Author name code: veronig
ADS astronomy entries on 2022-09-14
author:"Veronig, Astrid M."
------------------------------------------------------------------------
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
Bibcode: 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
~1024-1025 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.
Title: Detecting stellar CMEs through post-flare coronal dimmings
Authors: Veronig, Astrid; Hudson, Hugh S.; Odert, Petra; Leitzinger,
Martin; Dissauer, Karin; Fleck, Nikolaus
Bibcode: 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
Title: First analyses of SEP events with PSP & 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
Bibcode: 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).
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
Bibcode: 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.
Title: Coronal dimmings as indicators of the CME evolution close to
the Sun
Authors: Chikunova, Galina; Podladchikova, Tatiana; Veronig, Astrid;
Dissauer, Karin
Bibcode: 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.
Title: Magnetic helicity and energy budget around large confined
and eruptive solar flares
Authors: Gupta, Manu; Veronig, Astrid; Thalmann, Julia K.
Bibcode: 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.
Title: Determination of CME orientation and consequences for their
propagation
Authors: Martinic, Karmen; Vrsnak, Bojan; Veronig, Astrid; Dumbovic,
Mateja; Temmer, Manuela
Bibcode: 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.
Title: Development and evaluation of Drag-Based Ensemble Model (DBEM)
Authors: Čalogović, Jaša; Vrsnak, Bojan; Veronig, Astrid; Dumbovic,
Mateja; Temmer, Manuela
Bibcode: 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 (< 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.
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
Bibcode: 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
(<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.
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
Bibcode: 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.
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
Bibcode: 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.
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.
Bibcode: 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.
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.
Bibcode: 2022A&A...663A..24P
Altcode: 2022arXiv220407396P
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.
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.
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.
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).
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
Bibcode: 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.
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
Bibcode: 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.
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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
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
Bibcode: 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.
Bibcode: 2022A&A...661A.149P
Altcode: 2022arXiv220311625P
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.
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.
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 (1024
− 1029 erg) with a power-law index α = 2.28 ±
0.03. The derived mean energy flux of (3.7 ± 1.6)×104
erg cm−2 s−1 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
× 105 erg cm−2 s−1) 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.
Conclusions: The
steep power-law slope (α > 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.
Bibcode: 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.
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.
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
Bibcode: 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 >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
Bibcode: 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 >100 MeV gamma-rays. The LAT detection lasted
for ~16 minutes, the peak flux was 3.6 ± 0.8 (10-5) ph
cm-2 s-1 with a significance >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
>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
Bibcode: 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
Bibcode: 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.
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.
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.
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.
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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
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
Bibcode: 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.
Title: Detection of stellar CMEs through post-flare coronal dimmings
Authors: Veronig, Astrid; Odert, Petra; Leitzinger, Martin; Dissauer,
Karin; Fleck, Nikolaus; Hudson, Hugh
Bibcode: 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
Bibcode: 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.
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.
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.
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.
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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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).
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, EF/E (energy
ratio), the fraction of non-potential (current-carrying) helicity,
|HJ|/|HV| (helicity ratio), and the normalized
current-carrying helicity, |HJ|/ϕ'2.
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, EF/E and
|HJ|/|HV|, and |HJ|/ϕ'2,
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.
Conclusions: If the corona of an AR exhibits characteristic values of
⟨|HJ|/|HV|⟩ > 0.1, ⟨EF/E⟩
> 0.2, and ⟨|HJ|/ϕ'2⟩ > 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 ⟨|HJ|/|HV|⟩ ≲ 0.1,
⟨EF/E⟩ ≲ 0.1, and ⟨|HJ|/ϕ'2⟩
≲ 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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
> 1.5 × 1010 km2 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.
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. Movies are available at https://www.aanda.org
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
Bibcode: 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
(ΦAR). Our results show that the slope of the flare-CME
association rate with flare intensity reveals a steep monotonic decrease
with ΦAR. This means that flares of the same GOES class but
originating from an AR of larger ΦAR, are much more likely
to be confined. Based on an AR flux as high as 1.0 × 1024
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 (LSGPIL),
the total photospheric free magnetic energy (Efree),
and the area with large shear angle (AΨ). We find that
confined flares tend to have larger values of LSGPIL,
Efree, and AΨ compared to eruptive flares. Each
nonpotential parameter shows a moderate positive correlation with
ΦAR. Our results imply that ΦAR 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.
Bibcode: 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.
Aims: In order to understand the initiation and
evolution of this particular event, we performed a comprehensive
analysis using a combined observational-modeling approach.
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.
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.
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). Movies are available at https://www.aanda.org
Title: Hemispheric sunspot numbers 1874-2020
Authors: Veronig, Astrid M.; Jain, Shantanu; Podladchikova, Tatiana;
Pötzi, Werner; Clette, Frederic
Bibcode: 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.
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.
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.
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.
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. The catalogue is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/652/A56
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.
Bibcode: 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 (<
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 ×10−7
km−1, w ≈ 425 km s−1) 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.
Bibcode: 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.
Bibcode: 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&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). (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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 2021A&A...646A..34K
Altcode: 2020arXiv201200786K
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.
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.
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 × 1028 - 2 × 1033 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 × 1016 - 6 × 1018 g, and the
highest projected velocities are ~300-700 km s-1.
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. Table C.1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr
(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/646/A34
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
Bibcode: 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 ≈105.5 to
107.5K. 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 )×108cm−3, and a mean emission measure
of (2.8 ±1.6 )×1026cm−5. 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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⊙) 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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. 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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. 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&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. 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. 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). 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. Additional comments made
during the visual inspection of all flaring spectra are added. (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.
Bibcode: 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.
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.
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.
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.
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. Movies are available at https://www.aanda.org
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.
Bibcode: 2020A&A...642A..15K
Altcode:
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.
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.
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
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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-1 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 τc = 28-32 hr,
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. 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
Bibcode: 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-2, followed by an extended phase with
accelerations up to 0.7 km s-2. 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 >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.
Bibcode: 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.
Bibcode: 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-1) 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-1
with acceleration ≍110 m s-2) 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.
Bibcode: 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.
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.
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.
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.
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
Bibcode: 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.
Bibcode: 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∘ from the solar
central meridian, whereas EJ-ICMEs originate predominantly (16/17, 94%)
from source regions that are outside ±30∘. 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
Bibcode: 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-1, 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.
Bibcode: 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 × 1011
km2 against 3.51 ± 0.71 × 1010 km2
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.
Bibcode: 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.
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.
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.
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)×108 km2 per day showing a reasonable
anti-correlation (ccPearson = -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-1) and the signed
magnetic flux (30.3 ± 31.5 1018 Mx day-1) were
also found to be dependent on solar activity (ccPearson =
0.50 and ccPearson = 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
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.
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.
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
(Rp/Rs) for an Earth-sized planet orbiting a
Sun-like star.
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.
Bibcode: 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
Bibcode: 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 Bz 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 Bz 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 Bz 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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. Guo et al. 2018,
A&A). Based on the large catalog of FDs at Mars compiled
by Papaioannou et
al. (2019, Solar Physics) as well as results from our previous
work (Freiherr von
Forstner et al., 2019, Space Weather), 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. 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 (Belov et al., 2008,
Abunin et al.,
2012). 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 <a href="https://doi.org/10.1029/2018JA025949>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.
Bibcode: 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. 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. 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.
Bibcode: 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. 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 (>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). 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-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
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.
Bibcode: 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.
Bibcode: 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. 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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). (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.
Bibcode: 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) ×
1022 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.
Bibcode: 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∘, for which we derive sizes between 1.6
×109 and 1.8 ×1011km2. 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
Bibcode: 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 > 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 > 40 h (cc = 0.88 ±
0.02). The remaining flux arises from magnetic elements with lifetimes
< 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). Movie associated to Fig. 2 is available at https://www.aanda.org
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.
Bibcode: 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
Bibcode: 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 R⊙. Over
that distance range, the CME undergoes a strong north-eastward
deflection of at least 30∘ 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
Bibcode: 2019ApJ...879...85V
Altcode: 2019arXiv190601517V
We study the coronal dimming caused by the fast halo CME (deprojected
speed v = 1250 km s-1) 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-1 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 × 109 cm-3 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 × 1012 g s-1),
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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
(<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.
Bibcode: 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
Bibcode: 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-1. 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-1. 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
Bibcode: 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
Bibcode: 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 (>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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
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. Movie attached to Fig. 1 is available at https://www.aanda.org
Title: The Scientific Foundation of Space Weather
Authors: Baker, Daniel; Balogh, André; Gombosi, Tamas; Koskinen,
Hannu E. J.; Veronig, Astrid; von Steiger, Rudolf
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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 s ) 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-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: Coronal holes detection using supervised classification
Authors: Delouille, Veronique; Hofmeister, Stefan; Reiss, Martin;
Mampaey, Benjamin; Temmer, Manuela; Veronig, Astrid
Bibcode: 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
Bibcode: 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 > 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.
Bibcode: 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
>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} > 0.5) are predominantly
eruptive. Flares originating from underneath the AR dipole field (d_{FC}
/ d_{PC} < 0.5) tend to be eruptive when they are launched from
a compact AR and confined when launched from an extended AR (d_{PC}
> 60 Mm). In confined events, the flare-relevant field adjusts its
orientation quickly to that of the underlying dipole field with height
(δ φ > 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} > 40 Mm) and eruptive flares (h_{crit}
< 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
Bibcode: 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 >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
Bibcode: 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 (>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>0.7) and the CME
mass (c>0.6). Their corresponding time derivatives, describing
the dimming dynamics, strongly correlate with the GOES flare class
(c>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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 ×
1010 km2, contain a total unsigned magnetic flux
of 1.75 × 1021 Mx, and show a total brightness decrease
of -1.91 × 106 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 (>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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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. 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. 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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 · 1010 km2 to 6 · 1010
km2, (b) keeps a rather constant area for about one month of
>9 · 1010 km2, and (c) finally decreases in
the following three months below 1 · 1010 km2
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-1, for the maximum
phase 600-720 km s-1, and for the decaying phase a more
irregular behavior connected to slow and fast solar wind speeds of
350-550 km s-1.
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
Bibcode: 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 &
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
Bibcode: 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
Bibcode: 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 <130
km/s. Simultaneously, the corresponding outflow jets are observed in the
AIA hot passbands with speeds of <740 km/s and a mean temperature
of <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
Bibcode: 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
Bibcode: 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}}>0.5) are
predominantly eruptive. Flares originating from underneath the AR
dipole field (d_{{FC}}/d_{{PC}}<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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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! 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
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.
Bibcode: 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.
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.
Bibcode: 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.
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.
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.
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.
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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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−1). 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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 FC) 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 PC. Flares originating
from underneath the AR dipole (d FC/d PC <
0.5) tend to be eruptive if launched from compact ARs (d PC
≤ 60 Mm) and confined if launched from extended ARs. Flares ejected
from the periphery of ARs (d FC/d PC > 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 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: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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 × 1023 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 × 1032
erg. Using a magnetic flux estimate of 6 × 1023 Mx for
the largest solar AR observed, we find that flares of GOES class
≈X500 could be produced (E bol ≈ 3 × 1033
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1) than the cooler one
(∼130 km s-1). 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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)sin2b (deg/day) for the DS
method and ω(b) = (14.50 ± 0.01)-(2.87 ± 0.12)sin2b
(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.
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.
Bibcode: 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.
Bibcode: 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” (2015,
ApJL, 801, L23)
Authors: Thalmann, J. K.; Su, Y.; Temmer, M.; Veronig, A. M.
Bibcode: 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
Bibcode: 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-1. Simultaneously, the corresponding outflow
jets are observed in the AIA hot passbands with speeds of ∼740 km
s-1 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
Bibcode: 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⊙. 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.
Bibcode: 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.
Bibcode: 2017A&A...602A..60G
Altcode: 2017arXiv170406089G
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.
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).
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.
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. The movie associated to Figs. 4 and 5 is available at http://www.aanda.org
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
Bibcode: 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 < 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
Bibcode: 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
& 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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
>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 >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
Bibcode: 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.
Bibcode: 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-1. 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
Bibcode: 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 > 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 >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 > 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 2017psio.confE.107G
Altcode:
No abstract at ADS
Title: Solar eruptions and energetic events
Authors: Veronig, Astrid
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1 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-1. 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
Bibcode: 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
Bibcode: 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.
Bibcode: 2016ApJ...830...92D
Altcode: 2016arXiv160705961D
We investigate the high-speed (v > 1000 km s-1)
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 & 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
Bibcode: 2016EGUGA..18.6857D
Altcode:
We investigate the high-speed (v > 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.
Bibcode: 2016A&A...588A...6G
Altcode: 2016arXiv160202145G
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.
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.
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-1, 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 × 109 cm-3 to 3.16 × 1010
cm-3 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 ×
1010 erg s-1 cm-2 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-1 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-1 for the upflowing
filament material.
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. A movie is available at http://www.aanda.org
Title: Ground-based Observations of the Solar Sources of Space Weather
Authors: Veronig, A. M.; Pötzi, W.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 ×1021Mx (AIA 1600 Å) and 7.9 ×1021Mx
(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 >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.
Bibcode: 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.
Bibcode: 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 (Bz). 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 Bz 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 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. Since the strength of the Bz
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
Bibcode: 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-1 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 1025
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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−1 (within a range of 100 - 630 km
s−1). For the mean (linear) velocity, the arithmetic
mean is 254±76 km s−1 (within a range of 130 - 470
km s−1). 52 % of all waves under study show a distinct
deceleration during their propagation (a≤−50 m s−2),
the other 48 % are consistent with a constant speed within the
uncertainties (−50≤a≤50 m s−2). 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−1, 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.
Bibcode: 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-1. 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-1 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.
Bibcode: 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.
Bibcode: 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-1 at 15 R ⊙ to ~1500 km s-1 at 154
R ⊙), the Earth-directed part showed an abrupt retardation
below 35 R ⊙ (from ~1700 to ~900 km s-1). 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.
Bibcode: 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.
Bibcode: 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-1). 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-1. 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-1. 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1 to ~700 km
s-1 and CME2 decelerates from ~1300 km s-1 to ~600
km s-1. 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
Bibcode: 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-1.
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.
Bibcode: 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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 (< 0.3
R⊙ above the solar surface) is found to rapidly increase
with values of ≈ 0.03 - 0.09 R⊙, 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−2) compared to the off-disk component (duration
t=340 s, acceleration a=1.5 km s−2).
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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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 >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.
Bibcode: 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−1 for the weakest up to ≈ 500 km s−1
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.
Bibcode: 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.
Bibcode: 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-1. 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
Bibcode: 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 ⊙ and is assumed to mostly contribute up to
20 R ⊙. The mass increase ranges from 2% to 6% per R
⊙ 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 (<3 R
⊙). 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 (<3 R ⊙). The
derived CME kinetic energies range between 1.0-66 × 1023
J, and the forces range between 2.2-510 × 1014 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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∘, 60∘, and
90∘. 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∘ sep: ϕ=W7;
60∘ sep: ϕ=W12; 90∘ 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∘ case, while with growing separation angle the ICME
speed at 1 AU is increasingly overestimated (30∘ sep:
ΔVarr≈− 50 km s−1, 60∘ sep:
ΔVarr≈+ 75 km s−1, 90∘ sep:
ΔVarr≈+ 125 km s−1). Especially for future
L4/L5 missions, the 60∘ 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
Bibcode: 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
Bibcode: 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 (< 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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-1. 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
Bibcode: 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
Bibcode: 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 >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.
Bibcode: 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&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 vmax550 ± 50 km/s and vmax400
± 50 km/s, respectively. However, 15 Feb 2011 CME is connected with
much more violent eruption associated with a prominence, with maximum
velocity of vmax 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1 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 RE
and 14.35 RE, respectively. When comparing with Fairfield's
(1971) classic result, we find that the subsolar magnetosheath is
thinner by ∼1 RE. 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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−1 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 RE and 14.35
RE, respectively. When comparing with Fairfield's (1971)
classic result, we find that the subsolar magnetosheath is thinner
by ∼1 RE. 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 0
and the non-thermal flare parameters, with the highest correlation of
h 0 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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-1) shows a strong deceleration over
the distance range at which it reaches the slower, preceding CME (CME1;
~700 km s-1). 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.
Bibcode: 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
Bibcode: 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-1 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-1. 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1. 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-1, 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.
Bibcode: 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-1. These redshifts are followed by blueshifts with
upward velocities up to -5 km s-1 indicating relaxation
of the plasma behind the wave front. During the wave evolution, the
downward velocity pulse steepens from a few km s-1 up to 20
km s-1 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-2 and a start velocity of v
0 ≈ 590 km s-1. 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
Bibcode: 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 ⊙, 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1) 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 >30° elongation to obtain arrival time errors < ± 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.
Bibcode: 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−1. 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−1, 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1. The fastest of
the events (2007 May 19) reveals a significant deceleration of ≈ -
190 m s-2, 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 ms,
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
Bibcode: 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.
Bibcode: 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.
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.
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.
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 BV2 and BV plays the central role in the process
of energy transfer from the solar wind to the magnetosphere.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-2
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 sun. 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
Bibcode: 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-1 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-1, 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-1. 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.
Bibcode: 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.
Bibcode: 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. 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. 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.
Bibcode: 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∘) 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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 BV2.
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. Appendices, Figs. 9-14, and table 4 are only available in electronic
form at http://www.aanda.org
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.
Bibcode: 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-1. The
last of these four coronal wave events was the strongest and fastest,
with a velocity of 337 ± 31 km s-1 and a peak perturbation
amplitude of ~1.24, corresponding to a magnetosonic Mach number of M
ms ~ 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 2011CEAB...35...19U
Altcode:
In this paper we derive an estimate of the energy content of small scale
magnetic 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.
Bibcode: 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 Dst = -72 nT,
maximum Kp = 8-), 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1 ~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.
Bibcode: 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.
Bibcode: 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-1) 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.
Bibcode: 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.
Aims: We aim to establish the relation between narrowband and
short-duration features (<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.
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.
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.
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.
Bibcode: 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-1) is larger than
that of the lateral expansion of the wave (v ~ 280 km s-1),
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 -2.5 ± 0.3, 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.
Bibcode: 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.
Bibcode: 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 sun is measured with a high time cadence of <=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 <= 0.4 R sun,
and the peak velocity at h <= 2.1 R sun (in one case,
as small as 0.5 R sun). 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.
Bibcode: 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.
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.
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.
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-1. 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-1. 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
Bibcode: 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.
Bibcode: 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-1 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1)
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 > 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.
Bibcode: 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.
Bibcode: 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 <A9/0.7 with/without
background), which occurred on July 4, 2006 in AR 10898.
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× 104 K),
transition region (e.g. O v, T∼ 2.6× 105 K), and
coronal temperatures (Si xii, T∼ 2× 106 K). RHESSI
X-ray spectra provide information about non-thermal electrons.
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-1), and upflows for the second
event (v ≲ 40 km s-1). During the third microflare, we
find upflows of ≲ 20 km s-1 and also weak downflows of
≲20 km s-1 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-1. 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-1) 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. 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.
Bibcode: 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-1. 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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 1.8×1021 Mx for the weakest event (GOES class B9.5)
and 15.5×1021 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.
Bibcode: 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⊙. 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Aims: The
size distribution of MBPs is derived for G-band images acquired by the
Hinode/SOT instrument.
Methods: For identification purposes, a new
automated segmentation and identification algorithm was developed.
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.
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.
Bibcode: 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 Rc = 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.
Bibcode: 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.
Bibcode: 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. 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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, 1046≲EM≲1047 cm−3,
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−1 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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-1,
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 =Bϕ0/√μ_0ρ represents the Alfvén speed based
on the equilibrium poloidal field Bϕ0.
Conclusions:
Combination of our measurements with some previous observations of
the same kind of oscillations shows good agreement with the proposed
interpretation. 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
Bibcode: 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.
Bibcode: 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 (27d) as well as
to the second (13.5d) and third (9d) 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.
Bibcode: 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.
Aims: We develop a scenario using multiwavelength observations
to explain the high coronal column density (≈1020
cm-2) present at the onset of the 14th April 2002 M3.7
hard X-ray event.
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.
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
Bibcode: 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−2, 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
Bibcode: 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.
Bibcode: 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*)]0.5,
where A(t*) 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*=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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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-1} to 11.8 {V cm-1}, whereas the positive
and the negative magnetic flux covered by the flare emission were
equal within 5-10%.
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.
Bibcode: 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-1). 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.
Bibcode: 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 (>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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 < 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.
Bibcode: 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
Bibcode: 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 104 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−1, whereas
at 1 MK it amounts to 5 km s−1; (b) Shrinking becomes
slower as the flare decays - ten hours after the impulsive phase,
the shrinkage velocity at 5 MK becomes 5 km s−1; (c) The
cooling rate decreases as the flare decays - in the 5 MK range it is
1 MK min−1 in the first hour of the loop-system growth,
whereas ten hours later it decreases to 0.2 MK min−1;
(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−2 in the T < 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 < 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.
Bibcode: 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 {Rn} and {Rs}
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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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-1 in the RHESSI 10-15 keV energy band to 45 km
s-1 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-1. 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 1010
cm-3. 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) × 1011
cm-3.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 2006CEAB...30...75B
Altcode:
We present general solutions of the time--dependent Petschek--type
model of magnetic reconnection for a compressible plasma. The
disruption of a tangential discontinuity because of a localized
decrease of the resistivity leads to the generation of several
MHD wave modes. By solving the Riemann problem, the behavior of
these modes can be visualized. Additionally, disturbances of the
ambient plasma environment by the propagating shock structures
can be modeled. As an observational feature, the determination
of the reconnection rate in a two--ribbon flare is 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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. (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.
Bibcode: 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<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.
Bibcode: 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
+40circ to +50circ 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
Bibcode: 2005ApJ...621..482V
Altcode:
The ``empirical Neupert effect'' (ENE) is the observed temporal
correlation of the hard X-ray (HXR) flux FHXR(t) with the
time derivative of the soft X-ray (SXR) flux F˙SXR(t) in
many flares. This is widely taken to mean that the energetic electrons
responsible for FHXR(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 Pbeam(t), inferred from the HXR
spectrum, and the actual power Pin(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 Pbeam(t) and Pin(t) inferred from data are
better correlated than FHXR(t) and F˙SXR(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 E1 is taken as constant, the
correlation of Pbeam(t), Pin(t) is no better
than that of FHXR(t),F˙SXR(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.
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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-1) 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-1. 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.
Bibcode: 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 amax≈ 600
± 150 m s−2 at a heliocentric distance 2.4 -2.5 solar
radii, whereas the prominence reached amax≈ 380± 50 m
s−2, 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 vmax≈ 1200 km
s−1 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−2,
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.
Bibcode: 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.
Bibcode: 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 >~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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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: [(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, [(b)] this N is consistent
with chromospheric evaporation by thermal conduction flux from the hot
coronal plasma rather than by electron beam heating, and [(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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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>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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 RN and
RS: 1975 - 2000
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
Bibcode: 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, Rn,
and southern, Rs, relative sunspot numbers for the
time span 1975-2000. In order to accord with the International
Sunspot Numbers Ri, the Rn and Rs
have been normalized to the Ri, which ensures that the
relation Rn+Rs = Ri is complied. For
validation, the derived Rn and Rs 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.
Bibcode: 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.
Bibcode: 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 >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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 Rn and Rs:
Catalogue and N-S asymmetry analysis
Authors: Temmer, M.; Veronig, A.; Hanslmeier, A.
Bibcode: 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, Rn,
and southern, Rs, relative sunspot numbers for the
time span 1975-2000. In order to accord with the International
Sunspot Numbers Ri, the Rn and Rs
have been normalized to the Ri, which ensures that the
relation Rn+Rs=Ri is fulfilled. For
validation, the derived Rn and Rs 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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(xii),
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 1996AGAb...12..165V
Altcode:
No abstract at ADS