explanation blue bibcodes open ADS page with paths to full text
Author name code: kontogiannis
ADS astronomy entries on 2022-09-14
author:"Kontogiannis, Ioannis"
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Title: Coronal effects of small-scale dynamic phenomena and their
traces in the lower solar atmosphere
Authors: Kontogiannis, Ioannis
2022cosp...44.1339K Altcode:
The magnetic field of the quiet Sun can produce complicated magnetic
configurations, giving rise to various eruptive phenomena with
profound effects in the corona. These often evade detection as they
occur at the resolution limits of current observations and their study
requires coordinated observations and synergies between space-borne
and ground-based facilities. The aim of this contribution is to
showcase recent detailed studies of small-scale activity, based on
coordinated observations. Their analysis combined spectropolarimetry,
spectroscopy in EUV, H$\alpha$ and H$\beta$, and photospheric flow-field
measurements. A small-scale magnetic flux emergence event was observed
by the Hinode instruments, the Michelson Doppler Imager onboard SoHO,
and the ground-based Dutch Open Telescope (DOT). The granular-scale
magnetic flux emergence led to a series of observable effects over
all heights from the photosphere to the corona, producing miniature
surges and intense variability at the smallest observable scales in
EUV and soft X-rays. The formation and eruption of a minifilament
were captured by the Solar Dynamics Observatory and the Vacuum Tower
Telescope (VTT) and were monitored for the first time in detail. The
minifilament formed above a group of small-scale photospheric magnetic
concentrations and erupted, producing a small-scale dimming as it swept
the nearby coronal magnetic structures. The size and abundance of these
dynamic phenomena make them ideal targets for the new generation of
ground-based telescopes and space missions. Synergies between observing
facilities in ground and space, especially in light of the observations
from the Solar Orbiter, can boost our understanding of fundamental
processes and help trace the origins of the recently-revealed fine
structure of the outer solar atmosphere.
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Title: Using sound and music in science shows to introduce fundamental
physics concepts and modern research on space science
Authors: Kontogiannis, Ioannis
2022cosp...44.1739K Altcode:
This contribution presents an inventory of science demonstrations
based on music and sound, which can be used to communicate concepts
from fundamental physics and space science. They bring together
fundamental physics, music history and recent results from space
research. They were put together into interactive science shows,
developed in the context of outreach activities in science centers,
science festivals, schools and research institutes. The concepts
include wave and sound characteristics (frequency/pitch and timbre),
electromagnetism (working principles of speakers and microphones), waves
in space plasmas, music and mathematics (Pythagoras and musical scales),
waveforms, wavelets, musical notes and musical notation, oscillations
on surfaces of musical instruments and helioseismology. The science
demonstrations include, but are not limited to, oscilloscope and tone
generator software, Faraday's experiment, the Pythagoras' monochord,
and Chladni plates. Simple musical instruments and Boomwhackers are
used to perform simple melodies with the audience. These science
demonstrations and activities are seamed into a coherent show which
relies heavily on the active participation of the audience, aiming
to link their everyday experience with fundamental concepts, modern
research and music, in the context of a fun narrative. The components
of the described action can be used in different combinations in many
contexts, depending on the specifics of the outreach activity and type
of audience, illustrating the potential of using arts, and music in
particular, to convey science-related information.
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Title: Automated detection of chromospheric swirls in the Halpha
spectral line and statistical analysis of their parameters
Authors: Dakanalis, Ioannis; Tziotziou, Kostas; Tsiropoula, Georgia;
Kontogiannis, Ioannis
2022cosp...44.2519D Altcode:
Ubiquitous vortical motions in the solar atmosphere have been recently
revealed by high-resolution observations of both space-borne and
ground-based observatories in quiet, as well as in active regions. In
chromospheric observations obtained in spectral lines, such as
the H$\alpha$ and Ca II IR, they manifest themselves as swirling
dark spiral- and circular-shaped patches labelled as "chromospheric
swirls". Their suggested contribution to the channelling of energy,
mass and momentum from the sub-photospheric levels to the higher layers
of the solar atmosphere places them amongst potential candidates for
atmospheric heating. In this context, their detection and statistical
information concerning their population and a number of significant
physical parameters and properties are vital. To complement visual
inspection and automated detection methods based on the velocity field
derivation we developed a novel automated detection method, which is
based on the morphological characteristics of these structures. The
algorithm was applied to H$\alpha$ high-resolution observations
obtained with the CRisp Imaging SpectroPolarimeter (CRISP) of the
Swedish 1-m Solar Telescope (SST) and revealed the existence of a
significantly larger number of chromospheric swirls compared to previous
reports. We will be presenting a brief description of the automated
detection algorithm, followed by the obtained results concerning their
surface density, occurrence rate, spatial distribution and temporal
evolution throughout the FOV, as well as a statistical analysis of some
significant physical parameters, such as radii and lifetimes that were
obtained by an unprecedented observational statistical sample of 577
swirls. Lifetimes have been derived by implementation of the survival
analysis method that is extensively used in several scientific fields,
but so far occasionally in Solar Physics, and provides more accurate
estimates of the mean lifetime of swirls. Moreover, a hinted by the
results linear correlation between lifetimes and radii is explored.
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Title: Chromospheric swirls. I. Automated detection in Hα
observations and their statistical properties
Authors: Dakanalis, I.; Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.
2022A&A...663A..94D Altcode: 2022arXiv220507720D
Context. Chromospheric swirls are related to convectively driven vortex
flows and considered to play a significant role in the dynamics and
heating of the upper solar atmosphere. It is important to automatically
detect and track them in chromospheric observations and determine their
properties. <BR /> Aims: We aim to detect and track chromospheric
swirls both in space and time by applying a newly developed novel
automated method on high quality time series of Hα observations and
to conduct a statistical analysis to determine their properties. <BR
/> Methods: We applied a recently developed automated chromospheric
swirl detection method to time-series observations of a quiet region
of the solar chromosphere obtained in the Hα-0.2 Å wavelength of
the Hα spectral line by the CRISP instrument at the Swedish 1-m Solar
Telescope. The algorithm exploits the morphological characteristics of
swirling events in high contrast chromospheric observations and results
in the detection of these structures in each frame of the time series
and their tracking over time. We conducted a statistical analysis
to determine their various properties, including a survival analysis
for deriving the mean lifetime. <BR /> Results: A mean number of 146
± 9 swirls was detected within the Hα-0.2 Å field of view at any
given time. The mean surface density is found equal to ∼0.08 swirls
Mm<SUP>−2</SUP> and the occurrence rate is ∼10<SUP>−2</SUP> swirls
Mm<SUP>−2</SUP> min<SUP>−1</SUP>. These values are much higher
than those previously reported from chromospheric observations. The
radii of the detected swirls range between 0.5 and 2.5 Mm, with a
mean value equal to 1.3 ± 0.3 Mm, which is slightly higher than
previous reports. The lifetimes range between 1.5 min and 33.7 min
(equal to the duration of the observations) with an arithmetic mean
value of ∼8.5 min. A survival analysis of the lifetimes, however,
using the Kaplan-Meier estimator in combination with a parametric model
results in a mean lifetime of 10.3 ± 0.6 min. <BR /> Conclusions:
Swirls are ubiquitous in the solar chromosphere. An automated method
sheds more light on their abundance than visual inspection, while
higher cadence, higher resolution observations will most probably
result in the detection of a higher number of such features on smaller
scales and with shorter lifetimes. <P />Movies is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243236/olm">https://www.aanda.org</A>
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Title: Multiple Stokes I inversions for inferring magnetic fields
in the spectral range around Cr I 5782 Å
Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.;
Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma,
M.; Kontogiannis, I.; Sobotka, M.
2021A&A...653A.165K Altcode: 2021arXiv210711116K
<BR /> Aims: In this work, we explore the spectral window containing
Fraunhofer lines formed in the solar photosphere, around the
magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0,
and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is
to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I,
Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer
the thermodynamic and magnetic properties in strongly magnetized
plasmas using an inversion code. <BR /> Methods: Our study is based
on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which
includes fast spectroscopic scans in the wavelength range around
the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all
spectral lines, as well as their response functions to temperature,
magnetic field, and Doppler velocity, were determined using the Stokes
Inversion based on Response functions (SIR) code. Snapshot 385 of the
enhanced network simulation from the Bifrost code serves to synthesize
all the lines, which are, in turn, inverted simultaneously with SIR to
establish the best inversion strategy. We applied this strategy to VTT
observations of a sunspot belonging to NOAA 12723 on 2018 September
30 and compared the results to full-disk vector field data obtained
with the Helioseismic and Magnetic Imager (HMI). <BR /> Results: The
15 simultaneously inverted intensity profiles (Stokes I) delivered
accurate temperatures and Doppler velocities when compared with the
simulations. The derived magnetic fields and inclinations achieve
the best level of accuracy when the fields are oriented along the
line-of-sight (LOS) and less accurate when the fields are transverse to
the LOS. In general, the results appear similar to what is reported in
the HMI vector-field data, although some discrepancies exist. <BR />
Conclusions: The analyzed spectral range has the potential to deliver
thermal, dynamic, and magnetic information for strongly magnetized
features on the Sun, such as pores and sunspots, even without the use
of polarimetry. The highest sensitivity of the lines is found in the
lower photosphere, on average, around log τ = −1. The multiple-line
inversions provide smooth results across the whole field of view
(FOV). The presented spectral range and inversion strategy will be
used for future VTT observing campaigns.
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Title: The flare likelihood and region eruption forecasting
(FLARECAST) project: flare forecasting in the big data & machine
learning era
Authors: Georgoulis, Manolis K.; Bloomfield, D. Shaun; Piana,
Michele; Massone, Anna Maria; Soldati, Marco; Gallagher, Peter T.;
Pariat, Etienne; Vilmer, Nicole; Buchlin, Eric; Baudin, Frederic;
Csillaghy, Andre; Sathiapal, Hanna; Jackson, David R.; Alingery,
Pablo; Benvenuto, Federico; Campi, Cristina; Florios, Konstantinos;
Gontikakis, Constantinos; Guennou, Chloe; Guerra, Jordan A.;
Kontogiannis, Ioannis; Latorre, Vittorio; Murray, Sophie A.; Park,
Sung-Hong; von Stachelski, Samuelvon; Torbica, Aleksandar; Vischi,
Dario; Worsfold, Mark
2021JSWSC..11...39G Altcode: 2021arXiv210505993G
The European Union funded the FLARECAST project, that ran from January
2015 until February 2018. FLARECAST had a research-to-operations
(R2O) focus, and accordingly introduced several innovations into the
discipline of solar flare forecasting. FLARECAST innovations were:
first, the treatment of hundreds of physical properties viewed as
promising flare predictors on equal footing, extending multiple
previous works; second, the use of fourteen (14) different machine
learning techniques, also on equal footing, to optimize the immense
Big Data parameter space created by these many predictors; third,
the establishment of a robust, three-pronged communication effort
oriented toward policy makers, space-weather stakeholders and the wider
public. FLARECAST pledged to make all its data, codes and infrastructure
openly available worldwide. The combined use of 170+ properties (a
total of 209 predictors are now available) in multiple machine-learning
algorithms, some of which were designed exclusively for the project,
gave rise to changing sets of best-performing predictors for the
forecasting of different flaring levels, at least for major flares. At
the same time, FLARECAST reaffirmed the importance of rigorous training
and testing practices to avoid overly optimistic pre-operational
prediction performance. In addition, the project has (a) tested new
and revisited physically intuitive flare predictors and (b) provided
meaningful clues toward the transition from flares to eruptive flares,
namely, events associated with coronal mass ejections (CMEs). These
leads, along with the FLARECAST data, algorithms and infrastructure,
could help facilitate integrated space-weather forecasting efforts
that take steps to avoid effort duplication. In spite of being
one of the most intensive and systematic flare forecasting efforts
to-date, FLARECAST has not managed to convincingly lift the barrier of
stochasticity in solar flare occurrence and forecasting: solar flare
prediction thus remains inherently probabilistic.
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Title: Classification of High-resolution Solar Hα Spectra Using
t-distributed Stochastic Neighbor Embedding
Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke,
Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert;
Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S.
2021ApJ...907...54V Altcode: 2020arXiv201113214V
The Hα spectral line is a well-studied absorption line
revealing properties of the highly structured and dynamic solar
chromosphere. Typical features with distinct spectral signatures in
Hα include filaments and prominences, bright active-region plages,
superpenumbrae around sunspots, surges, flares, Ellerman bombs,
filigree, and mottles and rosettes, among others. This study is
based on high-spectral resolution Hα spectra obtained with the
Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at
Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic
neighbor embedding (t-SNE) is a machine-learning algorithm, which
is used for nonlinear dimensionality reduction. In this application,
it projects Hα spectra onto a two-dimensional map, where it becomes
possible to classify the spectra according to results of cloud model
(CM) inversions. The CM parameters optical depth, Doppler width,
line-of-sight velocity, and source function describe properties of
the cloud material. Initial results of t-SNE indicate its strong
discriminatory power to separate quiet-Sun and plage profiles from
those that are suitable for CM inversions. In addition, a detailed
study of various t-SNE parameters is conducted, the impact of seeing
conditions on the classification is assessed, results for various types
of input data are compared, and the identified clusters are linked
to chromospheric features. Although t-SNE proves to be efficient
in clustering high-dimensional data, human inference is required at
each step to interpret the results. This exploratory study provides
a framework and ideas on how to tailor a classification scheme toward
specific spectral data and science questions.
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Title: A persistent quiet-Sun small-scale tornado. III. Waves
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.
2020A&A...643A.166T Altcode: 2020arXiv201006327T
Context. Vortex flows can foster a variety of wave modes. A recent
oscillatory analysis of a persistent 1.7 h vortex flow with a
significant substructure has suggested the existence of various
types of waves within it. <BR /> Aims: We investigate the nature and
characteristics of waves within this quiet-Sun vortex flow, over the
course of an uninterrupted 48-min observing time interval, in order to
better understand its physics and dynamics. <BR /> Methods: We used a
cross-wavelet spectral analysis between pairs of Hα and Ca II 8542 Å
intensity time series at different wavelengths and, hence, atmospheric
heights, acquired with the CRisp Imaging SpectroPolarimeter at the
Swedish Solar Telescope, as well as the derived Hα Doppler velocity
and full width at half maximum time series. We constructed halftone
frequency-phase difference plots and investigated the existence and
propagation characteristics of different wave modes. <BR /> Results:
Our analysis suggests the existence of Alfvénic type waves within the
vortex flow that propagate upwards with phase speeds of ∼20-30 km
s<SUP>-1</SUP>. The dominant wave mode seems to be the fast kink wave
mode, however, our analysis also suggests the existence of localised
Alfvénic torsional waves, which are related to the dynamics of
individual chromospheric swirls that characterise the substructure
of the vortex flow. The Hα V-I phase difference analysis seems to
imply the existence of a standing wave pattern that is possibly
arising from the interference of upwards propagating kink waves
with downwards propagating ones that are reflected at the transition
region or the corona. Moreover, the results provide further evidence
that the central chromospheric swirl drives the dynamics of the vortex
flow. <BR /> Conclusions: This is the first exhaustive phase difference
analysis within a vortex flow that explores the nature and dynamics
of different wave modes within it. The question, however, of whether,
and how, the dissipation of the derived wave modes occurs remains open,
and given that such structures are ubiquitous on the solar surface,
it's also important to investigate whether they might ultimately play
a significant role in the energy budget of the upper layers of the
solar atmosphere.
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Title: Differential Emission Measure Evolution as a Precursor of
Solar Flares
Authors: Gontikakis, C.; Kontogiannis, I.; Georgoulis, M. K.; Guennou,
C.; Syntelis, P.; Park, S. H.; Buchlin, E.
2020arXiv201106433G Altcode:
We analyse the temporal evolution of the Differential Emission Measure
(DEM) of solar active regions and explore its usage in solar flare
prediction. The DEM maps are provided by the Gaussian Atmospheric
Imaging Assembly (GAIA-DEM) archive, calculated assuming a Gaussian
dependence of the DEM on the logarithmic temperature. We analyse
time-series of sixteen solar active regions and a statistically
significant sample of 9454 point-in-time observations corresponding to
hundreds of regions observed during solar cycle 24. The time-series
analysis shows that the temporal derivatives of the Emission Measure
dEM/dt and the maximum DEM temperature dTmax/dt frequently exhibit
high positive values a few hours before M- and X-class flares,
indicating that flaring regions become brighter and hotter as the flare
onset approaches. From the point-in-time observations we compute the
conditional probabilities of flare occurrences using the distributions
of positive values of the dEM/dt, and dTmax/dt and compare them with
corresponding flaring probabilities of the total unsigned magnetic flux,
a conventionally used, standard flare predictor. For C-class flares,
conditional probabilities have lower or similar values with the ones
derived for the unsigned magnetic flux, for 24 and 12 hours forecast
windows. For M- and X-class flares, these probabilities are higher
than those of the unsigned flux for higher parameter values. Shorter
forecast windows improve the conditional probabilities of dEM/dt,
and dTmax/dt in comparison to those of the unsigned magnetic flux. We
conclude that flare forerunner events such as preflare heating or small
flare activity prior to major flares reflect on the temporal evolution
of EM and Tmax. Of these two, the temporal derivative of the EM could
conceivably be used as a credible precursor, or short-term predictor,
of an imminent flare.
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Title: Observational study of chromospheric heating by acoustic waves
Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.;
García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis,
I.; Koza, J.; Korda, D.; Kuckein, C.
2020A&A...642A..52A Altcode: 2020arXiv200802688A
<BR /> Aims: Our aim is to investigate the role of acoustic and
magneto-acoustic waves in heating the solar chromosphere. Observations
in strong chromospheric lines are analyzed by comparing the deposited
acoustic-energy flux with the total integrated radiative losses. <BR
/> Methods: Quiet-Sun and weak-plage regions were observed in the Ca
II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph
(FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and
in the Hα and Hβ lines with the echelle spectrograph attached
to the Vacuum Tower Telescope on 2018 December 11 and 2019 June
6. The deposited acoustic energy flux at frequencies up to 20 mHz
was derived from Doppler velocities observed in line centers and
wings. Radiative losses were computed by means of a set of scaled
non-local thermodynamic equilibrium 1D hydrostatic semi-empirical
models obtained by fitting synthetic to observed line profiles. <BR />
Results: In the middle chromosphere (h = 1000-1400 km), the radiative
losses can be fully balanced by the deposited acoustic energy flux in
a quiet-Sun region. In the upper chromosphere (h > 1400 km), the
deposited acoustic flux is small compared to the radiative losses in
quiet as well as in plage regions. The crucial parameter determining
the amount of deposited acoustic flux is the gas density at a given
height. <BR /> Conclusions: The acoustic energy flux is efficiently
deposited in the middle chromosphere, where the density of gas is
sufficiently high. About 90% of the available acoustic energy flux in
the quiet-Sun region is deposited in these layers, and thus it is a
major contributor to the radiative losses of the middle chromosphere. In
the upper chromosphere, the deposited acoustic flux is too low, so that
other heating mechanisms have to act to balance the radiative cooling.
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Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.
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Title: SpaceGates Academy: Teaching science communication and outreach
of Astronomy, Planetary and Space Science to Physics Students.
Authors: Moutsouroufi, Konstantina; Tsilia, Styliani; Papadopoulos,
Alexis; Stratigou-Psarra, Maria; Michalopoulou, Eleni; Kontogiannis,
Ioannis; Dialynas, Kostas; Petakos, Dimitris; Andrikopoulou, Marilena;
Poulis, Konstantinos; Anastasia Metallinou, Fiori; Daglis, Ioannis
2020EPSC...14..829M Altcode:
Science Communication is a practice that is increasingly gaining ground
among the STEM sciences as a practice that needs to be approached
with the same scientific and robust methods as the sciences it aims
to communicate. It has the potential to reach a wide variety of large
audiences and increase the visibility and apprehension of Astronomy
and Planetary science. The 20th century has regrettably witnessed
the rise of pseudo-scientific practices and a lack of confidence
in science, scientists, and scientific practices. It is therefore
now, more important than ever, to diffuse and separate science from
un-scientific practices and inform the non-specialist public in a
concise, clear, and most importantly, scientific way. It is equally
important, for young researchers, like physics students, to develop the
ability to evaluate the quality of the overwhelming volume of scientific
information in order for them to distill and communicate that, but also
communicate their own work and research in an approachable way. To
achieve this, the SpaceGates Team, an outreach team consisting of
Physics Students with interest in Astronomy, Astrophysics and Space,
decided to launch an ambitious initiative; the SpaceGates Academy. The
Academy invited experts in different subjects with the aim to provide
training on science communication to early career researchers (ECR)
from undergraduate to PhD level. This training aimed to fill a gap
in the core and optional academic curriculum that so far does not
provide a course dedicated to the communication of science. The
objective of the training was the development of communication
skills of the participants with emphasis on Astronomy, Astrophysics
and Space, and their application in a safe and scientifically robust
environment. The Academy was delivered in the form of weekly, two-hour
seminars organized by the SpaceGates team under the auspices of the
Department of Astrophysics, Astronomy and Mechanics of the National
and Kapodistrian University of Athens. This reflects the department's
commitment to provide training for science communication. Highly
experienced outreach professionals, educators and science communicators
voluntarily shared their experience and expertise with the learners
participating over a period of 15weeks. The topics covered were:
creative writing, storytelling, public speaking, science performance,
science communication, scientific research writing and communicating
it with the public, communicating planetary science through music,
teaching Astronomy using digital tools, STEM education, organizing
outreach activities etc. The learners had to deliver a written or
verbal project, design and co-develop a team outreach activity. They
also participated in team building activities at the beginning of each
session and were asked to fill google-forms evaluation questionnaires
for every session. From the planned 17 sessions, 13 were delivered in
person, 2 were delivered virtually and the last 2, affected by COVID-19
were cancelled. As the post pandemic phase is now developing, we are
currently exploring ways to organize virtual team outreach activities
and maybe some social distance safe ones, to facilitate the conclusion
of the Academy, as per its original plan. SpaceGates Academy is a much
needed, ambitious educational program that introduced the science of
communication to the Greek ECR that participated in the program. This
endeavor will be repeated next year and it is hoped that it will evolve
in an established practice that covers both the needs of the learners
but also the needs of the core and optional academic curriculum. the
Academy logo was printed on the coton book bags shared to the learners
---------------------------------------------------------
Title: High-resolution Spectroscopy of an Erupting Minifilament and
Its Impact on the Nearby Chromosphere
Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein,
C.; Balthasar, H.; Denker, C.
2020ApJ...898..144K Altcode: 2020arXiv200701564K
We study the evolution of a minifilament eruption in a quiet region
at the center of the solar disk and its impact on the ambient
atmosphere. We used high spectral resolution imaging spectroscopy in
Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope,
Tenerife, Spain; photospheric magnetic field observations from the
Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric
Imaging Assembly of the Solar Dynamics Observatory. The Hα line
profiles were noise-stripped using principal component analysis
and then inverted to produce physical and cloud model parameter
maps. The minifilament formed between small-scale, opposite-polarity
magnetic features through a series of small reconnection events, and
it erupted within an hour after its appearance in Hα. Its development
and eruption exhibited similarities to large-scale erupting filaments,
indicating the action of common mechanisms. Its eruption took place in
two phases, namely, a slow rise and a fast expansion, and it produced
a coronal dimming, before the minifilament disappeared. During its
eruption, we detected a complicated velocity pattern, indicative of
a twisted, thread-like structure. Part of its material returned to
the chromosphere, producing observable effects on nearby low-lying
magnetic structures. Cloud model analysis showed that the minifilament
was initially similar to other chromospheric fine structures, in terms
of optical depth, source function, and Doppler width, but it resembled a
large-scale filament on its course to eruption. High spectral resolution
observations of the chromosphere can provide a wealth of information
regarding the dynamics and properties of minifilaments and their
interactions with the surrounding atmosphere.
---------------------------------------------------------
Title: High-resolution spectroscopy of a surge in an emerging
flux region
Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar,
H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M.
2020A&A...639A..19V Altcode: 2020arXiv200503966V
<BR /> Aims: The regular pattern of quiet-Sun magnetic fields was
disturbed by newly emerging magnetic flux, which led a day later to
two homologous surges after renewed flux emergence, affecting all
atmospheric layers. Hence, simultaneous observations in different
atmospheric heights are needed to understand the interaction of
rising flux tubes with the surrounding plasma, in particular by
exploiting the important diagnostic capabilities provided by the
strong chromospheric Hα line regarding morphology and energetic
processes in active regions. <BR /> Methods: A newly emerged active
region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT)
at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High
spectral resolution observations using the echelle spectrograph in the
chromospheric Hαλ6562.8 Å line were obtained in the early growth
phase. Noise-stripped Hα line profiles yield maps of line-core and
bisector velocities, which were contrasted with velocities inferred
from Cloud Model inversions. A high-resolution imaging system recorded
simultaneously broad- and narrowband Hα context images. The Solar
Dynamics Observatory provided additional continuum images, line-of-sight
(LOS) magnetograms, and UV and extreme UV (EUV) images, which link the
different solar atmospheric layers. <BR /> Results: The active region
started as a bipolar region with continuous flux emergence when a new
flux system emerged in the leading part during the VTT observations,
resulting in two homologous surges. While flux cancellation at the
base of the surges provided the energy for ejecting the cool plasma,
strong proper motions of the leading pores changed the magnetic
field topology making the region susceptible to surging. Despite
the surge activity in the leading part, an arch filament system in
the trailing part of the old flux remained stable. Thus, stable
and violently expelled mass-loaded ascending magnetic structures
can coexist in close proximity. Investigating the height dependence
of LOS velocities revealed the existence of neighboring strong up-
and downflows. However, downflows occur with a time lag. The opacity
of the ejected cool plasma decreases with distance from the base of
the surge, while the speed of the ejecta increases. The location at
which the surge becomes invisible in Hα corresponds to the interface
where the surge brightens in He IIλ304 Å. Broad-shouldered and
dual-lobed Hα profiles suggests accelerated or decelerated and
highly structured LOS plasma flows. Significantly broadened Hα
profiles imply significant heating at the base of the surges, which
is also supported by bright kernels in UV and EUV images uncovered
by swaying motions of dark fibrils at the base of the surges. <BR />
Conclusions: The interaction of newly emerging flux with pre-existing
flux concentrations of a young, diffuse active region provided
suitable conditions for two homologous surges. High-resolution
spectroscopy revealed broadened and dual-lobed Hα profiles
tracing accelerated or decelerated flows of cool plasma along the
multi-threaded structure of the surge. <P />Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936762/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Magnetic Flux Emergence in a Coronal Hole
Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova,
Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma,
Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván;
Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea;
Kontogiannis, Ioannis; Cid, Consuelo
2020SoPh..295...64P Altcode: 2020arXiv200611779P
A joint campaign of various space-borne and ground-based observatories,
comprising the Japanese Hinode mission (Hinode Observing Plan 338,
20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum
Tower Telescope (VTT), investigated numerous targets such as pores,
sunspots, and coronal holes. In this study, we focus on the coronal
hole region target. On 24 September 2017, a very extended non-polar
coronal hole developed patches of flux emergence, which contributed
to the decrease of the overall area of the coronal hole. These flux
emergence patches erode the coronal hole and transform the area into a
more quiet-Sun-like area, whereby bipolar magnetic structures play an
important role. Conversely, flux cancellation leads to the reduction
of opposite-polarity magnetic fields and to an increase in the area
of the coronal hole.
---------------------------------------------------------
Title: The magnetic structure and dynamics of a decaying active region
Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González
Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar,
Horst; Denker, Carsten
2020IAUS..354...53K Altcode:
We study the evolution of the decaying active region NOAA 12708, from
the photosphere up to the corona using high resolution, multi-wavelength
GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric
scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph
(GRIS), spectral imaging time-series in the Na ID<SUP>2</SUP> spectral
line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context
imaging in the Ca IIH and blue continuum by the High-resolution Fast
Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric
Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
complements our dataset. The region under study contains one pore with a
light-bridge, a few micro-pores and extended clusters of magnetic bright
points. We study the magnetic structure from the photosphere up to the
upper chromosphere through the spectropolarimetric observations in He
II and Si I and through the magnetograms provided by the Helioseismic
and Magnetic Imager (HMI). The high-resolution photospheric images
reveal the complex interaction between granular-scale convective
motions and a range of scales of magnetic field concentrations in
unprecedented detail. The pore itself shows a strong interaction with
the convective motions, which eventually leads to its decay, while,
under the influence of the photospheric flow field, micro-pores
appear and disappear. Compressible waves are generated, which are
guided towards the upper atmosphere along the magnetic field lines of
the various magnetic structures within the field-of-view. Modelling
of the He i absorption profiles reveals high velocity components,
mostly associated with magnetic bright points at the periphery
of the active region, many of which correspond to asymmetric Si I
Stokes-V profiles revealing a coupling between upper photospheric
and upper chromospheric dynamics. Time-series of Na ID<SUP>2</SUP>
spectral images reveal episodic high velocity components at the same
locations. State-of-the-art multi-wavelength GREGOR observations allow
us to track and understand the mechanisms at work during the decay
phase of the active region.
---------------------------------------------------------
Title: Emergence of small-scale magnetic flux in the quiet Sun
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Gontikakis,
C.; Kuckein, C.; Verma, M.; Denker, C.
2020A&A...633A..67K Altcode: 2019arXiv191202496K
Context. We study the evolution of a small-scale emerging flux region
(EFR) in the quiet Sun, from its emergence in the photosphere to
its appearance in the corona and its decay. <BR /> Aims: We track
processes and phenomena that take place across all atmospheric layers;
we explore their interrelations and compare our findings with those from
recent numerical modelling studies. <BR /> Methods: We used imaging
as well as spectral and spectropolarimetric observations from a suite
of space-borne and ground-based instruments. <BR /> Results: The EFR
appears in the quiet Sun next to the chromospheric network and shows all
morphological characteristics predicted by numerical simulations. The
total magnetic flux of the region exhibits distinct evolutionary phases,
namely an initial subtle increase, a fast increase with a Co-temporal
fast expansion of the region area, a more gradual increase, and a slow
decay. During the initial stages, fine-scale G-band and Ca II H bright
points coalesce, forming clusters of positive- and negative-polarity
in a largely bipolar configuration. During the fast expansion, flux
tubes make their way to the chromosphere, pushing aside the ambient
magnetic field and producing pressure-driven absorption fronts that
are visible as blueshifted chromospheric features. The connectivity
of the quiet-Sun network gradually changes and part of the existing
network forms new connections with the newly emerged bipole. A few
minutes after the bipole has reached its maximum magnetic flux, the
bipole brightens in soft X-rays forming a coronal bright point. The
coronal emission exhibits episodic brightenings on top of a long
smooth increase. These coronal brightenings are also associated
with surge-like chromospheric features visible in Hα, which can
be attributed to reconnection with adjacent small-scale magnetic
fields and the ambient quiet-Sun magnetic field. <BR /> Conclusions:
The emergence of magnetic flux even at the smallest scales can be the
driver of a series of energetic phenomena visible at various atmospheric
heights and temperature regimes. Multi-wavelength observations reveal
a wealth of mechanisms which produce diverse observable effects during
the different evolutionary stages of these small-scale structures.
---------------------------------------------------------
Title: Revisiting the building blocks of solar magnetic fields
by GREGOR
Authors: Utz, Dominik; Kuckein, Christoph; Campos Rozo, Jose Iván;
González Manrique, Sergio Javier; Balthasar, Horst; Gömöry,
Peter; Hernández, Judith Palacios; Denker, Carsten; Verma, Meetu;
Kontogiannis, Ioannis; Krikova, Kilian; Hofmeister, Stefan; Diercke,
Andrea
2020IAUS..354...38U Altcode:
The Sun is our dynamic host star due to its magnetic fields causing
plentiful of activity in its atmosphere. From high energetic flares
and coronal mass ejections (CMEs) to lower energetic phenomena such
as jets and fibrils. Thus, it is of crucial importance to learn about
formation and evolution of solar magnetic fields. These fields cover a
wide range of spatial and temporal scales, starting on the larger end
with active regions harbouring complex sunspots, via isolated pores,
down to the smallest yet resolved elements - so-called magnetic bright
points (MBPs). Here, we revisit the various manifestations of solar
magnetic fields by the largest European solar telescope in operation,
the 1.5-meter GREGOR telescope. We show images from the High-resolution
Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared
Spectrograph (GRIS). Besides, we outline resolved convective features
inside the larger structures - so-called light-bridges occurring on
large to mid-sized scales.
---------------------------------------------------------
Title: Which Photospheric Characteristics Are Most Relevant to
Active-Region Coronal Mass Ejections?
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Guerra,
Jordan A.; Park, Sung-Hong; Bloomfield, D. Shaun
2019SoPh..294..130K Altcode: 2019arXiv190906088K
We investigate the relation between characteristics of coronal mass
ejections and parameterizations of the eruptive capability of solar
active regions widely used in solar flare-prediction schemes. These
parameters, some of which are explored for the first time, are
properties related to topological features, namely, magnetic
polarity-inversion lines (MPILs) that indicate large amounts of
stored non-potential (i.e. free) magnetic energy. We utilize the
Space Weather Database of Notifications, Knowledge, Information
(DONKI) and the Large Angle and Spectrometric Coronograph (LASCO)
databases to find flare-associated coronal mass ejections and
their kinematic characteristics, while properties of MPILs are
extracted from Helioseismic and Magnetic Imager (HMI) vector
magnetic-field observations of active regions to extract the
properties of source-region MPILs. The correlation between all
properties and the characteristics of CMEs ranges from moderate to
very strong. More significant correlations hold particularly for
fast CMEs, which are most important in terms of adverse space-weather
manifestations. Non-neutralized currents and the length of the main
MPIL exhibit significantly stronger correlations than the rest of the
properties. This finding supports a causal relationship between coronal
mass ejections and non-neutralized electric currents in highly sheared,
conspicuous MPILs. In addition, non-neutralized currents and MPIL length
carry distinct, independent information as to the eruptive potential of
active regions. The combined total amount of non-neutralized electric
currents and the length of the main polarity-inversion line, therefore,
reflect more efficiently than other parameters the eruptive capacity
of solar active regions and the CME kinematic characteristics stemming
from these regions.
---------------------------------------------------------
Title: A persistent quiet-Sun small-scale tornado. II. Oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.
2019A&A...623A.160T Altcode: 2019arXiv190304796T
Context. Recently, the appearance, characteristics, and dynamics of
a persistent 1.7 h vortex flow, resembling a small-scale tornado,
have been investigated with observations both from the ground and from
space in a quiet-Sun region in several lines and channels and for the
first time in the Hα line centre. The vortex flow showed significant
substructure in the form of several intermittent chromospheric
swirls. <BR /> Aims: We investigate the oscillatory behaviour of
various physical parameters in the vortex area in an attempt to better
understand the physics of the reported vortex flow. This is the first
analysis of this extent. <BR /> Methods: We used the same data set of
high spatial and temporal resolution CRisp Imaging SpectroPolarimeter
(CRISP) observations in several wavelengths along the Hα and Ca II
8542 Å line profiles, as well as Doppler velocities and full-width at
half-maximum (FWHM) derived from the Hα line profiles. The spectral
analysis of oscillations is based on a two-dimensional wavelet analysis
performed within the vortex flow area and in a quiet-Sun region (used
for comparison), as well as along line and circular slices. <BR />
Results: The vortex flow shows significant oscillatory power in the
range of 3-5 min, peaking around 4 min. This power behaves differently
than the reference quiet-Sun region. The derived oscillations reflect
the cumulative action of different components such as swaying motions,
rotation, and waves. The derived periods for swaying motions are in the
range of 200-220 s, and the rotation periods are ∼270 s for Hα and
∼215 s for Ca II 8542 Å. Periods increase with atmospheric height
and seem to decrease with radial distance from the vortex centre,
suggesting a deviation from a rigid rotation. The behaviour of power
within the vortex flow as a function of period and height implies the
existence of evanescent waves. Moreover, considerable power is obtained
even for periods as long as 10 min, not only at photospheric but also
at chromospheric heights, while the formation of vortexes is related to
turbulent convection or to twisting motions exercised in the magnetic
field concentrations. These imply that different types of waves may be
excited, such as magnetoacoustic (e.g. kink) or Alfvén waves. <BR />
Conclusions: The vortex flow seems to be dominated by two motions:
a transverse (swaying) motion, and a rotational motion. The obtained
oscillations point to the propagation of waves within it. Nearby
fibril-like flows could play an important role in the rotational
modulation of the vortex flow. There also exists indirect evidence that
the structure is magnetically supported, and one of the swirls, close to
its centre, seems to be acting as a "central engine" to the vortex flow.
---------------------------------------------------------
Title: sTools - a software package for data reduction of GREGOR
instruments and general data analysis
Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar,
Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva,
Ekaterina; Kontogiannis, Ioannis; Shen, Zili
2018csc..confE.105K Altcode:
The optical solar physics group at AIP is responsible for the GREGOR
Fabry-Perot Interferometer (GFPI) and the large-format facility cameras
(Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI))
at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since
the »Early Science Phase« of the telescope in 2014, the group
developed a data reduction pipeline for these two instruments. The
pipeline »sTools« is based on the Interactive Data Language
(IDL) and delivers reduced and image-restored data with a minimum
of user interaction. Furthermore, it creates quick-look data and
builds a webpage with an overview of the observations and their
statistics (http://gregor.aip.de). However, during the last years,
sTools continuously evolved and currently hosts many additional
routines for data analysis: (1) A local correlation tracking (LCT)
algorithm adapted for both high-resolution (GREGOR and Hinode) and
synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e.,
a Background-subtracted Solar Activity Map (BaSAM), to assess and
visualize the temporal variation of the photospheric magnetic field
and the EUV 160 nm intensity. This method utilizes SDO data and is
applicable to both full-disk observations and regions-of-interest. (3)
Calibration of synoptic full-disk data from the Chromospheric Telescope
(ChroTel) including extraction of Doppler velocities from He I 1083
nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy
for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle
Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed
under a creative commons license and is freely available, after
registration, at the abovementioned website.
---------------------------------------------------------
Title: A persistent quiet-Sun small-scale tornado. I. Characteristics
and dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion,
E.; Doyle, J. G.
2018A&A...618A..51T Altcode:
Context. Vortex flows have been extensively observed over a wide range
of spatial and temporal scales in different spectral lines, and thus
layers of the solar atmosphere, and have been widely found in numerical
simulations. However, signatures of vortex flows have only recently
been reported in the wings of the Hα, but never so far in the Hα line
centre. <BR /> Aims: We investigate the appearance, characteristics,
substructure, and dynamics of a 1.7 h persistent vortex flow observed
from the ground and from space in a quiet-Sun region in several
lines/channels covering all atmospheric layers from the photosphere up
to the low corona. <BR /> Methods: We use high spatial and temporal
resolution CRisp Imaging SpectroPolarimeter (CRISP) observations in
several wavelengths along the Hα and Ca II 8542 Å line profiles,
simultaneous Atmospheric Imaging Assembly (AIA) observations in several
Ultraviolet (UV) and Extreme ultraviolet (EUV) channels and Helioseismic
and Magnetic Imager (HMI) magnetograms to study a persistent vortex flow
located at the south solar hemisphere. Doppler velocities were derived
from the Hα line profiles. Our analysis involves visual inspection and
comparison of all available simultaneous/near-simultaneous observations
and detailed investigation of the vortex appearance, characteristics
and dynamics using time slices along linear and circular slits. <BR />
Results: The most important characteristic of the analysed clockwise
rotating vortex flow is its long duration (at least 1.7 h) and its
large radius ( 3″). The vortex flow shows different behaviours in
the different wavelengths along the Hα and Ca II 8542 Å profiles
reflecting the different formation heights and mechanisms of the two
lines. Ground-based observations combined with AIA observations reveal
the existence of a funnel-like structure expanding with height, possibly
rotating rigidly or quasi-rigidly. However, there is no clear evidence
that the flow is magnetically driven as no associated magnetic bright
points have been observed in the photosphere. Hα and Ca II 8542 Å
observations also reveal significant substructure within the flow,
manifested as several individual intermittent chromospheric swirls
with typical sizes and durations. They also exhibit a wide range of
morphological patterns, appearing as dark absorbing features, associated
mostly with mean upwards velocities around 3 km s<SUP>-1</SUP> and
up to 8 km s<SUP>-1</SUP>, and occupying on average 25% of the total
vortex area. The radial expansion of the spiral flow occurs with
a mean velocity of 3 km s<SUP>-1</SUP>, while its dynamics can be
related to the dynamics of a clockwise rigidly rotating logarithmic
spiral with a swinging motion that is, however, highly perturbed by
nearby flows associated with fibril-like structures. A first rough
estimate of the rotational period of the vortex falls in the range of
200-300 s. <BR /> Conclusions: The vortex flow resembles a small-scale
tornado in contrast to previously reported short-lived swirls and
in analogy to persistent giant tornadoes. It is unclear whether
the observed substructure is indeed due to the physical presence
of individual intermittent, recurring swirls or a manifestation of
wave-related instabilities within a large vortex flow. Moreover,
we cannot conclusively demonstrate that the long duration of
the observed vortex is the result of a central swirl acting as an
"engine" for the vortex flow, although there is significant supporting
evidence inferred from its dynamics. It also cannot be excluded that
this persistent vortex results from the combined action of several
individual smaller swirls further assisted by nearby flows or that
this is a new case in the literature of a hydrodynamically driven
vortex flow. <P />The movie associated to Fig. 4 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833101/olm">https://www.aanda.org</A>
---------------------------------------------------------
Title: Eruptive Flare Initiation and the CME Magnetic Field
Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Kontogiannis,
Ioannis
2018cosp...42E1180G Altcode:
We recount very recent results on the correlation between photospheric
characteristics of eruptive solar active regions and coronal mass
ejection (CME) occurrence / characteristics. In particular, we
argue that one of the most relevant parameters for CME occurrence
is the non-neutralized electric currents appearing exclusively along
intense, shear-ridden magnetic polarity-inversion lines (PILs) in the
photosphere of eruptive active regions. These currents are simply
lacking in the absence of strong PILs and shear. While the physics
underlying non-neutralized currents is rich and shows far-reaching
ramifications, we will focus on the injection of magnetic helicity
due to non-neutralized currents in the pre-eruption phase, that will
then be bodily transported via the CME. For a conductive plasma of
high magnetic Reynolds number, such as that of the solar corona,
we show how the fundamental helicity conservation principle can lead
to estimates of, first, the CME's axial magnetic field strength and,
second, the anticipated magnetic field strength of the interplanetary
CME (ICME) on the verge of geospace. We discuss how this analysis
can be viewed as a meaningful initial or boundary condition for more
elaborate inner-heliospheric propagation models that further consider
the orientation of the ICME magnetic field, thus leading to an improved
understanding and prediction of ICME geoeffectiveness. Part of this
work has been supported by the EU Horizon-2020 FLARECAST project
(grant agreement no. 640216).
---------------------------------------------------------
Title: Testing and Improving a Set of Morphological Predictors of
Flaring Activity
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park,
Sung-Hong; Guerra, Jordan A.
2018SoPh..293...96K Altcode: 2018arXiv180706371K
Efficient prediction of solar flares relies on parameters that
quantify the eruptive capability of solar active regions. Several
such quantitative predictors have been proposed in the literature,
inferred mostly from photospheric magnetograms and/or white-light
observations. Two of them are the Ising energy and the sum of the total
horizontal magnetic field gradient. The former has been developed from
line-of-sight magnetograms, while the latter uses sunspot detections
and characteristics, based on continuum images. Aiming to include
these parameters in an automated prediction scheme, we test their
applicability on regular photospheric magnetic field observations
provided by the Helioseismic and Magnetic Imager (HMI) instrument
onboard the Solar Dynamics Observatory (SDO). We test their efficiency
as predictors of flaring activity on a representative sample of active
regions and investigate possible modifications of these quantities. The
Ising energy appears to be an efficient predictor, and the efficiency
is even improved if it is modified to describe interacting magnetic
partitions or sunspot umbrae. The sum of the horizontal magnetic
field gradient appears to be slightly more promising than the three
variations of the Ising energy we implement in this article. The new
predictors are also compared with two very promising predictors: the
effective connected magnetic field strength and the total unsigned
non-neutralized current. Our analysis shows that the efficiency of
morphological predictors depends on projection effects in a nontrivial
way. All four new predictors are found useful for inclusion in an
automated flare forecasting facility, such as the Flare Likelihood
and Region Eruption Forecasting (FLARECAST), but their utility, among
others, will ultimately be determined by the validation effort underway
in the framework of the FLARECAST project.
---------------------------------------------------------
Title: Probing the Quiet Solar Atmosphere from the Photosphere to
the Corona
Authors: Kontogiannis, Ioannis; Gontikakis, Costis; Tsiropoula,
Georgia; Tziotziou, Kostas
2018SoPh..293...56K Altcode: 2018arXiv180307934K
We investigate the morphology and temporal variability of a quiet-Sun
network region in different solar layers. The emission in several
extreme ultraviolet (EUV) spectral lines through both raster and
slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on
board the Hinode spacecraft is studied along with Hα observations and
high-resolution spectropolarimetric observations of the photospheric
magnetic field. The photospheric magnetic field is extrapolated up to
the corona, showing a multitude of large- and small-scale structures. We
show for the first time that the smallest magnetic structures at both
the network and internetwork contribute significantly to the emission
in EUV lines, with temperatures ranging from 8 ×10<SUP>4</SUP>K to
6 ×10<SUP>5</SUP>K. Two components of transition region emission
are present, one associated with small-scale loops that do not reach
coronal temperatures, and another component that acts as an interface
between coronal and chromospheric plasma. Both components are associated
with persistent chromospheric structures. The temporal variability
of the EUV intensity at the network region is also associated with
chromospheric motions, pointing to a connection between transition
region and chromospheric features. Intensity enhancements in the
EUV transition region lines are preferentially produced by Hα
upflows. Examination of two individual chromospheric jets shows that
their evolution is associated with intensity variations in transition
region and coronal temperatures.
---------------------------------------------------------
Title: Forecasting Solar Flares Using Magnetogram-based Predictors
and Machine Learning
Authors: Florios, Kostas; Kontogiannis, Ioannis; Park, Sung-Hong;
Guerra, Jordan A.; Benvenuto, Federico; Bloomfield, D. Shaun;
Georgoulis, Manolis K.
2018SoPh..293...28F Altcode: 2018arXiv180105744F
We propose a forecasting approach for solar flares based on data from
Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI)
on board the Solar Dynamics Observatory (SDO) mission. In particular,
we use the Space-weather HMI Active Region Patches (SHARP) product that
facilitates cut-out magnetograms of solar active regions (AR) in the
Sun in near-realtime (NRT), taken over a five-year interval (2012 -
2016). Our approach utilizes a set of thirteen predictors, which are
not included in the SHARP metadata, extracted from line-of-sight and
vector photospheric magnetograms. We exploit several machine learning
(ML) and conventional statistics techniques to predict flares of
peak magnitude >M1 and >C1 within a 24 h forecast window. The
ML methods used are multi-layer perceptrons (MLP), support vector
machines (SVM), and random forests (RF). We conclude that random
forests could be the prediction technique of choice for our sample,
with the second-best method being multi-layer perceptrons, subject to
an entropy objective function. A Monte Carlo simulation showed that
the best-performing method gives accuracy ACC =0.93 (0.00 ), true
skill statistic TSS =0.74 (0.02 ), and Heidke skill score HSS =0.49
(0.01 ) for >M1 flare prediction with probability threshold 15%
and ACC =0.84 (0.00 ), TSS =0.60 (0.01 ), and HSS =0.59 (0.01 ) for
>C1 flare prediction with probability threshold 35%.
---------------------------------------------------------
Title: Active Region Photospheric Magnetic Properties Derived from
Line-of-Sight and Radial Fields
Authors: Guerra, J. A.; Park, S. -H.; Gallagher, P. T.; Kontogiannis,
I.; Georgoulis, M. K.; Bloomfield, D. S.
2018SoPh..293....9G Altcode: 2017arXiv171206902G
The effect of using two representations of the normal-to-surface
magnetic field to calculate photospheric measures that are related
to the active region (AR) potential for flaring is presented. Several
AR properties were computed using line-of-sight (B<SUB>los</SUB>) and
spherical-radial (B<SUB>r</SUB>) magnetograms from the Space-weather HMI
Active Region Patch (SHARP) products of the Solar Dynamics Observatory,
characterizing the presence and features of magnetic polarity inversion
lines, fractality, and magnetic connectivity of the AR photospheric
field. The data analyzed correspond to ≈4 ,000 AR observations,
achieved by randomly selecting 25% of days between September 2012 and
May 2016 for analysis at 6-hr cadence. Results from this statistical
study include: i) the B<SUB>r</SUB> component results in a slight
upwards shift of property values in a manner consistent with a
field-strength underestimation by the B<SUB>los</SUB> component;
ii) using the B<SUB>r</SUB> component results in significantly lower
inter-property correlation in one-third of the cases, implying more
independent information as regards the state of the AR photospheric
magnetic field; iii) flaring rates for each property vary between
the field components in a manner consistent with the differences
in property-value ranges resulting from the components; iv) flaring
rates generally increase for higher values of properties, except the
Fourier spectral power index that has flare rates peaking around a
value of 5 /3 . These findings indicate that there may be advantages
in using B<SUB>r</SUB> rather than B<SUB>los</SUB> in calculating
flare-related AR magnetic properties, especially for regions located
far from central meridian.
---------------------------------------------------------
Title: The Next Level in Automated Solar Flare Forecasting: the EU
FLARECAST Project
Authors: Georgoulis, M. K.; Bloomfield, D.; Piana, M.; Massone,
A. M.; Gallagher, P.; Vilmer, N.; Pariat, E.; Buchlin, E.; Baudin,
F.; Csillaghy, A.; Soldati, M.; Sathiapal, H.; Jackson, D.; Alingery,
P.; Argoudelis, V.; Benvenuto, F.; Campi, C.; Florios, K.; Gontikakis,
C.; Guennou, C.; Guerra, J. A.; Kontogiannis, I.; Latorre, V.; Murray,
S.; Park, S. H.; Perasso, A.; Sciacchitano, F.; von Stachelski, S.;
Torbica, A.; Vischi, D.
2017AGUFMSA21C..07G Altcode:
We attempt an informative description of the Flare Likelihood And
Region Eruption Forecasting (FLARECAST) project, European Commission's
first large-scale investment to explore the limits of reliability
and accuracy achieved for the forecasting of major solar flares. We
outline the consortium, top-level objectives and first results of
the project, highlighting the diversity and fusion of expertise
needed to deliver what was promised. The project's final product,
featuring an openly accessible, fully modular and free to download
flare forecasting facility will be delivered in early 2018. The
project's three objectives, namely, science, research-to-operations and
dissemination / communication, are also discussed: in terms of science,
we encapsulate our close-to-final assessment on how close (or far)
are we from a practically exploitable solar flare forecasting. In
terms of R2O, we briefly describe the architecture of the FLARECAST
infrastructure that includes rigorous validation for each forecasting
step. From the three different communication levers of the project we
finally focus on lessons learned from the two-way interaction with the
community of stakeholders and governmental organizations. The FLARECAST
project has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreement No. 640216.
---------------------------------------------------------
Title: Non-neutralized Electric Currents in Solar Active Regions
and Flare Productivity
Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park,
Sung-Hong; Guerra, Jordan A.
2017SoPh..292..159K Altcode: 2017arXiv170807087K
We explore the association of non-neutralized currents with solar
flare occurrence in a sizable sample of observations, aiming to show
the potential of such currents in solar flare prediction. We used
the high-quality vector magnetograms that are regularly produced by
the Helioseismic Magnetic Imager, and more specifically, the Space
weather HMI Active Region Patches (SHARP). Through a newly established
method that incorporates detailed error analysis, we calculated
the non-neutralized currents contained in active regions (AR). Two
predictors were produced, namely the total and the maximum unsigned
non-neutralized current. Both were tested in AR time-series and a
representative sample of point-in-time observations during the interval
2012 - 2016. The average values of non-neutralized currents in flaring
active regions are higher by more than an order of magnitude than in
non-flaring regions and correlate very well with the corresponding
flare index. The temporal evolution of these parameters appears to
be connected to physical processes, such as flux emergence and/or
magnetic polarity inversion line formation, that are associated with
increased solar flare activity. Using Bayesian inference of flaring
probabilities, we show that the total unsigned non-neutralized current
significantly outperforms the total unsigned magnetic flux and other
well-established current-related predictors. It therefore shows good
prospects for inclusion in an operational flare-forecasting service. We
plan to use the new predictor in the framework of the FLARECAST project
along with other highly performing predictors.
---------------------------------------------------------
Title: Solar Magnetic Data Analysis for the FLARECAST Project
Authors: Guerra, J. A.; Park, S. H.; Kontogiannis, I.; Bloomfield,
D.; Gallagher, P.; Georgoulis, M. K.
2016AGUFMSH11C2234G Altcode:
The Flare Likelihood And Region Eruption foreCASTing (FLARECAST) project
is an EU H2020-funded consortium project aiming to develop an advanced
solar flare forecasting system by implementing state-of-the-art
solar data analysis and flare prediction algorithms. The Solar
Physics Group at Trinity College Dublin is in charge of the analysis
of observational data to extract solar active region properties
that serve as input for the prediction algorithms. The calculated
active region properties correspond to a non-exhaustive list of
parameters that have demonstrated a strong flare association, such as
Schrijver's R-value, the Fourier power spectrum exponent, the effective
connected magnetic field (Beff), the horizontal field decay index,
and the weighted length of strong-gradient polarity inversion lines
(WLSG). Parameters were calculated from Spaceweather HMI Active Region
Patch (SHARP) magnetograms, a data product of the Helioseismic and
Magnetic Imager (HMI) magnetograph on the Solar Dynamics Observatory
(SDO). SHARPs provide photospheric vector-magnetic field (B) images
in near-realtime. For this study, results from a statistical study
performed on a robust subsample of the entire SHARP dataset will be
presented. In the framework of the FLARECAST predictor component,
this study focuses, for the first time, on differences between
parameter values found when the radial magnetic field component, Br,
is used instead of the line-of-sight component, Blos. The effect of
active region longitudinal position is discussed, as well as the flare
association of the properties.
---------------------------------------------------------
Title: Enabling Solar Flare Forecasting at an Unprecedented Level:
the FLARECAST Project
Authors: Georgoulis, Manolis K.; Pariat, Etienne; Massone, Anna
Maria; Vilmer, Nicole; Jackson, David; Buchlin, Eric; Csillaghy,
Andre; Bommier, Veronique; Kontogiannis, Ioannis; Gallagher, Peter;
Gontikakis, Costis; Guennou, Chloé; Murray, Sophie; Bloomfield,
D. Shaun; Alingery, Pablo; Baudin, Frederic; Benvenuto, Federico;
Bruggisser, Florian; Florios, Konstantinos; Guerra, Jordan; Park,
Sung-Hong; Perasso, Annalisa; Piana, Michele; Sathiapal, Hanna;
Soldati, Marco; Von Stachelski, Samuel; Argoudelis, Vangelis;
Caminade, Stephane
2016cosp...41E.657G Altcode:
We attempt a brief but informative description of the Flare
Likelihood And Region Eruption Forecasting (FLARECAST) project,
European Commission's first large-scale investment to explore the
limits of reliability and accuracy for the forecasting of major solar
flares. The consortium, objectives, and first results of the project
- featuring an openly accessible, interactive flare forecasting
facility by the end of 2017 - will be outlined. In addition, we will
refer to the so-called "explorative research" element of project,
aiming to connect solar flares with coronal mass ejections (CMEs)
and possibly pave the way for CME, or eruptive flare, prediction. We
will also emphasize the FLARECAST modus operandi, namely the diversity
of expertise within the consortium that independently aims to science,
infrastructure development and dissemination, both to stakeholders and
to the general public. Concluding, we will underline that the FLARECAST
project responds squarely to the joint COSPAR - ILWS Global Roadmap
to shield society from the adversities of space weather, addressing
its primary goal and, in particular, its Research Recommendations
1, 2 and 4, Teaming Recommendations II and III, and Collaboration
Recommendations A, B, and D. The FLARECAST project has received funding
from the European Union's Horizon 2020 research and innovation programme
under grant agreement No. 640216.
---------------------------------------------------------
Title: The New Solar Telescope at the National Observatory of Athens
Authors: Kontogiannis, I.; Tsiropoula, G.
2016ASPC..504..317K Altcode:
In the context of a new space weather facility, the National Observatory
of Athens has installed a small full-disk solar telescope. Its aim is
to provide full disk images of the Sun and active region cut-outs in
the Hα line. Here, we describe the specificiations of the telescope
and the data reduction procedure.
---------------------------------------------------------
Title: First simultaneous SST/CRISP and IRIS observations of a
small-scale quiet Sun vortex
Authors: Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.; Tziotziou,
K.; Scullion, E.; Doyle, J. G.
2016A&A...586A..25P Altcode: 2015arXiv151206032P
Context. Ubiquitous small-scale vortices have recently been found
in the lower atmosphere of the quiet Sun in state-of-the-art solar
observations and in numerical simulations. <BR /> Aims: We investigate
the characteristics and temporal evolution of a granular-scale vortex
and its associated upflows through the photosphere and chromosphere
of a quiet Sun internetwork region. <BR /> Methods: We analyzed high
spatial and temporal resolution ground- and spaced-based observations
of a quiet Sun region. The observations consist of high-cadence time
series of wideband and narrowband images of both Hα 6563 Å and Ca
II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter
(CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well
as ultraviolet imaging and spectral data simultaneously obtained by
the Interface Region Imaging Spectrograph (IRIS). <BR /> Results:
A small-scale vortex is observed for the first time simultaneously
in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the
vortex, Hα narrowband images at -0.77 Å and Ca II 8542 Å narrowband
images at -0.5 Å, and their corresponding Doppler signal maps, clearly
show consecutive high-speed upflow events in the vortex region. These
high-speed upflows with a size of 0.5-1 Mm appear in the shape of
spiral arms and exhibit two distinctive apparent motions in the plane
of sky for a few minutes: (1) a swirling motion with an average speed
of 13 km s<SUP>-1</SUP> and (2) an expanding motion at a rate of
4-6 km s<SUP>-1</SUP>. Furthermore, the spectral analysis of Mg II k
and Mg II subordinate lines in the vortex region indicates an upward
velocity of up to ~8 km s<SUP>-1</SUP> along with a higher temperature
compared to the nearby quiet Sun chromosphere. <BR /> Conclusions:
The consecutive small-scale vortex events can heat the upper
chromosphere by driving continuous high-speed upflows through the lower
atmosphere. <P />Movies associated to Figs. 2 and 3 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527440/olm">http://www.aanda.org</A>
---------------------------------------------------------
Title: Building a new space weather facility at the National
Observatory of Athens
Authors: Kontogiannis, Ioannis; Belehaki, Anna; Tsiropoula, Georgia;
Tsagouri, Ioanna; Anastasiadis, Anastasios; Papaioannou, Athanasios
2016AdSpR..57..418K Altcode:
The PROTEAS project has been initiated at the Institute of Astronomy,
Astrophysics, Space Applications and Remote Sensing (IAASARS) of the
National Observatory of Athens (NOA). One of its main objectives is to
provide observations, processed data and space weather nowcasting and
forecasting products, designed to support the space weather research
community and operators of commercial and industrial systems. The space
weather products to be released by this facility, will be the result of
the exploitation of ground-based, as well as space-borne observations
and of model results and tools already available or under development
by IAASARS researchers. The objective will be achieved through: (a)
the operation of a small full-disk solar telescope to conduct regular
observations of the Sun in the H-alpha line; (b) the construction of a
database with near real-time solar observations which will be available
to the community through a web-based facility (HELIOSERVER); (c) the
development of a tool for forecasting Solar Energetic Particle (SEP)
events in relation to observed solar eruptive events; (d) the upgrade
of the Athens Digisonde with digital transceivers and the capability
of operating in bi-static link mode and (e) the sustainable operation
of the European Digital Upper Atmosphere Server (DIAS) upgraded with
additional data sets integrated in an interface with the HELIOSERVER
and with improved models for the real-time quantification of the
effects of solar eruptive events in the ionosphere.
---------------------------------------------------------
Title: Wave propagation in a solar quiet region and the influence
of the magnetic canopy
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2016A&A...585A.110K Altcode: 2015arXiv151108618K
<BR /> Aims: We seek indications or evidence of transmission/conversion
of magnetoacoustic waves at the magnetic canopy, as a result of its
impact on the properties of the wave field of the photosphere and
chromosphere. <BR /> Methods: We use cross-wavelet analysis to measure
phase differences between intensity and Doppler signal oscillations
in the Hα, Ca II h, and G-band. We use the height of the magnetic
canopy to create appropriate masks to separate internetwork (IN) and
magnetic canopy regions. We study wave propagation and differences
between these two regions. <BR /> Results: The magnetic canopy affects
wave propagation by lowering the phase differences of progressive waves
and allowing the propagation of waves with frequencies lower than the
acoustic cut-off. We also find indications in the Doppler signals of
Hα of a response to the acoustic waves at the IN, observed in the Ca
II h line. This response is affected by the presence of the magnetic
canopy. <BR /> Conclusions: Phase difference analysis indicates
the existence of a complicated wave field in the quiet Sun, which
is composed of a mixture of progressive and standing waves. There
are clear imprints of mode conversion and transmission due to the
interaction between the p-modes and small-scale magnetic fields of
the network and internetwork.
---------------------------------------------------------
Title: Energy and helicity injection in solar quiet regions
Authors: Tziotziou, K.; Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.
2015A&A...581A..61T Altcode:
<BR /> Aims: We investigate the free magnetic energy and relative
magnetic helicity injection in solar quiet regions. <BR /> Methods:
We use the DAVE4VM method to infer the photospheric velocity field
and calculate the free magnetic energy and relative magnetic helicity
injection rates in 16 quiet-Sun vector magnetograms sequences. <BR />
Results: We find that there is no dominant sense of helicity injection
in quiet-Sun regions, and that both helicity and energy injections are
mostly due to surface shuffling motions that dominate the respective
emergence by factors slightly larger than two. We, furthermore,
estimate the helicity and energy rates per network unit area as
well as the respective budgets over a complete solar cycle. <BR />
Conclusions: Derived helicity and energy budgets over the entire solar
cycle are similar to respective budgets derived in a recent work from
the instantaneous helicity and free magnetic energy budgets and higher
than previously reported values that relied on similar approaches to
this analysis. Free-energy budgets, mostly generated like helicity
at the network, are high enough to power the dynamics of fine-scale
structures residing at the network, such as mottles and spicules,
while corresponding estimates of helicity budgets are provided,
pending future verification from high-resolution magneto-hydrodynamic
simulations and/or observations.
---------------------------------------------------------
Title: Transmission and conversion of magnetoacoustic waves on the
magnetic canopy in a quiet Sun region
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2014A&A...567A..62K Altcode: 2014arXiv1406.5066K
Context. We present evidence for the conversion and transmission of
wave modes on the magnetic flux tubes that constitute mottles and form
the magnetic canopy in a quiet Sun region. <BR /> Aims: Our aim is
to highlight the details and the key parameters of the mechanism that
produces power halos and magnetic shadows around the magnetic network
observed in Hα. <BR /> Methods: We use our previous calculations of
the magnetic field vector and the height of the magnetic canopy, and
based on simple assumptions, we determine the turning height, i.e.,
the height at which the fast magnetoacoustic waves reflect at the
chromosphere. We compare the variation of 3, 5, and 7 min power in the
magnetic shadow and the power halo with the results of a two-dimensional
model on mode conversion and transmission. The key parameter of the
model is the attack angle, which is related to the inclination of the
magnetic field vector at the canopy height. Our analysis takes also
into account that 1) there are projection effects on the propagation of
waves; 2) the magnetic canopy and the turning height are curved layers;
3) waves with periods longer than 3 min only reach the chromosphere
in the presence of inclined magnetic fields (ramp effect); 4) mottles
in Hα are canopy structures; and 5) the wings of Hα contain mixed
signal from low- and high-β plasma. <BR /> Results: The dependence of
the measured power on the attack angle follows the anticipated by the
two-dimensional model very well. Long-period slow waves are channeled
to the upper chromospheric layers following the magnetic field lines of
mottles, while short-period fast waves penetrate the magnetic canopy and
are reflected back higher, at the turning height. <BR /> Conclusions:
Although both magnetoacoustic modes contribute to velocity signals,
making the interpretation of observations a challenging task, we
conclude that conversion and transmission of the acoustic waves into
fast and slow magnetoacoustic waves are responsible for forming power
halos and magnetic shadows in the quiet Sun region.
---------------------------------------------------------
Title: Energy and helicity budgets of solar quiet regions
Authors: Tziotziou, K.; Tsiropoula, G.; Georgoulis, M. K.;
Kontogiannis, I.
2014A&A...564A..86T Altcode: 2014arXiv1403.0730T
<BR /> Aims: We investigate the free magnetic energy and relative
magnetic helicity budgets of solar quiet regions. <BR /> Methods:
Using a novel nonlinear force-free method that requires single solar
vector magnetograms we calculated the instantaneous free magnetic
energy and relative magnetic helicity budgets in 55 quiet-Sun vector
magnetograms. <BR /> Results: As in a previous work on active regions,
we constructed here for the first time the (free) energy-(relative)
helicity diagram of quiet-Sun regions. We find that quiet-Sun regions
have no dominant sense of helicity and show monotonic correlations
a) between free magnetic energy/relative helicity and magnetic
network area and, consequently, b) between free magnetic energy and
helicity. Free magnetic energy budgets of quiet-Sun regions represent
a rather continuous extension of respective active-region budgets
towards lower values, but the corresponding helicity transition is
discontinuous because of the incoherence of the helicity sense in
contrast to active regions. We furthermore estimated the instantaneous
free magnetic-energy and relative magnetic-helicity budgets of the
entire quiet Sun, as well as the respective budgets over an entire solar
cycle. <BR /> Conclusions: Derived instantaneous free magnetic energy
budgets and, to a lesser extent, relative magnetic helicity budgets
over the entire quiet Sun are similar to the respective budgets of a
sizeable active region, while total budgets within a solar cycle are
found to be higher than previously reported. Free-energy budgets are
similar to the energy needed to power fine-scale structures residing
at the network, such as mottles and spicules.
---------------------------------------------------------
Title: Free magnetic energy and relative magnetic helicity in active
and quiet solar regions and their role in solar dynamics
Authors: Tziotziou, Konstantinos; Archontis, Vasilis; Tsiropoula,
Georgia; Georgoulis, Manolis K.; Moraitis, Kostas; Kontogiannis,
Ioannis
2014cosp...40E3428T Altcode:
We present a novel non-linear force-free method for the calculation of
the instantaneous free magnetic energy and relative magnetic helicity
budgets of a solar region from a single photospheric/chromospheric
vector magnetogram. Our objective is to study the role of these
quantities both in solar eruptions and in quiet-Sun dynamics. The
validity of the method is tested using both observations and synthetic
magnetohydrodynamical (MHD) models. The method is applied for the
derivation of the energy-helicity (EH) diagram of solar active regions
(ARs) from a sample of 162 vector magnetograms corresponding to 42
different ARs, suggesting the existence of 4×10(31) erg and 2×10(42)
Mx(2) thresholds in free energy and relative helicity, respectively, for
ARs to enter eruptive territory. Furthermore, the dynamical evolution
of both quantities in eruptive NOAA AR 11158, using a high-cadence
5-day time series of vector magnetograms, suggests the formation of
increasingly helical pre-eruption structures and a causal relation
between flares and Coronal Mass Ejections (CMEs). The method is
also used to derive helicity and energy budgets in quiet Sun regions
and construct the respective EH diagram. Our results highlight the
importance of both energy and helicity in AR evolution and quiet-Sun
dynamics and instigate further research on the underlying physics with
three-dimensional MHD models. This work is supported by EU's Seventh
Framework Programme via a Marie Curie Fellowship.
---------------------------------------------------------
Title: Free Magnetic Energy and Helicity in Active and Quiet Solar
Regions and their role in Solar
Authors: Tziotziou, K.; Georgoulis, M. K.; Tsiropoula, G.; Moraitis,
K.; Kontogiannis, I.
2013hell.conf....6T Altcode:
We present a novel nonlinear force-free method designed to calculate
the instantaneous free magnetic energy and relative magnetic helicity
budgets of a solar region from a single photospheric/chromospheric
vector magnetogram of the region. Our objective is to study the role of
these quantities in solar eruptions and quiet-Sun dynamics. We apply the
method to (1) derive the energy/helicity diagram of solar active regions
from a sample of 162 vector magnetograms corresponding to 42 different
active regions (ARs), suggesting that there exist 4 1031 erg and 2 1042
Mx2 thresholds in free energy and relative helicity, respectively, for
ARs to enter eruptive territory, (2) study the dynamics of eruptive NOAA
AR 11158 using a high-cadence 5-day time series of vector magnetograms,
suggesting the formation of increasingly helical pre-eruption structures
and a causal relation between flares and Coronal Mass Ejections (CMEs)
and, (3) derive helicity and energy budgets in quiet Sun regions and
construct the respective energy/helicity diagram. Our results highlight
the importance of these two parameters in AR evolution and quiet-Sun
dynamics and instigate further research including detailed analysis
with synthetic, magnetohydrodynamical models. This work is supported by
EU's Seventh Framework Programme via a Marie Curie Fellowship and by
the Hellenic National Space Weather Research Network (HNSWRN) via the
THALIS Programme.
---------------------------------------------------------
Title: Mode conversion and transmission of waves in quiet solar
regions
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia; Tziotziou,
Konstantinos
2013EGUGA..15..383K Altcode:
We investigate the interaction between acoustic oscillations and the
fine-scale structures found at the chromospheric network boundaries
that form the magnetic canopy. We use high precision photospheric
magnetograms obtained by SOT/SP on-board the Hinode satellite and time
series of high spatial resolution filtergrams in five wavelengths
along the Hα line profile taken by the Dutch Open Telescope. We
extrapolate the photospheric magnetic field using the current-free
hypothesis to calculate the vector of the magnetic field and reconstruct
the magnetic configuration of the chromosphere. Assuming the VAL-C
atmospheric model we are able to estimate the height of formation of
the magnetic canopy. We use the wavelet analysis on the Ha observations
and obtain the 2-D distribution of the oscillatory power at different
atmospheric heights. We then compare the obtained distribution of power
with the one predicted by the 2-D model of Schunker & Cally at
various magnetic field inclination angles. Our results show that the
magnetic shadow and power halo phenomena observed in network regions
may be attributed to the conversion/transmission of magneto-acoustic
waves on the magnetic canopy. The amount of transmission/conversion
depends on the attack angle, i.e. the angle between the wave vector
and magnetic field direction. Waves which experience mode conversion
and/or transmission can propagate to greater atmospheric heights while
some fraction of their energy escapes into the solar wind.
---------------------------------------------------------
Title: Μελέτη του ρόλου της λεπτής υφής
της χρωμόσφαιρας στο σχηματισμό του
μαγνητικού θόλου και στη διάδοση
των κυμάτων
---------------------------------------------------------
Title: Μελέτη του ρόλου της
λεπτής υφής της χρωμόσφαιρας στο
σχηματισμό του μαγνητικού θόλου και
στη διάδοση των κυμάτων
---------------------------------------------------------
Title: The role of
chromospheric fine structure on the formation of the magnetic canopy
and the propagation of waves;
Authors: Kontogiannis, Ioannis
2013PhDT.......694K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Fine-Scale Structures. I. Spicules and Other Small-Scale,
Jet-Like Events at the Chromospheric Level: Observations and Physical
Parameters
Authors: Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.; Madjarska,
M. S.; Doyle, J. G.; Suematsu, Y.
2012SSRv..169..181T Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T
Over the last two decades the uninterrupted, high resolution
observations of the Sun, from the excellent range of telescopes aboard
many spacecraft complemented with observations from sophisticated
ground-based telescopes have opened up a new world producing
significantly more complete information on the physical conditions of
the solar atmosphere than before. The interface between the lower solar
atmosphere where energy is generated by subsurface convection and the
corona comprises the chromosphere, which is dominated by jet-like,
dynamic structures, called mottles when found in quiet regions,
fibrils when found in active regions and spicules when observed at
the solar limb. Recently, space observations with Hinode have led to
the suggestion that there should exist two different types of spicules
called Type I and Type II which have different properties. Ground-based
observations in the Ca ii H and K filtergrams reveal the existence of
long, thin emission features called straws in observations close to
the limb, and a class of short-lived events called rapid blue-shifted
excursions characterized by large Doppler shifts that appear only
in the blue wing of the Ca ii infrared line. It has been suggested
that the key to understanding how the solar plasma is accelerated
and heated may well be found in the studies of these jet-like,
dynamic events. However, while these structures are observed and
studied for more than 130 years in the visible, but also in the UV
and EUV emission lines and continua, there are still many questions
to be answered. Thus, despite their importance and a multitude of
observations performed and theoretical models proposed, questions
regarding their origin, how they are formed, their physical parameters,
their association with the underlying photospheric magnetic field, how
they appear in the different spectral lines, and the interrelationship
between structures observed in quiet and active regions on the disk
and at the limb, as well as their role in global processes has not
yet received definitive answers. In addition, how they affect the
coronal heating and solar wind need to be further explored. In this
review we present observations and physical properties of small-scale
jet-like chromospheric events observed in active and quiet regions,
on the disk and at the limb and discuss their interrelationship.
---------------------------------------------------------
Title: Study of spicules observed in the CaII H and Ha lines with
Hinode/SOT
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2012hell.conf...11K Altcode:
We use a dataset of simultaneous image sequences obtained by Hinode/SOT
with the Ca II H filter, as well as in Ha+-0.2A. SOT was looking at
the SW solar limb. The high temporal and spatial resolution allows us
to study the structure and dynamics of spicules seen at the different
filters. Individual spicules have been selected and intensity and
velocity distributions at different heights along their central axes
are examined along with transversal fluctuations.
---------------------------------------------------------
Title: Multi-wavelengths observations of oscillatory phenomena in
a solar network region and their relation to the magnetic field
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2012hell.conf....6K Altcode:
The chromosphere is an inhomogeneous and highly dynamic layer of
the solar atmosphere. New high resolution observations have revealed
that it consists mainly of fine-scale structures which are directly
related to the magnetic field. In this work we use multi-wavelength
observations to study oscillatory phenomena in the quiet Sun and
their relation to the magnetic field and the chromospheric fine-scale
structures. The observations were obtained during a coordinated
campaign which included space-borne instruments (i.e. the Transition
Region and Coronal Explorer, the Michelson Doppler Imager onboard
SoHO, and the Specropolarimeter onboard the Hinode spacecraft) and a
ground-based telescope (i.e. the Dutch Open Telescope). The analysed
data consist of time series of filtergrams of a solar network region
observed at different atmospheric layers from the photosphere through
the temperature minimum region and well into the chromosphere and also
of high resolution magnetograms. Using wavelet analysis we investigate
the oscillatory power distribution in the 2D field-of-view, as well
as its vertical distribution and its relation with the fine-scale
chromospheric mottles, while through phase difference analysis we
investigate wave propagation characteristics. Our results show that the
oscillatory power has a fibrilar distribution and that chromospheric
mottles are directly related to power enhancement (power halo) or
suppression (magnetic shadow). This finding is attributed to the
interaction between acoustic oscillations and mottles which outline
inclined magnetic fields and clearly indicate that mottles are the loci
of wave tranmission, reflection and refraction. It also leads to the
conclusion that these structures are directly related to the formation
of the magnetic canopy, i.e. the layer that divides the atmosphere into
two components, a magnetized and a non magnetized one. Extrapolation
of the photospheric magnetic field up to the chromosphere using the
current-free assumption and use of the VAL C atmospheric model allows
the determination of the height of formation of the magnetic canopy
and provide the opportunity to highlight the details of the interaction
between acoustic o scillations and the magnetic field.
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Title: Hinode SOT/SP and SoHO/MDI quiet Sun magnetic
field. Implications of their differences on the extrapolated
chromospheric field and the height of the magnetic canopy
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2011A&A...531A..66K Altcode:
<BR /> Aims: We explore the differences in the measurement of the
magnetic field of the quiet solar photosphere provided by the Michelson
Doppler Imager (MDI) onboard SoHO and the SpectroPolarimeter (SOT/SP)
onboard Hinode and the ensuing implications for the extrapolated
chromospheric magnetic field and the determination of the location
of the magnetic canopy. <BR /> Methods: We employ potential field
extrapolation to reconstruct the chromospheric magnetic field
using the magnetic field of the photosphere provided by the two
instruments. We also calculate the plasma-β parameter using the VAL
C model atmosphere of the quiet Sun to determine the height of the
magnetic canopy. <BR /> Results: MDI underestimates the magnetic
field of the quiet Sun sometimes by a factor of five, which leads
to an overestimation of the height of the magnetic canopy by up
to ~550 km. Although the overall magnetic field configuration does
not differ significantly when calculated with either MDI or SOT/SP,
the data of the latter lead to lower and more extended canopies. The
difference in the resolution of the two instruments does not seem
to affect the chromospheric magnetic field higher than 1000 km. <BR
/> Conclusions: The height of the magnetic canopy is an important
parameter to consider when investigating wave propagation and the
oscillatory properties of the quiet Sun regions in the network and
internetwork. The canopy height's derivation depends very much on
the sensitivity of the instruments used to measure the photospheric
magnetic field. Consequently precise measurements of the photospheric
magnetic field are crucial to accurately reconstruct the chromospheric
magnetic field and to distinguish between the various wave modes.
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Title: Oscillations in a network region observed in the Hα line
and their relation to the magnetic field
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Georgoulis,
M. K.
2010A&A...524A..12K Altcode:
<BR /> Aims: Our aim is to gain a better understanding of the
interaction between acoustic oscillations and the small-scale magnetic
fields of the Sun. To this end, we examine the oscillatory properties
of a network region and their relation to the magnetic configuration of
the chromosphere. We link the oscillatory properties of a network region
and their spatial variation with the variation of the parameters of the
magnetic field. We investigate the effect of the magnetic canopy and the
diverging flux tubes of the chromospheric network on the distribution
of oscillatory power over the network and internetwork. <BR /> Methods:
We use a time series of high resolution filtergrams at five wavelengths
along the Hα profile observed with the Dutch Open Telescope, as
well as high resolution magnetograms taken by the SOT/SP onboard
HINODE. Using wavelet analysis, we construct power maps of the 3,
5 and 7 min oscillations of the Doppler signals calculated at ±0.35
Å and ±0.7 Å from the Hα line center. These represent velocities
at chromospheric and photospheric levels respectively. Through
a current-free (potential) field extrapolation we calculate the
chromospheric magnetic field and compare its morphology with the
Hα filtergrams. We calculate the plasma β and the magnetic field
inclination angle and compare their distribution with the oscillatory
power at the 3, 5 and 7 min period bands. <BR /> Results: Chromospheric
mottles seem to outline the magnetic field lines. The Hα ± 0.35
Å Doppler signals are formed above the canopy, while the Hα ± 0.7
Å corresponding ones below it. The 3 min power is suppressed at the
chromosphere around the network, where the canopy height is lower than
1600 km, while at the photosphere it is enhanced due to reflection. 3,
5 and 7 min oscillatory power is increased around the network at the
photosphere due to reflection of waves on the overlying canopy, while
increased 5 and 7 min power at the chromosphere is attributed mainly
to wave refraction on the canopy. At these high periods, power is also
increased due to p-mode leakage because of the high inclinations of the
magnetic field. <BR /> Conclusions: Our high resolution Hα observations
and photospheric magnetograms provide the opportunity to highlight
the details of the interaction between acoustic oscillations and the
magnetic field of a network region. We conclude that several mechanisms
that have been proposed such as p-mode leakage, mode conversion,
reflection and refraction of waves on the magnetic canopy may act
together and result to the observed properties of network oscillations.
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Title: Comparative Analysis of Oscillations of a Solar Quiet Region
Using Multi-Wavelength Observations
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2010ASPC..424...31K Altcode:
We analyze the temporal behavior of a solar quiet region using a
set of multi-wavelength observations obtained during a coordinated
campaign. The observations were acquired by the ground-based Dutch
Open Telescope (DOT), the Michelson Doppler Imager (MDI) on-board
SOHO and the UV filters of the Transition Region and Coronal
Explorer (TRACE). A large range of height in the solar atmosphere,
from the deep photosphere to the upper chromosphere is covered by
these instruments. We investigate the oscillation properties of
the intensities and velocities in distinct regions of the quiet Sun,
i.e. internetwork, bright points (NBP) defining the network boundaries
and dark mottles forming a well-defined rosette, as observed by the
different instruments and in the different heights. The variations of
the intensities and velocities are studied with wavelet analysis. The
aim of our work is to find similarities and/or differences in the
oscillatory phenomena observed in the different examined regions, as
well as comprehensive information on the interaction of the oscillations
and the magnetic field.
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Title: Power halo and magnetic shadow in a solar quiet region observed
in the Hα line
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2010A&A...510A..41K Altcode:
Context. We investigate the oscillatory behavior of the quiet solar
chromosphere and its discrete components in terms of oscillation
properties, i.e. network and internetwork. For this purpose, we use a
time series of high resolution filtergrams at five wavelengths along
the Hα profile, obtained by the Dutch Open Telescope. <BR /> Aims:
We aim to gain insight on the distribution of power in different
period bands and its variation between network and internetwork. Our
spectral resolution provides information on the vertical distribution
of power, since the Hα line has both photospheric and chromospheric
components. We investigate the effect of Hα mottles on chromospheric
oscillations, since they are the most prominent feature of the Hα
chromosphere and outline inclined magnetic fields. <BR /> Methods: We
use wavelet and phase difference analyses of Hα intensities and Doppler
signals. Two-dimensional power maps in the 3, 5 and 7 min period bands
as well as coherence and phase difference maps were constructed. <BR
/> Results: At photospheric heights, where the Hα ± 0.7 Å wing is
formed, the 3 and 5 min power is enhanced around the network, and forms
power halos. Higher in the chromosphere these areas are replaced by
magnetic shadows, i.e. places of power suppression. Interestingly, the
power maps show a filamentary structure in the network which correlates
very well with mottles. These areas show positive phase differences at
the 3 min period band. At the 5 min and 7 min period bands both positive
and negative phase differences are obtained with an increased number
of pixels with high coherence, indicating the existence of both upward
and downward propagating waves. <BR /> Conclusions: We attribute our
findings to the interaction between acoustic oscillations and the
magnetic fields that constitute the magnetic network. The network
flux tubes diverge at chromospheric levels and obtain a significant
horizontal component, which is betrayed by the presence of mottles. The
variation of power reveals the discrete role of the magnetic field
at different heights, which guides or suppresses the oscillations,
depending on its inclination. Spectral resolution in Hα provides
useful information on the coupling between the acoustic sub-canopy
atmosphere and the magnetized chromosphere.
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Title: Study of spicules observed in the Ca II H and Ha lines with
Hinode/SOT
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia
2010cosp...38.2949K Altcode: 2010cosp.meet.2949K
We use a dataset of simultaneous image sequences obtained by Hinode/SOT
with the Ca II H filter, as well as in Hα ±0.2 ˚. SOT was looking at
the SW solar limb. The high temporal A and spatial resolution allows us
to study the structure and dynamics of spicules seen at the different
filters. Individual spicules have been selected and intensity and
velocity distributions at different heights along their central axes are
examined along with transversal fluctuations. Their temporal variations
are also examined through wavelet and phase difference analyses
---------------------------------------------------------
Title: Power halo and magnetic shadow observed in a network region
by Hinode/SOT and the Dutch Open Telescope
Authors: Tsiropoula, Georgia; Tziotziou, Konstantinos; Kontogiannis,
Ioannis
2010cosp...38.2920T Altcode: 2010cosp.meet.2920T
We use time series of G-band and Ca II H filtergrams obtained by
SOT on-board Hinode, as well as Hα filtergrams in 5 wavelengths
along the line profile obtained by the Dutch Open Telescope during a
coordinated campaign. Our goal is to study the oscillatory behavior of
a network region as seen at different heights of the solar atmosphere
and to gain insight on the distribution of power in different period
bands and its spatial variation. We use wavelet and phase difference
analyses of intensities and doppler signals. Enhanced or suppressed
power (power halo and magnetic shadow, respectively) is observed in
the network region at the differ-ent heights. Interestingly, the
power spatial distribution shows a filamentary structure, while a
correlation analysis reveals that this structure is clearly related
to the dark mottles. We at-tribute our findings to the interaction
between acoustic oscillations and the inclined magnetic fields that
outline the mottles and mark the presence of the magnetic canopy.
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Title: A study of spicules from space observations
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas
2009IAUS..257..165K Altcode:
We have studied spicules observed at the northern solar limb by
using simultaneous high resolution image sequences. The images were
obtained by Hinode/SOT (in the Ca II H passband) and TRACE (in the
1600 Å passband) during a coordinated campaign. Both data sets were
reduced and then carefully co-aligned in order to compare the observed
patterns in this highly dynamic region of the Sun. The identification
of individual structures in both spectral bands allows us to trace
their spatial and temporal behaviour. Persistent intensity variations
at certain locations, indicate that at least some spicules have a
recurrent behavior. Using wavelet analysis we investigate oscillatory
phenomena along the axis of off-limb spicules and we construct 2-D
maps of the solar limb with the observed oscillations.
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Title: Study of H-alpha Spicule Profiles with Line Inversion
Techniques
Authors: Tziotziou, K.; Kontogiannis, I.; Tsiropoula, G.; Kotrc, P.
2008ESPM...12.2.42T Altcode:
High resolution optical spectra of chromospheric spicules obtained in
the H? line are studied together with slit-jaw filtergrams. The spectra
were recorded along a vertical slit parallel to the solar limb with
the HSFA2 (Horizontal-Sonnen-Forschungs-Anlage) Solar Spectrograph
at Ondrejov Observatory on August 19, 2007 and show H? line profiles
taken in spicules - due to the limb curvature - at different heights
from the solar limb. A multi-cloud model that considers two or more
spicules along the line-of-sight (LOS), together with a statistical
approach that takes into account a large set of initial conditions for
solving the radiative transfer equation, is used for the fitting of the
observed profiles and the derivation of several parameters such as the
LOS velocity, the source function, the optical thickness and the Doppler
width that describe the respective spicules. The height-dependence
of the shape of the observed profiles, as well as their dependence
on the values of the derived parameters are studied in detail. The
derived results are compared with the statistical theoretical results
of a multi-cloud model where the aforementioned physical parameters,
as well as a random number of spicules along the LOS were taken into
account, in order to define the dependence of several spicule profile
characteristics on them. Specific steps of the used procedures, as
well as crucial problems are discussed.
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Title: Study of Spicules from Space Observations
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2008ESPM...12.2.43K Altcode:
We present a study of the northern solar limb using simultaneous high
resolution observations by HINODE/SOT (CaII H line) and TRACE (1600
Å) filtergrams, acquired during a coordinated campaign on October
15, 2007. Both data sets were reduced and then carefully coaligned
in order to compare the observed patterns and topology in this
highly dynamical region of the solar atmosphere. The identification
of the same structures in both spectral bands allows us to trace
their spatial and temporal variation. A multitude of spicules and
small loops is revealed highlighting their association with magnetic
field concentrations. Persistent plasma motions at certain locations,
indicative of the recurrency of some structures, are visible throughout
the entire time series. Cuts across and parallel to the limb provide
information on these motions and their temporal evolution. Using wavelet
and cross-correlation analyses we investigate oscillatory phenomena
along the axis of off-limb spicules, as well as along lines parallel to
the solar limb, and examine their interconnection with wave propagation.
