphere by launching an Interstellar Probe (IP) which
  will also provide within a shorter time than previously believed
  the first comprehensive measurements of key parameters of the local
  interstellar environment such as its composition, state, and magnetic
  field. Together with an accurate determination of the state of the
  heliospheric plasma across the heliosphere, these quantities are crucial
  to our understanding of how the heliosphere, and, much more generally,
  astrospheres, are formed and how they react to varying interstellar
  environments.

---------------------------------------------------------
Title: A Hot Cusp-shaped Confined Solar Flare
Authors: Hernandez-Perez, Aaron; Su, Yang; Thalmann, Julia; Veronig,
   Astrid M.; Dickson, Ewan C.; Dissauer, Karin; Joshi, Bhuwan; Chandra,
   Ramesh
2019ApJ...887L..28H    Altcode: 2019arXiv191110859H
  We analyze a confined flare that developed a hot cusp-like structure
  high in the corona (H ∼ 66 Mm). A growing cusp-shaped flare arcade
  is a typical feature in the standard model of eruptive flares, caused
  by magnetic reconnection at progressively larger coronal heights. In
  contrast, we observe a static hot cusp during a confined flare. Despite
  an initial vertical temperature distribution similar to that in eruptive
  flares, we observe a distinctly different evolution during the late
  (decay) phase, in the form of prolonged hot emission. The distinct
  cusp shape, rooted at locations of nonthermal precursor activity, was
  likely caused by a magnetic field arcade that kinked near the top. Our
  observations indicate that the prolonged heating was a result of slow
  local reconnection and an increased thermal pressure near the kinked
  apexes due to continuous plasma upflows.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Coronal hole parameters
    (Heinemann+, 2019)
Authors: Heinemann, S. G.; Temmer, M.; Heinemann, N.; Dissauer, K.;
   Samara, E.; Jercic, V.; Hofmeister, S. J.; Veronig, A. M.
2019yCatp058029401H    Altcode:
  Coronal hole parameters such as morphological properties, the intensity,
  boundary stability as well as properties of the underlying photospheric
  magnetic field and its fine structure are presented. 718 coronal holes
  between 2010 and 2019 have been extracted and analyzed from 193A
  filtergrams taken by AIA/SDO. For each coronal hole the following
  parameters are given (including uncertainties). Date, Threshold,
  Category Factor, Area, Intensity (Mean + Median), Position, Extension,
  Mean Magnetic Field Strength (Signed + Unsigned), Magnetic Flux (Signed
  + Unsigned), Flux Balance, Skewness (Magnetic Field Distribution),
  Flux Tube Number (Weak + Strong), Flux Tube Area Ratio (Weak + Strong),
  Flux Tube Flux Ratio (Weak + Strong). <P />(1 data file).

---------------------------------------------------------
Title: Lorentz Force Evolution Reveals the Energy Build-up Processes
    during Recurrent Eruptive Solar Flares
Authors: Sarkar, Ranadeep; Srivastava, Nandita; Veronig, Astrid M.
2019ApJ...885L..17S    Altcode: 2019arXiv191013264S
  The energy release and build-up processes in the solar corona have
  significant implications in particular for the case of large recurrent
  flares, which pose challenging questions about the conditions that lead
  to the episodic energy release processes. It is not yet clear whether
  these events occur due to the continuous supply of free magnetic energy
  to the solar corona or because not all of the available free magnetic
  energy is released during a single major flaring event. In order to
  address this question, we report on the evolution of photospheric
  magnetic field and the associated net Lorentz force changes in ARs
  11261 and 11283, each of which gave rise to recurrent eruptive M-
  and X-class flares. Our study reveals that after the abrupt downward
  changes during each flare, the net Lorentz force increases by (2-5) ×
  10<SUP>22</SUP> dyne in between the successive flares. This distinct
  rebuild-up of net Lorentz forces is the first observational evidence
  found in the evolution of any nonpotential parameter of solar active
  regions (ARs), which suggests that new energy was supplied to the
  ARs in order to produce the recurrent large flares. The rebuild-up of
  magnetic free energy of the ARs is further confirmed by the observations
  of continuous shearing motion of moving magnetic features of opposite
  polarities near the polarity inversion line. The evolutionary pattern
  of the net Lorentz force changes reported in this study has significant
  implications, in particular, for the forecasting of recurrent large
  eruptive flares from the same AR and hence the chances of interaction
  between the associated CMEs.

---------------------------------------------------------
Title: Statistical Analysis and Catalog of Non-polar Coronal Holes
    Covering the SDO-Era Using CATCH
Authors: Heinemann, Stephan G.; Temmer, Manuela; Heinemann, Niko;
   Dissauer, Karin; Samara, Evangelia; Jerčić, Veronika; Hofmeister,
   Stefan J.; Veronig, Astrid M.
2019SoPh..294..144H    Altcode: 2019arXiv190701990H
  Coronal holes are usually defined as dark structures seen in the extreme
  ultraviolet and X-ray spectrum which are generally associated with
  open magnetic fields. Deriving reliably the coronal hole boundary is
  of high interest, as its area, underlying magnetic field, and other
  properties give important hints as regards high speed solar wind
  acceleration processes and compression regions arriving at Earth. In
  this study we present a new threshold-based extraction method,
  which incorporates the intensity gradient along the coronal hole
  boundary, which is implemented as a user-friendly SSW-IDL GUI. The
  Collection of Analysis Tools for Coronal Holes (CATCH) enables the
  user to download data, perform guided coronal hole extraction and
  analyze the underlying photospheric magnetic field. We use CATCH
  to analyze non-polar coronal holes during the SDO-era, based on 193
  Å filtergrams taken by the Atmospheric Imaging Assembly (AIA) and
  magnetograms taken by the Heliospheric and Magnetic Imager (HMI),
  both on board the Solar Dynamics Observatory (SDO). Between 2010 and
  2019 we investigate 707 coronal holes that are located close to the
  central meridian. We find coronal holes distributed across latitudes
  of about ±60<SUP>∘</SUP>, for which we derive sizes between 1.6
  ×10<SUP>9</SUP> and 1.8 ×10<SUP>11</SUP><SUP>km2</SUP>. The absolute
  value of the mean signed magnetic field strength tends towards an
  average of 2.9 ±1.9 G. As far as the abundance and size of coronal
  holes is concerned, we find no distinct trend towards the northern
  or southern hemisphere. We find that variations in local and global
  conditions may significantly change the threshold needed for reliable
  coronal hole extraction and thus, we can highlight the importance of
  individually assessing and extracting coronal holes.

---------------------------------------------------------
Title: Photospheric magnetic structure of coronal holes
Authors: Hofmeister, Stefan J.; Utz, Dominik; Heinemann, Stephan G.;
   Veronig, Astrid; Temmer, Manuela
2019A&A...629A..22H    Altcode: 2019arXiv190903806H
  In this study, we investigate in detail the photospheric magnetic
  structure of 98 coronal holes using line-of-sight magnetograms of
  SDO/HMI, and for a subset of 42 coronal holes using HINODE/SOT G-band
  filtergrams. We divided the magnetic field maps into magnetic elements
  and quiet coronal hole regions by applying a threshold at ±25 G. We
  find that the number of magnetic bright points in magnetic elements
  is well correlated with the area of the magnetic elements (cc =
  0.83 ± 0.01). Further, the magnetic flux of the individual magnetic
  elements inside coronal holes is related to their area by a power law
  with an exponent of 1.261 ± 0.004 (cc = 0.984 ± 0.001). Relating
  the magnetic elements to the overall structure of coronal holes, we
  find that on average (69 ± 8)% of the overall unbalanced magnetic
  flux of the coronal holes arises from long-lived magnetic elements
  with lifetimes &gt; 40 h. About (22 ± 4)% of the unbalanced magnetic
  flux arises from a very weak background magnetic field in the quiet
  coronal hole regions with a mean magnetic field density of about
  0.2-1.2 G. This background magnetic field is correlated to the flux
  of the magnetic elements with lifetimes of &gt; 40 h (cc = 0.88 ±
  0.02). The remaining flux arises from magnetic elements with lifetimes
  &lt; 40 h. By relating the properties of the magnetic elements to the
  overall properties of the coronal holes, we find that the unbalanced
  magnetic flux of the coronal holes is completely determined by
  the total area that the long-lived magnetic elements cover (cc =
  0.994 ± 0.001). <P />Movie associated to Fig. 2 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201935918/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: EVE Flare Diagnostics of in situ Observed Electron Events
Authors: Miteva, R.; Samwel, S. W.; Veronig, A.; Koleva, K.; Dechev,
   M.; Dissauer, K.; Temmer, M.; Kozarev, K.; Zabunov, S.
2019simi.conf..196M    Altcode:
  We present a comparative study between SDO/EVE flare intensity and the
  peak intensity of solar energetic electrons and protons over solar
  cycle 24 (2010–2017). For the analysis we selected flare emission
  in three EUV wavelengths: 94, 133 and 304 Å. Data from 103–175 and
  175–315 keV ACE/EPAM energy channels are used to identify and analyze
  the flux of the in situ observed electrons. SOHO/ERNE data in five
  energy channels (17–22, 26–32, 40–51, 64–80, 101–131 MeV) is
  used for the proton signatures of the so-identified electron events. We
  calculated Pearson correlation coefficients between the electron and
  proton particle fluxes and the flare EUV intensities, and compare the
  results with the respective correlations between particle flux and
  the solar flare GOES class and speed of the coronal mass ejections.

---------------------------------------------------------
Title: CME-HSS Interaction and Characteristics Tracked from Sun
    to Earth
Authors: Heinemann, Stephan G.; Temmer, Manuela; Farrugia, Charles J.;
   Dissauer, Karin; Kay, Christina; Wiegelmann, Thomas; Dumbović, Mateja;
   Veronig, Astrid M.; Podladchikova, Tatiana; Hofmeister, Stefan J.;
   Lugaz, Noé; Carcaboso, Fernando
2019SoPh..294..121H    Altcode: 2019arXiv190810161H
  In a thorough study, we investigate the origin of a remarkable plasma
  and magnetic field configuration observed in situ on June 22, 2011, near
  L1, which appears to be a magnetic ejecta (ME) and a shock signature
  engulfed by a solar wind high-speed stream (HSS). We identify the
  signatures as an Earth-directed coronal mass ejection (CME), associated
  with a C7.7 flare on June 21, 2011, and its interaction with a HSS,
  which emanates from a coronal hole (CH) close to the launch site of the
  CME. The results indicate that the major interaction between the CME and
  the HSS starts at a height of 1.3 R⊙ up to 3 <SUB>R⊙</SUB>. Over
  that distance range, the CME undergoes a strong north-eastward
  deflection of at least 30<SUP>∘</SUP> due to the open magnetic field
  configuration of the CH. We perform a comprehensive analysis for the
  CME-HSS event using multi-viewpoint data (from the Solar TErrestrial
  RElations Observatories, the Solar and Heliospheric Observatory and the
  Solar Dynamics Observatory), and combined modeling efforts (nonlinear
  force-free field modeling, Graduated Cylindrical Shell CME modeling,
  and the Forecasting a CME's Altered Trajectory - ForeCAT model). We aim
  at better understanding its early evolution and interaction process as
  well as its interplanetary propagation and related in situ signatures,
  and finally the resulting impact on the Earth's magnetosphere.

---------------------------------------------------------
Title: Spectroscopy and Differential Emission Measure Diagnostics
    of a Coronal Dimming Associated with a Fast Halo CME
Authors: Veronig, Astrid M.; Gömöry, Peter; Dissauer, Karin; Temmer,
   Manuela; Vanninathan, Kamalam
2019ApJ...879...85V    Altcode: 2019arXiv190601517V
  We study the coronal dimming caused by the fast halo CME (deprojected
  speed v = 1250 km s<SUP>-1</SUP>) associated with the C3.7 two-ribbon
  flare on 2012 September 27, using Hinode/EIS spectroscopy and Solar
  Dynamics Observatory (SDO)/AIA Differential Emission Measure (DEM)
  analysis. The event reveals bipolar core dimmings encompassed by
  hook-shaped flare ribbons located at the ends of the flare-related
  polarity inversion line, and marking the footpoints of the erupting
  filament. In coronal emission lines of log T [K] = 5.8-6.3, distinct
  double-component spectra indicative of the superposition of a stationary
  and a fast upflowing plasma component with velocities up to 130 km
  s<SUP>-1</SUP> are observed at these regions, which were mapped by the
  scanning EIS slit close in time to their impulsive dimming onset. The
  outflowing plasma component is found to be of the same order as and
  even dominant over the stationary one, with electron densities in the
  upflowing component of 2 × 10<SUP>9</SUP> cm<SUP>-3</SUP> at log T
  [K] = 6.2. The density evolution in core-dimming regions derived from
  SDO/AIA DEM analysis reveals impulsive reductions by 40%-50% within
  ≲10 minutes and remains at these reduced levels for hours. The
  mass-loss rate derived from the EIS spectroscopy in the dimming
  regions is of the same order as the mass increase rate observed in the
  associated white-light CME (1 × 10<SUP>12</SUP> g s<SUP>-1</SUP>),
  indicating that the CME mass increase in the coronagraphic field of
  view results from plasma flows from below and not from material piled
  up ahead of the outward-moving and expanding CME front.

---------------------------------------------------------
Title: Unusual Plasma and Particle Signatures at Mars and STEREO-A
    Related to CME-CME Interaction
Authors: Dumbović, Mateja; Guo, Jingnan; Temmer, Manuela; Mays,
   M. Leila; Veronig, Astrid; Heinemann, Stephan G.; Dissauer, Karin;
   Hofmeister, Stefan; Halekas, Jasper; Möstl, Christian; Amerstorfer,
   Tanja; Hinterreiter, Jürgen; Banjac, Saša; Herbst, Konstantin; Wang,
   Yuming; Holzknecht, Lukas; Leitner, Martin; Wimmer–Schweingruber,
   Robert F.
2019ApJ...880...18D    Altcode: 2019arXiv190602532D
  On 2017 July 25 a multistep Forbush decrease (FD) with a remarkable
  total amplitude of more than 15% was observed by Mars Science
  Laboratory/Radiation Assessment Detector at Mars. We find that these
  particle signatures are related to very pronounced plasma and magnetic
  field signatures detected in situ by STEREO-A on 2017 July 24, with
  a higher-than-average total magnetic field strength reaching more
  than 60 nT. In the observed time period STEREO-A was at a relatively
  small longitudinal separation (46°) to Mars, and both were located at
  the back side of the Sun as viewed from Earth. We analyze a number of
  multispacecraft and multi-instrument (both in situ and remote-sensing)
  observations and employ modeling to understand these signatures. We
  find that the solar sources are two coronal mass ejections (CMEs)
  that erupted on 2017 July 23 from the same source region on the back
  side of the Sun as viewed from Earth. Moreover, we find that the
  two CMEs interact nonuniformly, inhibiting the expansion of one of
  the CMEs in the STEREO-A direction, whereas allowing it to expand
  more freely in the Mars direction. The interaction of the two CMEs
  with the ambient solar wind adds up to the complexity of the event,
  resulting in a long, substructured interplanetary disturbance at Mars,
  where different substructures correspond to different steps of the FD,
  adding up to a globally large-amplitude FD.

---------------------------------------------------------
Title: Magnetohydrodynamic Simulation of Magnetic Null-point
    Reconnections and Coronal dimmings in NOAA AR 11283
Authors: Prasad, Avijeet; Dissauer, Karin; Hu, Qiang; Bhattacharyya,
   Ramitendranth; Veronig, Astrid; Kumar, Sanjay; Joshi, Bhuwan
2019AAS...23431004P    Altcode:
  The magnetohydrodynamics of active region NOAA 11283 is simulated
  using an initial non-force-free magnetic field, extrapolated using the
  photospheric vector magnetogram of the active region. Particularly,
  we focus on the magnetic reconnections (MRs) occurring close to a
  magnetic null point that resulted in the X2.1 flare on 2011 September 06
  around 22:12 UT followed by the appearance of circular chromospheric
  flare ribbons and coronal dimming. Importantly, the extrapolated
  initial non-force-free field shows the presence of a twisted flux
  rope near the polarity inversion line and a three-dimensional (3D)
  null situated near one of the major polarities. In the simulated
  dynamics, we find MRs occurring below the rope that leads to an
  increase in the twist and consequent rise of the flux-rope. As one
  end of the rising rope approaches the 3D null point, reconnections
  ensue - leading to the main flare and the subsequent formation of
  circular flare ribbons. Interestingly, the MRs open up the flux-rope
  that can potentially lead to the loss of plasma confined in the rope
  and provide a viable explanation for coronal dimming and jet-like
  eruptions. Furthermore, the location of the footpoints of the rope
  during the reconnections are found to be in good correlation with
  the dimming regions inferred from Extreme-Ultraviolet images observed
  after the flare.

---------------------------------------------------------
Title: The Focusing Optics X-ray Solar Imager (FOXSI)
Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener,
   Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Gburek, Szymon;
   Steslicki, Marek; Allred, Joel C.; Battaglia, Marina; Baumgartner,
   Wayne H.; Drake, James; Goetz, Keith; Grefenstette, Brian; Hannah,
   Iain; Holman, Gordon D.; Inglis, Andrew; Ireland, Jack; Klimchuk,
   James A.; Ishikawa, Shin-Nosuke; Kontar, Eduard; Massone, Anna-maria;
   Piana, Michele; Ramsey, Brian; Schwartz, Richard A.; Woods, Thomas N.;
   Chen, Bin; Gary, Dale E.; Hudson, Hugh S.; Kowalski, Adam; Warmuth,
   Alexander; White, Stephen M.; Veronig, Astrid; Vilmer, Nicole
2019AAS...23422501C    Altcode:
  The Focusing Optics X-ray Solar Imager (FOXSI), a SMEX mission concept
  in Phase A, is the first-ever solar-dedicated, direct-imaging, hard
  X-ray telescope. FOXSI provides a revolutionary new approach to
  viewing explosive magnetic-energy release on the Sun by detecting
  signatures of accelerated electrons and hot plasma directly in
  and near the energy-release sites of solar eruptive events (e.g.,
  solar flares). FOXSI's primary science objective is to understand the
  mystery of how impulsive energy release leads to solar eruptions, the
  primary drivers of space weather at Earth, and how those eruptions are
  energized and evolve. FOXSI addresses three important science questions:
  (1) How are particles accelerated at the Sun? (2) How do solar plasmas
  get heated to high temperatures? (3) How does magnetic energy released
  on the Sun lead to flares and eruptions? These fundamental physics
  questions are key to our understanding of phenomena throughout
  the Universe from planetary magnetospheres to black hole accretion
  disks. FOXSI measures the energy distributions and spatial structure of
  accelerated electrons throughout solar eruptive events for the first
  time by directly focusing hard X-rays from the Sun. This naturally
  enables high imaging dynamic range, while previous instruments have
  typically been blinded by bright emission. FOXSI provides 20-100 times
  more sensitivity as well as 20 times faster imaging spectroscopy
  than previously available, probing physically relevant timescales
  (&lt;1 second) never before accessible. FOXSI's launch in July 2022
  is aligned with the peak of the 11-year solar cycle, enabling FOXSI
  to observe the many large solar eruptions that are expected to take
  place throughout its two-year mission.

---------------------------------------------------------
Title: Heliospheric Evolution of Magnetic Clouds
Authors: Vršnak, B.; Amerstorfer, T.; Dumbović, M.; Leitner, M.;
   Veronig, A. M.; Temmer, M.; Möstl, C.; Amerstorfer, U. V.; Farrugia,
   C. J.; Galvin, A. B.
2019ApJ...877...77V    Altcode: 2019arXiv190408266V
  The interplanetary evolution of 11 magnetic clouds (MCs) recorded by at
  least two radially aligned spacecraft is studied. The in situ magnetic
  field measurements are fitted to a cylindrically symmetric Gold-Hoyle
  force-free uniform-twist flux-rope configuration. The analysis
  reveals that in a statistical sense, the expansion of the studied
  MCs is compatible with self-similar behavior. However, individual
  events expose a large scatter of expansion rates, ranging from very
  weak to very strong expansion. Individually, only four events show an
  expansion rate compatible with isotropic self-similar expansion. The
  results indicate that the expansion has to be much stronger when
  the MCs are still close to the Sun than in the studied 0.47-4.8 au
  distance range. The evolution of the magnetic field strength shows a
  large deviation from the behavior expected for the case of isotropic
  self-similar expansion. In the statistical sense, as well as in most
  of the individual events, the inferred magnetic field decreases much
  slower than expected. Only three events show behavior compatible
  with self-similar expansion. There is also a discrepancy between the
  magnetic field decrease and the increase of the MC size, indicating that
  magnetic reconnection and geometrical deformations play a significant
  role in the MC evolution. About half of the events show a decay of the
  electric current as expected for self-similar expansion. Statistically,
  the inferred axial magnetic flux is broadly consistent with remaining
  constant. However, events characterized by a large magnetic flux show
  a clear tendency toward decreasing flux.

---------------------------------------------------------
Title: Three-dimensional Reconstructions of Extreme-ultraviolet Wave
    Front Heights and Their Influence on Wave Kinematics
Authors: Podladchikova, Tatiana; Veronig, Astrid M.; Dissauer, Karin;
   Temmer, Manuela; Podladchikova, Olena
2019ApJ...877...68P    Altcode: 2019arXiv190409427P
  EUV waves are large-scale disturbances in the solar corona initiated
  by coronal mass ejections. However, solar EUV images show only the
  wave front projections along the line of sight of the spacecraft. We
  perform 3D reconstructions of EUV wave front heights using multipoint
  observations from STEREO-A and STEREO-B, and we study their evolution
  to properly estimate the EUV wave kinematics. We develop two different
  methods to solve the matching problem of the EUV wave crest on
  pairs of STEREO-A/B images by combining epipolar geometry with the
  investigation of perturbation profiles. The proposed approaches are
  applicable at the early and maximum stage of the event when STEREO-A/B
  see different facets of the EUV wave, but also at the later stage when
  the wave front becomes diffusive and faint. The techniques developed
  are demonstrated on two events observed at different separations of
  the STEREO spacecraft (42° and 91°). For the 2007 December 7 event,
  we find that the emission of the EUV wave front mainly comes from a
  height range up to 90-104 Mm, decreasing later to 7-35 Mm. Including
  the varying height of the EUV wave front allows us to correct the
  wave kinematics for the projection effects, resulting in velocities
  in the range of 217-266 km s<SUP>-1</SUP>. For the 2009 February 13
  event, the wave front height almost doubled from 54 to 93 Mm over 10
  minutes, and the velocity derived is 205-208 km s<SUP>-1</SUP>. In
  the two events under study, the corrected speeds differ by up to 25%
  from the uncorrected ones, depending on the wave front height evolution.

---------------------------------------------------------
Title: Pre-eruption Processes: Heating, Particle Acceleration, and the
    Formation of a Hot Channel before the 2012 October 20 M9.0 Limb Flare
Authors: Hernandez-Perez, Aaron; Su, Yang; Veronig, Astrid M.;
   Thalmann, Julia; Gömöry, Peter; Joshi, Bhuwan
2019ApJ...874..122H    Altcode: 2019arXiv190208436H
  We report a detailed study of the pre-eruption activities that led to
  the occurrence of an M9.0 flare/CME event on 2012 October 20 in NOAA
  AR 11598. This includes the study of the preceding confined C2.4 flare
  that occurred on the same AR ∼25 minutes earlier. We observed that the
  M9.0 flare occurred as a consequence of two distinct triggering events
  well separated in time. The first triggering episode occurred as early
  as ∼20 minutes before the onset of the M9.0 flare, evidenced by the
  destabilization and rise of a pre-existing filament to a new position of
  equilibrium at a higher coronal altitude during the decay phase of the
  C2.4 flare. This brought the system to a magnetic configuration where
  the establishment of the second triggering event was favorable. The
  second triggering episode occurred ∼17 minutes later, during the
  early phase of the M9.0 flare, evidenced by the further rise of the
  filament and successful ejection. The second trigger is followed by a
  flare precursor phase, characterized by nonthermal emission and the
  sequential formation of a hot channel as shown by the SDO/AIA DEM
  (differential emission measure) maps, the RHESSI X-ray images and
  spectra. These observations are suggestive of magnetic reconnection
  and particle acceleration that can explain the precursor phase and can
  be directly related to the formation of the hot channel. We discuss
  the triggering mechanisms, their implications during the early and
  precursor phases and highlight the importance of early activities and
  preceding small confined flares to understand the initiation of large
  eruptive flares.

---------------------------------------------------------
Title: Genesis, magnetic morphology and impulsive evolution of
    the coronal mass ejection associated with the X8.2 flare on 2017
    September 10
Authors: Veronig, Astrid; Podladchikova, Tatiana; Dissauer, Karin;
   Temmer, Manuela; Seaton, Daniel; Long, David; Guo, Jingnan; Vrsnak,
   Bojan; Harra, Louise; Kliem, Bernhard
2019EGUGA..21.9243V    Altcode:
  The extreme X8.2 event of 2017 September 10 provides unique observations
  to study the genesis, magnetic morphology, impulsive dynamics and
  shock formation in a very fast coronal mass ejection (CME). Combining
  GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot (T ≈ 10-15
  MK) bright rim around a quickly expanding cavity, embedded inside a
  much larger CME shell (T ≈ 1-2 MK). The CME shell develops from a
  dense set of large AR loops (&gt;0.5Rs) and seamlessly evolves into
  the CME front observed in LASCO C2. The strong lateral overexpansion
  of the CME shell acts as a piston initiating the fast EUV shock
  wave. The hot cavity rim is demonstrated to be a manifestation of
  the dominantly poloidal flux and frozen-in plasma added to the rising
  flux rope by magnetic reconnection in the current sheet beneath. The
  same structure is later observed as the core of the white-light CME,
  challenging the traditional interpretation of the CME three-part
  morphology. The large amount of added magnetic flux suggested by these
  observations explains the extreme accelerations of the radial and
  lateral expansion of the CME shell and cavity, all reaching values
  up to 5-10 km s-2. The acceleration peaks occur simultaneously with
  the first RHESSI 100-300 keV hard X-ray burst of the associated flare,
  further underlining the importance of the reconnection process for the
  impulsive CME evolution. Finally, the much higher radial propagation
  speed of the flux rope in relation to the CME shell causes a distinct
  deformation of the white-light CME front and shock.

---------------------------------------------------------
Title: Statistics of Coronal Dimmings Associated with Coronal Mass
    Ejections. II. Relationship between Coronal Dimmings and Their
    Associated CMEs
Authors: Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova, T.
2019ApJ...874..123D    Altcode: 2018arXiv181001589D
  We present a statistical study of 62 coronal dimming events associated
  with Earth-directed coronal mass ejections (CMEs) during the
  quasi-quadrature period of STEREO and the Solar Dynamics Observatory
  (SDO). This unique setting allows us to study both phenomena in great
  detail and compare characteristic quantities statistically. Coronal
  dimmings are observed on-disk by the SDO/Atmospheric Imaging Assembly
  and the Helioseismic and Magnetic Imager, while the CME kinematics
  during the impulsive acceleration phase is studied close to the limb
  with STEREO/EUVI and COR, minimizing projection effects. The dimming
  area, its total unsigned magnetic flux, and its total brightness,
  reflecting properties of the total dimming region at its final extent,
  show the highest correlations with the CME mass (c ∼ 0.6-0.7). Their
  corresponding time derivatives, describing the dynamics of the dimming
  evolution, show the strongest correlations with the CME peak velocity
  (c ∼ 0.6). The highest correlation of c = 0.68 ± 0.08 is found
  with the mean intensity of dimmings, indicating that the lower the
  CME starts in the corona, the faster it propagates. No significant
  correlation between dimming parameters and the CME acceleration was
  found. However, for events where high-cadence STEREO observations were
  available, the mean unsigned magnetic field density in the dimming
  regions tends to be positively correlated with the CME peak acceleration
  (c = 0.42 ± 0.20). This suggests that stronger magnetic fields result
  in higher Lorentz forces providing stronger driving force for the CME
  acceleration. Specific coronal dimming parameters correlate with both
  CME and flare quantities providing further evidence for the flare-CME
  feedback relationship. For events in which the CME occurs together
  with a flare, coronal dimmings statistically reflect the properties
  of both phenomena.

---------------------------------------------------------
Title: Stellar CMEs from an observational point of view
Authors: Leitzinger, Martin; Odert, Petra; Vida, Krisztian; Koller,
   Florian; Veronig, Astrid; Korhonen, Heidi; Guenther, Eike; Hanslmeier,
   Arnold; Temmer, Manuela; Dissauer, Karin; Greimel, Robert; Kriskovics,
   Levente; Lammer, Helmut
2019EGUGA..21.6786L    Altcode:
  Stellar activity is mainly characterized by the high energy phenomena
  such as outbreaks of radiation (flares) and sporadic expulsions
  of particles into the astrosphere termed coronal mass ejections
  (CMEs). Both phenomena are known to cause space weather in our solar
  system. On stars, flares and their parameters are well determined,
  in contrast to CMEs; their parameters are still not determined
  statistically. Both phenomena may have severe effects on planetary
  atmospheres and, in addition, stellar CMEs may play an important
  role in stellar mass and angular momentum loss and therefore in
  stellar evolution. Flares are directly detectable from photometric
  observations, whereas the detection of CMEs requires different
  observational methods. CMEs have different signatures in different
  wavelength regimes. Most of the stellar CMEs were detected so far
  using the method of Doppler-shifted Balmer flux which is accessible via
  spectroscopic measurements. Several observational programs have been
  carried out and are planned for the future, including new observations
  and archival data. Also several attempts to detect stellar CMEs via
  radio emission have been carried out in the past decades. Finally,
  the X-ray regime may provide a valuable data pool to look for so-called
  dimmings, well-known from the Sun, which are closely related to CMEs and
  which are detectable in X-ray light curves. So far stellar CMEs have
  been detected rarely and only a handful of distinct events is known,
  mainly for dMe stars. We report on past, ongoing and future campaigns
  of stellar CMEs on F-, G-, K-, and M-type pre- and main-sequence stars.

---------------------------------------------------------
Title: The in situ Solar Wind and Galactic Cosmic Ray correlation
    at Mars and its comparison with Earth observations
Authors: Guo, Jingnan; Temmer, Manuela; Veronig, Astrid; Janvier,
   Miho; Hofmeister, Stefan; Wimmer-Schweingruber, Robert; Halekas, Jasper
2019EGUGA..21.9366G    Altcode:
  The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have
  been observing the in situ solar wind properties since its arrival to
  Mars at the end of 2014. Together with the Galactic Cosmic Ray (GCR)
  observation continuously monitored by the Radiation Assessment Detector
  (RAD) on the Martian ground, we are able to analyze the correlation of
  the solar wind evolution and the modulated GCR variations at Mars. The
  transient variations (mostly observed as short-term decreases) in
  these in situ observations are usually related to either the impact
  of Coronal Mass Ejections (CMEs) erupted from Solar active regions or
  the pass-by of High Speed Streams (HSS) in the solar wind arising from
  Coronal Holes (CHs) on the Sun. During the opposition phase in 2016
  when Earth and Mars were radially aligned on the same side of the Sun,
  we observe the stable evolution of a few CHs on the solar surface over
  several solar rotations and analyze the re-current in situ solar wind
  and GCR signatures at both Earth and Mars.

---------------------------------------------------------
Title: Unusual plasma and particle signatures at Mars and STEREO-A
    related to inhibited expansion caused by CME-CME interaction
Authors: Dumbovic, Mateja; Guo, Jingnan; Temmer, Manuela; Mays, Leila;
   Veronig, Astrid; Hofmeister, Stefan; Halekas, Jasper
2019EGUGA..21.6957D    Altcode:
  On July 25 2017 a multi-step Forbush decrease (FD) with the total
  amplitude of more than 15% was observed by MSL/RAD at Mars and this
  is one of the biggest FDs ever detected on Mars. We find that these
  particle signatures are related to very pronounced plasma and magnetic
  field signatures detected in situ by STEREO-A on July 24 2017, with a
  higher than average total magnetic field strength reaching more than
  60 nT. In the observed time period STEREO-A was longitudinally close
  to Mars and both were located at the back side of Sun as viewed from
  Earth. Using multi-spacecraft and multi-instrument (both in situ and
  remote-sensing) observations, as well as modelling, we find that the
  solar sources of these in situ signatures are 2 CMEs which erupted on
  July 23 2017 from the same source region on the back side of the Sun as
  viewed from Earth and interacted in the interplanetary space, inhibiting
  the expansion of one of the CMEs. We present a detailed investigation
  on this complex interaction event on its way from Sun to Mars. This
  project has received funding from the European Union's Horizon 2020
  research and innovation programme under the Marie Skłodowska-Curie
  grant agreement No 745782.

---------------------------------------------------------
Title: Multiple EUV wave reflection from a coronal hole
Authors: Podladchikova, Tatiana; Veronig, Astrid M.; Podladchikova,
   Olena; Dissauer, Karin; Vršnak, Bojan; Saqri, Jonas; Piantschitsch,
   Isabell; Temmer, Manuela
2019EGUGA..21.9793P    Altcode:
  EUV waves are large-scale propagating disturbances in the solar corona
  initiated by coronal mass ejections. We investigate the multiple EUV
  wave reflections at a coronal hole boundary, as observed by SDO/AIA on 1
  April 2017. The EUV wave originates from Active Region (AR) 12645 close
  to the disk center and propagates toward the south polar coronal hole
  with an average velocity of 430 km/s. The interaction of the EUV wave
  with the coronal hole, which represents a region of high Alfven speed,
  is observed as a splitting into two wave components: one continues
  propagation inside the coronal hole with an increased velocity of 850
  km/s (transmitted wave), while the other one moves back toward the AR,
  also with an increased velocity of 600 km/s (reflected wave). The
  reflected EUV wave is subsequently reflected again from the AR and
  propagates toward the coronal hole with an average velocity of 350
  km/s, where it is reflected for the second time at the coronal hole
  boundary and propagates again toward the AR with a velocity of 300
  km/s. These events are observed over an interval of 40 minutes. The
  high cadence SDO imagery allows us to study in detail the kinematics
  of the direct and multiple times reflected EUV wave. In addition, its
  multi-wavelength EUV imagery allows us to derive the plasma properties
  of the corona and the EUV wave pulse via Differential Emission Measure
  analysis. These results are used to compare the observed characteristics
  of the wave interaction with the coronal hole with simulations.

---------------------------------------------------------
Title: The Birth of a Coronal Mass Ejection
Authors: Liu, Rui; Gou, Tingyu; Kliem, Bernhard; Wang, Yuming;
   Veronig, Astrid
2019EGUGA..21.5194L    Altcode:
  The Sun's atmosphere is frequently disrupted by coronal mass ejections
  (CMEs), coupled with flares and energetic particles. In the standard
  picture, the coupling is explained by magnetic reconnection at
  a vertical current sheet connecting the flare loops and the CME,
  with the latter embedding a helical magnetic structure known as flux
  rope. As it jumps upward due to instabilities or loss of equilibrium,
  the flux rope stretches the overlying coronal loops so that oppositely
  directed field is brought together underneath, creating the current
  sheet. However, both the origin of flux ropes and their nascent paths
  toward eruption remain elusive. Here we present an observation of how
  a stellar-sized CME bubble evolves continuously from plasmoids, mini
  flux ropes that are barely resolved, within half an hour. The eruption
  initiates when plasmoids springing from a vertical current sheet
  merge into a leading plasmoid occupying the upper tip of the current
  sheet. Rising at increasing speed to stretch the overlying loops,
  this leading plasmoid then expands impulsively into the CME bubble,
  in tandem with hard X-ray bursts. This observation illuminates for
  the first time a complete CME evolutionary path that has the capacity
  to accommodate a wide variety of plasma phenomena by bridging the gap
  between micro-scale dynamics and macro-scale activities.

---------------------------------------------------------
Title: Radial and Tangential Kinematics and Angular Extent of EUV
    Coronal Bright Fronts
Authors: Kozarev, Kamen; Veronig, Astrid; Temmer, Manuela; Miteva,
   Rositsa; Dissauer, Karin; Koleva, Kostadinka; Dechev, Momchil;
   Duchlev, Peter
2019EGUGA..21.9290K    Altcode:
  Large-scale solar coronal compressive waves are often observed
  in extreme UV (EUV) and white light to precede nascent coronal
  mass ejections (CMEs), which previous work has shown develop most
  dynamically (expansion, acceleration) in the low and middle solar corona
  (below 5-8 solar radii). Multiple studies in the last ten years have
  suggested that these waves may be manifestations of driven coronal
  shock waves, and may accelerate ions to solar energetic particle
  (SEP) energies. A commonly invoked condition for the generation of
  EUV waves and their capability to produce energetic particles is the
  presence of rapid lateral expansion of the front and driver behind
  it. As a step to characterizing this capability, we study the radial
  and lateral kinematics of a number of EUV off-limb waves in the low
  corona, and their departure from spherical expansion. We characterize
  their time-dependent angular extent. We compare the results with
  the later-stage CME angular sizes and radial kinematics deduced from
  SOHO/LASCO observations of the events.

---------------------------------------------------------
Title: Analysis of SDO/EVE Flares in Relation to Solar Energetic
    Protons
Authors: Miteva, Rositsa; Koleva, Kostadinka; Dechev, Momchil; Veronig,
   Astrid; Dissauer, Karin; Kozarev, Kamen; Temmer, Manuela
2019EGUGA..2115190M    Altcode:
  Solar energetic proton (SEP) events from SOHO/ERNE instruments
  and SDO/EVE solar flares in solar cycle 24 are considered. The
  SEP-associated flare emission is analyzed in multiple wavelength
  ranges characterizing flare emission. Background subtraction of
  the pre-event particle flux and flare emission is performed for
  each event. Finally, a Pearson correlation analysis is completed
  between the peak values of the SEP events and the UV and EUV flare
  intensities. Comparison with the results from flare soft X-ray, hard
  X-ray and radio emission is presented. This work is supported by the
  Bilateral project Bulgaria-Austria with the National Science Fund of
  Bulgaria contract No. NTS/AUSTRIA 01/23 (28.02.2017) and Austria OeAD
  Project No. BG 11/2017.

---------------------------------------------------------
Title: ICMEs Propagating Towards Mars Observed in Heliospheric
    Imagers and their Associated Forbush Decreases at MSL/RAD
Authors: von Forstner, Johan; Guo, Jingnan; Wimmer-Schweingruber,
   Robert F.; Temmer, Manuela; Dumbović, Mateja; Veronig, Astrid; Möstl,
   Christian; Hassler, Donald M.; Zeitlin, Cary J.; Ehresmann, Bent
2019EGUGA..21.8305V    Altcode:
  The Radiation Assessment Detector (RAD) onboard the Mars Science
  Laboratory (MSL) mission's Curiosity rover has been measuring galactic
  cosmic rays (GCR) as well as solar energetic particles (SEP) on the
  surface of Mars for more than 6 years since its landing in August
  2012 and in interplanetary space during its 8-month cruise to Mars
  between 2011 and 2012. The observations include a large number of
  Forbush decreases (FD) caused by interplanetary coronal mass ejections
  (ICMEs) and their associated shocks passing MSL. Our previous work
  (Freiherr von Forstner et al. 2018, JGR: Space Physics) studied 15
  ICME events close to oppositions of Mars as seen from Earth or the
  STEREO A and B spacecraft, where in situ Forbush decrease observations
  at both locations could be used to derive the propagation time of the
  ICME from 1 AU to Mars. We found that on average, ICMEs in our sample
  continued to decelerate beyond 1 AU. We now investigate a different
  constellation where MSL/RAD Forbush decrease measurements are combined
  with remote tracking of ICMEs using the STEREO Heliospheric Imager (HI)
  telescopes. A large catalog of such remote observations was created
  by the HELCATS project (Möstl et al. 2017, Space Weather), not only
  including ICMEs propagating towards Earth, but also some that passed
  Mars. This allows to enlarge our sample for a statistical study of
  ICMEs at Mars. We associate STEREO-HI observations from the catalog with
  corresponding FDs at MSL/RAD and study the accuracy when predicting the
  arrival of an ICME at Mars using common models applied to HI data. Based
  on the catalogue of events built using this method, we also investigate
  the properties of the corresponding Forbush decreases at RAD, such
  as their magnitude, steepness and duration. We find both correlations
  between the parameters themselves as well as possible relations to the
  ICME properties (derived from HI data). These data are also compared
  to findings from previous studies using Earth-based observations.

---------------------------------------------------------
Title: The Birth of A Coronal Mass Ejection
Authors: Gou, Tingyu; Liu, Rui; Kliem, Bernhard; Wang, Yuming; Veronig,
   Astrid M.
2019SciA....5.7004G    Altcode: 2018arXiv181104707G
  The Sun's atmosphere is frequently disrupted by coronal mass ejections
  (CMEs), coupled with flares and energetic particles. The coupling
  is usually attributed to magnetic reconnection at a vertical current
  sheet connecting the flare and CME, with the latter embedding a helical
  magnetic structure known as flux rope. However, both the origin of flux
  ropes and their nascent paths toward eruption remain elusive. Here,
  we present an observation of how a stellar-sized CME bubble evolves
  continuously from plasmoids, mini flux ropes that are barely resolved,
  within half an hour. The eruption initiates when plasmoids springing
  from a vertical current sheet merge into a leading plasmoid, which
  rises at increasing speeds and expands impulsively into the CME
  bubble, producing hard x-ray bursts simultaneously. This observation
  illuminates a complete CME evolutionary path capable of accommodating a
  wide variety of plasma phenomena by bridging the gap between microscale
  and macroscale dynamics.

---------------------------------------------------------
Title: Photospheric plasma and magnetic field dynamics during the
    formation of solar AR 11190
Authors: Campos Rozo, J. I.; Utz, D.; Vargas Domínguez, S.; Veronig,
   A.; Van Doorsselaere, T.
2019A&A...622A.168C    Altcode: 2019arXiv190102437C
  Context. The Sun features on its surface typical flow patterns called
  the granulation, mesogranulation, and supergranulation. These patterns
  arise due to convective flows transporting energy from the interior
  of the Sun to its surface. The other well known elements structuring
  the solar photosphere are magnetic fields arranged from single,
  isolated, small-scale flux tubes to large and extended regions
  visible as sunspots and active regions. <BR /> Aims: In this paper
  we will shed light on the interaction between the convective flows
  in large-scale cells as well as the large-scale magnetic fields in
  active regions, and investigate in detail the statistical distribution
  of flow velocities during the evolution and formation of National
  Oceanic and Atmospheric Administration active region 11190. <BR />
  Methods: To do so, we employed local correlation tracking methods
  on data obtained by the Solar Dynamics Observatory in the continuum
  as well as on processed line-of-sight magnetograms. <BR /> Results:
  We find that the flow fields in an active region can be modelled by a
  two-component distribution. One component is very stable, follows a
  Rayleigh distribution, and can be assigned to the background flows,
  whilst the other component is variable in strength and velocity
  range and can be attributed to the flux emergence visible both in
  the continuum maps as well as magnetograms. Generally, the plasma
  flows, as seen by the distribution of the magnitude of the velocity,
  follow a Rayleigh distribution even through the time of formation
  of active regions. However, at certain moments of large-scale fast
  flux emergence, a second component featuring higher velocities is
  formed in the velocity magnitudes distribution. <BR /> Conclusions:
  The plasma flows are generally highly correlated to the motion of
  magnetic elements and vice versa except during the times of fast
  magnetic flux emergence as observed by rising magnetic elements. At
  these times, the magnetic fields are found to move faster than the
  corresponding plasma. <P />Movie attached to Fig. 1 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201832760/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: The Scientific Foundation of Space Weather
Authors: Baker, Daniel; Balogh, André; Gombosi, Tamas; Koskinen,
   Hannu E. J.; Veronig, Astrid; von Steiger, Rudolf
2019sfsw.book.....B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Achievements and Challenges in the Science of Space Weather
Authors: Koskinen, Hannu E. J.; Baker, Daniel N.; Balogh, André;
   Gombosi, Tamas; Veronig, Astrid; von Steiger, Rudolf
2019sfsw.book....1K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Origin, Early Evolution and Predictability of Solar
    Eruptions
Authors: Green, Lucie M.; Török, Tibor; Vršnak, Bojan; Manchester,
   Ward, IV; Veronig, Astrid
2019sfsw.book..113G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Study of reconnection rates and light curves in solar flares
    from low and mid chromosphere
Authors: Sindhuja, G.; Srivastava, Nandita; Veronig, A. M.; Pötzi, W.
2019MNRAS.482.3744S    Altcode: 2018MNRAS.tmp.2748S
  We study the flare evolution process using both H α and Ca-K data sets
  to understand the variations between the two. The reconnection rates
  and fluxes from low and mid chromosphere using the high cadence Ca-K
  and H α time lapse images and low-noise 720-s Helioseismic Magnetic
  Imager line-of-sight magnetograms, respectively, are studied. From the
  past studies it is understood that the surface magnetic flux swept by
  the flare ribbons relates to a global reconnection rate. Therefore in
  order to measure the abovesaid parameters, the observables like the
  newly brightened area and magnetic field of the area are calculated. We
  report the results of the analysis carried out for nine flare events
  observed during 2010-2015 from Kanzelhöhe Solar Observatory for Solar
  and Environmental Research. The parameters like reconnection flux and
  reconnection rate estimated using Ca-K and H α images are compared. We
  infer that the reconnection flux parameter estimated from Ca-K and H
  α follow a similar trend and shows a linear relation in the log-log
  plot. Further our study also reveals that Ca-K light curve during the
  course of the flare is dominated by impulsive and gradual components
  and follows the trend of the non-thermally dominated Reuven Ramaty
  High Energy Solar Spectroscopic Imager (RHESSI) (25-50 keV) light
  curves. Whereas, H α light curve is dominated by a gradual component
  and follows the trend and shape of the thermally dominated RHESSI HXR
  (6-12 keV) light curves.

---------------------------------------------------------
Title: Successive Flux Rope Eruptions from δ-sunspots Region of
    NOAA 12673 and Associated X-class Eruptive Flares on 2017 September 6
Authors: Mitra, Prabir K.; Joshi, Bhuwan; Prasad, Avijeet; Veronig,
   Astrid M.; Bhattacharyya, R.
2018ApJ...869...69M    Altcode: 2018arXiv181013146M
  In this article, we present a multiwavelength analysis of two X-class
  solar eruptive flares of classes X2.2 and X9.3 that occurred in the
  sigmoidal active region NOAA 12673 on 2017 September 6, by combining
  observations of Atmospheric Imaging Assembly and Helioseismic Magnetic
  Imager instruments on board the Solar Dynamics Observatory. On the
  day of the reported activity, the photospheric structure of the
  active region displayed a very complex network of δ-sunspots that
  gave rise to the formation of a coronal sigmoid observed in the hot
  extreme-ultraviolet channels. Both X-class flares initiated from the
  core of the sigmoid sequentially within an interval of ∼3 hr and
  progressed as a single sigmoid-to-arcade event. Differential emission
  measure analysis reveals strong heating of plasma at the core of the
  active region right from the preflare phase, which further intensified
  and spatially expanded during each event. The identification of a
  preexisting magnetic null by non-force-free-field modeling of the
  coronal magnetic fields at the location of early flare brightenings
  and remote faint ribbon-like structures during the preflare phase,
  which were magnetically connected with the core region, provide
  support for the breakout model of solar eruption. The magnetic
  extrapolations also reveal flux rope structures before both flares,
  which are subsequently supported by the observations of the eruption
  of hot extreme-ultraviolet channels. The second X-class flare diverged
  from the standard flare scenario in the evolution of two sets of flare
  ribbons, which are spatially well separated, providing firm evidence
  of magnetic reconnections at two coronal heights.

---------------------------------------------------------
Title: Genesis and Impulsive Evolution of the 2017 September 10
    Coronal Mass Ejection
Authors: Veronig, Astrid M.; Podladchikova, Tatiana; Dissauer, Karin;
   Temmer, Manuela; Seaton, Daniel B.; Long, David; Guo, Jingnan; Vršnak,
   Bojan; Harra, Louise; Kliem, Bernhard
2018ApJ...868..107V    Altcode: 2018arXiv181009320V
  The X8.2 event of 2017 September 10 provides unique observations
  to study the genesis, magnetic morphology, and impulsive dynamics
  of a very fast coronal mass ejection (CME). Combining GOES-16/SUVI
  and SDO/AIA EUV imagery, we identify a hot (T ≈ 10-15 MK) bright
  rim around a quickly expanding cavity, embedded inside a much larger
  CME shell (T ≈ 1-2 MK). The CME shell develops from a dense set of
  large AR loops (≳0.5R <SUB> s </SUB>) and seamlessly evolves into
  the CME front observed in LASCO C2. The strong lateral overexpansion
  of the CME shell acts as a piston initiating the fast EUV wave. The
  hot cavity rim is demonstrated to be a manifestation of the dominantly
  poloidal flux and frozen-in plasma added to the rising flux rope by
  magnetic reconnection in the current sheet beneath. The same structure
  is later observed as the core of the white-light CME, challenging the
  traditional interpretation of the CME three-part morphology. The large
  amount of added magnetic flux suggested by these observations explains
  the extreme accelerations of the radial and lateral expansion of the CME
  shell and cavity, all reaching values of 5-10 km s<SUP>-2</SUP>. The
  acceleration peaks occur simultaneously with the first RHESSI 100-300
  keV hard X-ray burst of the associated flare, further underlining
  the importance of the reconnection process for the impulsive CME
  evolution. Finally, the much higher radial propagation speed of the
  flux rope in relation to the CME shell causes a distinct deformation
  of the white-light CME front and shock.

---------------------------------------------------------
Title: Coronal holes detection using supervised classification
Authors: Delouille, Veronique; Hofmeister, Stefan; Reiss, Martin;
   Mampaey, Benjamin; Temmer, Manuela; Veronig, Astrid
2018csc..confE..93D    Altcode:
  We demonstrate the use of machine learning algorithms in combination
  with segmentation techniques in order to distinguish coronal holes
  and filaments in solar EUV images. We used the Spatial Possibilistic
  Clustering Algorithm (SPoCA) to prepare data sets of manually labeled
  coronal hole and filament channel regions present on the Sun during
  the time range 2010-2016. By mapping the extracted regions from EUV
  observations onto HMI line-of-sight magnetograms we also include
  their magnetic characteristics. We computed average latitude, area,
  shape measures from the segmented binary maps as well as first order,
  and second order texture statistics from the segmented regions in the
  EUV images and magnetograms. These attributes were used for data mining
  investigations to identify the most performant rule to differentiate
  between coronal holes and filament channels, taking into account the
  imbalance in our dataset which contains one filament channel for 15
  coronal holes. We tested classifiers such as Support Vector Machine,
  Linear Support Vector Machine, Decision Tree, k-Nearest Neighbors, as
  well as ensemble classifier based on Decision Trees. Best performance
  in terms of True Skill Statistics are obtained with cost-sensitive
  learning, Support Vector Machine classifiers, and when HMI attributes
  are included in the dataset.

---------------------------------------------------------
Title: The photospheric structure of coronal holes: magnetic elements
Authors: Hofmeister, Stefan; Utz, Dominik; Heinemann, Stephan; Veronig,
   Astrid; Temmer, Manuela
2018csc..confE.129H    Altcode:
  Coronal holes attracted recently more attention by the scientific
  community as they represent the source region for the fast solar wind
  which is ifself an important ingredient in understanding the space
  environment and space weather. Nevertheless, our knowledge about
  the detailed magnetic field structure below coronal holes is quite
  limited, maybe since such a research would necessarily involve the high
  atmospheric and photospheric community. In this contribution we would
  like to bridge this gap and investigate in detail the magnetic field
  distribution below coronal holes and its relationship to the large-scale
  coronal hole topology. To do so, we investigate the distribution and
  properties of photospheric magnetic elements below 106 low and medium
  latitude coronal holes using SDO/HMI line-of-sight magnetogram data from
  2010 to 2016, and relate them to the overall properties of the coronal
  holes. Since magnetic elements produce clearly visible photospheric
  structures, they can be well observed and give us valuable insights into
  the structure of coronal holes. We find that the distribution of the
  magnetic flux of magnetic elements follows an exponential function. The
  area and flux of magnetic elements are strongly related to each other
  by a power law with an exponent of 1.25. The larger magnetic elements
  are located at the edges of the magnetic network and seem to be the
  "core" structure of coronal holes. They have lifetimes &gt; 4 days,
  i.e., longer than the timescale of the supergranulation. Further, they
  contain up to 50 magnetic bright points as observed by Hinode/SOT in
  the G-Band, meaning that the large magnetic elements are large clusters
  of individual magnetic elements. The mean magnetic field density of
  the overall coronal holes and thus their unbalanced magnetic flux
  is determined by their percentage coverage with magnetic elements
  at cc=0.98. Since magnetic elements are the foot points of magnetic
  funnels and thus the small-scale source regions of high-speed solar
  wind streams, the dependence of the coverage with magnetic elements
  on the strength of coronal holes also explains the dependence of the
  plasma density of high-speed streams near the Sun to the strength of
  its source coronal hole. The rotation rates of the magnetic elements
  match the rotation rate of the coronal hole and is surprisingly similar
  to the differential rotation rate of active regions at low- and medium
  latitudes, suggesting they are rooted at similar deep layers. This
  also means that coronal holes do not show an abnormal rotation rate
  as suggested by various authors. Finally, by projecting the magnetic
  elements to AIA-171 and 193 filtergrams, we surprisingly find that the
  magnetic elements are not located in the darkest regions of coronal
  holes. Therefore, the vertical plasma outflow from magnetic funnels
  is probably not the primary reason why coronal holes appear as dark
  patches in EUV images. We conclude that magnetic elements are the
  basic building blocks of coronal holes which completely determine
  their magnetic properties.

---------------------------------------------------------
Title: Which factors of an active region determine whether a strong
    flare will be CME associated or not?
Authors: Baumgartner, Christian; Thalmann, Julia K.; Veronig, Astrid M.
2018csc..confE..10B    Altcode:
  We study how the magnetic field determines whether a strong flare
  launched from an active region (AR) will be eruptive or confined,
  i.e. associated with a coronal mass ejection (CME) or not. To this aim,
  we selected all large flares that were observed by the SDO HMI and
  AIA instruments during the period 2011 to 2015 within 50° from the
  disk center. In total, our data set comprises 44 flares of GOES class
  &gt;M5.0. Out of these, 12 events were confined (7 M and 5 X-flares) and
  32 were eruptive (18 M- and 14 X-flares). We used 3D potential magnetic
  field models to study their location within the host AR (using the flare
  distance from the flux-weighted AR center, d_{FC}) and the strength
  of the overlying coronal field (via decay index n). We also present a
  first systematic study of the orientation of the coronal magnetic field
  changing with height, using the orientation φ of the flare-relevant
  polarity inversion line as a measure. We analyzed all quantities with
  respect to the size of the underlying active-region dipole field,
  defined by the distance between the flux-weighted opposite-polarity
  centers, d_{PC}. We find that flares originating from the periphery
  of an AR dipole field (d_{FC} / d_{PC} &gt; 0.5) are predominantly
  eruptive. Flares originating from underneath the AR dipole field (d_{FC}
  / d_{PC} &lt; 0.5) tend to be eruptive when they are launched from
  a compact AR and confined when launched from an extended AR (d_{PC}
  &gt; 60 Mm). In confined events, the flare-relevant field adjusts its
  orientation quickly to that of the underlying dipole field with height
  (δ φ &gt; 40° between the surface and the apex of the active-region
  dipole field), in contrast to eruptive events where it changes more
  slowly. The critical height for torus instability discriminates best
  between confined (h_{crit} &gt; 40 Mm) and eruptive flares (h_{crit}
  &lt; 40 Mm). It discriminates better than δ φ, implying that the decay
  of the confining field plays a stronger role in the eruptive/confined
  character of a flare than its orientation at different heights.

---------------------------------------------------------
Title: Evolution of flux rope, CME and associated EUV wave in the
    10-Sep-2018 X8.2 event
Authors: Podladchikova, Tatiana; Veronig, Astrid M.; Dissauer, Karin;
   Temmer, Manuela; Seaton, Daniel B.; Long, David; Guo, Jingnan; Vršnak,
   Bojan; Harra, Louise; Kliem, Bernhard
2018csc..confE..38P    Altcode:
  We combine the high-cadence and large field-of-view EUV imagery of
  the Atmospheric Imaging Assembly (AIA) onboard SDO and the Solar
  Ultraviolet Imager (SUVI) onboard GOES-16 to study the origin and
  impulsive evolution of the fast CME that originated in the September
  10th 2017 X8.2 event as well as the initiation of the associated EUV
  wave. In the LASCO field-of-view, the CME reveals speeds &gt;3000
  km/s. In the low-to-mid corona, it shows a distinct bubble in the EUV
  imagery that reveals a significant lateral overexpansion. In addition,
  is also shows a distinct expanding cavity that is interpreted as
  manifestation of the flux rope driving the eruption. We present a method
  to automatically identify and segment the CME bubble in SUVI images and
  to derive its radial and lateral evolution up to about 2 solar radii,
  in terms of velocity and acceleration. These measurements are set into
  context with the evolution of the embedded flux rope/cavity observed by
  AIA. The observations show clear signatures of new poloidal flux added
  to the flux rope by magnetic reconnection in the current sheet beneath
  the eruptive structure, which is important for the high accelerations
  observed in this event. The radial propagation of the CME shell revealed
  a peak value of the acceleration of about 5.3 km/s2, whereas the lateral
  expansion reached a peak value of 10.1 km/s2, which is the largest value
  reported so far. The flux rope/cavity reveals a radial acceleration of
  6.7 km/s2 and lateral acceleration of 5.3 km/s2. We note that at this
  early evolution phase, the speed of the cavity/flux rope is higher
  than that of the CME bubble (front). The EUV wave associated with
  this eruption was observed by AIA, SUVI and STEREO-A EUVI, which had
  a separation angle with Earth of 128°, and the common field of view
  of the spacecraft was 52°. AIA and SUVI images above the solar limb
  reveal the initiation of the EUV wave by the accelerating flanks of
  the CME bubble, followed by detachment and propagation of the wave
  with a speed of 1100 km/s. The EUV wave shows a global propagation
  over the full hemisphere visible to Earth view as well as into the
  STEREO-A field-of-view. We study the propagation and kinematics of
  the direct as well as the various reflected and refracted EUV wave
  components on the solar sphere, finding speeds in the range from 370
  to 1010 km/s. Finally, we note that this EUV wave is also distinct as
  it reveals propagation and transmission through the polar coronal holes.

---------------------------------------------------------
Title: Studying the dynamics of coronal dimmings and their
    relationship to flares and coronal mass ejections
Authors: Dissauer, Karin; Veronig, Astrid M.; Temmer, Manuela;
   Podladchikova, Tatiana; Vanninathan, Kamalam
2018csc..confE..26D    Altcode:
  Coronal dimmings are observed as localized regions of reduced emission
  in the EUV and soft X-rays, interpreted as density depletions due to
  mass loss during the CME expansion. They contain crucial information on
  the evolution and early propagation phase of CMEs low in the corona. For
  a set of 62 dimming events, characteristic parameters, describing
  their dynamics, morphology, magnetic properties and the brightness
  evolution are derived, statistically analyzed and compared with basic
  flare and CME quantities. We use optimized multi-point observations,
  where the on-disk dimming evolution is studied in high-cadence
  SDO/AIA filtergrams and SDO/HMI line-of-sight magnetograms, while
  STEREO/EUVI, COR1 and COR2 data is used to measure the associated CME
  kinematics close to the limb with low projection effects. For 60% of
  the events we identified core dimmings, i.e. potential footpoints of
  the erupting CME structure. These regions contain 20% of the magnetic
  flux covering only 5% of the total dimming area. The majority of the
  total dimming area consists of secondary dimmings mapping overlying
  fields that are stretched during the eruption and closed down by
  magnetic reconnection, thus adding flux to the erupting structure
  via magnetic reconnection. This interpretation is supported by the
  high correlation between the magnetic fluxes of secondary dimmings
  and flare reconnection fluxes (c=0.63±0.08), the balance between
  positive and negative magnetic fluxes (c=0.83±0.04) within the total
  dimmings and the fact that for strong flares (&gt;M1.0) the flare
  reconnection and secondary dimming fluxes are roughly equal. The area
  of the total dimming, i.e. including both core and secondary dimmmings,
  its total brightness and the total unsigned magnetic flux show the
  highest correlations with the flare fluence (c&gt;0.7) and the CME
  mass (c&gt;0.6). Their corresponding time derivatives, describing
  the dimming dynamics, strongly correlate with the GOES flare class
  (c&gt;0.6). Events where high-cadence observations from STEREO are
  available show a moderate correlation between the area growth rate of
  the dimming and the maximum speed of the CME.

---------------------------------------------------------
Title: Hard X-ray Diagnostic of Proton Producing Solar Flares Compared
    to Other Emission Signatures
Authors: Miteva, Rositsa; Koleva, Kostadinka; Dechev, Momchil;
   Veronig, Astrid; Kozarev, Kamen; Temmer, Manuela; Dissauer, Karin;
   Duchlev, Peter
2018PASRB..18..117M    Altcode:
  We present results on the correlation analysis between the peak
  intensity of the in situ proton events from SOHO/ERNE instrument
  and the properties of their solar origin, solar flares and coronal
  mass ejections (CMEs). Starting at the RHESSI mission launch after
  2002, 70 flares well-observed in hard X-rays (HXRs) that are also
  accompanied with in situ proton events are selected. In addition
  to HXRs, flare emission at several other wavelengths, namely in the
  soft X-ray (SXR), ultraviolet (UV) and microwave (MW), is used. We
  calculated Pearson correlation coefficients between the proton peak
  intensities from one side, and, from another, the peak flare flux at
  various wavelengths or the speed of the accompanied CME. We obtain the
  highest correlations with the CME speed, with the SXR flare class and
  with MWs, lower ones with the SXR derivative, UV and 12-50 keV HXRs
  and the lowest correlation coefficients are obtained with the 50-300
  keV HXRs. Possible interpretations are discussed.

---------------------------------------------------------
Title: Three-phase Evolution of a Coronal Hole. II. The Magnetic Field
Authors: Heinemann, Stephan G.; Hofmeister, Stefan J.; Veronig,
   Astrid M.; Temmer, Manuela
2018ApJ...863...29H    Altcode: 2018arXiv180610052H
  We investigate the magnetic characteristics of a persistent coronal hole
  (CH) extracted from EUV imagery using Heliospheric and Magnetic Imager
  filtergrams over the period 2012 February-October. The magnetic field,
  its distribution, and the magnetic fine structure in the form of flux
  tubes (FTs) are analyzed in different evolutionary states of the CH. We
  find a strong linear correlation between the magnetic properties (e.g.,
  signed/unsigned magnetic field strength) and the area of the CH. As
  such, the evolutionary pattern in the magnetic field clearly follows
  a three-phase evolution (growing, maximum, and decaying) as found from
  EUV data (Part I). This evolutionary process is most likely driven by
  strong FTs with a mean magnetic field strength exceeding 50 G. During
  the maximum phase they entail up to 72% of the total signed magnetic
  flux of the CH, but only cover up to 3.9% of the total CH area, whereas
  during the growing and decaying phases, strong FTs entail 54%-60% of the
  signed magnetic flux and cover around 1%-2% of the CH’s total area. We
  conclude that small-scale structures of strong unipolar magnetic field
  are the fundamental building blocks of a CH and govern its evolution.

---------------------------------------------------------
Title: Filament Eruptions Associated with Flares, Coronal Mass
    Ejections and Solar Energetic Particle Events
Authors: Koleva, K.; Duchlev, P.; Dechev, M.; Miteva, R.; Kozarev,
   K.; Veronig, A.; Temmer, M.
2018simi.conf...19K    Altcode:
  We present analysis of three cases of filament eruptions (FEs)
  that occurred on 04 Aug 2011, 09 Nov 2011 and 05 Apr 2012 and their
  associations with flares as sources of solar energetic particles (SEPs)
  and coronal mass ejections. The associated FEs and SEP-related solar
  flares were selected by simultaneous observations in X-ray, EUV and
  radio wavelengths.

---------------------------------------------------------
Title: Statistics of Coronal Dimmings Associated with Coronal Mass
    Ejections. I. Characteristic Dimming Properties and Flare Association
Authors: Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova,
   T.; Vanninathan, K.
2018ApJ...863..169D    Altcode: 2018arXiv180705056D
  Coronal dimmings, localized regions of reduced emission in the
  extreme-ultraviolet and soft X-rays (SXRs), are interpreted as density
  depletions due to mass loss during the coronal mass ejection (CME)
  expansion. They contain crucial information on the early evolution
  of CMEs low in the corona. For 62 dimming events, characteristic
  parameters are derived, statistically analyzed, and compared with basic
  flare quantities. On average, coronal dimmings have a size of 2.15 ×
  10<SUP>10</SUP> km<SUP>2</SUP>, contain a total unsigned magnetic flux
  of 1.75 × 10<SUP>21</SUP> Mx, and show a total brightness decrease
  of -1.91 × 10<SUP>6</SUP> DN, which results in a relative decrease
  of ∼60% compared to the pre-eruption intensity level. Their main
  evacuation phase lasts for ∼50 minutes. The dimming area, the total
  dimming brightness, and the total unsigned magnetic flux show the
  highest correlation with the flare SXR fluence (c ≳ 0.7). Their
  corresponding time derivatives, describing the dimming dynamics,
  strongly correlate with the GOES flare class (c ≳ 0.6). For 60%
  of the events we identified core dimmings, i.e., signatures of an
  erupting flux rope. They contain 20% of the magnetic flux covering
  only 5% of the total dimming area. Secondary dimmings map overlying
  fields that are stretched during the eruption and closed down by
  magnetic reconnection, thus adding flux to the erupting flux rope
  via magnetic reconnection. This interpretation is supported by the
  strong correlation between the magnetic fluxes of secondary dimmings
  and flare reconnection fluxes (c = 0.63 ± 0.08), the balance between
  positive and negative magnetic fluxes (c = 0.83 ± 0.04) within the
  total dimmings, and the fact that for strong flares (&gt;M1.0) the
  reconnection and secondary dimming fluxes are roughly equal.

---------------------------------------------------------
Title: Dynamcis and magnetic properties in coronal holes using
    high-resolution multi-instrument solar observations
Authors: Krikova, K.; Utz, D.; Veronig, A.; Gömöry, P.; Hofmeister,
   S.; Temmer, M.
2018simi.conf...31K    Altcode:
  Using high-resolution solar observations from the Hinode Instruments
  SOT/SP, EIS and XRT as well as IRIS from a coronal hole on the 26th of
  September 2017, we are investigating the dynamics within the coronal
  hole visible on the specified date. Further satellite data support is
  given by full disc images from SDO with the AIA and HMI instruments. EIS
  and IRIS data provide us with crucial information about the plasma and
  energy flow from the Sun's chromosphere into the corona using the EUV
  and UV spectra and images. Investigating the magnetic configuration
  as well as the dynamics and changes within the coronal hole by using
  the SOT/SP data will give us additional crucial insights about the
  physical processes leading to the corresponding changes in the higher
  atmosphere. We compare the Hinode data with AIA and HMI data to get
  a firm comprehensive picture about the connection from high resolved
  photospheric fields and its dynamics within the higher layer. Within the
  timeframe of the analysed EIS dataset two microflare events associated
  with a solar jet were captured, originating inside the coronal hole
  under investigation. We believe that it is totally worthwhile to study
  these features in full detail as not so much attention was paid to high
  energy processes within coronal holes and their basic relationship to
  the harboring coronal hole and they show surprisingly high downflows
  in the Fe XII iron line (up to 140 km/s). In the current proceeding
  we will outline the state of the art of this investigation and give
  an overview of the further steps necessary. The mentioned data were
  obtained during a recent GREGOR campaign with the joint support of
  IRIS and Hinode (HOP 338).

---------------------------------------------------------
Title: Modeling the Evolution and Propagation of 10 September 2017
    CMEs and SEPs Arriving at Mars Constrained by Remote Sensing and In
    Situ Measurement
Authors: Guo, Jingnan; Dumbović, Mateja; Wimmer-Schweingruber,
   Robert F.; Temmer, Manuela; Lohf, Henning; Wang, Yuming; Veronig,
   Astrid; Hassler, Donald M.; Mays, Leila M.; Zeitlin, Cary; Ehresmann,
   Bent; Witasse, Olivier; Freiherr von Forstner, Johan L.; Heber, Bernd;
   Holmström, Mats; Posner, Arik
2018SpWea..16.1156G    Altcode: 2018arXiv180300461G
  On 10 September 2017, solar energetic particles originating from the
  active region 12673 produced a ground level enhancement at Earth. The
  ground level enhancement on the surface of Mars, 160 longitudinally
  east of Earth, observed by the Radiation Assessment Detector (RAD)
  was the largest since the landing of the Curiosity rover in August
  2012. Based on multipoint coronagraph images and the Graduated
  Cylindrical Shell model, we identify the initial 3-D kinematics of
  an extremely fast coronal mass ejection (CME) and its shock front,
  as well as another two CMEs launched hours earlier with moderate
  speeds. The three CMEs interacted as they propagated outward into the
  heliosphere and merged into a complex interplanetary CME (ICME). The
  arrival of the shock and ICME at Mars caused a very significant Forbush
  decrease seen by RAD only a few hours later than that at Earth, which
  was about 0.5 AU closer to the Sun. We investigate the propagation
  of the three CMEs and the merged ICME together with the shock, using
  the drag-based model and the WSA-ENLIL plus cone model constrained
  by the in situ observations. The synergistic study of the ICME and
  solar energetic particle arrivals at Earth and Mars suggests that to
  better predict potentially hazardous space weather impacts at Earth
  and other heliospheric locations for human exploration missions, it is
  essential to analyze (1) the eruption of the flare and CME at the Sun,
  (2) the CME kinematics, especially during their interactions, and
  (3) the spatially and temporally varying heliospheric conditions,
  such as the evolution and propagation of the stream interaction regions.

---------------------------------------------------------
Title: Long-term trends of magnetic bright points: The evolution of
    MBP size
Authors: Utz, D.; Van Doorsselaere, T.; Gagelmans, E.; O'Rourke, C.;
   Vuerinckx, A.; Muller, R.; Veronig, A.
2018simi.conf..179U    Altcode:
  Magnetic Bright Points (MBPs) are small-scale, very strong,
  solar magnetic field concentrations visible in the lower solar
  atmosphere. While there is a large and ever-increasing knowledge base
  and understanding of large-scale solar magnetic fields, i.e., sunspots
  and active regions, and their involvement in the solar cycle, much
  less is known about small-scale fields such as MBPs. Thus, we aim on
  contributing to our understanding of these tiny, but, important solar
  features by investigating the size distribution and its variation over
  time. <P />For this purpose, we obtained the synoptic G-band data set
  of the Hinode mission which is now since nearly 12 years in space and
  operational (launched in October 2006). After careful image calibration
  and selection we analysed the G-band data set with an automated MBP
  identification algorithm to calculate in a next step the equivalent
  diameter of the MBPs. <P />The so gained size distribution follows a
  Gamma distribution with pronounced changes during the solar activity
  cycle. The MBP sizes appear to be somewhat smaller during the solar
  minimum and somewhat more extended during the solar maxima as expressed
  by the scaleparameter of the Gamma distribution.

---------------------------------------------------------
Title: What can we learn from coronal dimmings about the early
    evolution of Earth-directed CMEs?
Authors: Dissauer, Karin; Podladchikova, Tatiana; Vanninathan, Kamalam;
   Veronig, Astrid; Temmer, Manuela
2018cosp...42E.846D    Altcode:
  Earth-directed coronal mass ejections (CMEs) are the main
  drivers for severe space weather events affecting the near-Earth
  environment. However, they allow the least accurate measurements of
  their properties due to strong projection effects and especially their
  early evolution is not well observed with traditional coronagraphs.The
  most distinct phenomena associated with CMEs are coronal dimmings,
  i.e. localized regions of reduced emission in the extreme-ultraviolet
  (EUV) and soft X-rays low in the corona. They are interpreted
  as density depletions due to mass loss or rapid expansion of the
  overlying corona during the CME lift off.We extract characteristic
  parameters describing the dynamics, morphology, magnetic properties
  and the brightness evolution of coronal dimming regions in order to
  obtain additional information on the initiation and early evolution of
  Earth-directed CMEs. To this aim, we developed an automatic dimming
  detection algorithm (based on logarithmic base-ratio images) that
  allows us also to distinguish between core and secondary dimming
  regions. Using this newly developed method, we extract the physical
  properties of 76 coronal dimming events in optimized multi-point
  observations and compare them with characteristic parameters describing
  their corresponding CMEs. The on-disk dimming evolution is studied
  using the high-cadence, multi-wavelengths data of SDO/AIA and the
  line-of-sight (LOS) magnetograms of SDO/HMI, while STEREO/EUVI, COR1 and
  COR2 data is used to measure the associated CME close to the limb with
  low projection effects.The impulsive phase of the dimming (i.e. main
  expansion phase of its area) starts co-temporal with the onset of the
  CME and the associated flare and the overall dimming region expands
  around locations that are identified as core dimming regions. On average
  this main evacuation phase lasts for about 50 minutes. For the majority
  of events, the total unsigned magnetic flux involved in the dimming
  regions is balanced and for selected events up to 30% of this flux
  results from the localized core dimming regions covering only ∼10% of
  the total dimming area. The size of the total dimming region, the total
  unsigned magnetic flux, as well as its intensity decrease are strongly
  correlated with the CME mass. Events where high-cadence observations
  from STEREO are available show in addition also a moderate correlations
  between the growth rate of the dimming and the maximum speed of the CME.

---------------------------------------------------------
Title: The September 2017 events and their imprints at Earth, Mars
    and STEREO-A
Authors: Guo, Jingnan; Wang, Yuming; Mays, M. Leila; Heber, Bernd;
   Holmstroem, Mats; Ehresmann, Bent; Olivier Witasse, .; Zeitlin,
   Cary; Taut, Andreas; Veronig, Astrid; Wimmer-Schweingruber, Robert;
   Dumbovic, Mateja; Lohf, Henning; Temmer, Manuela; Hassler, Donald M.;
   von Forstner, Johan Lauritz Freiherr
2018cosp...42E1321G    Altcode:
  During the declining phase of the current solar cycle, heliospheric
  activity has suddenly and drastically increased starting from a simple
  sunspot in Active Region (AR) 2673, which transformed into a complex
  region with three X-class flares accompanied by several Earth-directed
  Coronal Mass Ejections (CME) from 4th to 6th of September. Only a few
  days later, on 10th September, the same AR 2673 produced solar energetic
  particles (SEPs) which were registered as a ground level enhancement
  (GLE) at Earth and the biggest GLE on the surface of Mars as observed
  by the Radiation Assessment Detector (RAD) since the landing of the
  Curiosity rover in August 2012. Both Earth and Mars saw an impulsive and
  intense enhancement of the accelerated protons with energies larger
  than hundreds of MeV whereas STEREO-A, despite being at the back
  side of the event, detected gradually increasing fluxes of particles
  transported there across the heliospheric magnetic field. These high
  energy particles were mainly accelerated by the flares and shocks
  which were associated with three consecutive CMEs launched on 9th
  and 10th of September. Based on STEREO-A and SOHO coronograph images,
  we identified the initial three-dimensional kinematics of the three
  CMEs using the Graduated Cylindrical Shell (GCS) model. The first two
  CMEs had moderate launch speeds while the last one was extremely fast
  (larger than 2500 km/s at 20 solar radii). These three CMEs interacted
  as they propagated outwards into the heliosphere and the resulting
  complex interplanetary CME (ICME) together with its associated shock
  was highly likely related to the effective acceleration of particles
  at such high energies causing GLE at both Earth and Mars. The arrival
  of the ICME at Mars caused a very significant Forbush decrease seen
  by the Radiation Assessment Detector (RAD) on the surface of Mars
  and the arrival time is only a few hours later than that at Earth
  which is about 0.5 AU closer to the Sun than Mars. We investigated
  the interaction of three CMEs and propagation of the consequent ICME
  using the Drag Based Model (DBM) as well as the WSA-ENLIL plus cone
  model and the simulated results are compared with in-situ measurements
  at both Earth and Mars. The comparison shows that in order to better
  predict the ICME arrival and its potential space weather impact at
  Earth and other heliospheric locations, it is essential to 1) analyze
  the evolution of the ICME kinematics, especially during interactions
  of different CMEs and 2) better understand the spatially and temporally
  varying interplanetary conditions of the heliosphere.

---------------------------------------------------------
Title: Development of adaptive Kalman filter for solar wind forecast
Authors: Podladchikova, Tatiana; Veronig, Astrid; Temmer, Manuela;
   Hofmeister, Stefan
2018cosp...42E2698P    Altcode:
  Accurate solar wind modeling is important for predicting the arrival
  and geomagnetic response of high-speed solar wind streams as well as for
  modeling the transit of coronal mass ejections in interplanetary space
  and their impact at Earth. Data assimilation techniques combining the
  strength of models and observations provide a very useful tool for
  accurate solar wind forecasts. We develop a method to predict the
  solar wind speed at Earth 1-day ahead by using coronal hole areas
  derived from SDO AIA images in combination with in situ solar wind
  plasma and field data (speed, density, and magnetic field magnitude)
  from ACE and Wind spacecraft. To forecast the solar wind speed, we form
  a multidimensional linear regression model relating the solar wind speed
  one day ahead with the fractional coronal hole area observed three days
  before the current moment, as well as proton density, magnetic field
  magnitude, and solar wind speed at the current moment. One of the major
  concerns with such data assimilation scheme is that the regression
  coefficients do not remain constant and are time-varying. To avoid
  the fitting of regression coefficients to a particular situation,
  that can be changed in future, we develop an adaptive Kalman filter
  to create a dynamic linear regression for the 1-day ahead prediction
  of the solar wind speed. Testing the developed forecasting technique
  for the period 2010-2017, we obtain a correlation coefficient between
  the predicted and observed solar wind speed of 0.93, with an RMS error
  of prediction of 33 km/s. These results demonstrate that the proposed
  adaptive Kalman filter method significantly improves the quality of
  the solar wind forecasts and can be applied for reliable real-time
  warnings of the space weather conditions in the near-Earth environment.

---------------------------------------------------------
Title: CME acceleration and EUV wave kinematics for September 10th
    2017 event
Authors: Podladchikova, Tatiana; Dissauer, Karin; Veronig, Astrid;
   Temmer, Manuela; Seaton, Daniel
2018cosp...42E2697P    Altcode:
  On September 10th 2017 a large solar eruption, accompanied by an X8.2
  solar flare, from NOAA active region 12673 was observed on the Sun's
  western limb by the new Solar Ultraviolet Imager (SUVI) on the GOES-16
  spacecraft. We present a method to identify the CME bubble shape and
  to determine its radial and lateral acceleration. The large field of
  view of SUVI allows us to study the early impulsive CME acceleration
  up to 2 solar radii. The CME bubble reveals a fast evolution and
  strong overexpansion. The radial propagation of the CME revealed
  a peak value of the acceleration of about 4.8 km/s^{2}, whereas
  the lateral expansion reached a peak value of 8.9 km/s^{2}. The EUV
  wave associated with this eruption was observed by SUVI and STEREO-A,
  which had a separation angle with Earth of 128°, and the common field
  of view of both spacecraft was 52°. SUVI images above the solar limb
  reveal the initiation of the EUV wave by the accelerating flanks of the
  CME bubble, followed by detachment and propagation of the wave with
  a speed of 1100 km/s. Above the limb, the wave front can be observed
  as high as 0.7 solar radii. The EUV wave shows a global propagation
  over the full SUVI disk as well as into the STEREO-A field-of-view,
  and can be followed up to distances of about 1727 Mm from the source
  region. We study the propagation and kinematics of the direct as well
  as the various reflected and refracted EUV wave components on the solar
  sphere, finding speeds in the range from 370 to 1010 km/s. Finally,
  we note that this EUV wave is also distinct as it reveals propagation
  and transmission through a polar coronal hole.

---------------------------------------------------------
Title: Three-phase Evolution of a Coronal Hole. I. 360° Remote
    Sensing and In Situ Observations
Authors: Heinemann, Stephan G.; Temmer, Manuela; Hofmeister, Stefan
   J.; Veronig, Astrid M.; Vennerstrøm, Susanne
2018ApJ...861..151H    Altcode: 2018arXiv180609495H
  We investigate the evolution of a well-observed, long-lived,
  low-latitude coronal hole (CH) over 10 solar rotations in the
  year 2012. By combining extreme ultraviolet (EUV) imagery from
  the Solar TErrestrial RElations Observatories (STEREO-A/B) and the
  Solar Dynamics Observatory (SDO), we are able to track and study the
  entire evolution of the CH having a continuous 360° coverage of the
  Sun. The remote sensing data are investigated together with in situ
  solar wind plasma and magnetic field measurements from STEREO-A/B, the
  Advanced Composition Explorer (ACE), and WIND. From this, we obtain
  how different evolutionary states of the CH as observed in the solar
  atmosphere (changes in EUV intensity and area) affect the properties
  of the associated high-speed stream measured at 1 au. Most distinctly
  pronounced for the CH area, three development phases are derived:
  (a) growing, (b) maximum, and (c) decaying phase. During these phases
  the CH area (a) increases over a duration of around three months from
  about 1 · 10<SUP>10</SUP> km<SUP>2</SUP> to 6 · 10<SUP>10</SUP>
  km<SUP>2</SUP>, (b) keeps a rather constant area for about one month of
  &gt;9 · 10<SUP>10</SUP> km<SUP>2</SUP>, and (c) finally decreases in
  the following three months below 1 · 10<SUP>10</SUP> km<SUP>2</SUP>
  until the CH cannot be identified anymore. The three phases manifest
  themselves also in the EUV intensity and in in situ measured solar wind
  proton bulk velocity. Interestingly, the three phases are related to
  a different range in solar wind speed variations, and we find for the
  growing phase a range of 460-600 km s<SUP>-1</SUP>, for the maximum
  phase 600-720 km s<SUP>-1</SUP>, and for the decaying phase a more
  irregular behavior connected to slow and fast solar wind speeds of
  350-550 km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: Evidence of accelerated particles in the reconnection outflows
    above two flare cusps
Authors: Su, Yang; Li, Youping; Gan, Weiqun; Dennis, Brian; Veronig,
   Astrid; Krucker, Samuel
2018cosp...42E3283S    Altcode:
  Energetic particles carry a large fraction of released energy in
  solar flares. Some of them travel downward to the lower atmosphere
  and heat the local plasma. Others could escape from the corona into
  interplanetary space and become a component of SEP (Solar Energetic
  Particles) event. Although particle acceleration have been extensively
  studied in theory and simulations, observational details of the
  process in flares are far from complete. The discovery and studies
  of the above-loop-top source (Masuda et al. 1994, Krucker, Säm &amp;
  Battaglia 2014, Chen et al. 2015) have revealed the acceleration process
  around the termination shock. Here we report the discovery of above-cusp
  sources and evidence of accelerated particles therein. The analysis
  of imaging spectroscopy with RHESSI data and the DEM (Differential
  Emission Measure) diagnostic with our improved Sparse method (Cheung
  et al. 2015, Su et al. 2018, submitted) for two flares revealed that
  the acceleration starts in the current sheet and outflows, at places
  even higher than the Masuda source. This finding provides important
  clues for future observations and simulations of magnetic reconnection.

---------------------------------------------------------
Title: Magnetic reconnection fluxes in solar flares and their
    implications for solar and stellar superflares
Authors: Veronig, Astrid; Tschernitz, Johannes; Thalmann, Julia K.;
   Hinterreiter, Jürgen; Pötzi, Werner
2018cosp...42E3538V    Altcode:
  We study the energy release process of a set of 51 solar flares
  which span almost four orders of magnitude in flare energy, from GOES
  class B3 to X17. 19 events of our sample are eruptive, i.e. have a
  CME associated, and 32 are confined (no CME associated). We use Hα
  filtergrams from Kanzelhöhe Observatory together with SDO HMI and SOHO
  MDI magnetograms to derive magnetic reconnection fluxes and reconnection
  rates. We find that the flare reconnection flux is strongly correlated
  with the peak of the GOES 1-8 Å soft X-ray flux (r=0.9, in log-log
  space), both for confined and eruptive flares. In the largest events,
  up to ≈50% of the total magnetic flux of the host active region
  (AR) is involved in the flare magnetic reconnection. Based on these
  findings, we extrapolate the properties of the largest flares that may
  be launched from our present day's Sun. A complex solar AR that hosts
  a magnetic flux of 2\cdot 10^{23} {Mx}, which is supported by the
  largest active-region magnetic fluxes directly measured, is capable
  of producing an X80 flare (corresponding to a bolometric energy of
  about 7 \cdot 10^{32} ergs). Using a magnetic flux estimate of 6\cdot
  10^{23} {Mx} for the largest solar AR observed, we find that flares
  of GOES class ≈X500 could be produced (E_{bol} ≈ 3 \cdot 10^{33}
  ergs). Our results lie on the lower end of the energies of superflares
  on solar-type stars recently detected in Kepler data. Furthermore, they
  suggest that the present day's Sun is capable of producing flares and
  related space weather events more than an order of magnitude stronger
  than observed in the past.

---------------------------------------------------------
Title: Two-step Magnetic Reconnection in a Solar Flare
Authors: Gou, Tingyu; Liu, Rui; Veronig, Astrid; Dickson, Ewan;
   Hernandez-Perez, Aaron
2018cosp...42E1267G    Altcode:
  We report observations of an eruptive X2.8 flare on 2013 May 13,
  which shows two distinct episodes of energy release in the impulsive
  phase. The first episode is characterized by the eruption of a
  magnetic flux rope, similar to the energy-release process in most
  standard eruptive flares. The second episode, which is stronger
  than the first normal one and shows enhanced high-energy X-ray
  and even ≥-ray emissions, is closely associated with magnetic
  reconnection of a large-scale loop in the aftermath of the eruption. The
  reconnection inflow of the loop leg is observed in the Solar Dynamics
  Observatory (SDO)/Atmospheric Imaging Assembly (AIA) 304 A passband and
  accelerates toward the reconnection region to speeds as high as &lt;130
  km/s. Simultaneously, the corresponding outflow jets are observed in the
  AIA hot passbands with speeds of &lt;740 km/s and a mean temperature
  of &lt;14 MK. RHESSI observations show a strong burst of hard X-ray
  (HXR) and ≥-ray emissions with hard electron spectra of δ∼3,
  exhibiting a soft-hard-harder behavior. A distinct altitude decrease of
  the HXR loop-top source coincides with the inward swing of the loop leg
  observed in the AIA 304 A_ passband, which is suggested to be related
  to the coronal implosion. This fast inflow of magnetic flux contained in
  the loop leg greatly enhances the reconnection rate and results in very
  efficient particle acceleration in the second-step reconnection, which
  also helps to achieve a second higher temperature peak up to T∼30 MK.

---------------------------------------------------------
Title: Modeling the evolution and propagation of the 2017 September
    9th and 10th CMEs and SEPs arriving at Mars constrained by
    remote-sensing and in-situ measurement
Authors: Guo, Jingnan; Dumbović, Mateja; Wimmer-Schweingruber,
   Robert F.; Temmer, Manuela; Lohf, Henning; Wang, Yuming; Veronig,
   Astrid; Hassler, Donald M.; Mays, Leila M.; Zeitlin, Cary; Ehresmann,
   Bent; Witasse, Olivier; von Forstner, Johan L. Freiherr; Heber, Bernd;
   Holmström, Mats; Posner, Arik
2018shin.confE..84G    Altcode:
  On 2017-09-10, solar energetic particles (SEPs) originating from the
  active region 12673 were registered as a ground level enhancement (GLE)
  at Earth and the biggest GLE on the surface of Mars as observed by the
  Radiation Assessment Detector (RAD) since the landing of the Curiosity
  rover in August 2012. Based on multi-point coronagraph im-

---------------------------------------------------------
Title: Which factors of an active region determine whether a flare
    will be eruptive or confined?
Authors: Veronig, Astrid; Thalmann, Julia K.; Baumgartner, Christian
2018cosp...42E3539V    Altcode:
  We study how the magnetic field determines whether a strong flare
  launched from an active region (AR) will be eruptive or confined. To
  this aim, we analyzed 44 flares above GOES class M5.0 that occurred
  during 2011-2015. We used 3D potential magnetic field models to study
  their location within the host AR (using the flare distance from the
  flux-weighted AR center, d_{{FC}}) and the strength of the overlying
  coronal field (via decay index n). We also present a first systematic
  study of the orientation of the coronal magnetic field changing
  with height, using the orientation φ of the flare-relevant polarity
  inversion line as a measure. We analyzed all quantities with respect to
  the size of the underlying active-region dipole field, characterized
  by the distance between the flux-weighted opposite-polarity centers,
  d_{{PC}}. We find that flares originating from the periphery
  of an active-region dipole field (d_{{FC}}/d_{{PC}}&gt;0.5) are
  predominantly eruptive. Flares originating from underneath the AR
  dipole field (d_{{FC}}/d_{{PC}}&lt;0.5) tend to be eruptive when they
  are launched from a compact AR (d_{{PC}}≤60 Mm) and confined when
  launched from an extended AR. In confined events the flare-relevant
  field adjusts its orientation quickly to that of the underlying dipole
  field with height (Δφ≳40° between the surface and the apex of
  the active-region dipole field), in contrast to eruptive events where
  it changes more slowly with height. The critical height for torus
  instability, h_{{crit}}=h(n=1.5), discriminates best between confined
  (h_{{crit}}≳40 Mm) and eruptive flares (h_{{crit}}≲40 Mm). It
  discriminates better than Δφ, implying that the decay of the confining
  field plays a stronger role than its orientation at different heights.

---------------------------------------------------------
Title: Drag-based ensemble model (DBEM)
Authors: Dumbovic, Mateja; Möstl, Christian; Mays, M. Leila; Vrsnak,
   Bojan; Veronig, Astrid; Salogovic, Jara; Piantschitsch, Isabell;
   Amerstorfer, Tanja; Temmer, Manuela; Sudar, Davor
2018cosp...42E.918D    Altcode:
  The drag-based model (DBM) for heliospheric propagation of ICMEs is
  a widely used simple analytical model which can predict ICME arrival
  time and speed at a given heliospheric distance (Vr_nak et al.,
  2013, SolPhys). It is based on the assumption that the heliospheric
  propagation of ICMEs, is solely under the influence of MHD drag,
  where ICME propagation is determined based on CME properties as
  well as the properties of the ambient solar wind. The current
  version of the DBM is operational as part of ESA's SSA programme
  (http://swe.ssa.esa.int/web/guest/graz-dbm-federated). The DBM takes
  into account the ICME geometry to track the whole leading edge of an
  ICME, it can estimate whether or not an ICME will reach the observer
  and calculate the transit time and impact speed. To estimate the
  uncertainty for a single event, Drag-Based Ensemble Model (DBEM) was
  developed (Dumbovic et al., 2018, ApJ) which utilizes an ensemble of the
  observation-based CME input and synthetic values of the ambient solar
  wind speed and drag parameter. Using multiple runs with different input
  parameters, distributions of predicted arrival times and speeds are
  obtained allowing to forecast the confidence in the likelihood of the
  ICME arrival. The DBEM was further developed to an on-line application
  to provide the real-time CME forecast, which is currently in a test
  phase, and will soon be a part of ESA-SSA Heliospheric Weather Expert
  Service Group (http://swe.ssa.esa.int/heliospheric-weather). We test
  the model and the on-line application using observations and compare
  the performance with other CME propagation models.

---------------------------------------------------------
Title: Strong non-radial propagation of energetic electrons in
    solar corona
Authors: Klassen, A.; Dresing, N.; Gómez-Herrero, R.; Heber, B.;
   Veronig, A.
2018A&A...614A..61K    Altcode:
  Analyzing the sequence of solar energetic electron events measured at
  both STEREO-A (STA) and STEREO-B (STB) spacecraft during 17-21 July
  2014, when their orbital separation was 34°, we found evidence of
  a strong non-radial electron propagation in the solar corona below
  the solar wind source surface. The impulsive electron events were
  associated with recurrent flare and jet (hereafter flare/jet) activity
  at the border of an isolated coronal hole situated close to the solar
  equator. We have focused our study on the solar energetic particle
  (SEP) event on 17 July 2014, during which both spacecraft detected a
  similar impulsive and anisotropic energetic electron event suggesting
  optimal connection of both spacecraft to the parent particle source,
  despite the large angular separation between the parent flare and
  the nominal magnetic footpoints on the source surface of STA and STB
  of 68° and 90°, respectively. Combining the remote-sensing extreme
  ultraviolet (EUV) observations, in-situ plasma, magnetic field, and
  energetic particle data we investigated and discuss here the origin
  and the propagation trajectory of energetic electrons in the solar
  corona. We find that the energetic electrons in the energy range of
  55-195 keV together with the associated EUV jet were injected from the
  flare site toward the spacecraft's magnetic footpoints and propagate
  along a strongly non-radial and inclined magnetic field below the
  source surface. From stereoscopic (EUV) observations we estimated the
  inclination angle of the jet trajectory and the respective magnetic
  field of 63° ± 11° relative to the radial direction. We show how
  the flare accelerated electrons reach very distant longitudes in the
  heliosphere, when the spacecraft are nominally not connected to the
  particle source. This example illustrates how ballistic backmapping
  can occasionally fail to characterize the magnetic connectivity during
  SEP events. This finding also provides an additional mechanism (one
  among others), which may explain the origin of widespread SEP events.

---------------------------------------------------------
Title: An Event-Based Verification Scheme for the Real-Time Flare
    Detection System at Kanzelhöhe Observatory
Authors: Pötzi, W.; Veronig, A. M.; Temmer, M.
2018SoPh..293...94P    Altcode:
  In the framework of the Space Situational Awareness program of the
  European Space Agency (ESA/SSA), an automatic flare detection system
  was developed at Kanzelhöhe Observatory (KSO). The system has been in
  operation since mid-2013. The event detection algorithm was upgraded
  in September 2017. All data back to 2014 was reprocessed using the new
  algorithm. In order to evaluate both algorithms, we apply verification
  measures that are commonly used for forecast validation. In order to
  overcome the problem of rare events, which biases the verification
  measures, we introduce a new event-based method. We divide the
  timeline of the Hα observations into positive events (flaring period)
  and negative events (quiet period), independent of the length of
  each event. In total, 329 positive and negative events were detected
  between 2014 and 2016. The hit rate for the new algorithm reached 96%
  (just five events were missed) and a false-alarm ratio of 17%. This
  is a significant improvement of the algorithm, as the original system
  had a hit rate of 85% and a false-alarm ratio of 33%. The true skill
  score and the Heidke skill score both reach values of 0.8 for the new
  algorithm; originally, they were at 0.5. The mean flare positions are
  accurate within ±1 heliographic degree for both algorithms, and the
  peak times improve from a mean difference of 1.7 ±2.9 minutes to 1.3
  ±2.3 minutes. The flare start times that had been systematically late
  by about 3 minutes as determined by the original algorithm, now match
  the visual inspection within −0.47 ±4.10 minutes.

---------------------------------------------------------
Title: "Chapter 15 - Coronal Holes Detection Using Supervised
    Classification
Authors: Delouille, Véronique; Hofmeister, Stefan J.; Reiss, Martin
   A.; Mampaey, Benjamin; Temmer, Manuela; Veronig, Astrid
2018mlts.book..365D    Altcode:
  We demonstrate the use of machine learning algorithms in combination
  with segmentation techniques in order to distinguish coronal holes and
  filaments in solar extreme ultraviolet (EUV) images recorded by the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. We
  used the Spatial Possibilistic Clustering Algorithm to prepare datasets
  of manually labeled coronal hole and filament channel regions present
  on the Sun during the time range 2010-16. By mapping the extracted
  regions from EUV observations onto Helioseismic and Magnetic Imager
  (HMI) line-of-sight magnetograms, we also include their magnetic
  characteristics. We computed average latitude, area, and shape measures
  from the segmented binary maps, as well as first-order and second-order
  texture statistics from the segmented regions in the EUV images and
  magnetograms. These attributes were used for data-mining investigations
  to identify the best rule for differentiating between coronal holes
  and filame! <P />nt channels, taking into account the imbalance in our
  dataset, which contains 1 filament channel for 15 coronal holes. We
  tested classifiers such as support vector machine (SVM), linear SVM,
  decision tree, k-nearest neighbors, as well as an ensemble classifier
  based on decision trees. The best performance in terms of true skill
  statistics is obtained with cost-sensitive learning, SVM classifiers,
  and when HMI attributes are included in the dataset.

---------------------------------------------------------
Title: The Reported Durations of GOES Soft X-Ray Flares in Different
    Solar Cycles
Authors: Swalwell, Bill; Dalla, Silvia; Kahler, Stephen; White,
   Stephen M.; Ling, Alan; Viereck, Rodney; Veronig, Astrid
2018SpWea..16..660S    Altcode: 2018arXiv180510246S
  The Geostationary Orbital Environmental Satellites (GOES) Soft X-ray
  (SXR) sensors have provided data relating to, inter alia, the time,
  intensity, and duration of solar flares since the 1970s. The GOES
  SXR Flare List has become the standard reference catalogue for
  solar flares and is widely used in solar physics research and space
  weather. We report here that in the current version of the list there
  are significant differences between the mean duration of flares which
  occurred before May 1997 and the mean duration of flares thereafter. Our
  analysis shows that the reported flare timings for the pre-May 1997
  data were not based on the same criteria as is currently the case. This
  finding has serious implications for all those who used flare duration
  (or fluence, which depends on the chosen start and end times) as part
  of their analysis of pre-May 1997 solar events or statistical analyses
  of large samples of flares, for example, as part of the assessment of
  a solar energetic particle forecasting algorithm.

---------------------------------------------------------
Title: Modelling the solar photospheric plasma and magnetic field
    dynamics in the quiet Sun and comparison of these results with the
    flow fields in an evolving active region
Authors: Campos Rozo, Jose Ivan; Utz, Dominik; Veronig, Astrid;
   Vargas Domínguez, Santiago
2018simi.conf...37C    Altcode:
  In the present work a detailed study of the flow velocities of a quiet
  solar region is made and then compared with the flow fields during the
  emergence and prior to the evolution of AR-11190 on 11-April-2010. The
  velocity fields are computed from intensity as well as LOS magnetograms
  by using Local Correlation Tracking (LCT) techniques. The magnitudes
  of the obtained velocity vectors can be modelled by a single and
  simple Rayleigh distribution in the case of the quiet Sun and by a
  combination of two different statistical distributions in the case of
  the active region. Primarily this combination consists of a Rayleigh
  distribution that models the background velocity magnitudes as well
  as the general behavior of the combined velocity distribution, plus
  a weaker additional component that recreates the fast changes within
  the field of view. We propose two different distributions (implying
  different physical interpretations) for this second component of our
  combined fitting model. Generally, we can say that all the distributions
  show a strong correlation between the plasma motions and the movements
  of magnetic elements except during time instances when strong and fast
  magnetic flux elements start to appear within the region of interest.

---------------------------------------------------------
Title: Numerical Simulation of Coronal Waves Interacting with Coronal
    Holes. III. Dependence on Initial Amplitude of the Incoming Wave
Authors: Piantschitsch, Isabell; Vršnak, Bojan; Hanslmeier, Arnold;
   Lemmerer, Birgit; Veronig, Astrid; Hernandez-Perez, Aaron; Čalogović,
   Jaša
2018ApJ...860...24P    Altcode: 2018arXiv181112735P
  We performed 2.5D magnetohydrodynamic (MHD) simulations showing the
  propagation of fast-mode MHD waves of different initial amplitudes and
  their interaction with a coronal hole (CH), using our newly developed
  numerical code. We find that this interaction results in, first, the
  formation of reflected, traversing, and transmitted waves (collectively,
  secondary waves) and, second, in the appearance of stationary features
  at the CH boundary. Moreover, we observe a density depletion that
  is moving in the opposite direction of the incoming wave. We find a
  correlation between the initial amplitude of the incoming wave and
  the amplitudes of the secondary waves as well as the peak values of
  the stationary features. Additionally, we compare the phase speed of
  the secondary waves and the lifetime of the stationary features to
  observations. Both effects obtained in the simulation, the evolution
  of secondary waves, as well as the formation of stationary fronts at
  the CH boundary, strongly support the theory that coronal waves are
  fast-mode MHD waves.

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Title: The Focusing Optics X-ray Solar Imager (FOXSI)
Authors: Christe, Steven; Shih, Albert Y.; Krucker, Sam; Glesener,
   Lindsay; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel C.; Chen,
   Bin; Battaglia, Marina; Drake, James Frederick; Gary, Dale E.; Goetz,
   Keith; Gburek, Szymon; Grefenstette, Brian; Hannah, Iain G.; Holman,
   Gordon; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa,
   Shin-nosuke; Klimchuk, James A.; Kontar, Eduard; Kowalski, Adam F.;
   Massone, Anna Maria; Piana, Michele; Ramsey, Brian; Schwartz, Richard;
   Steslicki, Marek; Ryan, Daniel; Warmuth, Alexander; Veronig, Astrid;
   Vilmer, Nicole; White, Stephen M.; Woods, Thomas N.
2018tess.conf40444C    Altcode:
  We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer
  (SMEX) Heliophysics mission that is currently undergoing a Phase A
  concept study. FOXSI will provide a revolutionary new perspective on
  energy release and particle acceleration on the Sun. FOXSI's primary
  instrument, the Direct Spectroscopic Imager (DSI), is a direct imaging
  X-ray spectrometer with higher dynamic range and better than 10x the
  sensitivity of previous instruments. Flown on a 3-axis-stabilized
  spacecraft in low-Earth orbit, DSI uses high-angular-resolution
  grazing-incidence focusing optics combined with state-of-the-art
  pixelated solid-state detectors to provide direct imaging of solar hard
  X-rays for the first time. DSI is composed of a pair of X-ray telescopes
  with a 14-meter focal length enabled by a deployable boom. DSI has a
  field of view of 9 arcminutes and an angular resolution of better than 8
  arcsec FWHM; it will cover the energy range from 3 up to 50-70 keV with
  a spectral resolution of better than 1 keV. DSI will measure each photon
  individually and will be able to create useful images at a sub-second
  temporal resolution. FOXSI will also measure soft x-ray emission down
  to 0.8 keV with a 0.25 keV resolution with its secondary instrument,
  the Spectrometer for Temperature and Composition (STC) provided by
  the Polish Academy of Sciences. Making use of an attenuator-wheel and
  high-rate-capable detectors, FOXSI will be able to observe the largest
  flares without saturation while still maintaining the sensitivity to
  detect X-ray emission from weak flares, escaping electrons, and hot
  active regions. This presentation will cover the data products and
  software that can be expected from FOXSI and how they could be used
  by the community.

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Title: Long-lasting injection of solar energetic electrons into
    the heliosphere
Authors: Dresing, N.; Gómez-Herrero, R.; Heber, B.; Klassen, A.;
   Temmer, M.; Veronig, A.
2018A&A...613A..21D    Altcode: 2018arXiv180204722D
  Context. The main sources of solar energetic particle (SEP) events are
  solar flares and shocks driven by coronal mass ejections (CMEs). While
  it is generally accepted that energetic protons can be accelerated by
  shocks, whether or not these shocks can also efficiently accelerate
  solar energetic electrons is still debated. In this study we present
  observations of the extremely widespread SEP event of 26 Dec 2013
  To the knowledge of the authors, this is the widest longitudinal
  SEP distribution ever observed together with unusually long-lasting
  energetic electron anisotropies at all observer positions. Further
  striking features of the event are long-lasting SEP intensity
  increases, two distinct SEP components with the second component mainly
  consisting of high-energy particles, a complex associated coronal
  activity including a pronounced signature of a shock in radio type-II
  observations, and the interaction of two CMEs early in the event. <BR
  /> Aims: The observations require a prolonged injection scenario not
  only for protons but also for electrons. We therefore analyze the data
  comprehensively to characterize the possible role of the shock for
  the electron event. <BR /> Methods: Remote-sensing observations of
  the complex solar activity are combined with in situ measurements of
  the particle event. We also apply a graduated cylindrical shell (GCS)
  model to the coronagraph observations of the two associated CMEs to
  analyze their interaction. <BR /> Results: We find that the shock alone
  is likely not responsible for this extremely wide SEP event. Therefore
  we propose a scenario of trapped energetic particles inside the CME-CME
  interaction region which undergo further acceleration due to the shock
  propagating through this region, stochastic acceleration, or ongoing
  reconnection processes inside the interaction region. The origin of
  the second component of the SEP event is likely caused by a sudden
  opening of the particle trap.

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Title: Meridional Motions and Reynolds Stress Determined by Using
    Kanzelhöhe Drawings and White Light Solar Images from 1964 to 2016
Authors: Ruždjak, Domagoj; Sudar, Davor; Brajša, Roman; Skokić,
   Ivica; Poljančić Beljan, Ivana; Jurdana-Šepić, Rajka; Hanslmeier,
   Arnold; Veronig, Astrid; Pötzi, Werner
2018SoPh..293...59R    Altcode: 2018arXiv180401344R
  Sunspot position data obtained from Kanzelhöhe Observatory for
  Solar and Environmental Research (KSO) sunspot drawings and white
  light images in the period 1964 to 2016 were used to calculate the
  rotational and meridional velocities of the solar plasma. Velocities
  were calculated from daily shifts of sunspot groups and an iterative
  process of calculation of the differential rotation profiles was used
  to discard outliers. We found a differential rotation profile and
  meridional motions in agreement with previous studies using sunspots as
  tracers and conclude that the quality of the KSO data is appropriate
  for analysis of solar velocity patterns. By analyzing the correlation
  and covariance of meridional velocities and rotation rate residuals
  we found that the angular momentum is transported towards the solar
  equator. The magnitude and latitudinal dependence of the horizontal
  component of the Reynolds stress tensor calculated is sufficient to
  maintain the observed solar differential rotation profile. Therefore,
  our results confirm that the Reynolds stress is the dominant mechanism
  responsible for transport of angular momentum towards the solar equator.

---------------------------------------------------------
Title: Numerical Simulation of Coronal Waves Interacting with Coronal
    Holes. II. Dependence on Alfvén Speed Inside the Coronal Hole
Authors: Piantschitsch, Isabell; Vršnak, Bojan; Hanslmeier, Arnold;
   Lemmerer, Birgit; Veronig, Astrid; Hernandez-Perez, Aaron; Čalogović,
   Jaša
2018ApJ...857..130P    Altcode: 2018arXiv181112726P
  We used our newly developed magnetohydrodynamic (MHD) code to perform
  2.5D simulations of a fast-mode MHD wave interacting with coronal holes
  (CHs) of varying Alfvén speed that result from assuming different
  CH densities. We find that this interaction leads to effects like
  reflection, transmission, stationary fronts at the CH boundary,
  and the formation of a density depletion that moves in the opposite
  direction to the incoming wave. We compare these effects with regard
  to the different CH densities and present a comprehensive analysis of
  morphology and kinematics of the associated secondary waves. We find
  that the density value inside the CH influences the phase speed and
  the amplitude values of density and magnetic field for all different
  secondary waves. Moreover, we observe a correlation between the
  CH density and the peak values of the stationary fronts at the CH
  boundary. The findings of reflection and transmission on the one hand
  and the formation of stationary fronts caused by the interaction of
  MHD waves with CHs on the other hand strongly support the theory that
  large-scale disturbances in the corona are fast-mode MHD waves.

---------------------------------------------------------
Title: Characteristics of ribbon evolution and reconnection electric
    fields in Hα two-ribbon flares
Authors: Hinterreiter, Jürgen; Veronig, Astrid; Thalmann, Julia;
   Tschernitz, Johannes; Pötzi, Werner
2018EGUGA..20.9819H    Altcode:
  We perform a statistical study of magnetic reconnection related
  parameters in Hα two-ribbon flares. 50 flare events, including 19
  eruptive flares (i.e. associated to a coronal mass ejection) and 31
  confined flares (i.e. CME-less) are analyzed, which are distributed
  over a wide range of GOES classes (from B3 to X17). The maximum ribbon
  separation, ribbon-separation velocity, mean magnetic-field strength,
  and reconnection electric field (i.e., local reconnection rate) are
  derived from Hα filtergrams obtained at Kanzelhöhe Observatory in
  combination with co-registered SOHO MDI and SDO HMI magnetograms. We
  find that the ribbon separation of eruptive flares correlates with the
  GOES flux and is statistically larger than that of confined flares,
  whereas no dependence was found for the maximum ribbon-separation
  velocity and the GOES flux. The local reconnection rate strongly
  correlates with the GOES flux. In addition, eruptive flares with a
  stronger peak reconnection electric field tend to be accompanied by
  faster CMEs. The estimated reconnection-related proxies for confined
  and eruptive events, however, appear in the form of two distinct
  but largely overlapping populations. This suggests that there is no
  significant difference in the underlying reconnection process.

---------------------------------------------------------
Title: The 3-Phase evolution of a long-lived low-latitude coronal
    hole.
Authors: Heinemann, Stephan; Temmer, Manuela; Hofmeister, Stefan;
   Veronig, Astrid; Vennerstrom, Susanne
2018EGUGA..20.6670H    Altcode:
  High speed solar wind streams (HSS) emanating from coronal holes, and
  associated stream interaction regions, may cause geomagnetic storms
  and deflect coronal mass ejections propagation in interplanetary
  space. By understanding the evolution and the relations between
  coronal holes and solar wind parameters, we increase our knowledge
  for improving space weather forecasts. We investigate the evolution
  of a persistent coronal hole using EUV data from STEREO-A/B and SDO
  over the timerange February 2012 -October 2012. Combined STEREO-SDO
  data enable a continuous observation of the CH covering 360° degrees
  over several rotations. Together with magnetic field measurements from
  SDO filtergrams and in-situ solar wind observations, we analyze during
  different evolutionary states of the CH, the solar surface properties
  of the CH (intensity, area, shape, magnetic flux) and its effects at
  1AU (solar wind speed). As a result we find an evolutionary pattern
  in most parameters, clearly showing a three-phase evolution (growing,
  maximum and decaying phase).

---------------------------------------------------------
Title: Hard X-ray, EUV, and radio signatures in relation to solar
    energetic particles
Authors: Koleva, Kostadinka; Miteva, Rositsa; Dechev, Momchil; Kozarev,
   Kamen; Veronig, Astrid; Temmer, Manuela
2018EGUGA..20.7408K    Altcode:
  In this report we present analysis of well-observed electromagnetic
  signatures related to solar energetic particles (SEPs). We selected
  cases with simultaneous observations in hard X-ray, EUV and radio
  wavelengths of the SEP-related solar flares and analyzed the properties
  of the emission (light curves, spectrum and temporal evolution). The
  non-thermal potential of solar flares is tested in terms of correlation
  studies between the particle intensities (protons and electrons) and
  the flare flux at various wavelengths. The results are compared with
  the outcomes when using GOES soft X-ray flare class. The solar origin
  of SEP events in terms of solar flares is discussed.

---------------------------------------------------------
Title: The September 2017 events and their imprints at Earth and Mars
Authors: Guo, Jingnan; Mays, Leila; Dumbovic, Mateja; Temmer, Manuela;
   Veronig, Astrid; Wimmer-Schweingruber, Robert; von Forstner, Johan
   Freiherr; Hassler, Donald; Heber, Bernd; Zeitlin, Cary; Ehresmann,
   Bent; Witasse, Oliver
2018EGUGA..2015655G    Altcode:
  During the declining phase of the current quiet solar cycle,
  heliospheric activity has suddenly and drastically increased starting
  from a simple sunspot in Active Region (AR) 2673, which transformed
  into a complex region with three X-flares accompanied by several
  Earth-directed Coronal Mass Ejections (CME) from 4th to 6th of
  September. Four days later, on 10th September, the same AR produced
  solar energetic particles (SEPs) which were registered as a ground
  level enhancement (GLE) at Earth and the biggest GLE on the surface
  of Mars as observed by the Radiation Assessment Detector (RAD) since
  the landing of the Curiosity rover in August 2012. Both Earth and Mars
  saw an impulsive and intense enhancement of the accelerated protons
  with energies larger than hundreds of MeV whereas STEREO-A, despite
  being at the back-side of the event, detected gradually increasing
  fluxes of particles transported there across the heliospheric magnetic
  field. Such high energetic particles were mainly accelerated by shocks
  associated with the CMEs also launched on 10th of September. Three CMEs
  with similar longitudinal launch directions (between Earth and Mars
  with the central axis approximately 100 degrees from Earth and 40-50
  degrees from Mars) can be identified based on STEREO-A and SOHO LASCO
  chronograph images. The first two had moderate launch speed while the
  last one had an extremely fast launch speed ( 2500 km/s). The merging
  and interactions of the three CMEs into an interplanetary CME (ICME)
  were very complex through the inner heliosphere and caused a very
  significant Forbush decrease at Mars three days later, even before the
  enhanced particle flux recovered to quiet-time level. The arrival of
  the ICME at Mars is only a few hours later than that at Earth, despite
  Mars being 0.5 AU further away from the Sun than Earth. This timing
  difference between the ICME arrival at Earth and Mars is likely due to
  (1) the earlier ICMEs from 4th and 6th which have considerably changed
  the interplanetary conditions and (2) the interaction of the ICME with
  a High Speed Stream structure passing by Mars. The 3D launch geometry
  and direction of the CMEs has been reconstructed based on the Graduated
  Cylindrical Shell (GCS) model and the subsequent ICME propagation has
  been performed using the WSA-ENLIL plus cone model, as well as the
  Drag Based Model (DBM) and CDPP propagation tool. Such modeled ICME
  arrivals at Earth and Mars are compared with in-situ measurements and
  the comparison shows that it is essential to consider the interactions
  of different CMEs as well as the spatially and temporally varying
  interplanetary conditions in order to better predict the ICME arrival
  at Earth and other planets.

---------------------------------------------------------
Title: Combining remote-sensing image data with in-situ measurements
    supported by modeling for Earth-affecting CME events
Authors: Temmer, Manuela; Thalmann, Julia; Dissauer, Karin; Veronig,
   Astrid; Tschernitz, Johannes; Hinterreiter, Jürgen; Rodriguez, Luciano
2018EGUGA..20.3999T    Altcode:
  We analyze the well observed flare-CME event from October 1, 2011
  and cover the complete chain of action - from the Sun to Earth. We
  study in detail the solar surface and atmosphere (SDO and ground-based
  instruments) associated to the flare/CME and also track the off-limb CME
  signatures in interplanetary space (STEREO-SoHO). This is complemented
  by surface magnetic field information and 3D coronal magnetic field
  modeling. From in-situ measurements (Wind), we extract the corresponding
  ICME characteristics. Results show that the flare reconnection flux is
  most probably a lower limit for estimating the magnetic flux within the
  flux rope as 1) magnetic reconnection processes were already ongoing
  before the start of the impulsive flare phase and 2) the dimming flux
  increased by more than 25% after the end of the flare, indicating that
  magnetic flux was still added to the flux rope after eruption. When
  comparing this to the in-situ axial magnetic flux of the magnetic cloud,
  we find that it is reduced by at least 75%, referring to substantial
  erosion in interplanetary space. Careful inspection of on-disk features
  associated with CMEs are essential for interpreting such scenarios.

---------------------------------------------------------
Title: Plasma Diagnostics of Coronal Dimming Events
Authors: Vanninathan, Kamalam; Veronig, Astrid M.; Dissauer, Karin;
   Temmer, Manuela
2018ApJ...857...62V    Altcode: 2018arXiv180206152V
  Coronal mass ejections are often associated with coronal dimmings,
  i.e., transient dark regions that are most distinctly observed in
  Extreme Ultra-violet wavelengths. Using Atmospheric Imaging Assembly
  (AIA) data, we apply Differential Emission Measure diagnostics to
  study the plasma characteristics of six coronal dimming events. In
  the core dimming region, we find a steep and impulsive decrease of
  density with values up to 50%-70%. Five of the events also reveal
  an associated drop in temperature of 5%-25%. The secondary dimming
  regions also show a distinct decrease in density, but less strong,
  decreasing by 10%-45%. In both the core and the secondary dimming the
  density changes are much larger than the temperature changes, confirming
  that the dimming regions are mainly caused by plasma evacuation. In
  the core dimming, the plasma density reduces rapidly within the first
  20-30 minutes after the flare start and does not recover for at least
  10 hr later, whereas the secondary dimming tends to be more gradual and
  starts to replenish after 1-2 hr. The pre-event temperatures are higher
  in the core dimming (1.7-2.6 MK) than in the secondary dimming regions
  (1.6-2.0 MK). Both core and secondary dimmings are best observed in
  the AIA 211 and 193 Å filters. These findings suggest that the core
  dimming corresponds to the footpoints of the erupting flux rope rooted
  in the AR, while the secondary dimming represents plasma from overlying
  coronal structures that expand during the CME eruption.

---------------------------------------------------------
Title: Determination of Differential Emission Measure from Solar
    Extreme Ultraviolet Images
Authors: Su, Yang; Veronig, Astrid M.; Hannah, Iain G.; Cheung, Mark
   C. M.; Dennis, Brian R.; Holman, Gordon D.; Gan, Weiqun; Li, Youping
2018ApJ...856L..17S    Altcode:
  The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic
  Observatory (SDO) has been providing high-cadence, high-resolution,
  full-disk UV-visible/extreme ultraviolet (EUV) images since 2010, with
  the best time coverage among all the solar missions. A number of codes
  have been developed to extract plasma differential emission measures
  (DEMs) from AIA images. Although widely used, they cannot effectively
  constrain the DEM at flaring temperatures with AIA data alone. This
  often results in much higher X-ray fluxes than observed. One way
  to solve the problem is by adding more constraint from other data
  sets (such as soft X-ray images and fluxes). However, the spatial
  information of plasma DEMs are lost in many cases. In this Letter,
  we present a different approach to constrain the DEMs. We tested the
  sparse inversion code and show that the default settings reproduce
  X-ray fluxes that could be too high. Based on the tests with both
  simulated and observed AIA data, we provided recommended settings of
  basis functions and tolerances. The new DEM solutions derived from AIA
  images alone are much more consistent with (thermal) X-ray observations,
  and provide valuable information by mapping the thermal plasma from
  ∼0.3 to ∼30 MK. Such improvement is a key step in understanding
  the nature of individual X-ray sources, and particularly important
  for studies of flare initiation.

---------------------------------------------------------
Title: The Dependence of the Peak Velocity of High-Speed Solar Wind
    Streams as Measured in the Ecliptic by ACE and the STEREO satellites
    on the Area and Co-latitude of Their Solar Source Coronal Holes
Authors: Hofmeister, Stefan J.; Veronig, Astrid; Temmer, Manuela;
   Vennerstrom, Susanne; Heber, Bernd; Vršnak, Bojan
2018JGRA..123.1738H    Altcode: 2018arXiv180409579H
  We study the properties of 115 coronal holes in the time range
  from August 2010 to March 2017, the peak velocities of the
  corresponding high-speed streams as measured in the ecliptic at 1
  AU, and the corresponding changes of the Kp index as marker of their
  geoeffectiveness. We find that the peak velocities of high-speed streams
  depend strongly on both the areas and the co-latitudes of their solar
  source coronal holes with regard to the heliospheric latitude of
  the satellites. Therefore, the co-latitude of their source coronal
  hole is an important parameter for the prediction of the high-speed
  stream properties near the Earth. We derive the largest solar wind
  peak velocities normalized to the coronal hole areas for coronal holes
  located near the solar equator and that they linearly decrease with
  increasing latitudes of the coronal holes. For coronal holes located
  at latitudes ≳60°, they turn statistically to zero, indicating
  that the associated high-speed streams have a high chance to miss the
  Earth. Similarly, the Kp index per coronal hole area is highest for the
  coronal holes located near the solar equator and strongly decreases
  with increasing latitudes of the coronal holes. We interpret these
  results as an effect of the three-dimensional propagation of high-speed
  streams in the heliosphere; that is, high-speed streams arising from
  coronal holes near the solar equator propagate in direction toward and
  directly hit the Earth, whereas solar wind streams arising from coronal
  holes at higher solar latitudes only graze or even miss the Earth.

---------------------------------------------------------
Title: Statistical Properties of Ribbon Evolution and Reconnection
    Electric Fields in Eruptive and Confined Flares
Authors: Hinterreiter, J.; Veronig, A. M.; Thalmann, J. K.; Tschernitz,
   J.; Pötzi, W.
2018SoPh..293...38H    Altcode: 2018arXiv180103370H
  A statistical study of the chromospheric ribbon evolution in Hα
  two-ribbon flares was performed. The data set consists of 50 confined
  (62%) and eruptive (38%) flares that occurred from June 2000 to
  June 2015. The flares were selected homogeneously over the Hα and
  Geostationary Operational Environmental Satellite (GOES) classes, with
  an emphasis on including powerful confined flares and weak eruptive
  flares. Hα filtergrams from the Kanzelhöhe Observatory in combination
  with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic
  Imager (HMI) magnetograms were used to derive the ribbon separation,
  the ribbon-separation velocity, the magnetic-field strength, and
  the reconnection electric field. We find that eruptive flares reveal
  statistically larger ribbon separation and higher ribbon-separation
  velocities than confined flares. In addition, the ribbon separation
  of eruptive flares correlates with the GOES SXR flux, whereas no clear
  dependence was found for confined flares. The maximum ribbon-separation
  velocity is not correlated with the GOES flux, but eruptive flares
  reveal on average a higher ribbon-separation velocity (by ≈ 10 km
  s<SUP>−1</SUP>). The local reconnection electric field of confined
  (c c =0.50 ±0.02 ) and eruptive (c c =0.77 ±0.03 ) flares correlates
  with the GOES flux, indicating that more powerful flares involve
  stronger reconnection electric fields. In addition, eruptive flares
  with higher electric-field strengths tend to be accompanied by faster
  coronal mass ejections.

---------------------------------------------------------
Title: On the Detection of Coronal Dimmings and the Extraction of
    Their Characteristic Properties
Authors: Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova,
   T.; Vanninathan, K.
2018ApJ...855..137D    Altcode: 2018arXiv180203185D
  Coronal dimmings are distinct phenomena associated with coronal mass
  ejections (CMEs). The study of coronal dimmings and the extraction
  of their characteristic parameters help us to obtain additional
  information regarding CMEs, especially on the initiation and early
  evolution of Earth-directed CMEs. We present a new approach to detect
  coronal dimming regions based on a thresholding technique applied
  on logarithmic base-ratio images. Characteristic dimming parameters
  describing the dynamics, morphology, magnetic properties, and the
  brightness of coronal dimming regions are extracted by cumulatively
  summing newly dimmed pixels over time. It is also demonstrated how core
  dimming regions are identified as a subset of the overall identified
  dimming region. We successfully apply our method to two well-observed
  coronal dimming events. For both events, the core dimming regions are
  identified and the spatial evolution of the dimming area reveals the
  expansion of the dimming region around these footpoints. We also show
  that in the early impulsive phase of the dimming expansion the total
  unsigned magnetic flux involved in the dimming regions is balanced and
  that up to 30% of this flux results from the localized core dimming
  regions. Furthermore, the onset in the profile of the area growth rate
  is cotemporal with the start of the associated flares and in one case
  also with the fast rise of the CME, indicating a strong relationship
  of coronal dimmings with both flares and CMEs.

---------------------------------------------------------
Title: The Origin, Early Evolution and Predictability of Solar
    Eruptions
Authors: Green, Lucie M.; Török, Tibor; Vršnak, Bojan; Manchester,
   Ward; Veronig, Astrid
2018SSRv..214...46G    Altcode: 2018arXiv180104608G
  Coronal mass ejections (CMEs) were discovered in the early 1970s
  when space-borne coronagraphs revealed that eruptions of plasma
  are ejected from the Sun. Today, it is known that the Sun produces
  eruptive flares, filament eruptions, coronal mass ejections and failed
  eruptions; all thought to be due to a release of energy stored in
  the coronal magnetic field during its drastic reconfiguration. This
  review discusses the observations and physical mechanisms behind this
  eruptive activity, with a view to making an assessment of the current
  capability of forecasting these events for space weather risk and impact
  mitigation. Whilst a wealth of observations exist, and detailed models
  have been developed, there still exists a need to draw these approaches
  together. In particular more realistic models are encouraged in order
  to asses the full range of complexity of the solar atmosphere and the
  criteria for which an eruption is formed. From the observational side,
  a more detailed understanding of the role of photospheric flows and
  reconnection is needed in order to identify the evolutionary path that
  ultimately means a magnetic structure will erupt.

---------------------------------------------------------
Title: On the Factors Determining the Eruptive Character of Solar
    Flares
Authors: Baumgartner, Christian; Thalmann, Julia K.; Veronig, Astrid M.
2018ApJ...853..105B    Altcode: 2017arXiv171205106B
  We investigated how the magnetic field in solar active regions (ARs)
  controls flare activity, i.e., whether a confined or eruptive flare
  occurs. We analyzed 44 flares of GOES class M5.0 and larger that
  occurred during 2011-2015. We used 3D potential magnetic field models to
  study their location (using the flare distance from the flux-weighted
  AR center d <SUB>FC</SUB>) and the strength of the magnetic field in
  the corona above (via decay index n and flux ratio). We also present a
  first systematic study of the orientation of the coronal magnetic field,
  using the orientation φ of the flare-relevant polarity inversion line
  as a measure. We analyzed all quantities with respect to the size of
  the underlying dipole field, characterized by the distance between
  the opposite-polarity centers, d <SUB>PC</SUB>. Flares originating
  from underneath the AR dipole (d <SUB>FC</SUB>/d <SUB>PC</SUB> &lt;
  0.5) tend to be eruptive if launched from compact ARs (d <SUB>PC</SUB>
  ≤ 60 Mm) and confined if launched from extended ARs. Flares ejected
  from the periphery of ARs (d <SUB>FC</SUB>/d <SUB>PC</SUB> &gt; 0.5)
  are predominantly eruptive. In confined events, the flare-relevant field
  adjusts its orientation quickly to that of the underlying dipole with
  height (Δφ ≳ 40° until the apex of the dipole field), in contrast
  to eruptive events where it changes more slowly with height. The
  critical height for torus instability, h <SUB>crit</SUB> = h(n = 1.5),
  discriminates best between confined (h <SUB>crit</SUB> ≳ 40 Mm)
  and eruptive flares (h <SUB>crit</SUB> ≲ 40 Mm). It discriminates
  better than Δφ, implying that the decay of the confining field plays
  a stronger role than its orientation at different heights.

---------------------------------------------------------
Title: The Drag-based Ensemble Model (DBEM) for Coronal Mass Ejection
    Propagation
Authors: Dumbović, Mateja; Čalogović, Jaša; Vršnak, Bojan; Temmer,
   Manuela; Mays, M. Leila; Veronig, Astrid; Piantschitsch, Isabell
2018ApJ...854..180D    Altcode: 2018arXiv180107473D
  The drag-based model for heliospheric propagation of coronal mass
  ejections (CMEs) is a widely used analytical model that can predict
  CME arrival time and speed at a given heliospheric location. It is
  based on the assumption that the propagation of CMEs in interplanetary
  space is solely under the influence of magnetohydrodynamical drag,
  where CME propagation is determined based on CME initial properties
  as well as the properties of the ambient solar wind. We present
  an upgraded version, the drag-based ensemble model (DBEM), that
  covers ensemble modeling to produce a distribution of possible ICME
  arrival times and speeds. Multiple runs using uncertainty ranges for
  the input values can be performed in almost real-time, within a few
  minutes. This allows us to define the most likely ICME arrival times
  and speeds, quantify prediction uncertainties, and determine forecast
  confidence. The performance of the DBEM is evaluated and compared
  to that of ensemble WSA-ENLIL+Cone model (ENLIL) using the same
  sample of events. It is found that the mean error is ME = -9.7 hr,
  mean absolute error MAE = 14.3 hr, and root mean square error RMSE =
  16.7 hr, which is somewhat higher than, but comparable to ENLIL errors
  (ME = -6.1 hr, MAE = 12.8 hr and RMSE = 14.4 hr). Overall, DBEM and
  ENLIL show a similar performance. Furthermore, we find that in both
  models fast CMEs are predicted to arrive earlier than observed, most
  likely owing to the physical limitations of models, but possibly also
  related to an overestimation of the CME initial speed for fast CMEs.

---------------------------------------------------------
Title: Long time trends of MBP characteristics
Authors: Utz, D.; Muller, R.; Van Doorsselaere, T.; Veronig, A.;
   Gagelmans, E.; O'Rourke, C.; Vuerinckx, A.
2018CEAB...42...13U    Altcode:
  The change of Magnetic Bright Points (MBPs) characteristics over
  time periods of the solar sunspot cycle is studied. MBPs are
  small-scale solar magnetic field features reaching well beyond kG
  magnetic field strength and visible in intergranular lines within
  the solar photosphere. They are very variable and dynamic on time
  scales of just a few minutes. Due to their strong magnetic field,
  which resembles in shape the ideal concept of vertical flux tubes,
  as well as their dynamic behaviour, they are of special interest for
  wave triggering and propagation processes. On the other hand these
  small-scale structures appear brighter on the solar photosphere and thus
  their long time behaviour in respect of number, size, and intensity
  is of great importance for the total solar irradiance variability and
  thus also for climate change studies. In the current contribution we
  want to have a detailed look on exactly these parameters over the
  time period from end of 2006 until spring 2017 when unfortunately
  the Hinode SOT/BFI and NFI CCD cameras failed and thus no more data
  could be taken by the Hinode spacecrafts BFI instrument. The key
  findings can be summarized as that the number at the disc centre is
  variable and correlated to the sunspot cycle but shifted in regards
  to it. Moreover the size distribution of MBPs varies with the cycle
  indicating that fundamental magneto-convective properties might change
  on the 11th-year solar-cycle time-period.

---------------------------------------------------------
Title: Small-scale dynamcis in a coronal-hole related to microflaring
    events
Authors: Krikova, K.; Utz, D.; Veronig, A.; Hofmeister, S.; Temmer,
   M.; Gömöry, P.; Holzknecht, L.
2018CEAB...42....8K    Altcode:
  Using high-resolution solar imagery and spectroscopy from the Hinode
  EIS and SDO instruments, we investigate the dynamics within a coronal
  hole observed on the 26th September 2017. Further data is given by
  full disc images from SDO with the AIA and HMI instruments. EIS
  spectra provide us with crucial information about the plasma and
  energy flows from the Sun's chromosphere into the corona. Within the
  timeframe of the analysed EIS dataset two microflares associated with a
  jet-like event were captured, originating inside the coronal hole under
  investigation. These two microflare events were analysed in the study at
  hand in detail. Such recurring solar transient events could contribute
  to the mass and energy input into the solar corona and also to the solar
  wind. Our analysis shows that microflare temperatures can reach up to
  3 MK with a hot component close to the reconnection site. Moreover an
  enhanced density at the microflare region was found. The obtained EIS
  ion line ratios suggest a density of up to 2.9 \cdot 10^{10} cm^{-3}.

---------------------------------------------------------
Title: 3D reconstruction and interplanetary expansion of the 2010
    April 3^{rd} CME
Authors: Rodari, M.; Dumbović, M.; Temmer, M.; Holzknecht, L.;
   Veronig, A.
2018CEAB...42...11R    Altcode: 2019arXiv190405611R
  We analyse the 2010 April 3^{rd} CME using spacecraft coronagraphic
  images at different vantage points (SOHO, STEREO-A and STEREO-B). We
  perform a 3D reconstruction of both the flux rope and shock using the
  Graduated Cylindrical Shell (GCS) model to calculate CME kinematic
  and morphologic parameters (e.g. velocity, acceleration, radius). The
  obtained results are fitted with empirical models describing the
  expansion of the CME radius in the heliosphere and compared with in
  situ measurements from Wind spacecraft: the CME is found to expand
  linearly towards Earth. Finally, we relate the event with decreases
  in the Galactic Cosmic Ray (GCR) Flux, known as Forbush decreases
  (FD), detected by EPHIN instrument onboard SOHO spacecraft. We use the
  analytical diffusion-expansion model (ForbMod) to calculate the magnetic
  field power law index, obtaining a value of ∼1.6, thus estimating
  a starting magnetic field of ∼0.01 G and an axial magnetic flux of
  ∼5 \cdot 10^{20} Mx at 15.6 R_⊙.

---------------------------------------------------------
Title: Reconnection Fluxes in Eruptive and Confined Flares and
    Implications for Superflares on the Sun
Authors: Tschernitz, Johannes; Veronig, Astrid M.; Thalmann, Julia K.;
   Hinterreiter, Jürgen; Pötzi, Werner
2018ApJ...853...41T    Altcode: 2017arXiv171204701T
  We study the energy release process of a set of 51 flares (32 confined,
  19 eruptive) ranging from GOES class B3 to X17. We use Hα filtergrams
  from Kanzelhöhe Observatory together with Solar Dynamics Observatory
  HMI and Solar and Heliospheric Observatory MDI magnetograms to derive
  magnetic reconnection fluxes and rates. The flare reconnection flux
  is strongly correlated with the peak of the GOES 1-8 Å soft X-ray
  flux (c = 0.92, in log-log space) for both confined and eruptive
  flares. Confined flares of a certain GOES class exhibit smaller ribbon
  areas but larger magnetic flux densities in the flare ribbons (by a
  factor of 2). In the largest events, up to ≈50% of the magnetic flux
  of the active region (AR) causing the flare is involved in the flare
  magnetic reconnection. These findings allow us to extrapolate toward the
  largest solar flares possible. A complex solar AR hosting a magnetic
  flux of 2 × 10<SUP>23</SUP> Mx, which is in line with the largest
  AR fluxes directly measured, is capable of producing an X80 flare,
  which corresponds to a bolometric energy of about 7 × 10<SUP>32</SUP>
  erg. Using a magnetic flux estimate of 6 × 10<SUP>23</SUP> Mx for
  the largest solar AR observed, we find that flares of GOES class
  ≈X500 could be produced (E <SUB>bol</SUB> ≈ 3 × 10<SUP>33</SUP>
  erg). These estimates suggest that the present day’s Sun is capable
  of producing flares and related space weather events that may be more
  than an order of magnitude stronger than have been observed to date.

---------------------------------------------------------
Title: CME volume calculation from 3D GCS reconstruction
Authors: Holzknecht, L.; Temmer, M.; Dumbović, M.; Wellenzohn, S.;
   Krikova, K.; Heinemann, S. G.; Rodari, M.; Vršnak, B.; Veronig, A. M.
2018CEAB...42....3H    Altcode: 2019arXiv190411418H
  The mass evolution of a coronal mass ejection (CME) is an important
  parameter characterizing the drag force acting on a CME as it propagates
  through interplanetary space. Spacecraft measure in-situ plasma
  densities of CMEs during crossing events, but for investigating the
  mass evolution, we also need to know the CME geometry, more specific,
  its volume. Having derived the CME volume and mass from remote sensing
  data using 3D reconstructed CME geometry, we can calculate the CME
  density and compare it with in-situ proton density measurements near
  Earth. From that we may draw important conclusions on a possible
  mass increase as the CME interacts with the ambient solar wind in the
  heliosphere. In this paper we will describe in detail the method for
  deriving the CME volume using the graduated cylindrical shell (GCS)
  model tep[][see \ref{fig:GCSModel}]{thernisien06,thernisien09}. We show
  that, assuming self-similar expansion, one can derive the volume of the
  CME from two GCS parameters and that it furthermore can be expressed
  as a function of distance.

---------------------------------------------------------
Title: Formation Heights of HINODE SOT/BFI Filters
Authors: Kuehner, O.; Utz, D.; Muller, R.; Van Doorsselaere, T.;
   Magyar, N.; Veronig, A.; Campos Rozo, J. I.; Jelinek, P.
2018CEAB...42....9K    Altcode:
  Small-scale magnetic fields in the solar atmosphere are not static
  objects with height but expand. Thus, to understand the expansion,
  one can measure proxy features with various spectral filters forming in
  different heights. However, this is tricky as, it is well known that the
  formation height of spectral filters within the solar atmosphere depends
  on the atmospheric parameters itself. This means that the spectral line
  formation within small-scale magnetic fields is different compared to
  the quiet Sun. To investigate the dependency of these formation heights
  due to different atmospheric parameters we constructed an atmospheric
  model of the Sun with an embedded flux tube fulfilling magnetostatic
  conditions. We investigated the behavior of the formation heights of
  the HINODE SOT/BFI spectral bands (blue, green, red continuum, G-Band,
  Ca II H) in answer to varying input parameters of our atmospheric
  model. The currently seen effects are not tremendous. However, this
  is most likely due to the rather weak magnetic field strength achieved
  so far in our magnetic flux tube models.

---------------------------------------------------------
Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission
Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.;
   Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.;
   Drake, J. F.; Gary, D. E.; Goetz, K.; Gburek, S.; Grefenstette, B.;
   Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland,
   J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.;
   Massone, A. M.; Piana, M.; Ramsey, B.; Schwartz, R.; Steslicki, M.;
   Turin, P.; Ryan, D.; Warmuth, A.; Veronig, A.; Vilmer, N.; White,
   S. M.; Woods, T. N.
2017AGUFMSH44A..07C    Altcode:
  We present FOXSI (Focusing Optics X-ray Solar Imager), a Small Explorer
  (SMEX) Heliophysics mission that is currently undergoing a Phase A
  concept study. FOXSI will provide a revolutionary new perspective
  on energy release and particle acceleration on the Sun. FOXSI is
  a direct imaging X-ray spectrometer with higher dynamic range and
  better than 10x the sensitivity of previous instruments. Flown
  on a 3-axis-stabilized spacecraft in low-Earth orbit, FOXSI uses
  high-angular-resolution grazing-incidence focusing optics combined
  with state-of-the-art pixelated solid-state detectors to provide direct
  imaging of solar hard X-rays for the first time. FOXSI is composed of
  a pair of x-ray telescopes with a 14-meter focal length enabled by a
  deployable boom. Making use of a filter-wheel and high-rate-capable
  solid-state detectors, FOXSI will be able to observe the largest flares
  without saturation while still maintaining the sensitivity to detect
  x-ray emission from weak flares, escaping electrons, and hot active
  regions. This mission concept is made possible by past experience with
  similar instruments on two FOXSI sounding rocket flights, in 2012 and
  2014, and on the HEROES balloon flight in 2013. FOXSI's hard X-ray
  imager has a field of view of 9 arcminutes and an angular resolution
  of better than 8 arcsec; it will cover the energy range from 3 up to
  50-70 keV with a spectral resolution of better than 1 keV; and it will
  have sub-second temporal resolution.

---------------------------------------------------------
Title: 3D structure and kinematics characteristics of EUV wave front
Authors: Podladchikova, T.; Veronig, A.; Dissauer, K.
2017AGUFMSH51C2509P    Altcode:
  We present 3D reconstructions of EUV wave fronts using multi-point
  observations from the STEREO-A and STEREO-B spacecraft. EUV waves
  are large-scale disturbances in the solar corona that are initiated
  by coronal mass ejections, and are thought to be large-amplitude
  fast-mode MHD waves or shocks. The aim of our study is to investigate
  the dynamic evolution of the 3D structure and wave kinematics of EUV
  wave fronts. We study the events on December 7, 2007 and February 13,
  2009 using data from the STEREO/EUVI-A and EUVI-B instruments in the 195
  Å filter. The proposed approach is based on a complementary combination
  of epipolar geometry of stereo vision and perturbation profiles. We
  propose two different solutions to the matching problem of the wave
  crest on images from the two spacecraft. One solution is suitable for
  the early and maximum stage of event development when STEREO-A and
  STEREO-B see the different facets of the wave, and the wave crest is
  clearly outlined. The second one is applicable also at the later stage
  of event development when the wave front becomes diffuse and is faintly
  visible. This approach allows us to identify automatically the segments
  of the diffuse front on pairs of STEREO-A and STEREO-B images and to
  solve the problem of identification and matching of the objects. We
  find that the EUV wave observed on December 7, 2007 starts with a
  height of 30-50 Mm, sharply increases to a height of 100-120 Mm about
  10 min later, and decreases to 10-20 Mm in the decay phase. Including
  the 3D evolution of the EUV wave front allowed us to correct the wave
  kinematics for projection and changing height effects. The velocity
  of the wave crest (V=215-266 km/s) is larger than the trailing part
  of the wave pulse (V=103-163 km/s). For the February 9, 2009 event,
  the upward movement of the wave crest shows an increase from 20 to 100
  Mm over a period of 30 min. The velocity of wave crest reaches values
  of 208-211 km/s.

---------------------------------------------------------
Title: Plasma Diagnostics of Coronal Dimming Regions and Relation
    to Characteristic CME Parameters
Authors: Veronig, A.; Vanninathan, K.; Dissauer, K.; Temmer, M.
2017AGUFMSH52B..08V    Altcode:
  Coronal Mass Ejections (CMEs) are often associated with coronal
  dimmings, i.e. transient dark regions in the solar corona that are most
  prominently observed at Extreme Ultra-violet (EUV) wavelengths. Coronal
  dimmings are thought to be a result of the evacuation of mass related to
  the erupting CME structure. Using data from the six EUV channels of the
  Atmospheric Imaging Assembly (AIA) onboard SDO, we apply Differential
  Emission Measure (DEM) diagnostics, to study the plasma characteristics
  of on-disk coronal dimming regions. We analysed in detail seven
  coronal dimming events associated with CMEs distributed over a speed
  range from 300 to 1250 km/s. We derived the weighted emission measure,
  density and temperature as a function of time for both the core and
  the secondary dimming regions. In the core dimming regions, the plasma
  parameters reached a minimum within about 30 min after the CME onset,
  whereas the secondary dimming regions tend to show a more gradual
  evolution. For most of the events, the values of these parameters
  remained low within the core dimming region for the entire duration
  of this study ( 10 hrs after the flare) while the secondary dimming
  region showed a gradual increase after 1-2 hrs indicating refilling of
  these regions with plasma. The emission measure decrease in the core
  dimming region was found to lie in the range from 60-90%, the density
  decrease from 35-70% and the temperature decrease from 5-30%. In the
  secondary dimming region, the decreases of the plasma parameters derived
  are smaller. In addition, we performed a statistical analysis of 76
  dimming events during the time range 2010 - 2012, which were observed
  on-disk by SDO and close to the limb by at least one of the two STEREO
  spacecraft. Characteristic parameters of the early CME dynamics (initial
  velocity, peak acceleration, mass and initiation height) are derived
  and compared with decisive coronal dimming parameters like the magnetic
  flux involved, the area, the area growth rate and the intensity drop
  in the dimming region. The findings of our study are discussed with
  respect to the different coronal structures involved in the dimming
  regions and how they relate to decisive parameters of the CME.

---------------------------------------------------------
Title: Long-lasting solar energetic electron injection during the
    26 Dec 2013 widespread SEP event
Authors: Dresing, N.; Klassen, A.; Temmer, M.; Gomez-Herrero, R.;
   Heber, B.; Veronig, A.
2017AGUFMSH33C..03D    Altcode:
  The solar energetic particle (SEP) event on 26 Dec 2013 was detected
  all around the Sun by the two STEREO spacecraft and close-to-Earth
  observers. While the two STEREOs were separated by 59 degrees and
  situated at the front side of the associated large coronal event,
  it was a backside-event for Earth. Nevertheless, significant and
  long-lasting solar energetic electron anisotropies together with long
  rise times were observed at all three viewpoints, pointing to an
  extended electron injection. Although the CME-driven shock appears
  to account for the SEP event at a first glance a more detailed view
  reveals a more complex scenario: A CME-CME interaction takes place
  during the very early phase of the SEP event. Furthermore, four hours
  after the onset of the event, a second component is measured at all
  three viewpoints on top of the first SEP increase, mainly consisting
  of high energy particles. We find that the CME-driven shock alone
  can hardly account for the observed SEP event in total but a trapping
  scenario together with ongoing particle acceleration is more likely.

---------------------------------------------------------
Title: Observational and Model Analysis of a Two-ribbon Flare Possibly
    Induced by a Neighboring Blowout Jet
Authors: Joshi, Bhuwan; Thalmann, Julia K.; Mitra, Prabir K.; Chandra,
   Ramesh; Veronig, Astrid M.
2017ApJ...851...29J    Altcode: 2017arXiv171008099J
  In this paper, we present unique observations of a blowout coronal jet
  that possibly triggered a two-ribbon confined C1.2 flare in bipolar
  solar active region NOAA 12615 on 2016 December 5. The jet activity
  initiates at chromospheric/transition region heights with a small
  brightening that eventually increases in volume, with well-developed
  standard morphological jet features, viz., base and spire. The spire
  widens up with a collimated eruption of cool and hot plasma components,
  observed in the 304 and 94 Å channels of AIA, respectively. The speed
  of the plasma ejection, which forms the jet’s spire, was higher
  for the hot component (∼200 km s<SUP>-1</SUP>) than the cooler one
  (∼130 km s<SUP>-1</SUP>). The NLFF model of coronal fields at the
  pre- and post-jet phases successfully reveals openings of previously
  closed magnetic field lines with a rather inclined/low-lying jet
  structure. The peak phase of the jet emission is followed by the
  development of a two-ribbon flare that shows coronal loop emission in
  HXRs up to ∼25 keV energy. The coronal magnetic fields rooted at the
  location of EUV flare ribbons, derived from the NLFF model, demonstrate
  the pre-flare phase to exhibit an “X-type” configuration, while
  the magnetic fields at the post-flare phase are more or less oriented
  parallel. Comparisons of multi-wavelength measurements with the magnetic
  field extrapolations suggest that the jet activity likely triggered
  the two-ribbon flare by perturbing the field in the interior of the
  active region.

---------------------------------------------------------
Title: Anticipated Results from the FOXSI SMEX Mission
Authors: Shih, A. Y.; Christe, S.; Krucker, S.; Glesener, L.;
   Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen, B.;
   Drake, J. F.; Gary, D. E.; Gburek, S.; Goetz, K.; Grefenstette, B.;
   Gubarev, M.; Hannah, I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.;
   Ireland, J.; Ishikawa, S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski,
   A. F.; Massone, A. M.; Piana, M.; Ramsey, B.; Ryan, D.; Schwartz,
   R.; Steslicki, M.; Turin, P.; Veronig, A.; Vilmer, N.; Warmuth, A.;
   White, S. M.; Woods, T. N.
2017AGUFMSH43C..03S    Altcode:
  While there have been significant advances in our understanding
  of impulsive energy release at the Sun since the advent of RHESSI
  observations, there is a clear need for new X-ray observations that
  can capture the full range of emission in flares (e.g., faint coronal
  sources near bright chromospheric sources), follow the intricate
  evolution of energy release and changes in morphology, and search
  for the signatures of impulsive energy release in even the quiescent
  Sun. The FOXSI Small Explorer (SMEX) mission, currently undergoing a
  Phase A concept study, combines state-of-the-art grazing-incidence
  focusing optics with pixelated solid-state detectors to provide
  direct imaging of hard X-rays for the first time on a solar
  observatory. FOXSI's X-ray observations will provide quantitative
  information on (1) the non-thermal populations of accelerated electrons
  and (2) the thermal plasma distributions at the high temperatures
  inaccessible through other wavelengths. FOXSI's major science questions
  include: Where are electrons accelerated and on what time scales? Where
  do escaping flare-accelerated electrons originate? What is the energy
  input of accelerated electrons into the chromosphere and corona? How
  much do flare-like processes heat the corona above active regions? Here
  we present examples with simulated observations to show how FOXSI's
  capabilities will address and resolve these and other questions.

---------------------------------------------------------
Title: Sunspot Number Second Differences as a Precursor of the
    Following 11-year Sunspot Cycle
Authors: Podladchikova, Tatiana; Van der Linden, Ronald; Veronig,
   Astrid M.
2017ApJ...850...81P    Altcode: 2017arXiv171205782P
  Forecasting the strength of the sunspot cycle is highly important for
  many space weather applications. Our previous studies have shown the
  importance of sunspot number variability in the declining phase of the
  current 11-year sunspot cycle to predict the strength of the next cycle
  when the minimum of the current cycle has been observed. In this study
  we continue this approach and show that we can remove the limitation
  of having to know the minimum epoch of the current cycle, and that we
  can already provide a forecast of the following cycle strength in the
  early stage of the declining phase of the current cycle. We introduce
  a method to reliably calculate sunspot number second differences (SNSD)
  in order to quantify the short-term variations of sunspot activity. We
  demonstrate a steady relationship between the SNSD dynamics in the early
  stage of the declining phase of a given cycle and the strength of the
  following sunspot cycle. This finding may bear physical implications
  on the underlying dynamo at work. From this relation, a relevant
  indicator is constructed that distinguishes whether the next cycle
  will be stronger or weaker compared to the current one. We demonstrate
  that within 24-31 months after reaching the maximum of the cycle,
  it can be decided with high probability (0.96) whether the next cycle
  will be weaker or stronger. We predict that sunspot cycle 25 will be
  weaker than the current cycle 24.

---------------------------------------------------------
Title: Achievements and Challenges in the Science of Space Weather
Authors: Koskinen, Hannu E. J.; Baker, Daniel N.; Balogh, André;
   Gombosi, Tamas; Veronig, Astrid; von Steiger, Rudolf
2017SSRv..212.1137K    Altcode: 2017SSRv..tmp...80K
  In June 2016 a group of 40 space weather scientists attended the
  workshop on Scientific Foundations of Space Weather at the International
  Space Science Institute in Bern. In this lead article to the volume
  based on the talks and discussions during the workshop we review some of
  main past achievements in the field and outline some of the challenges
  that the science of space weather is facing today and in the future.

---------------------------------------------------------
Title: Presentation of the project "An investigation of the early
    stages of solar eruptions - from remote observations to energetic
    particles"
Authors: Kozarev, Kamen; Veronig, Astrid; Duchlev, Peter; Koleva,
   Kostadinka; Dechev, Momchil; Miteva, Rositsa; Temmer, Manuela;
   Dissauer, Karin
2017ses..conf...63K    Altcode:
  Coronal mass ejections (CMEs), one of the most energetic manifestations
  of solar activity, are complex events, which combine multiple related
  phenomena occurring on the solar surface, in the extended solar
  atmosphere (corona), as well as in interplanetary space. We present
  here an outline of a new collaborative project between scientists
  from the Bulgarian Academy of Sciences (BAS), Bulgaria and the
  University of Graz, Austria. The goal of the this research project
  is to answer the following questions: 1) What are the properties of
  erupting filaments, CMEs, and CME-driven shock waves near the Sun, and
  of associated solar energetic particle (SEP) fluxes in interplanetary
  space? 2) How are these properties related to the coronal acceleration
  of SEPs? To achieve the scientific goals of this project, we will use
  remote solar observations with high spatial and temporal resolution to
  characterize the early stages of coronal eruption events in a systematic
  way - studying the pre-eruptive behavior of filaments and flares during
  energy build-up, the kinematics and morphology of CMEs and compressive
  shock waves, and the signatures of high energy non-thermal particles
  in both remote and in situ observations.

---------------------------------------------------------
Title: A Numerical Simulation of Coronal Waves Interacting with
    Coronal Holes. I. Basic Features
Authors: Piantschitsch, Isabell; Vršnak, Bojan; Hanslmeier, Arnold;
   Lemmerer, Birgit; Veronig, Astrid; Hernandez-Perez, Aaron; Čalogović,
   Jaša; Žic, Tomislav
2017ApJ...850...88P    Altcode: 2018arXiv181112073P
  We have developed a new numerical code that is able to perform 2.5D
  simulations of a magnetohydrodynamic (MHD) wave propagation in the
  corona, and its interaction with a low-density region, such as a
  coronal hole (CH). We show that the impact of the wave on the CH
  leads to different effects, such as reflection and transmission of the
  incoming wave, stationary features at the CH boundary, or formation
  of a density depletion. We present a comprehensive analysis of the
  morphology and kinematics of primary and secondary waves, I.e.,
  we describe in detail the temporal evolution of density, magnetic
  field, plasma flow velocity, phase speed, and position of the wave
  amplitude. Effects like reflection, refraction, and transmission of
  the wave strongly support the theory that large-scale disturbances
  in the corona are fast MHD waves and distinguish that theory from the
  competing pseudo-wave theory. The formation of stationary bright fronts
  was one of the main reasons for the development of pseudo-waves. Here,
  we show that stationary bright fronts can be produced by interactions
  of an MHD wave with a CH. We find secondary waves that are traversing
  through the CH and we show that one part of these traversing waves
  leaves the CH again, while another part is being reflected at the CH
  boundary inside the CH. We observe a density depletion that is moving
  in the opposite direction of the primary wave propagation. We show
  that the primary wave pushes the CH boundary to the right, caused by
  the wave front exerting dynamic pressure on the CH.

---------------------------------------------------------
Title: Generation Mechanisms of Quasi-parallel and Quasi-circular
    Flare Ribbons in a Confined Flare
Authors: Hernandez-Perez, Aaron; Thalmann, Julia K.; Veronig, Astrid
   M.; Su, Yang; Gömöry, Peter; Dickson, Ewan C.
2017ApJ...847..124H    Altcode: 2017arXiv170808612H
  We analyze a confined multiple-ribbon M2.1 flare (SOL2015-01-29T11:42)
  that originated from a fan-spine coronal magnetic field configuration,
  within active region NOAA 12268. The observed ribbons form in
  two steps. First, two primary ribbons form at the main flare site,
  followed by the formation of secondary ribbons at remote locations. We
  observe a number of plasma flows at extreme-ultraviolet temperatures
  during the early phase of the flare (as early as 15 minutes before
  the onset) propagating toward the formation site of the secondary
  ribbons. The secondary ribbon formation is co-temporal with the
  arrival of the pre-flare generated plasma flows. The primary ribbons
  are co-spatial with Ramaty High Energy Spectroscopic Imager (RHESSI)
  hard X-ray sources, whereas no enhanced X-ray emission is detected at
  the secondary ribbon sites. The (E)UV emission, associated with the
  secondary ribbons, peaks ∼1 minute after the last RHESSI hard X-ray
  enhancement. A nonlinear force-free model of the coronal magnetic field
  reveals that the secondary flare ribbons are not directly connected to
  the primary ribbons, but to regions nearby. Detailed analysis suggests
  that the secondary brightenings are produced due to dissipation of
  kinetic energy of the plasma flows (heating due to compression), and
  not due to non-thermal particles accelerated by magnetic reconnection,
  as is the case for the primary ribbons.

---------------------------------------------------------
Title: Solar differential rotation in the period 1964-2016 determined
    by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Brajša, R.;
   Sudar, D.; Ruždjak, D.; Hržina, D.; Pötzi, W.; Hanslmeier, A.;
   Veronig, A.; Skokić, I.; Wöhl, H.
2017A&A...606A..72P    Altcode:
  Context. Kanzelhöhe Observatory for Solar and Environmental Research
  (KSO) provides daily multispectral synoptic observations of the Sun
  using several telescopes. In this work we made use of sunspot drawings
  and full disk white light CCD images. <BR /> Aims: The main aim of
  this work is to determine the solar differential rotation by tracing
  sunspot groups during the period 1964-2016, using the KSO sunspot
  drawings and white light images. We also compare the differential
  rotation parameters derived in this paper from the KSO with those
  collected fromf other data sets and present an investigation of the
  north - south rotational asymmetry. <BR /> Methods: Two procedures
  for the determination of the heliographic positions were applied: an
  interactive procedure on the KSO sunspot drawings (1964-2008, solar
  cycles Nos. 20-23) and an automatic procedure on the KSO white light
  images (2009-2016, solar cycle No. 24). For the determination of the
  synodic angular rotation velocities two different methods have been
  used: a daily shift (DS) method and a robust linear least-squares fit
  (rLSQ) method. Afterwards, the rotation velocities had to be converted
  from synodic to sidereal, which were then used in the least-squares
  fitting for the solar differential rotation law. A comparison of
  the interactive and automatic procedures was performed for the
  year 2014. <BR /> Results: The interactive procedure of position
  determination is fairly accurate but time consuming. In the case
  of the much faster automatic procedure for position determination,
  we found the rLSQ method for calculating rotational velocities to
  be more reliable than the DS method. For the test data from 2014,
  the rLSQ method gives a relative standard error for the differential
  rotation parameter B that is three times smaller than the corresponding
  relative standard error derived for the DS method. The best fit solar
  differential rotation profile for the whole time period is ω(b) =
  (14.47 ± 0.01)-(2.66 ± 0.10)sin<SUP>2</SUP>b (deg/day) for the DS
  method and ω(b) = (14.50 ± 0.01)-(2.87 ± 0.12)sin<SUP>2</SUP>b
  (deg/day) for the rLSQ method. A barely noticeable north - south
  asymmetry is observed for the whole time period 1964-2016 in the
  present paper. Rotation profiles, using different data sets, presented
  by other authors for the same time periods and the same tracer types,
  are in good agreement with our results. <BR /> Conclusions: The KSO
  data set used in this paper is in good agreement with the Debrecen
  Photoheliographic Data and Greenwich Photoheliographic Results and is
  suitable for the investigation of the long-term variabilities in the
  solar rotation profile. Also, the quality of the KSO sunspot drawings
  has gradually increased during the last 50 yr.

---------------------------------------------------------
Title: Structure of the solar photosphere studied from the radiation
    hydrodynamics code ANTARES
Authors: Leitner, P.; Lemmerer, B.; Hanslmeier, A.; Zaqarashvili,
   T.; Veronig, A.; Grimm-Strele, H.; Muthsam, H. J.
2017Ap&SS.362..181L    Altcode: 2017arXiv170801156L
  The ANTARES radiation hydrodynamics code is capable of simulating
  the solar granulation in detail unequaled by direct observation. We
  introduce a state-of-the-art numerical tool to the solar physics
  community and demonstrate its applicability to model the solar
  granulation. The code is based on the weighted essentially
  non-oscillatory finite volume method and by its implementation
  of local mesh refinement is also capable of simulating turbulent
  fluids. While the ANTARES code already provides promising insights
  into small-scale dynamical processes occurring in the quiet-Sun
  photosphere, it will soon be capable of modeling the latter in the
  scope of radiation magnetohydrodynamics. In this first preliminary
  study we focus on the vertical photospheric stratification by examining
  a 3-D model photosphere with an evolution time much larger than the
  dynamical timescales of the solar granulation and of particular large
  horizontal extent corresponding to 25”×25” on the solar surface to
  smooth out horizontal spatial inhomogeneities separately for up- and
  downflows. The highly resolved Cartesian grid thereby covers ∼4 Mm
  of the upper convection zone and the adjacent photosphere. Correlation
  analysis, both local and two-point, provides a suitable means to probe
  the photospheric structure and thereby to identify several layers
  of characteristic dynamics: The thermal convection zone is found to
  reach some ten kilometers above the solar surface, while convectively
  overshooting gas penetrates even higher into the low photosphere. An
  ≈145 km wide transition layer separates the convective from the
  oscillatory layers in the higher photosphere.

---------------------------------------------------------
Title: The Causes of Quasi-homologous CMEs
Authors: Liu, Lijuan; Wang, Yuming; Liu, Rui; Zhou, Zhenjun; Temmer,
   M.; Thalmann, J. K.; Liu, Jiajia; Liu, Kai; Shen, Chenglong; Zhang,
   Quanhao; Veronig, A. M.
2017ApJ...844..141L    Altcode: 2017arXiv170608878L
  In this paper, we identified the magnetic source locations of 142
  quasi-homologous (QH) coronal mass ejections (CMEs), of which 121
  are from solar cycle (SC) 23 and 21 from SC 24. Among those CMEs, 63%
  originated from the same source location as their predecessor (defined
  as S-type), while 37% originated from a different location within the
  same active region as their predecessor (defined as D-type). Their
  distinctly different waiting time distributions, peaking around 7.5 and
  1.5 hr for S- and D-type CMEs, suggest that they might involve different
  physical mechanisms with different characteristic timescales. Through
  detailed analysis based on nonlinear force-free coronal magnetic field
  modeling of two exemplary cases, we propose that the S-type QH CMES
  might involve a recurring energy release process from the same source
  location (by magnetic free energy replenishment), whereas the D-type
  QH CMEs can happen when a flux tube system is disturbed by a nearby CME.

---------------------------------------------------------
Title: Erratum: “The Confined X-class Flares of Solar Active Region
2192” (<A href="http://doi.org/10.1088/2041-8205/801/2/L23">2015,
    ApJL, 801, L23</A>)
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
2017ApJ...844L..27T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Direct Observation of Two-step Magnetic Reconnection in a
    Solar Flare
Authors: Gou, Tingyu; Veronig, Astrid M.; Dickson, Ewan C.;
   Hernandez-Perez, Aaron; Liu, Rui
2017ApJ...845L...1G    Altcode: 2017arXiv170706198G
  We report observations of an eruptive X2.8 flare on 2013 May 13,
  which shows two distinct episodes of energy release in the impulsive
  phase. The first episode is characterized by the eruption of a
  magnetic flux rope, similar to the energy-release process in most
  standard eruptive flares. The second episode, which is stronger than
  the first normal one and shows enhanced high-energy X-ray and even
  γ-ray emissions, is closely associated with magnetic reconnection of
  a large-scale loop in the aftermath of the eruption. The reconnection
  inflow of the loop leg is observed in the Solar Dynamics Observatory
  (SDO)/Atmospheric Imaging Assembly (AIA) 304 Å passband and
  accelerates toward the reconnection region to speeds as high as
  ∼130 km s<SUP>-1</SUP>. Simultaneously, the corresponding outflow
  jets are observed in the AIA hot passbands with speeds of ∼740 km
  s<SUP>-1</SUP> and a mean temperature of ∼14 MK. RHESSI observations
  show a strong burst of hard X-ray (HXR) and γ-ray emissions with hard
  electron spectra of δ ≈ 3, exhibiting a soft-hard-harder behavior. A
  distinct altitude decrease of the HXR loop-top source coincides with
  the inward swing of the loop leg observed in the AIA 304 Å passband,
  which is suggested to be related to the coronal implosion. This fast
  inflow of magnetic flux contained in the loop leg greatly enhances the
  reconnection rate and results in very efficient particle acceleration
  in the second-step reconnection, which also helps to achieve a second
  higher temperature peak up to T ≈ 30 MK.

---------------------------------------------------------
Title: On Flare-CME Characteristics from Sun to Earth Combining
    Remote-Sensing Image Data with In Situ Measurements Supported
    by Modeling
Authors: Temmer, Manuela; Thalmann, Julia K.; Dissauer, Karin;
   Veronig, Astrid M.; Tschernitz, Johannes; Hinterreiter, Jürgen;
   Rodriguez, Luciano
2017SoPh..292...93T    Altcode: 2017arXiv170300694T
  We analyze the well-observed flare and coronal mass ejection (CME)
  from 1 October 2011 (SOL2011-10-01T09:18) covering the complete chain of
  effects - from Sun to Earth - to better understand the dynamic evolution
  of the CME and its embedded magnetic field. We study in detail the
  solar surface and atmosphere associated with the flare and CME using the
  Solar Dynamics Observatory (SDO) and ground-based instruments. We also
  track the CME signature off-limb with combined extreme ultraviolet
  (EUV) and white-light data from the Solar Terrestrial Relations
  Observatory (STEREO). By applying the graduated cylindrical shell
  (GCS) reconstruction method and total mass to stereoscopic STEREO-SOHO
  (Solar and Heliospheric Observatory) coronagraph data, we track
  the temporal and spatial evolution of the CME in the interplanetary
  space and derive its geometry and 3D mass. We combine the GCS and
  Lundquist model results to derive the axial flux and helicity of
  the magnetic cloud (MC) from in situ measurements from Wind. This is
  compared to nonlinear force-free (NLFF) model results, as well as to
  the reconnected magnetic flux derived from the flare ribbons (flare
  reconnection flux) and the magnetic flux encompassed by the associated
  dimming (dimming flux). We find that magnetic reconnection processes
  were already ongoing before the start of the impulsive flare phase,
  adding magnetic flux to the flux rope before its final eruption. The
  dimming flux increases by more than 25% after the end of the flare,
  indicating that magnetic flux is still added to the flux rope after
  eruption. Hence, the derived flare reconnection flux is most probably a
  lower limit for estimating the magnetic flux within the flux rope. We
  find that the magnetic helicity and axial magnetic flux are lower in
  the interplanetary space by ∼ 50% and 75%, respectively, possibly
  indicating an erosion process. A CME mass increase of 10% is observed
  over a range of ∼4 -20 R<SUB>⊙</SUB>. The temporal evolution of
  the CME-associated core-dimming regions supports the scenario that
  fast outflows might supply additional mass to the rear part of the CME.

---------------------------------------------------------
Title: Solar differential rotation in the period 1964 - 2016
    determined by the Kanzelhöhe data set
Authors: Poljančić Beljan, I.; Jurdana-Šepić, R.; Brajša, R.;
   Sudar, D.; Ruždjak, D.; Hržina, D.; Pötzi, W.; Hanslmeier, A.;
   Veronig, A.; Skokić, I.; Wöhl, H.
2017arXiv170707886P    Altcode:
  The main aim of this work is to determine the solar differential
  rotation by tracing sunspot groups during the period 1964-2016, using
  the Kanzelhöhe Observatory for Solar and Environmental Research
  (KSO) sunspot drawings and white light images. Two procedures for
  the determination of the heliographic positions were applied: an
  interactive procedure on the KSO sunspot drawings (1964 - 2008, solar
  cycles nos. 20 - 23) and an automatic procedure on the KSO white light
  images (2009 - 2016, solar cycle no. 24). For the determination of the
  synodic angular rotation velocities two different methods have been
  used: a daily shift (DS) method and a robust linear least-squares fit
  (rLSQ) method. Afterwards, the rotation velocities had to be converted
  from synodic to sidereal, which were then used in the least-squares
  fitting for the solar differential rotation law. For the test
  data from 2014, we found the rLSQ method for calculating rotational
  velocities to be more reliable than the DS method. The best fit solar
  differential rotation profile for the whole time period is $\omega(b)$
  = (14.47 $\pm$ 0.01) - (2.66 $\pm$ 0.10) $\sin^2b$ (deg/day) for the
  DS method and $\omega(b)$ = (14.50 $\pm$ 0.01) - (2.87 $\pm$ 0.12)
  $\sin^2b$ (deg/day) for the rLSQ method. A barely noticeable north -
  south asymmetry is observed for the whole time period 1964 - 2016
  in the present paper. Rotation profiles, using different data sets
  (e.g. Debrecen Photoheliographic Data, Greenwich Photoheliographic
  Results), presented by other authors for the same time periods and the
  same tracer types, are in good agreement with our results. Therefore,
  the KSO data set is suitable for the investigation of the long-term
  variabilities in the solar rotation profile.

---------------------------------------------------------
Title: Flare-induced changes of the photospheric magnetic field in
    a δ-spot deduced from ground-based observations
Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.;
   Veronig, A. M.; González Manrique, S. J.; Kučera, A.; Schwartz,
   P.; Hanslmeier, A.
2017A&A...602A..60G    Altcode: 2017arXiv170406089G
  <BR /> Aims: Changes of the magnetic field and the line-of-sight
  velocities in the photosphere are being reported for an M-class
  flare that originated at a δ-spot belonging to active region NOAA
  11865. <BR /> Methods: High-resolution ground-based near-infrared
  spectropolarimetric observations were acquired simultaneously in
  two photospheric spectral lines, Fe I 10783 Å and Si I 10786 Å,
  with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope
  (VTT) in Tenerife on 2013 October 15. The observations covered several
  stages of the M-class flare. Inversions of the full-Stokes vector of
  both lines were carried out and the results were put into context using
  (extreme)-ultraviolet filtergrams from the Solar Dynamics Observatory
  (SDO). <BR /> Results: The active region showed high flaring activity
  during the whole observing period. After the M-class flare, the
  longitudinal magnetic field did not show significant changes along
  the polarity inversion line (PIL). However, an enhancement of the
  transverse magnetic field of approximately 550 G was found that
  bridges the PIL and connects umbrae of opposite polarities in the
  δ-spot. At the same time, a newly formed system of loops appeared
  co-spatially in the corona as seen in 171 Å filtergrams of the
  Atmospheric Imaging Assembly (AIA) on board SDO. However, we cannot
  exclude that the magnetic connection between the umbrae already existed
  in the upper atmosphere before the M-class flare and became visible
  only later when it was filled with hot plasma. The photospheric
  Doppler velocities show a persistent upflow pattern along the PIL
  without significant changes due to the flare. <BR /> Conclusions:
  The increase of the transverse component of the magnetic field after
  the flare together with the newly formed loop system in the corona
  support recent predictions of flare models and flare observations. <P
  />The movie associated to Figs. 4 and 5 is available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201730644/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Sunward-propagating Solar Energetic Electrons inside Multiple
    Interplanetary Flux Ropes
Authors: Gómez-Herrero, Raúl; Dresing, Nina; Klassen, Andreas;
   Heber, Bernd; Temmer, Manuela; Veronig, Astrid; Bučík, Radoslav;
   Hidalgo, Miguel A.; Carcaboso, Fernando; Blanco, Juan J.; Lario, David
2017ApJ...840...85G    Altcode:
  On 2013 December 2 and 3, the SEPT and STE instruments on board
  STEREO-A observed two solar energetic electron events with unusual
  sunward-directed fluxes. Both events occurred during a time
  interval showing typical signatures of interplanetary coronal mass
  ejections (ICMEs). The electron timing and anisotropies, combined with
  extreme-ultraviolet solar imaging and radio wave spectral observations,
  are used to confirm the solar origin and the injection times of the
  energetic electrons. The solar source of the ICME is investigated using
  remote-sensing observations and a three-dimensional reconstruction
  technique. In situ plasma and magnetic field data combined with
  energetic electron observations and a flux-rope model are used to
  determine the ICME magnetic topology and the interplanetary electron
  propagation path from the Sun to 1 au. Two consecutive flux ropes
  crossed the STEREO-A location and each electron event occurred inside
  a different flux rope. In both cases, the electrons traveled from the
  solar source to 1 au along the longest legs of the flux ropes still
  connected to the Sun. During the December 2 event, energetic electrons
  propagated along the magnetic field, while during the December 3 event
  they were propagating against the field. As found by previous studies,
  the energetic electron propagation times are consistent with a low
  number of field line rotations N &lt; 5 of the flux rope between the
  Sun and 1 au. The flux rope model used in this work suggests an even
  lower number of rotations.

---------------------------------------------------------
Title: The February 15 2011 CME-CME interaction and possibly
    associated radio emission
Authors: Magdalenic, Jasmina; Temmer, Manuela; Krupar, Vratislav;
   Marque, Christophe; Veronig, Astrid; Eastwood, Jonathan
2017EGUGA..19.9850M    Altcode:
  On February 15, 2011 a particular, continuum-like radio emission was
  observed by STEREO WAVES and WIND WAVES spacecraft. The radio event
  appeared to be associated with the complex interaction of two coronal
  mass ejections (CMEs) successively launched (February 14 and February
  15) from the same active region. Although the CME-CME interaction was
  widely studied (e.g. Temmer et al., 2014, Maricic et al., 2014, Mishra
  &amp; Srivastava, 2014) none of the analyses confirmed an association
  with the continuum-like radio emission. The usual method of establishing
  temporal coincidence of radio continuum and a CME-CME interaction is not
  applicable in this event due to a complex and long-lasting interaction
  of the CMEs. Therefore, we performed radio triangulation studies (see
  also Magdalenic et al., 2014) which provided us with the 3D source
  positions of the radio emission. Comparison of the positions of radio
  sources and the reconstructed positions of the interacting CMEs, shows
  that the source position of the continuum-like radio emission is about
  0.5 AU away from the interacting CMEs. We can therefore concluded that,
  in this event, the continuum-like emission is not the radio signature
  of the CME-CME interaction.

---------------------------------------------------------
Title: Understanding CMEs using plasma diagnostics of the related
    dimmings
Authors: Vanninathan, Kamalam; Veronig, Astrid; Gomory, Peter;
   Dissauer, Karin; Temmer, Manuela; Hannah, Iain; Kontar, Eduard
2017EGUGA..19.1571V    Altcode:
  Coronal Mass Ejections (CMEs) are often associated with dimmings that
  are well observed in Extreme Ultra-violet (EUV) wavelengths. Such
  dimmings are suggested to represent the evacuation of mass that is
  carried out by CMEs and are a unique and indirect means to study CME
  properties. While Earth-directed CMEs (on-disk CMEs) are difficult to
  observe due to the bright background solar disk and projection effects,
  their corresponding dimmings are clearly discernible and ideally suited
  for analysis. Using data from the 6 EUV channels of Solar Dynamics
  Observatory/Atmospheric Imaging Assembly for Differential Emission
  Measure (DEM) diagnostics, we determine the plasma characteristics of
  the dimming region. These data are well suited for this kind of study
  due to the good temperature ranges covered by the multiple passbands
  of the instrument. We analyse 7 on-disk and 5 off-limb events and
  derive the weighted density and temperature as a function of time,
  from the DEMs. From such an analysis we differentiate 2 types of dimming
  regions: core and secondary dimmings. Core dimmings often occur in pairs
  lying on either sides of the active region and in opposite polarity
  regions while the secondary dimming is more extended. In both the
  regions the derived plasma parameters reach a minimum within 30-60
  min after the flare. For each event the core dimming region shows
  a higher decrease in density and temperature than the corresponding
  secondary dimming regions. The values of these parameters remains low
  within the core dimming region for the entire duration of this study
  ( 10 hrs after the flare) while the secondary dimming region starts to
  show a gradual increase after 1-2 hrs. We also use spectroscopic data
  from Hinode/Extreme-Ultraviolet Imaging Spectrometer to differentiate
  core and secondary dimming regions. We find that the Fe XIII 202 Å
  line shows double component profiles within the core dimming region
  with strong blueshifts of 100 km/s while the secondary dimming region
  has weak upflows of 10 km/s. We conclude that the core dimming region
  corresponds to footpoints of the erupting flux rope from where there
  is continuous strong upflowing plasma for at least 10 hrs after the
  flare, while the secondary dimming region begins to refill within 1-2
  hrs. These measurements can be used to deduce information about the
  mass of on-disk CMEs where white light measurements can fail. We also
  confirm that the dimmings are mainly caused by density decrease and
  not temperature changes. DEM analysis is a strong tool to decipher
  CME properties from dimming regions.

---------------------------------------------------------
Title: Statistical analysis on how CME and SIR/CIR events effect
    the geomagnetic activity and the Earth's thermosphere
Authors: Krauss, Sandro; Temmer, Manuela; Edl, Martina; Veronig, Astrid
2017EGUGA..1915251K    Altcode:
  In order to estimate the impact of different types of solar wind
  on the geomagnetic activity and the neutral density in the Earth's
  thermosphere, we present a comprehensive statistical analysis based on
  interplanetary coronal mass ejections (ICME) covering the time range
  from July 2003 - 2016 and stream interaction as well as corotating
  interaction regions (SIR/CIR) from July 2003 - December 2009. In
  general, geomagnetic storms induced by CIR are characterized by lower
  energy input compared to ICME induced storms but a significantly longer
  duration time due to a long-term negative Bz component in the magnetic
  cloud region. Regarding the time of occurrence of ICME events, we rely
  on the catalogue maintained by Richardson and Cane. For the period of
  investigation more than 250 Earth-directed CME events are listed. All
  of them have been measured in situ by plasma and field instruments on
  board the ACE spacecraft. The arrival times of SIRs/CIRs are taken from
  the catalogue maintained by Lan Jian based on ACE and Wind in-situ
  measurements. From this list, we extracted 98 SIR/CIR events, from
  which the minimum Bz component is determined within a time window of
  36 hours starting at the arrival of the SIR/CIR (same procedure as for
  ICMEs). Accordingly, the peak in Earth's neutral density is determined
  in the same time window. The densities itself are estimated by using
  accelerometer measurements collected by the Gravity Recovery And Climate
  Experiment (GRACE) satellites and subsequently related to various
  geomagnetic indices (e.g. SYM-H, Polar cap, a-indices, ...) as well
  as characteristic CME parameters like the impact speed, the southward
  magnetic field strength Bz and resultant derivatives. We find high
  correlations (cc=0.9) between the CME characteristic (except the impact
  speed) and the thermospheric density enhancements as well as with most
  of the geomagnetic indices. However, considering only weaker ICME events
  (Bz up to -20nT) a lower correlation must be conceded. The same holds
  true for SIR/CIR events, as both cover compressed sheath regions with
  turbulent magnetic field. The absolute density increases for SIR/CIR
  induced storms is in the order of 1.7E-12kg/m3 for Bz values ranging
  from -4 to -19nT, with a related correlation coefficient of -0.41.

---------------------------------------------------------
Title: Quantification of disturbance periods of solar wind speed in
    interplanetary space due to coronal mass ejections
Authors: Temmer, Manuela; Reiss, Martin A.; Nikolic, Ljubomir;
   Hofmeister, Stefan J.; Veronig, Astrid M.
2017EGUGA..19.1940T    Altcode:
  Interplanetary space is characteristically structured mainly by
  high-speed solar wind streams emanating from coronal holes and transient
  disturbances such as coronal mass ejections (CMEs). While high-speed
  solar wind streams pose a continuous outflow, CMEs abruptly disrupt
  the rather steady structure causing large deviations from the quiet
  solar wind conditions. We present a quantification of the duration of
  disturbed conditions (preconditioning) for interplanetary space caused
  by CMEs by investigating the plasma speed component of the solar wind
  and the impact of in situ detected CMEs (ICMEs), compared to different
  background solar wind models (ESWF, WSA, persistence model) for the
  time range 2011-2015. We obtain for periods within an ICME interval
  an increase of 18-32% above the expected quiet Sun background and for
  the period of 2 days after the ICME an increase of 9-24%. The total
  duration of enhanced deviations is about 3 and up to 6 days after the
  ICME start, which is much longer than the average duration of an ICME
  disturbance itself (about 1.3 days), concluding that interplanetary
  space needs about 2-5 days to recover from the impact of ICMEs. The
  obtained results have strong implications for studying CME propagation
  behavior and also for space weather forecasting.

---------------------------------------------------------
Title: Magnetic reconnection rates in solar flares and implications
    for "superflares"
Authors: Veronig, Astrid; Tschernitz, Johannes; Hinterreiter, Jürgen;
   Thalmann, Julia
2017EGUGA..19.4751V    Altcode:
  We present a statistical study of magnetic reconnection rates and
  fluxes to study the energy release process in solar flares. Our data
  set covers 50 events, including 19 eruptive flares (i.e. flares
  associated with a coronal mass ejection) and 31 confined flares
  (i.e. not associated with a coronal mass ejection). The events under
  study are distributed over a wide range of GOES classes, from B to
  &gt;X10. Magnetic reconnection rates and fluxes are derived from the
  flare ribbon evolution studied in Halpha filtergrams from Kanzelhöhe
  Observatory and co-registered photospheric line-of-sight magnetic
  field maps from HMI/SDO and MDI/SOHO. We find a distinct correlation
  between the total flare reconnection flux with the GOES peak flux for
  both eruptive and confined flares. In the largest events, the flare
  reconnection fluxes may reach up to &gt;30% of the total active region
  magnetic flux. The implications of the distinct correlations obtained
  are discussed with respect to the recently detected superflares on
  solar-like stars and the largest flares expected on the Sun.

---------------------------------------------------------
Title: Flare-CME characteristics from Sun to Earth combining
    observations and modeling
Authors: Temmer, Manuela; Thalmann, Julia K.; Dissauer, Karin;
   Veronig, Astrid M.; Tschernitz, Johannes; Hinterreiter, Jürgen;
   Rodriguez, Luciano
2017EGUGA..19.1942T    Altcode:
  We analyze the well observed flare-CME event from October 1, 2011
  (SOL2011-10-01T09:18) covering the complete chain of action - from
  Sun to Earth - for a better understanding of the dynamic evolution
  of the CME and its embedded magnetic field. We study in detail the
  solar surface and atmosphere from SDO and ground-based instruments
  associated to the flare-CME and also track the CME signature offlimb
  from combined EUV and white-light data with STEREO. By applying 3D
  reconstruction techniques (GCS, total mass) to stereoscopic STEREO-SoHO
  coronagraph data, we track the temporal and spatial evolution of the
  CME in interplanetary space and derive its geometry and 3D-mass. We
  combine the GCS and Lundquist model results to derive the axial flux
  and helicity of the MC from in situ measurements (Wind). This is
  compared to nonlinear force-free (NLFF) model results as well as to
  the reconnected magnetic flux derived from the flare ribbons (flare
  reconnection flux) and the magnetic flux encompassed by the associated
  dimming (dimming flux). We find that magnetic reconnection processes
  were already ongoing before the start of the impulsive flare phase,
  adding magnetic flux to the flux rope before its final eruption. The
  dimming flux increases by more than 25% after the end of the flare,
  indicating that magnetic flux is still added to the flux rope after
  eruption. Hence, the derived flare reconnection flux is most probably a
  lower limit for estimating the magnetic flux within the flux rope. We
  obtain that the magnetic helicity and axial magnetic flux are reduced
  in interplanetary space by ∼50% and 75%, respectively, possibly
  indicating to an erosion process. A mass increase of 10% for the CME
  is observed over the distance range from about 4-20 Rs. The temporal
  evolution of the CME associated core dimming regions supports the
  scenario that fast outflows might supply additional mass to the rear
  part of the CME.

---------------------------------------------------------
Title: Preconditioning of Interplanetary Space Due to Transient
    CME Disturbances
Authors: Temmer, M.; Reiss, M. A.; Nikolic, L.; Hofmeister, S. J.;
   Veronig, A. M.
2017ApJ...835..141T    Altcode: 2016arXiv161206080T
  Interplanetary space is characteristically structured mainly by
  high-speed solar wind streams emanating from coronal holes and transient
  disturbances such as coronal mass ejections (CMEs). While high-speed
  solar wind streams pose a continuous outflow, CMEs abruptly disrupt
  the rather steady structure, causing large deviations from the quiet
  solar wind conditions. For the first time, we give a quantification
  of the duration of disturbed conditions (preconditioning) for
  interplanetary space caused by CMEs. To this aim, we investigate
  the plasma speed component of the solar wind and the impact of in
  situ detected interplanetary CMEs (ICMEs), compared to different
  background solar wind models (ESWF, WSA, persistence model) for the
  time range 2011-2015. We quantify in terms of standard error measures
  the deviations between modeled background solar wind speed and observed
  solar wind speed. Using the mean absolute error, we obtain an average
  deviation for quiet solar activity within a range of 75.1-83.1 km
  s<SUP>-1</SUP>. Compared to this baseline level, periods within
  the ICME interval showed an increase of 18%-32% above the expected
  background, and the period of two days after the ICME displayed an
  increase of 9%-24%. We obtain a total duration of enhanced deviations
  over about three and up to six days after the ICME start, which is
  much longer than the average duration of an ICME disturbance itself
  (∼1.3 days), concluding that interplanetary space needs ∼2-5 days
  to recover from the impact of ICMEs. The obtained results have strong
  implications for studying CME propagation behavior and also for space
  weather forecasting.

---------------------------------------------------------
Title: Characteristics of Low-latitude Coronal Holes near the Maximum
    of Solar Cycle 24
Authors: Hofmeister, Stefan J.; Veronig, Astrid; Reiss, Martin A.;
   Temmer, Manuela; Vennerstrom, Susanne; Vršnak, Bojan; Heber, Bernd
2017ApJ...835..268H    Altcode: 2017arXiv170202050H
  We investigate the statistics of 288 low-latitude coronal holes
  extracted from SDO/AIA-193 filtergrams over the time range of
  2011 January 01-2013 December 31. We analyze the distribution of
  characteristic coronal hole properties, such as the areas, mean AIA-193
  intensities, and mean magnetic field densities, the local distribution
  of the SDO/AIA-193 intensity and the magnetic field within the coronal
  holes, and the distribution of magnetic flux tubes in coronal holes. We
  find that the mean magnetic field density of all coronal holes under
  study is 3.0 ± 1.6 G, and the percentaged unbalanced magnetic flux
  is 49 ± 16%. The mean magnetic field density, the mean unsigned
  magnetic field density, and the percentaged unbalanced magnetic flux of
  coronal holes depend strongly pairwise on each other, with correlation
  coefficients cc &gt; 0.92. Furthermore, we find that the unbalanced
  magnetic flux of the coronal holes is predominantly concentrated in
  magnetic flux tubes: 38% (81%) of the unbalanced magnetic flux of
  coronal holes arises from only 1% (10%) of the coronal hole area,
  clustered in magnetic flux tubes with field strengths &gt;50 G (10
  G). The average magnetic field density and the unbalanced magnetic
  flux derived from the magnetic flux tubes correlate with the mean
  magnetic field density and the unbalanced magnetic flux of the overall
  coronal hole (cc &gt; 0.93). These findings give evidence that the
  overall magnetic characteristics of coronal holes are governed by the
  characteristics of the magnetic flux tubes.

---------------------------------------------------------
Title: Formation and Eruption of a Flux Rope from the Sigmoid Active
Region NOAA 11719 and Associated M6.5 Flare: A Multi-wavelength Study
Authors: Joshi, Bhuwan; Kushwaha, Upendra; Veronig, Astrid M.; Dhara,
   Sajal Kumar; Shanmugaraju, A.; Moon, Yong-Jae
2017ApJ...834...42J    Altcode: 2017arXiv170100967J
  We investigate the formation, activation, and eruption of a flux rope
  (FR) from the sigmoid active region NOAA 11719 by analyzing E(UV),
  X-ray, and radio measurements. During the pre-eruption period of
  ∼7 hr, the AIA 94 Å images reveal the emergence of a coronal
  sigmoid through the interaction between two J-shaped bundles
  of loops, which proceeds with multiple episodes of coronal loop
  brightenings and significant variations in the magnetic flux through
  the photosphere. These observations imply that repetitive magnetic
  reconnections likely play a key role in the formation of the sigmoidal
  FR in the corona and also contribute toward sustaining the temperature
  of the FR higher than that of the ambient coronal structures. Notably,
  the formation of the sigmoid is associated with the fast morphological
  evolution of an S-shaped filament channel in the chromosphere. The
  sigmoid activates toward eruption with the ascent of a large FR in the
  corona, which is preceded by the decrease in photospheric magnetic
  flux through the core flaring region, suggesting tether-cutting
  reconnection as a possible triggering mechanism. The FR eruption
  results in a two-ribbon M6.5 flare with a prolonged rise phase of
  ∼21 minutes. The flare exhibits significant deviation from the
  standard flare model in the early rise phase, during which a pair of
  J-shaped flare ribbons form and apparently exhibit converging motions
  parallel to the polarity inversion line, which is further confirmed
  by the motions of hard X-ray footpoint sources. In the later stages,
  the flare follows the standard flare model and the source region
  undergoes a complete sigmoid-to-arcade transformation.

---------------------------------------------------------
Title: Understanding the Physical Nature of Coronal "EIT Waves"
Authors: Long, D. M.; Bloomfield, D. S.; Chen, P. F.; Downs, C.;
   Gallagher, P. T.; Kwon, R. -Y.; Vanninathan, K.; Veronig, A. M.;
   Vourlidas, A.; Vršnak, B.; Warmuth, A.; Žic, T.
2017SoPh..292....7L    Altcode: 2016arXiv161105505L
  For almost 20 years the physical nature of globally propagating waves in
  the solar corona (commonly called "EIT waves") has been controversial
  and subject to debate. Additional theories have been proposed over the
  years to explain observations that did not agree with the originally
  proposed fast-mode wave interpretation. However, the incompatibility
  of observations made using the Extreme-ultraviolet Imaging Telescope
  (EIT) onboard the Solar and Heliospheric Observatory with the fast-mode
  wave interpretation was challenged by differing viewpoints from the twin
  Solar Terrestrial Relations Observatory spacecraft and data with higher
  spatial and temporal resolution from the Solar Dynamics Observatory. In
  this article, we reexamine the theories proposed to explain EIT waves
  to identify measurable properties and behaviours that can be compared
  to current and future observations. Most of us conclude that the
  so-called EIT waves are best described as fast-mode large-amplitude
  waves or shocks that are initially driven by the impulsive expansion
  of an erupting coronal mass ejection in the low corona.

---------------------------------------------------------
Title: Exploring impulsive solar magnetic energy release and particle
    acceleration with focused hard X-ray imaging spectroscopy
Authors: Christe, Steven; Krucker, Samuel; Glesener, Lindsay; Shih,
   Albert; Saint-Hilaire, Pascal; Caspi, Amir; Allred, Joel; Battaglia,
   Marina; Chen, Bin; Drake, James; Dennis, Brian; Gary, Dale; Gburek,
   Szymon; Goetz, Keith; Grefenstette, Brian; Gubarev, Mikhail; Hannah,
   Iain; Holman, Gordon; Hudson, Hugh; Inglis, Andrew; Ireland, Jack;
   Ishikawa, Shinosuke; Klimchuk, James; Kontar, Eduard; Kowalski, Adam;
   Longcope, Dana; Massone, Anna-Maria; Musset, Sophie; Piana, Michele;
   Ramsey, Brian; Ryan, Daniel; Schwartz, Richard; Stęślicki, Marek;
   Turin, Paul; Warmuth, Alexander; Wilson-Hodge, Colleen; White, Stephen;
   Veronig, Astrid; Vilmer, Nicole; Woods, Tom
2017arXiv170100792C    Altcode:
  How impulsive magnetic energy release leads to solar eruptions and how
  those eruptions are energized and evolve are vital unsolved problems
  in Heliophysics. The standard model for solar eruptions summarizes
  our current understanding of these events. Magnetic energy in the
  corona is released through drastic restructuring of the magnetic
  field via reconnection. Electrons and ions are then accelerated by
  poorly understood processes. Theories include contracting loops,
  merging magnetic islands, stochastic acceleration, and turbulence at
  shocks, among others. Although this basic model is well established,
  the fundamental physics is poorly understood. HXR observations
  using grazing-incidence focusing optics can now probe all of the key
  regions of the standard model. These include two above-the-looptop
  (ALT) sources which bookend the reconnection region and are likely
  the sites of particle acceleration and direct heating. The science
  achievable by a direct HXR imaging instrument can be summarized by the
  following science questions and objectives which are some of the most
  outstanding issues in solar physics (1) How are particles accelerated
  at the Sun? (1a) Where are electrons accelerated and on what time
  scales? (1b) What fraction of electrons is accelerated out of the
  ambient medium? (2) How does magnetic energy release on the Sun lead
  to flares and eruptions? A Focusing Optics X-ray Solar Imager (FOXSI)
  instrument, which can be built now using proven technology and at modest
  cost, would enable revolutionary advancements in our understanding of
  impulsive magnetic energy release and particle acceleration, a process
  which is known to occur at the Sun but also throughout the Universe.

---------------------------------------------------------
Title: High-resolution modeling of the solar photosphere with the
    ANTARES RHD code
Authors: Leitner, P.; Lemmerer, B.; Hanslmeier, A.; Zaqarashvili,
   T.; Veronig, A.; Muthsam, H.
2017psio.confE.110L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Flare induced changes of the photospheric magnetic field in
    a delta-spot deduced from ground-based observations
Authors: Gömöry, P.; Balthasar, H.; Kuckein, C.; Koza, J.;
   Kuĉera, A.; González Manrique, S. J.; Schwartz, P.; Veronig, A. M.;
   Hanslmeier, A.
2017psio.confE.107G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar eruptions and energetic events
Authors: Veronig, Astrid
2017psio.confE..64V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Focusing Optics X-ray Solar Imager (FOXSI) SMEX Mission
Authors: Christe, S.; Shih, A. Y.; Krucker, S.; Glesener, L.;
   Saint-Hilaire, P.; Caspi, A.; Allred, J. C.; Battaglia, M.; Chen,
   B.; Drake, J. F.; Gary, D. E.; Goetz, K.; Grefenstette, B.; Hannah,
   I. G.; Holman, G.; Hudson, H. S.; Inglis, A. R.; Ireland, J.; Ishikawa,
   S. N.; Klimchuk, J. A.; Kontar, E.; Kowalski, A. F.; Massone, A. M.;
   Piana, M.; Ramsey, B.; Gubarev, M.; Schwartz, R. A.; Steslicki, M.;
   Ryan, D.; Turin, P.; Warmuth, A.; White, S. M.; Veronig, A.; Vilmer,
   N.; Dennis, B. R.
2016AGUFMSH13A2281C    Altcode:
  We present FOXSI (Focusing Optics X-ray Solar Imager), a recently
  proposed Small Explorer (SMEX) mission that will provide a revolutionary
  new perspective on energy release and particle acceleration on the
  Sun. FOXSI is a direct imaging X-ray spectrometer with higher dynamic
  range and better than 10x the sensitivity of previous instruments. Flown
  on a 3-axis stabilized spacecraft in low-Earth orbit, FOXSI uses
  high-angular-resolution grazing-incidence focusing optics combined
  with state-of-the-art pixelated solid-state detectors to provide direct
  imaging of solar hard X-rays for the first time. FOXSI is composed of
  two individual x-ray telescopes with a 14-meter focal length enabled by
  a deployable boom. Making use of a filter-wheel and high-rate-capable
  solid-state detectors, FOXSI will be able to observe the largest flares
  without saturation while still maintaining the sensitivity to detect
  x-ray emission from weak flares, escaping electrons, and hot active
  regions. This SMEX mission is made possible by past experience with
  similar instruments on two sounding rocket flights, in 2012 and 2014,
  and on the HEROES balloon flight in 2013. FOXSI will image the Sun
  with a field of view of 9 arcminutes and an angular resolution of
  better than 8 arcsec; it will cover the energy range from 3 to 100
  keV with a spectral resolution of better than 1 keV; and it will have
  sub-second temporal resolution.

---------------------------------------------------------
Title: Pre-flare Coronal Jet and Evolutionary Phases of a Solar
Eruptive Prominence Associated with the M1.8 Flare: SDO and RHESSI
    Observations
Authors: Joshi, Bhuwan; Kushwaha, Upendra; Veronig, Astrid M.; Cho,
   K. -S.
2016ApJ...832..130J    Altcode: 2016arXiv161103629J
  We investigate the triggering, activation, and ejection of a solar
  eruptive prominence that occurred in a multi-polar flux system of
  active region NOAA 11548 on 2012 August 18 by analyzing data from the
  Atmospheric Imaging Assembly on board the Solar Dynamics Observatory,
  the Reuven Ramaty High Energy Solar Spectroscopic Imager, and the
  Extreme Ultraviolet Imager/Sun Earth Connection Coronal and Heliospheric
  Investigation on board the Solar Terrestrial Relation Observatory. Prior
  to the prominence activation, we observed striking coronal activities in
  the form of a blowout jet, which is associated with the rapid eruption
  of a cool flux rope. Furthermore, the jet-associated flux rope eruption
  underwent splitting and rotation during its outward expansion. These
  coronal activities are followed by the prominence activation during
  which it slowly rises with a speed of ∼12 km s<SUP>-1</SUP> while
  the region below the prominence emits gradually varying EUV and thermal
  X-ray emissions. From these observations, we propose that the prominence
  eruption is a complex, multi-step phenomenon in which a combination of
  internal (tether-cutting reconnection) and external (I.e., pre-eruption
  coronal activities) processes are involved. The prominence underwent
  catastrophic loss of equilibrium with the onset of the impulsive
  phase of an M1.8 flare, suggesting large-scale energy release by
  coronal magnetic reconnection. We obtained signatures of particle
  acceleration in the form of power-law spectra with hard electron
  spectral index (δ ∼ 3) and strong HXR footpoint sources. During
  the impulsive phase, a hot EUV plasmoid was observed below the apex
  of the erupting prominence that ejected in the direction of the
  prominence with a speed of ∼177 km s<SUP>-1</SUP>. The temporal,
  spatial, and kinematic correlations between the erupting prominence
  and the plasmoid imply that the magnetic reconnection supported the
  fast ejection of prominence in the lower corona.

---------------------------------------------------------
Title: 70 Years of Sunspot Observations at the Kanzelhöhe
Observatory: Systematic Study of Parameters Affecting the Derivation
    of the Relative Sunspot Number
Authors: Pötzi, Werner; Veronig, Astrid M.; Temmer, Manuela;
   Baumgartner, Dietmar J.; Freislich, Heinrich; Strutzmann, Heinz
2016SoPh..291.3103P    Altcode: 2016SoPh..tmp...43P; 2015arXiv151200270P
  The Kanzelhöhe Observatory (KSO) was founded during World War II by
  the Deutsche Luftwaffe (German Airforce) as one station of a network
  of observatories that were set up to provide information on solar
  activity in order to better assess the actual conditions of the Earth's
  ionosphere in terms of radio-wave propagation. Solar observations
  began in 1943 with photographs of the photosphere and drawings of
  sunspots, plage regions, and faculae, as well as patrol observations
  of the solar corona. At the beginning, all data were sent to Freiburg
  (Germany). After WW II, international cooperation was established and
  the data were sent to Zurich, Paris, Moscow, and Greenwich. Relative
  sunspot numbers have been derived since 1944. The agreement between
  relative sunspot numbers derived at KSO and the new International
  Sunspot Number (ISN) (SILSO World Data Center in International Sunspot
  Number Monthly Bulletin and online catalogue, 1945 - 2015) lies within
  ≈10 % . However, revisiting the historical data, we also find periods
  with larger deviations. The reasons for the deviations were twofold: On
  the one hand, a major instrumental change took place during which the
  instrument was relocated and modified. On the other hand, a period of
  frequent replacements of personnel caused significant deviations; this
  clearly shows the importance of experienced observers. In the long term,
  the instrumental improvements led to better image quality. Additionally,
  we find a long-term trend towards better seeing conditions that began
  in 2000.

---------------------------------------------------------
Title: Study of Plasma Heating in Solar Eruptive Events
Authors: Su, Yang; Veronig, Astrid M.; Hannah, Iain; Gan, Weiqun
2016usc..confE..78S    Altcode:
  The temperature of plasma is usually heated to over 10 MK by magnetic
  reconnection in Solar Eruptive Events. However, the details of the
  process are not known. With an improved way of DEM calculation, we are
  able to constrain the high-temperature DEMs using SDO/AIA data alone
  and study the heating process from the beginning to the end of SEEs. The
  results are also compared with other observations from RHESSI and GOES.

---------------------------------------------------------
Title: Projection Effects in Coronal Dimmings and Associated EUV
    Wave Event
Authors: Dissauer, K.; Temmer, M.; Veronig, A. M.; Vanninathan, K.;
   Magdalenić, J.
2016ApJ...830...92D    Altcode: 2016arXiv160705961D
  We investigate the high-speed (v &gt; 1000 km s<SUP>-1</SUP>)
  extreme-ultraviolet (EUV) wave associated with an X1.2 flare and coronal
  mass ejection (CME) from NOAA active region 11283 on 2011 September
  6 (SOL2011-09-06T22:12). This EUV wave features peculiar on-disk
  signatures in particular, we observe an intermittent “disappearance”
  of the front for 120 s in Solar Dynamics Observatory (SDO)/AIA 171,
  193, 211 Å data, whereas the 335 Å filter, sensitive to hotter
  plasmas (T ∼ 2.5 MK), shows a continuous evolution of the wave
  front. The eruption was also accompanied by localized coronal dimming
  regions. We exploit the multi-point quadrature position of SDO and
  STEREO-A, to make a thorough analysis of the EUV wave evolution, with
  respect to its kinematics and amplitude evolution and reconstruct
  the SDO line-of-sight (LOS) direction of the identified coronal
  dimming regions in STEREO-A. We show that the observed intensities
  of the dimming regions in SDO/AIA depend on the structures that are
  lying along their LOS and are the combination of their individual
  intensities, e.g., the expanding CME body, the enhanced EUV wave,
  and the CME front. In this context, we conclude that the intermittent
  disappearance of the EUV wave in the AIA 171, 193, and 211 Å filters,
  which are channels sensitive to plasma with temperatures below ∼2
  MK is also caused by such LOS integration effects. These observations
  clearly demonstrate that single-view image data provide us with limited
  insight to correctly interpret coronal features.

---------------------------------------------------------
Title: Understanding the Physical Nature of Coronal "EIT Waves"
Authors: Long, D. M.; Bloomfield, D. S.; Chen, P. -F.; Downs,
   C.; Gallagher, P. T.; Kwon, R. -Y.; Vanninathan, K.; Veronig, A.;
   Vourlidas, A.; Vrsnak, B.; Warmuth, A.; Zic, T.
2016usc..confE..24L    Altcode:
  For almost 20 years the physical nature of globally-propagating waves
  in the solar corona (commonly called "EIT waves") has been controversial
  and subject to debate. Additional theories have been proposed throughout
  the years to explain observations that did not fit with the originally
  proposed fast-mode wave interpretation. However, the incompatibility
  of observations made using the Extreme-ultraviolet Imaging Telescope
  (EIT) on the Solar and Heliospheric Observatory with the fast-mode
  wave interpretation have been challenged by differing viewpoints
  from the Solar Terrestrial Relations Observatory spacecraft and higher
  spatial/temporal resolution data from the Solar Dynamics Observatory. In
  this paper, we reexamine the theories proposed to explain "EIT waves"
  to identify measurable properties and behaviours that can be compared
  to current and future observations. Most of us conclude that "EIT
  waves" are best described as fast-mode large-amplitude waves/shocks,
  which are initially driven by the impulsive expansion of an erupting
  coronal mass ejection in the low corona.

---------------------------------------------------------
Title: Temporal and Spatial Relationship of Flare Signatures and
    the Force-free Coronal Magnetic Field
Authors: Thalmann, J. K.; Veronig, A.; Su, Y.
2016ApJ...826..143T    Altcode: 2016arXiv160503703T
  We investigate the plasma and magnetic environment of active
  region NOAA 11261 on 2011 August 2 around a GOES M1.4 flare/CME
  (SOL2011-08-02T06:19). We compare coronal emission at the (extreme)
  ultraviolet and X-ray wavelengths, using SDO AIA and RHESSI
  images, in order to identify the relative timing and locations of
  reconnection-related sources. We trace flare ribbon signatures at
  ultraviolet wavelengths in order to pin down the intersection
  of previously reconnected flaring loops in the lower solar
  atmosphere. These locations are used to calculate field lines from
  three-dimensional (3D) nonlinear force-free magnetic field models,
  established on the basis of SDO HMI photospheric vector magnetic
  field maps. Using this procedure, we analyze the quasi-static time
  evolution of the coronal model magnetic field previously involved
  in magnetic reconnection. This allows us, for the first time, to
  estimate the elevation speed of the current sheet’s lower tip during
  an on-disk observed flare as a few kilometers per second. A comparison
  to post-flare loops observed later above the limb in STEREO EUVI images
  supports this velocity estimate. Furthermore, we provide evidence for
  an implosion of parts of the flaring coronal model magnetic field,
  and identify the corresponding coronal sub-volumes associated with
  the loss of magnetic energy. Finally, we spatially relate the build
  up of magnetic energy in the 3D models to highly sheared fields,
  established due to the dynamic relative motions of polarity patches
  within the active region.

---------------------------------------------------------
Title: Extreme Geomagnetic Storms - 1868 - 2010
Authors: Vennerstrom, S.; Lefevre, L.; Dumbović, M.; Crosby, N.;
   Malandraki, O.; Patsou, I.; Clette, F.; Veronig, A.; Vršnak, B.;
   Leer, K.; Moretto, T.
2016SoPh..291.1447V    Altcode: 2016SoPh..tmp...73V
  We present the first large statistical study of extreme geomagnetic
  storms based on historical data from the time period 1868 - 2010. This
  article is the first of two companion papers. Here we describe how the
  storms were selected and focus on their near-Earth characteristics. The
  second article presents our investigation of the corresponding solar
  events and their characteristics. The storms were selected based
  on their intensity in the aa index, which constitutes the longest
  existing continuous series of geomagnetic activity. They are analyzed
  statistically in the context of more well-known geomagnetic indices,
  such as the Kp and Dcx/Dst index. This reveals that neither Kp nor
  Dcx/Dst provide a comprehensive geomagnetic measure of the extreme
  storms. We rank the storms by including long series of single magnetic
  observatory data. The top storms on the rank list are the New York
  Railroad storm occurring in May 1921 and the Quebec storm from March
  1989. We identify key characteristics of the storms by combining
  several different available data sources, lists of storm sudden
  commencements (SSCs) signifying occurrence of interplanetary shocks,
  solar wind in-situ measurements, neutron monitor data, and associated
  identifications of Forbush decreases as well as satellite measurements
  of energetic proton fluxes in the near-Earth space environment. From
  this we find, among other results, that the extreme storms are very
  strongly correlated with the occurrence of interplanetary shocks (91 -
  100 %), Forbush decreases (100 %), and energetic solar proton events
  (70 %). A quantitative comparison of these associations relative to less
  intense storms is also presented. Most notably, we find that most often
  the extreme storms are characterized by a complexity that is associated
  with multiple, often interacting, solar wind disturbances and that they
  frequently occur when the geomagnetic activity is already elevated. We
  also investigate the semiannual variation in storm occurrence and
  confirm previous findings that geomagnetic storms tend to occur less
  frequently near solstices and that this tendency increases with storm
  intensity. However, we find that the semiannual variation depends on
  both the solar wind source and the storm level. Storms associated
  with weak SSC do not show any semiannual variation, in contrast to
  weak storms without SSC.

---------------------------------------------------------
Title: Exceptions to the rule: the X-flares of AR 2192 Lacking
    Coronal Mass Ejections
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
2016ASPC..504..203T    Altcode:
  NOAA Active region (AR) 2192, that was present on the Sun in October
  2014, was the largest region which occurred since November 1990
  (see Figure 1). The huge size accompanied by a very high activity
  level, was quite unexpected as it appeared during the unusually weak
  solar cycle 24. Nevertheless, the AR turned out to be one of the most
  prolific flaring ARs of cycle 24. It produced in total 6 X, 29 M, 79
  C flares during its disk passage from October 18-29, 2014 (see Figure
  2). Surprisingly, all flares greater than GOES class M5 and X were
  confined, i.e. had no coronal mass ejections (CME) associated. All
  the flare events had some obvious similarity in morphology, as they
  were located in the core of the AR and revealed only minor separation
  motion away from the neutral line but a large initial separation of
  the conjugate flare ribbons. In the paper by Thalmann et al. (2015)
  we describe the series of flares and give details about the confined
  X1.6 flare event from October 22, 2014 as well as the single eruptive
  M4.0 flare event from October 24, 2014. The study of the X1.6 flare
  revealed a large initial separation of flare ribbons together with
  recurrent flare brightenings, which were related to two episodes of
  enhanced hard X-ray emission as derived from RHESSI observations. This
  suggests that magnetic field structures connected to specific regions
  were repeatedly involved in the process of reconnection and energy
  release. Opposite to the central location of the sequence of confined
  events within the AR, a single eruptive (M4.0) event occurred on
  the outskirt of the AR in the vicinity of open magnetic fields. Our
  investigations revealed a predominantly north-south oriented magnetic
  system of arcade fields overlying the AR that could have preserved
  the magnetic arcade to erupt, and consequently kept the energy release
  trapped in a localized volume of magnetic field high up in the corona
  (as supported by the absence of a lateral motion of the flare ribbons
  and the recurrent brightenings within them). We conclude that the
  background magnetic field configuration is an essential parameter
  for deriving the "eruptiveness" of flare events. Sun et al. (2015)
  supports this conclusion and derived for this AR a quite slow
  decay of the strength of the overlying magnetic field (decay index;
  see Török &amp; Kliem 2005). Interestingly, our magnetic field
  modellings revealed no flux rope inherent to the AR, indicating that
  further investigations are needed. In a recent paper by Veronig $
  Polanec (2015), who investigated in more detail the X-flares using
  also ground-based observations in Hα from Kanzelhöhe Observatory
  (Pötzi et al. 2015), it was shown that such confined events could be
  explained by the emerging-flux model, where newly emerging small flux
  tubes reconnect with pre-existing large coronal loops.

---------------------------------------------------------
Title: Projection effects in coronal dimmings and associated EUV
    wave event
Authors: Dissauer, Karin; Temmer, Manuela; Veronig, Astrid;
   Vanninathan, Kamalam; Magdalenic, Jasmina
2016EGUGA..18.6857D    Altcode:
  We investigate the high-speed (v &gt; 1000 km s-1) extreme-ultraviolet
  (EUV) wave associated with an X1.2 flare and coronal mass ejection (CME)
  from NOAA active region 11283. This EUV wave features peculiar on-disk
  signatures, in particular we observe an intermittent "disappearance"
  of the front for 120 s in SDO/AIA 171, 193, 211 Å data, whereas
  the 335 Å filter, sensitive to hotter plasmas (T∼ 2.5 MK), shows
  a continuous evolution of the wave front. We exploit the multi-point
  quadrature position of SDO and STEREO-A, to make a thorough analysis of
  the EUV wave evolution, with respect to its kinematics and amplitude
  evolution. We identify on-disk coronal dimming regions in SDO/AIA,
  reminiscent of core dimmings, that have no corresponding on-disk dimming
  signatures in STEREO-A/EUVI. Reconstructing the SDO line-of-sight (LOS)
  direction in STEREO-A clearly shows that the observed SDO on-disk
  dimming areas are not the footprints of the erupting fluxrope but
  result from decreased emission from the expanding CME body integrated
  along the LOS. In this context, we conclude that the intermittent
  disappearance of the EUV wave in the AIA 171, 193, 211 Å filters,
  which are channels sensitive to plasma with temperatures below ∼ 2
  MK is also caused by such LOS integration effects. These observations
  clearly demonstrate that single-view image data provide us with limited
  insight to correctly interpret coronal features.

---------------------------------------------------------
Title: Chromospheric evaporation flows and density changes deduced
    from Hinode/EIS during an M1.6 flare
Authors: Gömöry, P.; Veronig, A. M.; Su, Y.; Temmer, M.; Thalmann,
   J. K.
2016A&A...588A...6G    Altcode: 2016arXiv160202145G
  <BR /> Aims: We study the response of the solar atmosphere during a GOES
  M1.6 flare using spectroscopic and imaging observations. In particular,
  we examine the evolution of the mass flows and electron density together
  with the energy input derived from hard X-ray (HXR) in the context of
  chromospheric evaporation. <BR /> Methods: We analyzed high-cadence
  sit-and-stare observations acquired with the Hinode/EIS spectrometer
  in the Fe xiii 202.044 Å (log T = 6.2) and Fe xvi 262.980 Å (log T =
  6.4) spectral lines to derive temporal variations of the line intensity,
  Doppler shifts, and electron density during the flare. We combined these
  data with HXR measurements acquired with RHESSI to derive the energy
  input to the lower atmosphere by flare-accelerated electrons. <BR />
  Results: During the flare impulsive phase, we observe no significant
  flows in the cooler Fe xiii line but strong upflows, up to 80-150 km
  s<SUP>-1</SUP>, in the hotter Fe xvi line. The largest Doppler shifts
  observed in the Fe xvi line were co-temporal with the sharp intensity
  peak. The electron density obtained from a Fe xiii line pair ratio
  exhibited fast increase (within two minutes) from the pre-flare level
  of 5.01 × 10<SUP>9</SUP> cm<SUP>-3</SUP> to 3.16 × 10<SUP>10</SUP>
  cm<SUP>-3</SUP> during the flare peak. The nonthermal energy flux
  density deposited from the coronal acceleration site to the lower
  atmospheric layers during the flare peak was found to be 1.34 ×
  10<SUP>10</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP> for a low-energy
  cut-off that was estimated to be 16 keV. During the decline flare phase,
  we found a secondary intensity and density peak of lower amplitude
  that was preceded by upflows of ~15 km s<SUP>-1</SUP> that were
  detected in both lines. The flare was also accompanied by a filament
  eruption that was partly captured by the EIS observations. We derived
  Doppler velocities of 250-300 km s<SUP>-1</SUP> for the upflowing
  filament material. <BR /> Conclusions: The spectroscopic results
  for the flare peak are consistent with the scenario of explosive
  chromospheric evaporation, although a comparatively low value of the
  nonthermal energy flux density was determined for this phase of the
  flare. This outcome is discussed in the context of recent hydrodynamic
  simulations. It provides observational evidence that the response
  of the atmospheric plasma strongly depends on the properties of the
  electron beams responsible for the heating, in particular the steepness
  of the energy distribution. The secondary peak of line intensity and
  electron density detected during the decline phase is interpreted as a
  signature of flare loops being filled by expanding hot material that
  is due to chromospheric evaporation. <P />A movie is available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201527403/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Ground-based Observations of the Solar Sources of Space Weather
Authors: Veronig, A. M.; Pötzi, W.
2016ASPC..504..247V    Altcode: 2016arXiv160202721V
  Monitoring of the Sun and its activity is a task of growing importance
  in the frame of space weather research and awareness. Major space
  weather disturbances at Earth have their origin in energetic outbursts
  from the Sun: solar flares, coronal mass ejections and associated
  solar energetic particles. In this review we discuss the importance and
  complementarity of ground-based and space-based observations for space
  weather studies. The main focus is drawn on ground-based observations in
  the visible range of the spectrum, in particular in the diagnostically
  manifold Hα spectral line, which enables us to detect and study solar
  flares, filaments (prominences), filament (prominence) eruptions, and
  Moreton waves. Existing Hα networks such as the GONG and the Global
  High-Resolution Hα Network are discussed. As an example of solar
  observations from space weather research to operations, we present the
  system of real-time detection of Hα flares and filaments established
  at Kanzelhöhe Observatory (KSO; Austria) in the frame of the space
  weather segment of the ESA Space Situational Awareness programme
  (swe.ssa.esa.int). An evaluation of the system, which is continuously
  running since July 2013 is provided, covering an evaluation period
  of almost 2.5 years. During this period, KSO provided 3020 hours of
  real-time Hα observations at the ESA SWE portal. In total, 824 Hα
  flares were detected and classified by the real-time detection system,
  including 174 events of Hα importance class 1 and larger. For the total
  sample of events, 95 % of the automatically determined flare peak times
  lie within ±5 min of the values given in the official optical flares
  reports (by NOAA and KSO), and 76 % of the start times. The heliographic
  positions determined are better than ±5°. The probability of detection
  of flares of importance 1 or larger is 95 %, with a false alarm rate
  of 16 %. These numbers confirm the high potential of automatic flare
  detection and alerting from ground-based observatories.

---------------------------------------------------------
Title: Space Weather and confined CME events
Authors: Thalmann, Julia; Temmer, Manuela; Veronig, Astrid; Su, Yang
2016EGUGA..18.7517T    Altcode:
  The unusually large NOAA active region (AR) 2192, observed in October
  and November 2014, was outstanding in its productivity of major flares
  (GOES class M5 and larger). During the time when the AR faced Earth,
  major Space Weather events would have been expected. However, none of
  the X-flares was associated to a coronal mass ejection. Observational
  evidence for the confinement of the flare are large initial separation
  of the flare ribbons, together with an almost absent growth in ribbon
  separation. The low dynamic of the ribbons also suggests a reconnection
  site high up in the corona. From NLFF modeling we show that the
  arcade overlying the AR had a predominantly north-south oriented
  magnetic system, which served as a strong, also lateral, confinement
  for the flares at the core of the active region. From the magnetic
  field modeling we derived the decay of the constraining background,
  and it was found that the overlying field was only slowly decaying
  with height. We conclude that observational data of the solar surface,
  especially of flare ribbon dynamics as well as magnetic field models
  support Space Weather predictions.

---------------------------------------------------------
Title: Impact of coronal mass ejections on the Earth's thermosphere
and geoeffectiveness observed by ACE and GRACE: Statistical results
Authors: Krauss, Sandro; Temmer, Manuela; Veronig, Astrid; Baur, Oliver
2016EGUGA..18.9350K    Altcode:
  For the period July 2003 to August 2010, the interplanetary coronal
  mass ejection (ICME) catalogue maintained by Richardson and Cane
  lists 106 Earth-directed events, which have been measured in situ by
  plasma and field instruments on board the ACE satellite. We present a
  statistical investigation of the Earth's thermospheric neutral density
  response by means of accelerometer measurements collected by the
  Gravity Recovery And Climate Experiment (GRACE) satellites, which are
  available for 104 ICMEs in the data set. We relate the thermospheric
  density increase to various geomagnetic indices (e.g. Dst, AE, Kp,
  a-indices, ...) and characteristic ICME parameters (impact speed,
  southward magnetic field strength Bz). We find high correlations
  between the ICME Bz and thermospheric density enhancements as well as
  with most of the geomagnetic indices. Separating the response for the
  shock-sheath region and the magnetic structure of the ICME, we find
  for instance that the Dst and SYM-H indices reveal a tighter relation
  to the Bz minimum in the magnetic structure of the ICME, whereas the
  polar cap indices show higher correlations with the Bz minimum in the
  shock-sheath region. These results are expected to further stimulate
  progress in space weather understanding and applications regarding
  satellite operations.

---------------------------------------------------------
Title: Division E Commission 10: Solar Activity
Authors: Schrijver, Carolus J.; Fletcher, Lyndsay; van Driel-Gesztelyi,
   Lidia; Asai, Ayumi; Cally, Paul S.; Charbonneau, Paul; Gibson, Sarah
   E.; Gomez, Daniel; Hasan, Siraj S.; Veronig, Astrid M.; Yan, Yihua
2016IAUTA..29..245S    Altcode: 2015arXiv151003348S
  After more than half a century of community support related to the
  science of “solar activity”, IAU's Commission 10 was formally
  discontinued in 2015, to be succeeded by C.E2 with the same area
  of responsibility. On this occasion, we look back at the growth of
  the scientific disciplines involved around the world over almost a
  full century. Solar activity and fields of research looking into the
  related physics of the heliosphere continue to be vibrant and growing,
  with currently over 2,000 refereed publications appearing per year from
  over 4,000 unique authors, publishing in dozens of distinct journals
  and meeting in dozens of workshops and conferences each year. The
  size of the rapidly growing community and of the observational and
  computational data volumes, along with the multitude of connections
  into other branches of astrophysics, pose significant challenges;
  aspects of these challenges are beginning to be addressed through,
  among others, the development of new systems of literature reviews,
  machine-searchable archives for data and publications, and virtual
  observatories. As customary in these reports, we highlight some
  of the research topics that have seen particular interest over the
  most recent triennium, specifically active-region magnetic fields,
  coronal thermal structure, coronal seismology, flares and eruptions,
  and the variability of solar activity on long time scales. We close
  with a collection of developments, discoveries, and surprises that
  illustrate the range and dynamics of the discipline.

---------------------------------------------------------
Title: Injection of solar energetic particles into both loop legs
    of a magnetic cloud
Authors: Dresing, N.; Gómez-Herrero, R.; Heber, B.; Hidalgo, M. A.;
   Klassen, A.; Temmer, M.; Veronig, A.
2016A&A...586A..55D    Altcode: 2016arXiv160100491D
  Context. Each of the two Solar TErrestrial RElations Observatory
  (STEREO) spacecraft carries a Solar Electron and Proton Telescope
  (SEPT) which measures electrons and protons. Anisotropy observations
  are provided in four viewing directions: along the nominal magnetic
  field Parker spiral in the ecliptic towards the Sun (SUN) and
  away from the Sun (Anti-Sun/ASUN), and towards the north (NORTH)
  and south (SOUTH). The solar energetic particle (SEP) event on 7
  November 2013 was observed by both STEREO spacecraft, which were
  longitudinally separated by 68° at that time. While STEREO A observed
  the expected characteristics of an SEP event at a well-connected
  position, STEREO B detected a very anisotropic bi-directional
  distribution of near-relativistic electrons and was situated inside a
  magnetic-cloud-like structure during the early phase of the event. <BR
  /> Aims: We examine the source of the bi-directional SEP distribution
  at STEREO B. On the one hand this distribution could be caused by a
  double injection into both loop legs of the magnetic cloud (MC). On the
  other hand, a mirroring scenario where the incident beam is reflected in
  the opposite loop leg could be the reason. Furthermore, the energetic
  electron observations are used to probe the magnetic structure inside
  the magnetic cloud. <BR /> Methods: We investigate in situ plasma
  and magnetic field observations and show that STEREO B was embedded
  in an MC-like structure ejected three days earlier on 4 November from
  the same active region. We apply a Graduated Cylindrical Shell (GCS)
  model to the coronagraph observations from three viewpoints as well
  as the Global Magnetic Cloud (GMC) model to the in situ measurements
  at STEREO B to determine the orientation and topology of the MC
  close to the Sun and at 1 AU. We also estimate the path lengths of
  the electrons propagating through the MC to estimate the amount of
  magnetic field line winding inside the structure. <BR /> Results:
  The relative intensity and timing of the energetic electron increases
  in the different SEPT telescopes at STEREO B strongly suggest that the
  bi-directional electron distribution is formed by SEP injections in both
  loop legs of the MC separately instead of by mirroring farther away
  beyond the STEREO orbit. Observations by the Nançay Radioheliograph
  (NRH) of two distinct radio sources during the SEP injection further
  support the above scenario. The determined electron path lengths are
  around 50% longer than the estimated lengths of the loop legs of the
  MC itself (based on the GCS model) suggesting that the amount of field
  line winding is moderate.

---------------------------------------------------------
Title: 70 Years of Sunspot Observations at Kanzelhoehe Observatory
Authors: Pötzi, W.; Veronig, A.; Temmer, M.; Baumgartner, D. J.;
   Freislich, H.; Strutzmann, H.
2016CEAB...40..143P    Altcode:
  During World War II the German Airforce established a network of
  observatories, among them the Kanzelhöhe Observatory (KSO), which
  would provide information on solar activity in order to investigate
  the conditions of the Earth's ionosphere in terms of radio-wave
  propagation. Solar observations began already in 1943 with photographs
  of the photosphere and drawings of sunspots, plage regions and faculae,
  as well as patrol observations of the solar corona. Since 1944 relative
  sunspot numbers were derived, these relative numbers agree with the new
  International Sunspot Number tep[ISN,][]{SIDC,Clette2014} within ≈
  10%. However, revisiting the historical data, we also find periods with
  larger deviations. There were two main reasons for these deviations. On
  the one hand major instrumental changes took place and the instrument
  was relocated to another observation tower. On the other hand there
  were periods of frequent replacements of personnel. In the long term,
  the instrumental improvements led to better image quality, and a trend
  towards better seeing conditions since the year 2000 was found.

---------------------------------------------------------
Title: Formation of Coronal Large-Amplitude Waves and the
    Chromospheric Response
Authors: Vršnak, B.; Žic, T.; Lulić, S.; Temmer, M.; Veronig, A. M.
2016SoPh..291...89V    Altcode: 2015SoPh..tmp..175V
  An in-depth analysis of numerical simulations is performed to obtain
  a deeper insight into the nature of various phenomena occurring in the
  solar atmosphere as a consequence of the eruption of unstable coronal
  structures. Although the simulations take into account only the most
  basic characteristics of a flux-rope eruption, the simulation analysis
  reveals important information on various eruption-related effects. It
  quantifies the relation between the eruption dynamics and the evolution
  of the large-amplitude coronal magnetohydrodynamic wave and the
  associated chromospheric downward-propagating perturbation. We show that
  the downward propagation of the chromospheric Moreton-wave disturbance
  can be approximated by a constant-amplitude switch-on shock that moves
  through a medium of rapidly decreasing Alfvén velocity. The presented
  analysis reveals the nature of secondary effects that are observed
  as coronal upflows, secondary shocks, various forms of wave-trains,
  delayed large-amplitude slow disturbances, transient coronal depletions,
  etc. We also show that the eruption can cause an observable Moreton
  wave and a secondary coronal front only if it is powerful enough and
  is preferably characterized by significant lateral expansion. In weaker
  eruptions, only the coronal and transition-region signatures of primary
  waves are expected to be observed. In powerful events, the primary
  wave moves at an Alfvén Mach number significantly larger than 1 and
  steepens into a shock that is due to the nonlinear evolution of the
  wavefront. After the eruption-driven phase, the perturbation evolves
  as a freely propagating simple wave, characterized by a significant
  deceleration, amplitude decrease, and wave-profile broadening. In weak
  events the coronal wave does not develop into a shock and propagates
  at a speed close to the ambient magnetosonic speed.

---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
   Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
   Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
   M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
   Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
   V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
   P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
   A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W    Altcode:
  This document was created by the Solar Simulations for the Atacama
  Large Millimeter Observatory Network (SSALMON) in preparation of
  the first regular observations of the Sun with the Atacama Large
  Millimeter/submillimeter Array (ALMA), which are anticipated to start
  in ALMA Cycle 4 in October 2016. The science cases presented here
  demonstrate that a large number of scientifically highly interesting
  observations could be made already with the still limited solar
  observing modes foreseen for Cycle 4 and that ALMA has the potential
  to make important contributions to answering long-standing scientific
  questions in solar physics. With the proposal deadline for ALMA Cycle
  4 in April 2016 and the Commissioning and Science Verification campaign
  in December 2015 in sight, several of the SSALMON Expert Teams composed
  strategic documents in which they outlined potential solar observations
  that could be feasible given the anticipated technical capabilities
  in Cycle 4. These documents have been combined and supplemented
  with an analysis, resulting in recommendations for solar observing
  with ALMA in Cycle 4. In addition, the detailed science cases also
  demonstrate the scientific priorities of the solar physics community
  and which capabilities are wanted for the next observing cycles. The
  work on this White Paper effort was coordinated in close cooperation
  with the two international solar ALMA development studies led by
  T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
  further updated until the beginning of Cycle 4 in October 2016. In
  particular, we plan to adjust the technical capabilities of the solar
  observing modes once finally decided and to further demonstrate the
  feasibility and scientific potential of the included science cases by
  means of numerical simulations of the solar atmosphere and corresponding
  simulated ALMA observations.

---------------------------------------------------------
Title: Long-term trends of magnetic bright points. I. Number of
    magnetic bright points at disc centre
Authors: Utz, D.; Muller, R.; Thonhofer, S.; Veronig, A.; Hanslmeier,
   A.; Bodnárová, M.; Bárta, M.; del Toro Iniesta, J. C.
2016A&A...585A..39U    Altcode: 2015arXiv151107767U
  Context. The Sun shows an activity cycle that is caused by its varying
  global magnetic field. During a solar cycle, sunspots, I.e. extended
  regions of strong magnetic fields, occur in activity belts that are
  slowly migrating from middle to lower latitudes, finally arriving
  close to the equator during the cycle maximum phase. While this
  and other facts about the strong extended magnetic fields have been
  well known for centuries, much less is known about the solar cycle
  evolution of small-scale magnetic fields. Thus the question arises
  if similar principles exist for small-scale magnetic fields. <BR />
  Aims: To address this question, we study magnetic bright points (MBPs)
  as proxies for such small-scale, kG solar magnetic fields. This study is
  based on a homogeneous data set that covers a period of eight years. The
  number of detected MBPs versus time is analysed to find out if there
  is an activity cycle for these magnetic features too and, if so, how
  it is related to the sunspot cycle. <BR /> Methods: An automated MBP
  identification algorithm was applied to the synoptic Hinode/SOT G-band
  data over the period November 2006 to August 2014, I.e. covering the
  decreasing phase of Cycle 23 and the rise, maximum, and early decrease
  of Cycle 24. This data set includes, at the moment of investigation, a
  total of 4162 images, with about 2.9 million single MBP detections. <BR
  /> Results: After a careful preselection and monthly median filtering
  of the data, the investigation revealed that the number of MBPs close
  to the equator is coupled to the global solar cycle but shifted in time
  by about 2.5 yr. Furthermore, the instantaneous number of detected MBPs
  depends on the hemisphere, with one hemisphere being more prominent,
  I.e. showing a higher number of MBPs. After the end of Cycle 23 and at
  the starting point of Cycle 24, the more active hemisphere changed from
  south to north. Clear peaks in the detected number of MBPs are found
  at latitudes of about ±7°, in congruence with the positions of the
  sunspot belts at the end of the solar cycle. <BR /> Conclusions: These
  findings suggest that there is indeed a coupling between the activity of
  MBPs close to the equator with the global magnetic field. The results
  also indicate that a significant fraction of the magnetic flux that
  is visible as MBPs close to the equator originates from the sunspot
  activity belts. However, even during the minimum of MBP activity,
  a percentage as large as 60% of the maximum number of detected MBPs
  has been observed, which may be related to solar surface dynamo action.

---------------------------------------------------------
Title: The exceptional aspects of the confined X-class flares of
    solar active region 2192
Authors: Thalmann, Julia K.; Su, Yang; Temmer, Manuela; Veronig,
   Astrid M.
2016IAUS..320...60T    Altcode: 2016arXiv160503712T
  During late October 2014, active region NOAA 2192 caused an unusual high
  level of solar activity, within an otherwise weak solar cycle. While
  crossing the solar disk, during a period of 11 days, it was the source
  of 114 flares of GOES class C1.0 and larger, including 29 M- and 6
  X-flares. Surprisingly, none of the major flares (GOES class M5.0
  and larger) was accompanied by a coronal mass ejection, contrary to
  statistical tendencies found in the past. From modeling the coronal
  magnetic field of NOAA 2192 and its surrounding, we suspect that the
  cause of the confined character of the flares is the strong surrounding
  and overlying large-scale magnetic field. Furthermore, we find evidence
  for multiple magnetic reconnection processes within a single flare,
  during which electrons were accelerated to unusual high energies.

---------------------------------------------------------
Title: STEREO Observations of an SEP Event Injected Into Both Loop
    Legs of a Magnetic Cloud
Authors: Dresing, N.; Gomez-Herrero, R.; Heber, B.; Hidalgo, M. A. U.;
   Klassen, A.; Temmer, M.; Veronig, A.
2015AGUFMSH42A..06D    Altcode:
  On 7 Nov 2013 STEREO B was embedded in a magnetic-cloud (MC)
  like structure when an SEP event occurred reaching both STEREO
  spacecraft. The bi-drectional near relativistic electron distribution
  observed by STEREO B reveals such timing and relative intensity
  characteristics suggesting that the SEPs were injected separately into
  both loop legs of the MC. Observations by the Nancay Radioheliograph
  (NRH) of two distinct radio sources at the same time further support
  the above scenario. In order to derive the 3D morphology and average
  speed of the CME close to the Sun, we use the graduated cylindrical
  shell model (GCS) which is applied to the white-light coronagraph
  observations by the STEREO spacecraft and SOHO. Furthermore, a global
  magnetic topology model for magnetic clouds is applied to the in-situ
  measurements of the magnetic field. Both models suggest that the MC is
  strongly inclined with respect to the ecliptic yielding a north/south
  orientation. The energetic electron observations are used to probe the
  structure of the magnetic cloud: We determine the electron path lengths
  along both loop legs of the structure to infer the amount of field
  line twist inside the MC. The resulting path lengths are around 50%
  longer than the estimated lengths of the loop legs of the MC itself
  suggesting that the amount of field line winding is moderate.

---------------------------------------------------------
Title: Magnetic Reconnection Rates and Energy Release in a Confined
    X-class Flare
Authors: Veronig, A. M.; Polanec, W.
2015SoPh..290.2923V    Altcode: 2015SoPh..tmp..145V; 2015arXiv150907089V
  We study the energy-release process in the confined X1.6 flare that
  occurred on 22 October 2014 in AR 12192. Magnetic-reconnection rates
  and reconnection fluxes are derived from three different data sets:
  space-based data from the Atmospheric Imaging Assembly (AIA) 1600 Å
  filter onboard the Solar Dynamics Observatory (SDO) and ground-based
  Hα and Ca II K filtergrams from Kanzelhöhe Observatory. The
  magnetic-reconnection rates determined from the three data sets all
  closely resemble the temporal profile of the hard X-rays measured
  by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI),
  which are a proxy for the flare energy released into high-energy
  electrons. The total magnetic-reconnection flux derived lies between
  4.1 ×10<SUP>21</SUP>Mx (AIA 1600 Å) and 7.9 ×10<SUP>21</SUP>Mx
  (Hα ), which corresponds to about 2 to 4 % of the total unsigned
  flux of the strong source AR. Comparison of the magnetic-reconnection
  flux dependence on the GOES class for 27 eruptive events collected
  from previous studies (covering B to &gt;X 10 class flares) reveals
  a correlation coefficient of ≈0.8 in double-logarithmic space. The
  confined X1.6 class flare under study lies well within the distribution
  of the eruptive flares. The event shows a large initial separation
  of the flare ribbons and no separation motion during the flare. In
  addition, we note enhanced emission at flare-ribbon structures and
  hot loops connecting these structures before the event starts. These
  observations are consistent with the emerging-flux model, where newly
  emerging small flux tubes reconnect with pre-existing large coronal
  loops.

---------------------------------------------------------
Title: Coronal Response to an EUV Wave from DEM Analysis
Authors: Vanninathan, K.; Veronig, A. M.; Dissauer, K.; Madjarska,
   M. S.; Hannah, I. G.; Kontar, E. P.
2015ApJ...812..173V    Altcode: 2015arXiv150905269V
  Extreme-Ultraviolet (EUV) waves are globally propagating disturbances
  that have been observed since the era of the Solar and Heliospheric
  Observatory/Exteme-ultraviolet Imaging Telescope instrument. Although
  the kinematics of the wave front and secondary wave components have been
  widely studied, there is not much known about the generation and plasma
  properties of the wave. In this paper we discuss the effect of an EUV
  wave on the local plasma as it passes through the corona. We studied the
  EUV wave, generated during the 2011 February 15 X-class flare/coronal
  mass ejection event, using Differential Emission Measure diagnostics. We
  analyzed regions on the path of the EUV wave and investigated the local
  density and temperature changes. From our study we have quantitatively
  confirmed previous results that during wave passage the plasma visible
  in the Atmospheric Imaging Assembly (AIA) 171 Å channel is getting
  heated to higher temperatures corresponding to AIA 193 and 211 Å
  channels. We have calculated an increase of 6%-9% in density and 5%-6%
  in temperature during the passage of the EUV wave. We have compared
  the variation in temperature with the adiabatic relationship and
  have quantitatively demonstrated the phenomenon of heating due to
  adiabatic compression at the wave front. However, the cooling phase
  does not follow adiabatic relaxation but shows slow decay indicating
  slow energy release being triggered by the wave passage. We have also
  identified that heating is taking place at the front of the wave pulse
  rather than at the rear. Our results provide support for the case that
  the event under study here is a compressive fast-mode wave or a shock.

---------------------------------------------------------
Title: Thermospheric and geomagnetic responses to interplanetary
coronal mass ejections observed by ACE and GRACE: Statistical results
Authors: Krauss, S.; Temmer, M.; Veronig, A.; Baur, O.; Lammer, H.
2015JGRA..120.8848K    Altcode: 2015arXiv151003549K
  For the period July 2003 to August 2010, the interplanetary coronal mass
  ejection (ICME) catalogue maintained by Richardson and Cane lists 106
  Earth-directed events, which have been measured in situ by plasma and
  field instruments on board the ACE satellite. We present a statistical
  investigation of the Earth's thermospheric neutral density response by
  means of accelerometer measurements collected by the Gravity Recovery
  And Climate Experiment (GRACE) satellites, which are available for
  104 ICMEs in the data set, and its relation to various geomagnetic
  indices and characteristic ICME parameters such as the impact speed
  (vmax), southward magnetic field strength (B<SUB>z</SUB>). The majority
  of ICMEs causes a distinct density enhancement in the thermosphere,
  with up to a factor of 8 compared to the preevent level. We find high
  correlations between ICME B<SUB>z</SUB> and thermospheric density
  enhancements (≈0.9), while the correlation with the ICME impact speed
  is somewhat smaller (≈0.7). The geomagnetic indices revealing the
  highest correlations are Dst and SYM-H(≈0.9); the lowest correlations
  are obtained for Kp and AE (≈0.7), which show a nonlinear relation
  with the thermospheric density enhancements. Separating the response for
  the shock-sheath region and the magnetic structure of the ICME, we find
  that the Dst and SYM-H reveal a tighter relation to the B<SUB>z</SUB>
  minimum in the magnetic structure of the ICME, whereas the polar cap
  indices show higher correlations with the B<SUB>z</SUB> minimum in
  the shock-sheath region. Since the strength of the B<SUB>z</SUB>
  component—either in the sheath or in the magnetic structure of
  the ICME—is highly correlated (≈0.9) with the neutral density
  enhancement, we discuss the possibility of satellite orbital decay
  estimates based on magnetic field measurements at L1, i.e., before
  the ICME hits the Earth magnetosphere. These results are expected
  to further stimulate progress in space weather understanding and
  applications regarding satellite operations.

---------------------------------------------------------
Title: Dynamics of a Solar Prominence Tornado Observed by SDO/AIA
    on 2012 November 7-8
Authors: Mghebrishvili, Irakli; Zaqarashvili, Teimuraz V.; Kukhianidze,
   Vasil; Ramishvili, Giorgi; Shergelashvili, Bidzina; Veronig, Astrid;
   Poedts, Stefaan
2015ApJ...810...89M    Altcode: 2015arXiv150806788M
  We study the detailed dynamics of a solar prominence tornado using
  time series of 171, 304, 193, and 211 Å spectral lines obtained by
  the Solar Dynamics Observatory/Atmospheric Imaging Assembly during
  2012 November 7-8. The tornado first appeared at 08:00 UT, November 07,
  near the surface, gradually rose upwards with the mean speed of ∼1.5
  km s<SUP>-1</SUP> and persisted over 30 hr. Time-distance plots show
  two patterns of quasi-periodic transverse displacements of the tornado
  axis with periods of 40 and 50 minutes at different phases of the
  tornado evolution. The first pattern occurred during the rising phase
  and can be explained by the upward motion of the twisted tornado. The
  second pattern occurred during the later stage of evolution when the
  tornado already stopped rising and could be caused either by MHD kink
  waves in the tornado or by the rotation of two tornado threads around
  a common axis. The later hypothesis is supported by the fact that the
  tornado sometimes showed a double structure during the quasi-periodic
  phase. 211 and 193 Å spectral lines show a coronal cavity above
  the prominence/tornado, which started expansion at ∼13:00 UT and
  continuously rose above the solar limb. The tornado finally became
  unstable and erupted together with the corresponding prominence as
  coronal mass ejection (CME) at 15:00 UT, November 08. The final stage
  of the evolution of the cavity and the tornado-related prominence
  resembles the magnetic breakout model. On the other hand, the kink
  instability may destabilize the twisted tornado, and consequently
  prominence tornadoes can be used as precursors for CMEs.

---------------------------------------------------------
Title: 3D Tracking of small-scale convective upflows
Authors: Lemmerer, Birgit; Hanslmeier, Arnold; Veronig, Astrid;
   Muthsam, Herbert; Piantschitsch, Isabell
2015IAUGA..2247142L    Altcode:
  High resolution simulations and observations of the solar photosphere
  and convection zone show a new population of small granules with
  diameters less than 800 km. The mechanism of formation and dissipation
  is still unclear. We developed automated detection and tracking
  algorithms to study their evolution as well as their physical and
  statistical properties in 2D. We found that small granules may not
  result from the fragmentation of larger granules because they show a
  small variation in size from the point of appearance at the photosphere
  until their dissolution. In this study we present a newly developed 3D
  segmentation and tracking algorithm for the analysis of small-scale
  convective cells in high resolution simulations. We study the 3D
  topology and evolution of convective upflows and their interaction
  with strong vortex motions and magnetic flux tubes. We show that the
  evolution of small-scale convective upflows in the convection zone is
  mainly governed by strong vortex motions within downdrafts rather than
  by strong magnetic fields.

---------------------------------------------------------
Title: The exceptional aspects of the confined X-Flares of Solar
    Active Region 2192
Authors: Thalmann, Julia K.; Su, Yang; Temmer, Manuela; Veronig, Astrid
2015IAUGA..2215645T    Altcode:
  Active region NOAA 2192 showed an outstanding productivity
  of major (GOES class M5 and larger) two-ribbon flares lacking
  eruptive events. None of the X-flares was associated to a coronal
  mass ejection. The major confined flares on 2014 October 22 and 24
  originated from the active-region core and were prohibited to develop
  an associated mass ejection due to the confinement of the overlying
  strong magnetic field. In contrast, the single eruptive M-flare on
  October 24 originated from the outer parts of the active region, in the
  neighborhood of open large-scale fields, which allowed for the observed
  mass ejection. Analysis of the spacial and temporal characteristics
  of the major confined flares revealed exceptional aspects, including a
  large initial separation of the confined flares' ribbons and an almost
  absent growth in ribbon separation, suggesting a reconnection site
  high up in the corona. Furthermore, detailed analysis of a confined
  X-flare on October 22 provides evidence that magnetic field structures
  were repeatedly involved in magnetic reconnection, that a large number
  of electrons was accelerated to non-thermal energies but that only a
  small fraction out of these accelerated electrons was accelerated to
  high energies. We conclude the latter due to the unusual steepness
  of the associated power law spectrum. Finally, we demonstrate that
  a considerable portion of the magnetic energy released during the
  X-flare was consumed by the non-thermal flare energy.

---------------------------------------------------------
Title: Improvements on coronal hole detection in SDO/AIA images
    using supervised classification
Authors: Reiss, Martin A.; Hofmeister, Stefan J.; De Visscher, Ruben;
   Temmer, Manuela; Veronig, Astrid M.; Delouille, Véronique; Mampaey,
   Benjamin; Ahammer, Helmut
2015JSWSC...5A..23R    Altcode: 2015arXiv150606623R
  We demonstrate the use of machine learning algorithms in combination
  with segmentation techniques in order to distinguish coronal holes
  and filaments in SDO/AIA EUV images of the Sun. Based on two coronal
  hole detection techniques (intensity-based thresholding, SPoCA), we
  prepared datasets of manually labeled coronal hole and filament channel
  regions present on the Sun during the time range 2011-2013. By mapping
  the extracted regions from EUV observations onto HMI line-of-sight
  magnetograms we also include their magnetic characteristics. We computed
  shape measures from the segmented binary maps as well as first order
  and second order texture statistics from the segmented regions in
  the EUV images and magnetograms. These attributes were used for
  data mining investigations to identify the most performant rule to
  differentiate between coronal holes and filament channels. We applied
  several classifiers, namely Support Vector Machine (SVM), Linear Support
  Vector Machine, Decision Tree, and Random Forest, and found that all
  classification rules achieve good results in general, with linear SVM
  providing the best performances (with a true skill statistic of ≈
  0.90). Additional information from magnetic field data systematically
  improves the performance across all four classifiers for the SPoCA
  detection. Since the calculation is inexpensive in computing time,
  this approach is well suited for applications on real-time data. This
  study demonstrates how a machine learning approach may help improve
  upon an unsupervised feature extraction method.

---------------------------------------------------------
Title: Large-scale Contraction and Subsequent Disruption of Coronal
    Loops During Various Phases of the M6.2 Flare Associated with the
    Confined Flux Rope Eruption
Authors: Kushwaha, Upendra; Joshi, Bhuwan; Veronig, Astrid M.; Moon,
   Yong-Jae
2015ApJ...807..101K    Altcode: 2015arXiv150401888K
  We investigate evolutionary phases of an M6.2 flare and the associated
  confined eruption of a prominence. The pre-flare phase exhibits
  spectacular large-scale contraction of overlying extreme ultraviolet
  (EUV) coronal loops during which the loop system was subjected to
  an altitude decrease of ∼20 Mm (40% of the initial height) for an
  extended span of ∼30 minutes. This contraction phase is accompanied
  by sequential EUV brightenings associated with hard X-ray (HXR; up to 25
  keV) and microwave (MW) sources from low-lying loops in the core region
  which together with X-ray spectra indicate strong localized heating in
  the source region before the filament activation. With the onset of the
  flare’s impulsive phase, we detect HXR and MW sources that exhibit
  intricate temporal and spatial evolution in relation to the fast rise
  of the prominence. Following the flare maximum, the filament eruption
  slowed down and subsequently became confined within the large overlying
  active region loops. During the confinement process of the erupting
  prominence, we detect MW emission from the extended coronal region with
  multiple emission centroids, which likely represent emission from hot
  blobs of plasma formed after the collapse of the expanding flux rope and
  entailing prominence material. RHESSI spectroscopy reveals high plasma
  temperature (∼30 MK) and substantial non-thermal characteristics
  (δ ∼ 5) during the impulsive phase of the flare. The time evolution
  of thermal energy exhibits a good correspondence with the variations
  in cumulative non-thermal energy, which suggests that the energy of
  accelerated particles is efficiently converted to hot flare plasma,
  implying an effective validation of the Neupert effect.

---------------------------------------------------------
Title: Real-Time Solar Wind Prediction Based on SDO/AIA Coronal
    Hole Data
Authors: Rotter, T.; Veronig, A. M.; Temmer, M.; Vršnak, B.
2015SoPh..290.1355R    Altcode: 2015arXiv150106697R; 2015SoPh..tmp...37R
  We present an empirical model based on the visible area covered by
  coronal holes close to the central meridian with the aim to predict
  the solar wind speed at 1 AU with a lead time of up to four days in
  advance with a time resolution of one hour. Linear prediction functions
  are used to relate coronal hole areas to solar wind speed. The function
  parameters are automatically adapted by using the information from the
  previous three Carrington Rotations. Thus the algorithm automatically
  reacts to the changes of the solar wind speed during different phases
  of the solar cycle. The adaptive algorithm was applied to and tested
  on SDO/AIA-193 Å observations and ACE measurements during the years
  2011 - 2013, covering 41 Carrington Rotations. The solar wind needs
  on average 4.02±0.5 days to reach Earth. The algorithm produces good
  predictions for the 156 solar wind high-speed streams peak amplitudes
  with correlation coefficients of cc≈0.60. For 80 % of the peaks,
  the predicted arrival matches the ACE in situ measurements within a
  time window of 0.5 days. The same algorithm, using linear predictions,
  was also applied to predict the magnetic field strength in wind streams
  originating from coronal hole areas, but it did not give reliable
  predictions (cc≈0.15).

---------------------------------------------------------
Title: The Confined X-class Flares of Solar Active Region 2192
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
2015ApJ...801L..23T    Altcode: 2015arXiv150205157T
  The unusually large active region (AR) NOAA 2192, observed in 2014
  October, was outstanding in its productivity of major two-ribbon flares
  without coronal mass ejections. On a large scale, a predominantly
  north-south oriented magnetic system of arcade fields served as a strong
  top and lateral confinement for a series of large two-ribbon flares
  originating from the core of the AR. The large initial separation of
  the flare ribbons, together with an almost absent growth in ribbon
  separation, suggests a confined reconnection site high up in the
  corona. Based on a detailed analysis of the confined X1.6 flare on
  October 22, we show how exceptional the flaring of this AR was. We
  provide evidence for repeated energy release, indicating that the
  same magnetic field structures were repeatedly involved in magnetic
  reconnection. We find that a large number of electrons was accelerated
  to non-thermal energies, revealing a steep power-law spectrum, but
  that only a small fraction was accelerated to high energies. The total
  non-thermal energy in electrons derived (on the order of 10<SUP>25</SUP>
  J) is considerably higher than that in eruptive flares of class X1,
  and corresponds to about 10% of the excess magnetic energy present in
  the active-region corona.

---------------------------------------------------------
Title: Real-time Flare Detection in Ground-Based Hα Imaging at
    Kanzelhöhe Observatory
Authors: Pötzi, W.; Veronig, A. M.; Riegler, G.; Amerstorfer, U.;
   Pock, T.; Temmer, M.; Polanec, W.; Baumgartner, D. J.
2015SoPh..290..951P    Altcode: 2014arXiv1411.3896P; 2014SoPh..tmp..193P
  Kanzelhöhe Observatory (KSO) regularly performs high-cadence full-disk
  imaging of the solar chromosphere in the Hα and Ca II K spectral
  lines as well as in the solar photosphere in white light. In the frame
  of ESA's (European Space Agency) Space Situational Awareness (SSA)
  program, a new system for real-time Hα data provision and automatic
  flare detection was developed at KSO. The data and events detected
  are published in near real-time at ESA's SSA Space Weather portal
  (http://swe.ssa.esa.int/web/guest/kso-federated). In this article,
  we describe the Hα instrument, the image-recognition algorithms we
  developed, and the implementation into the KSO Hα observing system. We
  also present the evaluation results of the real-time data provision
  and flare detection for a period of five months. The Hα data provision
  worked in 99.96 % of the images, with a mean time lag of four seconds
  between image recording and online provision. Within the given criteria
  for the automatic image-recognition system (at least three Hα images
  are needed for a positive detection), all flares with an area ≥ 50
  micro-hemispheres that were located within 60° of the solar center
  and occurred during the KSO observing times were detected, a number of
  87 events in total. The automatically determined flare importance and
  brightness classes were correct in ∼ 85 %. The mean flare positions in
  heliographic longitude and latitude were correct to within ∼ 1°. The
  median of the absolute differences for the flare start and peak times
  from the automatic detections in comparison with the official NOAA
  (and KSO) visual flare reports were 3 min (1 min).

---------------------------------------------------------
Title: Geoeffectiveness of Coronal Mass Ejections in the SOHO Era
Authors: Dumbović, M.; Devos, A.; Vršnak, B.; Sudar, D.; Rodriguez,
   L.; Ruždjak, D.; Leer, K.; Vennerstrøm, S.; Veronig, A.
2015SoPh..290..579D    Altcode: 2014arXiv1410.3303D
  The main objective of the study is to determine the probability
  distributions of the geomagnetic Dst index as a function of the
  coronal mass ejection (CME) and solar flare parameters for the purpose
  of establishing a probabilistic forecast tool for the intensity of
  geomagnetic storms. We examined several CME and flare parameters as well
  as the effect of successive CME occurrence in changing the probability
  for a certain range of Dst index values. The results confirm some
  previously known relationships between remotely observed properties of
  solar eruptive events and geomagnetic storms: the importance of the
  initial CME speed, apparent width, source position, and the class of
  the associated solar flare. We quantify these relationships in a form
  that can be used for future space-weather forecasting. The results of
  the statistical study are employed to construct an empirical statistical
  model for predicting the probability of the geomagnetic storm intensity
  based on remote solar observations of CMEs and flares.

---------------------------------------------------------
Title: Initiation and Evolution of Global Coronal Waves
Authors: Vršnak, B.; Muhr, N.; Žic, T.; Lulić, S.; Kienreich,
   I. W.; Temmer, M.; Veronig, A. M.
2015CEAB...39...65V    Altcode:
  Some essential outcomes of a detailed analysis of the formation and
  evolution of the coronal EUV wave of 15 February 2011 are presented,
  focused on the relationship between the source region expansion, wave
  kinematics, and the evolution of the wave amplitude. The observations
  are explained in terms of the results of the numerical MHD simulations,
  providing new insights into the physical background of coronal waves,
  especially considering the nature of the relationship of the wave
  amplitude and propagation velocity in different phases of the wave
  evolution.

---------------------------------------------------------
Title: The real-time flare detection system at Kanzelhöhe Observatory
Authors: Pötzi, W.; Veronig, A.; Riegler, G.; Amerstorfer, U.; Pock,
   TH.; Temmer, M.; Polanec, W.; Baumgartner, D. J.
2015CEAB...39..125P    Altcode:
  Kanzelhöhe Observatory performs regular high-cadence full-disk
  observations of the solar chromosphere in the Hα and Ca II K spectral
  lines as well as the solar photosphere in white-light. In the frame
  of ESA's Space Situational Awareness (SSA) activities, a system for
  near real-time H-alpha image provision through the SSA Space Weather
  (SWE) portal (swe.ssa.esa.int) and for automatic alerting of flares
  and erupting filaments was developed. Image segmentation algorithms,
  for the automatic detection of solar filaments in real time H-alpha
  images have been developed and implemented at the Kanzelhöhe observing
  system. We present results of this system with respect to the automatic
  recognition and segmentation of flares on the Sun.

---------------------------------------------------------
Title: Forbush decreases associated to Stealth Coronal Mass Ejections
Authors: Heber, B.; Wallmann, C.; Galsdorf, D.; Herbst K.; Kühl,
   P.; Dumbovic, M.; Vršnak, B.; Veronig, A.; Temmer, M.; Möstl, C.;
   Dalla, S.
2015CEAB...39...75H    Altcode:
  Interplanetary coronal mass ejections (ICMEs) are structures in the
  solar wind that are the counterparts of coronal mass ejections (CMEs)
  at the Sun. It is commonly believed that enhanced magnetic fields
  in interplanetary shocks and solar ejecta as well as the increased
  turbulence in the solar wind sheath region are the cause of Forbush
  decreases (FDs) representing decreases of galactic cosmic ray (GCR)
  intensities. Recently, stealth CMEs i.e.~CMEs with no apparent solar
  surface association have become a subject in recent studies of solar
  activity. Whether all of such stealth CMEs can drive a FD is difficult
  to investigate on the basis of neutron monitor NM measurements because
  these measurements not only reflect the GCR intensity variation in
  interplanetary space but also the variation of the geomagnetic field as
  well as the conditions in the Earth atmosphere. Single detector counter
  from spacecraft instrumentation, here SOHO and Chandra EPHIN, exceed
  counting statistic of NMs allowing to determine intensity variation of
  less than 1 permil in interplanetary space on the basis of 30 minute
  count rate averages. Here we present the ongoing analysis of eleven
  stealth CMEs.

---------------------------------------------------------
Title: Statistical Analysis of Large-Scale EUV Waves Observed by
    STEREO/EUVI
Authors: Muhr, N.; Veronig, A. M.; Kienreich, I. W.; Vršnak, B.;
   Temmer, M.; Bein, B. M.
2014SoPh..289.4563M    Altcode: 2014arXiv1408.2513M; 2014SoPh..tmp..126M
  We statistically analyzed the kinematical evolution and wave pulse
  characteristics of 60 strong large-scale EUV wave events that
  occurred during January 2007 to February 2011 with the STEREO
  twin spacecraft. For the start velocity, the arithmetic mean
  is 312±115 km s<SUP>−1</SUP> (within a range of 100 - 630 km
  s<SUP>−1</SUP>). For the mean (linear) velocity, the arithmetic
  mean is 254±76 km s<SUP>−1</SUP> (within a range of 130 - 470
  km s<SUP>−1</SUP>). 52 % of all waves under study show a distinct
  deceleration during their propagation (a≤−50 m s<SUP>−2</SUP>),
  the other 48 % are consistent with a constant speed within the
  uncertainties (−50≤a≤50 m s<SUP>−2</SUP>). The start velocity
  and the acceleration are strongly anticorrelated with c≈−0.8,
  i.e. initially faster events undergo stronger deceleration than
  slower events. The (smooth) transition between constant propagation
  for slow events and deceleration in faster events occurs at an EUV wave
  start-velocity of v≈230 km s<SUP>−1</SUP>, which corresponds well to
  the fast-mode speed in the quiet corona. These findings provide strong
  evidence that the EUV waves under study are indeed large-amplitude
  fast-mode MHD waves. This interpretation is also supported by the
  correlations obtained between the peak velocity and the peak amplitude,
  impulsiveness, and build-up time of the disturbance. We obtained
  the following association rates of EUV wave events with other solar
  phenomena: 95 % are associated with a coronal mass ejection (CME),
  74 % to a solar flare, 15 % to interplanetary type II bursts, and 22
  % to coronal type II bursts. These findings are consistent with the
  interpretation that the associated CMEs are the driving agents of the
  EUV waves.

---------------------------------------------------------
Title: Heliospheric Propagation of Coronal Mass Ejections: Comparison
    of Numerical WSA-ENLIL+Cone Model and Analytical Drag-based Model
Authors: Vršnak, B.; Temmer, M.; Žic, T.; Taktakishvili, A.;
   Dumbović, M.; Möstl, C.; Veronig, A. M.; Mays, M. L.; Odstrčil, D.
2014ApJS..213...21V    Altcode:
  Real-time forecasting of the arrival of coronal mass ejections (CMEs) at
  Earth, based on remote solar observations, is one of the central issues
  of space-weather research. In this paper, we compare arrival-time
  predictions calculated applying the numerical "WSA-ENLIL+Cone
  model" and the analytical "drag-based model" (DBM). Both models use
  coronagraphic observations of CMEs as input data, thus providing an
  early space-weather forecast two to four days before the arrival of
  the disturbance at the Earth, depending on the CME speed. It is shown
  that both methods give very similar results if the drag parameter Γ =
  0.1 is used in DBM in combination with a background solar-wind speed
  of w = 400 km s<SUP>-1</SUP>. For this combination, the mean value
  of the difference between arrival times calculated by ENLIL and DBM
  is \overline{Δ }=0.09+/- 9.0 hr with an average of the absolute-value
  differences of \overline{\vert Δ \vert }=7.1 hr. Comparing the observed
  arrivals (O) with the calculated ones (C) for ENLIL gives O - C = -0.3
  ± 16.9 hr and, analogously, O - C = +1.1 ± 19.1 hr for DBM. Applying
  Γ = 0.2 with w = 450 km s<SUP>-1</SUP> in DBM, one finds O - C =
  -1.7 ± 18.3 hr, with an average of the absolute-value differences
  of 14.8 hr, which is similar to that for ENLIL, 14.1 hr. Finally,
  we demonstrate that the prediction accuracy significantly degrades
  with increasing solar activity.

---------------------------------------------------------
Title: Impulsive Energy Release and Non-thermal Emission in a Confined
    M4.0 Flare Triggered by Rapidly Evolving Magnetic Structures
Authors: Kushwaha, Upendra; Joshi, Bhuwan; Cho, Kyung-Suk; Veronig,
   Astrid; Tiwari, Sanjiv Kumar; Mathew, S. K.
2014ApJ...791...23K    Altcode: 2014arXiv1407.8115K
  We present observations of a confined M4.0 flare from NOAA 11302
  on 2011 September 26. Observations at high temporal, spatial, and
  spectral resolution from the Solar Dynamics Observatory, Reuven Ramaty
  High Energy Solar Spectroscopic Imager, and Nobeyama Radioheliograph
  observations enabled us to explore the possible triggering and energy
  release processes of this flare despite its very impulsive behavior
  and compact morphology. The flare light curves exhibit an abrupt rise
  of non-thermal emission with co-temporal hard X-ray (HXR) and microwave
  (MW) bursts that peaked instantly without any precursor emission. This
  stage was associated with HXR emission up to 200 keV that followed
  a power law with photon spectral index (γ) ~ 3. Another non-thermal
  peak, observed 32 s later, was more pronounced in the MW flux than the
  HXR profiles. Dual peaked structures in the MW and HXR light curves
  suggest a two-step magnetic reconnection process. Extreme ultraviolet
  (EUV) images exhibit a sequential evolution of the inner and outer core
  regions of magnetic loop systems while the overlying loop configuration
  remained unaltered. Combined observations in HXR, (E)UV, and Hα
  provide support for flare models involving the interaction of coronal
  loops. The magnetograms obtained by the Helioseismic and Magnetic
  Imager reveal emergence of magnetic flux that began ~five hr before the
  flare. However, the more crucial changes in the photospheric magnetic
  flux occurred about one minute prior to the flare onset with opposite
  polarity magnetic transients appearing at the early flare location
  within the inner core region. The spectral, temporal, and spatial
  properties of magnetic transients suggest that the sudden changes
  in the small-scale magnetic field have likely triggered the flare by
  destabilizing the highly sheared pre-flare magnetic configuration.

---------------------------------------------------------
Title: Combined Multipoint Remote and in situ Observations of the
    Asymmetric Evolution of a Fast Solar Coronal Mass Ejection
Authors: Rollett, T.; Möstl, C.; Temmer, M.; Frahm, R. A.; Davies,
   J. A.; Veronig, A. M.; Vršnak, B.; Amerstorfer, U. V.; Farrugia,
   C. J.; Žic, T.; Zhang, T. L.
2014ApJ...790L...6R    Altcode: 2014arXiv1407.4687R
  We present an analysis of the fast coronal mass ejection (CME) of 2012
  March 7, which was imaged by both STEREO spacecraft and observed in
  situ by MESSENGER, Venus Express, Wind, and Mars Express. Based on
  detected arrivals at four different positions in interplanetary space,
  it was possible to strongly constrain the kinematics and the shape of
  the ejection. Using the white-light heliospheric imagery from STEREO-A
  and B, we derived two different kinematical profiles for the CME
  by applying the novel constrained self-similar expansion method. In
  addition, we used a drag-based model to investigate the influence of
  the ambient solar wind on the CME's propagation. We found that two
  preceding CMEs heading in different directions disturbed the overall
  shape of the CME and influenced its propagation behavior. While the
  Venus-directed segment underwent a gradual deceleration (from ~2700 km
  s<SUP>-1</SUP> at 15 R <SUB>⊙</SUB> to ~1500 km s<SUP>-1</SUP> at 154
  R <SUB>⊙</SUB>), the Earth-directed part showed an abrupt retardation
  below 35 R <SUB>⊙</SUB> (from ~1700 to ~900 km s<SUP>-1</SUP>). After
  that, it was propagating with a quasi-constant speed in the wake of
  a preceding event. Our results highlight the importance of studies
  concerning the unequal evolution of CMEs. Forecasting can only be
  improved if conditions in the solar wind are properly taken into
  account and if attention is also paid to large events preceding the
  one being studied.

---------------------------------------------------------
Title: Solar Energetic Particles and Associated EIT Disturbances in
    Solar Cycle 23
Authors: Miteva, R.; Klein, K. -L.; Kienreich, I.; Temmer, M.; Veronig,
   A.; Malandraki, O. E.
2014SoPh..289.2601M    Altcode: 2014arXiv1402.1676M; 2014SoPh..tmp...37M
  We explore the link between solar energetic particles (SEPs) observed
  at 1 AU and large-scale disturbances propagating in the solar corona,
  named after the Extreme ultraviolet Imaging Telescope (EIT) as EIT
  waves, which trace the lateral expansion of a coronal mass ejection
  (CME). A comprehensive search for SOHO/EIT waves was carried out for
  179 SEP events during Solar Cycle 23 (1997 - 2006). 87 % of the SEP
  events were found to be accompanied by EIT waves. In order to test if
  the EIT waves play a role in the SEP acceleration, we compared their
  extrapolated arrival time at the footpoint of the Parker spiral with
  the particle onset in the 26 eastern SEP events that had no direct
  magnetic connection to the Earth. We find that the onset of proton
  events was generally consistent with this scenario. However, in a
  number of cases the first near-relativistic electrons were detected too
  early. Furthermore, the electrons had in general only weakly anisotropic
  pitch-angle distributions. This poses a problem for the idea that the
  SEPs were accelerated by the EIT wave or in any other spatially confined
  region in the low corona. The presence of weak electron anisotropies in
  SEP events from the eastern hemisphere suggests that transport processes
  in interplanetary space, including cross-field diffusion, play a role
  in giving the SEPs access to a broad range of helio-longitudes.

---------------------------------------------------------
Title: Connecting Speeds, Directions and Arrival Times of 22 Coronal
    Mass Ejections from the Sun to 1 AU
Authors: Möstl, C.; Amla, K.; Hall, J. R.; Liewer, P. C.; De Jong,
   E. M.; Colaninno, R. C.; Veronig, A. M.; Rollett, T.; Temmer, M.;
   Peinhart, V.; Davies, J. A.; Lugaz, N.; Liu, Y. D.; Farrugia, C. J.;
   Luhmann, J. G.; Vršnak, B.; Harrison, R. A.; Galvin, A. B.
2014ApJ...787..119M    Altcode: 2014arXiv1404.3579M
  Forecasting the in situ properties of coronal mass ejections (CMEs)
  from remote images is expected to strongly enhance predictions of
  space weather and is of general interest for studying the interaction
  of CMEs with planetary environments. We study the feasibility of using
  a single heliospheric imager (HI) instrument, imaging the solar wind
  density from the Sun to 1 AU, for connecting remote images to in situ
  observations of CMEs. We compare the predictions of speed and arrival
  time for 22 CMEs (in 2008-2012) to the corresponding interplanetary
  coronal mass ejection (ICME) parameters at in situ observatories
  (STEREO PLASTIC/IMPACT, Wind SWE/MFI). The list consists of front-
  and backsided, slow and fast CMEs (up to 2700 km s<SUP>-1</SUP>). We
  track the CMEs to 34.9 ± 7.1 deg elongation from the Sun with J maps
  constructed using the SATPLOT tool, resulting in prediction lead times
  of -26.4 ± 15.3 hr. The geometrical models we use assume different
  CME front shapes (fixed-Φ, harmonic mean, self-similar expansion) and
  constant CME speed and direction. We find no significant superiority
  in the predictive capability of any of the three methods. The absolute
  difference between predicted and observed ICME arrival times is 8.1 ±
  6.3 hr (rms value of 10.9 hr). Speeds are consistent to within 284 ±
  288 km s<SUP>-1</SUP>. Empirical corrections to the predictions enhance
  their performance for the arrival times to 6.1 ± 5.0 hr (rms value
  of 7.9 hr), and for the speeds to 53 ± 50 km s<SUP>-1</SUP>. These
  results are important for Solar Orbiter and a space weather mission
  positioned away from the Sun-Earth line.

---------------------------------------------------------
Title: Morphology of an ICME-event derived by Multi-point in Situ
    and Heliospheric Imaging Data
Authors: Rollett, Tanja; Möstl, Christian; Temmer, Manuela; Veronig,
   Astrid M.; Frahm, Rudy A.; Davies, Jackie A.; Vrsnak, Bojan; Farrugia,
   Charles J.; Amerstorfer, Ute V.
2014EGUGA..1610892R    Altcode:
  We show the analysis of an outstanding fast interplanetary coronal
  mass ejection (ICME) of 07 March 2012, which has been observed
  stereoscopically from both STEREO spacecraft. Assuming self-similar
  expansion and constant direction of motion we derive the kinematical
  profiles for the eastern and the western part of the roughly
  Earth-directed ICME. As additional constraints we use the huge
  advantage of in situ measurements at various locations during the
  ICME's propagation, namely from Venus Express, Messenger, Wind and
  Mars Express. We found that the eastern part of the ICME had a much
  higher propagation speed than its western part. Using the drag-based
  model, a model for the propagation of ICMEs in the inner heliosphere,
  we analyzed the influence of the drag on both sides of the ICME due
  to the surrounding solar wind conditions. These different solar wind
  conditions could have been the reason for the differing velocities
  and therefore for a distortion of the ICME front. These studies are
  fundamental in order to deepen the understanding of ICME evolution
  and to enhance existing forecasting methods.

---------------------------------------------------------
Title: Connecting speeds, directions and arrival times of 22 coronal
    mass ejections from the Sun to 1 AU
Authors: Möstl, Christian; Amla, Keshav; Hall, Jeff R.; Liewer,
   Paulett C.; DeJong, Eric M.; Colaninno, Robin C.; Veronig, Astrid M.;
   Rollett, Tanja; Temmer, Manuela; Peinhart, Vanessa; Davies, Jackie
   A.; Lugaz, Noé; Liu, Ying; Farrugia, Charles J.; Luhmann, Janet G.;
   Vrsnak, Bojan; Harrison, Richard A.; Galvin, Antoinette B.
2014EGUGA..16.1755M    Altcode:
  Forecasting in situ properties of coronal mass ejections (CMEs) from
  remote images is expected to strongly enhance predictions of space
  weather, and is of general interest for studying the interaction of
  the solar wind with planetary environments. We study the feasibility of
  using a heliospheric imager (HI) instrument, which is able to image the
  solar wind density along the full Sun to 1 AU distance, for connecting
  remote images to in situ observations of CMEs. Such an instrument
  is currently in operation on each of the two STEREO spacecraft. We
  compare the predictions for speed and arrival time for 22 different
  CME events (between 2008-2012), each observed remotely by one STEREO
  spacecraft, to the interplanetary coronal mass ejection (ICME) speed and
  arrival time observed at in situ observatories (STEREO PLASTIC/IMPACT,
  Wind SWE/MFI). We use croissant modeling for STEREO/COR2, and with a
  single-spacecraft STEREO/HI instrument, we track each CME to 34.9 ± 7.1
  degree elongation from the Sun with J-maps constructed with the SATPLOT
  tool. We then fit geometrical models to each track, assuming different
  CME front shapes (Fixed-Φ, Harmonic Mean, Self-Similar Expansion),
  and constant CME speed and direction. We find no significant preference
  in the predictive capability for any of the three geometrical modeling
  methods used on the full event list, consisting of front- and backsided,
  slow and fast CMEs (up to 2700 km s-1). The absolute difference between
  predicted and observed ICME arrival times is 8.1 ± 6.4 hours (rms
  value of 10.9h), and speeds are consistent within 284 ± 291 km s-1,
  including the geometric effects of CME apex or flank encounters. We
  derive new empirical corrections to the imaging results, enhancing
  the performance of the arrival time predictions to 6.1 ± 5.0 hours
  (rms value of 7.9h), and the speed predictions to 53 ± 50 km s-1,
  for this particular set of events. The prediction lead time is around
  1 day (-26.4 ± 15.3h). CME directions given by the HI methods differ
  considerably, and biases are found on the order of 30-50 degree in
  heliospheric longitude, consistent with theoretical expectations. These
  results are of interest concerning future missions such as Solar Orbiter
  or a dedicated space weather mission positioned remotely from the Earth.

---------------------------------------------------------
Title: Comparative Study of MHD Modeling of the Background Solar Wind
Authors: Gressl, C.; Veronig, A. M.; Temmer, M.; Odstrčil, D.;
   Linker, J. A.; Mikić, Z.; Riley, P.
2014SoPh..289.1783G    Altcode: 2013arXiv1312.1220G
  Knowledge about the background solar wind plays a crucial role in
  the framework of space-weather forecasting. In-situ measurements
  of the background solar wind are only available for a few points in
  the heliosphere where spacecraft are located, therefore we have to
  rely on heliospheric models to derive the distribution of solar-wind
  parameters in interplanetary space. We test the performance of different
  solar-wind models, namely Magnetohydrodynamic Algorithm outside
  a Sphere/ENLIL (MAS/ENLIL), Wang-Sheeley-Arge/ENLIL (WSA/ENLIL),
  and MAS/MAS, by comparing model results with in-situ measurements
  from spacecraft located at 1 AU distance to the Sun (ACE, Wind). To
  exclude the influence of interplanetary coronal mass ejections
  (ICMEs), we chose the year 2007 as a time period with low solar
  activity for our comparison. We found that the general structure of the
  background solar wind is well reproduced by all models. The best model
  results were obtained for the parameter solar-wind speed. However,
  the predicted arrival times of high-speed solar-wind streams have
  typical uncertainties of the order of about one day. Comparison of
  model runs with synoptic magnetic maps from different observatories
  revealed that the choice of the synoptic map significantly affects
  the model performance.

---------------------------------------------------------
Title: Response of the Earth's thermosphere to interplanetary coronal
    mass ejections
Authors: Krauss, S.; Temmer, M.; Lammer, H.; Veronig, A.; Baur, O.;
   Pfleger, M.; Boudjada, M. Y.; Leitzinger, M.; Besser, B. P.
2014EPSC....9..724K    Altcode:
  In this contribution we address the Earth's thermospheric response to
  interplanetary coronal mass ejections. We investigate several ICME
  events by means of neutral density measurements from the low-Earth
  orbiting satellites GRACE. Furthermore we correlate these observations
  with data from the ACE satellite located at L1 upstream of the Earth. By
  analyzing the data, high correlations between the neutral density and
  various combinations of ICME parameters can be found.

---------------------------------------------------------
Title: Asymmetry in the CME-CME Interaction Process for the Events
    from 2011 February 14-15
Authors: Temmer, M.; Veronig, A. M.; Peinhart, V.; Vršnak, B.
2014ApJ...785...85T    Altcode: 2014arXiv1402.6891T
  We present a detailed study of the interaction process of two coronal
  mass ejections (CMEs) successively launched on 2011 February 14 (CME1)
  and 2011 February 15 (CME2). Reconstructing the three-dimensional
  shape and evolution of the flux ropes, we verify that the two CMEs
  interact. The frontal structure of both CMEs, measured along different
  position angles (PAs) over the entire latitudinal extent, reveals
  differences in the kinematics for the interacting flanks and the
  apexes. The interaction process is strongly PA-dependent in terms of
  timing as well as kinematical evolution. The central interaction occurs
  along PA-100°, which shows the strongest changes in kinematics. During
  interaction, CME1 accelerates from ~400 km s<SUP>-1</SUP> to ~700 km
  s<SUP>-1</SUP> and CME2 decelerates from ~1300 km s<SUP>-1</SUP> to ~600
  km s<SUP>-1</SUP>. Our results indicate that a simplified scenario such
  as inelastic collision may not be sufficient to describe the CME-CME
  interaction. The magnetic field structures of the intertwining flux
  ropes and the momentum transfer due to shocks each play an important
  role in the interaction process.

---------------------------------------------------------
Title: Solar Magnetized Tornadoes: Rotational Motion in a Tornado-like
    Prominence
Authors: Su, Yang; Gömöry, Peter; Veronig, Astrid; Temmer, Manuela;
   Wang, Tongjiang; Vanninathan, Kamalam; Gan, Weiqun; Li, YouPing
2014ApJ...785L...2S    Altcode: 2013arXiv1312.5226S
  Su et al. proposed a new explanation for filament formation and
  eruption, where filament barbs are rotating magnetic structures driven
  by underlying vortices on the surface. Such structures have been noticed
  as tornado-like prominences when they appear above the limb. They may
  play a key role as the source of plasma and twist in filaments. However,
  no observations have successfully distinguished rotational motion of
  the magnetic structures in tornado-like prominences from other motions
  such as oscillation and counter-streaming plasma flows. Here we report
  evidence of rotational motions in a tornado-like prominence. The
  spectroscopic observations in two coronal lines were obtained from a
  specifically designed Hinode/EIS observing program. The data revealed
  the existence of both cold and million-degree-hot plasma in the
  prominence leg, supporting the so-called prominence-corona transition
  region. The opposite velocities at the two sides of the prominence and
  their persistent time evolution, together with the periodic motions
  evident in SDO/AIA dark structures, indicate a rotational motion of
  both cold and hot plasma with a speed of ~5 km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: Two-dimensional segmentation of small convective patterns in
    radiation hydrodynamics simulations
Authors: Lemmerer, B.; Utz, D.; Hanslmeier, A.; Veronig, A.; Thonhofer,
   S.; Grimm-Strele, H.; Kariyappa, R.
2014A&A...563A.107L    Altcode: 2015arXiv150500325L
  Context. Recent results from high-resolution solar granulation
  observations indicate the existence of a population of small granular
  cells that are smaller than 600 km in diameter. These small convective
  cells strongly contribute to the total area of granules and are located
  in the intergranular lanes, where they form clusters and chains. <BR />
  Aims: We study high-resolution radiation hydrodynamics simulations of
  the upper convection zone and photosphere to detect small granular
  cells, define their spatial alignment, and analyze their physical
  properties. <BR /> Methods: We developed an automated image-segmentation
  algorithm specifically adapted to high-resolution simulations to
  identify granules. The resulting segmentation masks were applied to
  physical quantities, such as intensity and vertical velocity profiles,
  provided by the simulation. A new clustering algorithm was developed
  to study the alignment of small granular cells. <BR /> Results:
  Small granules make a distinct contribution to the total area of
  granules and form clusters of chain-like alignments. The simulation
  profiles demonstrate a different nature for small granular cells
  because they exhibit on average lower intensities, lower horizontal
  velocities, and are located deeper inside of convective layers than
  regular granules. Their intensity distribution deviates from a normal
  distribution as known for larger granules, and follows a Weibull
  distribution.

---------------------------------------------------------
Title: Kinematics of Interacting ICMEs and Related Forbush Decrease:
    Case Study
Authors: Maričić, D.; Vršnak, B.; Dumbović, M.; Žic, T.; Roša,
   D.; Hržina, D.; Lulić, S.; Romštajn, I.; Bušić, I.; Salamon, K.;
   Temmer, M.; Rollett, T.; Veronig, A.; Bostanjyan, N.; Chilingarian,
   A.; Mailyan, B.; Arakelyan, K.; Hovhannisyan, A.; Mujić, N.
2014SoPh..289..351M    Altcode:
  We study heliospheric propagation and some space weather aspects of
  three Earth-directed interplanetary coronal mass ejections (ICMEs),
  successively launched from the active region AR 11158 in the period
  13 - 15 February 2011. From the analysis of the ICME kinematics,
  morphological evolution, and in situ observations, we infer that the
  three ICMEs interacted on their way to Earth, arriving together at 1
  AU as a single interplanetary disturbance. Detailed analysis of the
  in situ data reveals complex internal structure of the disturbance,
  where signatures of the three initially independent ICMEs could be
  recognized. The analysis also reveals compression and heating of the
  middle ICME, as well as ongoing magnetic reconnection between the
  leading and the middle ICME. We present evidence showing that the
  propagation of these two, initially slower ICMEs, was boosted by the
  fastest, third ICME. Finally, we employ the ground-based cosmic ray
  observations, to show that this complex disturbance produced a single
  cosmic ray event, i.e., a simple Forbush decrease (FD). The results
  presented provide a better understanding of the ICME interactions and
  reveal effects that should be taken into account in forecasting of
  the arrival of such compound structures.

---------------------------------------------------------
Title: Detection of small convective patterns in observations and
    simulations
Authors: Lemmerer, B.; Utz, D.; Hanslmeier, A.; Veronig, A.;
   Grimm-Strele, H.; Thonhofer, S.; Piantschitsch, I.
2014CEAB...38...19L    Altcode:
  Recent results from high resolution solar granulation observations
  indicate the existence of a population of small granular cells on
  scales below 600 km in diameter, located in the intergranular lanes. We
  studied a set of Hinode SOT images and high resolution radiation
  hydrodynamics simulations in order to analyze small granular cells and
  to study their physical properties. An automated image segmentation
  algorithm specifically adapted to high resolution simulations for the
  identification of granules was developed. The algorithm was also used
  to analyze and compare physical quantities provided by the simulation
  and the observations. We found that small granules make a distinct
  contribution to the total area of granules. Both in observations and
  simulations, small granular cells exhibit on average lower intensities
  and vertical velocities.

---------------------------------------------------------
Title: Identification of coronal holes and filament channels in
    SDO/AIA 193Å images via geometrical classification methods
Authors: Reiss, M.; Temmer, M.; Rotter, T.; Hofmeister, S. J.; Veronig,
   A. M.
2014CEAB...38...95R    Altcode: 2014arXiv1408.2777R
  In this study, we describe and evaluate shape measures for
  distinguishing between coronal holes and filament channels as
  observed in Extreme Ultraviolet (EUV) images of the Sun. For a set
  of well-observed coronal hole and filament channel regions extracted
  from SDO/AIA 193Å images we analyze their intrinsic morphology during
  the period 2011 to 2013, by using well known shape measures from the
  literature and newly developed geometrical classification methods. The
  results suggest an asymmetry in the morphology of filament channels
  giving support for the sheared arcade or weakly twisted flux rope model
  for filaments. We find that the proposed shape descriptors have the
  potential to reduce coronal hole classification errors and are eligible
  for screening techniques in order to improve the forecasting of solar
  wind high-speed streams from CH observations in solar EUV images.

---------------------------------------------------------
Title: Signatures of magnetic reconnection during the evolutionary
    phases of a prominence eruption and associated X1.8 flare
Authors: Joshi, Bhuwan; Kushwaha, Upendra; Cho, KyungSuk; Veronig,
   Astrid
2014IAUS..300..424J    Altcode:
  In this paper, we present RHESSI and TRACE observations of multiple
  flare activity that occurred in the active region NOAA 10656 on 2004
  August 18. Out of four successive flares, there were three events
  of class-C while the final event was a major X1.8 solar eruptive
  flare. During localized C-class flares, the filament undergoes slow yet
  crucial morphological evolution. The filament eruption is accompanied
  with an X1.8 flare during which multiple HXR bursts are observed up to
  100-300 keV energies. From the location, timing, strength, and spectrum
  of HXR emission, we conclude that the prominence eruption is driven by
  the distinct events of magnetic reconnection occurring in the current
  sheet below the erupting prominence. These multi-wavelength observations
  also provide evidence for tether-cutting reconnection as the triggering
  mechanism for filament eruption and associated X-class flare.

---------------------------------------------------------
Title: A system for near real-time detection of filament eruptions
    at Kanzelhöhe Observatory
Authors: Pötzi, Werner; Riegler, Gernot; Veronig, Astrid; Pock,
   Thomas; Möstl, Ute
2014IAUS..300..519P    Altcode:
  Kanzelhöhe Observatory (kso.ac.at) performs regular high-cadence
  full-disk observations of the solar chromosphere in the Hα and CaIIK
  spectral lines as well as the solar photosphere in white-light. In the
  frame of ESA's Space Situational Awareness (SSA) activities, a new
  system for near real-time Hα image provision through the SSA Space
  Weather (SWE) portal (swe.ssa.esa.int) and for automatic alerting of
  flares and erupting filaments is under development. Image segmentation
  algorithms, based on optical flow image registration, for the automatic
  detection of solar filaments in real time Hα images have been developed
  and implemented at the Kanzelhöhe observing system. We present first
  results of this system with respect to the automatic recognition and
  segmentation of filaments and filament eruptions on the Sun.

---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections by Sunspot Rotation
Authors: Valori, G.; Török, T.; Temmer, M.; Veronig, A. M.; van
   Driel-Gesztelyi, L.; Vršnak, B.
2014IAUS..300..201V    Altcode:
  We report observations of a filament eruption, two-ribbon flare, and
  coronal mass ejection (CME) that occurred in Active Region NOAA 10898
  on 6 July 2006. The filament was located South of a strong sunspot that
  dominated the region. In the evolution leading up to the eruption, and
  for some time after it, a counter-clockwise rotation of the sunspot of
  about 30 degrees was observed. We suggest that the rotation triggered
  the eruption by progressively expanding the magnetic field above the
  filament. To test this scenario, we study the effect of twisting
  the initially potential field overlying a pre-existing flux rope,
  using three-dimensional zero-β MHD simulations. We consider a magnetic
  configuration whose photospheric flux distribution and coronal structure
  is guided by the observations and a potential field extrapolation. We
  find that the twisting leads to the expansion of the overlying field. As
  a consequence of the progressively reduced magnetic tension, the flux
  rope quasi-statically adapts to the changed environmental field, rising
  slowly. Once the tension is sufficiently reduced, a distinct second
  phase of evolution occurs where the flux rope enters an unstable regime
  characterized by a strong acceleration. Our simulation thus suggests
  a new mechanism for the triggering of eruptions in the vicinity of
  rotating sunspots.

---------------------------------------------------------
Title: The Wave-Driver System of the Off-Disk Coronal Wave of 17
    January 2010
Authors: Temmer, M.; Vrsnak, B.; Veronig, A. M.
2013SoPh..287..441T    Altcode: 2012arXiv1207.2857T; 2012SoPh..tmp..194T
  We study the 17 January 2010 flare-CME-wave event by using
  STEREO/SECCHI-EUVI and -COR1 data. The observational study is combined
  with an analytic model that simulates the evolution of the coronal wave
  phenomenon associated with the event. From EUV observations, the wave
  signature appears to be dome shaped having a component propagating
  on the solar surface (\overline{v}≈280~km s^{-1}) as well as one
  off-disk (\overline{v}≈ 600~km s^{-1}) away from the Sun. The off-disk
  dome of the wave consists of two enhancements in intensity, which
  conjointly develop and can be followed up to white-light coronagraph
  images. Applying an analytic model, we derive that these intensity
  variations belong to a wave-driver system with a weakly shocked wave,
  initially driven by expanding loops, which are indicative of the early
  evolution phase of the accompanying CME. We obtain the shock standoff
  distance between wave and driver from observations as well as from
  model results. The shock standoff distance close to the Sun (&lt; 0.3
  R<SUB>⊙</SUB> above the solar surface) is found to rapidly increase
  with values of ≈ 0.03 - 0.09 R<SUB>⊙</SUB>, which gives evidence
  of an initial lateral (over)expansion of the CME. The kinematical
  evolution of the on-disk wave could be modeled using input parameters
  that require a more impulsive driver (duration t=90 s, acceleration
  a=1.7 km s<SUP>−2</SUP>) compared to the off-disk component (duration
  t=340 s, acceleration a=1.5 km s<SUP>−2</SUP>).

---------------------------------------------------------
Title: Initiation of Coronal Mass Ejections by Sunspot Rotation
Authors: Török, T.; Temmer, M.; Valori, G.; Veronig, A. M.; van
   Driel-Gesztelyi, L.; Vršnak, B.
2013SoPh..286..453T    Altcode: 2014arXiv1401.2922T
  We study a filament eruption, two-ribbon flare, and coronal mass
  ejection (CME) that occurred in NOAA Active Region 10898 on 6 July
  2006. The filament was located South of a strong sunspot that dominated
  the region. In the evolution leading up to the eruption, and for some
  time after it, a counter-clockwise rotation of the sunspot of about
  30 degrees was observed. We suggest that the rotation triggered the
  eruption by progressively expanding the magnetic field above the
  filament. To test this scenario, we study the effect of twisting
  the initially potential field overlying a pre-existing flux-rope,
  using three-dimensional zero-β MHD simulations. We first consider
  a relatively simple and symmetric system, and then study a more
  complex and asymmetric magnetic configuration, whose photospheric-flux
  distribution and coronal structure are guided by the observations and a
  potential field extrapolation. In both cases, we find that the twisting
  leads to the expansion of the overlying field. As a consequence of the
  progressively reduced magnetic tension, the flux-rope quasi-statically
  adapts to the changed environmental field, rising slowly. Once the
  tension is sufficiently reduced, a distinct second phase of evolution
  occurs where the flux-rope enters an unstable regime characterised by
  a strong acceleration. Our simulations thus suggest a new mechanism
  for the triggering of eruptions in the vicinity of rotating sunspots.

---------------------------------------------------------
Title: Formation of Coronal Shock Waves
Authors: Lulić, S.; Vršnak, B.; Žic, T.; Kienreich, I. W.; Muhr,
   N.; Temmer, M.; Veronig, A. M.
2013SoPh..286..509L    Altcode: 2013arXiv1303.2786L
  Magnetosonic wave formation driven by an expanding cylindrical
  piston is numerically simulated to obtain better physical insight
  into the initiation and evolution of large-scale coronal waves caused
  by coronal eruptions. Several very basic initial configurations are
  employed to analyze intrinsic characteristics of MHD wave formation
  that do not depend on specific properties of the environment. It turns
  out that these simple initial configurations result in piston/wave
  morphologies and kinematics that reproduce common characteristics of
  coronal waves. In the initial stage, the wave and the expanding source
  region cannot be clearly resolved; i.e. a certain time is needed before
  the wave detaches from the piston. Thereafter, it continues to travel
  as what is called a "simple wave." During the acceleration stage of the
  source region inflation, the wave is driven by the piston expansion, so
  its amplitude and phase-speed increase, whereas the wavefront profile
  steepens. At a given point, a discontinuity forms in the wavefront
  profile; i.e. the leading edge of the wave becomes shocked. The
  time/distance required for the shock formation is shorter for a more
  impulsive source-region expansion. After the piston stops, the wave
  amplitude and phase speed start to decrease. During the expansion,
  most of the source region becomes strongly rarefied, which reproduces
  the coronal dimming left behind the eruption. However, the density
  increases at the source-region boundary, and stays enhanced even after
  the expansion stops, which might explain stationary brightenings
  that are sometimes observed at the edges of the erupted coronal
  structure. Also, in the rear of the wave a weak density depletion
  develops, trailing the wave, which is sometimes observed as weak
  transient coronal dimming. Finally, we find a well-defined relationship
  between the impulsiveness of the source-region expansion and the wave
  amplitude and phase speed. The results for the cylindrical piston are
  also compared with the outcome for a planar wave that is formed by a
  one-dimensional piston, to find out how different geometries affect
  the evolution of the wave.

---------------------------------------------------------
Title: Imaging coronal magnetic-field reconnection in a solar flare
Authors: Su, Yang; Veronig, Astrid M.; Holman, Gordon D.; Dennis,
   Brian R.; Wang, Tongjiang; Temmer, Manuela; Gan, Weiqun
2013NatPh...9..489S    Altcode: 2013arXiv1307.4527S
  Magnetic-field reconnection is believed to play a fundamental role
  in magnetized plasma systems throughout the Universe, including
  planetary magnetospheres, magnetars and accretion disks around black
  holes. This letter presents extreme ultraviolet and X-ray observations
  of a solar flare showing magnetic reconnection with a level of clarity
  not previously achieved. The multi-wavelength extreme ultraviolet
  observations from SDO/AIA show inflowing cool loops and newly formed,
  outflowing hot loops, as predicted. RHESSI X-ray spectra and images
  simultaneously show the appearance of plasma heated to &gt;10MK at
  the expected locations. These two data sets provide solid visual
  evidence of magnetic reconnection producing a solar flare, validating
  the basic physical mechanism of popular flare models. However, new
  features are also observed that need to be included in reconnection
  and flare studies, such as three-dimensional non-uniform, non-steady
  and asymmetric evolution.

---------------------------------------------------------
Title: Solar TErrestrial Relations Observatory-A (STEREO-A) and
    PRoject for On-Board Autonomy 2 (PROBA2) Quadrature Observations of
    Reflections of Three EUV Waves from a Coronal Hole
Authors: Kienreich, I. W.; Muhr, N.; Veronig, A. M.; Berghmans, D.;
   De Groof, A.; Temmer, M.; Vršnak, B.; Seaton, D. B.
2013SoPh..286..201K    Altcode: 2012SoPh..tmp..138K
  We investigate the interaction of three consecutive large-scale coronal
  waves with a polar coronal hole, simultaneously observed on-disk by the
  Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on
  the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on
  27 January 2011. All three extreme ultraviolet (EUV) waves originate
  from the same active region, NOAA 11149, positioned at N30E15 in the
  STEREO-A field of view and on the limb in PROBA2. For the three primary
  EUV waves, we derive starting velocities in the range of ≈ 310 km
  s<SUP>−1</SUP> for the weakest up to ≈ 500 km s<SUP>−1</SUP>
  for the strongest event. Each large-scale wave is reflected at the
  border of the extended coronal hole at the southern polar region. The
  average velocities of the reflected waves are found to be smaller than
  the mean velocities of their associated direct waves. However, the
  kinematical study also reveals that in each case the ending velocity
  of the primary wave matches the initial velocity of the reflected
  wave. In all three events, the primary and reflected waves obey the
  Huygens-Fresnel principle, as the incident angle with ≈ 10° to
  the normal is of the same magnitude as the angle of reflection. The
  correlation between the speed and the strength of the primary EUV waves,
  the homologous appearance of both the primary and the reflected waves,
  and in particular the EUV wave reflections themselves suggest that the
  observed EUV transients are indeed nonlinear large-amplitude MHD waves.

---------------------------------------------------------
Title: Propagation of Interplanetary Coronal Mass Ejections: The
    Drag-Based Model
Authors: Vršnak, B.; Žic, T.; Vrbanec, D.; Temmer, M.; Rollett, T.;
   Möstl, C.; Veronig, A.; Čalogović, J.; Dumbović, M.; Lulić, S.;
   Moon, Y. -J.; Shanmugaraju, A.
2013SoPh..285..295V    Altcode: 2012SoPh..tmp..124V
  We present the "Drag-Based Model" (DBM) of heliospheric propagation
  of interplanetary coronal mass ejections (ICMEs). The DBM is based on
  the hypothesis that the driving Lorentz force, which launches a CME,
  ceases in the upper corona and that beyond a certain distance the
  dynamics becomes governed solely by the interaction of the ICME and
  the ambient solar wind. In particular, we consider the option where
  the drag acceleration has a quadratic dependence on the ICME relative
  speed, which is expected in a collisionless environment, where the
  drag is caused primarily by emission of magnetohydrodynamic (MHD)
  waves. In this paper we present the simplest version of DBM, where
  the equation of motion can be solved analytically, providing explicit
  solutions for the Sun-Earth ICME transit time and impact speed. This
  offers easy handling and straightforward application to real-time
  space-weather forecasting. Beside presenting the model itself, we
  perform an analysis of DBM performances, applying a statistical and
  case-study approach, which provides insight into the advantages and
  drawbacks of DBM. Finally, we present a public, DBM-based, online
  forecast tool.

---------------------------------------------------------
Title: RHESSI and TRACE Observations of Multiple Flare Activity in
    AR 10656 and Associated Filament Eruption
Authors: Joshi, Bhuwan; Kushwaha, Upendra; Cho, K. -S.; Veronig,
   Astrid M.
2013ApJ...771....1J    Altcode: 2013arXiv1305.1493J
  We present Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
  and Transition Region and Coronal Explorer (TRACE) observations of
  multiple flare activity that occurred in the NOAA active region 10656
  over a period of 2 hr on 2004 August 18. Out of four successive flares,
  three were class C events, and the final event was a major X1.8 solar
  eruptive flare. The activities during the pre-eruption phase, i.e.,
  before the X1.8 flare, are characterized by three localized episodes of
  energy release occurring in the vicinity of a filament that produces
  intense heating along with non-thermal emission. A few minutes before
  the eruption, the filament undergoes an activation phase during which
  it slowly rises with a speed of ~12 km s<SUP>-1</SUP>. The filament
  eruption is accompanied by an X1.8 flare, during which multiple hard
  X-ray (HXR) bursts are observed up to 100-300 keV energies. We observe
  a bright and elongated coronal structure simultaneously in E(UV)
  and 50-100 keV HXR images underneath the expanding filament during
  the period of HXR bursts, which provides strong evidence for ongoing
  magnetic reconnection. This phase is accompanied by very high plasma
  temperatures of ~31 MK, followed by the detachment of the prominence
  from the solar source region. From the location, timing, strength,
  and spectrum of HXR emission, we conclude that the prominence eruption
  is driven by the distinct events of magnetic reconnection occurring in
  the current sheet below the erupting prominence. These multi-wavelength
  observations also suggest that the localized magnetic reconnections
  associated with different evolutionary stages of the filament in
  the pre-eruption phase play an important role in destabilizing the
  active-region filament through the tether-cutting process, leading to
  large-scale eruption and X-class flare.

---------------------------------------------------------
Title: Variations of Magnetic Bright Point Properties with Longitude
    and Latitude as Observed by Hinode/SOT G-band Data
Authors: Utz, D.; Hanslmeier, A.; Veronig, A.; Kühner, O.; Muller,
   R.; Jurčák, J.; Lemmerer, B.
2013SoPh..284..363U    Altcode: 2012arXiv1212.1310U
  Small-scale magnetic fields can be observed on the Sun in
  high-resolution G-band filtergrams as magnetic bright points (MBPs). We
  study Hinode/Solar Optical Telescope (SOT) longitude and latitude scans
  of the quiet solar surface taken in the G-band in order to characterise
  the centre-to-limb dependence of MBP properties (size and intensity). We
  find that the MBP's sizes increase and their intensities decrease
  from the solar centre towards the limb. The size distribution can be
  fitted using a log-normal function. The natural logarithm of the mean
  (μ parameter) of this function follows a second-order polynomial
  and the generalised standard deviation (σ parameter) follows a
  fourth-order polynomial or equally well (within statistical errors)
  a sine function. The brightness decrease of the features is smaller
  than one would expect from the normal solar centre-to-limb variation;
  that is to say, the ratio of a MBP's brightness to the mean intensity
  of the image increases towards the limb. The centre-to-limb variations
  of the intensities of the MBPs and the quiet-Sun field can be fitted by
  a second-order polynomial. The detailed physical process that results
  in an increase of a MBP's brightness and size from Sun centre to the
  limb is not yet understood and has to be studied in more detail in
  the future.

---------------------------------------------------------
Title: Magnetic field strength distribution of magnetic bright points
    inferred from filtergrams and spectro-polarimetric data
Authors: Utz, D.; Jurčák, J.; Hanslmeier, A.; Muller, R.; Veronig,
   A.; Kühner, O.
2013A&A...554A..65U    Altcode: 2013arXiv1304.5508U
  Context. Small scale magnetic fields can be observed on the Sun in
  G-band filtergrams as magnetic bright points (MBPs) or identified in
  spectro-polarimetric measurements due to enhanced signals of Stokes
  profiles. These magnetic fields and their dynamics play a crucial role
  in understanding the coronal heating problem and also in surface dynamo
  models. MBPs can theoretically be described to evolve out of a patch of
  a solar photospheric magnetic field with values below the equipartition
  field strength by the so-called convective collapse model. After the
  collapse, the magnetic field of MBPs reaches a higher stable magnetic
  field level. <BR /> Aims: The magnetic field strength distribution of
  small scale magnetic fields as seen by MBPs is inferred. Furthermore,
  we want to test the model of convective collapse and the theoretically
  predicted stable value of about 1300 G. <BR /> Methods: We used four
  different data sets of high-resolution Hinode/SOT observations that were
  recorded simultaneously with the broadband filter device (G-band, Ca
  II-H) and the spectro-polarimeter. To derive the magnetic field strength
  distribution of these small scale features, the spectropolarimeter
  (SP) data sets were treated by the Merlin inversion code. The four data
  sets comprise different solar surface types: active regions (a sunspot
  group and a region with pores), as well as quiet Sun. <BR /> Results:
  In all four cases the obtained magnetic field strength distribution of
  MBPs is similar and shows peaks around 1300 G. This agrees well with the
  theoretical prediction of the convective collapse model. The resulting
  magnetic field strength distribution can be fitted in each case by a
  model consisting of log-normal components. The important parameters,
  such as geometrical mean value and multiplicative standard deviation,
  are similar in all data sets, so only the relative weighting of the
  components is different.

---------------------------------------------------------
Title: The Height Evolution of the "True" Coronal Mass Ejection Mass
    derived from STEREO COR1 and COR2 Observations
Authors: Bein, B. M.; Temmer, M.; Vourlidas, A.; Veronig, A. M.;
   Utz, D.
2013ApJ...768...31B    Altcode: 2013arXiv1303.3372B
  Using combined STEREO-A and STEREO-B EUVI, COR1, and COR2 data, we
  derive deprojected coronal mass ejection (CME) kinematics and CME "true"
  mass evolutions for a sample of 25 events that occurred during 2007
  December to 2011 April. We develop a fitting function to describe the
  CME mass evolution with height. The function considers both the effect
  of the coronagraph occulter, at the beginning of the CME evolution,
  and an actual mass increase. The latter becomes important at about
  10-15 R <SUB>⊙</SUB> and is assumed to mostly contribute up to
  20 R <SUB>⊙</SUB>. The mass increase ranges from 2% to 6% per R
  <SUB>⊙</SUB> and is positively correlated to the total CME mass. Due
  to the combination of COR1 and COR2 mass measurements, we are able to
  estimate the "true" mass value for very low coronal heights (&lt;3 R
  <SUB>⊙</SUB>). Based on the deprojected CME kinematics and initial
  ejected masses, we derive the kinetic energies and propelling forces
  acting on the CME in the low corona (&lt;3 R <SUB>⊙</SUB>). The
  derived CME kinetic energies range between 1.0-66 × 10<SUP>23</SUP>
  J, and the forces range between 2.2-510 × 10<SUP>14</SUP> N.

---------------------------------------------------------
Title: 2.5D MHD Simulations of the Kelvin-Helmholtz Instability at
    CME-Boundaries in the Solar Corona
Authors: Möstl, Ute; Temmer, Manuela; Veronig, Astrid
2013EGUGA..15.4171M    Altcode:
  We discuss the observation of a coronal mass ejection (CME) by the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory from
  2011 February 24. This CME with an embedded filament shows periodic
  vortex-like structures at the northern side of the filament boundary
  with a wavelength of approximately 14.4 Mm and a propagation speed of
  about 310 ± 20 km/s. The morphological analysis hints at structures
  produced by the Kelvin-Helmholtz (KH) instability on the boundary of the
  filament. We conduct 2.5D numerical simulations of the KH instability,
  whose results yield qualitative as well as quantitative agreements with
  the observations. Furthermore, we study the absence of KH vortex-like
  structures on the southern side of the filament boundary and find that
  a magnetic field component parallel to the boundary with a strength
  of about 20% of the total magnetic field has stabilizing effects
  resulting in an asymmetric development of the instability. This work
  receives funding from the Austrian Science Fund (FWF): P21051-N16,
  V195-N16 and P24092-N16.

---------------------------------------------------------
Title: The Kanzelhöhe Observatory
Authors: Pötzi, Werner; Temmer, Manuela; Veronig, Astrid;
   Hirtenfellner-Polanec, Wolfgang; Baumgartner, Dietmar
2013EGUGA..15.1459P    Altcode:
  Kanzelhöhe Observatory (KSO; kso.ac.at) located in the South of
  Austria is part of the Institute of Physics of the University of
  Graz. Since the early 1940s, the Sun has been observed in various
  layers and wavelengths. Currently, KSO provides high-cadence full-disk
  observations of the solar disk in three wavelengths: H-alpha line,
  Ca II K line, white light. Real-time images are published online. For
  scientific use, the data is processed, and immediately available to
  the scientific community after each observing day via the Kanzelhöhe
  Online Data Archive archive (KODA; kanzelhohe.uni-graz.at). KSO is part
  of the Global H-Alpha Network and is also one of the contributing
  stations for the international sunspot number. In the frame of
  ESA's Space Situational Awareness program, methods are currently
  under development for near-real image recognition with respect to
  solar flares and filaments. These data products will give valuable
  complementary information for the solar sources of space weather.

---------------------------------------------------------
Title: Assessing the Constrained Harmonic Mean Method for Deriving
    the Kinematics of ICMEs with a Numerical Simulation
Authors: Rollett, T.; Temmer, M.; Möstl, C.; Lugaz, N.; Veronig,
   A. M.; Möstl, U. V.
2013SoPh..283..541R    Altcode: 2013arXiv1301.6945R
  In this study we use a numerical simulation of an artificial coronal
  mass ejection (CME) to validate a method for calculating propagation
  directions and kinematical profiles of interplanetary CMEs (ICMEs). In
  this method observations from heliospheric images are constrained
  with in-situ plasma and field data at 1 AU. These data are used
  to convert measured ICME elongations into distance by applying the
  harmonic mean approach, which assumes a spherical shape of the ICME
  front. We used synthetic white-light images, similar to those observed
  by STEREO-A/HI, for three different separation angles between remote
  and in-situ spacecraft of 30<SUP>∘</SUP>, 60<SUP>∘</SUP>, and
  90<SUP>∘</SUP>. To validate the results of the method, the images were
  compared to the apex speed profile of the modeled ICME, as obtained
  from a top view. This profile reflects the "true" apex kinematics
  because it is not affected by scattering or projection effects. In
  this way it is possible to determine the accuracy of the method for
  revealing ICME propagation directions and kinematics. We found that
  the direction obtained by the constrained harmonic mean method is not
  very sensitive to the separation angle (30<SUP>∘</SUP> sep: ϕ=W7;
  60<SUP>∘</SUP> sep: ϕ=W12; 90<SUP>∘</SUP> sep: ϕ=W15; true dir.:
  E0/W0). For all three cases the derived kinematics agree relatively
  well with the real kinematics. The best consistency is obtained for the
  30<SUP>∘</SUP> case, while with growing separation angle the ICME
  speed at 1 AU is increasingly overestimated (30<SUP>∘</SUP> sep:
  ΔV<SUB>arr</SUB>≈− 50 km s<SUP>−1</SUP>, 60<SUP>∘</SUP> sep:
  ΔV<SUB>arr</SUB>≈+ 75 km s<SUP>−1</SUP>, 90<SUP>∘</SUP> sep:
  ΔV<SUB>arr</SUB>≈+ 125 km s<SUP>−1</SUP>). Especially for future
  L<SUB>4</SUB>/L<SUB>5</SUB> missions, the 60<SUP>∘</SUP> separation
  case is highly interesting in order to improve space-weather forecasts.

---------------------------------------------------------
Title: Evolution of CMEs in the inner heliosphere - observations
    versus models
Authors: Temmer, Manuela; Vrsnak, Bojan; Möstl, Christian; Veronig,
   Astrid; Rollett, Tanja; Bein, Bianca
2013EGUGA..15.1328T    Altcode:
  With the SECCHI instrument suite aboard STEREO, coronal mass ejections
  (CMEs) can be observed from multiple vantage points during their entire
  propagation all the way from the Sun to 1 AU. The propagation behavior
  of CMEs in the interplanetary space is mainly influenced by the ambient
  solar wind flow. CMEs that are faster than the ambient solar wind get
  decelerated, whereas slower ones are accelerated until the CME speed
  is finally adjusted to the solar wind speed. On a statistical basis,
  empirical models taking into account the drag force acting on CMEs,
  are able to describe the observed kinematical behaviors. For several
  well observed events, we will present a comparative study showing
  the kinematical evolution of CMEs derived from remote sensing and
  in situ data, as well as from empirical models using 2D and 3D input
  parameters. From this we aim to obtain the distance regime at which
  the solar wind drag force is dominating the CME propagation.

---------------------------------------------------------
Title: Forecasting coronal mass ejections at 1 AU using Heliospheric
    Imagers
Authors: Möstl, Christian; Amla, Keshav; Hall, Jeffrey R.; Liewer,
   Paulett C.; De Jong, Eric; Temmer, Manuela; Davies, Jackie A.; Lugaz,
   Noé; Rollett, Tanja; Veronig, Astrid M.; Farrugia, Charles J.; Liu,
   Ying; Luhmann, Janet G.; Galvin, Antoinette B.; Zhang, Tielong
2013EGUGA..15.1311M    Altcode:
  We study the feasibility of using a Heliospheric Imager (HI) instrument,
  such as STEREO/HI, for operational space weather forecasting of
  interplanetary coronal mass ejections (ICMEs) at 1 AU. We compare the
  predictions for speed and arrival time for about 20 ICME events, each
  observed remotely by one STEREO spacecraft, to the speed and arrival
  time observed at various in situ observatories. We use geometrical
  modeling, which means we approximate the ICME fronts with various shapes
  (Fixed-Phi, Harmonic Mean, Self-Similar Expansion). These models are
  applied to the time-elongation functions extracted from STEREO/SECCHI
  images with the SolarSoft SATPLOT package. We use these techniques for
  a single-spacecraft HI observer, and consequently assume constant ICME
  speed and direction. Partly, the configuration mimics the situation of
  a single HI observatory parked at the L4 or L5 point in the Sun-Earth
  system. For assessing the accuracy of these predictions we look at
  plasma and magnetic field in situ data by Wind (MFI, SWE instruments)
  and STEREO-A/B (IMPACT, PLASTIC) around 1 AU. Wherever possible we
  include ICME arrivals in the inner heliosphere (&lt; 1 AU), from the
  magnetic field data by Venus Express and MESSENGER. We also look at
  the ratio of prediction lead time to its accuracy, and see if there
  is a preferred value for the ICME width.

---------------------------------------------------------
Title: Filament and Flare Detection in H{\alpha} image sequences
Authors: Riegler, Gernot; Pock, Thomas; Pötzi, Werner; Veronig, Astrid
2013arXiv1304.7132R    Altcode:
  Solar storms can have a major impact on the infrastructure of the
  earth. Some of the causing events are observable from ground in
  the H{\alpha} spectral line. In this paper we propose a new method
  for the simultaneous detection of flares and filaments in H{\alpha}
  image sequences. Therefore we perform several preprocessing steps to
  enhance and normalize the images. Based on the intensity values we
  segment the image by a variational approach. In a final postprecessing
  step we derive essential properties to classify the events and further
  demonstrate the performance by comparing our obtained results to the
  data annotated by an expert. The information produced by our method
  can be used for near real-time alerts and the statistical analysis of
  existing data by solar physicists.

---------------------------------------------------------
Title: Radial evolution of magnetic cloud properties
Authors: Rollett, Tanja; Veronig, Astrid M.; Leitner, Martin; Vrsnak,
   Bojan; Möstl, Christian; Farrugia, Charles J.; Temmer, Manuela
2013EGUGA..15.2710R    Altcode:
  Magnetic clouds (MCs) are characterized as intervals of enhanced,
  smoothly rotating interplanetary magnetic field, low plasma beta and
  temperature in spacecraft in situ data and can be part of ICMEs. In
  this study we analyze the radial evolution of MCs using a sample of
  events detected by radial aligned spacecrafts at different heliocentric
  distances. The data-sets are fitted with a force-free, constant-alpha
  flux rope model. Using the outcome of this fitting model we calculate
  the estimated cross section diameter (assuming a cylindrical flux tube),
  the poloidal and the axial magnetic field, the current, the magnetic
  flux and the inductance. All these parameter are further studied as a
  function of heliocentric distance. Strong variations of the current or
  the magnetic flux could be a hint for magnetic reconnection between
  the MC and the solar wind. This work has received funding from the
  European Commission FP7 Project COMESEP (263252).

---------------------------------------------------------
Title: The Kelvin-Helmholtz Instability at Coronal Mass Ejection
Boundaries in the Solar Corona: Observations and 2.5D MHD Simulations
Authors: Möstl, U. V.; Temmer, M.; Veronig, A. M.
2013ApJ...766L..12M    Altcode: 2013arXiv1304.5884M
  The Atmospheric Imaging Assembly on board the Solar Dynamics Observatory
  observed a coronal mass ejection with an embedded filament on 2011
  February 24, revealing quasi-periodic vortex-like structures at
  the northern side of the filament boundary with a wavelength of
  approximately 14.4 Mm and a propagation speed of about 310 ± 20 km
  s<SUP>-1</SUP>. These structures could result from the Kelvin-Helmholtz
  instability occurring on the boundary. We perform 2.5D numerical
  simulations of the Kelvin-Helmholtz instability and compare the
  simulated characteristic properties of the instability with the
  observations, where we obtain qualitative as well as quantitative
  accordance. We study the absence of Kelvin-Helmholtz vortex-like
  structures on the southern side of the filament boundary and find that
  a magnetic field component parallel to the boundary with a strength of
  about 20% of the total magnetic field has stabilizing effects resulting
  in an asymmetric development of the instability.

---------------------------------------------------------
Title: The role of solar "tornadoes" and vortices in filament
    fromation and eruption
Authors: Su, Yang; Wang, Tongjiang; Veronig, Astrid; Temmer, Manuela;
   Gan, Weiqun
2013enss.confE..51S    Altcode:
  Solar magnetized "tornadoes" are rotating vertical magnetic
  structures in the corona probably driven by underlying vortex flows
  in the photosphere. They usually exist as a group and are related
  to filaments/prominences. Detailed case studies show that these
  tornadoes may play a distinct role in the supply of mass and twists
  to filaments. The findings could lead to a new explanation of filament
  formation and eruption.

---------------------------------------------------------
Title: Direct Observations of Coronal Magnetic Reconnection
Authors: Su, Yang; Veronig, Astrid; Dennis, Brian R.; Holman, Gordon
   D.; Wang, Tongjiang; Temmer, Manuela; Gan, Weiqun
2013enss.confE..53S    Altcode:
  Magnetic field reconnection is believed to play a fundamental role in
  magnetized plasma systems throughout the universe, but never before
  has it been so clearly demonstrated as in the EUV and X-ray movies
  of a GOES-C-class solar flare presented here. The multiwavelength EUV
  observations from SDO/AIA show the predicted inflowing cool loops and
  newly formed outflowing hot loops while simultaneous RHESSI X-ray
  spectra and images show the appearance of plasma heated to &gt;10
  MK at the expected locations. These two data sets provide solid
  visual evidence of magnetic reconnection producing a solar flare. The
  non-uniform, nonsteady, and asymmetric nature of the observed process,
  together with the measured reconnection rates, supports the so called
  flux-pile-up reconnection. These new features of plasma inflows should
  be included in reconnection and flare studies.

---------------------------------------------------------
Title: The Successive CME on 13th; 14th and 15th February 2011 and
    Forbush decrease on 18 February 2011
Authors: Maričić, D.; Bostasyan, N.; Dumbović, M.; Chilingarian,
   A.; Mailyan, B.; Rostomyan, H.; Arakelyan, K.; Vršnak, B.; Roša,
   D.; Hržina, D.; Romštajn, I.; Veronig, A.
2013JPhCS.409a2158M    Altcode:
  Aims. We analyze the kinematics of three interplanetary coronal mass
  ejections (ICMEs) that occurred on 13th, 14th and 15th February
  2011 in the active region AR 11155 and have shown that they
  appeared at the Earth orbit on February, 18th and caused Forbush
  decrease (FD). Methods. The solar coordinates of flares are (S19W03),
  (S20W14) and (S21W18). The kinematic curves were obtained using STEREO
  (A&amp;B) data. Additionally, we explore the possibility of the CME-CME
  interaction for these three events. We compare obtained estimates of
  ICME arrival with the in-situ measurements from WIND satellite at
  L1 point and with ground-based cosmic ray data obtained from SEVAN
  network. Results. The acceleration of each CME is highly correlated
  with the associated SXR flares energy release. CMEs that erupted at 13
  and 14 Feb 2011 are not associated with prominence eruption; maximum
  velocity was v<SUB>max</SUB>550 ± 50 km/s and v<SUB>max</SUB>400
  ± 50 km/s, respectively. However, 15 Feb 2011 CME is connected with
  much more violent eruption associated with a prominence, with maximum
  velocity of v<SUB>max</SUB> 1400 ± 50 km/s. The last overtakes 13th
  and 14th Feb CMEs at distances of 32 and 160 Rsolar, respectively.

---------------------------------------------------------
Title: Solar eruptive filament studies at USO for the COMESEP project
Authors: Srivastava, N.; Crosby, N.; Veronig, A.; Robrrecht, E.;
   Vršnak, B.; Vennerstrom, S.; Malandraki, O.; Dalla, S.; Rodriguez,
   L.; Hesse, M.; Odstrcil, D.
2013ASInC..10...67S    Altcode:
  The Coronal Mass Ejections and Solar Energetic Particles (COMESEP)
  project is developing tools for forecasting geomagnetic storms and solar
  energetic particle (SEP) radiation storms. By analysis of historical
  solar and interplanetary data, complemented with the extensive data
  coverage of solar cycle 23, the key ingredients that lead to geomagnetic
  storms, SEP events and the factors that are responsible for false
  alarms are being identified. Based on the insights gained, and making
  use of algorithms for the automated detection of CMEs, forecasting
  tools for geomagnetic and SEP radiation storms will be developed and
  optimised. Validation and implementation of the developed tools into
  an operational Space Weather Alert system will be performed. COMESEP
  is a unique cross collaboration effort and bridges the gap between the
  SEP, CME and terrestrial effects scientific communities. The role of
  the Udaipur Solar Observatory (USO) in addressing some of the goals
  of this project are highlighted in this paper. In particular, USO is
  engaged in studying the CMEs associated with eruptive filaments. We
  describe the studies undertaken to understand space weather effects
  related to these CMEs.

---------------------------------------------------------
Title: A Magnetic Bright Point Case Study
Authors: Utz, D.; Jurčák, J.; Bellot-Rubio, L.; del Toro Iniesta,
   J. C.; Thonhofer, S.; Hanslmeier, A.; Veronig, A.; Muller, R.;
   Lemmerer, B.
2013CEAB...37..459U    Altcode:
  Due to its magnetic fields our host star - the Sun - becomes the
  interesting object for research as we know it. The magnetic fields
  themselves cover different spatial, lifetime and strength scales and
  reach down from enormous flux concentrations like active sunspot
  groups to single isolated magnetic flux tubes and even weaker,
  predominantly inclined intranetwork structures. Flux tubes can be seen
  in filtergram observations as magnetic bright points (MBPs). They are
  of interest for research not only due to their sheer existence but
  due to their important role in atmospheric heating (wave heating as
  well as reconnection processes), to their role in the understanding
  of creation and annihilation of magnetic fields as well as to their
  influence on the total solar irradiance variation. In this study we
  present a close look onto an evolutionary track of an MBP from its
  formation to its disintegration. Physical quantities of MBPs like
  their magnetic field strength and inclination, their line-of-sight
  velocity, and their temperature at different heights are inferred
  from the inversion of spectropolarimetric data. Original data are
  taken from the Sunrise/IMaX instrument and constitute a time series
  of some 60 min. The presented case resembles the convective collapse
  model and is in agreement with previous studies.

---------------------------------------------------------
Title: 3D Image Segmentation Applied to Solar RHD Simulations
Authors: Lemmerer, B.; Utz, D.; Hanslmeier, A.; Veronig, A.;
   Grimm-Strele, H.; Thonhofer, S.; Muthsam, H.
2013CEAB...37..477L    Altcode:
  3D simulation models based on Magneto-hydrodynamics (MHD) and
  Radiation-hydrodynamics (RHD) equations give insight into the evolution
  of magnetic fields and convective motions in the solar atmosphere. The
  analysis of huge amount of data require the development of automated
  segmentation algorithms. A newly developed 3D segmentation algorithm
  will be introduced in order to extract and trace convective downflows
  and is applied to the numerical simulation code ANTARES. The algorithm
  segments strong downflow velocities resulting in tube-like structures
  which enables us to analyze the motions with respect to variations
  of physical parameters over height as well as their evolution with
  time. Analysis of the segmented structures shows that narrower parts
  tend to have higher velocities. High temporal variations in the lower
  model photosphere indicate less stable structures over time in this
  layer. The mean temperature within the downflow is cooler than in the
  horizontally averaged simulation box. The analysis of the behavior of
  vortex flows demonstrates a constant high vorticity within the segment
  and a linear dependency to the vertical velocity. It appears that
  vortex flows are strongly present within dominant convective downflows.

---------------------------------------------------------
Title: Relation Between Coronal Hole Areas on the Sun and the Solar
    Wind Parameters at 1 AU
Authors: Rotter, T.; Veronig, A. M.; Temmer, M.; Vršnak, B.
2012SoPh..281..793R    Altcode: 2012SoPh..tmp..202R
  We analyze the relationship between the coronal hole (CH)
  characteristics on the Sun (area, position, and intensity levels)
  and the corresponding solar wind parameters (solar wind speed v,
  proton temperature T, proton density n, and magnetic field strength B)
  measured in situ at 1 AU with a 6-h time resolution. We developed a
  histogram-based intensity thresholding method to obtain fractional CH
  areas from SOHO/EIT 195 Å images. The algorithm was applied to 6-h
  cadence EIT 195 Å images for the year 2005, which were characterized
  by a low solar activity. In calculating well-defined peaks of the solar
  wind parameters corresponding to the peaks in CH area, we found that the
  solar wind speed v shows a high correlation with correlation coefficient
  cc=0.78, medium correlation for T and B with cc=0.41 and cc=0.41. No
  significant correlation was found with the proton density n. Applying
  an intensity-weighted CH area did not improve the relations, since
  the size and the mean intensity of the CH areas are not independent
  parameters but strongly correlated (cc=− 0.72). Comparison of the
  fractional CH areas derived from GOES/SXI and SOHO/EIT and the related
  solar wind predictions shows no systematic differences (cc=0.79).

---------------------------------------------------------
Title: Forecasting coronal mass ejections at 1 AU using Heliospheric
    Imagers
Authors: Moestl, C.; Amla, K.; Temmer, M.; Hall, J. R.; Liewer, P. C.;
   De Jong, E. M.; Davies, J.; Lugaz, N.; Rollett, T.; Veronig, A.; Liu,
   Y.; Farrugia, C. J.; Luhmann, J. G.; Galvin, A. B.; Zhang, T.
2012AGUFMSH31A2208M    Altcode:
  We study the feasibility of using a Heliospheric Imager (HI) instrument,
  such as STEREO/HI, for space weather forecasting of interplanetary
  coronal mass ejections (ICMEs) at 1 AU. We compare the predictions for
  speed and arrival time for ~15 ICME events, each observed remotely by
  one STEREO spacecraft, to the speed and arrival time observed at in
  situ observatories. We use three different models with varying ICME
  geometry, from point-like (Fixed-Phi) to a circle with a given width
  (Self-Similar-Expansion) to a very wide circle (Harmonic Mean). The
  models are fitted to density tracks on HI Jmaps with the SolarSoft
  SATPLOT tool. All these techniques assume constant ICME speed and
  direction. Partly, the configuration mimics the situation of a
  single HI observatory parked at the L4 or L5 point in the Sun-Earth
  system. We discuss problems associated with this study, such as CME-CME
  interactions leading to complicated Jmaps. For assessing the accuracy
  of these predictions we look at in situ data by Wind/ACE, STEREO-A/B,
  and Venus Express and MESSENGER. We also look at the ratio of prediction
  lead time to its accuracy, and see if there is a preferred value for
  the ICME width.

---------------------------------------------------------
Title: Relation between the impulsive CME acceleration and the
    nonthermal flare characteristics
Authors: Veronig, A. M.; Berkebile-Stoiser, S.; Bein, B. M.; Temmer, M.
2012AGUFMSH54A..03V    Altcode:
  We investigate the relationship between the main acceleration phase of
  CMEs and the particle acceleration in the associated flares observed
  by RHESSI for a set of 37 impulsive flare-CME events. Both the CME peak
  velocity and peak acceleration yield distinct correlations with various
  parameters characterizing the flare-accelerated electron spectra. The
  highest correlation coefficient is obtained for the relation of the
  CME peak velocity and the total energy in accelerated electrons (c =
  0.85), supporting the idea that the acceleration of the CME and the
  particle acceleration in the associated flare draw their energy from
  a common source, probably magnetic reconnection in the current sheet
  behind the erupting structure. In general, the CME peak velocity shows
  somewhat higher correlations with the non-thermal flare parameters
  than the CME peak acceleration, except for the spectral index of the
  accelerated electron spectrum, which yields a higher correlation with
  the CME peak acceleration (c = -0.6), indicating that the hardness
  of the flare-accelerated electron spectrum is tightly coupled to
  the impulsive acceleration process of the rising CME structure. We
  also obtained high correlations between the CME initiation height h0
  and the non-thermal flare parameters, with the highest correlation
  of h0 to the spectral index δ of flare-accelerated electrons (c =
  0.8). This means that CMEs erupting at low coronal heights, i.e., in
  regions of stronger magnetic fields, are accompanied by flares that are
  more efficient at accelerating electrons to high energies. In 80% of the
  events, the non-thermal flare emission starts after the CME acceleration
  (on average 6 min), which corresponds to a mean current sheet length
  at the onset of magnetic reconnection of 21 ± 7 Mm. The flare hard
  X-ray peaks are well synchronized with the peak of the CME acceleration
  profile, and in 75% of the cases they occur within ±5 minutes. Our
  findings provide strong evidence for the tight coupling between the
  CME dynamics and the particle acceleration in the associated flare
  in impulsive events, with the total energy in accelerated electrons
  being closely correlated with the peak velocity (and thus the kinetic
  energy) of the CME, whereas the number of electrons accelerated to
  high energies is decisively related to the CME peak acceleration and
  the height of the pre-eruptive structure.

---------------------------------------------------------
Title: Deep Solar Activity Minimum 2007-2009: Solar Wind Properties
    and Major Effects on the Terrestrial Magnetosphere
Authors: Farrugia, C. J.; Harris, B. S.; Leitner, M.; Moestl, C.;
   Galvin, A. B.; Simunac, K.; Torbert, R. B.; Temmer, M.; Veronig, A.;
   Erkaev, N.; Szabo, A.; Ogilvie, K. W.; Luhmann, J. G.; Osherovich, V.
2012AGUFMSM41C2226F    Altcode:
  We discuss the temporal variations and frequency distributions of
  solar wind and IMF parameters during the solar minimum of 2007-2009
  from measurements returned by the IMPACT and PLASTIC instruments on
  STEREO-A. We find that the density and total field strength were
  significantly weaker than in the previous minimum. The Alfvén
  Mach number was higher than typical.This reflects the weakness of
  magnetohydrodynamic (MHD) forces, and has a direct effect on the
  solar wind-magnetosphere interactions. We then discuss two major
  aspects that this weak solar activity had on the magnetosphere,
  using data from textit{Wind} and ground-based observations: (a) the
  dayside contribution to the cross-polar cap potential (CPCP), and (b)
  the shapes of the magnetopause and bow shock. For (a) we find a low
  interplanetary electric field of 1.3 ± 0.9 mV m<SUP>-1</SUP> and a
  CPCP of 37.3 ± 20.2 kV. The auroral activity is closely correlated to
  the prevalent stream-stream interactions. We suggest that the Alfvén
  wave trains in the fast streams and Kelvin-Helmholtz instability were
  the predominant agents mediating the transfer of solar wind momentum
  and energy to the magnetosphere during this three-year period. For
  (b) we determine 328 magnetopause and 271 bow shock crossings made by
  textit{Geotail, Cluster 1}, and the THEMIS B and C spacecraft during
  a three-month interval when the daily averages of the magnetic and
  kinetic energy densities attained their lowest value during the three
  years under survey. We use the same numerical approach as in Fairfield's
  (textit{J. Geophys. Res.} 76, 7600, 1971) empirical model and compare
  our findings with three magnetopause models. The stand-off distance
  of the subsolar magnetopause and bow shock were 11.8 R<SUB>E</SUB>
  and 14.35 R<SUB>E</SUB>, respectively. When comparing with Fairfield's
  (1971) classic result, we find that the subsolar magnetosheath is
  thinner by ∼1 R<SUB>E</SUB>. This is mainly due to the low dynamic
  pressure which results in a sunward shift of the magnetopause The
  magnetopause is more flared than in Fairfield's model. By contrast
  the bow shock is less flared, and the latter is the result of weaker
  MHD forces.

---------------------------------------------------------
Title: Validating a new method for deriving the kinematics of ICMEs
    with a numerical simulation
Authors: Rollett, T.; Temmer, M.; Moestl, C.; Lugaz, N.; Veronig,
   A.; Moestl, U. V.
2012AGUFMSH31A2209R    Altcode:
  Using a numerical simulation of a very wide coronal mass ejection
  (CME) we validate a method for calculating propagation directions
  and kinematical profiles of interplanetary CMEs (ICMEs). In this
  method observations from heliospheric images are constrained with the
  in-situ arrival time at 1 AU. This additional boundary condition is
  used to calculate the propagation direction and to convert measured
  ICME elongations into distance by applying the Harmonic Mean approach
  that assumes a spherical shape of the ICME front. We use synthetic
  white light images, similar as observed by STEREO-A/HI, for three
  different separation angles between remote and in-situ spacecraft,
  of 30°, 60° and 90°. For validation, the results of the method are
  compared to the "true" speed profile of the modeled ICME, as obtained
  from top view density images, for every separation case. In this way
  it is possible to determine the accuracy of the method for revealing
  ICME propagation directions and kinematics. We found that the direction
  yield by the constrained Harmonic Mean method is not very sensitive
  on the separation angle. For all three cases the derived kinematics
  are in a relatively good agreement with the real kinematics. The best
  consistency is obtained for the 30° case, while with growing separation
  the ICME speed at 1 AU is increasingly overestimated. Especially for
  future L4/L5 missions the 60° separation case is highly interesting
  in order to improve space weather forecasts.

---------------------------------------------------------
Title: Spectrometer Telescope for Imaging X-rays (STIX)
Authors: Benz, A. O.; Gallagher, P.; Veronig, A.; Grimm, O.; Sylwester,
   J.; Orleanski, P.; Arnold, N.; Bednarzik, M.; Farnik, F.; Hurford,
   G.; Krucker, S.; Limousin, O.; Mann, G.; Vilmer, N.
2012IAUSS...6E.509B    Altcode:
  The Solar Orbiter Mission has been confirmed within ESA's M-class
  Cosmic Vision plan. Launch date is January 2017 into an orbit that
  reaches nearly one quarter AU in the perihelion. STIX is one of
  the 10 instruments selected for close cooperation. STIX applies
  a Fourier-imaging technique using shading tungsten grids. A total
  of 32 pixelized CdTe detectors will permit high resolution imaging
  spectroscopy. The design has passed ESA's Preliminary Design Review
  and will be finalized by the end of 2012. The instrument specification
  will be presented and its scientific potential discussed.

---------------------------------------------------------
Title: Deep Solar Activity Minimum 2007 - 2009: Solar Wind Properties
    and Major Effects on the Terrestrial Magnetosphere
Authors: Farrugia, C. J.; Harris, B.; Leitner, M.; Möstl, C.; Galvin,
   A. B.; Simunac, K. D. C.; Torbert, R. B.; Temmer, M. B.; Veronig,
   A. M.; Erkaev, N. V.; Szabo, A.; Ogilvie, K. W.; Luhmann, J. G.;
   Osherovich, V. A.
2012SoPh..281..461F    Altcode: 2012SoPh..tmp..222F
  We discuss the temporal variations and frequency distributions of
  solar wind and interplanetary magnetic field parameters during the
  solar minimum of 2007 - 2009 from measurements returned by the IMPACT
  and PLASTIC instruments on STEREO-A. We find that the density and
  total field strength were significantly weaker than in the previous
  minimum. The Alfvén Mach number was higher than typical. This
  reflects the weakness of magnetohydrodynamic (MHD) forces, and has a
  direct effect on the solar wind-magnetosphere interactions. We then
  discuss two major aspects that this weak solar activity had on the
  magnetosphere, using data from Wind and ground-based observations:
  i) the dayside contribution to the cross-polar cap potential (CPCP),
  and ii) the shapes of the magnetopause and bow shock. For i) we find a
  low interplanetary electric field of 1.3±0.9 mV m<SUP>−1</SUP> and
  a CPCP of 37.3±20.2 kV. The auroral activity is closely correlated to
  the prevalent stream-stream interactions. We suggest that the Alfvén
  wave trains in the fast streams and Kelvin-Helmholtz instability were
  the predominant agents mediating the transfer of solar wind momentum
  and energy to the magnetosphere during this three-year period. For
  ii) we determine 328 magnetopause and 271 bow shock crossings made
  by Geotail, Cluster 1, and the THEMIS B and C spacecraft during a
  three-month interval when the daily averages of the magnetic and kinetic
  energy densities attained their lowest value during the three years
  under survey. We use the same numerical approach as in Fairfield's
  (J. Geophys. Res.76, 7600, 1971) empirical model and compare our
  findings with three magnetopause models. The stand-off distance of the
  subsolar magnetopause and bow shock were 11.8 R<SUB>E</SUB> and 14.35
  R<SUB>E</SUB>, respectively. When comparing with Fairfield's (1971)
  classic result, we find that the subsolar magnetosheath is thinner
  by ∼1 R<SUB>E</SUB>. This is mainly due to the low dynamic pressure
  which results in a sunward shift of the magnetopause. The magnetopause
  is more flared than in Fairfield's model. By contrast the bow shock
  is less flared, and the latter is the result of weaker MHD forces.

---------------------------------------------------------
Title: Multi-point Shock and Flux Rope Analysis of Multiple
    Interplanetary Coronal Mass Ejections around 2010 August 1 in the
    Inner Heliosphere
Authors: Möstl, C.; Farrugia, C. J.; Kilpua, E. K. J.; Jian, L. K.;
   Liu, Y.; Eastwood, J. P.; Harrison, R. A.; Webb, D. F.; Temmer, M.;
   Odstrcil, D.; Davies, J. A.; Rollett, T.; Luhmann, J. G.; Nitta, N.;
   Mulligan, T.; Jensen, E. A.; Forsyth, R.; Lavraud, B.; de Koning,
   C. A.; Veronig, A. M.; Galvin, A. B.; Zhang, T. L.; Anderson, B. J.
2012ApJ...758...10M    Altcode: 2012arXiv1209.2866M
  We present multi-point in situ observations of a complex
  sequence of coronal mass ejections (CMEs) which may serve as
  a benchmark event for numerical and empirical space weather
  prediction models. On 2010 August 1, instruments on various
  space missions, Solar Dynamics Observatory/Solar and Heliospheric
  Observatory/Solar-TErrestrial-RElations-Observatory (SDO/SOHO/STEREO),
  monitored several CMEs originating within tens of degrees from the
  solar disk center. We compare their imprints on four widely separated
  locations, spanning 120° in heliospheric longitude, with radial
  distances from the Sun ranging from MESSENGER (0.38 AU) to Venus
  Express (VEX, at 0.72 AU) to Wind, ACE, and ARTEMIS near Earth and
  STEREO-B close to 1 AU. Calculating shock and flux rope parameters at
  each location points to a non-spherical shape of the shock, and shows
  the global configuration of the interplanetary coronal mass ejections
  (ICMEs), which have interacted, but do not seem to have merged. VEX
  and STEREO-B observed similar magnetic flux ropes (MFRs), in contrast
  to structures at Wind. The geomagnetic storm was intense, reaching
  two minima in the Dst index (≈ - 100 nT), and was caused by the
  sheath region behind the shock and one of two observed MFRs. MESSENGER
  received a glancing blow of the ICMEs, and the events missed STEREO-A
  entirely. The observations demonstrate how sympathetic solar eruptions
  may immerse at least 1/3 of the heliosphere in the ecliptic with their
  distinct plasma and magnetic field signatures. We also emphasize the
  difficulties in linking the local views derived from single-spacecraft
  observations to a consistent global picture, pointing to possible
  alterations from the classical picture of ICMEs.

---------------------------------------------------------
Title: Solar Magnetized "Tornadoes:" Relation to Filaments
Authors: Su, Yang; Wang, Tongjiang; Veronig, Astrid; Temmer, Manuela;
   Gan, Weiqun
2012ApJ...756L..41S    Altcode: 2012arXiv1208.0138S
  Solar magnetized "tornadoes," a phenomenon discovered in the solar
  atmosphere, appear as tornado-like structures in the corona but are
  rooted in the photosphere. Like other solar phenomena, solar tornadoes
  are a feature of magnetized plasma and therefore differ distinctly
  from terrestrial tornadoes. Here we report the first analysis of solar
  "tornadoes" (two papers which focused on different aspects of solar
  tornadoes were published in the Astrophysical Journal Letters and
  Nature, respectively, during the revision of this Letter). A detailed
  case study of two events indicates that they are rotating vertical
  magnetic structures probably driven by underlying vortex flows
  in the photosphere. They usually exist as a group and are related
  to filaments/prominences, another important solar phenomenon whose
  formation and eruption are still mysteries. Solar tornadoes may play
  a distinct role in the supply of mass and twists to filaments. These
  findings could lead to a new explanation of filament formation and
  eruption.

---------------------------------------------------------
Title: The spectrometer telescope for imaging x-rays on board the
    Solar Orbiter mission
Authors: Benz, A. O.; Krucker, S.; Hurford, G. J.; Arnold, N. G.;
   Orleanski, P.; Gröbelbauer, H. -P.; Klober, S.; Iseli, L.; Wiehl,
   H. J.; Csillaghy, A.; Etesi, L.; Hochmuth, N.; Battaglia, M.;
   Bednarzik, M.; Resanovic, R.; Grimm, O.; Viertel, G.; Commichau, V.;
   Meuris, A.; Limousin, O.; Brun, S.; Vilmer, N.; Skup, K. R.; Graczyk,
   R.; Stolarski, M.; Michalska, M.; Nowosielski, W.; Cichocki, A.;
   Mosdorf, M.; Seweryn, K.; Przepiórka, A.; Sylwester, J.; Kowalinski,
   M.; Mrozek, T.; Podgorski, P.; Mann, G.; Aurass, H.; Popow, E.;
   Onel, H.; Dionies, F.; Bauer, S.; Rendtel, J.; Warmuth, A.; Woche,
   M.; Plüschke, D.; Bittner, W.; Paschke, J.; Wolker, D.; Van Beek,
   H. F.; Farnik, F.; Kasparova, J.; Veronig, A. M.; Kienreich, I. W.;
   Gallagher, P. T.; Bloomfield, D. S.; Piana, M.; Massone, A. M.;
   Dennis, B. R.; Schwarz, R. A.; Lin, R. P.
2012SPIE.8443E..3LB    Altcode:
  The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10
  instruments on board Solar Orbiter, a confirmed Mclass mission of the
  European Space Agency (ESA) within the Cosmic Vision program scheduled
  to be launched in 2017. STIX applies a Fourier-imaging technique
  using a set of tungsten grids (at pitches from 0.038 to 1 mm) in
  front of 32 pixelized CdTe detectors to provide imaging spectroscopy
  of solar thermal and non-thermal hard X-ray emissions from 4 to 150
  keV. The status of the instrument reviewed in this paper is based on
  the design that passed the Preliminary Design Review (PDR) in early
  2012. Particular emphasis is given to the first light of the detector
  system called Caliste-SO.

---------------------------------------------------------
Title: Dependence of Velocity Distributions of Small-Scale Magnetic
    Fields Derived from Hinode/SOT G-band Filtergrams on the Temporal
    Resolution of the Used Data Sets
Authors: Utz, D.; Hanslmeier, A.; Muller, R.; Veronig, A.; Rybák,
   J.; Muthsam, H.
2012ASPC..454...55U    Altcode:
  The dynamics of isolated small-scale fields in terms of velocities of
  magnetic bright points (MBPs) is addressed in this contribution. The
  empirically determined linear relation between the observed width
  parameter for the Rayleigh velocity distribution of MBPs versus the
  temporal cadence of the acquired data is studied by simulations and a
  simple analytical model. The results of the model and the simulation
  agree with the found relation for the observations. The conclusion we
  draw from the model is that there may be no characteristic velocity
  for MBPs at all.

---------------------------------------------------------
Title: Impulsive Acceleration of Coronal Mass Ejections. II. Relation
    to Soft X-Ray Flares and Filament Eruptions
Authors: Bein, B. M.; Berkebile-Stoiser, S.; Veronig, A. M.; Temmer,
   M.; Vršnak, B.
2012ApJ...755...44B    Altcode: 2012arXiv1206.2144B
  Using high time cadence images from the STEREO EUVI, COR1, and COR2
  instruments, we derived detailed kinematics of the main acceleration
  stage for a sample of 95 coronal mass ejections (CMEs) in comparison
  with associated flares and filament eruptions. We found that CMEs
  associated with flares reveal on average significantly higher peak
  accelerations and lower acceleration phase durations, initiation
  heights, and heights, at which they reach their peak velocities and peak
  accelerations. This means that CMEs that are associated with flares are
  characterized by higher and more impulsive accelerations and originate
  from lower in the corona where the magnetic field is stronger. For CMEs
  that are associated with filament eruptions we found only for the CME
  peak acceleration significantly lower values than for events that were
  not associated with filament eruptions. The flare rise time was found
  to be positively correlated with the CME acceleration duration and
  negatively correlated with the CME peak acceleration. For the majority
  of the events the CME acceleration starts before the flare onset (for
  75% of the events) and the CME acceleration ends after the soft X-ray
  (SXR) peak time (for 77% of the events). In ~60% of the events, the
  time difference between the peak time of the flare SXR flux derivative
  and the peak time of the CME acceleration is smaller than ±5 minutes,
  which hints at a feedback relationship between the CME acceleration and
  the energy release in the associated flare due to magnetic reconnection.

---------------------------------------------------------
Title: Multi-wavelength investigation of pre-flare activity and
    magnetic reconnection during the evolutionary phases of a solar
    eruptive flare
Authors: Joshi, Bhuwan; Veronig, Astrid; Cho, Kyung-Suk; Bong, Su-chan;
   Tiwari, Sanjiv Kumar; Lee, J.
2012cosp...39..845J    Altcode: 2012cosp.meet..845J
  No abstract at ADS

---------------------------------------------------------
Title: Relation between the Coronal Mass Ejection Acceleration and
    the Non-thermal Flare Characteristics
Authors: Berkebile-Stoiser, S.; Veronig, A. M.; Bein, B. M.; Temmer, M.
2012ApJ...753...88B    Altcode:
  We investigate the relationship between the main acceleration phase
  of coronal mass ejections (CMEs) and the particle acceleration in
  the associated flares as evidenced in Reuven Ramaty High Energy
  Solar Spectroscopic Imager non-thermal X-rays for a set of 37
  impulsive flare-CME events. Both the CME peak velocity and peak
  acceleration yield distinct correlations with various parameters
  characterizing the flare-accelerated electron spectra. The highest
  correlation coefficient is obtained for the relation of the CME peak
  velocity and the total energy in accelerated electrons (c = 0.85),
  supporting the idea that the acceleration of the CME and the particle
  acceleration in the associated flare draw their energy from a common
  source, probably magnetic reconnection in the current sheet behind the
  erupting structure. In general, the CME peak velocity shows somewhat
  higher correlations with the non-thermal flare parameters than the CME
  peak acceleration, except for the spectral index of the accelerated
  electron spectrum, which yields a higher correlation with the CME
  peak acceleration (c ≈ -0.6), indicating that the hardness of the
  flare-accelerated electron spectrum is tightly coupled to the impulsive
  acceleration process of the rising CME structure. We also obtained
  high correlations between the CME initiation height h <SUB>0</SUB>
  and the non-thermal flare parameters, with the highest correlation of
  h <SUB>0</SUB> to the spectral index δ of flare-accelerated electrons
  (c ≈ 0.8). This means that CMEs erupting at low coronal heights,
  i.e., in regions of stronger magnetic fields, are accompanied by flares
  that are more efficient at accelerating electrons to high energies. In
  the majority of events (~80%), the non-thermal flare emission starts
  after the CME acceleration, on average delayed by ≈6 minutes, in line
  with the standard flare model where the rising flux rope stretches the
  field lines underneath until magnetic reconnection sets in. We find
  that the current sheet length at the onset of magnetic reconnection
  is 21 ± 7 Mm. The flare hard X-ray peaks are well synchronized with
  the peak of the CME acceleration profile, and in 75% of the cases they
  occur within ±5 minutes. Our findings provide strong evidence for the
  tight coupling between the CME dynamics and the particle acceleration
  in the associated flare in impulsive events, with the total energy in
  accelerated electrons being closely correlated with the peak velocity
  (and thus the kinetic energy) of the CME, whereas the number of
  electrons accelerated to high energies is decisively related to the
  CME peak acceleration and the height of the pre-eruptive structure.

---------------------------------------------------------
Title: The Kelvin-Helmholtz Instability at CME-Boundaries in the
Solar Corona: Observations and Preliminary 2.5D MHD Simulations
Authors: Moestl, Ute Verena; Temmer, M.; Veronig, A. M.
2012shin.confE..85M    Altcode:
  Just recently, the Solar Dynamics Observatory (SDO) observedfor the
  first time Kelvin-Helmholtz vortices at the boundary of acoronal mass
  ejection (CME). The importance of the Kelvin-Helmholtz instability might
  lie in its effect on the CME kinematics due to exerting a drag force
  via anomalous viscosity.We discuss the observation of a CME by SDO from
  February 24th2011. This event shows periodic vortex-like structures
  on the boundary to the filament. First analysis of these structures
  reveals a periodic appearance with a wavelength of approximately 14 Mm
  and a height of 3-4 Mm.Another striking feature of this observation
  is an apparent asymmetric evolution of the periodic structures on
  only one side of the boundary layer. This asymmetry is also seen in
  other observations. Such observed asymmetry could be due to different
  magnetic field directions, for example. We test this hypothesis and
  present results of preliminary 2.5D magnetohydrodynamic simulations
  of the February 24th 2011event using different input parameters for
  the plasma background. Our aim is to check if the observed structures
  can be produced by the Kelvin-Helmholtz instability and to investigate
  the effect of different magnetic field directions on the evolution of
  the instability.

---------------------------------------------------------
Title: Kinematics of Coronal Mass Ejections in the Inner Heliosphere
    Constrained with In Situ Signatures
Authors: Rollett, Tanja; Möstl, Christian; Temmer, Manuela; Veronig,
   Astrid; Farrugia, Charles J.
2012shin.confE..80R    Altcode:
  On the basis of the Harmonic Mean and Fixed-Phi methods we developed
  a new approach to derive kinematics and propagation directions of
  interplanetary coronal mass ejections (ICMEs). By combining remote
  observations performed by STEREO/HI with in situ measurements of the
  Wind and STEREO-B spacecraft at 1 AU, we make the derived kinematical
  ICME profiles as consistent as possible with in situ data. Within the
  limitations of the geometrical assumptions that are used for the shape
  of the ICME, the improved methods aim to isolate the kinematics from
  that part of the CME which is most probably directed towards the in
  situ spacecraft. The methods are applied and tested on observational
  data from well observed ICME events (1-6 June 2008, 13-18 February
  2009). This work has received funding from the European Commission
  FP7 Project COMESEP (263252).

---------------------------------------------------------
Title: Multi-point shock and flux rope analysis of multiple ICMEs
    around 2010 August 1 in the inner heliosphere
Authors: Moestl, Christian; Farrugia, C. J.; Kilpua, E. K. J.; Jian,
   L.; Liu, Y.; Jensen, L.; Mulligan, T.; Eastwood, J.; Rollett, T.;
   Temmer, M.; Luhmann, J. G.; Harrison, R.; Davies, J. A.; Webb, D.;
   Forsyth, R.; Lavraud, B.; Odstrcil, D.; de Koning, C. A.; Nitta, N.;
   Veronig, A. M.; Galvin, A. B.; Zhang, T. L.
2012shin.confE..77M    Altcode:
  We present multi-point in situ observations of a complex sequence
  of coronal mass ejections which may serve as a benchmark event for
  numerical and empirical space weather prediction models. On 2010 August
  1, instruments on various space missions (SDO/SOHO/STEREO) monitored
  repeated coronal mass ejections originating within tens of degrees from
  solar disk center. We compare their imprints on four widely separated
  locations, covering 120 degree in heliospheric longitude, with radial
  distances from the Sun ranging from MESSENGER (0.38 AU) to Venus Express
  (VEX, at 0.72 AU) to Wind, ACE and ARTEMIS near Earth and STEREO-B close
  to 1 AU. Calculating shock and flux rope parameters at each location
  points to a non-spherical shape of the shock, and shows the global
  configuration of the interplanetary coronal mass ejections (ICMEs),
  which have interacted but not merged, making individual identifications
  still possible. VEX and STEREO-B observed similar magnetic flux ropes,
  in contrast to the structures at Wind. The geomagnetic storm was
  moderate to major, reaching two minima in the Dst index, caused by the
  sheath region behind the shock and one of two observed magnetic flux
  ropes. MESSENGER received a glancing blow of the ICMEs, and the events
  missed STEREO-A entirely. The observations demonstrate how sympathetic
  solar eruptions may immerse at least 1/3 of the heliosphere in the
  ecliptic with their distinct plasma and magnetic field signatures
  and emphasize the difficulties in linking the local views derived
  from single-spacecraft observations to a consistent global picture,
  pointing to possible alterations from the classical picture of ICMEs.

---------------------------------------------------------
Title: Comparison of MHD Simulations of the Solar Wind with In-Situ
    Measurements
Authors: Gressl, Corinna; Veronig, A. M.; Temmer, M.; Odstrcil, D.
2012shin.confE..31G    Altcode:
  ENLIL is a time-dependent 3D MHD model to simulate the structure
  and evolution of the solar wind parameters in the inner and
  mid heliosphere. ENLIL can be coupled to the coronal models
  "Magnetohydrodynamics Around Sphere" (MAS) and "Wang-Sheeley-Arge"
  (WSA) which use synoptic magnetograms of the solar photosphere as input
  parameter. We tested the performance of the coupled models ENLIL/MAS and
  ENLIL/WSA by comparing the modeled solar wind speed, proton density,
  temperature, and radial and total magnetic field strength to in-situ
  measurements from Wind and ACE at 1 AU. For the comparison we chose the
  year 2005 as a time period with low solar activity. We requested model
  runs with the aim to produce a stationary solution of the background
  solar wind. All simulations were carried out by CCMC/NASA. For the
  analysis of the model results we extracted the data at the exact
  position of the spacecraft. We calculated correlation coefficients to
  quantify the agreement between model predictions and measurements. The
  accuracy of the predicted arrival times of solar wind structures was
  quantified by carrying out cross-correlations. The results show that
  ENLIL/MAS and ENLIL/WSA are able to simulate the general features of
  the background solar wind and to reproduce recurring structures in the
  heliosphere. The best results were obtained for the parameter solar
  wind speed. However, the predicted arrival times of high speed solar
  wind streams have typical uncertainties of the order of 1 - 1.5 days,
  and the absolute values of the magnetic field were systematically too
  low. The sector structure of the interplanetary magnetic field was
  well reproduced by both models.

---------------------------------------------------------
Title: CME acceleration and non-thermal flare characteristics
Authors: Berkebile-Stoiser, S.; Veronig, A. M.; Bein, B. M.; Temmer, M.
2012arXiv1205.2539B    Altcode:
  We investigate the relationship between the main acceleration phase
  of coronal mass ejections (CMEs) and the particle acceleration in
  the associated flares as evidenced in RHESSI non-thermal X-rays for
  a set of 37 impulsive flare-CME events. CME peak velocity and peak
  acceleration yield distinct correlations with various parameters
  characterizing the flare-accelerated electron spectra. The highest
  correlation coefficient is obtained for the relation of the CME peak
  velocity and the total energy in accelerated electrons (c = 0.85),
  supporting the idea that the acceleration of the CME and the particle
  acceleration in the associated flare draw their energy from a common
  source, probably magnetic reconnection in the current sheet behind
  the erupting structure. In general, the CME peak velocity shows
  somewhat higher correlations with the non-thermal flare parameters
  than the CME peak acceleration, except for the spectral index of the
  accelerated electron spectrum which yields a higher correlation with
  the CME peak acceleration (c = -0.6), indicating that the hardness
  of the flare-accelerated electron spectrum is tightly coupled to the
  impulsive acceleration process of the rising CME structure. We also
  obtained high correlations between the CME initiation height $h_0$
  and the non-thermal flare parameters, with the highest correlation
  of $h_0$ to the spectral index of flare-accelerated electrons (c =
  0.8). This means that CMEs erupting at low coronal heights, i.e.\
  in regions of stronger magnetic fields, are accompanied with flares
  which are more efficient to accelerate electrons to high energies. In
  the majority of events (80%), the non-thermal flare emission starts
  after the CME acceleration (6 min), giving a current sheet length at
  the onset of magnetic reconnection of 21 \pm 7 Mm. The flare HXR peaks
  are well synchronized with the peak of the CME acceleration profile.

---------------------------------------------------------
Title: Forecasting Geomagnetic Storms and Solar Energetic Particle
Events: the COMESEP Project
Authors: Crosby, N.; Veronig, A.; Robbrecht, E.; Vrsnak, B.;
   Vennerstrøm, S.; Malandraki, O.; Dalla, S.; Srivastava, N.; Hesse,
   M.; Odstrcil, D.
2012EGUGA..1412544C    Altcode:
  COMESEP (COronal Mass Ejections and Solar Energetic Particles),
  funded by the European Union Framework 7 programme, is a three-year
  collaborative project that has been running for one year. Tools for
  forecasting geomagnetic storms and solar energetic particle (SEP)
  radiation storms are being developed under the project. By analysis
  of historical data, complemented by the extensive data coverage of
  solar cycle 23, the key ingredients that lead to magnetic storms and
  SEP events and the factors that are responsible for false alarms are
  being identified. To enhance our understanding of the 3D kinematics
  and interplanetary propagation of coronal mass ejections (CMEs), the
  structure, propagation and evolution of CMEs are being investigated. In
  parallel, the sources and propagation of SEPs are being examined and
  modeled. Based on the insights gained, and making use of algorithms for
  the automated detection of CMEs, forecasting tools for geomagnetic and
  SEP radiation storms are being developed and optimised. Validation and
  implementation of the produced tools into an operational Space Weather
  Alert system will be performed. Geomagnetic and SEP radiation storm
  alerts will be based on the COMESEP definition of risk. COMESEP is a
  unique cross-collaboration effort and bridges the gap between the SEP
  and CME scientific communities. For more information about the project,
  see the COMESEP website http://www.comesep.eu/ . This work has received
  funding from the European Commission FP7 Project COMESEP (263252).

---------------------------------------------------------
Title: STEREO-A and PROBA2 Quadrature Observations of Reflections
    of three EUV Waves from a Coronal Hole
Authors: Kienreich, Ines Waltraud; Muhr, Nicole; Veronig, Astrid;
   Berghmans, David; de Groof, Anik; Temmer, Manuela; Vršnak, Bojan;
   Seaton, Dan
2012arXiv1204.6472K    Altcode: 2012arXiv1204.6472W
  We investigate the interaction of three consecutive large-scale coronal
  waves with a polar coronal hole, simultaneously observed on-disk by the
  Solar TErrestrial Relations Observatory (STEREO)-A spacecraft and on
  the limb by the PRoject for On-Board Autonomy 2 (PROBA2) spacecraft on
  January 27, 2011. All three extreme-ultraviolet(EUV) waves originate
  from the same active region NOAA 11149 positioned at N30E15 in the
  STEREO-A field-of-view and on the limb in PROBA2. We derive for the
  three primary EUV waves start velocities in the range of ~310 km/s for
  the weakest up to ~500 km/s for the strongest event. Each large-scale
  wave is reflected at the border of the extended coronal hole at the
  southern polar region. The average velocities of the reflected waves
  are found to be smaller than the mean velocities of their associated
  direct waves. However, the kinematical study also reveals that in each
  case the end velocity of the primary wave matches the initial velocity
  of the reflected wave. In all three events the primary and reflected
  waves obey the Huygens-Fresnel principle, as the incident angle with
  ~10° to the normal is of the same size as the angle of reflection. The
  correlation between the speed and the strength of the primary EUV waves,
  the homologous appearance of both the primary and the reflected waves,
  and in particular the EUV wave reflections themselves implicate that the
  observed EUV transients are indeed nonlinear large-amplitude MHD waves.

---------------------------------------------------------
Title: CME-CME interaction during the 2010 August 1 events
Authors: Temmer, M.; Vrsnak, B.; Rollett, T.; Bein, B.; deKoning,
   C. A.; Liu, Y.; Bosman, E.; Davies, J. A.; Möstl, C.; Zic, T.;
   Veronig, A. M.; Bothmer, V.; Harrison, R.; Nitta, N.; Bisi, M.; Flor,
   O.; Eastwood, J.; Odstrcil, D.; Forsyth, R.
2012EGUGA..14.1677T    Altcode:
  We study a CME-CME interaction that occurred during the 2010 August 1
  events using STEREO/SECCHI data (COR and HI). The CMEs were Earth
  directed where clear signatures of magnetic flux ropes could be
  measured from in situ Wind data. To give evidence of the actual
  interaction we derive the direction of motion for both CMEs applying
  several independent methods. From this we obtain that both CMEs head
  into similar directions enabling us to actually observe the merging
  in the HI1 field-of-view (and rule out the possibility that this is
  just a line of sight effect). The full de-projected kinematics of the
  faster CME from Sun to Earth is derived when combining data points from
  remote observations with in situ parameters of the ICME measured at
  1 AU. We study the evolution of the kinematical profile of the faster
  CME by applying a drag based model.

---------------------------------------------------------
Title: CME mass evolution derived from stereoscopic observations of
    STEREO/SECCHI instruments COR1 and COR2
Authors: Bein, B.; Temmer, M.; Vourlidas, A.; Veronig, A.
2012EGUGA..14.7174B    Altcode:
  The STEREO mission consists of two nearly identical spacecraft STEREO-A
  and STEREO-B, which observe simultaneously the Sun from two different
  vantage points. We use observations from both coronagraphs, COR1 and
  COR2 of the SECCHI instrument suite aboard STEREO-A and STEREO-B,
  to derive the CME mass evolution for a height range from 1.4 to 15
  RSun. Due to the fact that we have observations from two different
  vantage points, we measure not only the projected mass but can
  estimate the 'true' CME mass evolution with height. We developed a
  fit function, which considers the mass increase based on the geometry
  of the instrument (mass hidden behind the occulter) and a possible
  'real' mass increase with height. The fit parameters are compared with
  characteristic CME quantities.

---------------------------------------------------------
Title: Deep Solar Activity Minimum 2007-2009: Solar Wind Properties
    and Major Effects on the Terrestrial Magnetosphere
Authors: Farrugia, C. J.; Harris, B.; Leitner, M.; Möstl, C.; Galvin,
   A. B.; Simunac, K. D. C.; Torbert, R. B.; Temmer, M. B.; Veronig,
   A. M.; Erkaev, N. V.; Szabo, A.; Ogilvie, K. W.; Luhmann, J. G.;
   Osherovich, V. A.
2012EGUGA..14.6381F    Altcode:
  We discuss the temporal variations and frequency distributions of
  solar wind and interplanetary magnetic field parameters during the
  solar minimum of 2007- 2009 from measurements returned by the IMPACT
  and PLASTIC instruments on STEREO-A. We find that the density and
  total field strength were considerably weaker than in the previous
  minimum. The Alfvén Mach number was higher than typical. This reflects
  the weakness of magnetohydrodynamic (MHD) forces, and has a direct
  effect on the solar wind-magnetosphere interactions. We then discuss two
  major aspects that this weak solar activity had on the magnetosphere
  using data from Wind and ground-based observations: (a) the level
  of solar wind driving and the associated dayside contribution to the
  crosspolar cap potential (CPCP), and (b) the shapes of the magnetopause
  and bow shock. For (a) we find very weak interplanetary electric
  field (V xBz = -0.05 ± 0.83 mV/m) and a CPCP of 36.6 ± 18.2 kV. The
  auroral activity is closely correlated to the prevalent stream-stream
  interactions.We argue that the Alfvén waves in the fast streams and
  Kelvin-Helmholtz instability were the predominant agents mediating the
  transfer of solar wind momentum and energy to the magnetosphere during
  this 3-year period. For (b) we determine 328 magnetopause and 271 bow
  shock crossings made by the Cluster 1, Themis B and C spacecraft during
  a 3-month interval when the daily averages of the magnetic and kinetic
  energy densities attained their lowest value during the 3 years under
  survey. We use the same numerical approach as in Fairfield's (1971)
  empirical model and compare our findings with his classic result. The
  stand-off distance of the subsolar magnetopause and bow shock were
  11.8 RE and 14.35 RE, respectively, making the subsolar magnetosheath
  thinner by ≈ 1RE. This is mainly due to the low dynamic pressure
  which result in a sunward shift of the magnetopause The magnetopause
  is more flared than Fairfield's result. By contrast the bow shock is
  less flared, and the latter is the result of weaker MHD forces.

---------------------------------------------------------
Title: Characteristics of Kinematics of a Coronal Mass Ejection
    during the 2010 August 1 CME-CME Interaction Event
Authors: Temmer, Manuela; Vršnak, Bojan; Rollett, Tanja; Bein, Bianca;
   de Koning, Curt A.; Liu, Ying; Bosman, Eckhard; Davies, Jackie A.;
   Möstl, Christian; Žic, Tomislav; Veronig, Astrid M.; Bothmer, Volker;
   Harrison, Richard; Nitta, Nariaki; Bisi, Mario; Flor, Olga; Eastwood,
   Jonathan; Odstrcil, Dusan; Forsyth, Robert
2012ApJ...749...57T    Altcode: 2012arXiv1202.0629T
  We study the interaction of two successive coronal mass ejections (CMEs)
  during the 2010 August 1 events using STEREO/SECCHI COR and heliospheric
  imager (HI) data. We obtain the direction of motion for both CMEs by
  applying several independent reconstruction methods and find that the
  CMEs head in similar directions. This provides evidence that a full
  interaction takes place between the two CMEs that can be observed in the
  HI1 field of view. The full de-projected kinematics of the faster CME
  from Sun to Earth is derived by combining remote observations with in
  situ measurements of the CME at 1 AU. The speed profile of the faster
  CME (CME2; ~1200 km s<SUP>-1</SUP>) shows a strong deceleration over
  the distance range at which it reaches the slower, preceding CME (CME1;
  ~700 km s<SUP>-1</SUP>). By applying a drag-based model we are able
  to reproduce the kinematical profile of CME2, suggesting that CME1
  represents a magnetohydrodynamic obstacle for CME2 and that, after
  the interaction, the merged entity propagates as a single structure
  in an ambient flow of speed and density typical for quiet solar wind
  conditions. Observational facts show that magnetic forces may contribute
  to the enhanced deceleration of CME2. We speculate that the increase
  in magnetic tension and pressure, when CME2 bends and compresses the
  magnetic field lines of CME1, increases the efficiency of drag.

---------------------------------------------------------
Title: Calculation of CME kinematics and propagation directions by
    constraining STEREO HI-images with in situ signatures at 1 AU
Authors: Rollett, T.; Möstl, C.; Temmer, M.; Veronig, A. M.; Farrugia,
   C. J.; Biernat, H. K.
2012EGUGA..14.4778R    Altcode:
  We present a new approach to combine remote observations and in
  situ measurements by STEREO/HI and Wind, respectively, to derive the
  kinematics and propagation directions of interplanetary coronal mass
  ejections (ICMEs). We use two methods, Fixed-Phi and Harmonic Mean,
  to convert ICME elongations into distance. The ICME direction is
  constrained such that the ICME distance-time and speed-time profiles
  are most consistent with in situ measurements of the arrival time and
  speed at 1 AU. These methods are applied to two ICME events of 02 - 06
  June 2008 and 13 - 18 February 2009. Due to the geometrical assumptions
  HM delivers the propagation direction further away from the observing
  spacecraft with a mean difference of 25°. This work has received
  funding from the European Commission FP7 Project COMESEP (263252).

---------------------------------------------------------
Title: Observations of a Two-stage Solar Eruptive Event (SEE):
    Evidence for Secondary Heating
Authors: Su, Yang; Dennis, Brian R.; Holman, Gordon D.; Wang,
   Tongjiang; Chamberlin, Phillip C.; Savage, Sabrina; Veronig, Astrid
2012ApJ...746L...5S    Altcode:
  We present RHESSI, SDO/AIA, SOHO/LASCO, STEREO, and GOES observations
  of a partially occulted solar eruptive event that occurred at the
  southwest limb on 2011 March 8. The GOES X-ray light curve shows two
  peaks separated by almost 2 hr that we interpret as two stages of a
  single event associated with the delayed eruption of a coronal mass
  ejection (CME). A hot flux rope formed during the first stage and
  continued expanding and rising throughout the event. The speed of the
  flux rope decreased from ~120 to 14 km s<SUP>-1</SUP> during the decay
  phase of the first stage and increased again during the second stage to
  become the CME with a speed of ~516 km s<SUP>-1</SUP>. RHESSI and GOES
  data analyses show that the plasma temperature reached over 20 MK in
  the first stage, then decreased to ~10 MK and increased to 15 MK in the
  second stage. This event provides clear evidence for a secondary heating
  phase. The enhanced EUV and X-ray emission came from the high corona
  (~60 arcsec above the limb) in the second stage, ~40 arcsec higher than
  the site of the initial flare emission. STEREO-A on-disk observations
  indicate that the post-flare loops during this stage were of larger
  scale sizes and spatially distinct from those in the first stage.

---------------------------------------------------------
Title: Flare-generated Type II Burst without Associated Coronal
    Mass Ejection
Authors: Magdalenić, J.; Marqué, C.; Zhukov, A. N.; Vršnak, B.;
   Veronig, A.
2012ApJ...746..152M    Altcode:
  We present a study of the solar coronal shock wave on 2005 November
  14 associated with the GOES M3.9 flare that occurred close to the
  east limb (S06° E60°). The shock signature, a type II radio burst,
  had an unusually high starting frequency of about 800 MHz, indicating
  that the shock was formed at a rather low height. The position of the
  radio source, the direction of the shock wave propagation, and the
  coronal electron density were estimated using Nançay Radioheliograph
  observations and the dynamic spectrum of the Green Bank Solar Radio
  Burst Spectrometer. The soft X-ray, Hα, and Reuven Ramaty High Energy
  Solar Spectroscopic Imager observations show that the flare was compact,
  very impulsive, and of a rather high density and temperature, indicating
  a strong and impulsive increase of pressure in a small flare loop. The
  close association of the shock wave initiation with the impulsive
  energy release suggests that the impulsive increase of the pressure
  in the flare was the source of the shock wave. This is supported by
  the fact that, contrary to the majority of events studied previously,
  no coronal mass ejection was detected in association with the shock
  wave, although the corresponding flare occurred close to the limb.

---------------------------------------------------------
Title: Constraining the Kinematics of Coronal Mass Ejections in the
    Inner Heliosphere with In-Situ Signatures
Authors: Rollett, T.; Möstl, C.; Temmer, M.; Veronig, A. M.; Farrugia,
   C. J.; Biernat, H. K.
2012SoPh..276..293R    Altcode: 2011SoPh..tmp..414R; 2011SoPh..tmp..412R; 2011arXiv1110.0300R
  We present a new approach to combine remote observations and in-situ
  data by STEREO/HI and Wind, respectively, to derive the kinematics
  and propagation directions of interplanetary coronal mass ejections
  (ICMEs). We use two methods, Fixed-ϕ (Fϕ) and Harmonic Mean (HM),
  to convert ICME elongations into distance, and constrain the ICME
  direction such that the ICME distance-time and velocity-time profiles
  are most consistent with in-situ measurements of the arrival time and
  velocity. The derived velocity-time functions from the Sun to 1 AU for
  the three events under study (1 - 6 June 2008, 13 - 18 February 2009,
  3 - 5 April 2010) do not show strong differences for the two extreme
  geometrical assumptions of a wide ICME with a circular front (HM)
  or an ICME of small spatial extent in the ecliptic (Fϕ). Due to the
  geometrical assumptions, HM delivers the propagation direction further
  away from the observing spacecraft with a mean difference of ≈ 25°.

---------------------------------------------------------
Title: Signatures of Magnetic Reconnection in Solar Eruptive Flares:
    A Multi-wavelength Perspective
Authors: Joshi, Bhuwan; Veronig, Astrid; Manoharan, P. K.; Somov,
   Boris V.
2012ASSP...33...29J    Altcode: 2012msdp.book...29J; 2012arXiv1211.2914J
  In this article, we review some key aspects of a multi-wavelength
  flare which have essentially contributed to form a standard flare
  model based on the magnetic reconnection. The emphasis is given on
  the recent observations taken by the Reuven Ramaty High Energy Solar
  Spectroscopic Imager (RHESSI) on the X-ray emission originating from
  different regions of the coronal loops. We also briefly summarize those
  observations which do not seem to accommodate within the canonical
  flare picture and discuss the challenges for future investigations.

---------------------------------------------------------
Title: Solar Hα and white light telescope at Hvar Observatory
Authors: Čalogović, J.; Dumbović, M.; Novak, N.; Vršnak, B.;
   Brajša, R.; Pötzi, W.; Hirtenfellner-Polanec, W.; Veronig, A.;
   Hanslmeier$, A.; Klvaňa, M.; Ambrož, P.
2012CEAB...36...83C    Altcode:
  Recently, the double solar telescope at Hvar Observatory was equipped
  with the fourth generation of acquisition hardware and software. It
  provides a valuable instrument to study rapid changes of chromospheric
  and photospheric features in great detail. The telescope consists of
  two Carl Zeiss refractors (photosphere d=217mm, chromosphere d=130mm)
  mounted as one unit on a German parallax mounting. Using a field
  of view of about 7 and 11 arcmin, it aims to produce high-resolution
  high-cadence imaging of active regions on the Sun. New Pulnix TM-4200GE
  12-bit CCD cameras allow to obtain time series with a cadence up to
  30 images per minute.

---------------------------------------------------------
Title: Centre to limb intensity variation of magnetic bright points
Authors: Utz, D.; Kühner, O.; Hanslmeier, A.; Veronig, A.; Muller,
   R.; Lemmerer, B.; Pauritsch, J.; Thonhofer, S.
2012CEAB...36...17U    Altcode:
  The solar activity cycle is strongly related and rooted to photospheric
  magnetic fields. Up to the present, it was mostly or even solely
  studied by extended fields such as sunspots, sunspot groups or active
  regions. Interestingly, the domain of magnetic fields on the Sun is
  not only limited to extended and strong magnetic fields but reaches
  down to small elements like single flux tubes. These flux elements
  can be identified in G-band filtergrams as so called magnetic bright
  points (MBPs). In this study we want to investigate the centre limb
  variation of the mean MBP intensity for the period of the recent
  solar minimum up to present (10/2008 - 10/2011). We found that a
  4th order polynomial describes the centre limb variation fairly
  well. Furthermore we established for the symmetrized and normalized
  centre limb variation (for which the 1st and 3rd order parameter of
  the polynomial is fixed to zero) a relationship between the 2nd and
  4th order fit parameter. Hence it is possible to derive a description
  with only one free parameter. Finally, we studied the variation with
  time of this parameter for the period of October 2008 to present,
  showing a slight increase and a weak correlation to solar activity as
  given by the relative sunspot number.

---------------------------------------------------------
Title: Relation Between the 3D-Geometry of the Coronal Wave and
    Associated CME During the 26 April 2008 Event
Authors: Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.
2012esrs.book..115T    Altcode:
  We study the kinematical characteristics and 3D geometry of
  a large-scale coronal wave that occurred in association with the
  26 April 2008 flare-CME event. The wave was observed with the EUVI
  instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B)
  with a mean speed of ∼ 240 km s<SUP>-1</SUP>. The wave is more
  pronounced in the eastern propagation direction, and is thus, better
  observable in STEREO-B images. From STEREO-B observations we derive
  two separate initiation centers for the wave, and their locations fit
  with the coronal dimming regions. Assuming a simple geometry of the
  wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B
  observations. We find that the wave structure is asymmetric with an
  inclination toward East. The associated CME has a deprojected speed
  of ∼ 750±50 km s<SUP>-1</SUP>, and it shows a non-radial outward
  motion toward the East with respect to the underlying source region
  location. Applying the forward fitting model developed by Thernisien,
  Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the
  CME flux rope position on the solar surface to be close to the dimming
  regions. We conclude that the expanding flanks of the CME most likely
  drive and shape the coronal wave.

---------------------------------------------------------
Title: Plasma Diagnostics of an EIT Wave Observed by Hinode/EIS
    and SDO/AIA
Authors: Veronig, A. M.; Gömöry, P.; Kienreich, I. W.; Muhr, N.;
   Vršnak, B.; Temmer, M.; Warren, H. P.
2011ApJ...743L..10V    Altcode: 2011arXiv1111.3505V
  We present plasma diagnostics of an Extreme-Ultraviolet
  Imaging Telescope (EIT) wave observed with high cadence in
  Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) sit-and-stare
  spectroscopy and Solar Dynamics Observatory/Atmospheric Imaging
  Assembly imagery obtained during the HOP-180 observing campaign on 2011
  February 16. At the propagating EIT wave front, we observe downward
  plasma flows in the EIS Fe XII, Fe XIII, and Fe XVI spectral lines
  (log T ≈ 6.1-6.4) with line-of-sight (LOS) velocities up to 20
  km s<SUP>-1</SUP>. These redshifts are followed by blueshifts with
  upward velocities up to -5 km s<SUP>-1</SUP> indicating relaxation
  of the plasma behind the wave front. During the wave evolution, the
  downward velocity pulse steepens from a few km s<SUP>-1</SUP> up to 20
  km s<SUP>-1</SUP> and subsequently decays, correlated with the relative
  changes of the line intensities. The expected increase of the plasma
  densities at the EIT wave front estimated from the observed intensity
  increase lies within the noise level of our density diagnostics from
  EIS Fe XIII 202/203 Å line ratios. No significant LOS plasma motions
  are observed in the He II line, suggesting that the wave pulse was not
  strong enough to perturb the underlying chromosphere. This is consistent
  with the finding that no Hα Moreton wave was associated with the
  event. The EIT wave propagating along the EIS slit reveals a strong
  deceleration of a ≈ -540 m s<SUP>-2</SUP> and a start velocity of v
  <SUB>0</SUB> ≈ 590 km s<SUP>-1</SUP>. These findings are consistent
  with the passage of a coronal fast-mode MHD wave, pushing the plasma
  downward and compressing it at the coronal base.

---------------------------------------------------------
Title: Influence of the Ambient Solar Wind Flow on the Propagation
    Behavior of Interplanetary Coronal Mass Ejections
Authors: Temmer, Manuela; Rollett, Tanja; Möstl, Christian; Veronig,
   Astrid M.; Vršnak, Bojan; Odstrčil, Dusan
2011ApJ...743..101T    Altcode: 2011arXiv1110.0827T
  We study three coronal mass ejection (CME)/interplanetary coronal mass
  ejection (ICME) events (2008 June 1-6, 2009 February 13-18, and 2010
  April 3-5) tracked from Sun to 1 AU in remote-sensing observations
  of Solar Terrestrial Relations Observatory Heliospheric Imagers and
  in situ plasma and magnetic field measurements. We focus on the ICME
  propagation in interplanetary (IP) space that is governed by two
  forces: the propelling Lorentz force and the drag force. We address
  the question: which heliospheric distance range does the drag become
  dominant and the CME adjust to the solar wind flow. To this end,
  we analyze speed differences between ICMEs and the ambient solar
  wind flow as a function of distance. The evolution of the ambient
  solar wind flow is derived from ENLIL three-dimensional MHD model
  runs using different solar wind models, namely, Wang-Sheeley-Arge and
  MHD-Around-A-Sphere. Comparing the measured CME kinematics with the
  solar wind models, we find that the CME speed becomes adjusted to the
  solar wind speed at very different heliospheric distances in the three
  events under study: from below 30 R <SUB>⊙</SUB>, to beyond 1 AU,
  depending on the CME and ambient solar wind characteristics. ENLIL can
  be used to derive important information about the overall structure of
  the background solar wind, providing more reliable results during times
  of low solar activity than during times of high solar activity. The
  results from this study enable us to obtain greater insight into the
  forces acting on CMEs over the IP space distance range, which is an
  important prerequisite for predicting their 1 AU transit times.

---------------------------------------------------------
Title: Elliptical approximation for the fronts of ICMEs and
    application to STEREO events in August 2010 and February 2011
Authors: Moestl, C.; Davies, J. A.; Rollett, T.; Temmer, M.; Lugaz,
   N.; Farrugia, C. J.; Liu, Y.; Veronig, A. M.
2011AGUFMSH23C1971M    Altcode:
  Geo-effective solar eruptions can now be followed continuously
  from the Sun to 1 AU from a viewpoint far away from the Sun-Earth
  line (with STEREO/SECCHI), thus making it possible to link solar,
  heliospheric and in situ observations unambiguously. A very basic
  problem is that only the elongation of the interplanetary coronal mass
  ejection's (ICME) density enhancements, and not the radial distances,
  are measured by an observer when the ICME is propagating at large
  angles to the Sun. Additionally, this is complicated by the effects
  of Thomson scattering. Nevertheless, the community has worked so far
  with increasingly realistic geometrical approximations to convert the
  observed elongations to radial distance, such as Point-P (a circle
  around the Sun), Fixed-Phi (a point), Harmonic Mean (a circle always
  attached to the Sun at one end), and Self-Similar Expansion (a circle
  with a given angular width). We add to this an analytical formula
  which is based on an elliptical geometry (abbreviated EL), with the
  assumption, similar to HM and SSE, that the observer looks along the
  tangent of the ellipse which approximates the ICME front. In this way
  we still ignore Thomson-scattering, but otherwise the free parameters
  direction, angular width and aspect ratio allow more freedom to derive
  ICME radial distances and speeds from heliospheric imager observations,
  which should improve the consistency with in situ ICME observations
  and the CME directions and speeds in coronagraphs. An application to
  combined STEREO heliospheric imager and multi-point in situ observations
  of the multiple ICME events on 1-4 August 2010 and 15-17 February 2011
  is presented, and the possibility of using EL for real-time forecasts
  by means of inverse fitting and triangulation is discussed.

---------------------------------------------------------
Title: High Energy Solar Physics Data in Europe (HESPE): a European
    project for the exploitation of hard X-ray data in solar flare physics
Authors: Piana, M.; Csillaghy, A.; Kontar, E. P.; Fletcher, L.;
   Veronig, A. M.; Vilmer, N.; Hurford, G. J.; Dennis, B. R.; Schwartz,
   R. A.; Massone, A.; Krucker, S.; Benvenuto, F.; Etesi, L. I.; Guo,
   J.; Hochmuth, N.; Reid, H.
2011AGUFMSH33B2068P    Altcode:
  It has been recognized since the early days of the space program that
  high-energy observations play a crucial role in understanding the basic
  mechanisms of solar eruptions. Unfortunately, the peculiar nature of
  this radiation makes it so difficult to extract useful information
  from it that non-conventional observational techniques together with
  complex data analysis procedures must be adopted. HESPE is a European
  project funded within the seventh Framework Program, with the aim of
  realizing computational methods for solar high-energy data analysis and
  technological tools for the intelligent exploitation of science-ready
  products. Such products and methods are put at disposal of the solar,
  heliospheric and space weather communities, who will exploit them in
  order to build flare prediction models and to integrate the information
  extracted from hard X-rays and gamma rays data, with the one extracted
  from other wavelengths data.

---------------------------------------------------------
Title: Pre-flare Activity and Magnetic Reconnection during the
    Evolutionary Stages of Energy Release in a Solar Eruptive Flare
Authors: Joshi, Bhuwan; Veronig, Astrid M.; Lee, Jeongwoo; Bong,
   Su-Chan; Tiwari, Sanjiv Kumar; Cho, Kyung-Suk
2011ApJ...743..195J    Altcode: 2011arXiv1109.3415J
  In this paper, we present a multi-wavelength analysis of an eruptive
  white-light M3.2 flare that occurred in active region NOAA 10486 on
  2003 November 1. The excellent set of high-resolution observations
  made by RHESSI and the TRACE provides clear evidence of significant
  pre-flare activities for ~9 minutes in the form of an initiation
  phase observed at EUV/UV wavelengths followed by an X-ray precursor
  phase. During the initiation phase, we observed localized brightenings
  in the highly sheared core region close to the filament and interactions
  among short EUV loops overlying the filament, which led to the opening
  of magnetic field lines. The X-ray precursor phase is manifested in
  RHESSI measurements below ~30 keV and coincided with the beginning of
  flux emergence at the flaring location along with early signatures of
  the eruption. The RHESSI observations reveal that both plasma heating
  and electron acceleration occurred during the precursor phase. The main
  flare is consistent with the standard flare model. However, after the
  impulsive phase, an intense hard X-ray (HXR) looptop source was observed
  without significant footpoint emission. More intriguingly, for a brief
  period, the looptop source exhibited strong HXR emission with energies
  up to ~50-100 keV and significant non-thermal characteristics. The
  present study indicates a causal relation between the activities in
  the pre-flare and the main flare. We also conclude that pre-flare
  activities, occurring in the form of subtle magnetic reorganization
  along with localized magnetic reconnection, played a crucial role in
  destabilizing the active region filament, leading to a solar eruptive
  flare and associated large-scale phenomena.

---------------------------------------------------------
Title: Propagation behavior of interplanetary CMEs: driving versus
    drag force
Authors: Temmer, M.; Rollett, T.; Moestl, C.; Veronig, A. M.;
   Vrsnak, B.
2011AGUFMSH23C1968T    Altcode:
  The evolution of coronal mass ejections (CMEs) is governed by the
  Lorentz and the drag force. Initially, the CME is launched and driven
  by the Lorentz force, whereas the drag force owing to the ambient solar
  wind controls the CME kinematics as it propagates into interplanetary
  (IP) space. The subject of the current study is to infer a heliospheric
  distance at which the drag force starts to prevail over the driving
  force. With the SECCHI instrument suite aboard STEREO, CMEs can be
  observed during their entire propagation all the way from Sun to 1
  AU. In combination with in-situ measurements at 1 AU we are able to
  derive the direction and speed of a CME. This information is used as
  input to derive the kinematical behavior of well observed CME events
  in the IP distance regime, which is subsequently compared to the output
  from ENLIL (NASA/CCMC) MHD model runs for the ambient solar wind flow.

---------------------------------------------------------
Title: Validation of a New Method to Derive Sun-to-1 AU Kinematics
    of ICMEs with a Numerical Simulation
Authors: Rollett, T.; Moestl, C.; Lugaz, N.; Temmer, M.; Veronig, A. M.
2011AGUFMSH23C1970R    Altcode:
  The Heliospheric Imagers (HI) aboard the NASA STEREO mission offer the
  possibility to follow coronal mass ejections (CMEs) continuously on
  their way from close to the Sun up to ~ 1 AU. The interpretation of
  these images is challenging because line-of-sight as well as Thomson
  scattering effects influence the white-light signal. There are different
  methods to derive the velocity profiles and propagation directions of
  CMEs in the interplanetary space, e.g. Fixed-Φ (Kahler and Webb, 2007)
  and Harmonic Mean (Lugaz, Vourlidas and Roussev, 2009), which make the
  assumptions of a point like structure and a circle shaped front of the
  CME, respectively. These two approaches can be constrained using in situ
  measurements at 1 AU as shown in Rollett et al. (2011). To validate the
  applied methods, we perform the same procedures for a simulated CME as
  modeled in the space weather modeling framework (SWMF, Toth, et al.,
  2005). The measurements are outlined for synthetic HI images (Lugaz et
  al., 2005) at different observing points. The research leading to these
  results has received funding from the European Union Seventh Framework
  Programme (FP7/2007-2013) under grant agreement no. 263252 [COMESEP].

---------------------------------------------------------
Title: Comparison between MHD modeled and in situ measured solar
    wind parameters
Authors: Gressl, C.; Veronig, A. M.; Temmer, M.; Moestl, C.
2011AGUFMSH23C1977G    Altcode:
  The numerical MHD model ENLIL enables us to simulate the solar wind
  conditions from Sun to 1 AU based on synoptic magnetograms over an
  entire Carrington rotation (runs are performed at the NASA/CCMC and
  are available on request under http://ccmc.gsfc.nasa.gov/). We use
  ENLIL for the inner-heliosphere coupled with the coronal model MAS
  (MHD-Around-A-Sphere) and the combined empirical and physics-based
  model WSA (Wang-Sheeley-Arge), respectively, to extract solar wind
  parameters at the distance of 1AU. The results from the simulation are
  compared to measured solar wind parameters at 1AU from ACE and Wind
  spacecraft. The study aims to test the accuracy and reliability for
  forecasting solar wind parameters like density, speed, temperature, and
  magnetic field from numerical models on time scales smaller than 1 day.

---------------------------------------------------------
Title: Arrival Time Calculation for Interplanetary Coronal Mass
    Ejections with Circular Fronts and Application to STEREO Observations
    of the 2009 February 13 Eruption
Authors: Möstl, C.; Rollett, T.; Lugaz, N.; Farrugia, C. J.; Davies,
   J. A.; Temmer, M.; Veronig, A. M.; Harrison, R. A.; Crothers, S.;
   Luhmann, J. G.; Galvin, A. B.; Zhang, T. L.; Baumjohann, W.; Biernat,
   H. K.
2011ApJ...741...34M    Altcode: 2011arXiv1108.0515M
  One of the goals of the NASA Solar TErestrial RElations Observatory
  (STEREO) mission is to study the feasibility of forecasting the
  direction, arrival time, and internal structure of solar coronal
  mass ejections (CMEs) from a vantage point outside the Sun-Earth
  line. Through a case study, we discuss the arrival time calculation
  of interplanetary CMEs (ICMEs) in the ecliptic plane using data from
  STEREO/SECCHI at large elongations from the Sun in combination with
  different geometric assumptions about the ICME front shape [fixed-Φ
  (FP): a point and harmonic mean (HM): a circle]. These forecasting
  techniques use single-spacecraft imaging data and are based on the
  assumption of constant velocity and direction. We show that for the
  slow (350 km s<SUP>-1</SUP>) ICME on 2009 February 13-18, observed at
  quadrature by the two STEREO spacecraft, the results for the arrival
  time given by the HM approximation are more accurate by 12 hr than
  those for FP in comparison to in situ observations of solar wind
  plasma and magnetic field parameters by STEREO/IMPACT/PLASTIC, and by
  6 hr for the arrival time at Venus Express (MAG). We propose that the
  improvement is directly related to the ICME front shape being more
  accurately described by HM for an ICME with a low inclination of its
  symmetry axis to the ecliptic. In this case, the ICME has to be tracked
  to &gt;30° elongation to obtain arrival time errors &lt; ± 5 hr. A
  newly derived formula for calculating arrival times with the HM method
  is also useful for a triangulation technique assuming the same geometry.

---------------------------------------------------------
Title: Relation Between the 3D-Geometry of the Coronal Wave and
    Associated CME During the 26 April 2008 Event
Authors: Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.
2011SoPh..273..421T    Altcode: 2011SoPh..tmp...75T; 2011arXiv1103.0196T; 2011SoPh..tmp..227T;
   2011SoPh..tmp..158T
  We study the kinematical characteristics and 3D geometry of a
  large-scale coronal wave that occurred in association with the 26
  April 2008 flare-CME event. The wave was observed with the EUVI
  instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B)
  with a mean speed of ∼ 240 km s<SUP>−1</SUP>. The wave is more
  pronounced in the eastern propagation direction, and is thus, better
  observable in STEREO-B images. From STEREO-B observations we derive
  two separate initiation centers for the wave, and their locations fit
  with the coronal dimming regions. Assuming a simple geometry of the
  wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B
  observations. We find that the wave structure is asymmetric with an
  inclination toward East. The associated CME has a deprojected speed
  of ∼ 750±50 km s<SUP>−1</SUP>, and it shows a non-radial outward
  motion toward the East with respect to the underlying source region
  location. Applying the forward fitting model developed by Thernisien,
  Howard, and Vourlidas (Astrophys. J. 652, 763, 2006), we derive the
  CME flux rope position on the solar surface to be close to the dimming
  regions. We conclude that the expanding flanks of the CME most likely
  drive and shape the coronal wave.

---------------------------------------------------------
Title: Coronal Dimmings and the Early Phase of a CME Observed with
    STEREO and Hinode/EIS
Authors: Miklenic, C.; Veronig, A. M.; Temmer, M.; Möstl, C.; Biernat,
   H. K.
2011SoPh..273..125M    Altcode: 2011arXiv1110.0362M; 2011SoPh..tmp..350M
  We investigate the early phase of the 13 February 2009 coronal
  mass ejection (CME). Observations with the twin STEREO spacecraft
  in quadrature allow us to compare for the first time in one and the
  same event the temporal evolution of coronal EUV dimmings, observed
  simultaneously on-disk and above-the-limb. We find that these dimmings
  are synchronized and appear during the impulsive acceleration phase of
  the CME, with the highest EUV intensity drop occurring a few minutes
  after the maximum CME acceleration. During the propagation phase two
  confined, bipolar dimming regions, appearing near the footpoints of a
  pre-flare sigmoid structure, show an apparent migration away from the
  site of the CME-associated flare. Additionally, they rotate around the
  `center' of the flare site, i.e., the configuration of the dimmings
  exhibits the same `sheared-to-potential' evolution as the postflare
  loops. We conclude that the motion pattern of the twin dimmings reflects
  not only the eruption of the flux rope, but also the ensuing stretching
  of the overlying arcade. Finally, we find that: i) the global-scale
  dimmings, expanding from the source region of the eruption, propagate
  with a speed similar to that of the leaving CME front; ii) the mass
  loss occurs mainly during the period of strongest CME acceleration. Two
  hours after the eruption Hinode/EIS observations show no substantial
  plasma outflow, originating from the `open' field twin dimming regions.

---------------------------------------------------------
Title: The LSO/KSO Hα prominence catalogue: cross-calibration of data
Authors: Rybák, J.; Gömöry, P.; Mačura, R.; Kučera, A.; Rušin,
   V.; Pötzi, W.; Baumgartner, D.; Hanslmeier, A.; Veronig, A.;
   Temmer, M.
2011CoSka..41..133R    Altcode:
  We present work on the extension of the homogeneous prominence
  catalogue created for the epoch 1967 — 2009 at the Lomnicky Peak
  Observatory (LSO) by incorporating new data acquired at the Kanzelhöhe
  Observatory for Solar and Environmental Research (KSO). We use data of
  20 Hα prominences observed almost simultaneously at both observatories
  during four days in August/September 2009 to analyze the significance
  of differences of the determined parameters used in the Hα prominence
  catalogue. A reduction of the data from KSO and adaptation of the
  resulting parameters to fit the parameters of the LSO catalogue confirm
  that no special homogenization is needed to create a common catalogue
  data set. Thus, we justified that the LSO catalogue could be extended
  onward in the future using a more comprehensive database of observations
  from KSO.

---------------------------------------------------------
Title: Analysis of Characteristic Parameters of Large-scale Coronal
    Waves Observed by the Solar-Terrestrial Relations Observatory/Extreme
    Ultraviolet Imager
Authors: Muhr, N.; Veronig, A. M.; Kienreich, I. W.; Temmer, M.;
   Vršnak, B.
2011ApJ...739...89M    Altcode:
  The kinematical evolution of four extreme ultraviolet waves,
  well observed by the Extreme Ultraviolet Imager on board the
  Solar-Terrestrial Relations Observatory (STEREO), is studied by visually
  tracking wave fronts as well as by a semi-automatized perturbation
  profile method, which leads to results matching each other within
  the error limits. The derived mean velocities of the events under
  study lie in the range of 220-350 km s<SUP>-1</SUP>. The fastest of
  the events (2007 May 19) reveals a significant deceleration of ≈ -
  190 m s<SUP>-2</SUP>, while the others are consistent with a constant
  velocity during wave propagation. The evolution of maximum-intensity
  values reveals initial intensification of 20%-70% and decays to original
  levels within 40-60 minutes, while the widths at half-maximum and
  full-maximum of the perturbation profiles broaden by a factor of two
  to four. The integral below the perturbation profile remains basically
  constant in two cases, while it shows a decrease by a factor of three
  to four in the other two cases. From the peak perturbation amplitudes,
  we estimate the corresponding magnetosonic Mach numbers M <SUB>ms</SUB>,
  which range from 1.08-1.21. The perturbation profiles reveal three
  distinct features behind the propagating wave fronts: coronal dimmings,
  stationary brightenings, and rarefaction regions. All features appear
  after the wave passage and only slowly fade away. Our findings indicate
  that the events under study are weak-shock fast-mode magnetohydrodynamic
  waves initiated by the CME lateral expansion.

---------------------------------------------------------
Title: Propagation and impact of multiple coronal mass ejections
    events on August 1 2010 in the heliosphere
Authors: Möstl, Christian; Farrugia, Charles J.; Harrison, Richard
   A.; Davies, J. A.; Kilpua, Emilia K. J.; Odstrcil, Dusan; Rollett,
   Tanja; Temmer, Manuela; Veronig, Astrid; Jian, Lan; Liu, Ying;
   Eastwood, Jonathan; Forsyth, Robert; Webb, David; Bisi, Mario M.;
   Jackson, Bernard V.; Mulligan, Tamitha; Jensen, Liz; Lavraud, Benoit;
   de Koning, Curt A.; Nitta, Nariaki; Luhmann, Janet; Galvin, Antoinette
   B.; Zhang, Tielong
2011sdmi.confE..69M    Altcode:
  On August 1 2010 a large region of the solar northern hemisphere
  displayed major activity involving a complex set of central meridian and
  remote active regions, and two large prominence channels (Schrijver
  and Title, JGR, 2011). We witnessed the eruption of four coronal
  mass ejections (CMEs) which partly impacted Earth and lead to one
  of the first geomagnetic storms of the new solar cycle. We present an
  overview of the results of several analyses exploiting the extraordinary
  completeness of the imaging data (SDO/STEREO/SOHO) in combination with
  numerical simulations (ENLIL) and in situ observations. The imprints of
  the CMEs, including a prior event on July 30, were observed in situ in
  an almost laboratory-like configuration at 4 widely separated locations
  spanning over 120 degrees of heliospheric longitude (STEREO-B, Venus
  Express, ACE/Wind, ARTEMIS, and MESSENGER). The CME density enhancements
  could be followed with the STEREO-A/HI and Coriolis/SMEI instruments
  continuously from the Sun to 1 AU. Evidences of CME-CME interactions
  and resulting overlapping tracks in Jmaps make the analysis complex,
  but nevertheless we find robust interpretations for linking two magnetic
  flux ropes at Earth, one of them geo-effective and including elevated
  alpha particles related to possible filament material, to their solar
  counterparts. Additionally, we discuss the relationship between the
  in situ observations and the global picture given by the ENLIL model.

---------------------------------------------------------
Title: Solar wind high-speed streams and related geomagnetic activity
    in the declining phase of solar cycle 23
Authors: Verbanac, G.; Vršnak, B.; Živković, S.; Hojsak, T.;
   Veronig, A. M.; Temmer, M.
2011A&A...533A..49V    Altcode:
  Context. Coronal holes (CHs) are the source of high-speed streams
  (HSSs) in the solar wind, whose interaction with the slow solar wind
  creates corotating interaction regions (CIRs) in the heliosphere. <BR
  /> Aims: We investigate the magnetospheric activity caused by CIR/HSS
  structures, focusing on the declining phase of the solar cycle 23
  (years 2005 and 2006), when the occurrence rate of coronal mass
  ejections (CMEs) was low. We aim to (i) perform a systematic analysis
  of the relationship between the CH characteristics, basic parameters of
  HSS/CIRs, and the geomagnetic indices Dst, Ap and AE; (ii) study how the
  magnetospheric/ionospheric current systems behave when influenced by
  HSS/CIR; (iii) investigate if and how the evolution of the background
  solar wind from 2005 to 2006 affected the correlations between CH,
  CIR, and geomagnetic parameters. <BR /> Methods: The cross-correlation
  analysis was applied to the fractional CH area (CH) measured in the
  central meridian distance interval ± 10°, the solar wind velocity (V),
  the interplanetary magnetic field (B), and the geomagnetic indices Dst,
  Ap, and AE. <BR /> Results: The performed analysis shows that Ap and
  AE are better correlated with CH and solar wind parameters than Dst,
  and quantitatively demonstrates that the combination of solar wind
  parameters BV<SUP>2</SUP> and BV plays the central role in the process
  of energy transfer from the solar wind to the magnetosphere. <BR />
  Conclusions: We provide reliable relationships between CH properties,
  HSS/CIR parameters, and geomagnetic indices, which can be used in
  forecasting the geomagnetic activity in periods of low CME activity.

---------------------------------------------------------
Title: An Observational Overview of Solar Flares
Authors: Fletcher, L.; Dennis, B. R.; Hudson, H. S.; Krucker, S.;
   Phillips, K.; Veronig, A.; Battaglia, M.; Bone, L.; Caspi, A.; Chen,
   Q.; Gallagher, P.; Grigis, P. T.; Ji, H.; Liu, W.; Milligan, R. O.;
   Temmer, M.
2011SSRv..159...19F    Altcode: 2011SSRv..tmp..261F; 2011arXiv1109.5932F
  We present an overview of solar flares and associated phenomena,
  drawing upon a wide range of observational data primarily from the
  RHESSI era. Following an introductory discussion and overview of
  the status of observational capabilities, the article is split into
  topical sections which deal with different areas of flare phenomena
  (footpoints and ribbons, coronal sources, relationship to coronal mass
  ejections) and their interconnections. We also discuss flare soft X-ray
  spectroscopy and the energetics of the process. The emphasis is to
  describe the observations from multiple points of view, while bearing
  in mind the models that link them to each other and to theory. The
  present theoretical and observational understanding of solar flares is
  far from complete, so we conclude with a brief discussion of models,
  and a list of missing but important observations.

---------------------------------------------------------
Title: Microflares and the Statistics of X-ray Flares
Authors: Hannah, I. G.; Hudson, H. S.; Battaglia, M.; Christe, S.;
   Kašparová, J.; Krucker, S.; Kundu, M. R.; Veronig, A.
2011SSRv..159..263H    Altcode: 2011SSRv..tmp..262H; 2011SSRv..tmp...87H; 2011arXiv1108.6203H;
   2011SSRv..tmp..243H; 2011SSRv..tmp..163H
  This review surveys the statistics of solar X-ray flares, emphasising
  the new views that RHESSI has given us of the weaker events (the
  microflares). The new data reveal that these microflares strongly
  resemble more energetic events in most respects; they occur solely
  within active regions and exhibit high-temperature/nonthermal emissions
  in approximately the same proportion as major events. We discuss the
  distributions of flare parameters (e.g., peak flux) and how these
  parameters correlate, for instance via the Neupert effect. We also
  highlight the systematic biases involved in intercomparing data
  representing many decades of event magnitude. The intermittency of
  the flare/microflare occurrence, both in space and in time, argues
  that these discrete events do not explain general coronal heating,
  either in active regions or in the quiet Sun.

---------------------------------------------------------
Title: Impulsive Acceleration of Coronal Mass Ejections. I. Statistics
    and Coronal Mass Ejection Source Region Characteristics
Authors: Bein, B. M.; Berkebile-Stoiser, S.; Veronig, A. M.; Temmer,
   M.; Muhr, N.; Kienreich, I.; Utz, D.; Vršnak, B.
2011ApJ...738..191B    Altcode: 2011arXiv1108.0561B
  We use high time cadence images acquired by the STEREO EUVI and
  COR instruments to study the evolution of coronal mass ejections
  (CMEs) from their initiation through impulsive acceleration to the
  propagation phase. For a set of 95 CMEs we derived detailed height,
  velocity, and acceleration profiles and statistically analyzed
  characteristic CME parameters: peak acceleration, peak velocity,
  acceleration duration, initiation height, height at peak velocity,
  height at peak acceleration, and size of the CME source region. The CME
  peak accelerations we derived range from 20 to 6800 m s<SUP>-2</SUP>
  and are inversely correlated with the acceleration duration and the
  height at peak acceleration. Seventy-four percent of the events reach
  their peak acceleration at heights below 0.5 R <SUB>sun</SUB>. CMEs that
  originate from compact sources low in the corona are more impulsive and
  reach higher peak accelerations at smaller heights. These findings can
  be explained by the Lorentz force, which drives the CME accelerations
  and decreases with height and CME size.

---------------------------------------------------------
Title: Spectroscopic Observations of a Coronal Moreton Wave
Authors: Harra, Louise K.; Sterling, Alphonse C.; Gömöry, Peter;
   Veronig, Astrid
2011ApJ...737L...4H    Altcode:
  We observed a coronal wave (EIT wave) on 2011 February 16, using
  EUV imaging data from the Solar Dynamics Observatory/Atmospheric
  Imaging Assembly (AIA) and EUV spectral data from the Hinode/EUV
  Imaging Spectrometer (EIS). The wave accompanied an M1.6 flare that
  produced a surge and a coronal mass ejection (CME). EIS data of the
  wave show a prominent redshifted signature indicating line-of-sight
  velocities of ~20 km s<SUP>-1</SUP> or greater. Following the main
  redshifted wave front, there is a low-velocity period (and perhaps
  slightly blueshifted), followed by a second redshift somewhat weaker
  than the first; this progression may be due to oscillations of the EUV
  atmosphere set in motion by the initial wave front, although alternative
  explanations may be possible. Along the direction of the EIS slit the
  wave front's velocity was ~500 km s<SUP>-1</SUP>, consistent with
  its apparent propagation velocity projected against the solar disk
  as measured in the AIA images, and the second redshifted feature had
  propagation velocities between ~200 and 500 km s<SUP>-1</SUP>. These
  findings are consistent with the observed wave being generated by the
  outgoing CME, as in the scenario for the classic Moreton wave. This
  type of detailed spectral study of coronal waves has hitherto been a
  challenge, but is now possible due to the availability of concurrent
  AIA and EIS data.

---------------------------------------------------------
Title: Analysis of characteristic parameters of large-scale coronal
    waves observed by STEREO/EUVI
Authors: Muhr, N.; Veronig, A. M.; Kienreich, I. W.; Temmer, M.;
   Vrsnak, B.
2011arXiv1107.0921M    Altcode:
  The kinematical evolution of four EUV waves, well observed by the
  Extreme UltraViolet Imager (EUVI) onboard the Solar-Terrestrial
  Relations Observatory (STEREO), is studied by visually tracking the
  wave fronts as well as by a semiautomatized perturbation profile
  method leading to results matching each other within the error
  limits. The derived mean velocities of the events under study lie
  in the range of 220-350 km/s. The fastest of the events (May 19,
  2007) reveals a significant deceleration of \approx -190 m s-2 while
  the others are consistent with a constant velocity during the wave
  propagation. The evolution of the maximum intensity values reveals
  initial intensification by 20 up to 70%, and decays to original
  levels within 40-60 min, while the width at half maximum and full
  maximum of the perturbation profiles are broadening by a factor of
  2 - 4. The integral below the perturbation profile remains basically
  constant in two cases, while it shows a decrease by a factor of 3 -
  4 in the other two cases. From the peak perturbation amplitudes we
  estimate the corresponding magnetosonic Mach numbers Mms which are
  in the range of 1.08-1.21. The perturbation profiles reveal three
  distinct features behind the propagating wave fronts: coronal dimmings,
  stationary brightenings and rarefaction regions. All of them appear
  after the wave passage and are only slowly fading away. Our findings
  indicate that the events under study are weak shock fast-mode MHD
  waves initiated by the CME lateral expansion.

---------------------------------------------------------
Title: The Drag Based Model of ICME Propagation
Authors: Dumbović, M.; Vršnak, B.; Žic, T.; Vrbanec, D.; Veronig,
   A.; Temmer, M.; Rollett, T.; Moestl, C.; Moon, Y. -J.
2011simi.confR...2D    Altcode:
  One of central issues of space weather is the propagation of
  interplanetary coronal mass ejections (ICMEs). At the heliospheric
  distances beyond R=20 solar radii the "aerodynamic" drag is presumably
  the dominant force governing ICME propagation; therefore, a drag based
  model (DBM) was established, which can be used to forecast the ICME
  arrival at the Earth. <P />First, the model was tested on a sample
  of CMEs by combining remote observations of the CME take-off gained
  by the LASCO onboard SOHO, and in situ measurements from ACE and Wind
  satellites. The results of the DBM were compared to observational data
  and a fairly good agreement of the two was found. The model was then
  tested against STEREO observations. The ICME kinematics was inferred
  from STEREO observations by applying the Harmonic Mean method and
  compared to the DBM results. In this way we were able to reproduce
  the propagation of both slow and fast ICMEs, as well as to identify
  ICME-ICME interactions and a transition from fast-to-slow solar wind
  regimes. Finally, a statistical study was performed, where parameters
  were varied within a model in order to obtain optimal values, for
  which the average difference in the observed and calculated TT is zero
  (O-C=0) and the O-C scatter gets minimum. The source of the scatter
  in O–C values was investigated. <P />The research leading to the
  results presented in this paper has received funding from European
  Community's Seventh Framework Programme (FP7/2007-2013) under grant
  agreement No. 218816.

---------------------------------------------------------
Title: Multiple, distant (40°) in situ observations of a magnetic
    cloud and a corotating interaction region complex
Authors: Farrugia, C. J.; Berdichevsky, D. B.; Möstl, C.; Galvin,
   A. B.; Leitner, M.; Popecki, M. A.; Simunac, K. D. C.; Opitz, A.;
   Lavraud, B.; Ogilvie, K. W.; Veronig, A. M.; Temmer, M.; Luhmann,
   J. G.; Sauvaud, J. A.
2011JASTP..73.1254F    Altcode:
  We report a comprehensive analysis of in situ observations made
  by Wind and the STEREO probes (STA, STB) of a complex interaction
  between a magnetic cloud (MC) and a corotating interaction region (CIR)
  occurring near the heliospheric current sheet (HCS) on November 19-21,
  2007. The probes were separated by 0.7 AU (∼40<SUP>∘</SUP>) with
  a spread in heliographic latitudes (4.8,° 2.2,° and -0.4,° for STB,
  Wind and STA, respectively). We employ data from the MFI, SWE and 3DP
  instruments on Wind, and the PLASTIC and IMPACT suites on STEREO. STB,
  located east of Earth, observed a forward shock followed by signatures
  of a MC. The MC took the role of the HCS in that the polarity of the
  interplanetary magnetic field (IMF) on exit was the reverse of that
  on entry. A passage through a plasma sheet was observed. Along the
  Sun-Earth line Wind observed a stream interface (SI) between a forward
  and a reverse shock. A MC, compressed by the CIR, was entrained in
  this. STA, located 20° to the west of Earth, saw a MC which was not
  preceded by a shock. A SI trailed the transient. The shocks are examined
  using various methods and from this it is concluded that the forward
  shock at Wind—but not at STB—was driven by the MC. Examining the MC
  by Grad-Shafranov reconstruction, we find evidence of a double-flux rope
  structure at Wind and STA and possibly also at STB. The orientations are
  at variance with the notion of a large-scale flux tube being observed at
  the three spacecraft. We find consistency of this with the directional
  properties of the solar wind "strahl" electrons. We examine aspects of
  the geomagnetic response and find a double-dip storm corresponding to
  the two interplanetary triggers. The minimum Dst phase was prolonged
  and the geoeffects were intensified due to the interaction. We conclude
  that while the formation of compound streams is a common feature of
  interplanetary space, understanding their components when CIRs are
  involved is a complicated matter needing numerical simulations and/or
  more in situ observations for its complete elucidation.

---------------------------------------------------------
Title: Evidence for Magnetic Reconnection in a Flare and CME Observed
    By RHESSI and SDO/AIA
Authors: Su, Yang; Wang, T.; Holman, G. D.; Dennis, B. R.; Veronig, A.
2011SPD....42.2222S    Altcode: 2011BAAS..43S.2222S
  The double coronal X-ray sources (Sui and Holman 2003, Liu et al. 2008)
  observed by RHESSI are believed to be evidence for the existence of
  a current sheet in between. On the other hand, evidence for magnetic
  reconnection (inflows, outflows, flux rope, cusp, current sheet and
  down flows) has been reported in EUV observations. However, there
  are few (Liu et al. 2010, but with no RHESSI observation) that show
  the combined features expected from reconnection theory. We report
  a study of two limb flares and a related CME observed by RHESSI
  and SDO/AIA at 18:00 UT-21:00 UT on Mar. 08 2011. The SDO-AIA data
  show the formation and eruption of the flux rope (CME). The X-ray
  emission observed by RHESSI shows an extended source at both thermal
  and non-thermal energies above the flaring loop. During the two hard
  X-ray peaks, RHESSI images indicate a reverse Y-shape structure above
  the flaring loop and a Y-shape structure high in the corona. We also
  observe inflows between the two RHESSI coronal sources after the
  second peak at 18:19 UT. The flux rope erupted one hour later. Down
  flows were seen above the post flare loops at this time. These provide
  evidence for magnetic reconnection and a failed eruption, inhibited
  by an overlying magnetic structure in the corona at least an hour
  before the successful CME. We will compare the results with previous
  observations and flare/CME models.

---------------------------------------------------------
Title: Equatorial coronal holes, solar wind high-speed streams,
    and their geoeffectiveness
Authors: Verbanac, G.; Vršnak, B.; Veronig, A.; Temmer, M.
2011A&A...526A..20V    Altcode:
  Context. Solar wind high-speed streams (HSSs), originating in equatorial
  coronal holes (CHs), are the main driver of the geomagnetic activity in
  the late-declining phase of the solar cycle. <BR /> Aims: We analyze
  correlations between CH characteristics, HSSs parameters, and the
  geomagnetic activity indices, to establish empirical relationships
  that would provide forecasting of the solar wind characteristics,
  as well as the effect of HSSs on the geomagnetic activity in periods
  when the effect of coronal mass ejections is low. <BR /> Methods:
  We apply the cross-correlation analysis to the fractional CH area
  (CH) measured between central meridian distances ±10°, solar wind
  parameters (flow velocity V, proton density n, temperature T, and
  the magnetic field B), and the geomagnetic indices Dst and Ap. <BR
  /> Results: The cross-correlation analysis reveals a high degree
  of correlation between all studied parameters. In particular, we
  show that the Ap index is considerably more sensitive to HSS and CH
  characteristics than Dst. The Ap and Dst indices are most tightly
  correlated with the solar wind parameter BV<SUP>2</SUP>. <BR />
  Conclusions: From the point of view of space weather, the most
  important result is that the established empirical relationships
  provide a few-days-in-advance forecasting of the HSS characteristics
  and the related geomagnetic activity at the six-hour resolution. <P
  />Appendices, Figs. 9-14, and table 4 are only available in electronic
  form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Case Study of Four Homologous Large-scale Coronal Waves
    Observed on 2010 April 28 and 29
Authors: Kienreich, I. W.; Veronig, A. M.; Muhr, N.; Temmer, M.;
   Vršnak, B.; Nitta, N.
2011ApJ...727L..43K    Altcode: 2011arXiv1101.5232K
  On 2010 April 28 and 29, the Solar TErrestrial Relations Observatory
  B/Extreme Ultraviolet Imager observed four homologous large-scale
  coronal waves, the so-called EIT-waves, within 8 hr. All waves emerged
  from the same source active region, were accompanied by weak flares and
  faint coronal mass ejections, and propagated into the same direction
  at constant velocities in the range of ~220-340 km s<SUP>-1</SUP>. The
  last of these four coronal wave events was the strongest and fastest,
  with a velocity of 337 ± 31 km s<SUP>-1</SUP> and a peak perturbation
  amplitude of ~1.24, corresponding to a magnetosonic Mach number of M
  <SUB>ms</SUB> ~ 1.09. The magnetosonic Mach numbers and velocities of
  the four waves are distinctly correlated, suggestive of the nonlinear
  fast-mode magnetosonic wave nature of the events. We also found a
  correlation between the magnetic energy buildup times and the velocity
  and magnetosonic Mach number.

---------------------------------------------------------
Title: Implementation of a Calcium telescope at Kanzelhöhe
    Observatory (KSO)
Authors: Hirtenfellner-Polanec, W.; Temmer, M.; Pötzi, W.; Freislich,
   H.; Veronig, A. M.; Hanslmeier, A.
2011CEAB...35..205H    Altcode:
  A new telescope is implemented at Kanzelhöhe Observatory in order to
  observe the chromosphere in the Ca II K line at 393.4 nm (FWHM 0.3
  nm). The design of the new Ca camera system is very similar to the
  well established Kanzelhöhe Photosphere Digital Camera and the Hα
  system and allows obtaining automatically full disc Ca~II~K 2k×2k
  images time series with a cadence of a few seconds. The main purpose
  of this new instrument is a high precision full disc imaging of the
  chromosphere in order to observe flares, plages and the chromospheric
  network. The Ca emission is also an indicator for magnetic activity
  on the sun. Therefore the Ca data will be taken for analysing the
  variations in the structures of the magnetic field.

---------------------------------------------------------
Title: Multiwavelength Investigations of Magnetic Bright Points
Authors: Kühner, O.; Utz, D.; Hanslmeier, A.; Veronig, A.; Roudier,
   T.; Muller, R.; Muthsam, H.
2011CEAB...35...29K    Altcode:
  In this contribution we present our results regarding the study
  of small scale magnetic fields as seen by magnetic bright points
  (MBPs) in different wavelengths and hence different heights. By the
  determination of the size distribution of these features we are able
  to derive the value of the scale height parameter for the photosphere:
  107 km ± 18.5 km. For the Fe I line at 630.25 nm we derived a formation
  height of 225 km.

---------------------------------------------------------
Title: Magnetic energy estimation for small scale magnetic fields
Authors: Utz, D.; Hanslmeier, A.; Veronig, A.; Kühner, O.; Muller,
   R.; Muthsam, H.
2011CEAB...35...19U    Altcode:
  In this paper we derive an estimate of the energy content of small scale
  magnetic <P />fields as observed by magnetic bright points (MBPs). For
  our estimations we use as inputs the size, lifetime, magnetic field
  strength of MBPs and the average number density of those features in the
  quiet Sun. Furthermore we introduce an evolutionary model for MBPs. Our
  results suggest that there is enough magnetic field energy stored in kG
  fields as seen by MBPs to heat the chromosphere and corona. The actual
  heating mechanism and process has to be investigated in the future.

---------------------------------------------------------
Title: STEREO and Wind observations of a fast ICME flank triggering
    a prolonged geomagnetic storm on 5-7 April 2010
Authors: Möstl, C.; Temmer, M.; Rollett, T.; Farrugia, C. J.; Liu,
   Y.; Veronig, A. M.; Leitner, M.; Galvin, A. B.; Biernat, H. K.
2010GeoRL..3724103M    Altcode: 2010arXiv1010.4150M
  On 5 April 2010 an interplanetary (IP) shock was detected by the
  Wind spacecraft ahead of Earth, followed by a fast (average speed
  650 km/s) IP coronal mass ejection (ICME). During the subsequent
  moderate geomagnetic storm (minimum D<SUB>st</SUB> = -72 nT,
  maximum K<SUB>p</SUB> = 8<SUP>-</SUP>), communication with the
  Galaxy 15 satellite was lost. We link images from STEREO/ SECCHI to
  the near-Earth in situ observations and show that the ICME did not
  decelerate much between Sun and Earth. The ICME flank was responsible
  for a long storm growth phase. This type of glancing collision was
  for the first time directly observed with the STEREO Heliospheric
  Imagers. The magnetic cloud (MC) inside the ICME cannot be modeled with
  approaches assuming an invariant direction. These observations confirm
  the hypotheses that parts of ICMEs classified as (1) long-duration
  MCs or (2) magnetic-cloud-like (MCL) structures can be a consequence
  of a spacecraft trajectory through the ICME flank.

---------------------------------------------------------
Title: Application of data assimilation to solar wind forecasting
    models
Authors: Innocenti, M.; Lapenta, G.; Vrsnak, B.; Temmer, M.; Veronig,
   A.; Bettarini, L.; Lee, E.; Markidis, S.; Skender, M.; Crespon, F.;
   Skandrani, C.; Soteria Space-Weather Forecast; Data Assimilation Team
2010AGUFMSM54A..08I    Altcode:
  Data Assimilation through Kalman filtering [1,2] is a powerful
  statistical tool which allows to combine modeling and observations
  to increase the degree of knowledge of a given system. We apply this
  technique to the forecast of solar wind parameters (proton speed, proton
  temperature, absolute value of the magnetic field and proton density) at
  1 AU, using the model described in [3] and ACE data as observations. The
  model, which relies on GOES 12 observations of the percentage of the
  meridional slice of the sun covered by coronal holes, grants 1-day and
  6-hours in advance forecasts of the aforementioned quantities in quiet
  times (CMEs are not taken into account) during the declining phase
  of the solar cycle and is tailored for specific time intervals. We
  show that the application of data assimilation generally improves
  the quality of the forecasts during quiet times and, more notably,
  extends the periods of applicability of the model, which can now provide
  reliable forecasts also in presence of CMEs and for periods other than
  the ones it was designed for. Acknowledgement: The research leading
  to these results has received funding from the European Commission’s
  Seventh Framework Programme (FP7/2007-2013) under the grant agreement
  N. 218816 (SOTERIA project: http://www.soteria-space.eu). References:
  [1] R. Kalman, J. Basic Eng. 82, 35 (1960); [2] G. Welch and G. Bishop,
  Technical Report TR 95-041, University of North Carolina, Department
  of Computer Science (2001); [3] B. Vrsnak, M. Temmer, and A. Veronig,
  Solar Phys. 240, 315 (2007).

---------------------------------------------------------
Title: Multiple, Distant (40 deg) in situ Observations of a Magnetic
    Cloud and a Corotating Interaction Region Complex
Authors: Farrugia, C. J.; Berdichevsky, D. B.; Moestl, C.; Galvin,
   A. B.; Leitner, M.; Popecki, M.; Simunac, K. D.; Opitz, A.; Lavraud,
   B.; Ogilvie, K.; Veronig, A.; Temmer, M.; Luhmann, J. G.; Sauvaud, J.
2010AGUFMSH51C1689F    Altcode:
  We report a comprehensive analysis of in situ observations made
  by Wind and the STEREO probes (STA, STB) of a complex interaction
  between a magnetic cloud (MC) and a corotating interaction region (CIR)
  occurring near the heliospheric current sheet (HCS) on November 19-21,
  2007. The probes were separated by 0.7 AU (~40 deg) with a spread in
  heliographic latitudes (4.8, 2.2, and -0.4 deg for STB, Wind and STA,
  respectively). We employ data from the MFI, SWE and 3DP instruments
  on Wind, and the PLASTIC and IMPACT suites on STEREO. STB, located
  east of Earth, observed a forward shock followed by signatures of
  a MC. The MC took the role of the HCS in that the polarity of the
  interplanetary magnetic field (IMF) on exit was the reverse of that on
  entry. A passage through a plasma sheet is observed. Along the Sun-Earth
  line Wind observed a stream interface (SI) between a forward and a
  reverse shock. A MC, compressed by the CIR, was entrained in this. STA,
  located 20 deg to the west of Earth, saw a MC which was not preceded
  by a shock. A SI trailed the transient. The shocks are examined using
  various methods and from this it is concluded that the forward shock
  at Wind - but not at STB - was driven by the MC. Examining the MC by
  Grad-Shafranov reconstruction, we find evidence of a double-flux rope
  structure at Wind and STA and possibly also at STB. The orientations are
  at variance with the notion of a large-scale flux tube being observed at
  the three spacecraft. We find consistency of this with the directional
  properties of the solar wind "strahl" electrons. We examine aspects of
  the geomagnetic response and find a double-dip storm corresponding to
  the two interplanetary triggers. The minimum Dst phase was prolonged
  and the geoffects were intensified due to the interaction. We conclude
  that while the formation of compound streams is a common feature of
  interplanetary space, understanding their components when CIRs are
  involved is a complicated matter needing numerical simulations and/or
  morein situ observations for its complete elucidation.

---------------------------------------------------------
Title: Propagation Directions and Kinematics of STEREO CME/ICMEs
    Events
Authors: Rollett, T.; Moestl, C.; Temmer, M.; Veronig, A.; Lugaz,
   N.; Biernat, H. K.
2010AGUFMSH41A1775R    Altcode:
  The Heliospheric Imagers on board the two STEREO twin satellites give
  us the possibilities to track Coronal Mass Ejections up to a distance
  of 1 AU. For events of our interest, remote sensing data as well as
  in situ measurements from the other STEREO spacecraft or Wind are
  available. The combination of both allows us to calculate a constant
  propagation direction in the ecliptic plane by using different methods
  (Fixed-Phi and the Harmonic Mean). These methods convert the measured
  elongation into distance by making different assumptions on the
  shape of the CME. With the combined data sets we can also derive the
  kinematics (distance-velocity plots) and try to crosscheck the results
  by taking care of the ambient solar wind. Moreover, we use inverse
  fitting methods for both the Fixed-Phi and Harmonic Mean approaches
  (which assume constant velocity) to fit our measurements and compare
  it to the results calculated by our combined method.

---------------------------------------------------------
Title: The CME/ICME relationship for the 3-5 April 2010 and Aug 1-4
    2010 events
Authors: Moestl, C.; Temmer, M.; Rollett, T.; Kilpua, E. K.; Farrugia,
   C. J.; Veronig, A.; Galvin, A. B.; Biernat, H. K.
2010AGUFMSH43C..07M    Altcode:
  For two coronal mass ejections (CMEs) associated with interplanetary
  CMEs (ICMEs) causing moderate geomagnetic storms in 2010, we discuss
  properties such as interplanetary propagation, orientation and
  arrival time calculation. We study heliospheric images of the CMEs
  provided by STEREO / HI in combination with in situ observations by
  the Wind spacecraft near Earth. The 3-5 April 2010 event was the
  first fast (800 km/s) ICME including a magnetic cloud observed by
  both the STEREO/HI instruments and a near Earth spacecraft. During
  the subsequent geomagnetic storm (minimum Dst = -72 nT, maximum Kp =
  8-), communication with the Galaxy 15 satellite was lost. Using forward
  modeling in combination with HI techniques and the in situ velocity, we
  show that the ICME did not decelerate much between Sun and Earth. Earth
  was not hit directly, but the ICME flank was responsible for a long
  storm growth phase. The magnetic cloud (MC) inside the ICME cannot
  be modeled with approaches assuming an invariant direction. These
  observations confirm the hypotheses that parts of ICMEs classified as
  (1) long-duration MCs or (2) magnetic-cloud-like (MCL) structures
  can be a consequence of a spacecraft trajectory through the ICME
  flank. The 1-4 Aug 2010 events consisted of several CMEs accompanied
  by multiple ICME signatures near Earth, responsible for a two-step
  geomagnetic storm. We discuss which of the ICMEs correspond to the
  flare/filaments/CMEs observed by STEREO/COR/HI and SDO HMI/AIA observed
  closer to the Sun. We apply reconstruction methods to estimate the
  local flux rope orientation and other properties. The ICME signatures
  are linked to HI observations of the CME fronts, which yields full
  CME kinematics between the Sun and Earth. STEREO Ahead HI1/2 images
  of the 3-5 April 2010 Earth-directed coronal mass ejection.

---------------------------------------------------------
Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
   M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
   Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
   B.; White, S. M.
2010ApJ...723..587B    Altcode:
  We analyzed ground- and space-based observations of the eruptive flare
  (3B/X6.5) and associated Moreton wave (~850 km s<SUP>-1</SUP> ~270°
  azimuthal span) of 2006 December 6 to determine the wave driver—either
  flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
  analysis favors a CME driver of the wave, despite key gaps in coronal
  data. The CME scenario has a less constrained/smoother velocity versus
  time profile than is the case for the flare hypothesis and requires an
  acceleration rate more in accord with observations. The CME picture is
  based, in part, on the assumption that a strong and impulsive magnetic
  field change observed by a GONG magnetograph during the rapid rise phase
  of the flare corresponds to the main acceleration phase of the CME. The
  Moreton wave evolution tracks the inferred eruption of an extended
  coronal arcade, overlying a region of weak magnetic field to the west
  of the principal flare in NOAA active region 10930. Observations of
  Hα foot point brightenings, disturbance contours in off-band Hα
  images, and He I 10830 Å flare ribbons trace the eruption from 18:42
  to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
  observations show strong blueshifts at foot points of this arcade
  during the post-eruption phase, indicating mass outflow. At 18:45
  UT, the Moreton wave exhibited two separate arcs (one off each flank
  of the tip of the arcade) that merged and coalesced by 18:47 UT to
  form a single smooth wave front, having its maximum amplitude in
  the southwest direction. We suggest that the erupting arcade (i.e.,
  CME) expanded laterally to drive a coronal shock responsible for the
  Moreton wave. We attribute a darkening in Hα from a region underlying
  the arcade to absorption by faint unresolved post-eruption loops.

---------------------------------------------------------
Title: Observations of Chromospheric Flare Re-brightenings
Authors: Miklenic, C. H.; Veronig, A. M.; Vršnak, B.; Bárta, M.
2010ApJ...719.1750M    Altcode:
  We investigate an active region that produced three C-class flares
  and one M-class flare within 2.5 hr. The morphology and location of
  the C-flares indicate that these events constitute a set of homologous
  flares. Radio observations indicate the occurrence of a downward-moving
  plasmoid during the impulsive phase of the M flare. We use TRACE
  1700 Å filtergrams and SOHO Michelson Doppler Imager magnetograms
  to examine the character of the UV brightenings; i.e., we search
  for re-brightenings of former flare areas both across the series of
  events and within one and the same event. We find that essentially the
  same footpoints re-brighten in each C flare. Based on the progression
  of both the derived magnetic flux change rate and the observed Radio
  Solar Telescope Network microwave emission, we speculate about a further
  re-brightening during the decay phase of the M flare as a further member
  of the series of homologous flares. We conclude that the "postflare"
  field is driven to repeated eruption by continuous, shear-increasing,
  horizontal, photospheric flows, as one end of the involved magnetic
  arcade is anchored in the penumbra of a large sunspot. The observed
  motion pattern of the UV kernels indicates that the arcade evolves
  during the series of events from a both highly sheared and heavily
  entangled state to a still sheared but more organized state.

---------------------------------------------------------
Title: Multiwavelength Imaging and Spectroscopy of Chromospheric
    Evaporation in an M-class Solar Flare
Authors: Veronig, A. M.; Rybák, J.; Gömöry, P.; Berkebile-Stoiser,
   S.; Temmer, M.; Otruba, W.; Vršnak, B.; Pötzi, W.; Baumgartner, D.
2010ApJ...719..655V    Altcode: 2010arXiv1007.0930V
  We study spectroscopic observations of chromospheric evaporation mass
  flows in comparison with the energy input by electron beams derived
  from hard X-ray (HXR) data for the white-light M2.5 flare of 2006 July
  6. The event was captured in high-cadence spectroscopic observing mode
  by SOHO/CDS combined with high-cadence imaging at various wavelengths
  in the visible, extreme ultraviolet, and X-ray domain during the joint
  observing campaign JOP171. During the flare peak, we observe downflows
  in the He I and O V lines formed in the chromosphere and transition
  region, respectively, and simultaneous upflows in the hot coronal
  Si XII line. The energy deposition rate by electron beams derived
  from RHESSI HXR observations is suggestive of explosive chromospheric
  evaporation, consistent with the observed plasma motions. However, for
  a later distinct X-ray burst, where the site of the strongest energy
  deposition is exactly located on the Coronal Diagnostics Spectrometer
  (CDS) slit, the situation is intriguing. The O V transition region
  line spectra show the evolution of double components, indicative of
  the superposition of a stationary plasma volume and upflowing plasma
  elements with high velocities (up to 280 km s<SUP>-1</SUP>) in single
  CDS pixels on the flare ribbon. However, the energy input by electrons
  during this period is too small to drive explosive chromospheric
  evaporation. These unexpected findings indicate that the flaring
  transition region is much more dynamic, complex, and fine structured
  than is captured in single-loop hydrodynamic simulations.

---------------------------------------------------------
Title: A microflare with hard X-ray-correlated gyroresonance line
    emission at 314 MHz
Authors: Aurass, H.; Rausche, G.; Berkebile-Stoiser, S.; Veronig, A.
2010A&A...515A...1A    Altcode:
  Context. Small energy release events in the solar corona can give
  insights into the flare process which are regularly hidden in the
  complex morphology of larger events. For one case we find a narrowband
  radio signal well correlated with the hard X-ray flare. We investigate
  wether these signals are probes for the flare current sheet. <BR
  /> Aims: We aim to establish the relation between narrowband and
  short-duration features (&lt;1% of the observing frequency in the
  spectral range 250-340 MHz, and some 5 s until 2 min, respectively)
  in dynamic radio spectral diagrams and simultaneously occuring
  HXR bursts. <BR /> Methods: We use dynamic radio spectra from the
  Astrophysical Institute Potsdam, HXR images of RHESSI, TRACE coronal and
  chromospheric images, SOHO-MDI high resolution magnetogram data, and
  its potential field extrapolation for the analysis of one small flare
  event in AR10465 on September 26, 2003. We point to similar effects in
  e.g. the X-class flare on November 03, 2003 to demonstrate that we are
  not dealing with a singular phenomenon. <BR /> Results: We confirm the
  solar origin of the extremely narrowband radio emission. From RHESSI
  images and the magnetic field data we identify the probable site of
  the radio source as well as the HXR footpoint and the SXR flare loop
  emission. The flare loop is included in an ongoing change of magnetic
  connectivity as confirmed by TRACE images of hot coronal loops. The
  flare energy is stored in the nonpotential magnetic field substructure
  around the microflare site which is relaxed to a potential one. <BR />
  Conclusions: We conclude that the correlated HXR footpoint/narrowband
  radio emission, and the transition to a second energy release in
  HXR without associated radio emission are direct probes of changing
  magnetic connectivity during the flare. We suppose that the narrowband
  radio emission is due to gyroresonance radiation at the second harmonic
  of the local electron cyclotron frequency. It follows an upper limit
  of the magnetic field in the radio source volume of less than 50%
  of the mean potential field in the same height range. This supports
  the idea that the narrowband radio source is situated in the immediate
  surroundings of the flare current sheet.

---------------------------------------------------------
Title: First Observations of a Dome-shaped Large-scale Coronal
    Extreme-ultraviolet Wave
Authors: Veronig, A. M.; Muhr, N.; Kienreich, I. W.; Temmer, M.;
   Vršnak, B.
2010ApJ...716L..57V    Altcode: 2010arXiv1005.2060V
  We present first observations of a dome-shaped large-scale
  extreme-ultraviolet coronal wave, recorded by the Extreme Ultraviolet
  Imager instrument on board STEREO-B on 2010 January 17. The main
  arguments that the observed structure is the wave dome (and not the
  coronal mass ejection, CME) are (1) the spherical form and sharpness of
  the dome's outer edge and the erupting CME loops observed inside the
  dome; (2) the low-coronal wave signatures above the limb perfectly
  connecting to the on-disk signatures of the wave; (3) the lateral
  extent of the expanding dome which is much larger than that of the
  coronal dimming; and (4) the associated high-frequency type II burst
  indicating shock formation low in the corona. The velocity of the upward
  expansion of the wave dome (v ~ 650 km s<SUP>-1</SUP>) is larger than
  that of the lateral expansion of the wave (v ~ 280 km s<SUP>-1</SUP>),
  indicating that the upward dome expansion is driven all the time,
  and thus depends on the CME speed, whereas in the lateral direction it
  is freely propagating after the CME lateral expansion stops. We also
  examine the evolution of the perturbation characteristics: first the
  perturbation profile steepens and the amplitude increases. Thereafter,
  the amplitude decreases with r <SUP>-2.5 ± 0.3</SUP>, the width
  broadens, and the integral below the perturbation remains constant. Our
  findings are consistent with the spherical expansion and decay of a
  weakly shocked fast-mode MHD wave.

---------------------------------------------------------
Title: Calculating the propagation direction of coronal mass ejections
    by connecting in situ observations with heliospheric images
Authors: Rollett, Tanja; Möstl, Christian; Temmer, Manuela; Veronig,
   Astrid; Biernat, Helfried K.
2010EGUGA..12.3468R    Altcode:
  We determined the propagation direction of two coronal mass ejections
  by using data provided by the Heliospheric Imagers (HI) and the PLASTIC
  and IMPACT instruments onboard the two STEREO satellites. To facilitate
  the tracking of the CME's leading edge we made time-elongation plots
  (J-plots) for the investigated events and tracked the apparent leading
  edge therein several times in order to estimate the measurement
  error. For converting elongation to distance we compared several
  methods (Point-P, Fixed-Phi and their harmonic mean). To determine the
  direction of the CME's propagation in the ecliptic we connected the
  CME-track derived from HI J-plots with the measured in situ arrival
  time by modifying the propagation direction within the used model
  equations. The resulting directions and their errors are discussed
  with respect to the different assumptions used for each technique.

---------------------------------------------------------
Title: Combined STEREO/RHESSI Study of Coronal Mass Ejection
    Acceleration and Particle Acceleration in Solar Flares
Authors: Temmer, M.; Veronig, A. M.; Kontar, E. P.; Krucker, S.;
   Vršnak, B.
2010ApJ...712.1410T    Altcode: 2010arXiv1002.3080T
  Using the potential of two unprecedented missions, Solar Terrestrial
  Relations Observatory (STEREO) and Reuven Ramaty High-Energy Solar
  Spectroscopic Imager (RHESSI), we study three well-observed fast coronal
  mass ejections (CMEs) that occurred close to the limb together with
  their associated high-energy flare emissions in terms of RHESSI hard
  X-ray (HXR) spectra and flux evolution. From STEREO/EUVI and STEREO/COR1
  data, the full CME kinematics of the impulsive acceleration phase up to
  ~4 R <SUB>sun</SUB> is measured with a high time cadence of &lt;=2.5
  minutes. For deriving CME velocity and acceleration, we apply and
  test a new algorithm based on regularization methods. The CME maximum
  acceleration is achieved at heights h &lt;= 0.4 R <SUB>sun</SUB>,
  and the peak velocity at h &lt;= 2.1 R <SUB>sun</SUB> (in one case,
  as small as 0.5 R <SUB>sun</SUB>). We find that the CME acceleration
  profile and the flare energy release as evidenced in the RHESSI HXR flux
  evolve in a synchronized manner. These results support the "standard"
  flare/CME model which is characterized by a feedback relationship
  between the large-scale CME acceleration process and the energy release
  in the associated flare.

---------------------------------------------------------
Title: Dynamics of isolated magnetic bright points derived from
    Hinode/SOT G-band observations
Authors: Utz, D.; Hanslmeier, A.; Muller, R.; Veronig, A.; Rybák,
   J.; Muthsam, H.
2010A&A...511A..39U    Altcode: 2009arXiv0912.1965U
  Context. Small-scale magnetic fields in the solar photosphere can
  be identified in high-resolution magnetograms or in the G-band as
  magnetic bright points (MBPs). Rapid motions of these fields can
  cause magneto-hydrodynamical waves and can also lead to nanoflares by
  magnetic field braiding and twisting. The MBP velocity distribution is
  a crucial parameter for estimating the amplitudes of those waves and
  the amount of energy they can contribute to coronal heating. <BR />
  Aims: The velocity and lifetime distributions of MBPs are derived from
  solar G-band images of a quiet sun region acquired by the Hinode/SOT
  instrument with different temporal and spatial sampling rates. <BR
  /> Methods: We developed an automatic segmentation, identification
  and tracking algorithm to analyse G-Band image sequences to obtain
  the lifetime and velocity distributions of MBPs. The influence of
  temporal/spatial sampling rates on these distributions is studied and
  used to correct the obtained lifetimes and velocity distributions for
  these digitalisation effects. <BR /> Results: After the correction of
  algorithm effects, we obtained a mean MBP lifetime of (2.50 ± 0.05)
  min and mean MBP velocities, depending on smoothing processes, in
  the range of (1-2) km~s<SUP>-1</SUP>. Corrected for temporal sampling
  effects, we obtained for the effective velocity distribution a Rayleigh
  function with a coefficient of (1.62 ± 0.05) km~s<SUP>-1</SUP>. The
  x- and y-components of the velocity distributions are Gaussians. The
  lifetime distribution can be fitted by an exponential function.

---------------------------------------------------------
Title: STEREO quadrature observations of the large-scale EUV wave
    of Feb 13th, 2009
Authors: Ines Kienreich, Mag.; Veronig, Astrid; Temmer, Manuela
2010cosp...38.1841I    Altcode: 2010cosp.meet.1841I
  The event on Feb 13th, 2009 was the first case of a global coronal
  wave observed by the STEREO twin satellites in quadrature. The wave's
  initiation site was at the disk center in EUVI STEREO-B and precisely at
  the limb in STEREO-A. Therefore it was possible to determine the wave's
  on-disk as well as edge-on kinematics and to study its three-dimensional
  structure. From the two STEREO observations we derive the height of
  propagation of the wave, which was found to be in the range between
  80-100 Mm above the photosphere. Comparison of the early phases of
  the contemporaneous CME and the wave's kinematics suggest that the
  wave is set off by the CME lateral expansion. The wave propagates
  globally over the whole hemisphere with a constant velocity 263 16 km
  s-1, which is close to the fast magnetosonic speed in the quiet solar
  corona. Thus we conclude that the observed EUV wave is consistent with
  a MHD fast-mode wave.

---------------------------------------------------------
Title: Analysis of a Global Moreton Wave Observed on 2003 October 28
Authors: Muhr, N.; Vršnak, B.; Temmer, M.; Veronig, A. M.;
   Magdalenić, J.
2010ApJ...708.1639M    Altcode: 2009arXiv0911.4405M
  We study the well-pronounced Moreton wave that occurred in association
  with the X17.2 flare/CME event of 2003 October 28. This Moreton wave is
  striking for its global propagation and two separate wave centers, which
  implies that two waves were launched simultaneously. The mean velocity
  of the Moreton wave, tracked within different sectors of propagation
  direction, lies in the range of v ≈ 900-1100 km s<SUP>-1</SUP> with
  two sectors showing wave deceleration. The perturbation profile analysis
  of the wave indicates amplitude growth followed by amplitude weakening
  and broadening of the perturbation profile, which is consistent with
  a disturbance first driven and then evolving into a freely propagating
  wave. The Extreme-Ultraviolet Imaging Telescope wave front is found to
  lie on the same kinematical curve as the Moreton wave fronts indicating
  that both are different signatures of the same physical process. Bipolar
  coronal dimmings are observed on the same opposite east-west edges of
  the active region as the Moreton wave ignition centers. The radio type
  II source, which is cospatially located with the first wave front,
  indicates that the wave was launched from an extended source region
  (gsim60 Mm). These findings suggest that the Moreton wave is initiated
  by the coronal mass ejection expanding flanks.

---------------------------------------------------------
Title: Automated detection of coronal hole areas
Authors: Rotter, Mag. Thomas; Veronig, Astrid; Temmer, Manuela
2010cosp...38.1890R    Altcode: 2010cosp.meet.1890R
  Coronal holes, as regions of low-density plasma on the sun, have
  magnetic fields that open freely into interplanetary space and thus
  shape our heliosphere. Along these open magnetic fields, charged
  particles leave the Sun to form the high speed component of the solar
  wind. SOHO EIT (Extreme ultraviolet Imaging Telescope) provides for the
  first time continuous observations of coronal holes over a full solar
  cycle (no.23). These data enable us to study the solar cycle evolution
  of coronal holes and their relation to in-situ solar wind magnetic
  field and plasma parameters at 1 AU. In the poster we will present
  first results of an automated coronal hole detection algorithm that
  is currently under development. The algorithm uses a histogram-based
  intensity treshholding technique to determine coronal hole areas and
  their positions.

---------------------------------------------------------
Title: Calculation of CME kinematics and propagation directions by
    connecting STEREO HI-images with in situ data
Authors: Rollett, Tanja; Moestl, Christian; Temmer, Manuela; Veronig,
   Astrid; Biernat, Helfried K.
2010cosp...38.1894R    Altcode: 2010cosp.meet.1894R
  On a sample of selected events we determined the propagation directions
  and the kinematics of several coronal mass ejections by using data
  provided by the Heliospheric Imagers (HI) and the PLASTIC and IMPACT
  instruments onboard the two STEREO satellites and the Wind spacecraft
  near Earth. We tracked for each CME the leading edge and core within
  time-elongation plots (Jplots) and converted the measured elongation
  angle into distance by using different methods (Point-P, Fixed-Phi
  and their harmonic mean). Furthermore, we used the Sheeley-method to
  fit our measurements and calculate the propagation angles and arrival
  times at the other spacecraft assuming that the CMEs propagate with
  constant velocity. Finally we discuss our results by comparing the
  kinematics derived from the different techniques.

---------------------------------------------------------
Title: Multiwavelength alignment of Hinode/SOT Data
Authors: Kuehner, O.; Utz, D.; Hanslmeier, A.; Veronig, A.; Roudier,
   T.; Muller, R.; Muthsam, H.
2010CEAB...34...31K    Altcode:
  First results regarding the spatial alignment of observations taken at
  different wavelengths are presented. An exceptionally long time series
  (48 hours) of data, obtained by the Solar Optical Telescope (SOT)
  of the Hinode satellite, has been analysed. Hinode delivers (among
  other data) high resolution seeing free filtergrams in the magnetic
  sensitive G-band, blue continuum, chromospheric Ca II H line and Fe I
  line. For the study of the position and dynamics of small scale fields
  (MBPs; Magnetic Bright Points) at different wavelengths (at different
  heights in the photosphere and chromosphere) the alignment of these
  data at pixel and subpixel level will be essential. Results concerning
  the height dependence of MBPs will also be of vital importance for
  questions regarding the coronal heating.

---------------------------------------------------------
Title: G-band to Blue-Continuum Excess as quasi total field strength
    magnetogram
Authors: Utz, D.; Hanslmeier, A.; Veronig, A.; Rybák, J.; Muller,
   R.; Muthsam, H.
2010CEAB...34...13U    Altcode:
  The dynamics of the solar plasma is driven by strong localized magnetic
  fields. It is well known that activity like flares and CMEs are related
  to the dissipation and reconnection of these magnetic fields. These
  energetic releases influence and make up the so called space weather. It
  is therefore of vital importance to get a deeper understanding of the
  magnetic fields of the Sun. To get this insights, it is crucial to
  obtain information on the magnetic fields with spatial and temporal
  resolutions as high as possible. In this paper we outline an easy to
  apply method to obtain quasi total magnetic field strength magnetograms
  out of two simple filtergrams (blue continuum and G-band). We will
  present our simple approach and the first results of this method and
  give finally an outlook what has to be done in the future.

---------------------------------------------------------
Title: Evolution of solar wind energy densities during solar minimum
    2007-2009, and features of its effects on the Earth's magnetopause
    and magnetosheath
Authors: Farrugia, Charles; Harris, B.; Leitner, Mag. Martin; Moestl,
   Christian; Simunac, Kristin; Galvin, Antoinette; Veronig, Astrid;
   Temmer, Manuela; Luhmann, Janet G.; Szabo, Adam; Biernat, Helfried K.;
   Lucek, Elizabeth A.
2010cosp...38.1898F    Altcode: 2010cosp.meet.1898F
  We quantify the distribution of magnetic and kinetic energies densities
  of the solar wind at 1 AU as the deep solar activity minimum 2007-2009
  progressed. For this we use near -Earth spacecraft Wind and the STEREO-A
  and B probes, the latter giving us a more comprehensive description
  by extending the longitudinal coverage. We relate general trends in
  interplanetary data to observations on the Sun. We then pick out a
  4-month period, characterized by minima in both the kinetic and magnetic
  energy densities, and examine the profiles of the plasma and magnetic
  field parameters. They show slow-slower solar wind interactions with
  pronounced compressions, and low field strengths in slow solar wind
  streams. These are compared with the general plasma and field properties
  of the slow solar wind and differences are noted. Using Cluster data,
  we determine the average shapes of the bow shock and magnetopause for
  this period. We compare these with gas dynamic and MHD predictions for
  the average Alfven Mach number realized. Major features of observations
  in the Earth's magnetosheath are discussed. This work is meant as a
  contribution to Sun-Earth connection studies.

---------------------------------------------------------
Title: Magnetic field strength distribution of MBPs infered from
    Hinode/SOT filtergram and spectro-polarimetric data
Authors: Utz, Dominik; Veronig, Astrid; Hanslmeier, Arnold; Muller,
   Richard; Muthsam, Herbert
2010cosp...38.2944U    Altcode: 2010cosp.meet.2944U
  Small scale magnetic fields can be observed on the Sun in G-band
  filtergrams as magnetic bright points (MBPs), or by inversions
  of spectro-polarimetric data. In this study we used three
  different data sets of Hinode/SOT observations which were recorded
  simultaneously with the broadband filter device (G-band, Ca II-H) and
  the spectro-polarimeter. The spectro-polarimetric data were already
  prepared as magnetograms (level 2 data). For the identification of the
  MBPs we used an automated identification algorithm. The three data sets
  comprise active regions (a sunspot group and a small sunspot in the
  other case) as well as quiet Sun. The obtained magnetic field strength
  distribution of MBPs is in all three cases similar and shows a peaked
  maximum at 1250 G, which agrees well with theoretical predictions of
  the convectice collapse model.

---------------------------------------------------------
Title: Brightness profiles and size distributions of MBPs observed
    in different heights by HINODE/SOT data
Authors: Kühner, Otmar; Veronig, Astrid; Utz, Dominik; Hanslmeier,
   Arnold; Muthsam, Herbert; Muller, Richard; Roudier, Thierry
2010cosp...38.2948K    Altcode: 2010cosp.meet.2948K
  We study the characteristics of Magnetic Bright Points (MBPs)
  observed at different wave-lenghts and hence different heights of
  the photosphere and chromosphere. The data sets were obtained with
  the Solar Optical Telescope (SOT) of the Hinode satellite. Hinode
  delivers (among other data) high resolution seeing free filtergrams in
  the blue continuum, the Fe I line, the magnetic sensitive G-band and
  the chromospheric Ca II H line. Due to the small scale structure of
  MBPs it was essential for our study to develop an algorithm for the
  image co-alignment at subpixel level for the images taken at these
  four wavelenghts. We studied an exceptionally long time series (48h)
  and analyzed the brightness profiles and size distributions of MBPs
  at different heights. The mean size of the features increases with
  increasing height and shows an exponential behavior. We obtained the
  scale height parameter of the photosphere to be 110 km.

---------------------------------------------------------
Title: New insights into large-scale coronal waves with EUVI/STEREO
Authors: Veronig, Astrid
2010cosp...38.1790V    Altcode: 2010cosp.meet.1790V
  We discuss recent studies on large-scale coronal waves (so-called "EIT
  waves") obtained with the EUVI instruments onboard the twin STEREO
  spacecraft. EUVI has several advantages for coronal wave studies: a)
  high cadence full-disk imaging, which allows us to catch the wave
  evolution and kinematics, b) a large field-of-view, which allows
  simultaneous observations of the erupting CME, and c) observations
  from two vantage points, which enable us to get insight into the
  three-dimensional structure of the wave. The present understanding
  is basically split into different groups of "wave" versus "non-wave"
  interpretations of the physical process behind the phenomenon, as well
  as "flare" versus "CME" for the driving agent. Recent EUVI studies
  suggest that these large-scale coronal waves are fast-mode MHD waves
  initiated by the erupting CME. We will discuss evidence for this
  scenario, but review also alternative explanations.

---------------------------------------------------------
Title: Relation between the dynamics of coronal mass ejections and
    solar flare energetics derived from STEREO and RHESSI observations
Authors: Bein, Bianca; Veronig, Astrid; Berkebile-Stoiser, Sigrid;
   Temmer, Manuela
2010cosp...38.3019B    Altcode: 2010cosp.meet.3019B
  We aim to explore the relation of the energy release in solar flares
  to the dynamical evolution of their associated coronal mass ejections
  for a statistically representative sample of events. For our study,
  we use EUV (171˚, 195˚) and white light coronographic observations
  from A A the STEREO (Solar Terrestial Relations Observatory) SECCHI
  instrument suite. Due to the high time cadence of the STEREO EUVI
  and COR images, the detailed CME kinematics from the initiation
  through the impulsive acceleration to the propagation phase can
  be derived. Information on the energy release in the flares under
  study comes from hard X-ray observations of the RHESSI instrument
  (Ramaty High Energy Solar Spectroscopic Imager). RHESSI non-thermal
  lightcurves as well as the derivative of the GOES soft X-ray flux are
  compared with the acceleration curve of the associated CME.

---------------------------------------------------------
Title: Flare-generated coronal shock on 14 November 2005
Authors: Magdalenic, Jasmina; Marque, Christophe; Zhukov, Andrei;
   Veronig, Astrid; Vrsnak, Bojan
2010cosp...38.1798M    Altcode: 2010cosp.meet.1798M
  Origin of coronal shock waves is still not completely understood. Since
  the flare impulsive phase and the acceleration phase of a CME are
  usually well synchronized, it is difficult to give a conclusive
  answer on the shock wave origin in flare/CME events. We present
  multiwave-length study of a shock wave associated with the flare event
  recorded on 14 November 2005. The evolution of the shock wave signature
  -type II radio burst -is analysed using dynamic spectra recorded by the
  Green Bank Solar Radio Bursts Spectrometer and Nançay Radioheliograph
  imaging. The observations of the plasma dynamics in the low and high
  corona were provided by EIT and LASCO instruments onboard SOHO. The
  strong type II emission starts at unusually high frequency of 700
  MHz. The obtained values for the shock velocity, Alfven velocity and
  Alfven Mach number are in the range of typical shock parameters. The
  shock wave was closely associated with the impulsive phase of the
  compact M3.9 flare in the NOAA AR 10822 (located at S06E60). The
  short impulsive phase of the flare (4 minutes), suggests that a
  strong pressure pulse was ignited by the flare. Additionally, RHESSI
  observations show compact event of a rather high density and high
  temperature which gives indication of a strong, impulsive increase
  of pressure in the small flare loop. SOHO/LASCO observations do not
  show any CME associated with this event. Since the active region
  is rather close to the limb, the possibility that the corresponding
  CME is not observed due to the unfavorable geometry is unlikely. We
  therefore conclude that the shock wave recorded on 14 November 2005
  was a blast wave launched by the impulsive energy release in the course
  of the flare.

---------------------------------------------------------
Title: Study of the kinematics and driver of the global Moreton wave
    observed on 2003 October 28
Authors: Muhr, Mmag. Nicole; Vrsnak, Bojan; Temmer, Manuela; Veronig,
   Astrid; Magdalenic, Jasmina
2010cosp...38.1844M    Altcode: 2010cosp.meet.1844M
  We analyze the evolution and kinematics of the fast, globally
  propagating Moreton wave of 2003 October 28 associated with the extreme
  X17.2 solar flare/CME event. This Moreton wave is distinct due to its
  strengths and azimuthal span of span 360. We study the wave kinematics
  in different propagation directions, and compare it with the following
  associated phenomena: EIT wave, coronal dimmings, fast halo CME, flare,
  and type II burst. The sectoral analysis yield mean velocity values
  in the range 900-1000 km/s; two sectors show wave deceleration. The
  perturbation profile evolution indicates an amplitude growth followed
  by amplitude weakening and broadening, which is consistent with a
  disturbance first driven and then evolving into a freely propagating
  wave. We find two `'radiant points" for the Moreton wave fronts on
  opposite east-west edges of the source region, roughly co-spatial with
  the bipolar coronal dimming. The co-spatiality of the associated radio
  type II burst source and the first Moreton wave fronts indicate that
  the wave was launched from an extended region. These findings indicate
  that the wave is initiated by the CME expanding flanks.

---------------------------------------------------------
Title: Evolution of X-ray sources and magnetic reconnection in solar
    eruptive flares
Authors: Joshi, Bhuwan; Veronig, Astrid; Somov, Boris; Manoharan, P. K.
2010cosp...38.2968J    Altcode: 2010cosp.meet.2968J
  We present detailed multi-wavelength investigations of two solar
  eruptive flares that occurred near the limb of the Sun with the
  aim to study the primary energy release process in the corona and
  associated phenomena at different heights of solar atmosphere. The
  events under investigation are: M7.6 flare from active region NOAA 10486
  on 24 October 2003 and X2.7 flare from active region NOAA 10488 on 3
  November 2003. Being close to the limb, these events provide excellent
  opportunity to examine the motion of X-ray looptop (LT) source. The
  RHESSI X-ray images of both events show similar morphology with well
  defined LT and two distinct footpoint (FP) sources. In both events,
  the X-ray LT source undergoes an apparent downward motion during the
  rise phase. The descending LT source was observed for ∼11 and ∼5
  minutes respectively for the first and second event. We provide an
  interpretation of LT source motion during the rise phase of flares
  in the framework of rainbow reconnection model. The initial phase of
  descending LT source is followed by a long duration phase of upward
  motion of LT source and appearance of HXR FP sources. We combine Hα,
  E(UV) and X-ray spectral analysis to understand the energetic processes
  during the flare evolution.

---------------------------------------------------------
Title: Direction and orientation of CME/ICME events observed by STEREO
Authors: Moestl, Christian; Rollett, Tanja; Temmer, Manuela; Farrugia,
   Charles; Veronig, Astrid; Galvin, Antoinette; Biernat, Helfried K.
2010cosp...38.1881M    Altcode: 2010cosp.meet.1881M
  The two NASA STEREO spacecraft are now approaching a quadrature
  configuration with respect to the Earth. In conjunction with the rising
  solar activity this represents a great opportunity to study coronal
  mass ejections (CMEs) during their journey from the Sun to 1 AU. We
  are in particular concerned with those events which were observed by
  the STEREO/SECCHI imaging instrument in the inner heliosphere and which
  were also detected in situ at 1 AU with STEREO (IMPACT/PLASTIC) or WIND
  (SWE/MFI). This allows for example to check (1) if the direction of
  propagation given by various direction-finding techniques is indeed
  correlated with the signatures which are later observed in situ and (2)
  if the orientation of the magnetic flux rope inside the ICME, which we
  model using the Grad-Shafranov technique, is reflected in properties of
  the CME. Also, the classic three-part structure of CMEs can be related
  to the in situ data. The results are discussed regarding the possibility
  to forecast ICME properties from observations closer to the Sun.

---------------------------------------------------------
Title: Linking remote imagery of two coronal mass ejections to their
    in situ signatures at 1 AU
Authors: Moestl, C.; Farrugia, C. J.; Temmer, M.; Miklenic, C.;
   Veronig, A.; Galvin, A. B.; Leitner, M.; Biernat, H. K.
2009AGUFMSH41A1629M    Altcode:
  We report on how the internal structure of two coronal mass ejections
  at 1 AU might be deduced from white-light images of the heliosphere
  taken from a remote observation point. On June 6-7 2008 the STEREO-B
  spacecraft encountered typical signatures of a magnetic flux rope inside
  an interplanetary coronal mass ejection (ICME). Its axis was inclined
  at 45° to the solar equatorial plane, crossing it at approximately
  30° east of Earth. This direction matches well with various CME
  direction-finding techniques to within 15°, and a possible westward
  deflection of 10° took place between the Sun and 1 AU. Further, we use
  remote images from STEREO-A to show that (1) the CME is unambiguously
  connected to the ICME which swept over STEREO B and can be tracked all
  the way to the 1 AU event, (2) the particular arc-like morphology of the
  CME pointing to an inclined axis, and (3) the three-part structure of
  the CME may be plausibly related to the in situ data with clear density
  variations. The CME event on Feb 13 2009 followed by a magnetic cloud
  on Feb 18 2009 is discussed from the same viewpoint, though the in-situ
  signatures are more complex than for the simple event discussed above.

---------------------------------------------------------
Title: Magnetic Reconnection During the Two-phase Evolution of a
    Solar Eruptive Flare
Authors: Joshi, Bhuwan; Veronig, Astrid; Cho, K. -S.; Bong, S. -C.;
   Somov, B. V.; Moon, Y. -J.; Lee, Jeongwoo; Manoharan, P. K.; Kim,
   Y. -H.
2009ApJ...706.1438J    Altcode: 2008arXiv0809.2484J
  We present a detailed multi-wavelength analysis and interpretation of
  the evolution of an M7.6 flare that occurred near the southeast limb on
  2003 October 24. Pre-flare images at TRACE 195 Å show that the bright
  and complex system of coronal loops already existed at the flaring
  site. The X-ray observations of the flare taken from the Reuven Ramaty
  High Energy Solar Spectroscopic Imager (RHESSI) spacecraft reveal two
  phases of the flare evolution. The first phase is characterized by the
  altitude decrease of the X-ray looptop (LT) source for ~11 minutes. Such
  a long duration of the descending LT source motion is reported for
  the first time. The EUV loops, located below the X-ray LT source,
  also undergo contraction with similar speed (~15 km s<SUP>-1</SUP>)
  in this interval. During the second phase the two distinct hard X-ray
  footpoint (FP) sources are observed which correlate well with UV and
  Hα flare ribbons. The X-ray LT source now exhibits upward motion as
  anticipated from the standard flare model. The RHESSI spectra during the
  first phase are soft and indicative of hot thermal emission from flaring
  loops with temperatures T &gt; 25 MK at the early stage. On the other
  hand, the spectra at high energies (ɛ gsim 25 keV) follow hard power
  laws during the second phase (γ = 2.6-2.8). We show that the observed
  motion of the LT and FP sources can be understood as a consequence
  of three-dimensional magnetic reconnection at a separator in the
  corona. During the first phase of the flare, the reconnection releases
  an excess of magnetic energy related to the magnetic tensions generated
  before a flare by the shear flows in the photosphere. The relaxation
  of the associated magnetic shear in the corona by the reconnection
  process explains the descending motion of the LT source. During the
  second phase, the ordinary reconnection process dominates describing
  the energy release in terms of the standard model of large eruptive
  flares with increasing FP separation and upward motion of the LT source.

---------------------------------------------------------
Title: Linking Remote Imagery of a Coronal Mass Ejection to Its In
    Situ Signatures at 1 AU
Authors: Möstl, C.; Farrugia, C. J.; Temmer, M.; Miklenic, C.;
   Veronig, A. M.; Galvin, A. B.; Leitner, M.; Biernat, H. K.
2009ApJ...705L.180M    Altcode: 2009arXiv0910.1188M
  In a case study (2008 June 6-7) we report on how the internal structure
  of a coronal mass ejection (CME) at 1 AU can be anticipated from
  remote observations of white-light images of the heliosphere. Favorable
  circumstances are the absence of fast equatorial solar wind streams and
  a low CME velocity which allow us to relate the imaging and in situ
  data in a straightforward way. The STEREO-B spacecraft encountered
  typical signatures of a magnetic flux rope inside an interplanetary
  CME (ICME) whose axis was inclined at 45° to the solar equatorial
  plane. Various CME direction-finding techniques yield consistent
  results to within 15°. Further, remote images from STEREO-A show that
  (1) the CME is unambiguously connected to the ICME and can be tracked
  all the way to 1 AU, (2) the particular arc-like morphology of the CME
  points to an inclined axis, and (3) the three-part structure of the CME
  may be plausibly related to the in situ data. This is a first step in
  predicting both the direction of travel and the internal structure of
  CMEs from complete remote observations between the Sun and 1 AU, which
  is one of the main requirements for forecasting the geo-effectiveness
  of CMEs.

---------------------------------------------------------
Title: Multi-wavelength fine structure and mass flows in solar
    microflares
Authors: Berkebile-Stoiser, S.; Gömöry, P.; Veronig, A. M.; Rybák,
   J.; Sütterlin, P.
2009A&A...505..811B    Altcode:
  Aims: We study the multi-wavelength characteristics at high spatial
  resolution, as well as chromospheric evaporation signatures of solar
  microflares. To this end, we analyze the fine structure and mass
  flow dynamics in the chromosphere, transition region and corona of
  three homologous microflares (GOES class &lt;A9/0.7 with/without
  background), which occurred on July 4, 2006 in AR 10898. <BR
  />Methods: A multi-wavelength analysis using temporally and spatially
  highly resolved imaging data from the Dutch open telescope (Hα,
  Ca ii H), the transition region and coronal explorer (17.1 nm),
  the extreme-ultraviolet imaging telescope (19.5 nm), and the Reuven
  Ramaty high energy solar spectroscopic imager (≳3 keV) was carried
  out. EUV line spectra provided by the coronal diagnostic spectrometer
  are searched for Doppler shifts in order to study associated
  plasma flows at chromospheric (He i, T∼3.9× 10<SUP>4</SUP> K),
  transition region (e.g. O v, T∼ 2.6× 10<SUP>5</SUP> K), and
  coronal temperatures (Si xii, T∼ 2× 10<SUP>6</SUP> K). RHESSI
  X-ray spectra provide information about non-thermal electrons. <BR
  />Results: The multi-wavelength appearance of the microflares is in
  basic agreement with the characteristics of large flares. For the
  first event, a complex flare sequence is observed in TRACE 17.1 nm
  images (T≈ 1 MK), which show several brightenings, narrow loops
  of enhanced emission, and an EUV jet. EIT 19.5 nm data (T≈ 1.5 MK)
  exhibit similar features for the third event. DOT measurements show
  finely structured chromospheric flare brightenings for all three events,
  loop-shaped fibrils of increased emission between Hα brightenings, as
  well as a similar feature in Ca ii. For all three events, a RHESSI X-ray
  source (3-8 keV, T ≳ 10 MK) is located in between two chromospheric
  brightenings situated in magnetic flux of opposite polarity. We find
  the flow dynamics associated with the events to be very complex. In
  the chromosphere and transition region, CDS observed downflows for
  the first (v ≲ 40 km s<SUP>-1</SUP>), and upflows for the second
  event (v ≲ 40 km s<SUP>-1</SUP>). During the third microflare, we
  find upflows of ≲ 20 km s<SUP>-1</SUP> and also weak downflows of
  ≲20 km s<SUP>-1</SUP> in two separate brightenings. For all three
  microflares, multi-component fitting is needed for several profiles
  of He i, O v, and Ne vi lines observed at the flare peaks, which
  indicate spatially unresolved, oppositely directed flows of ≲180
  km s<SUP>-1</SUP>. We interpret these flows as twisting motions of
  the flare loops. Loop-shaped fibrils in between Hα brightenings
  showing opposite flow directions (v≈5 km s<SUP>-1</SUP>) are also
  observed in DOT Hα Dopplergrams. RHESSI X-ray spectra show evidence
  of non-thermal bremsstrahlung for two of the three microflares. The
  electron beam flux density deposited in the chromosphere for these
  events is estimated to straddle the threshold heating flux between
  gentle and explosive evaporation. <P />Appendix A and the movie are
  only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: STEREO Quadrature Observations of the Three-Dimensional
    Structure and Driver of a Global Coronal Wave
Authors: Kienreich, I. W.; Temmer, M.; Veronig, A. M.
2009ApJ...703L.118K    Altcode: 2009arXiv0908.3571K
  We present the first observations of a global coronal wave ("EIT wave")
  from the two STEREO satellites in quadrature. The wave's initiation
  site was at the disk center in STEREO-B and precisely on the limb in
  STEREO-A. These unprecedented observations from the STEREO Extreme
  Ultraviolet Imaging (EUVI) instruments enable us to gain insight into
  the wave's kinematics, initiation, and three-dimensional structure. The
  wave propagates globally over the whole solar hemisphere visible to
  STEREO-B with a constant velocity of ~263 ± 16 km s<SUP>-1</SUP>. From
  the two STEREO observations, we derive a height of the wave in the
  range of ~80-100 Mm. Comparison of the wave kinematics with the early
  phase of the erupting coronal mass ejection (CME) structure indicates
  that the wave is initiated by the CME lateral expansion, and then
  propagates freely with a velocity close to the fast magnetosonic speed
  in the quiet solar corona.

---------------------------------------------------------
Title: Analytic Modeling of the Moreton Wave Kinematics
Authors: Temmer, M.; Vršnak, B.; Žic, T.; Veronig, A. M.
2009ApJ...702.1343T    Altcode: 2009arXiv0908.3746T
  The issue whether Moreton waves are flare-ignited or coronal mass
  ejection (CME)-driven, or a combination of both, is still a matter of
  debate. We develop an analytical model describing the evolution of a
  large-amplitude coronal wave emitted by the expansion of a circular
  source surface in order to mimic the evolution of a Moreton wave. The
  model results are confronted with observations of a strong Moreton
  wave observed in association with the X3.8/3B flare/CME event from
  2005 January 17. Using different input parameters for the expansion
  of the source region, either derived from the real CME observations
  (assuming that the upward moving CME drives the wave), or synthetically
  generated scenarios (expanding flare region, lateral expansion of the
  CME flanks), we calculate the kinematics of the associated Moreton
  wave signature. Those model input parameters are determined which
  fit the observed Moreton wave kinematics best. Using the measured
  kinematics of the upward moving CME as the model input, we are not able
  to reproduce the observed Moreton wave kinematics. The observations
  of the Moreton wave can be reproduced only by applying a strong and
  impulsive acceleration for the source region expansion acting in a
  piston mechanism scenario. Based on these results we propose that the
  expansion of the flaring region or the lateral expansion of the CME
  flanks is more likely the driver of the Moreton wave than the upward
  moving CME front.

---------------------------------------------------------
Title: Temporal comparison of nonthermal flare emission and
    magnetic-flux change rates
Authors: Miklenic, C. H.; Veronig, A. M.; Vršnak, B.
2009A&A...499..893M    Altcode: 2009arXiv0910.1701M
  Context: To understand the mechanisms that trigger solar flares,
  we require models describing and quantifying observable responses
  to the original energy release process, since the coronal energy
  release site itself cannot be resolved with current technical
  equipment. Testing the usefulness of a particular model requires the
  comparison of its predictions with flare observations. <BR />Aims:
  To test the standard flare model (CSHKP-model), we measured the
  magnetic-flux change rate in five flare events of different GOES
  classes using chromospheric/photospheric observations and compared
  its progression with observed nonthermal flare emission. We calculated
  the cumulated positive and negative magnetic flux participating in the
  reconnection process, as well as the total reconnection flux. Finally,
  we investigated the relations between the total reconnection flux,
  the GOES class of the events, and the linear velocity of the
  flare-associated CMEs. <BR />Methods: Using high-cadence Hα and
  TRACE 1600 Å image time-series data and MDI/SOHO magnetograms, we
  measured the required observables (newly brightened flare area and
  magnetic-field strength inside this area). RHESSI and INTEGRAL hard
  X-ray time profiles in nonthermal energy bands were used as observable
  proxies for the flare-energy release rate. <BR />Results: We detected
  strong temporal correlations between the derived magnetic-flux change
  rate and the observed nonthermal emission of all events. The cumulated
  positive and negative fluxes, with flux ratios of between 0.64 and 1.35,
  were almost equivalent to each other. Total reconnection fluxes ranged
  between 1.8×10<SUP>21</SUP> Mx for the weakest event (GOES class B9.5)
  and 15.5×10<SUP>21</SUP> Mx for the most energetic one (GOES class
  X17.2). The amount of magnetic flux participating in the reconnection
  process was higher in more energetic events than in weaker ones. Flares
  with more reconnection flux were associated with faster CMEs.

---------------------------------------------------------
Title: CME Projection Effects Studied with STEREO/COR and SOHO/LASCO
Authors: Temmer, M.; Preiss, S.; Veronig, A. M.
2009SoPh..256..183T    Altcode:
  Based on a set of 11 CME events we study the impact of projection
  effects by tracking CME leading edge features in the plane of sky
  (traditional CME tracking) from combined STEREO-SECCHI and SOHO-LASCO
  observations up to 20R<SUB>⊙</SUB>. By using CME observations from two
  vantage points and applying triangulation techniques, the source region
  location of the CME on the solar surface was determined (heliospheric
  longitude and latitude) to correct for projection effects. With
  this information, the directivity and "true" speed of a CME can be
  estimated in a simple way. The comparison of the results obtained from
  the spacecraft pairs SOHO-LASCO/STEREO-A and SOHO-LASCO/STEREO-B allows
  us to study the reliability of the method. The determined CME source
  region is generally coincident within ≲10°.

---------------------------------------------------------
Title: Multispacecraft recovery of a magnetic cloud and its origin
    from magnetic reconnection on the Sun
Authors: Möstl, C.; Farrugia, C. J.; Miklenic, C.; Temmer, M.;
   Galvin, A. B.; Luhmann, J. G.; Kilpua, E. K. J.; Leitner, M.;
   Nieves-Chinchilla, T.; Veronig, A.; Biernat, H. K.
2009JGRA..114.4102M    Altcode: 2009JGRA..11404102M
  Multipoint spacecraft observations of a magnetic cloud on 22 May 2007
  have given us the opportunity to apply a multispacecraft technique
  to infer the structure of this large-scale magnetic flux rope in
  the solar wind. Combining WIND and STEREO-B magnetic field and
  plasma measurements, we construct a combined magnetic field map by
  integrating the Grad-Shafranov equation, this being one of the very
  first applications of this technique in the interplanetary context. From
  this we obtain robust results on the shape of the cross section,
  the orientation and magnetic fluxes of the cloud. The only slightly
  “flattened” shape is discussed with respect to its heliospheric
  environment and theoretical expectations. We also relate these results
  to observations of the solar source region and its associated two-ribbon
  flare on 19 May 2007, using Hα images from the Kanzelhöhe observatory,
  SOHO/MDI magnetograms and SECCHI/EUVI 171 Å images. We find a close
  correspondence between the magnetic flux reconnected in the flare and
  the poloidal flux of the magnetic cloud. The axial flux of the cloud
  agrees with the prediction of a recent 3-D finite sheared arcade
  model to within a factor of 2, which is evidence for formation of
  at least half of the magnetic flux of the ejected flux rope during
  the eruption. We outline the relevance of this result to models of
  coronal mass ejection initiation, and find that to explain the solar
  and interplanetary observations elements from sheared arcade as well
  as erupting-flux-rope models are needed.

---------------------------------------------------------
Title: Multi-spacecraft STEREO observations of magnetic clouds
Authors: Möstl, C.; Farrugia, C. J.; Miklenic, C.; Temmer, M.;
   Veronig, A.; Biernat, H. K.; Kilpua, E. K. J.; Galvin, A. B.; Luhmann,
   J. G.; Ogilvie, K. W.
2009EGUGA..11.4987M    Altcode:
  In addition to 3D imaging capabilities, the two STEREO spacecraft
  also provide unprecedented in-situ observations of the local solar
  wind plasma and magnetic field at 1 AU at increasing longitudinal
  separation from Earth. This presents a very good opportunity to
  model interplanetary coronal mass ejections with a clearly rotating
  magnetic field (magnetic clouds) using more than one spacecraft
  to probe their full spatial extent and flux content. This is
  important not only for space weather prediction purposes but also
  for understanding CME initiation processes. To this end, we employ
  the Grad-Shafranov reconstruction technique suitably extended for
  the use of multi-spacecraft data. We present a summary of results on
  some magnetic clouds seen by STEREO and WIND where this approach was
  feasible. Furthermore, we search for the solar sources of these events
  and, wherever possible, also discuss comparisons with CME triangulation
  techniques.

---------------------------------------------------------
Title: The size distribution of magnetic bright points derived from
    Hinode/SOT observations
Authors: Utz, D.; Hanslmeier, A.; Möstl, C.; Muller, R.; Veronig,
   A.; Muthsam, H.
2009A&A...498..289U    Altcode: 2009arXiv0912.2637U
  Context: Magnetic bright points (MBPs) are small-scale magnetic features
  in the solar photosphere. They may be a possible source of coronal
  heating by rapid footpoint motions that cause magnetohydrodynamical
  waves. The number and size distribution are of vital importance in
  estimating the small scale-magnetic-field energy. <BR />Aims: The
  size distribution of MBPs is derived for G-band images acquired by the
  Hinode/SOT instrument. <BR />Methods: For identification purposes, a new
  automated segmentation and identification algorithm was developed. <BR
  />Results: For a sampling of 0.108 arcsec/pixel, we derived a mean
  diameter of (218 ± 48) km for the MBPs. For the full resolved data set
  with a sampling of 0.054 arcsec/pixel, the size distribution shifted
  to a mean diameter of (166 ± 31) km. The determined diameters are
  consistent with earlier published values. The shift is most probably
  due to the different spatial sampling. <BR />Conclusions: We conclude
  that the smallest magnetic elements in the solar photosphere cannot
  yet be resolved by G-band observations. The influence of discretisation
  effects (sampling) has also not yet been investigated sufficiently.

---------------------------------------------------------
Title: Cosmic ray modulation by corotating interaction regions
Authors: Čalogović, Jaša; Vršnak, Bojan; Temmer, Manuela; Veronig,
   Astrid M.
2009IAUS..257..425C    Altcode:
  We analyzed the relationship between the ground-based modulation of
  cosmic rays (CR) and corotating interaction regions (CIRs). Daily
  averaged data from 8 different neutron monitor (NM) stations were
  used, covering rigidities from R<SUB>c</SUB> = 0 - 12.91 GeV. The in
  situ solar wind data were taken from the Advanced Composition Explorer
  (ACE) database, whereas the coronal hole (CH) areas were derived from
  the Solar X-Ray Imager onboard GOES-12. For the analysis we have
  chosen a period in the declining phase of solar cycle 23, covering
  the period 25 January-5 May 2005. During the CIR periods CR decreased
  typically from 0.5% to 2%. A cross-correlation analysis showed a
  distinct anti-correlation between the magnetic field and CR, with the
  correlation coefficient (r) ranging from -0.31 to -0.38 (mean: -0.36)
  and with the CR time delay of 2 to 3 days. Similar anti-correlations
  were found for the solar wind density and velocity characterized by
  the CR time lag of 4 and 1 day, respectively. The relationship was also
  established between the CR modulation and the area of the CIR-related CH
  with the CR time lag of 5 days after the central-meridian passage of CH.

---------------------------------------------------------
Title: Structure Analysis of a Model Solar Photosphere
Authors: Leitner, P.; Hanslmeier, A.; Muthsam, H. J.; Veronig, A.;
   Löw-Baselli, B.; Obertscheider, C.
2009CEAB...33...69L    Altcode:
  The structure of the solar photosphere has been studied by means of
  correlation analysis. The data analysis is based on a 3D radiation
  hydrodynamics-code modelling solar surface convection with high
  resolution in both, space and time. The variation of thermodynamic
  quantities with depth have been evaluated as well as the dependencies
  among those quantities as a function of depth. This gives an insight
  into the structure of the convective-radiative transition layer. We
  determined height levels for regions of thermal convection, convective
  overshoot, and for the near-surface layer up from where radiation
  takes over the role of the outward energy transport.

---------------------------------------------------------
Title: Observations of Chromospheric Evaporation Flows in RHESSI
    Microflares
Authors: Berkebile-Stoiser, S.; Gömöry, P.; Veronig, A.; Rybák, J.
2009CEAB...33..169B    Altcode:
  We present the analysis of two homologous microflares of GOES class
  A9 with respect to mass flows in the chromosphere and transition
  region. Both events show non-thermal emission (evidence for beamed
  electrons) in RHESSI X-ray spectra. As outlined by observations of
  the Coronal Diagnostic Spectrometer, we find for the first event
  downflows in the He I, O V and Ne VI line reaching speeds up to 40
  km s^{-1} at the position of chromospheric flare brightenings. On
  the other hand, upflows with velocities ≲40 km^{-1} are observed
  for the second microflare. <P />According to hydrodynamic flare
  simulations, the non-thermal electron energy density F deposited in
  the chromosphere determines if chromospheric evaporation is `gentle' or
  `explosive'. Thus, we derive rough estimates for F in our microflares
  and compare the results to the observed CDS flow properties.

---------------------------------------------------------
Title: Magnetic Flux Change Rates and Nonthermal Flare Emission
Authors: Miklenic, C.; Veronig, A.; Vršnak, B.
2009CEAB...33..197M    Altcode:
  We tested the standard flare model by measuring the magnetic flux
  change rate in five flares of different GOES classes and compared it
  to the observed nonthermal flare hard X-ray emission. In addition we
  calculated the cumulated positive and negative magnetic reconnection
  flux, as well as the total reconnection flux. We also investigated the
  relations between the total reconnection flux, the GOES importance of
  the events, and the linear velocity of the flare-associated CMEs. The
  required observables (newly brightened flare area and magnetic field
  strength inside this area) were measured using high-cadence Hα and
  TRACE 1600 Å image time series along with MDI/SOHO magnetograms. RHESSI
  and INTEGRAL hard X-ray time profiles in nonthermal energy bands served
  as observable proxies for the flare energy release rate. We found
  good temporal correlations between the derived magnetic flux change
  rate and the observed nonthermal emission in all events. Cumulated
  positive and negative fluxes were roughly balanced. The amount of
  magnetic reconnection flux was larger in more energetic events than in
  weaker ones. Flares with more reconnection flux were associated with
  faster CMEs. The findings indicate that the standard flare model is
  applicable to the analysed events.

---------------------------------------------------------
Title: Radio Bursts and Magnetic Field Structure During Microflares
Authors: Aurass, H.; Rausche, G.; Hofmann, A.; Berkebile-Stoiser,
   S.; Veronig, A.
2009CEAB...33..159A    Altcode:
  This paper presents an analysis of two selected microflares seen
  in dynamic radio spectra recorded by the Astrophysical Institute
  Potsdam and imaged by the Nançay Multifrequency Radioheliograph. The
  microflares were observed in hard X-rays by the Ramaty High Energy
  Solar Spectroscopic Imager in AR 10465 on September 26, 2003. Magnetic
  field connections are selected compatible with the spatial extent of
  the HXR sources and the Transition Region and Coronal Explorer-detected
  chromospheric UV continuum brightenings. The selected field lines are a
  small subset of the potential extrapolation of a SOHO--Michelson Doppler
  Imager high resolution magnetogram. For a type III-associated microflare
  a loop-like magnetic field structure is found with a spatial extent
  of ≈35 arcsec. A type II-precursor-associated (stronger) microflare
  brightened in a smaller-scale circularly arranged arcade formed by
  field lines of about 12 arcsec foot point distance. All microflare
  site-compatible field lines have turning points in heights of 5--20
  arcsec and are situated underneath larger-scale arcades joining the
  main leading and trailing field concentrations. For understanding type
  III-burst source positions, an electron path must exist between the
  HXR source site and large-scale open field lines in the trailing part
  of AR 10465. This demands for reconnection of the selected small-scale
  closed field lines with overlying field systems, electron propagation
  to the trailing spot, and diffusion from closed to open field lines
  leading out into the solar wind. The type II burst precursor sources
  are formed in a magnetic hole of the potential field. This supports
  the view of a growing large amplitude flare wave which is not intense
  enough to raise to a spatially extended type II-exciting shock front but
  to smaller-scale sub-shocks forming the radio precursor burst sources.

---------------------------------------------------------
Title: Multi-wavelength Observations of Microflares Near an Active
    Region
Authors: Bein, B.; Veronig, A.; Rybak, J.; Gömöry, P.;
   Berkebile-Stoiser, S.; Sütterlin, P.
2009CEAB...33..179B    Altcode:
  We study the multi-wavelength characteristics of a microflaring active
  region (AR 10898) near disc centre. The analysed data were from the
  4^{th} of July 2006, and were recorded by DOT (Hα, Ca II H), RHESSI
  (X-rays), TRACE (EUV) and SOHO/MDI (magnetograms). The identified
  microflare events were studied with respect to their magnetic field
  configuration and their multi-wavelength time evolution.

---------------------------------------------------------
Title: Discretization Effects on the Size Distribution of Magnetic
    Bright Points
Authors: Utz, D.; Hanslmeier, A.; Muller, R.; Veronig, A.; Muthsam,
   H.; Möstl, C.
2009CEAB...33...29U    Altcode:
  We developed an automated identification algorithm for magnetic bright
  points to derive the size distribution of MBPs in a quiet region near
  solar disc centre. For this purpose two different data sets from the
  Hinode/SOT mission were used. The first data set had a pixel spatial
  sampling of 0.108 arcsec/pixel, whereas the second data set had the full
  achievable spatial sampling of 0.54 arcsec/pixel. We found, that the
  size distribution shifted from a mean value of 218 km in diameter to
  a smaller value of about 166 km in diameter when the spatial sampling
  was higher. Therefore, we suggest that discretization effects play a
  crucial role for the study of small scale features. How the shift of
  the two distributions could be explained, and how a deeper insight
  into the discretization problem could be gained, is discussed.

---------------------------------------------------------
Title: Multi-spacecraft Recovery of a Magnetic Cloud and its Origin
    From Magnetic Reconnection on the Sun
Authors: Möstl, C.; Farrugia, C. J.; Miklenic, C.; Temmer, M.; Galvin,
   A. B.; Luhmann, J. G.; Biernat, H. K.; Huttunen, K. E.; Leitner, M.;
   Nieves-Chinchilla, T.; Veronig, A.
2008AGUFMSH23B1634M    Altcode:
  Multi-point spacecraft observations of a magnetic cloud on May 22, 2007
  has given us the opportunity to apply a multi-spacecraft technique
  to infer the structure of this large-scale magnetic flux rope in
  the solar wind. Combining WIND and STEREO-B magnetic field and plasma
  measurements, since these spacecraft entered the ejecta, we construct a
  combined magnetic field map by integrating the Grad-Shafranov equation,
  this being one of the very first applications of this technique in
  the interplanetary context. From this we obtain robust results on the
  shape of the cross-section, the orientation and magnetic fluxes of the
  cloud. The only slightly "flattened" shape is discussed with respect
  to its heliospheric environment and theoretical expectations. We also
  relate these results to observations of the Solar source region and
  its associated two- ribbon flare on May 19, 2007 using Hα images from
  the Kanzelhöhe observatory, SOHO/MDI magnetograms and SECCHI/EUVI
  171~Å~images. We find a close correspondence between the magnetic
  flux reconnected in the flare and the poloidal flux of the magnetic
  cloud. The axial flux of the cloud agrees with the prediction of a
  recent 3D finite sheared arcade model to within a factor of 2, which
  is evidence for formation of at least half of the magnetic flux of the
  ejected flux rope during the eruption. We outline the relevance of
  this result to models of coronal mass ejection initiation, and find
  that to explain the solar and interplanetary observations elements
  from sheared-arcade as well as erupting-flux-rope models are needed.

---------------------------------------------------------
Title: Global thermospheric density variations caused by high-speed
    solar wind streams during the declining phase of solar cycle 23
Authors: Lei, Jiuhou; Thayer, Jeffrey P.; Forbes, Jeffrey M.; Sutton,
   Eric K.; Nerem, R. Steven; Temmer, Manuela; Veronig, Astrid M.
2008JGRA..11311303L    Altcode:
  Thermosphere densities at 400 km altitude from accelerometer
  measurements on the CHAMP satellite are used to investigate oscillations
  at periods of less than 13 days during the declining phase of solar
  cycle 23 (2002-2007). The periodic oscillations around 7 and 9 days in
  neutral density tend to occur during the latter part of the declining
  solar cycle when periodically recurrent fast streams in the solar
  wind modulate the level of geomagnetic activity in the geospace
  environment. It is interesting that the periodic oscillations in
  neutral density are felt globally and are proportional to the periodic
  Kp perturbations at the same frequency. Moreover, the periods of 7
  and 9 days apparently reflect subharmonics of the 27-day rotation
  and may be related to the longitudinal distribution of coronal holes;
  however the comparison of the temporal evolution of the periodicities
  between the coronal holes area and solar wind in 2005 indicates that
  their relationships are rather complex.

---------------------------------------------------------
Title: Two-spacecraft reconstruction of a magnetic cloud and
    comparison to its solar source
Authors: Möstl, C.; Miklenic, C.; Farrugia, C. J.; Temmer, M.;
   Veronig, A.; Galvin, A. B.; Vršnak, B.; Biernat, H. K.
2008AnGeo..26.3139M    Altcode:
  This paper compares properties of the source region with those inferred
  from satellite observations near Earth of the magnetic cloud which
  reached 1 AU on 20 November 2003. We use observations from space
  missions SOHO and TRACE together with ground-based data to study
  the magnetic structure of the active region NOAA 10501 containing
  a highly curved filament, and determine the reconnection rates and
  fluxes in an M4 flare on 18 November 2003 which is associated with
  a fast halo CME. This event has been linked before to the magnetic
  cloud on 20 November 2003. We model the near-Earth observations with
  the Grad-Shafranov reconstruction technique using a novel approach in
  which we optimize the results with two-spacecraft measurements of the
  solar wind plasma and magnetic field made by ACE and WIND. The two
  probes were separated by hundreds of Earth radii. They pass through
  the axis of the cloud which is inclined -50 degree to the ecliptic. The
  magnetic cloud orientation at 1 AU is consistent with an encounter with
  the heliospheric current sheet. We estimate that 50% of its poloidal
  flux has been lost through reconnection in interplanetary space. By
  comparing the flare ribbon flux with the original cloud fluxes we infer
  a flux rope formation during the eruption, though uncertainties are
  still significant. The multi-spacecraft Grad-Shafranov method opens
  new vistas in probing of the spatial structure of magnetic clouds in
  STEREO-WIND/ACE coordinated studies.

---------------------------------------------------------
Title: Large-scale Coronal Waves Observed with EUVI/STEREO
Authors: Veronig, A.; Temmer, M.; Vrsnak, B.
2008ESPM...12.2.97V    Altcode:
  We report first observations and analysis of flare/CME associated
  large-scale coronal waves (so-called "EIT waves") observed with
  high time cadence by the EUVI instruments onboard the recent STEREO
  mission. The EIT instrument onboard SOHO for the first time directly
  imaged global disturbances in the solar corona, but the observations
  are severely hampered by the low cadence of EIT (12-15 min). Thus,
  the nature and origin of these large-scale disturbances are still
  not sufficiently constraint by observations, and it is an intense
  matter of debate whether EIT waves: a) are the coronal counterparts of
  Moreton waves observed in the chromosphere; b) are caused by the flare
  explosive energy release or by the erupting CME; c) are waves at all or
  rather propagating disturbances related to magnetic field line opening
  and restructuring associated with the CME lift-off. The high cadence
  full-disk coronal imaging by the EUVI instruments on the twin STEREO
  spacecraft provide us with the unprecedented opportunity to study the
  dynamics and origin of flare/CME associated coronal waves. We present
  first studies of global coronal waves observed with EUVI finding wave
  deceleration, indicative of an MHD blast wave (Veronig et al. 2008,
  ApJ Lett., in press).

---------------------------------------------------------
Title: Relation between CME SchmiederAcceleration Profile and Flare
    Energy Release derived from Combined STEREO and RHESSI Observations
Authors: Temmer, M.; Veronig, A. M.; Vrsnak, B.
2008ESPM...12.2.96T    Altcode:
  In the standard flare/CME picture magnetic reconnection occurs in
  a current sheet formed behind the CME, which may provide a feedback
  relationship between both phenomena. To study the relationship of the
  large-scale CME acceleration and the energy release in the associated
  flare we analyze three well observed events. The observations cover
  the early (low corona) evolution of the CMEs with the EUVI instruments
  aboard the twin STEREO spacecraft and the RHESSI hard X-ray emission
  of the associated flare. Since the flare hard X-rays are due to fast
  electrons, they provide the most direct indicator of the evolution of
  the flare energy release in the flare. The results are compared to case
  studies for halo-CMEs where a close synchronization between the CME
  acceleration and the flare energy release was found (Temmer et al.,
  ApJ, 2008, 673, L95).

---------------------------------------------------------
Title: RHESSI Microflares: II. Implications for Loop Structure
    and Evolution
Authors: Stoiser, S.; Brown, J. C.; Veronig, A. M.
2008SoPh..250..315S    Altcode: 2008SoPh..tmp..127S
  We present simple analytic models which predict the peak X-ray
  emission measure and temperature attained in flares in which the
  chromospheric evaporation process takes place either in a single
  `monolithic' loop or in a loop consisting of several filaments that
  are created successively as the energy release process proceeds
  in time. As possible mechanisms driving chromospheric evaporation
  we consider both classical heat conduction from the loop top and
  non-thermal electron beams. The model predictions are tested for a
  set of 18 well studied RHESSI microflares. The results suggest beam
  driven evaporation in filamented loops as being capable of accounting
  for the observed emission measures and temperatures though there are
  issues with the very high beam densities needed. On the other hand,
  estimates of the emission measures achieved by conductive evaporation
  which are derived by using the Rosner - Tucker - Vaiana (RTV) scaling
  law are much larger than the observed ones. Possible reasons for this
  discrepancy are discussed.

---------------------------------------------------------
Title: High-Cadence Observations of a Global Coronal Wave by
    STEREO EUVI
Authors: Veronig, Astrid M.; Temmer, Manuela; Vršnak, Bojan
2008ApJ...681L.113V    Altcode: 2008arXiv0806.0710V
  We report a large-scale coronal wave (so-called EIT wave) observed
  with high cadence by EUVI on board STEREO in association with the GOES
  B9.5 flare and double CME event on 2007 May 19. The EUVI instruments
  provide us with the unprecedented opportunity to study the dynamics of
  flare/CME associated coronal waves. The coronal wave under study reveals
  deceleration, indicative of a freely propagating MHD wave. Complementary
  analysis of the associated flare and erupting filament/CME hint at wave
  initiation by the CME expanding flanks, which drive the wave only over
  a limited distance. The associated flare is very weak and occurs too
  late to account for the wave initiation.

---------------------------------------------------------
Title: Analysis of a Moreton Wave Associated with the X17.2/4B
    Flare/CME of 28-10-2003
Authors: Muhr, M.; Temmer, M.; Veronig, A.; Vršnak, B.; Hanslmeier, A.
2008CEAB...32...79M    Altcode:
  The fast Moreton wave of 28-Oct-2003 associated with the extreme X17.2
  solar flare/CME event is studied. It can be followed in four sectors,
  spanning almost over 360° on the visible solar disc. The mean wave
  velocity lies in the range of v∼900-1000 km s^{-1}. We find two
  wave ignition centres on opposite edges of the source region, which
  may indicate that the wave is driven by the CME expanding flanks.

---------------------------------------------------------
Title: Acceleration in Fast Halo CMEs and Synchronized Flare HXR
    Bursts
Authors: Temmer, M.; Veronig, A. M.; Vršnak, B.; Rybák, J.; Gömöry,
   P.; Stoiser, S.; Maričić, D.
2008ApJ...673L..95T    Altcode:
  We study two well-observed, fast halo CMEs, covering the full CME
  kinematics including the initiation and impulsive acceleration phase,
  and their associated flares. We find a close synchronization between the
  CME acceleration profile and the flare energy release as indicated by
  the RHESSI hard X-ray flux onsets, as well as peaks occur simultaneously
  within 5 minutes. These findings indicate a close physical connection
  between both phenomena and are interpreted in terms of a feedback
  relationship between the CME dynamics and the reconnection process in
  the current sheet beneath the CME.

---------------------------------------------------------
Title: Large-scale coronal waves observed with STEREO/EUVI
Authors: Veronig, Astrid; Temmer, Manuela; Vrsnak, Bojan
2008cosp...37.3328V    Altcode: 2008cosp.meet.3328V
  The EUVI instruments onboard the twin STEREO spacecraft provide
  high-cadence full-disk imaging of the solar atmosphere with four
  different filters at EUV wavelengths. These observations are highly
  suitable to study the kinematics and dynamics of flare/CME associated
  coronal waves, so-called "EIT waves". We present a detailed analysis
  of one coronal wave captured by the EUVI instruments, with particular
  emphasis on the wave dynamics and its connection to the associated
  flare (RHESSI hard X-rays) and CME (STEREO COR1) in terms of blast
  wave versus driven wave scenario.

---------------------------------------------------------
Title: Synchronization between the CME acceleration and the energy
    release in the associated flare
Authors: Temmer, Manuela; Veronig, Astrid; Vrsnak, Bojan
2008cosp...37.3167T    Altcode: 2008cosp.meet.3167T
  In the standard flare/CME picture magnetic reconnection occurs in a
  current sheet formed behind the CME, which is indicative of a feedback
  relationship between both phenomena. We analyze two X-class flare/CME
  events which were well covered by RHESSI hard X-ray observations,
  and the early evolution of the CMEs could be observed in TRACE and
  GOES/SXI images. Since the flare hard X-rays are due to fast electrons,
  they provide the most direct indicator of the evolution of the energy
  release in the flare. This data set enables us to study in detail
  the relationship of the large-scale CME acceleration and the energy
  release in the associated flare.

---------------------------------------------------------
Title: Flare and Erupting Filament of 19th May, 2007 - Sources of
    a Magnetic Cloud Observed by Stereo
Authors: Culhane, J. Leonard; Bone, Laura; Hara, Hirohisa; Farrugia,
   Charles; Galvin, Antoinette; van Driel-Gesztelyi, Lidia; Popecki,
   Mark; Luhmann, Janet G.; Veronig, Astrid
2008cosp...37..609C    Altcode: 2008cosp.meet..609C
  A GOES Class B9.5 flare was observed on the Sun starting 19-May-2007
  at 12:51 UT. Data obtained by the Hinode, TRACE, RHESSI, STEREO and
  SOHO spacecraft will be discussed. The evolution and eventual eruption
  of a related Halpha filament were monitored by patrol observations at
  Kanzelhoehe. These observations and associated detection of EUV-emitting
  filament material will also be presented. The flare energetics and
  the possible role of the flare in the filament eruption will be
  examined. Finally the relationship of the magnetic configuration
  of the solar eruption along with the temperature and composition of
  erupting material will be assessed in relation to the properties of
  a magnetic cloud later detected by STEREO in-situ instruments near
  Earth on 22-May-2007.

---------------------------------------------------------
Title: On the relation between in situ observations of a magnetic
    cloud and its solar source
Authors: Christiane, Miklenic; Möstl, Christian; Temmer, Manuela;
   Veronig, Astrid; Farrugia, Charles; Biernat, Helfried K.
2008cosp...37..543C    Altcode: 2008cosp.meet..543C
  During flare/CME events, fast plasma clouds and shocks may be generated,
  which propagate through interplanetary space. Interplanetary coronal
  mass ejections, which contain a magnetic cloud, can induce, if
  Earth-directed, geomagnetic storms, which can cause deleterious effects
  on space-borne and ground-based installations. Since our dependency
  on space-borne technical equipment is increasing, the importance of
  reliable space weather forecasts is indisputable. To achieve better
  space weather forecasts, it is essential to understand the relation
  between solar source observations and in situ observations of the
  magnetic cloud. For the CME/flare event on July 6, 2006, we present
  a detailed analysis of the magnetic field configuration of the solar
  source and the reconnection flux of the flare, which is related to the
  associated magnetic cloud properties observed at the Earth. The event is
  well covered by multi-wavelength observations from SoHO, TRACE, RHESSI,
  as well as ground-based Hα observations. The magnetic field geometry
  of the magnetic cloud at 1 AU is modeled with the Grad-Shafranov
  reconstruction technique, applying observations from two satellites,
  namely WIND and ACE.

---------------------------------------------------------
Title: Projection effects in coronal mass ejections studied with
    STEREO and SoHO
Authors: Temmer, Manuela; Preiss, Stefanie; Veronig, Astrid; Vrsnak,
   Bojan
2008cosp...37.3168T    Altcode: 2008cosp.meet.3168T
  The STEREO mission consists of two identical satellites, positioned
  ahead (A) and behind (B) the Earth, which observe the Sun from viewing
  angles different from that of LASCO aboard SoHO (positioned at L1). The
  kinematics (speed) and width of a coronal mass ejection (CME) is derived
  by measuring distinct CME features observed in projection against the
  plane of sky. As STEREO-A, STEREO-B, and LASCO/SoHO, observe a CME
  from three different viewing angles, the resulting CME kinematics and
  widths differ. By combining the observations from the three satellites
  we study for several well observed CMEs the importance of projection
  effects for the CME kinematics and expansion.

---------------------------------------------------------
Title: RHESSI Microflares: I. X-Ray Properties and Multiwavelength
    Characteristics
Authors: Stoiser, S.; Veronig, A. M.; Aurass, H.; Hanslmeier, A.
2007SoPh..246..339S    Altcode:
  We study the general X-ray and multiwavelength characteristics
  of microflares of GOES class A0.7 to B7.4 (background subtracted)
  detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager
  (RHESSI) on 26 September 2003 comparing them with the properties of
  regular flares. All the events for which X-ray imaging was feasible
  originated in one active region and were accumulated in areas with
  intermixed magnetic polarities. During the events' rise and peak phase,
  the RHESSI X-ray spectra show a steep nonthermal power-law component
  (4≲γ≲10) for energies ≳ 10 keV. Further evidence for the
  presence of electron beams is provided by the association with radio
  type III bursts in 5 out of 11 events where AIP radio spectra were
  available. The strongest event in our sample shows radio signatures
  of a type II precursor. The thermally emitting flare plasma observed
  by RHESSI is found to be hot, 11≲T≲15 MK, with small emission
  measures, 10<SUP>46</SUP>≲EM≲10<SUP>47</SUP> cm<SUP>−3</SUP>,
  concentrated in the flare loop. In the EUV (TRACE 171 Å), the UV (TRACE
  1600 Å) and Kanzelhöhe Solar Observatory Hα, impulsive brightenings
  at both ends of the RHESSI 3 - 6 keV X-ray loop source are observed,
  situated in opposite magnetic polarity fields. During the decay phase,
  a postflare loop at the location of the RHESSI loop source is observed
  in the TRACE 171 Å channel showing plasma that is cooled from ≳ 10
  MK to ≈ 1 MK. Correlations between various thermal and nonthermal
  parameters derived from the RHESSI microflare spectra compared to
  the same correlations obtained for a set of small and large flares by
  Battaglia et al. (Astron. Astrophys.439, 737, 2005) indicate that the
  RHESSI instrument gives us a spectrally biased view since it detects
  only hot (T≳10 MK) microflares, and thus the correlations between
  RHESSI microflare parameters have to be interpreted with caution. The
  thermal and nonthermal energies derived for the RHESSI microflares
  are \bar{E}_{th}=7× 10^{27} ergs and \bar{E}_{nth}=2× 10^{29} ergs,
  respectively. Possible reasons for the order-of-magnitude difference
  between the thermal and nonthermal microflare energies, which was also
  found in previous studies, are discussed. The determined event rate
  of 3.7 h<SUP>−1</SUP> together with the average microflare energies
  indicate that the total energy in the observed RHESSI microflares is
  far too small to account for the heating of the active region corona
  in which they occur.

---------------------------------------------------------
Title: Two-spacecraft Reconstruction of a Magnetic Cloud and
    Comparison to its Solar Source
Authors: Moestl, C.; Miklenic, C.; Farrugia, C.; Temmer, M.; Veronig,
   A.; Galvin, A.; Biernat, H.
2007AGUFMSH32A0781M    Altcode:
  Relating observations of coronal mass ejections (CMEs) and their
  interplanetary counterpart (ICMEs) is a centerpoint of Sun-Earth
  connection studies and our ability to forecast space weather. Here we
  focus on the ICME containing a magnetic cloud which reached Earth on
  November 20, 2003 and gave rise to the strongest storm of solar cycle
  23, with a minimum Dst of -472 nT. Its strong geoeffective impact
  came about two weeks after the massive eruptions known as "Halloween"
  events resulted in comparable geo-effects. The aims of this study
  are threefold. We first apply an advanced methodology to analyze with
  diverse observations the event on the solar disk, which occurred on
  Nov 18, 2003, and was associated with an M4 flare and a halo CME. We
  then employ a Grad-Shafranov reconstruction technique to model the
  magnetic field geometry at 1 AU. To this end, we use measurements
  acquired by spacecraft WIND and ACE, ~400 RE apart. We show how these
  twin-spacecraft observations allow us to optimize the reconstructed
  map. Finally, we relate the solar to the interplanetary observations,
  paying special attention to the orientations and the magnetic fluxes
  involved at the two locales. By comparing the flare with the original
  cloud fluxes we infer a possible in-situ flux rope formation during
  the eruption, though uncertainties are still significant. The error
  margins in the comparisons are also carefully assessed.

---------------------------------------------------------
Title: Study of Two Long Duration Eruptive Flares with the Hinode
    and RHESSI Spacecraft
Authors: Culhane, J. L.; Bone, L.; Williams, D. R.; Brooks, D. H.;
   Vandriel-Gesztelyi, L.; Hara, H.; Veronig, A.
2007AGUFMSH52C..05C    Altcode:
  Two eruptive flares that occurred on 17 December 2006 and 19 May
  2007 were observed by the instruments on the Hinode and RHESSI
  spacecraft. Both share some of the characteristics of the well known
  event observed with Yohkoh in February, 1992 (Tsuneta et al., 1992)
  in that they seem largely thermal in character and exhibit many of
  the features of the standard Carmichael, Hirayama, Sturrock, Kopp,
  Pneuman (CHSKP) flare model. However for these events, much additional
  (e.g. SOHO) data is available including the observation of an associated
  erupting filament on 19th May that was seen at the Kanzelhoehe Solar
  Observatory. In this talk the role of the outflow termination shock
  in heating the flare plasma will be re-examined. In particular the
  presence of plasma over a wide temperature range in the flare cusps
  and the possibility of non-thermal effects following the shock heating,
  will be assessed. The behaviour of the erupting filament material will
  also be discussed.

---------------------------------------------------------
Title: Large amplitude oscillatory motion along a solar filament
Authors: Vršnak, B.; Veronig, A. M.; Thalmann, J. K.; Žic, T.
2007A&A...471..295V    Altcode: 2007arXiv0707.1752V
  Context: Large amplitude oscillations of solar filaments is a phenomenon
  that has been known for more than half a century. Recently, a new mode
  of oscillations, characterized by periodical plasma motions along
  the filament axis, was discovered. <BR />Aims: We analyze such an
  event, recorded on 23 January 2002 in Big Bear Solar Observatory Hα
  filtergrams, to infer the triggering mechanism and the nature of the
  restoring force. <BR />Methods: Motion along the filament axis of a
  distinct buldge-like feature was traced, to quantify the kinematics of
  the oscillatory motion. The data were fitted by a damped sine function
  to estimate the basic parameters of the oscillations. To identify the
  triggering mechanism, morphological changes in the vicinity of the
  filament were analyzed. <BR />Results: The observed oscillations of the
  plasma along the filament were characterized by an initial displacement
  of 24 Mm, an initial velocity amplitude of 51 km s<SUP>-1</SUP>,
  a period of 50 min, and a damping time of 115 min. We interpret
  the trigger in terms of poloidal magnetic flux injection by magnetic
  reconnection at one of the filament legs. The restoring force is caused
  by the magnetic pressure gradient along the filament axis. The period of
  oscillations, derived from the linearized equation of motion (harmonic
  oscillator) can be expressed as P=π√{2}L/v_Aϕ≈4.4L/v_Aϕ, where
  v_Aϕ =B<SUB>ϕ0</SUB>/√μ_0ρ represents the Alfvén speed based
  on the equilibrium poloidal field B<SUB>ϕ0</SUB>. <BR />Conclusions:
  Combination of our measurements with some previous observations of
  the same kind of oscillations shows good agreement with the proposed
  interpretation. <P />Movie to Fig. 1 is only available in electronic
  form at http://www.aanda.org

---------------------------------------------------------
Title: Multi-Wavelength Signatures of Magnetic Reconnection of a
    Flare-Associated Coronal Mass Ejection
Authors: Joshi, Bhuwan; Manoharan, P. K.; Veronig, Astrid M.; Pant,
   P.; Pandey, Kavita
2007SoPh..242..143J    Altcode: 2007astro.ph..1368J
  The evolution of an X2.7 solar flare, that occurred in a complex
  βγδ magnetic configuration region on 3 November 2003 is discussed
  by utilizing a multi-wavelength data set. The very first signature of
  pre-flare coronal activity is observed in radio wavelengths as a type
  III burst that occurred several minutes prior to the flare signature in
  Hα. This type III burst is followed by the appearance of a loop-top
  source in hard X-ray (HXR) images obtained from RHESSI. During the
  main phase of the event, Hα images observed from ARIES solar tower
  telescope, Nainital, reveal well-defined footpoint (FP) and loop-top
  (LT) sources. As the flare evolves, the LT source moves upward and
  the separation between the two FP sources increases. The co-alignment
  of Hα with HXR images shows spatial correlation between Hα and HXR
  footpoints, whereas the rising LT source in HXR is always located
  above the LT source seen in Hα. The evolution of LT and FP sources
  is consistent with the reconnection models of solar flares. The EUV
  images at 195 Å taken by SOHO/EIT reveal intense emission on the disk
  at the flaring region during the impulsive phase. Further, slow-drifting
  type IV bursts, observed at low coronal heights at two time intervals
  along the flare period, indicate rising plasmoids or loop systems. The
  intense type II radio burst at a time in between these type IV bursts,
  but at a relatively greater height, indicates the onset of CME and
  its associated coronal shock wave. The study supports the standard
  CSHKP model of flares, which is consistent with nearly all eruptive
  flare models. More importantly, the results also contain evidence for
  breakout reconnection before the flare phase.

---------------------------------------------------------
Title: Periodic Appearance of Coronal Holes and the Related Variation
    of Solar Wind Parameters
Authors: Temmer, Manuela; Vršnak, Bojan; Veronig, Astrid M.
2007SoPh..241..371T    Altcode:
  We compared the variability of coronal hole (CH) areas (determined
  from daily GOES/SXI images) with solar wind (daily ACE data) and
  geomagnetic parameters for the time span 25 January 2005 until 11
  September 2005 (late declining phase of solar cycle 23). Applying
  wavelet spectral analysis, a clear 9-day period is found in the
  CH time series. The GOES/SXI image sequence suggests that this
  periodic variation is caused by a mutual triangular distribution of
  CHs ∼120° apart in longitude. From solar wind parameters a 9-day
  periodicity was obtained as well, simultaneously with the 9-day period
  in the CH area time series. These findings provide strong evidence
  that the 9-day period in solar wind parameters, showing up as higher
  harmonic of the solar rotation frequency, is caused by the "periodic"
  longitudinal distribution of CHs on the Sun recurring for several
  solar rotations. The shape of the wavelet spectrum from the Dst index
  matches only weakly with that from the CH areas and is more similar to
  the wavelet spectrum of the solar wind magnetic field magnitude. The
  distinct 9-day period does not show up in sunspot group areas which
  gives further evidence that the solar wind modulation is strongly
  related to CH areas but not to active region complexes. The wavelet
  power spectra for the whole ACE data range (∼1998 - 2006) suggest that
  the 9-day period is not a singular phenomenon occurring only during
  a specific time range close to solar minimum but is occasionally also
  present during the maximum and decay phase of solar cycle 23. The main
  periods correspond to the solar rotation (27<SUP>d</SUP>) as well as
  to the second (13.5<SUP>d</SUP>) and third (9<SUP>d</SUP>) harmonic.

---------------------------------------------------------
Title: Birth and evolution of a dense coronal loop in a complex
    flare region
Authors: Bone, L.; Brown, J. C.; Fletcher, L.; Veronig, A.; White, S.
2007A&A...466..339B    Altcode:
  Context: During the 14th/15th of April 2002, several flares occurred
  in NOAA active region complex 9893/9910. Two of these were previously
  interpreted as having anomalously high coronal column densities. <BR
  />Aims: We develop a scenario using multiwavelength observations
  to explain the high coronal column density (≈10<SUP>20</SUP>
  cm<SUP>-2</SUP>) present at the onset of the 14th April 2002 M3.7
  hard X-ray event. <BR />Methods: Prior to this event a series of
  flares occurred in close temporal and spatial proximity. We observe
  the sequence of flares in a multiwavelength regime from radio to hard
  X-rays. This allows us to study the particle acceleration and plasma
  evaporation in these events. <BR />Results: The observations of these
  flares lead us to propose a sequence of reconnections between multiple
  systems of loops in a 3 dimensional field geometry. We suggest that
  the dense loops in the M3.7 event can be explained as being already
  filled with plasma from the earlier events; these loops then themselves
  become unstable or reconnect leading to particle acceleration into
  an overdense coronal environment. We explore the possibility that a
  high-beta disruption is behind the instability of these dense loops,
  leading to the 14th April 2002 M3.7 event and the observation of hard
  X-rays in the corona at energies up to ≈50 keV.

---------------------------------------------------------
Title: Acceleration Phase of Coronal Mass Ejections: I. Temporal
    and Spatial Scales
Authors: Vršnak, Bojan; Maričić, Darije; Stanger, Andrew L.;
   Veronig, Astrid M.; Temmer, Manuela; Roša, Dragan
2007SoPh..241...85V    Altcode:
  We study kinematics of 22 coronal mass ejections (CMEs) whose
  motion was traced from the gradual pre-acceleration phase up to
  the post-acceleration stage. The peak accelerations in the studied
  sample range from 40, up to 7000 m s<SUP>−2</SUP>, and are inversely
  proportional to the acceleration phase duration and the height range
  involved. Accelerations and velocities are, on average, larger in CMEs
  launched from a compact source region. The acceleration phase duration
  is proportional to the source region dimensions; i.e., compact CMEs
  are accelerated more impulsively. Such behavior is interpreted as
  a consequence of stronger Lorentz force and shorter Alfvén time
  scales involved in compact CMEs (with stronger magnetic field and
  larger Alfvén speed being involved at lower heights). CMEs with
  larger accelerations and velocities are on average wider, whereas the
  widths are not related to the source region dimensions. Such behavior is
  explained in terms of the field pile-up ahead of the erupting structure,
  which is more effective in the case of a strongly accelerated structure.

---------------------------------------------------------
Title: Acceleration Phase of Coronal Mass Ejections:
    II. Synchronization of the Energy Release in the Associated Flare
Authors: Maričić, Darije; Vršnak, Bojan; Stanger, Andrew L.;
   Veronig, Astrid M.; Temmer, Manuela; Roša, Dragan
2007SoPh..241...99M    Altcode:
  We analyze the relationship between the acceleration of coronal mass
  ejections (CMEs) and the energy release in associated flares, employing
  a sample of 22 events in which the CME kinematics were measured from
  the pre-eruption stage up to the post-acceleration phase. The data
  show a distinct correlation between the duration of the acceleration
  phase and the duration of the associated soft X-ray (SXR) burst rise,
  whereas the CME peak acceleration and velocity are related to the
  SXR peak flux. In the majority of events the acceleration started
  earlier than the SXR burst, and it is usually prolonged after the
  SXR burst maximum. In about one half of the events the acceleration
  phase is very closely synchronized with the fastest growth of the SXR
  burst. An additional one quarter of the events may be still considered
  as relatively well-synchronized, whereas in the remaining quarter of the
  events there is a considerable mismatch. The results are interpreted
  in terms of the feedback relationship between the CME dynamics and
  the reconnection process in the wake of the CME.

---------------------------------------------------------
Title: Coronal Holes and Solar Wind High-Speed Streams:
    II. Forecasting the Geomagnetic Effects
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid M.
2007SoPh..240..331V    Altcode:
  We present a simple method of forecasting the geomagnetic storms caused
  by high-speed streams (HSSs) in the solar wind. The method is based
  on the empirical correlation between the coronal hole area/position
  and the value of the Dst index, which is established in a period of
  low interplanetary coronal mass ejection (ICME) activity. On average,
  the highest geomagnetic activity, i.e., the minimum in Dst, occurs
  four days after a low-latitude coronal hole (CH) crosses the central
  meridian. The amplitude of the Dst dip is correlated with the CH area
  and depends on the magnetic polarity of the CH due to the Russell -
  McPherron effect. The Dst variation may be predicted by employing the
  expression Dst(t)=(−65±25×cos λ)[A(t<SUP>*</SUP>)]<SUP>0.5</SUP>,
  where A(t<SUP>*</SUP>) is the fractional CH area measured in the
  central-meridian slice [−10°,10°] of the solar disc, λ is the
  ecliptic longitude of the Earth, ± stands for positive/negative CH
  polarity, and t−t<SUP>*</SUP>=4 days. In periods of low ICME activity,
  the proposed expression provides forecasting of the amplitude of the
  HSS-associated Dst dip to an accuracy of ≈30%. However, the time of
  occurrence of the Dst minimum cannot be predicted to better than ±2
  days, and consequently, the overall mean relative difference between
  the observed and calculated daily values of Dst ranges around 50%.

---------------------------------------------------------
Title: Coronal Holes and Solar Wind High-Speed Streams: I. Forecasting
    the Solar Wind Parameters
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid M.
2007SoPh..240..315V    Altcode:
  We analyze the relationship between the coronal hole (CH) area/position
  and physical characteristics of the associated corotating high-speed
  stream (HSS) in the solar wind at 1 AU. For the analysis we utilize the
  data in the period DOY 25 - 125 of 2005, characterized by a very low
  coronal mass ejection (CME) activity. Distinct correlations between
  the daily averaged CH parameters and the solar wind characteristics
  are found, which allows us to forecast the solar wind velocity v,
  proton temperature T, proton density n, and magnetic field strength B,
  several days in advance in periods of low CME activity. The forecast
  is based on monitoring fractional areas A, covered by CHs in the
  meridional slices embracing the central meridian distance ranges
  [−40°,−20°], [−10°,10°], and [20°,40°]. On average, the
  peaks in the daily values of n, B, T, and v appear delayed by 1, 2,
  3, and 4 days, respectively, after the area A attains its maximum
  in the central-meridian slice. The peak values of the solar wind
  parameters are correlated to the peak values of A, which provides
  also forecasting of the peak values of n, B, T, and v. The most
  accurate prediction can be obtained for the solar wind velocity, for
  which the average relative difference between the calculated and the
  observed peak values amounts to \overline{\vertδ\vert}≈10 %. The
  forecast reliability is somewhat lower in the case of T, B, and n (
  \overline{\vertδ\vert}≈20 , 30, and 40%, respectively). The space
  weather implications are discussed, including the perspectives for
  advancing the real-time calculation of the Sun - Earth transit times
  of coronal mass ejections and interplanetary shocks, by including more
  realistic real-time estimates of the solar wind characteristics.

---------------------------------------------------------
Title: Observational Characteristics of Magnetic Reconnection in a
    Two-Ribbon Flare
Authors: Miklenic, C. H.; Veronig, A. M.; Vršnak, B.; Hanslmeier, A.
2007CEAB...31...39M    Altcode:
  A well-observed GOES M3.9 two-ribbon flare was analysed in order
  to derive the local reconnection rate (coronal electric field) and
  the global reconnection rate (magnetic flux change rate), as well
  as the energy release rate (Poynting flux) in a two-ribbon flare
  from chromospheric/photospheric observations, using TRACE 1600 Å,
  Kanzelhöhe Hα, SOHO/MDI, and RHESSI hard X-ray (HXR) data. We found
  good temporal correlations between the derived time profiles and
  observed HXR flux. Furthermore, it was confirmed that equal shares of
  positive and negative magnetic flux participated in the reconnection
  process. The findings indicate that the 2D reconnection model is
  applicable to the analysed flare.

---------------------------------------------------------
Title: Analysis of the Flare Wave Associated with the 3B/X3.8 Flare
    of January 17, 2005
Authors: Thalmann, J. K.; Veronig, A. M.; Temmer, M.; Vršnak, B.;
   Hanslmeier, A.
2007CEAB...31..187T    Altcode:
  The flare wave associated with the 3B/X3.8 flare and coronal mass
  ejection (CME) of January 17, 2005 are studied using imaging data
  in the Hα and EUV spectral channels. Due to the high-cadence Hα
  observations from Kanzelhöhe Solar Observatory (KSO), a distinct
  Moreton wave can be identified in ∼40 Hα frames over a period
  of ∼7 minutes. The associated coronal EIT wave is identifiable in
  only one EUV frame and appears close to the simultaneously observed
  Moreton wave front, indicating that they are closely associated
  phenomena. Beside the morphology of the wave across the solar disc
  (covering an angular extend of ∼130°), the evolution in different
  directions is studied to analyse the influence of a coronal hole (CH)
  on the wave propagation. The Moreton wave shows a decelerating character
  which can be interpreted in terms of a freely propagating fast-mode MHD
  shock. The parts of the wave front moving towards the CH show a lower
  initial and mean speed, and a greater amount of deceleration than the
  segments moving into the undisturbed direction. This is interpreted
  as the tendency of high Alfvén velocity regions to influence the
  propagation of wave packets.

---------------------------------------------------------
Title: Spatial Restriction to HXR Footpoint Locations by Reconnection
    Site Geometries
Authors: Temmer, M.; Vršnak, B.; Veronig, A.; Miklenic, M.
2007CEAB...31...49T    Altcode: 2007astro.ph..1203T
  It is assumed that HXR sources map to the primary energy release site in
  flares where particle acceleration occurs. Strong HXR sources are mostly
  observed at confined regions along the reconnecting magnetic arcade. We
  make a general approach on how the geometry of the reconnecting current
  sheet (CS) may influence the strength and localization of observed HXR
  sources. For this we use results from an analysis on the 3B/X3.8 flare
  on January 17, 2005 (Temmer et al., 2007), as well as measurements from
  the associated CME. Due to the close match of the CME acceleration
  profile and the flare HXR flux, we suppose that the CME might play a
  certain role in modifying the geometry of the CS (“symmetric” versus
  “asymmetric” vertically stretched CS). This could be the driver for
  “guiding” the accelerated particles to confined areas along the
  flaring arcade and might explain the spatially limited occurrence of
  strong HXR sources in comparison to elongated ribbons as seen in Hα
  and UV.

---------------------------------------------------------
Title: Reconnection and energy release rates in a two-ribbon flare
Authors: Miklenic, C. H.; Veronig, A. M.; Vršnak, B.; Hanslmeier, A.
2007A&A...461..697M    Altcode:
  Aims:The aim of this study was to derive the local reconnection
  rate (coronal electric field) and the global reconnection rate
  (magnetic flux change rate), as well as the energy release rate
  (Poynting flux), in a two-ribbon flare from chromospheric/photospheric
  observations. Furthermore, we tested whether equal shares of positive
  and negative magnetic flux are involved in the flare process. <BR
  />Methods: A well-observed GOES M3.9 two-ribbon flare was analyzed. The
  required observables (ribbon expansion velocity, newly brightened area,
  and magnetic field strength at the ribbon front) were extracted from
  the TRACE 1600 Å and Kanzelhöhe Hα image time series, and a SOHO
  MDI magnetogram. Furthermore, the ratio of the converted positive
  vs. negative magnetic flux was determined. Both RHESSI hard X-ray
  20-60 keV full-disk time profiles and subregion time profiles derived
  from a time series of RHESSI images in the same energy range were used
  as independent, observable proxies for the energy release rate. The
  RHESSI images were also used to localize the sites where the bulk
  of the energy was deposited by fast electrons. <BR />Results: We
  found good temporal correlations between the derived time profiles
  (local and global reconnection rate, Poynting flux) and observed
  HXR flux. The local reconnection-rate peak values ranged from 2.7 {V
  cm<SUP>-1</SUP>} to 11.8 {V cm<SUP>-1</SUP>}, whereas the positive
  and the negative magnetic flux covered by the flare emission were
  equal within 5-10%. <BR />Conclusions: .The results indicate that
  the local reconnection rate, the global reconnection rate, and the
  energy release rate in a simple two-ribbon flare can be derived from
  chromospheric/photospheric observations. Furthermore, it was confirmed
  that equal shares of positive and negative magnetic flux participated
  in the reconnection process.

---------------------------------------------------------
Title: Energy Release Rates along Hα Flare Ribbons and the Location
    of Hard X-Ray Sources
Authors: Temmer, M.; Veronig, A. M.; Vršnak, B.; Miklenic, C.
2007ApJ...654..665T    Altcode:
  Local reconnection and energy release rates for an X3.8 flare that
  occurred on 2005 January 17 are derived. In particular, we distinguish
  between Hα flare ribbon segments that were accompanied by RHESSI
  hard X-ray (HXR) footpoints and those without HXRs. We find that the
  reconnection and energy release rates are not uniform along the flare
  ribbons but much larger at the locations where the HXR footpoints are
  observed. The difference is about 2 orders of magnitude in the case of
  the energy release rates and 1 order of magnitude for the reconnection
  rates (with peak values up to 8 kV m<SUP>-1</SUP>). These differences
  are enough to explain the different flare morphologies typically
  observed in HXRs (compact footpoints) and Hα/UV (extended ribbons)
  by the limited dynamic range of present HXR instruments. Our results
  are consistent with a scenario in which the electrons are accelerated
  primarily along a certain subsystem of magnetic loops as outlined by
  the HXR footpoints, and only a minor fraction (for the 2005 January
  17 flare estimated to be about 1/15) go into the large flare arcade
  outlined by the Hα ribbons and EUV postflare loops.

---------------------------------------------------------
Title: RHESSI Results   Time for a Rethink?
Authors: Brown, J. C.; Kontar, E. P.; Veronig, A. M.
2007LNP...725...65B    Altcode: 2006astro.ph..7440B
  Hard X-rays and γ-rays are the most direct signatures of energetic
  electrons and ions in the sun’s atmosphere which is optically thin at
  these energies and their radiation involves no coherent processes. Being
  collisional they are complementary to gyro-radiation in probing
  atmospheric density as opposed to magnetic field and the electrons
  are primarily 10 100~keV in energy, complementing the (&gt;100 keV)
  electrons likely responsible for microwave bursts. The pioneering
  results of the Ramaty High Energy Solar Spectroscopic Imager (RHESSI)
  are raising the first new major questions concerning solar energetic
  particles in many years. Some highlights of these results are discussed
  primarily around RHESSI topics on which the authors have had direct
  research involvement particularly when they are raising the need for
  re-thinking of entrenched ideas. Results and issues are broadly divided
  into discoveries in the spatial, temporal and spectral domains, with the
  main emphasis on flare hard X-rays/fast electrons but touching also on
  γ-rays/ions, non-flare emissions, and the relationship to radio bursts.

---------------------------------------------------------
Title: Multi-wavelength Analysis of an X2.7 Flare on 3 November 2003
    from Active Region NOAA 10488
Authors: Joshi, B.; Manoharan, P. K.; Veronig, A. M.; Pant, P.;
   Pandey, K.
2006SunGe...1b..17J    Altcode: 2006SunGe...1...17J
  The evolution of an X2.7 solar flare, that occurred in a complex
  βγδ-type active region on 2003 November 3, is discussed utilizing
  multi-wavelength data set. The Hα images taken from solar tower
  telescope at ARIES, Nainital, India, reveal well-defined footpoint
  (FP) and looptop (LT) sources. As the flare evolves, LT source moves
  upward and the separation between the two FP sources increases which is
  consistent with the reconnection models of solar flares. The coalignment
  of Hα with hard X-ray (HXR) images obtained from RHESSI shows spatial
  correlation between Hα and HXR footpoints, while the upward moving
  HXR LT source is always located above Hα LT source. The EUV images of
  flaring region at 195 Å taken from SOHO/EIT reveal intense emission
  from low-lying loops near the active region during the impulsive
  phase. On the other hand, two bright loops are seen well outside the
  active region which undergo large scale reorganization during the
  flare. In radio wavelengths, type III radio bursts are observed few
  minutes prior to start of HXR LT emission indicating the pre-flare
  coronal activity. A type II radio burst followed the main phase of
  the event. The observations support the "break-out" model of solar
  eruptions proposed by S.Antiochos and coworkers.

---------------------------------------------------------
Title: Interaction of a Moreton/EIT Wave and a Coronal Hole
Authors: Veronig, Astrid M.; Temmer, Manuela; Vršnak, Bojan; Thalmann,
   Julia K.
2006ApJ...647.1466V    Altcode: 2006astro.ph..4613V
  We report high-cadence Hα observations of a distinct Moreton wave
  observed at Kanzelhöhe Solar Observatory associated with the 3B/X3.8
  flare and coronal mass ejection (CME) event of 2005 January 17. The
  Moreton wave can be identified in about 40 Hα frames over a period of
  7 minutes. The EIT wave is observed in only one frame, but the derived
  propagation distance is close to that of the simultaneously measured
  Moreton wave fronts, indicating that they are closely associated
  phenomena. The large angular extent of the Moreton wave allows us to
  study the wave kinematics in different propagation directions with
  respect to the location of a polar coronal hole (CH). In particular, we
  find that the wave segment whose propagation direction is perpendicular
  to the CH boundary (“frontal encounter”) is stopped by the CH, which
  is in accordance with observations reported from EIT waves. However,
  we also find that at a tongue-shaped edge of the coronal hole, where
  the front orientation is perpendicular to the CH boundary (the wave
  “slides along” the boundary), the wave signatures can be found up
  to 100 Mm inside the CH. These findings are briefly discussed in the
  frame of recent modeling results.

---------------------------------------------------------
Title: Multi-Wavelength Observations with High Resolution of a M5.4
    Flare from Ground and Space
Authors: Kucera, A.; Wöhl, H.; Rybák, J.; Gömöry, P.; Veronig, A.
2006ESASP.617E..68K    Altcode: 2006soho...17E..68K
  No abstract at ADS

---------------------------------------------------------
Title: The Neupert Effect in Filamented versus Monolithic Solar
    Flare Loop Structures
Authors: Stoiser, Sigrid; Brown, J. C.; Veronig, A. M.
2006SPD....37.1304S    Altcode: 2006BAAS...38R.241S
  In many flares, the soft X-ray light curves resemble the time integral
  of the corresponding hard X-ray lightcurves, a phenomenon called the
  Neupert effect. The favoured explanation is that non-thermal electrons
  which emit bremsstrahlung in hard X-rays deposit the bulk of their
  energy in collisions in the dense chromosphere. In turn, the cool plasma
  in the chromosphere is heated to high temperatures and evaporated into
  the corona, which is discernible as a rise of the soft X-ray light
  curve and the emission measure.We have investigated if we can attribute
  the observed emission measure enhancement at the flare peaks to the
  described process of beam driven chromospheric evaporation using a set
  of RHESSI microflares (GOES class &lt; C1.4). In contrast, we consider
  the case of a thermal flare origin, i.e. if the peak emission measures
  of the analysed events agree with the theoretically expected values from
  chromospheric evaporation driven by heat conduction. For both cases,
  we consider a single loop and a filamentary loop model. We do not
  use detailed hydromodelling but use simple analytic expressions. The
  work is intended to find explanations for problems encountered when
  comparing the empirical to the theoretical Neupert effect as well as
  to distinguish between possible formation processes of the analysed
  flares. The parameters involved (peak emission measure, temperature,
  electron spectral indices, flare geometry variables) are determined
  from RHESSI spectroscopy and TRACE 1600 A data in combination with
  RHESSI imaging.

---------------------------------------------------------
Title: Reconnection and Energy Release Rates in aTwo-Ribbon Flare
Authors: Miklenic, Christiane H.; Veronig, A. M.; Vrsnak, B.
2006SPD....37.0801M    Altcode: 2006BAAS...38..230M
  We tried to verify whether the local reconnection rate (coronal
  electric field) and the global reconnection rate (magnetic flux
  change rate) as well as the energy release rate (Poynting flux) in
  a two-ribbon flare can be derived from chromospheric/photospheric
  observations. Furthermore, we tested whether equal shares of positive
  and negative magnetic flux are involved in the flare process.A
  well observed GOES M3.9 two-ribbon flare was analyzed. The required
  observables (ribbon expansion velocity, magnetic field strength at the
  ribbon front, and newly brightened area) were extracted from TRACE
  1600 Å and Kanzelhöhe H-alpha image time series, and a SOHO MDI
  magnetogram, respectively. Furthermore, the ratio of the converted
  positive vs. negative magnetic flux was determined. RHESSI Hard X-ray
  20 - 60 keV full-disk time profiles as well as subregion imaging light
  curves derived from a time series of RHESSI images in the same energy
  range, were used as independent, observable proxies of the reconnection
  and the energy release rate, respectively. The RHESSI images were also
  used to localize the sites where the bulk of the energy was deposited
  by fast electrons.We found good temporal correlations between derived
  time profiles (local and global reconnection rate, Poynting flux) and
  observed HXR flux. The local reconnection rate peak values ranged from
  1.4 V/cm to 4.6 V/cm, and the ratio of converted positive vs. negative
  magnetic flux deviated from the theoretically expected value by
  only 5 - 10%.The results indicate that the local reconnection rate,
  the global reconnection rate as well as the energy release rate in a
  simple two-ribbon flare can be derived from chromospheric/photospheric
  observations. Furthermore, it was confirmed that equal shares of
  positive and negative magnetic flux participated in the reconnection
  process.This work is supported by the Austrian ‘Fonds zur Förderung
  der wissenschaftlichen Forschung’ under project P15344.

---------------------------------------------------------
Title: Shrinking and Cooling of Flare Loops in a Two-Ribbon Flare
Authors: Vršnak, Bojan; Temmer, Manuela; Veronig, Astrid; Karlický,
   Marian; Lin, Jun
2006SoPh..234..273V    Altcode:
  We analyze the evolution of the flare/postflare-loop system in the
  two-ribbon flare of November 3, 2003, utilizing multi-wavelength
  observations that cover the temperature range from several tens of
  MK down to 10<SUP>4</SUP> K. A non-uniform growth of the loop system
  enables us to identify analogous patterns in the height-time, h(t),
  curves measured at different temperatures. The "knees," "plateaus,"
  and "bends" in a higher-temperature curve appear after a certain time
  delay at lower heights in a lower-temperature curve. We interpret such
  a shifted replication as a track of a given set of loops (reconnected
  field lines) while shrinking and cooling after being released from the
  reconnection site. Measurements of the height/time shifts between h(t)
  curves of different temperatures provide a simultaneous estimate of
  the shrinkage speed and cooling rate in a given temperature domain,
  for a period of almost ten hours after the flare impulsive phase. From
  the analysis we find the following: (a) Loop shrinkage is faster at
  higher temperatures - in the first hour of the loop-system growth,
  the shrinkage velocity at 5 MK is 20 - 30 km s<SUP>−1</SUP>, whereas
  at 1 MK it amounts to 5 km s<SUP>−1</SUP>; (b) Shrinking becomes
  slower as the flare decays - ten hours after the impulsive phase,
  the shrinkage velocity at 5 MK becomes 5 km s<SUP>−1</SUP>; (c) The
  cooling rate decreases as the flare decays - in the 5 MK range it is
  1 MK min<SUP>−1</SUP> in the first hour of the loop-system growth,
  whereas ten hours later it decreases to 0.2 MK min<SUP>−1</SUP>;
  (d) During the initial phase of the loop-system growth, the cooling
  rate is larger at higher temperatures, whereas in the late phases
  the cooling rate apparently does not depend on the temperature; (e)
  A more detailed analysis of shrinking/cooling around one hour after
  the impulsive phase reveals a deceleration of the loop shrinkage,
  amounting to ā ≈ 10 m s<SUP>−2</SUP> in the T &lt; 5 MK range;
  (f) In the same interval, conductive cooling dominates down to T ≈
  3 MK, whereas radiation becomes dominant below T ≈ 2 MK; (g) A few
  hours after the impulsive phase, radiation becomes dominant across the
  whole T &lt; 5 MK range. These findings are compared with results of
  previous studies and discussed in the framework of relevant models.

---------------------------------------------------------
Title: Multi-wavelength study of coronal waves associated with the
    CME-flare event of 3 November 2003
Authors: Vršnak, B.; Warmuth, A.; Temmer, M.; Veronig, A.;
   Magdalenić, J.; Hillaris, A.; Karlický, M.
2006A&A...448..739V    Altcode:
  The large flare/CME event that occurred close to the west solar limb on
  3 November 2003 launched a large-amplitude large-scale coronal wave that
  was observed in Hα and Fe xii 195 Å spectral lines, as well as in the
  soft X-ray and radio wavelength ranges. The wave also excited a complex
  decimeter-to-hectometer type II radio burst, revealing the formation of
  coronal shock(s). The back-extrapolation of the motion of coronal wave
  signatures and the type II burst sources distinctly marks the impulsive
  phase of the flare (the hard X-ray peak, drifting microwave burst,
  and the highest type III burst activity), favoring a flare-ignited
  wave scenario. On the other hand, comparison of the kinematics of
  the CME expansion with the propagation of the optical wave signatures
  and type II burst sources shows a severe discrepancy in the CME-driven
  scenario. However, the CME is quite likely associated with the formation
  of an upper-coronal shock revealed by the decameter-hectometer type II
  burst. Finally, some six minutes after the launch of the first coronal
  wave, another coronal disturbance was launched, exciting an independent
  (weak) decimeter-meter range type II burst. The back-extrapolation
  of this radio emission marks the revival of the hard X-ray burst,
  and since there was no CME counterpart, it was clearly ignited by the
  new energy release in the flare.

---------------------------------------------------------
Title: Hemispheric sunspot numbers {R<SUB>n</SUB>} and {R<SUB>s</SUB>}
from 1945-2004: catalogue and N-S asymmetry analysis for solar
    cycles 18-23
Authors: Temmer, M.; Rybák, J.; Bendík, P.; Veronig, A.; Vogler,
   F.; Otruba, W.; Pötzi, W.; Hanslmeier, A.
2006A&A...447..735T    Altcode:
  From sunspot drawings provided by the Kanzelhöhe Solar Observatory,
  Austria, and the Skalnaté Pleso Observatory, Slovak Republic, we
  extracted a data catalogue of hemispheric Sunspot Numbers covering
  the time span 1945-2004. The validated catalogue includes daily,
  monthly-mean, and smoothed-monthly relative sunspot numbers
  for the northern and southern hemispheres separately and is
  available for scientific use. These data we then investigated with
  respect to north-south asymmetries for almost 6 entire solar cycles
  (Nos. 18-23). For all the cycles studied, we found that the asymmetry
  based on the absolute asymmetry index is enhanced near the cycle
  maximum, which contradicts to previous results that are based on the
  normalized asymmetry index. Moreover, the weak magnetic interdependence
  between the two solar hemispheres is confirmed by their self-contained
  evolution during a cycle. For the time span 1945-2004, we found that
  the cycle maxima and also the declining and increasing phases are
  clearly shifted, whereas the minima seem to be in phase for both
  hemispheres. The asymmetric behavior reveals no obvious connection
  to either the sunspot cycle period of ~11- or the magnetic cycle of
  ~22-years. The most striking excess of activity is observed for the
  northern hemisphere in cycles 19 and 20.

---------------------------------------------------------
Title: X-ray sources and magnetic reconnection in the X3.9 flare of
    2003 November 3
Authors: Veronig, A. M.; Karlický, M.; Vršnak, B.; Temmer, M.;
   Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2006A&A...446..675V    Altcode:
  Context: .Recent RHESSI observations indicate an apparent altitude
  decrease of flare X-ray loop-top (LT) sources before changing to the
  commonly observed upward growth of the flare loop system.<BR /> Aims:
  .We performed a detailed study of the LT altitude decrease for one well
  observed flare in order to find further hints on the physics of this
  phenomenon and how it is related to the magnetic reconnection process in
  solar flares.<BR /> Methods: .RHESSI X-ray source motions in the 2003
  November 3, X3.9 flare are studied together with complementary data
  from SXI, EIT, and Kanzelhöhe Hα. We particularly concentrate on the
  apparent altitude decrease of the RHESSI X-ray LT source early in the
  flare and combine kinematical and X-ray spectral analysis. Furthermore,
  we present simulations from a magnetic collapsing trap model embedded
  in a standard 2-D magnetic reconnection model of solar flares.<BR />
  Results: .We find that at higher photon energies the LT source is
  located at higher altitudes and shows higher downward velocities
  than at lower energies. The mean downward velocities range from
  14 km s<SUP>-1</SUP> in the RHESSI 10-15 keV energy band to 45 km
  s<SUP>-1</SUP> in the 25-30 keV band. For this flare, the LT altitude
  decrease was also observed by the SXI instrument with a mean speed of
  12 km s<SUP>-1</SUP>. RHESSI spectra indicate that during the time
  of LT altitude decrease the emission of the LT source is thermal
  bremsstrahlung from a "superhot" plasma with temperatures increasing
  from 35 MK to 45 MK and densities of the order of 10<SUP>10</SUP>
  cm<SUP>-3</SUP>. The temperature does not significantly increase
  after this early (pre-impulsive superhot LT) phase, whereas the
  LT densities increase to a peak value of (3-4) × 10<SUP>11</SUP>
  cm<SUP>-3</SUP>.<BR /> Conclusions: .Modeling of a collapsing magnetic
  trap embedded in a standard 2D magnetic reconnection model can reproduce
  the key observational findings in case that the observed emission is
  thermal bremsstrahlung from the hot LT plasma. This agrees with the
  evaluated RHESSI spectra for this flare.

---------------------------------------------------------
Title: Hemispheric Sunspot Numbers 1945--2004: data merging from
    two observatories
Authors: Temmer, M.; Rybák, J.; Bendík, P.; Veronig, A.; Vogler,
   F.; Pötzi, W.; Otruba, W.; Hanslmeier, A.
2006CEAB...30...65T    Altcode:
  For the time span 1945--2004 from daily sunspot drawings northern
  and southern relative sunspot numbers are extracted using drawings
  provided by Kanzelhöhe Solar Observatory, Austria, and Skalnaté Pleso
  Observatory, Slovak Republic. The derived data will be used to improve
  and extend an already existing catalogue of hemispheric sunspot numbers
  (Temmer et al., 2002). Since northern and southern solar hemispheres
  do not evolve in phase during the cycle, hemispheric data are very
  important for activity studies. In the present paper the compilation
  of the data for the period 1945--2004 is described. Furthermore as a
  quality check of the derived hemispheric data a regression analysis and
  the comparison to the international hemispheric sunspot numbers from
  the Sunspot Index Data Center for the time span 1992--2004 is presented.

---------------------------------------------------------
Title: Model of Motion of the X-Ray Loop-Top Source at the Beginning
    of Cusp-Type Flares
Authors: Karlický, M.; Veronig, A.; Vršnak, B.
2006CEAB...30...85K    Altcode:
  A model with a 1-D collapsing magnetic trap is proposed for
  an explanation of the motion of the X-ray loop-top source at the
  beginning of cusp-type flares. Considering plasma heating due to the
  betatron mechanism an analytic formula for the temporal and spatial
  evolution of heated plasma temperature in the trap is derived. Using
  the formula and the relation for thermal bremsstrahlung flux, the
  time evolution of the X-ray intensity profile in the trap is computed
  numerically. The model explains not only the downward motion of the
  X-ray loop-top source observed at the beginning of cusp-type flares,
  but also the upward motion which follows.

---------------------------------------------------------
Title: Theoretical and Observational Features of Magnetic Reconnection
Authors: Biernat, H. K.; Semenov, V. S.; Penz, T.; Miklenic, C.;
   Veronig, A.; Hanslmeier, A.; Vršnak, B.; Heyn, M. F.; Ivanov, I. B.;
   Ivanova, V. V.; Kiehas, S. A.; Langmayr, D.
2006CEAB...30...75B    Altcode:
  We present general solutions of the time--dependent <P />Petschek--type
  model of magnetic reconnection for a compressible <P />plasma. The
  disruption of a tangential discontinuity because of <P />a localized
  decrease of the resistivity leads to the generation <P />of several
  MHD wave modes. By solving the Riemann problem, the <P />behavior of
  these modes can be visualized. Additionally, <P />disturbances of the
  ambient plasma environment by the propagating <P />shock structures
  can be modeled. As an observational feature, the <P />determination
  of the reconnection rate in a two--ribbon flare is <P />presented.

---------------------------------------------------------
Title: Periodical patterns in major flare occurrence and their
    relation to magnetically complex active regions
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
   A.
2006AdSpR..38..886T    Altcode:
  A periodical occurrence rate of major solar flares (observed in hard
  X-rays) of ∼24 days (synodic) was first reported by Bai (1987)
  [Bai, T. Distribution of flares on the sun superactive regions and
  active zones of 1980 1985. ApJ 314, 795 807, 1987] for the years 1980
  1985. Here, we report a significant relation between the appearance of
  the 24-day period in major Hα flares and magnetically complex sunspot
  groups (i.e., including a γ and/or δ configuration). From synoptic
  maps of magnetograms (NSO/KP) patterns in the magnetic flux evolution
  are traced which might be the cause of the 24-day period observed in
  flare activity.

---------------------------------------------------------
Title: X-Ray Sources and Magnetic Reconnection in AN X-Class Flare
Authors: Veronig, A. M.; Vršnak, B.; Karlický, M.; Temmer, M.;
   Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2005ESASP.600E..32V    Altcode: 2005ESPM...11...32V; 2005dysu.confE..32V
  No abstract at ADS

---------------------------------------------------------
Title: Hemispheric Sunspot Numbers RN and RS from 1945-2004: Extended
    and Improved Catalogue
Authors: Temmer, M.; Rybák, J.; Veronig, A.; Bendík, P.; Vogler,
   F.; Pötzi, W.; Otruba, W.; Hanslmeier, A.
2005ESASP.600E..52T    Altcode: 2005ESPM...11...52T; 2005dysu.confE..52T
  No abstract at ADS

---------------------------------------------------------
Title: Wave Phenomena Associated with the X3.8 Flare/cme of
    17-JAN-2005
Authors: Temmer, M.; Veronig, A.; Vršnak, B.; Thalmann, J.;
   Hanslmeier, A.
2005ESASP.600E.144T    Altcode: 2005ESPM...11..144T; 2005dysu.confE.144T
  No abstract at ADS

---------------------------------------------------------
Title: Analysis of Selected Rhessi Microflares
Authors: Stoiser, S.; Veronig, A. M.; Brown, J. C.; McTiernan, J. M.;
   Hanslmeier, A.
2005ESASP.600E.142S    Altcode: 2005dysu.confE.142S; 2005ESPM...11..142S
  No abstract at ADS

---------------------------------------------------------
Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers
    1945-2004 (Temmer+, 2006)
Authors: Temmer, M.; Rybak, J.; Bendik, P.; Veronig, A.; Vogler, F.;
   Otruba, W.; Poetzi, W.; Hanslmeier, A.
2005yCat..34470735T    Altcode:
  From sunspot drawings provided by the Kanzelhoehe Solar Observatory,
  Austria, and the Skalnate Pleso Observatory, Slovak Republic,
  a data catalogue of hemispheric Sunspot Numbers covering the time
  span 1945-2004 is extracted. The validated catalogue includes daily,
  monthly-mean and smoothed-monthly relative sunspot numbers for the
  northern and southern hemispheres separately and is available for
  scientific use. Based on this data set an analysis concerning the
  North-South asymmetry is made within this paper. <P />(2 data files).

---------------------------------------------------------
Title: Broadband Metric-Range Radio Emission Associated with a
    Moreton/EIT Wave
Authors: Vršnak, B.; Magdalenić, J.; Temmer, M.; Veronig, A.;
   Warmuth, A.; Mann, G.; Aurass, H.; Otruba, W.
2005ApJ...625L..67V    Altcode:
  We present the evolution and kinematics of a broadband radio source
  that propagated collaterally with an Hα/EIT wave, linking it with the
  type II burst that was excited higher up in the corona. The NRH wave
  emission extended from the frequency f~327 to f&lt;151 MHz and was
  considerably weaker than the flare-related type IV burst. The emission
  centroid propagated at a height of 0-200 Mm above the solar limb and
  was intensified when the disturbance passed over enhanced coronal
  structures. We put forward the ad hoc hypothesis that the NRH wave
  signature is optically thin gyrosynchrotron emission excited by the
  passage of the coronal MHD fast-mode shock. The identification of radio
  emission associated with the coronal wave front is important since it
  offers us new diagnostic information that could provide us with better
  insight into the physical conditions in the disturbance itself.

---------------------------------------------------------
Title: What causes the 24-day period observed in solar flares?
Authors: Temmer, M.; Rybák, J.; Veronig, A.; Hanslmeier, A.
2005A&A...433..707T    Altcode:
  Previous studies report a 24-day (synodic) period in the occurrence
  rate of solar flares for each of the solar cycles studied, Nos. 19-22
  (Bai 1987, ApJ, 314, 795; Temmer et al. 2004, Sol. Phys. 221,
  325). Here we study the 24-day period in the solar flare occurrence
  for solar cycles 21 and 22 by means of wavelet power spectra together
  with the solar flare locations in synoptic magnetic maps. We find
  that the 24-day peak revealed in the power spectra is just the
  result of a particular statistical clumping of data points, most
  probably caused by a characteristic longitudinal separation of about
  +40<SUP>circ</SUP> to +50<SUP>circ</SUP> of activity complexes in
  successive Carrington rotations. These complexes appear as parallel,
  diverging or converging branches in the synoptic magnetic maps and
  are particularly flare-productive.

---------------------------------------------------------
Title: Physics of the Neupert Effect: Estimates of the Effects of
    Source Energy, Mass Transport, and Geometry Using RHESSI and GOES Data
Authors: Veronig, Astrid M.; Brown, John C.; Dennis, Brian R.;
   Schwartz, Richard A.; Sui, Linhui; Tolbert, A. Kimberley
2005ApJ...621..482V    Altcode:
  The “empirical Neupert effect” (ENE) is the observed temporal
  correlation of the hard X-ray (HXR) flux F<SUB>HXR</SUB>(t) with the
  time derivative of the soft X-ray (SXR) flux F˙<SUB>SXR</SUB>(t) in
  many flares. This is widely taken to mean that the energetic electrons
  responsible for F<SUB>HXR</SUB>(t) by thick-target collisional
  bremsstrahlung are the main source of heating and mass supply (via
  chromospheric evaporation) of the SXR-emitting hot coronal plasma. If
  this interpretation were correct, one would expect better correlation
  between the beam power supply P<SUB>beam</SUB>(t), inferred from the HXR
  spectrum, and the actual power P<SUB>in</SUB>(t) required to explain
  the SXR flux and spectrum, allowing for variations in both emission
  measure (EM) and temperature T, for radiative and conductive cooling
  losses, and for complexities of geometry like multiple loops. We call
  this the “theoretical Neupert effect” (TNE). To test if it is true
  that P<SUB>beam</SUB>(t) and P<SUB>in</SUB>(t) inferred from data are
  better correlated than F<SUB>HXR</SUB>(t) and F˙<SUB>SXR</SUB>(t),
  we use an approximate approach for a simple single-loop geometry
  and rough estimates of the particle and energy transport and apply
  the model to RHESSI and GOES data on four flares. We find that if
  the beam low cutoff energy E<SUB>1</SUB> is taken as constant, the
  correlation of P<SUB>beam</SUB>(t), P<SUB>in</SUB>(t) is no better
  than that of F<SUB>HXR</SUB>(t),F˙<SUB>SXR</SUB>(t). While our
  modeling contains many approximations to cooling and other physics,
  ignored entirely from ENE data considerations, there seems to be no
  reason why their order-of-magnitude inclusion should make the TNE worse
  rather than better, although this should be checked by more accurate
  simulations. These results suggest that one or more of the following
  must be true: (1) fast electrons are not the main source of SXR plasma
  supply and heating, (2) the beam low cutoff energy varies with time, or
  (3) the TNE is strongly affected by source geometry. These options are
  discussed in relation to possible future directions for TNE research.

---------------------------------------------------------
Title: Testing the Neupert Effect
Authors: Veronig, A. M.; Brown, J. C.; Dennis, B. R.; Schwartz, R. A.;
   Sui, L.; Tolbert, A. K.
2005ASSL..320..263V    Altcode: 2005smp..conf..263V
  No abstract at ADS

---------------------------------------------------------
Title: Evidence for a solar coronal thick-target hard X-ray source
    observed by RHESSI
Authors: Veronig, Astrid M.; Brown, John C.; Bone, Laura
2005AdSpR..35.1683V    Altcode:
  We study a solar flare hard X-ray (HXR) source observed by the Reuven
  Ramaty high energy solar spectroscopic imager (RHESSI) in which the
  HXR emission is almost entirely in a coronal loop so dense as to be
  collisionally thick at electron energies up to ∼45-60 keV. This
  contrasts with most events previously reported in which the HXR
  emission is primarily from the loop footpoints in the collisionally
  dense chromosphere. In particular, we show that the high loop column
  densities inferred from the GOES and RHESSI soft X-ray emission
  measure and the volume of the flare loop are consistent with the
  coronal thick-target interpretation of the HXR images and spectra. The
  high column densities observed already at the very beginning of the
  impulsive phase are explained by chromospheric evaporation during a
  preflare which, as Nobeyama 17 GHz radio images reveal, took place in
  the same set of nested loops as the main flare.

---------------------------------------------------------
Title: Solar Magnetic Phenomena
Authors: Hanslmeier, Arnold; Veronig, Astrid; Messerotti, Mauro
2005ASSL..320.....H    Altcode: 2005smp..conf.....H
  This book contains the proceedings of the Summerschool and Workshop
  "Solar Magnetic Phenomena" held from 25 August to 5 September 2003
  at the Solar Observatory Kanzelhoehe, which belongs to the Institute
  for Geophysics, Astrophysics and Meteorology of the University of
  Graz, Austria. The book contains the contributions from six invited
  lecturers, They give an overview on the following topics: observations
  of the photosphere and chromosphere, solar flares observations and
  theory, coronal mass ejections and the relevance of magnetic helicity,
  high-energy radiation from the Sun, the physics of solar prominences
  and highlights from the SOHO mission. The lectures contain about 25
  to 30 pages each and provide a valuable introduction to the topics
  mentioned above. The comprehensive lists of references at the end
  of each contribution enable the interested reader to go into more
  detail. The second part of the book contains contributed papers. These
  papers were presented and discussed in the workshop sessions during
  the afternoons. The sessions stimulated intensive discussions between
  the participants and the lecturers.

---------------------------------------------------------
Title: On the Relation Between the Coronal Free Energy and Solar
    Flare Occurrence
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2005HvaOB..29..109T    Altcode:
  A significant delay with a 22-year modulation in solar flare occurrence
  was found by te{temmer03solph} with respect to the solar cycle defined
  on the basis of the relative sunspot number. These observational results
  were modelled by te{litvi03} through a time-dependent balance of the
  magnetic free energy in the solar corona. The free magnetic energy is
  assumed to be depleted mainly by flares and lags behind the variation
  of the energy supply (emerging magnetic flux - proxy: relative sunspot
  numbers) to this system. For solar cycles 21 and 23, in accordance with
  the delay obtained for flare rates, the rate of sunspot group numbers
  lags behind the solar cycle maximum. Theses findings suggest that
  the energy supply itself is delayed, most prominent in odd numbered
  solar cycles which subsequently causes the delay observed for flare
  and sunspot group occurrences.

---------------------------------------------------------
Title: Loop-Top Altitude Decrease in an X-Class Flare
Authors: Veronig, A.; Vršnak, B.; Karlický, M.; Temmer, M.;
   Magdalenić, J.; Dennis, B. R.; Otruba, W.; Pötzi, W.
2005HvaOB..29..127V    Altcode:
  We study RHESSI X-ray source motions in the X3.9 flare of 2003 November
  3. Particular attention is drawn to the apparent altitude decrease
  of a distinct loop-top (LT) source at the early flare phase before
  then changing to the commonly observed upward expansion of the flare
  loop system. We obtain that the downward motion is more pronounced
  at higher X-ray energies (peak values up to 50 km s^{-1}) consistent
  with recent findings by Sui et al. (2004). RHESSI spectra indicate
  that the emission process in the LT source is thermal bremsstrahlung
  from a super hot plasma (∼40 MK) with high densities increasing from
  ∼10^{10} cm^{-3} early in the flare to several times 10^{11} cm^{-3}
  at the end of RHESSI observations.

---------------------------------------------------------
Title: On the 24- and 155-Day Periodicity Observed in Solar Hα Flares
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2005ASSL..320..211T    Altcode: 2005smp..conf..211T
  No abstract at ADS

---------------------------------------------------------
Title: Coronal Mass Ejection of 15 May 2001: II. Coupling of the
    Cme Acceleration and the Flare Energy Release
Authors: Vršnak, B.; Maričić, D.; Stanger, A. L.; Veronig, A.
2004SoPh..225..355V    Altcode:
  We analyze the relationship between the dynamics of the coronal mass
  ejection (CME) of 15 May 2001 and the energy release in the associated
  flare. The flare took place behind the east limb and was disclosed by a
  growing system of hot soft X-ray (SXR) loops that appeared from behind
  the limb around the onset of the rapid acceleration of the CME. The
  highly correlated behavior of the SXR light-curve derivative and the
  time profile of the CME acceleration reveals an intrinsic relationship
  between the CME dynamics and the flare energy release. Furthermore,
  we found that the CME acceleration peak occurs simultaneously with the
  fastest growth (100 km s<SUP>-1</SUP>) of X-ray loops, indicating that
  the reconnection plays an essential role in the eruption. Inspecting
  the CME/flare morphology we recognized in the Yohkoh-SXT images an
  oval feature that formed within the rising structure at the onset
  of the rapid acceleration phase, simultaneously with the appearance
  of the X-ray loops. The eruptive prominence was imbedded within
  the lower half of the oval, suggestive of a flux-rope/prominence
  magnetic configuration. We interpret the observed morphological
  evolution in terms of a reconnection process in the current sheet that
  presumably formed below the erupting flux-rope at the onset of the CME
  acceleration. Measurements of the tip-height of the cusped X-ray loop
  system and the height of the lower edge of the oval, enable us to trace
  the stretching of the current sheet. The initial distance between the
  oval and the loops amounted to 35 - 40 Mm. In about 1 h the inferred
  length of the current sheet increased to 150 - 200 Mm, which corresponds
  to a mean elongation speed of 35 - 45 km s<SUP>-1</SUP>. The results
  are discussed in the framework of CME models that include the magnetic
  reconnection below the erupting flux-rope.

---------------------------------------------------------
Title: Coronal Mass Ejection of 15 May 2001: I. Evolution of
    Morphological Features of the Eruption
Authors: Maričić, D.; Vršnak, B.; Stanger, A. L.; Veronig, A.
2004SoPh..225..337M    Altcode:
  We study the initiation and development of the limb coronal mass
  ejection (CME) of 15 May 2001, utilizing observations from Mauna Loa
  Solar Observatory (MLSO), the Solar and Heliospheric Observatory (SOHO),
  and Yohkoh. The pre-eruption images in various spectral channels show
  a quiescent prominence imbedded in the coronal void, being overlaid
  by the coronal arch. After the onset of rapid acceleration, this
  three-element structure preserved its integrity and appeared in the
  MLSO MK-IV coronagraph field of view as the three-part CME structure
  (the frontal rim, the cavity, and the prominence) and continued its
  motion through the field of view of the SOHO/LASCO coronagraphs up
  to 30 solar radii. Such observational coverage allows us to measure
  the relative kinematics of the three-part structure from the very
  beginning up to the late phases of the eruption. The leading edge and
  the prominence accelerated simultaneously: the rapid acceleration of
  the frontal rim and the prominence started at approximately the same
  time, the prominence perhaps being slightly delayed (4 - 6 min). The
  leading edge achieved the maximum acceleration a<SUB>max</SUB>≈ 600
  ± 150 m s<SUP>−2</SUP> at a heliocentric distance 2.4 -2.5 solar
  radii, whereas the prominence reached a<SUB>max</SUB>≈ 380± 50 m
  s<SUP>−2</SUP>, almost simultaneously with the leading edge. Such a
  distinct synchronization of different parts of the CME provides clear
  evidence that the entire magnetic arcade, including the prominence,
  erupts as an entity, showing a kind of self-similar expansion. The
  CME attained a maximum velocity of v<SUB>max</SUB>≈ 1200 km
  s<SUP>−1</SUP> at approximately the same time as the peak of the
  associated soft X-ray flare. Beyond about 10 solar radii, the leading
  edge of the CME started to decelerate at a≈−20 m s<SUP>−2</SUP>,
  most likely due to the aerodynamic drag. The deceleration of the
  prominence was delayed for 10 -30 min, which is attributed to its
  larger inertia.

---------------------------------------------------------
Title: On the 24-day period observed in solar flare occurrence
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
   A.
2004SoPh..221..325T    Altcode:
  Time series of daily numbers of solar Hα flares from 1955 to
  1997 are studied by means of wavelet power spectra with regard to
  predominant periods in the range of ∼ 24 days (synodic). A 24-day
  period was first reported by Bai (1987) for the occurrence rate of
  hard X-ray flares during 1980-1985. Considering the northern and
  southern hemisphere separately, we find that the 24-day period is not
  an isolated phenomenon but occurs in each of the four solar cycles
  investigated (No. 19-22). The 24-day period can be established also
  in the occurrence rate of subflares but occurs more prominently in
  major flares (importance classes ≥ 1). A comparative analysis of
  magnetically classified active regions subdivided into magnetically
  complex (i.e., including a γ and/or δ configuration) and non-complex
  (α, β) reveals a significant relation between the appearance of
  the 24-day period in Hα flares and magnetically complex sunspot
  groups, whereas it cannot be established for non-complex groups. It is
  suggested that the 24-day period in solar flare occurrence is related
  to a periodic emergence of new magnetic flux rather than to the surface
  rotation of sunspots.

---------------------------------------------------------
Title: A Coronal Thick-Target Interpretation of Two Hard X-Ray
    Loop Events
Authors: Veronig, Astrid M.; Brown, John C.
2004ApJ...603L.117V    Altcode:
  We report a new class of solar flare hard X-ray (HXR) sources in
  which the emission is mainly in a coronal loop so dense as to be
  collisionally thick at electron energies up to &gt;~50 keV. In most
  of the events previously reported, most of the emission is at the
  dense loop footpoints, although sometimes with a faint high-altitude
  component. HXR RHESSI data on loop dimensions and nonthermal electron
  parameters and GOES soft X-ray data on hot loop plasma parameters
  are used to model coronal thick-target physics for two “discovery”
  events (2002 April 14 [23:56 UT] and 2002 April 15 [23:05 UT]). We
  show that loop column densities N are consistent with (1) a nonthermal
  coronal thick-target interpretation of the HXR image and spectrum;
  (2) chromospheric evaporation by thermal conduction from the hot loop
  rather than by electron beam heating; and (3) the hot loop temperature
  being due to a balance of thick-target collisional heating and (mainly)
  conductive cooling.

---------------------------------------------------------
Title: Merging two data sets of hemispheric Sunspot Numbers
Authors: Rybák, J.; Bendík, P.; Temmer, M.; Veronig, A.; Hanslmeier,
   A.
2004HvaOB..28...63R    Altcode:
  First results on merging two data sets of hemispheric sunspot numbers
  -- from the Kanzelhöhe Solar Observatory and the Skalnaté Pleso
  Observatory -- for the time span 1977 -- 1978 are presented. A total
  coverage of 86% was reached for the merged data set. In order to have
  a homogeneous time series, the daily sunspot numbers for the full disk
  from both observing stations were normalized to the international
  relative sunspot number of the day. The derived hemispheric sunspot
  numbers from Kanzelhöhe and Skalnaté Pleso Observatory %compared
  for 290 common observing show very high correlations (r ≳ 0.95), and
  the estimated data noise yields significant differences only for small
  values of sunspot numbers. These outcomes demonstrate the high potential
  of the applied merging procedure, and are the basis for an ongoing
  project to derive hemispheric sunspot numbers back to the year 1945
  using sunspot drawings from Kanzelhöhe and Skalnaté Pleso Observatory.

---------------------------------------------------------
Title: Importance of magnetically complex active regions on solar
    flare occurrence
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Brajša, R.; Hanslmeier,
   A.
2004HvaOB..28...95T    Altcode:
  Daily numbers of solar Hα flares from 1955 to 1997 and daily numbers
  of magnetically classified active regions for the time span 1964--1997
  are studied applying wavelet power spectra. The occurrence of dominant
  periods in the range of ∼24 days (synodic) is investigated considering
  the northern and southern hemisphere separately. From the flare events
  it is revealed that the 24-day period occurs in each of the four solar
  cycles investigated (no. 19--22). The 24-day period can be established
  also in the occurrence rate of subflares but occurs more prominently
  in major flares (importance classes ≥1). Magnetically complex active
  regions, i.e. including a γ and/or δ configuration, show the 24-day
  period closely related to those found for major Hα flares, whereas
  it cannot be established for non-complex α, β groups.

---------------------------------------------------------
Title: Periodical patterns in major flare occurrence and their
    relation to magnetically complex active regions
Authors: Temmer, M.; Veronig, A.; Rybak, J.; Brajsa, R.; Hanslmeier, A.
2004cosp...35.1395T    Altcode: 2004cosp.meet.1395T
  A periodical occurrence rate of solar major flares (observed in
  hard X-rays) of about 24 days (synodic) was first reported by Bai
  (1987) for the years 1980--1985. Its origin is still far from being
  understood. Applying wavelet analyses for daily numbers of Hα flare
  events covering almost four entire solar cycles (no. 19--22) reveals a
  24-day period in each of the cycles studied. This can be established
  primarily in the occurrence rate of major flares but is also seen
  in subflares. Since large flares occur preferentially in association
  with active regions of complex magnetic configuration a comparative
  study of magnetically classified active regions, subdivided into
  magnetically complex (i.e. including a γ and/or δ configuration)
  and non-complex (α, β) was performed. A significant relation
  between the appearance of the 24-day period in major Hα flares and
  magnetically complex sunspot groups is found, whereas it cannot be
  established for non-complex groups. From solar rotation studies based
  on tracing sunspots practically no siderial rotation velocities as high
  as 16 deg/day (which corresponds to a synodic period of ∼24 days)
  are reported. Thus the cause of the 24-day period is very likely not
  related to solar surface rotation. Alternatively it might be due to
  periodical patterns in magnetic flux emergence which is an important
  driver of flare eruptions. We test this hypothesis by investigating
  synoptic maps of magnetograms (National Solar Observatory/Kitt Peak)
  for selected time ranges in which the 24-day period is revealed for
  both flares and magnetically complex active regions.

---------------------------------------------------------
Title: RHESSI discovery of solar coronal thick target hard X-ray
    sources
Authors: Veronig, A.; Brown, J.
2004cosp...35.1393V    Altcode: 2004cosp.meet.1393V
  We report the discovery of a new class of solar flare hard X-ray (HXR)
  source observed by the Reuven Ramaty High Energy Solar Spectroscopic
  Imager (RHESSI) in which the HXR emission is almost entirely in
  a coronal loop so dense as to be collisionally thick at electron
  energies up to ≳50 keV. This contrasts with most events previously
  reported in which the bulk of emission is at the loop footpoints in
  the collisionally dense chromosphere though sometimes with a faint high
  altitude component such as in Masuda `above the loop-top' sources. We
  use HXR data from RHESSI to infer loop dimensions and nonthermal
  electron parameters and soft X-ray (SXR) data from GOES to obtain
  hot loop plasma parameters. These are used to model the physics of
  coronal thick target loops for the 14 and 15 April 2002 `discovery'
  events both of which have very steep HXR spectra. In particular we
  show that: <P />[(a)] the loop column density N derived from the SXR
  emission measure and loop geometry is consistent with the coronal thick
  target interpretation of the HXR image, <P />[(b)] this N is consistent
  with chromospheric evaporation by thermal conduction flux from the hot
  coronal plasma rather than by electron beam heating, and <P />[(c)]
  the temperature of the hot loop plasma (and hence the conductively
  driven N value) is consistent with thick target collisional heating
  balanced by (mainly) conductive cooling.

---------------------------------------------------------
Title: The solar soft X-ray background flux and its relation to
    flare occurrence
Authors: Veronig, Astrid M.; Temmer, Manuela; Hanslmeier, Arnold
2004SoPh..219..125V    Altcode:
  The soft X-ray background flux (XBF) based on GOES 1-8 Å measurements
  for the period 1975-2003 is studied. There is strong evidence that
  in the XBF the flare contribution is not eliminated but the XBF is
  dominated by flare and post-flare emission of intense events. The
  significant delay (∼ 2 years) of the peak of the X-ray background
  flux with regard to sunspot numbers reported for cycle 21 recurs in
  the present cycle 23. The relation between monthly XBF and sunspot
  numbers can be well represented by a power law. For cycles 21 and 23
  the derived fit values are the same within the uncertainties, whereas
  the values for cycle 22 are significantly different. It is suggested
  that the lag of the XBF in cycles 21 and 23 is a secondary effect
  related to the substantial contribution of energetic flares which is
  not fully subtracted out by the actual XBF definition.

---------------------------------------------------------
Title: On rotational patterns of the solar magnetic field
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Hanslmeier, A.
2003ESASP.535..157T    Altcode: 2003iscs.symp..157T
  Solar magnetic field variations (NSO/Kitt Peak data) through solar cycle
  23 with respect to rotational modulations are analyzed. A comparative
  study to solar cycles 21 and 22 is performed. The results are compared
  to the rotational behavior of activity tracers like sunspots and solar
  Hα flares. Periodical occurrences of flares often match the 27-day
  solar rotation due to recurrent stable sunspot groups and complexes
  of activity which likely produce more flare events than short-living
  small sunspots. However, periods with strong deviations from the 27-day
  period are obtained for higher energetic flares. The solar magnetic
  field is found to vary on similar time scales, which suggests a close
  relation to the occurrence of strong flare events.

---------------------------------------------------------
Title: Solar cycle variations of the soft X-ray background flux and
    its relation to flare occurrence
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.
2003ESASP.535..259V    Altcode: 2003iscs.symp..259V
  The X-ray background flux (XBF) based on GOES 1-8 Å measurements for
  the period 1975-2000 is studied. We come to the conclusion that in the
  XBF the flare contribution is not eliminated but the XBF is dominated
  by flare and post-flare emission of intense events. Furthermore, we
  suggest that the characteristic lag of the X-ray background flux with
  regard to Sunspot Numbers reported for cycle 21 is a secondary effect
  related to the substantial contribution of large flares to the XBF.

---------------------------------------------------------
Title: Analysis of solar narrow band dm-spikes  observed at 1420
    and 2695 MHz
Authors: Mészárosová, H.; Veronig, A.; Zlobec, P.; Karlický, M.
2003A&A...407.1115M    Altcode:
  Using both linear and nonlinear methods, narrow band dm-spikes recorded
  at 1420 and 2695 MHz on June 6, 2000, July 8, 2000, July 12, 2000,
  July 20, 2000, and March 28, 2001 were analyzed. In particular their
  time profiles were studied statistically. The mean characteristic
  times of the ascending and of the decaying parts of their profiles are
  comparable, even if the dispersion of the values is very broad. For
  selected spikes at 1420 MHz a more precise fitting technique using
  exponential profiles was applied. While in the decaying part the
  exponential trend can be generally found, in the ascending part the
  exponential form can be confirmed only in few cases. The ascending
  and decaying phase of spikes presumably correspond to the source
  instability evolution and the plasma wave absorption. Furthermore,
  durations and polarization values of both 1420 and 2695 MHz spikes
  were determined and compared with the results in literature. All the
  analyzed spike events were located near the solar disk center. The
  polarization values and their trend in spike groups and the nearly
  constant duration suggest that the polarization originates at the
  source itself or near it. Selected time series of spikes were tested
  with respect to low-dimensional determinism and nonlinearity. We
  found that spikes recorded at fixed frequencies are not governed by a
  linear stochastic process, as the underlying physical system contains
  nonlinear signatures.

---------------------------------------------------------
Title: Does solar flare activity lag behind sunspot activity?
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2003SoPh..215..111T    Altcode:
  Recently, Wheatland and Litvinenko (2001) have suggested that over the
  solar cycle both the flaring rate and the magnetic free energy in the
  corona lag behind the energy supply to the system. To test this model
  result, we analyzed the evolution of solar flare occurrence with regard
  to sunspot numbers (as well as sunspot areas), using Hα flare data
  available for the period 1955-2002, and soft X-ray flare data (GOES
  1-8 Å) for the period 1976-2002. For solar cycles 19, 21, and 23,
  we find a characteristic time lag between flare activity and sunspot
  activity in the range 10≲τ≲15 months, consistent with the model
  predictions by Wheatland and Litvinenko (2001). The phenomenon turns
  out to be more prominent for highly energetic flares. The investigation
  of solar activity separately for the northern and southern hemisphere
  allows us to exclude any bias due to overlapping effects from the
  activity of both hemispheres and confirms the dynamic relevance of the
  delay phenomenon. Yet, no characteristic time lag τ&gt;0 is found for
  solar cycles 20 and 22. The finding that in odd-numbered cycles flare
  activity is statistically delayed with respect to sunspot activity,
  while in even-numbered cycles it is not, suggests a connection to the
  22-year magnetic cycle of the Sun. Further insight into the connection
  to the 22-year magnetic cycle could possibly be gained when a 22-year
  variation in the energy supply rate is taken into account in the
  Wheatland and Litvinenko (2001) model. The existence of a 22-year
  modulation in the energy supply rate is suggested by the empirical
  Gnevyshev - Ohl rule, and might be caused by a relic solar field.

---------------------------------------------------------
Title: Solar flares: the Neupert effect, the chromospheric evaporation
    model and coronal heating
Authors: Veronig, A.
2003Obs...123...58V    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Time profile, duration and polarization of high frequency
    spikes
Authors: Zlobec, P.; Mészárosová, H.; Veronig, A.; Karlický, M.;
   Magdaleníc, J.
2003HvaOB..27..115Z    Altcode:
  We analysed a large data set of spikes observed at frequencies 1420
  and 2695 MHz recorded with high time resolution by the Trieste Solar
  Radio System. Different types of analysis were performed in order to
  determine duration, polarization and time profiles of single spikes.

---------------------------------------------------------
Title: Analysis of periodical fine structures in type IV solar
    radio bursts
Authors: Magdaleníc, J.; Zlobec, P.; Vršnak, B.; Messerotti, M.;
   Auras, H.; Veronig, A.
2003HvaOB..27..131M    Altcode:
  Superimposed on the continuum of type IV solar radio bursts
  fine structures are often observed. We analysed a large data set
  of periodical fine structures recorded with high time resolution
  at single frequencies (metric to decimetric bands) by the Trieste
  Solar Radio System. Diverse classes of fine structures with similar
  periodical behaviour but different time profiles and polarization
  characteristics were identified. It is demonstrated that on the average
  pulsation periods decrease with increasing observing frequency, and
  that pulsations recorded above ≈ 600 MHz could be of different nature
  than pulsations below ≈ 400 MHz.

---------------------------------------------------------
Title: The neupert effect and new RHESSI measures of the total energy
    in electrons accelerated in solar flares
Authors: Dennis, B. R.; Veronig, A.; Schwartz, R. A.; Sui, L.; Tolbert,
   A. K.; Zarro, D. M.; Rhessi Team
2003AdSpR..32.2459D    Altcode:
  It is believed that a large fraction of the total energy released
  in a solar flare goes initially into acceleratedelectrons. These
  electrons generate the observed hard X-ray bremsstrahlung as they
  lose most of their energy by coulomb collisions in the lower corona
  and chromosphere. Results from the Solar Maximum Mission showed that
  there may be even more energy in accelerated electrons with energies
  above 25 keV than in the soft X-ray emitting thermal plasma. If this
  is the case, it is difficult to understand why the Neupert Effect —
  the empirical result that for many flares the time integral of the hard
  X-ray emission closely matches the temporal variation of the soft X-ray
  emission — is not more clearly observed in many flares. From recent
  studies, it appears that the fraction of the released energy going into
  accelerated electrons is lower, on average, for smaller flares than
  for larger flares. Also, from relative timing differences, about 25%
  of all flares are inconsistent with the Neupert Effect. The Reuven
  Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is uniquely
  capable of investigating the Neupert Effec since it covers soft X-rays
  down to 3 keV (when both attenuators are out of the field of view)
  and hard X-rays with keV energy resolution, arcsecond-class angular
  resolution, and sub-second time resolution. When combined with the
  anticipated observations from the Soft X-ray Imager on the next GOES
  satellite, these observations will provide us with the ability to track
  the Neupert Effect in space and time and learn more about the relation
  between plasma heating and particle acceleration. The early results
  from RHESSI show that the electron spectrum extends down to as low as
  10 keV in many flares, thus increasing the total energy estimates of
  the accelerated electrons by an order of magnitude or more compared
  with the SMM values. This combined with the possible effects of filling
  factors smaller than unity for the soft X-ray plasma suggest that there
  is significantly more energy in nonthermal electrons than in the soft
  X-ray emitting plasma in many flares.

---------------------------------------------------------
Title: The Neupert Effect
Authors: Veronig, A.
2003HvaOB..27...47V    Altcode:
  The Neupert effect describes the empirical result that for many
  solar flares the soft X-ray time derivative resembles the hard X-ray
  time profile. The Neupert effect suggests a causal relation between
  nonthermal and thermal flare emissions, and can be explained by a model
  in which the flare energy goes primarily into accelerated electrons
  and the electrons are the heating agent for the soft X-ray emitting
  plasma. We discuss recent efforts in trying to quantify the validity
  of the Neupert effect and to understand its relevance in the frame of
  the flare energetics.

---------------------------------------------------------
Title: Rotational modulation of northern and southern activity tracers
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Hanslmeier, A.
2003HvaOB..27...59T    Altcode:
  We study solar activity phenomena, Hα flares and sunspots, with respect
  to their periodical occurrence related to the solar rotation. The
  analysis is carried out separately for the northern and the southern
  hemisphere. Furthermore, flare occurrences are studied with respect
  to different importance classes, and the results are compared to
  the predominant periods derived from Sunspot Numbers. Significant
  asymmetries are obtained between the northern and southern activity for
  both Sunspot Numbers and flare occurrences. Differences between Sunspot
  Numbers and flares result particularly when only higher energetic
  flares are considered. A 24-day period is found for large flare events
  in both hemispheres which is not detected in Sunspot Numbers.

---------------------------------------------------------
Title: Statistical analysis of high-frequency narrowband dm-spikes
Authors: Mészárosová, H.; Veronig, A.; Zlobec, P.; Karlický, M.
2002ESASP.506..347M    Altcode: 2002ESPM...10..347M; 2002svco.conf..347M
  Using linear and nonlienar methods narrowband dm-spikes recorded at
  1420 and 2695 MHz were analyzed. In particular their time profiles were
  studied statistically. For selected spikes at 1420 MHz a more precise
  fitting technique using exponential profiles was applied. Generally,
  while in the decaying part the exponential trend can be found, in
  the ascending part the exponential form can be confirmed only in
  few cases. Furthermore, durations of 1420 and 2695 MHz spikes were
  determined and compared with the results in literature. Selected
  time series of spikes were tested with respect to nonlinearity. We
  found that spikes at fixed frequencies are not governed by a linear
  stochastic process, as the underlying physical system contains nonlinear
  signatures.

---------------------------------------------------------
Title: Catalogue of hemispheric sunspot numbers R<SUB>N</SUB> and
R<SUB>S</SUB>: 1975 - 2000
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002ESASP.506..855T    Altcode: 2002svco.conf..855T; 2002ESPM...10..855T
  Sunspot drawings are provided on a regular basis at the Kanzelhöhe
  Solar Obseratory, Austria, and the derived relative sunspot numbers
  are reported to the Sunspot Index Data Center in Brussels. From the
  daily sunspot drawings, we derived the northern, R<SUB>n</SUB>,
  and southern, R<SUB>s</SUB>, relative sunspot numbers for the
  time span 1975-2000. In order to accord with the International
  Sunspot Numbers R<SUB>i</SUB>, the R<SUB>n</SUB> and R<SUB>s</SUB>
  have been normalized to the R<SUB>i</SUB>, which ensures that the
  relation R<SUB>n</SUB>+R<SUB>s</SUB> = R<SUB>i</SUB> is complied. For
  validation, the derived R<SUB>n</SUB> and R<SUB>s</SUB> are compared
  to the international northern and southern relative sunspot numbers,
  which are available since 1992. The regression analysis performed for
  the period 1992-2000 reveals good agreement with the International
  hemispheric Sunspot Numbers. The monthly mean and the smoothed monthly
  mean hemispheric Sunspot Numbers are compiled to a catalogue. In
  addition, the daily hemispheric Sunspot Numbers are made available
  via Internet.

---------------------------------------------------------
Title: Cycle dependence of hemispheric activity
Authors: Temmer, M.; Veronig, A.; Rybák, J.; Hanslmeier, A.
2002ESASP.506..859T    Altcode: 2002ESPM...10..859T; 2002svco.conf..859T
  Data of daily hemispheric Sunspot Numbers are analyzed including the
  time span 1975-2001. The study of north-south asymmetries concerning
  solar activity and rotational behaviors is in particular relevant,
  as it is related to the solar dynamo and the generation of magnetic
  fields. As diagnostic tools we use wavelets and autocorrelation
  functions in combination with statistical significance tests that are
  applied separately to the northern and southern hemisphere. Pronounced
  differences between the northern and southern rotational periods
  are obtained. The northern hemisphere shows a rigid rotation of ~27
  days which can be followed up to ~15 periods in the autocorrelation
  function. The signal of the southern hemisphere is strongly attenuated
  after 3 recurrences showing variable periods in the range ~26-28.5
  days. The presence of these periods is not permanent during a cycle
  suggesting activity pulses in each hemisphere. For the northern
  hemisphere strong relations to the motions of deeper lying convective
  structures building up long-living 'active zones' are suggested.

---------------------------------------------------------
Title: The Neupert effect and the electron-beam-driven evaporation
    model
Authors: Veronig, A.; Vršnak, B.; Dennis, B. R.; Temmer, M.;
   Hanslmeier, A.; Magdalenić, J.
2002ESASP.506..367V    Altcode: 2002svco.conf..367V; 2002ESPM...10..367V
  Based on a sample of ~1100 solar flares observed simultaneously in
  hard and soft X-rays, we performed a statistical analysis of the
  Neupert effect. For a subset of ~500 events, supplementary Hα flare
  data were considered. The timing behavior of &gt;50% of the events
  is consistent with the Neupert effect. A high correlation between
  the soft X-ray peak flux and the hard X-ray fluence is obtained,
  being indicative of electron-beam-driven evaporation. However, about
  one fourth of the events (predominantly weak flares) reveal strong
  deviations from the predicted timing, with a prolonged increase of
  the thermal emission beyond the end of the hard X-rays. These findings
  suggest that electron-beam-driven evaporation plays an important role
  in solar flares. Yet, in a significant fraction of events there is also
  evidence for an additional energy transport mechanism from the energy
  release site other than electron beams, presumably thermal conduction.

---------------------------------------------------------
Title: The Neupert effect in solar flares and implications for
    coronal heating
Authors: Veronig, A.; Vrsnak, B.; Dennis, B. R.; Temmer, M.;
   Hanslmeier, A.; Magdalenić, J.
2002ESASP.505..599V    Altcode: 2002solm.conf..599V; 2002IAUCo.188..599V; 2002astro.ph..8089V
  Based on simultaneous observations of solar flares in hard and soft
  X-rays we studied several aspects of the Neupert effect. About half of
  1114 analyzed events show a timing behavior consistent with the Neupert
  effect. For these events, a high correlation between the soft X-ray
  peak flux and the hard X-ray fluence is obtained, being indicative of
  electron-beam-driven evaporation. However, for about one fourth of the
  events there is strong evidence for an additional heating agent other
  than electron beams. We discuss the relevance of these findings with
  respect to Parker's idea of coronal heating by nanoflares.

---------------------------------------------------------
Title: Hemispheric asymmetry of solar activity phenomena: north-south
    excesses rotational periods and their links to the magnetic field
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002ESASP.505..587T    Altcode: 2002solm.conf..587T; 2002IAUCo.188..587T
  We present a cycle dependent analysis of various solar activity
  phenomena, namely Sunspot Numbers and Hα flares, including the
  time range 1975-2000. The data are studied on a statistical basis
  with relation to their spatial distribution, significance of the
  north-south asymmetry and rotational periods. For the considered time
  span we obtain significant values of north-south asymmetries. For the
  northern hemisphere the significant excesses are revealed during the
  increasing and maximum phase of a solar cycle whereas a southern excess
  dominates near the end of a cycle. Furthermore, we obtain differences
  in rotational periods and activity gaps between both hemispheres that
  suggest an independent evolution in hemispheric activity for these
  indices. Hence, a weak interdependence of the magnetic field system
  originating in the two hemispheres is suggested. Additionally we find
  differences in the dominant rotational periods of photospheric and
  chromospheric tracers.

---------------------------------------------------------
Title: Investigation of the Neupert effect in solar
    flares. I. Statistical properties and the evaporation model
Authors: Veronig, A.; Vršnak, B.; Dennis, B. R.; Temmer, M.;
   Hanslmeier, A.; Magdalenić, J.
2002A&A...392..699V    Altcode: 2002astro.ph..7217V
  Based on a sample of 1114 flares observed simultaneously in hard X-rays
  (HXR) by the BATSE instrument and in soft X-rays (SXR) by GOES, we
  studied several aspects of the Neupert effect and its interpretation
  in the frame of the electron-beam-driven evaporation model. In
  particular, we investigated the time differences (Delta t) between
  the maximum of the SXR emission and the end of the HXR emission,
  which are expected to occur at almost the same time. Furthermore,
  we performed a detailed analysis of the SXR peak flux - HXR fluence
  relationship for the complete set of events, as well as separately for
  subsets of events which are likely compatible/incompatible with the
  timing expectations of the Neupert effect. The distribution of the time
  differences reveals a pronounced peak at Delta t = 0. About half of the
  events show a timing behavior which can be considered to be consistent
  with the expectations from the Neupert effect. For these events, a high
  correlation between the SXR peak flux and the HXR fluence is obtained,
  indicative of electron-beam-driven evaporation. However, there is also
  a significant fraction of flares (about one fourth), which show strong
  deviations from Delta t = 0, with a prolonged increase of the SXR
  emission distinctly beyond the end of the HXR emission. These results
  suggest that electron-beam-driven evaporation plays an important role
  in solar flares. Yet, in a significant fraction of events, there is
  also clear evidence for the presence of an additional energy transport
  mechanism other than nonthermal electron beams, where the relative
  contribution is found to vary with the flare importance.

---------------------------------------------------------
Title: Hemispheric Sunspot Numbers R<SUB>n</SUB> and R<SUB>s</SUB>:
    Catalogue and N-S asymmetry analysis
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002A&A...390..707T    Altcode: 2002astro.ph..8436T
  Sunspot drawings are provided on a regular basis at the Kanzelhöhe
  Solar Observatory, Austria, and the derived relative sunspot numbers
  are reported to the Sunspot Index Data Center in Brussels. From the
  daily sunspot drawings, we derived the northern, R<SUB>n</SUB>,
  and southern, R<SUB>s</SUB>, relative sunspot numbers for the
  time span 1975-2000. In order to accord with the International
  Sunspot Numbers R<SUB>i</SUB>, the R<SUB>n</SUB> and R<SUB>s</SUB>
  have been normalized to the R<SUB>i</SUB>, which ensures that the
  relation R<SUB>n</SUB>+R<SUB>s</SUB>=R<SUB>i</SUB> is fulfilled. For
  validation, the derived R<SUB>n</SUB> and R<SUB>s</SUB> are compared
  to the international northern and southern relative sunspot numbers,
  which are available from 1992. The regression analysis performed for
  the period 1992-2000 reveals good agreement with the International
  hemispheric Sunspot Numbers. The monthly mean and the smoothed
  monthly mean hemispheric Sunspot Numbers are compiled into a
  catalogue. Based on the derived hemispheric Sunspot Numbers,
  we study the significance of N-S asymmetries and the rotational
  behavior separately for both hemispheres. We obtain that ~ 60% of the
  monthly N-S asymmetries are significant at a 95% level, whereas the
  relative contributions of the northern and southern hemisphere are
  different for different cycles. From the analysis of power spectra
  and autocorrelation functions, we derive a rigid rotation with ~
  27 days for the northern hemisphere, which can be followed for up
  to 15 periods. Contrary to that, the southern hemisphere reveals a
  dominant period of ~ 28 days, whereas the autocorrelation is strongly
  attenuated after 3 periods. These findings suggest that the activity
  of the northern hemisphere is dominated by an active zone, whereas
  the southern activity is mainly dominated by individual long-lived
  sunspot groups. The catalogue is available in electronic form at the
  CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via
  http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/707

---------------------------------------------------------
Title: Relative timing of solar flares observed at different
    wavelengths
Authors: Veronig, A.; Vršnak, B.; Temmer, M.; Hanslmeier, A.
2002SoPh..208..297V    Altcode: 2002astro.ph..8088V
  The timing of 503 solar flares observed simultaneously in hard X-rays,
  soft X-rays and Hα is analyzed. We investigated the start and the peak
  time differences in different wavelengths, as well as the differences
  between the end of the hard X-ray emission and the maximum of the
  soft X-ray and Hα emission. In more than 90% of the analyzed events,
  a thermal pre-heating seen in soft X-rays is present prior to the
  impulsive flare phase. On average, the soft X-ray emission starts 3 min
  before the hard X-ray and the Hα emission. No correlation between the
  duration of the pre-heating phase and the importance of the subsequent
  flare is found. Furthermore, the duration of the pre-heating phase
  does not differ for impulsive and gradual flares. For at least half of
  the events, the end of the non-thermal emission coincides well with
  the maximum of the thermal emission, consistent with the beam-driven
  evaporation model. On the other hand, for ∼ 25% of the events there
  is strong evidence for prolonged evaporation beyond the end of the
  hard X-rays. For these events, the presence of an additional energy
  transport mechanism, most probably thermal conduction, seems to play
  an important role.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Hemispheric Sunspot Numbers
    1975-2000 (Temmer+, 2002)
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
2002yCat..33900707T    Altcode:
  Hemispheric sunspot numbers including the time span from 1975-2000 are
  presented. The Sunspot Numbers are calculated from sunspot drawings
  made at the Kanzelhoehe Solar Observatory (KSO), Austria. The counted
  northern and southern Sunspot Numbers are normalized and multiplied
  with the International Sunspot Numbers taken from SIDC for matching
  days in order to provide the data within an international usage. Days
  without observation by KSO (about 27 percent) were reconstructed
  applying a linear interpolation method. As validation of the data,
  regression methods and a cross-correlation analysis are made with
  hemispheric Sunspot Numbers from SIDC for the available time span
  1992-2000 obtaining very good agreements. The results are given in
  monthly mean and smoothed monthly mean Sunspot Numbers. Based on this
  data set an analysis concerning the North-South asymmetry is made in
  the paper. (1 data file).

---------------------------------------------------------
Title: Book Review: The Dynamic sun / Kluwer, 2001
Authors: Hanslmeier, A.; Messerotti, M.; Veronig, A.
2002Obs...122..115H    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Soft X-ray flares for the period 1975-2000
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.; Otruba, W.;
   Messerotti, M.
2002ESASP.477..175T    Altcode: 2002scsw.conf..175T
  Statistical aspects of solar soft X-ray (SXR) flares for the period
  September 1975 to December 2000 are investigated. In particular,
  we analyzed the spatial distribution of SXR flares with regard to
  the solar hemispheres, i.e. N-S and E-W asymmetries, as well as the
  occurrence of SXR flares in the course of the solar cycle. We obtain
  that the occurrence rate of SXR flares is delayed in relation to the
  Sunspot Numbers which can be interpreted as an interaction between
  the northern and southern hemisphere activity.

---------------------------------------------------------
Title: Temporal characteristics of solar soft X-ray and Hα flares
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.; Messerotti, M.;
   Otruba, W.; Moretti, P. F.
2002ESASP.477..187V    Altcode: 2002scsw.conf..187V
  Temporal aspects of solar soft X-ray and Hα flares for the period
  1997-2000 are investigated. For the considered time span about 8400
  SXR and 11400 Hα flares are reported in the SGD. Related flares
  observed in Hα as well as in SXR are identified amounting to about
  2100 events. Correlations among corresponding SXR and Hα events are
  analyzed and their relative timing is investigated. From the timing
  analysis we infer that for most of the events (84%) the start of the
  Hα emission is delayed with respect to the SXR emission. On average,
  the Hα flare starts 3 minutes after the SXR flare. The peaks occur
  preferentially simultaneously with a slight tendency that the Hα peak
  precedes the SXR peak.

---------------------------------------------------------
Title: Temporal aspects and frequency distributions of solar soft
    X-ray flares
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.; Otruba, W.;
   Messerotti, M.
2002A&A...382.1070V    Altcode: 2002astro.ph..7234V
  A statistical analysis of almost 50 000 soft X-ray (SXR) flares observed
  by GOES during the period 1976-2000 is presented. On the basis of
  this extensive data set, statistics on temporal properties of soft
  X-ray flares, such as duration, rise and decay times with regard to
  the SXR flare classes is presented. Correlations among distinct flare
  parameters, i.e. SXR peak flux, fluence and characteristic times,
  and frequency distributions of flare occurrence as function of the
  peak flux, the fluence and the duration are derived. We discuss the
  results of the analysis with respect to statistical flare models, the
  idea of coronal heating by nanoflares, and elaborate on implications
  of the obtained results on the Neupert effect in solar flares.

---------------------------------------------------------
Title: The energetic importance of accelerated electrons in solar
    flares
Authors: Dennis, B.; Veronig, A.
2002cosp...34E1104D    Altcode: 2002cosp.meetE1104D
  It has been claimed that a large fraction of the total energy released
  in a solar flare goes initially into accelerated electrons. These
  electrons generate the observed hard X-ray bremsstrahlung emission as
  they lose most of their energy by coulomb collisions in the lower corona
  and chromosphere to heat the plasma seen in soft X- rays. From several
  recent studies of the Neupert Effect - the empirical result that for
  many flares the time integral of the hard Xray emission closely matches
  the- temporal variation of the soft X-ray emission - it appears that
  the fraction of the released energy going into accelerated electrons
  is lower, on average, for smaller flares. Also, from relative timing
  differences, about 25% of all flares are inconsistent with the Neupert
  Effect. The Reuven Ramaty High Energy Solar Spectroscopic Imager
  (RHESSI) is uniquely capable of investigating the Neupert E fect
  since itf covers soft X-rays down to 3 keV (when both attenuators
  are out of the field of view) and hard X-rays with keV energy
  resolution. It has arcsecond-class angular resolution and sub-second
  time resolution. Several M-class flares have already been detected by
  RHESSI and we will present their detailed time histories for different
  energy ranges. W e will also present hard and soft X-ray images that
  reveal the spatial relation between the hot plasma and the accelerated
  electrons. The results are in agreement with the Neupert Effect for
  some flares , but they suggest for other flares that there must be
  other heating mechanisms besides the thermalization of accelerated
  electrons, even during the impulsive phase.

---------------------------------------------------------
Title: Frequency Distributions of solar Flares
Authors: Veronig, A.; Temmer, M.; Hanslmeier, A.
2002HvaOB..26....7V    Altcode:
  Flare frequency distributions as function of the soft X-ray peak flux
  and fluence are investigated. We analyse GOES 1--8 Å data for the
  period 1986--2000. The results are discussed with respect to avalanche
  flare models and the hypothesis of coronal heating by nanoflares.

---------------------------------------------------------
Title: Statistical analysis of solar Hα flares
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.; Otruba, W.;
   Messerotti, M.
2001A&A...375.1049T    Altcode: 2002astro.ph..7239T
  A statistical analysis of a large data set of Hα flares comprising
  almost 100 000 single events that occurred during the period
  January 1975 to December 1999 is presented. We analyzed the flares
  evolution steps, i.e. duration, rise times, decay times and event
  asymmetries. Moreover, these parameters characterizing the temporal
  behavior of flares, as well as the spatial distribution on the solar
  disk, i.e. N-S and E-W asymmetries, are analyzed in terms of their
  dependency on the solar cycle. The main results are: 1) The duration,
  rise and decay times increase with increasing importance class. The
  increase is more pronounced for the decay times than for the rise
  times. The same relation is valid with regard to the brightness
  classes but in a weaker manner. 2) The event asymmetry indices,
  which characterize the proportion of the decay to the rise time of
  an event, are predominantly positive (~90%). For about 50% of the
  events the decay time is even more than 4 times as long as the rise
  time. 3) The event asymmetries increase with the importance class. 4)
  The flare duration and decay times vary in phase with the solar cycle;
  the rise times do not. 5) The event asymmetries do not reveal a distinct
  correlation with the solar cycle. However, they drop during times of
  solar minima, which can be explained by the shorter decay times found
  during minimum activity. 6) There exists a significant N-S asymmetry
  over longer periods, and the dominance of one hemisphere over the
  other can persist for more than one cycle. 7) For certain cycles there
  may be evidence that the N-S asymmetry evolves with the solar cycle,
  but in general this is not the case. 8) There exists a slight but
  significant E-W asymmetry with a prolonged eastern excess.

---------------------------------------------------------
Title: The Dynamic Sun
Authors: Hanslmeier, Arnold; Messerotti, Mauro; Veronig, Astrid
2001ASSL..259.....H    Altcode: 2001dysu.conf.....H
  This book contains the proceedings of the Summerschool and Workshop
  "The Dynamic Sun" held from August 30th to September 10th, 1999, at
  the Solar Observatory Kanzelhoehe, which belongs to the Institute
  of Geophysics, Astrophysics and Meteorology of the University of
  Graz, Austria. This type of conference was the second one held at
  Kanzelhoehe and was again very successful in bringing together experts
  from specialized topics in solar physics and young scientists and
  students from different countries. Seven series of lectures were given
  by invited lecturers, experts in the relevant fields and twenty-seven
  constributions were presented at the workshop by the participants. The
  scientific topics addressed covered a wide range of subjects, from solar
  magnetohydrodynamics to the physics of the outer solar atmosphere and
  from a detailed description of the SOHO mission to space weather.

---------------------------------------------------------
Title: Comparison of Local and Global Fractal Dimension Determination
    Methods
Authors: Veronig, A.; Hanslmeier, A.; Messerotti, M.
2001ASSL..259..315V    Altcode: 2001dysu.conf..315V
  Local and global methods for the determination of fractal dimensions are
  applied to astrophysical time series. The analysis reveals that local
  dimension methods are better suitable for such kind of time series,
  which are non-stationary and which represent real-world systems. It
  is shown that local dimension methods can provide physical insights
  into the system even in cases in which pure determinism cannot be
  established.

---------------------------------------------------------
Title: Solar Activity Monitoring and Flare Alerting at Kanzelhöhe
    Solar Observatory
Authors: Steinegger, M.; Veronig, A.; Hanslmeier, A.; Messerotti,
   M.; Otruba, W.
2001ASSL..259..227S    Altcode: 2001dysu.conf..227S
  At the Kanzelhöhe Solar Observatory a solar activity monitoring and
  flare alerting system is under development, which will be based on
  the parametrization of solar flaring activity using photometric and
  magnetic full-disk images of the Sun obtained simultaneously with high
  time cadence. This system will rely on Artificial Neural Networks
  for pattern recognition, image segmentation, parameterization, and
  forecasting. In particular, relevant activity indices and indicators
  will be derived to be used as reliable precursors for flaring activity.

---------------------------------------------------------
Title: A Neural Network Approach to Solar Flare Alerting (CD-ROM
Directory: contribs/steinegg)
Authors: Steinegger, M.; Veronig, A.; Hanslmeier, A.; Messerotti,
   M.; Otruba, W.
2001ASPC..223.1165S    Altcode: 2001csss...11.1165S
  No abstract at ADS

---------------------------------------------------------
Title: Radio Pulsations in the m-dm Band: Case Studies
Authors: Messerotti, M.; Zlobec, P.; Veronig, A.; Hanslmeier, A.
2001pre5.conf..471M    Altcode:
  Radio pulsations are observed during several type IV bursts in the
  metric and decimetric band. A great variety of morphological and
  evolutionary features characterizes such events. Radio pulsations
  should carry information about the magnetic topology of the corona, the
  local particle density distribution, and about magnetic reconnection
  and particle acceleration processes at or near the radio source; the
  polarization degree should bring important clues about emission mode
  and propagation effects in the source and outside it. In this frame,
  we selected a representative set of radio pulsations, observed with high
  time resolution by the Trieste Solar Radio System in the meter-decimeter
  (m-dm) wavelength band, and performed a detailed morphological and
  spectral analysis to identify possible similarities in the descriptors
  relevant to different categories of events. Both classical and nonlinear
  techniques were applied in the attempt to investigate more deeply the
  physical nature of the emission process. The obtained results give
  the trend how the ratio magnetic field - characteristic dimension of
  the source increases at higher observing frequencies. A sudden rise of
  this ratio across the m-dm range was derived, indicating a different
  nature of pulsations in the two ranges.

---------------------------------------------------------
Title: Statistical Study of Solar Flares Observed in Soft X-Ray,
    Hard X-Ray and Hα Emission
Authors: Veronig, A.; Vršnak, B.; Temmer, M.; Magdalenić, J.;
   Hanslmeier, A.
2001HvaOB..25...39V    Altcode:
  Correlations among statistical properties of solar flares observed
  in soft X-rays, hard X-rays and Hα are studied. We investigate
  corresponding HXR flares measured by BATSE, SXR flares observed by GOES
  and Hα flares reported in the SGD for the period 1997--2000. Distinct
  correlations are found among the SXR peak flux and Hα area, as well
  as between the SXR peak flux and HXR fluence. This can be comprehended
  in the frame of the chromospheric evaporation model of flares.

---------------------------------------------------------
Title: Linear and nonlinear statistical analysis of narrow-band
    dm-spikes observed during the June 15, 1991 flare
Authors: Mészárosová, H.; Karlický, M.; Veronig, A.; Zlobec, P.;
   Messerotti, M.
2000A&A...360.1126M    Altcode:
  Narrow-band dm-spikes observed during the June 15, 1991 flare
  are statistically analysed. The character of their frequency
  distributions at 237, 327, 408 and 610 MHz in both L- and R-handed
  circular polarizations is studied. While for the complete time
  intervals no simple distributions of spikes (either exponential or
  power-law) are recognized, for shorter intervals both exponential
  and power-law distributions are observed. No significant difference
  is found in the distributions for L- and R-polarized data. Further
  analysis reveals that spikes appearing in dense groups and with high
  intensities preferentially have exponential distributions, while
  the sparse spikes with lower intensities are rather characterized
  by power-law distribution functions with high exponents. Groups of
  independent spikes (cases with low rates and low intensities) have
  power-law distributions trend in agreement with the coherent spike
  mechanisms. Tests are provided regarding statistical analyses. The
  nonlinear analysis reveals that the degree of complexity of the system
  varies. It decreases when the attractor dimensions and the Lyapunov
  exponents assume smaller values, which happens when very strong
  spikes are present. The changing characteristics of the statistical
  parameters are probably the result of a mutual interaction in the
  source environment or a product of propagation conditions.

---------------------------------------------------------
Title: Determination of fractal dimensions of solar radio bursts
Authors: Veronig, A.; Messerotti, M.; Hanslmeier, A.
2000A&A...357..337V    Altcode: 2002nlin......7021V
  We present a dimension analysis of a set of solar type I storms and
  type IV events with different kind of fine structures, recorded at the
  Trieste Astronomical Observatory. The signature of such types of solar
  radio events is highly structured in time. However, periodicities
  are rather seldom, and linear mode theory can provide only limited
  interpretation of the data. Therefore, we performed an analysis
  based on methods of the nonlinear dynamics theory. Additionally to the
  commonly used correlation dimension, we also calculated local pointwise
  dimensions. This alternative approach is motivated by the fact that
  astrophysical time series represent real-world systems, which cannot
  be kept in a controlled state and which are highly interconnected with
  their surroundings. In such systems pure determinism is rather unlikely
  to be realized, and therefore a characterization by invariants of the
  dynamics might probably be inadequate. In fact, the outcome of the
  dimension analysis does not give hints for low-dimensional determinism
  in the data, but we show that, contrary to the correlation dimension
  method, local dimension estimations can give physical insight into the
  events even in cases in which pure determinism cannot be established. In
  particular, in most of the analyzed radio events nonlinearity in the
  data is detected, and the local dimension analysis provides a basis
  for a quantitative description of the time series, which can be used
  to characterize the complexity of the related physical system in a
  comparative and non-invariant manner. In this frame, the degree of
  complexity we inferred for type I storms is on the average lower than
  that relevant to type IV events. For the type IV events significant
  differences occur with regard to the various subtypes, where pulsations
  and sudden reductions can be described by distinctly lower values than
  spikes and fast pulsations.

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Title: Automatic Image Processing in the Frame of a Solar Flare
    Alerting System
Authors: Veronig, A.; Steinegger, M.; Otruba, W.; Hanslmeier, A.;
   Messerotti, M.; Temmer, M.; Gonzi, S.; Brunner, G.
2000HvaOB..24..195V    Altcode:
  In the present paper we describe image processing techniques applied
  to solar H-alpha full-disk images, with the objective of automatic
  and quasi real-time detection of the onset of H-alpha flares and
  describing their evolution. For this purpose we utilize a combination
  of region-based and edge-based image segmentation methods.

---------------------------------------------------------
Title: Automatic Image Segmentation and Feature Detection in Solar
    Full-Disk Images
Authors: Veronig, A.; Steinegger, M.; Otruba, W.; Hanslmeier, A.;
   Messerotti, M.; Temmer, M.; Brunner, G.; Gonzi, S.
2000ESASP.463..455V    Altcode: 2000sctc.proc..455V
  At Kanzelhoehe Solar Observatory, Austria, a solar activity monitoring
  and flare alerting system is under development, which will be based
  on the parametrization of solar flare activity using photometric and
  magnetic full-disk images of the Sun obtained simultaneously with high
  time cadence. An important step in this project is the automatic image
  segmentation and feature detection of solar activity phenomena related
  to the occurrence of solar flares. In a first step we have developed
  a procedure for automatically detecting the onset and describing the
  evolution of flares in H-alpha full-disk images.

---------------------------------------------------------
Title: Applications of nonlinear time series analysis in solar physics
Authors: Veronig, A.; Messerotti, M.; Hanslmeier, A.
2000swms.work...41V    Altcode:
  We applied methods of nonlinear time series analysis to different
  aspects of the solar phenomenology, as the solar cycle, the solar
  granulation and solar radio bursts. The methods include tests for
  deterministic chaos hidden in the data, as the determination of
  global attractor dimensions. However, in solar physics we deal
  with "real world" time series, which hardly allow to detect pure
  determinism. Therefore we also applied tools, which enable to cope with
  non-stationarities in the data and provide statistical significance
  even in cases where the existence of low-dimensional chaos cannot be
  established, like local dimension estimations and recurrence plots. The
  relevant methods are described with application to different solar
  time series.

---------------------------------------------------------
Title: Statistical Properties Relevant to Solar Flare Prediction
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.; Steinegger, M.;
   Brunner, G.; Gonzi, S.; Otruba, W.; Messerotti, M.
2000HvaOB..24..185T    Altcode:
  We statistically analyzed the characteristic temporal properties of
  H-alpha flares, such as duration, rising and setting times, with the aim
  to determine a proper acquisition rate for H-alpha patrol observations,
  which will be the basis for the automatic flare alerting and prediction
  system at the Kanzelhoehe Solar Observatory, Austria. Furthermore,
  the comparison of absolute and normalized values reveals interesting
  aspects on how flares of different importance classes behave with
  respect to the rising and decay phase.

---------------------------------------------------------
Title: Power-law and Exponential Distributions of Narrowband dm-Spikes
    Observed During the June 15, 1991 Flare
Authors: Meszarosova, H.; Karlický, M.; Veronig, A.; Zlobec, P.;
   Messerotti, M.
1999ESASP.448.1025M    Altcode: 1999mfsp.conf.1025M; 1999ESPM....9.1025M
  No abstract at ADS

---------------------------------------------------------
Title: Localized Measures of Solar Radio Bursts
Authors: Veronig, A.; Hanslmeier, A.; Messerotti, M.
1999ASSL..239..255V    Altcode: 1999msa..proc..255V
  We investigated localized measures of solar radio bursts by analyzing
  local pointwise dimensions and recurrence plots of a set of type I
  and type IV solar radio bursts. The analysis indicates that type IV
  bursts are a more complex phenomenon than type I bursts.

---------------------------------------------------------
Title: Determination of Local Pointwise Dimensions for Solar Radio
    Bursts
Authors: Veronig, A.; Messerotti, M.; Hanslmeier, A.; Rucker, H. O.
1998cee..workE..66V    Altcode:
  We analyzed a set of type I and type IV solar radio bursts. The data
  sets are high time resolution, single frequency recordings from the
  multichannel radio polarimeter of the Trieste Astronomical Observatory
  operating in the meter range. In order to get indications about the
  complexity of the underlying physical system we determined the fractal
  dimension of a tentative attractor. As especially indicated by localized
  measures (Mayer-Kress, 1994), as, e.g., the local pointwise dimension,
  type IV bursts seem to be phenomena of higher complexity and higher
  diversity from one event to another than type I bursts (Veronig et al.,
  1998). Figure 1 represents the time series of pulsations in a type IV
  event and the related local pointwise dimension D_p(xi<SUB>i</SUB>),
  respectively D_p(t_i), showing a clear convergence behaviour
  interrupted by a few sections of high values of D_p(t_i), indicating
  non-uniformities of the system's attractor. Figure 1. Top panel: Time
  series of a type IV event with quasi-periodic pulsations. Bottom panel:
  The related local pointwise dimension, converging to an average value
  of bar{D}_p ~4.1. A fractal dimension of ~4.1 means that the number of
  free parameters, needed to describe the underlying dynamical system,
  should be at least 5. In future we plan to develop an extension of
  the dimension algorithm to be applied to two dimensional time series
  in order to include the additional information given by dynamic radio
  spectra. The radio spectra will be acquired by the newly developed
  digital spectropolarimeter with time resolution Delta t = 1ms and
  spectral resolution Delta f = 10kHz to be installed at the radio
  station Lustbuhel, Graz, Austria (Kleewein, 1997).

---------------------------------------------------------
Title: Case studies of magnetic topology evolution in active regions
Authors: Cacciani, A.; di Martino, V.; Hanslmeier, A.; Messerotti,
   M.; Moretti, P. F.; Pettauer, Th.; Veronig, A.
1998ASPC..155..229C    Altcode: 1998sasp.conf..229C
  We give a preliminary report on the evolution of the magnetic field
  topology extrapolated in the current-free approximation for two solar
  active regions observed through an MOF imaging magnetograph.

---------------------------------------------------------
Title: A MOF-based full vector imaging magnetograph
Authors: Cacciani, A.; Comari, M.; Furlani, S.; Hanslmeier, A.;
   Messerotti, M.; Moretti, P. F.; Pettauer, Th.; Veronig, A.
1998ASPC..155..265C    Altcode: 1998sasp.conf..265C
  The scheme and the operating principles of a fast, compact,
  magneto-optical filter-based, full-vector imaging magnetograph,
  currently under development for solar observations, are briefly outlined
  as well as planned improvements and possible applications.

---------------------------------------------------------
Title: Determining fractal dimensions of solar radio bursts
Authors: Veronig, A.; Messerotti, M.; Hanslmeier, A.
1998joso.proc..166V    Altcode:
  We determined fractal dimensions of solar radio bursts, namely the
  correlation dimension and the local pointwise dimension of a set of
  type I and type IV solar radio bursts. The data sets are high time
  resolution (50Hz), single frequency recordings from the multichannel
  radio polarimeter of the Trieste Observatory. A comparative study of the
  analysis methodology shows that the local pointwise dimension yields
  more stable and reliable results than the widely used correlation
  dimension. The outcome of the dimension analysis indicates that type
  IV bursts are a more complex and diverse phenomenon than type I bursts.

---------------------------------------------------------
Title: The architecture of the New JOSO WWW Server
Authors: Messerotti, M.; Veronig, A.
1998ASPC..155..287M    Altcode: 1998sasp.conf..287M
  The general structure and the most prominent features of the new
  implementation of the World Wide Web (WWW) server designed for the
  Joint Organization for Solar Observations (JOSO) are described. The
  URL of the JOSO WWW site is http://joso.oat.ts.astro.it.

---------------------------------------------------------
Title: Nonlinear Analysis of Solar Radio Events: A Preliminary
    Approach
Authors: Veronig, A.; Messerotti, M.; Hanslmeier, A.
1997pre4.conf..463V    Altcode: 1997pre4.proc..463V
  We analysed a set of time series related to different types of solar
  radio events (type I, type IV and spikes) in order to determine the
  nature of the underlying generating process through the methods of
  nonlinear dynamics. The Grassberger-Procaccia method was used to
  evaluate the correlation dimension of a possible attractor in subsets
  which fulfilled the stationarity condition. The majority of samples
  do not show a low dimensionality, suggesting stochasticity or a high
  dimensional system; only two overlapping subsets of one type IV event
  with spikes exhibit a finite dimension (D 3.5 and D 3.7). The limited
  datasets do not allow to draw any definite conclusion, but the varied
  results indicate that a critical analysis on the physical character
  of solar radio events is needed to give a consistent interpretation.

---------------------------------------------------------
Title: Non-linear analysis of the dynamics of solar radio events.
Authors: Veronig, A.; Messerotti, M.; Hanslmeier, A.
1996AGAb...12..165V    Altcode:
  No abstract at ADS