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Author name code: tziotziou
ADS astronomy entries on 2022-09-14
author:"Tziotziou, K."
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Title: Short poster presentations
Authors: Tziotziou, Kostas
2022cosp...44.2527T Altcode:
Short presentations of posters related to event E2.4.
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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: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
M.; the EST team
2022arXiv220710905Q Altcode:
The European Solar Telescope (EST) is a project aimed at studying
the magnetic connectivity of the solar atmosphere, from the deep
photosphere to the upper chromosphere. Its design combines the knowledge
and expertise gathered by the European solar physics community during
the construction and operation of state-of-the-art solar telescopes
operating in visible and near-infrared wavelengths: the Swedish 1m Solar
Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
the French Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
(DOT). With its 4.2 m primary mirror and an open configuration, EST will
become the most powerful European ground-based facility to study the Sun
in the coming decades in the visible and near-infrared bands. EST uses
the most innovative technological advances: the first adaptive secondary
mirror ever used in a solar telescope, a complex multi-conjugate
adaptive optics with deformable mirrors that form part of the optical
design in a natural way, a polarimetrically compensated telescope design
that eliminates the complex temporal variation and wavelength dependence
of the telescope Mueller matrix, and an instrument suite containing
several (etalon-based) tunable imaging spectropolarimeters and several
integral field unit spectropolarimeters. This publication summarises
some fundamental science questions that can be addressed with the
telescope, together with a complete description of its major subsystems.
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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: A Diligent Analysis of the Flash and Coronal Spectrum of the
Total Solar Eclipse of 20 March 2015
Authors: Voulgaris, Aristeidis G.; Mouratidis, C.; Tziotziou, K.;
Seiradakis, J. H.; Pasachoff, J. M.
2022SoPh..297...49V Altcode:
During totality of the solar eclipse of 20 March 2015, at Svalbard,
Norway, the emission spectra of the solar chromosphere and corona were
captured with a slitless spectrograph. A very lucky coincidence of a
large number of sunspots and Active Regions (ARs) around the solar limb
allowed us to observe a number of different spectroscopic effects. This
eclipse took place about one year after the second solar maximum of the
double-peaked Solar Cycle 24, which produced less activity than the
previous stronger solar maxima. The spectra taken during the eclipse
show strong and high activity of the green coronal line Fe XIV (5303 Å)
and the lower intensity of the red coronal line Fe X (6374 Å). After
subtraction of the emitted continuum of K+(F) corona, the detection
and identification of several extremely weak emission lines, including
the two forbidden emission lines of Ca XV (5694 Å and 5446 Å) and
also Ni XIII (5116 Å) and Ni XV (6702 Å), was possible. The large
number of ARs also led to the observation of a continuum brightening
in ARs and a continuum darkening in surrounding areas.
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Title: Automated Detection of Chromospheric Swirls Based on Their
Morphological Characteristics
Authors: Dakanalis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas;
Koutroumbas, Konstantinos
2021SoPh..296...17D Altcode:
High-resolution observations have revealed that rotating structures
known as "chromospheric swirls" are ubiquitous in the solar
chromosphere. These structures have circular or spiral shapes, are
present across a broad range of spatial and temporal scales and are
considered as viable candidates for providing an alternative mechanism
for the heating of the chromosphere and corona. Therefore, an accurate
determination of their number and a statistical study of their physical
properties are deemed necessary. In this work we present a novel,
automated swirl detection method, which utilizes image pre-processing,
curved structure tracing and machine learning techniques that allow
for the detection of swirling events based on their morphological
features as they appear in chromosphere filtergrams. The method is
applied to Hα chromospheric spectral line images obtained by the
CRisp Imaging Spectropolarimeter (CRISP) at the Swedish 1-m Solar
Telescope (SST). It is also tested on grayscale images of vortical
sea current flows represented/visualized by synthetic streamlines
from the NASA/Goddard Space Flight Center Scientific Visualization
Studio. The results are rather encouraging since swirling events are
successfully identified. Further improvements of the algorithm, its
prospects for the detection and statistical studies of the properties
of these events using a wide range of imaging data and its potential
application in other scientific fields for the detection of rotating
motions are discussed.
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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: 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: An overview of methodologies for real-time detection,
characterisation and tracking of traveling ionospheric disturbances
developed in the TechTIDE project
Authors: Belehaki, Anna; Tsagouri, Ioanna; Altadill, David; Blanch,
Estefania; Borries, Claudia; Buresova, Dalia; Chum, Jaroslav; Galkin,
Ivan; Juan, José Miguel; Segarra, Antoni; Timoté, Cristhian Camilo;
Tziotziou, Kostas; Verhulst, Tobias G. W.; Watermann, Jurgen
2020JSWSC..10...42B Altcode:
The main objective of the TechTIDE project (warning and mitigation
technologies for travelling ionospheric disturbances effects) is the
development of an identification and tracking system for travelling
ionospheric disturbances (TIDs) which will issue warnings of electron
density perturbations over large world regions. The TechTIDE project has
put in operation a real-time warning system that provides the results of
complementary TID detection methodologies and many potential drivers to
help users assess the risks and develop mitigation techniques tailored
to their applications. The TechTIDE methodologies are able to detect
in real time activity caused by both large-scale and medium-scale TIDs
and characterize background conditions and external drivers, as an
additional information required by the users to assess the criticality
of the ongoing disturbances in real time. TechTIDE methodologies
are based on the exploitation of data collected in real time from
Digisondes, Global Navigation Satellite System (GNSS) receivers and
Continuous Doppler Sounding System (CDSS) networks. The results are
obtained and provided to users in real time. The paper presents the
achievements of the project and discusses the challenges faced in the
development of the final TechTIDE warning system.
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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.
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Title: Quantifying Ionospheric Disturbances for User Oriented
Applications as a Contribution of the ISWAT Ionosphere Variability
Cluster
Authors: Belehaki, A.; Tsagouri, I.; Tziotziou, K.; Xenaki, I.; Juan,
J. M.; Magdaleno, S.
2019AGUFMSM31C3184B Altcode:
The reliable identification of space weather effects on the Earth's
ionosphere and the effective communication of ionospheric alerts and
warnings in support of technological systems' operations are always
considered key users' requirements. The requirements differ for
different applications and effects of different temporal and spatial
scales (i.e. large-scale and small-scale ionospheric effects) and
therefore, the close collaboration with users for the development of
really actionable products is necessary. This is a challenging task,
involving coordination at international level such as the Ionosphere
Variability ISWAT Cluster that anticipates and embraces relevant
activities. To help the efforts, this work takes advantage of the
European TechTIDE network (http://www.tech-tide.eu/) to report results
regarding the quantification of the ionospheric activity level with
respect to relevant systems' performances (e.g. EGNOS). To this effect,
the deviations of observed ionospheric characteristics from their
background values are statistically analyzed during quiet and disturbed
conditions to indicate quantitative criteria for the determination of
significant ionospheric disturbances. The sophisticated representation
of the background conditions by running averages with variable time
windows (ranging from 60 minutes to 30-days) allows the distinction of
ionospheric disturbances at different scales (e.g. ionospheric storm
effects and travelling ionospheric disturbances, TIDs) in real time
mode, while the comparison of the results with ionosphere activity
indicators related to users' requirements, such as the AATR (Along
Track TEC Rate) index supports fine tuning of different ionospheric
activity levels in conjunction to the relevance of each level in
systems' underperformances. The analysis applies to electron densities
at various altitudes in the bottomside and topside ionosphere and
the critical frequency foF2, aiming to cover the needs in the middle
latitude ionosphere.
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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.
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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: 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: X-Ray, Radio and SEP Observations of Relativistic Gamma-Ray
Events
Authors: Klein, Karl-Ludwig; Tziotziou, Kostas; Zucca, Pietro;
Valtonen, Eino; Vilmer, Nicole; Malandraki, Olga E.; Hamadache,
Clarisse; Heber, Bernd; Kiener, Jürgen
2018ASSL..444..133K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Predicting Flares and Solar Energetic Particle Events: The
FORSPEF Tool
Authors: Anastasiadis, A.; Papaioannou, A.; Sandberg, I.; Georgoulis,
M.; Tziotziou, K.; Kouloumvakos, A.; Jiggens, P.
2017SoPh..292..134A Altcode:
A novel integrated prediction system for solar flares (SFs) and solar
energetic particle (SEP) events is presented here. The tool called
forecasting solar particle events and flares (FORSPEF) provides
forecasts of solar eruptive events, such as SFs with a projection
to occurrence and velocity of coronal mass ejections (CMEs), and
the likelihood of occurrence of an SEP event. In addition, the
tool provides nowcasting of SEP events based on actual SF and CME
near real-time data, as well as the SEP characteristics (e.g. peak
flux, fluence, rise time, and duration) per parent solar event. The
prediction of SFs relies on the effective connected magnetic field
strength (B<SUB>eff</SUB>) metric, which is based on an assessment
of potentially flaring active-region (AR) magnetic configurations,
and it uses a sophisticated statistical analysis of a large number
of AR magnetograms. For the prediction of SEP events, new statistical
methods have been developed for the likelihood of the SEP occurrence
and the expected SEP characteristics. The prediction window in the
forecasting scheme is 24 hours with a refresh rate of 3 hours, while
the respective prediction time for the nowcasting scheme depends on
the availability of the near real-time data and ranges between 15 - 20
minutes for solar flares and 6 hours for CMEs. We present the modules
of the FORSPEF system, their interconnection, and the operational
setup. Finally, we demonstrate the validation of the modules of the
FORSPEF tool using categorical scores constructed on archived data,
and we also discuss independent case studies.
---------------------------------------------------------
Title: Multi-spacecraft solar energetic particle analysis of FERMI
gamma-ray flare events within the HESPERIA H2020 project
Authors: Tziotziou, Kostas; Malandraki, Olga; Valtonen, Eino; Heber,
Bernd; Zucca, Pietro; Klein, Karl-Ludwig; Vainio, Rami; Tsiropoula,
Georgia; Share, Gerald
2017EGUGA..1913786T Altcode:
Multi-spacecraft observations of solar energetic particle (SEP)
events are important for understanding the acceleration processes and
the interplanetary propagation of particles released during eruptive
events. In this work, we have carefully studied 25 gamma-ray flare
events observed by FERMI and investigated possible associations with
SEP-related events observed with STEREO and L1 spacecraft in the
heliosphere. A data-driven velocity dispersion analysis (VDA) and
Time-Shifting Analysis (TSA) are used for deriving the release times
of protons and electrons at the Sun and for comparing them with the
respective times stemming from the gamma-ray event analysis and their
X-ray signatures, in an attempt to interconnect the SEPs and Fermi
events and better understand the physics involved. Acknowledgements:
This project has received funding from the European Union's Horizon
2020 research and innovation program under grant agreement No 637324.
---------------------------------------------------------
Title: Solar flares, coronal mass ejections and solar energetic
particle event characteristics
Authors: Papaioannou, Athanasios; Sandberg, Ingmar; Anastasiadis,
Anastasios; Kouloumvakos, Athanasios; Georgoulis, Manolis K.;
Tziotziou, Kostas; Tsiropoula, Georgia; Jiggens, Piers; Hilgers, Alain
2016JSWSC...6A..42P Altcode:
A new catalogue of 314 solar energetic particle (SEP) events extending
over a large time span from 1984 to 2013 has been compiled. The
properties as well as the associations of these SEP events with their
parent solar sources have been thoroughly examined. The properties of
the events include the proton peak integral flux and the fluence for
energies above 10, 30, 60 and 100 MeV. The associated solar events
were parametrized by solar flare (SF) and coronal mass ejection (CME)
characteristics, as well as related radio emissions. In particular,
for SFs: the soft X-ray (SXR) peak flux, the SXR fluence, the
heliographic location, the rise time and the duration were exploited;
for CMEs the plane-of-sky velocity as well as the angular width were
utilized. For radio emissions, type III, II and IV radio bursts were
identified. Furthermore, we utilized element abundances of Fe and
O. We found evidence that most of the SEP events in our catalogue
do not conform to a simple two-class paradigm, with the 73% of them
exhibiting both type III and type II radio bursts, and that a continuum
of event properties is present. Although, the so-called hybrid or mixed
events are found to be present in our catalogue, it was not possible
to attribute each SEP event to a mixed/hybrid sub-category. Moreover,
it appears that the start of the type III burst most often precedes
the maximum of the SF and thus falls within the impulsive phase of the
associated SF. At the same time, type III bursts take place within
≈5.22 min, on average, in advance from the time of maximum of the
derivative of the SXR flux (Neupert effect). We further performed
a statistical analysis and a mapping of the logarithm of the proton
peak flux at E > 10 MeV, on different pairs of the parent solar
source characteristics. This revealed correlations in 3-D space and
demonstrated that the gradual SEP events that stem from the central part
of the visible solar disk constitute a significant radiation risk. The
velocity of the associated CMEs, as well as the SXR peak flux and
fluence, are all fairly significantly correlated to both the proton peak
flux and the fluence of the SEP events in our catalogue. The strongest
correlation to SEP characteristics is manifested by the CME velocity.
---------------------------------------------------------
Title: Solar Flare Prediction Science-to-Operations: the ESA/SSA
SWE A-EFFort Service
Authors: Georgoulis, Manolis K.; Tziotziou, Konstantinos; Themelis,
Konstantinos; Magiati, Margarita; Angelopoulou, Georgia
2016cosp...41E.656G Altcode:
We attempt a synoptical overview of the scientific origins of the
Athens Effective Solar Flare Forecasting (A-EFFort) utility and
the actions taken toward transitioning it into a pre-operational
service of ESA's Space Situational Awareness (SSA) Programme. The
preferred method for solar flare prediction, as well as key efforts
to make it function in a fully automated environment by coupling
calculations with near-realtime data-downloading protocols (from the
Solar Dynamics Observatory [SDO] mission), pattern recognition (solar
active-region identification) and optimization (magnetic connectivity
by simulated annealing) will be highlighted. In addition, the entire
validation process of the service will be described, with its results
presented. We will conclude by stressing the need for across-the-board
efforts and synergistic work in order to bring science of potentially
limited/restricted interest into realizing a much broader impact
and serving the best public interests. The above presentation was
partially supported by the ESA/SSA SWE A-EFFort project, ESA Contract
No. 4000111994/14/D/MRP. Special thanks go to the ESA Project Officers
R. Keil, A. Glover, and J.-P. Luntama (ESOC), M. Bobra and C. Balmer
of the SDO/HMI team at Stanford University, and M. Zoulias at the
RCAAM of the Academy of Athens for valuable technical help.
---------------------------------------------------------
Title: Quiet Sun and its Dynamics as Viewed from the Ground and
from Space
Authors: Tziotziou, K.
2016ASPC..504....3T Altcode:
Over the last years, state-of-the-art ground-based and/or space-based
observations using imaging, spectroscopic and spectropolarimetric
instruments, at a wide range of wavelengths, reveal that the quiet
Sun, just like active regions, is a highly inhomogeneous and dynamic
environment that plays an important role in the dynamics of the
entire solar atmosphere. This dynamic quiet Sun is manifested through
a number of different types of features and phenomena that occur
in a large range of spatial and temporal scales and are nowadays
believed to be mostly driven by the local magnetic field and its
dynamics. Ground-based observations processed with state-of-the-art,
post-processing reconstruction techniques, often combined with
simultaneous space-based observations from a variety of instruments on
different spacecraft, offer a unique opportunity to investigate and
understand the physical conditions of the local plasma, the nature,
formation mechanisms and evolution of quiet Sun phenomena and possible
interrelationships between quiet Sun phenomena occurring at different
heights of the quiet Sun solar atmosphere, from the photosphere and
chromosphere to the transition region and low corona. We provide a
comprehensive review of our latest understanding of quiet Sun and
its dynamics as viewed from the ground and from space and discuss the
advantages/disadvantages of ground- and space-based observations and
future advents in solar observations with new solar instruments.
---------------------------------------------------------
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: The Major Geoeffective Solar Eruptions of 2012 March 7:
Comprehensive Sun-to-Earth Analysis
Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos,
A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou,
G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.;
Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.;
Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou,
K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.;
Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.;
Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris,
E.; Tsinganos, K.; Vlahos, L.
2016ApJ...817...14P Altcode:
During the interval 2012 March 7-11 the geospace experienced a
barrage of intense space weather phenomena including the second
largest geomagnetic storm of solar cycle 24 so far. Significant
ultra-low-frequency wave enhancements and relativistic-electron dropouts
in the radiation belts, as well as strong energetic-electron injection
events in the magnetosphere were observed. These phenomena were
ultimately associated with two ultra-fast (>2000 km s<SUP>-1</SUP>)
coronal mass ejections (CMEs), linked to two X-class flares launched
on early 2012 March 7. Given that both powerful events originated from
solar active region NOAA 11429 and their onsets were separated by less
than an hour, the analysis of the two events and the determination
of solar causes and geospace effects are rather challenging. Using
satellite data from a flotilla of solar, heliospheric and magnetospheric
missions a synergistic Sun-to-Earth study of diverse observational
solar, interplanetary and magnetospheric data sets was performed. It was
found that only the second CME was Earth-directed. Using a novel method,
we estimated its near-Sun magnetic field at 13 R<SUB>⊙</SUB> to be
in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun
CME magnetic field are required to match the magnetic fields of the
corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream
solar-wind conditions, as resulting from the shock associated with the
Earth-directed CME, offer a decent description of its kinematics. The
magnetospheric compression caused by the arrival at 1 AU of the shock
associated with the ICME was a key factor for radiation-belt dynamics.
---------------------------------------------------------
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: The European Ionosonde Service: nowcasting and forecasting
ionospheric conditions over Europe for the ESA Space Situational
Awareness services
Authors: Belehaki, Anna; Tsagouri, Ioanna; Kutiev, Ivan; Marinov,
Pencho; Zolesi, Bruno; Pietrella, Marco; Themelis, Kostas; Elias,
Panagiotis; Tziotziou, Kostas
2015JSWSC...5A..25B Altcode:
The Earth's ionosphere is a magnetoionic medium imbedded in a background
neutral atmosphere, exhibiting very interesting refractive properties,
including anisotropy, dispersion, and dissipation. As such, it poses a
challenge for several radio systems that make use of signal transmission
through all or some portion of the medium. It is important therefore to
develop prediction systems able to inform the operators of such systems
about the current state of the ionosphere, about the expected effects
of forthcoming space weather disturbances and about support long-term
planning of operations and data post-processing projects for improving
modelling and mitigation techniques. The European Space Agency (ESA)
in the framework of the Space Situational Awareness (SSA) Programme has
supported the development of the European Ionosonde Service (EIS) that
releases a set of products to characterise the bottomside and topside
ionosphere over Europe. The Service is based on a set of prediction
models driven by data from ground-based ionosondes and supportive data
from satellites and spacecraft. The service monitors the foF2 and the
electron density profile up to the height of the Global Navigation
Satellite System (GNSS) at European middle and high latitudes and
provides estimates for forthcoming disturbances mainly triggered by
geo-effective Coronal Mass Ejections (CMEs). The model's performance
has been validated and based on these results, it was possible to issue
together with the products, quality metrics characterizing the product's
reliability. The EIS products meet the requirements of various SSA
service domains, especially the transionospheric radio link and the
spacecraft operations. Currently, the service is freely available to
all interested users, and access is possible upon registration.
---------------------------------------------------------
Title: Relationship between Solar Energetic Particles and Properties
of Flares and CMEs: Statistical Analysis of Solar Cycle 23 Events
Authors: Dierckxsens, M.; Tziotziou, K.; Dalla, S.; Patsou, I.; Marsh,
M. S.; Crosby, N. B.; Malandraki, O.; Tsiropoula, G.
2015SoPh..290..841D Altcode: 2014arXiv1410.6070D; 2015SoPh..tmp....1D
A statistical analysis of the relationship between solar energetic
particles (SEPs) and properties of solar flares and coronal mass
ejections (CMEs) is presented. SEP events during Solar Cycle 23 are
selected that are associated with solar flares originating in the
visible hemisphere of the Sun and that are at least of magnitude
M1. Taking into account all flares and CMEs that occurred during
this period, the probability for the occurrence of an SEP event near
Earth is determined. A strong rise of this probability is observed
for increasing flare intensities, more western locations, higher
CME speeds, and halo CMEs. The correlations between the proton peak
flux and these solar parameters are derived for a low (> 10 MeV)
and high (> 60 MeV) energy range excluding any flux enhancement
due to the passage of fast interplanetary shocks. The obtained
correlation coefficients are 0.55±0.07 (0.63±0.06) with flare
intensity, and 0.56±0.08 (0.40±0.09) with CME speed for E>10 MeV
(E>60 MeV). For both energy ranges, the correlations with flare
longitude and CME width are very weak or non-existent. Furthermore, the
occurrence probabilities, correlation coefficients, and mean peak fluxes
are derived in multi-dimensional bins combining the aforementioned
solar parameters. The correlation coefficients are also determined in
different proton energy channels ranging from 5 to 200 MeV. The results
show that the correlation between the proton peak flux and the CME speed
decreases with energy, while the correlation with the flare intensity
shows the opposite behaviour. Furthermore, the correlation with the CME
speed is stronger than the correlation with the flare intensity below
15 MeV and becomes weaker above 20 MeV. When the enhancements in the
flux profiles due to interplanetary shocks are not excluded, only a
small but not very significant change is observed in the correlation
coefficients between the proton peak flux below 7 MeV and the CME speed.
---------------------------------------------------------
Title: Validation and Benchmarking of a Practical Free Magnetic
Energy and Relative Magnetic Helicity Budget Calculation in Solar
Magnetic Structures
Authors: Moraitis, K.; Tziotziou, K.; Georgoulis, M. K.; Archontis, V.
2014SoPh..289.4453M Altcode: 2014arXiv1406.5381M; 2014SoPh..tmp..122M
In earlier works we introduced and tested a nonlinear force-free
(NLFF) method designed to self-consistently calculate the coronal
free magnetic energy and the relative magnetic helicity budgets of
observed solar magnetic structures. In principle, the method requires
only a single, photospheric or low-chromospheric, vector magnetogram
of a quiet-Sun patch or an active region and performs calculations
without three-dimensional magnetic and velocity-field information. In
this work we strictly validate this method using three-dimensional
coronal magnetic fields. Benchmarking employs both synthetic,
three-dimensional magnetohydrodynamic simulations and nonlinear
force-free field extrapolations of the active-region solar corona. Our
time-efficient NLFF method provides budgets that differ from those of
more demanding semi-analytical methods by a factor of approximately
three, at most. This difference is expected to come from the physical
concept and the construction of the method. Temporal correlations show
more discrepancies that are, however, soundly improved for more complex,
massive active regions, reaching correlation coefficients on the order
of, or exceeding, 0.9. In conclusion, we argue that our NLFF method
can be reliably used for a routine and fast calculation of the free
magnetic energy and relative magnetic helicity budgets in targeted
parts of the solar magnetized corona. As explained in this article and
in previous works, this is an asset that can lead to valuable insight
into the physics and triggering of solar eruptions.
---------------------------------------------------------
Title: Validation of the magnetic energy vs. helicity scaling in
solar magnetic structures
Authors: Tziotziou, K.; Moraitis, K.; Georgoulis, M. K.; Archontis, V.
2014A&A...570L...1T Altcode: 2014arXiv1409.8117T
<BR /> Aims: We assess the validity of the free magnetic energy -
relative magnetic helicity diagram for solar magnetic structures. <BR />
Methods: We used two different methods of calculating the free magnetic
energy and the relative magnetic helicity budgets: a classical,
volume-calculation nonlinear force-free (NLFF) method applied to
finite coronal magnetic structures and a surface-calculation NLFF
derivation that relies on a single photospheric or chromospheric vector
magnetogram. Both methods were applied to two different data sets,
namely synthetic active-region cases obtained by three-dimensional
magneto-hydrodynamic (MHD) simulations and observed active-region cases,
which include both eruptive and noneruptive magnetic structures. <BR
/> Results: The derived energy-helicity diagram shows a consistent
monotonic scaling between relative helicity and free energy with
a scaling index 0.84 ± 0.05 for both data sets and calculation
methods. It also confirms the segregation between noneruptive and
eruptive active regions and the existence of thresholds in both free
energy and relative helicity for active regions to enter eruptive
territory. <BR /> Conclusions: We consider the previously reported
energy-helicity diagram of solar magnetic structures as adequately
validated and envision a significant role of the uncovered scaling in
future studies of solar magnetism.
---------------------------------------------------------
Title: SEPServer catalogues of solar energetic particle events at
1 AU based on STEREO recordings: 2007-2012
Authors: Papaioannou, A.; Malandraki, O. E.; Dresing, N.; Heber, B.;
Klein, K. -L.; Vainio, R.; Rodríguez-Gasén, R.; Klassen, A.; Nindos,
A.; Heynderickx, D.; Mewaldt, R. A.; Gómez-Herrero, R.; Vilmer, N.;
Kouloumvakos, A.; Tziotziou, K.; Tsiropoula, G.
2014A&A...569A..96P Altcode:
The Solar Terrestrial Relations Observatory (STEREO) recordings
provide an unprecedented opportunity to study the evolution of
solar energetic particle (SEP) events from different observation
points in the heliosphere, allowing one to identify the effects of
the properties of the interplanetary magnetic field (IMF) and solar
wind structures on the interplanetary transport and acceleration of
SEPs. Two catalogues based on STEREO recordings, have been compiled as
a part of the SEPServer project, a three-year collaborative effort of
eleven European partners funded under the Seventh Framework Programme
of the European Union (FP7/SPACE). In particular, two instruments on
board STEREO have been used to identify all SEP events observed within
the descending phase of solar cycle 23 and the rising phase of solar
cycle 24 from 2007 to 2012, namely: the Low Energy Telescope (LET)
and the Solar Electron Proton Telescope (SEPT). A scan of STEREO/LET
protons within the energy range 6-10 MeV has been performed for each of
the two STEREO spacecraft. We have tracked all enhancements that have
been observed above the background level of this particular channel
and cross-checked with available lists of interplanetary coronal mass
ejections (ICMEs), stream interaction regions (SIRs), and shocks, as
well as with the reported events in literature. Furthermore, parallel
scanning of the STEREO near relativistic electrons has been performed
in order to pinpoint the presence (or absence) of an electron event in
the energy range of 55-85 keV, for all of the aforementioned proton
events included in our lists. We provide the onset and peak time as
well as the peak value of all events for both protons and electrons,
the relevant solar associations in terms of electromagnetic emissions,
soft and hard X-rays (SXRs and HXRs). Finally, a subset of events with
clear recordings at both STEREO spacecraft is presented together with
the parent solar events of these multispacecraft SEP events.
---------------------------------------------------------
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 diagnostics
for the quality of NLFF field extrapolations
Authors: Moraitis, Kostas; Archontis, Vasilis; Tziotziou, Konstantinos;
Georgoulis, Manolis K.
2014cosp...40E2169M Altcode:
We calculate the instantaneous free magnetic energy and relative
magnetic helicity of solar active regions using two independent
approaches: a) a non-linear force-free (NLFF) method that requires
only a single photospheric vector magnetogram, and b) well known
semi-analytical formulas that require the full three-dimensional (3D)
magnetic field structure. The 3D field is obtained either from MHD
simulations, or from observed magnetograms via respective NLFF field
extrapolations. We find qualitative agreement between the two methods
and, quantitatively, a discrepancy not exceeding a factor of 4. The
comparison of the two methods reveals, as a byproduct, two independent
tests for the quality of a given force-free field extrapolation. We find
that not all extrapolations manage to achieve the force-free condition
in a valid, divergence-free, magnetic configuration. This research has
been co-financed by the European Union (European Social Fund - ESF)
and Greek national funds through the Operational Program "Education
and Lifelong Learning" of the National Strategic Reference Framework
(NSRF) - Research Funding Program: Thales. Investing in knowledge
society through the European Social Fund.
---------------------------------------------------------
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: Transmission and conversion of magneto-acoustic waves in the
quiet solar chromosphere
Authors: Kontogiannis, I., Tsiropoula, G.; Tziotziou, K.
2013hell.conf....6K Altcode:
We investigate the interaction between acoustic oscillations and the
fine-scale structures found at the chromospheric network boundaries
that form the magnetic canopy. To this end, high precision photospheric
magnetograms obtained by SOT/SP on-board the Hinode space mission and
time series of high spatial-resolution filtergrams in five wavelengths
along the Hα line profile taken by the Dutch Open Telescope are
utilized. We extrapolate the photospheric magnetic field using the
current-free assumption to calculate the vector of the magnetic field
and reconstruct the magnetic configuration of the chromosphere. Assuming
the VAL-C atmospheric model we calculate the height of the magnetic
canopy. Through wavelet analysis on the Hα observations we 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 a 2-D theoretical model 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 in the magnetic
canopy. The amount of transmission/conversion depends on the frequency
of the waves and the "attack" angle, i.e. the angle between the wave
vector and magnetic field direction. This mechanism allows transmitted
waves to propagate to greater atmospheric heights.
---------------------------------------------------------
Title: Magnetic helicity and free energy in solar active regions
Authors: Moraitis, K.; Georgoulis, M.; Tziotziou, K.; Archontis, V.
2013hell.confS..21M Altcode:
We study the evolution of the non-potential free magnetic energy
and relative magnetic helicity budgets in solar active regions
(ARs). For this we use a time-series of a three-dimensional, synthetic
AR produced by magnetohydrodynamical (MHD) simulations. As a first
step, we calculate the potential magnetic field that has the same
normal components with the MHD field along all boundaries of the AR,
by solving Laplace's equation. The free magnetic energy of the AR is
then easily derived. From the two fields, MHD and potential one, we
calculate the corresponding vector potentials with a recently proposed
integration method. The knowledge of both fields and their respective
vector potentials throughout the AR, allows us to estimate the relative
magnetic helicity budget of the AR. Following this procedure for each
snapshot of the AR, we reconstruct the evolution of free energy and
helicity in the AR. Our method reproduces, for a synthetic AR, the
energy/helicity relations known to hold in real active regions.
---------------------------------------------------------
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: Solar Energetic Particles within the STEREO era: 2007-2012
Authors: Papaioannou, A.; Malandraki, O. E.; Heber, B.; Dresing,
N.; Klein, K. L.; Vainio, R.; Rodriguez-Gasen, R.; Klassen, A.;
Gomez-Herrero, R.; Vilmer, N.; Mewaldt, R. A.; Tziotziou, K.;
Tsiropoula, G.
2013hell.conf....9P Altcode:
STEREO (Solar TErrestrial RElations Observatory) recordings provide an
unprecedented opportunity to identify the evolution of Solar Energetic
Particles (SEPs) at different observing points in the heliosphere, which
is expected to provide new insight on the physics of solar particle
genesis, propagation and acceleration as well as on the properties of
the interplanetary magnetic field that control these acceleration and
propagation processes. In this work, two instruments onboard STEREO
have been used in order to identify all SEP events observed within
the rising phase of solar cycle 24 from 2007 to 2011, namely: the
Low Energy Telescope (LET) and the Solar Electron Proton Telescope
(SEPT). A scan over STEREO/LET protons within the energy range 6-10
MeV has been performed for each of the two STEREO spacecraft. We have
tracked all enhancements that have been observed above the background
level of this particular channel and cross checked with available
lists on STEREO/ICMEs, SIRs and shocks as well as with the reported
events in literature. Furthermore, parallel scanning of the STEREO/SEPT
electrons in order to pinpoint the presence (or not) of an electron
event has been performed in the energy range of 55-85 keV, for all of
the aforementioned proton events, included in our lists. We provide
the onset of all events for both protons and electrons, time-shifting
analysis for near relativistic electrons which lead to the inferred
solar release time and the relevant solar associations from radio
spectrographs (Nancay Decametric Array; STEREO/WAVES) to GOES Soft
X-rays and coronal mass ejections spotted by both SOHO/LASCO and
STEREO Coronographs
---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption
within the Framework of the
Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou,
K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.;
Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema,
P.; Sarris, M.; Sarris, T.
2013hell.conf...10P Altcode:
Transient expulsions of gigantic clouds of solar coronal plasma into
the interplanetary space in the form of Coronal Mass Ejections (CMEs)
and sudden, intense flashes of electromagnetic radiation, solar flares,
are well-established drivers of the variable Space Weather. Given the
innate, intricate links and connections between the solar drivers and
their geomagnetic effects, synergistic efforts assembling all pieces
of the puzzle along the Sun-Earth line are required to advance our
understanding of the physics of Space Weather. This is precisely the
focal point of the Hellenic National Space Weather Research Network
(HNSWRN) under the THALIS Programme. Within the HNSWRN framework,
we present here the first results from a coordinated multi-instrument
case study of a major solar eruption (X5.4 and X1.3 flares associated
with two ultra-fast (>2000 km/s) CMEs) which were launched early
on 7 March 2012 and triggered an intense geomagnetic storm (min Dst
=-147 nT) approximately two days afterwards. Several elements of
the associated phenomena, such as the flare and CME, EUV wave, WL
shock, proton and electron event, interplanetary type II radio burst,
ICME and magnetic cloud and their spatiotemporal relationships and
connections are studied all way from Sun to Earth. To this end, we
make use of satellite data from a flotilla of solar, heliospheric and
magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE,
Herschel, Planck and INTEGRAL). We also present our first steps toward
formulating a cohesive physical scenario to explain the string of the
observables and to assess the various physical mechanisms than enabled
and gave rise to the significant geoeffectiveness of the eruption.
---------------------------------------------------------
Title: Interpreting Eruptive Behavior in NOAA AR 11158 via the
Region's Magnetic Energy and Relative-helicity Budgets
Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Liu, Yang
2013ApJ...772..115T Altcode: 2013arXiv1306.2135T
In previous works, we introduced a nonlinear force-free method
that self-consistently calculates the instantaneous budgets of free
magnetic energy and relative magnetic helicity in solar active regions
(ARs). Calculation is expedient and practical, using only a single
vector magnetogram per computation. We apply this method to a time
series of 600 high-cadence vector magnetograms of the eruptive NOAA
AR 11158 acquired by the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory over a five-day observing interval. Besides
testing our method extensively, we use it to interpret the dynamical
evolution in the AR, including eruptions. We find that the AR builds
large budgets of both free magnetic energy and relative magnetic
helicity, sufficient to power many more eruptions than the ones it gave
within the interval of interest. For each of these major eruptions,
we find eruption-related decreases and subsequent free-energy and
helicity budgets that are consistent with the observed eruption (flare
and coronal mass ejection (CME)) sizes. In addition, we find that (1)
evolution in the AR is consistent with the recently proposed (free)
energy-(relative) helicity diagram of solar ARs, (2) eruption-related
decreases occur before the flare and the projected CME-launch times,
suggesting that CME progenitors precede flares, and (3) self terms of
free energy and relative helicity most likely originate from respective
mutual terms, following a progressive mutual-to-self conversion pattern
that most likely stems from magnetic reconnection. This results in the
non-ideal formation of increasingly helical pre-eruption structures
and instigates further research on the triggering of solar eruptions
with magnetic helicity firmly placed in the eruption cadre.
---------------------------------------------------------
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: Statistical analysis of solar energetic particle events and
related solar activity
Authors: Dierckxsens, Mark; Patsou, Ioanna; Tziotziou, Kostas; Marsh,
Michael; Lygeros, Nik; Crosby, Norma; Dalla, Silvia; Malandraki, Olga
2013EGUGA..15.8865D Altcode:
The FP7 COMESEP (COronal Mass Ejections and Solar Energetic Particles:
forecasting the space weather impact) project is developing tools
for forecasting geomagnetic storms and solar energetic particle
(SEP) radiation storms. Here we present preliminary results on a
statistical analysis of SEP events and their parent solar activity
during Solar Cycle 23. The work aims to identify correlations between
solar events and SEP events relevant for space weather, as well as
to quantify SEP event probabilities for use within the COMESEP alert
system. The data sample covers the SOHO era and is based on the SEPEM
reference event list [http://dev.sepem.oma.be/]. Events are subdivided
if separate enhancements are observed in higher energy channels as
defined for the list of Cane et al (2010). Energetic Storm Particle
(ESP) enhancements during these events are identified by associating
ESP-like increases in the proton channels with shocks detected in ACE
and WIND data. Their contribution has been estimated and subtracted from
the proton fluxes. Relationships are investigated between solar flare
parameters such as X-ray intensity and heliographic location on the
one hand, and the probability of occurrence and strength of energetic
proton flux increases on the other hand. The same exercise is performed
using the velocity and width of coronal mass ejections to examine their
SEP productiveness. Relationships between solar event characteristics
and SEP event spectral indices and fluences are also studied, as well
as enhancements in heavy ion fluxes measured by the SIS instrument
on board the ACE spacecraft during the same event periods. This work
has received funding from the European Commission FP7 Project COMESEP
(263252).
---------------------------------------------------------
Title: The first SEPServer event catalogue ~68-MeV solar proton
events observed at 1 AU in 1996-2010
Authors: Vainio, Rami; Valtonen, Eino; Heber, Bernd; Malandraki, Olga
E.; Papaioannou, Athanasios; Klein, Karl-Ludwig; Afanasiev, Alexander;
Agueda, Neus; Aurass, Henry; Battarbee, Markus; Braune, Stephan;
Dröge, Wolfgang; Ganse, Urs; Hamadache, Clarisse; Heynderickx, Daniel;
Huttunen-Heikinmaa, Kalle; Kiener, Jürgen; Kilian, Patrick; Kopp,
Andreas; Kouloumvakos, Athanasios; Maisala, Sami; Mishev, Alexander;
Miteva, Rositsa; Nindos, Alexander; Oittinen, Tero; Raukunen, Osku;
Riihonen, Esa; Rodríguez-Gasén, Rosa; Saloniemi, Oskari; Sanahuja,
Blai; Scherer, Renate; Spanier, Felix; Tatischeff, Vincent; Tziotziou,
Kostas; Usoskin, Ilya G.; Vilmer, Nicole
2013JSWSC...3A..12V Altcode:
SEPServer is a three-year collaborative project funded by the seventh
framework programme (FP7-SPACE) of the European Union. The objective
of the project is to provide access to state-of-the-art observations
and analysis tools for the scientific community on solar energetic
particle (SEP) events and related electromagnetic (EM) emissions. The
project will eventually lead to better understanding of the particle
acceleration and transport processes at the Sun and in the inner
heliosphere. These processes lead to SEP events that form one of the key
elements of space weather. In this paper we present the first results
from the systematic analysis work performed on the following datasets:
SOHO/ERNE, SOHO/EPHIN, ACE/EPAM, Wind/WAVES and GOES X-rays. A catalogue
of SEP events at 1 AU, with complete coverage over solar cycle 23,
based on high-energy (~68-MeV) protons from SOHO/ERNE and electron
recordings of the events by SOHO/EPHIN and ACE/EPAM are presented. A
total of 115 energetic particle events have been identified and analysed
using velocity dispersion analysis (VDA) for protons and time-shifting
analysis (TSA) for electrons and protons in order to infer the SEP
release times at the Sun. EM observations during the times of the
SEP event onset have been gathered and compared to the release time
estimates of particles. Data from those events that occurred during
the European day-time, i.e., those that also have observations from
ground-based observatories included in SEPServer, are listed and a
preliminary analysis of their associations is presented. We find that
VDA results for protons can be a useful tool for the analysis of proton
release times, but if the derived proton path length is out of a range
of 1 AU < s ≲ 3 AU, the result of the analysis may be compromised,
as indicated by the anti-correlation of the derived path length and
release time delay from the associated X-ray flare. The average path
length derived from VDA is about 1.9 times the nominal length of
the spiral magnetic field line. This implies that the path length of
first-arriving MeV to deka-MeV protons is affected by interplanetary
scattering. TSA of near-relativistic electrons results in a release
time that shows significant scatter with respect to the EM emissions
but with a trend of being delayed more with increasing distance between
the flare and the nominal footpoint of the Earth-connected field line.
---------------------------------------------------------
Title: The relation between Magnetic Energy and Helicity and their
accumulation in Eruptive Solar Active Regions
Authors: Tziotziou, K.; Georgoulis, M. K.; Raouafi, N. -E.
2013ASPC..470...59T Altcode:
Magnetic free energy and relative magnetic helicity are two important
quantities characterizing solar active regions (ARs). Although the
importance of free magnetic energy storage for solar eruptions is
widely accepted, the role of magnetic helicity, that quantifies the
stress and distortion of the magnetic field compared to its lowest
(potential) energy state, is still under debate. A new nonlinear
force-free method designed to calculate the instantaneous free magnetic
energy and relative magnetic helicity budgets of a solar active region
from a single vector magnetogram is presented. A sample of 40 vector
magnetograms corresponding to different eruptive and non-eruptive ARs
is used to calculate their free magnetic energy and relative magnetic
helicity budgets, aiming to find a statistically robust correlation
between them. The derived correlation implies that magnetic helicity,
besides free magnetic energy, is a crucial ingredient for active
regions hosting major (M-class and higher) solar eruptions. Eruptive
active regions appear well segregated from non-eruptive ones in both
free energy and relative helicity with eruptive major flares occurring
in ARs with free energy and helicity exceeding 4×10<SUP>31</SUP>
erg and 2×10<SUP>42</SUP> Mx<SUP>2</SUP>, respectively. Helicity is
expelled from ARs mainly in the form of coronal mass ejections (CMEs)
and the above helicity threshold agrees well with estimates of typical
helicity contents of CMEs.
---------------------------------------------------------
Title: Magnetic Energy and Helicity Properties of Eruptive Solar
Active Regions
Authors: Georgoulis, M. K.; Tziotziou, K.; Raouafi, N.
2012AGUFMSH53B..02G Altcode:
We outline a new nonlinear force-free method designed to
self-consistently calculate the magnetic energy and the relative
magnetic helicity budgets of solar active regions using only
a single vector magnetogram at the lower atmospheric boundary
of these regions. The method is fast and has been successfully
validated with well-known magnetic-energy and relative-helicity
formulas that, however, are model-dependent and more computationally
demanding. Application of the method to a sizable sample of vector
magnetograms reveals that eruptive active regions exceed well-defined,
physically meaningful thresholds in both their magnetic free-energy
and relative magnetic-helicity budgets. Moreover, application to
a high-cadence vector-magnetogram timeseries of an eruptive region
observed by the Helioseismic and Magnetic Imager onboard the Solar
Dynamics Observatory leads to a physical interpretation of the region's
dynamical evolution and reveals eruption-related energy and helicity
changes. Several intriguing possibilities suggesting promising research
avenues emerge from this analysis and are briefly discussed.
---------------------------------------------------------
Title: Magnetic Energy and Helicity Budgets in the Active-region
Solar Corona. II. Nonlinear Force-free Approximation
Authors: Georgoulis, Manolis K.; Tziotziou, Kostas; Raouafi,
Nour-Eddine
2012ApJ...759....1G Altcode: 2012arXiv1209.5606G
Expanding on an earlier work that relied on linear force-free (LFF)
magnetic fields, we self-consistently derive the instantaneous
free magnetic energy and relative magnetic helicity budgets of
an unknown three-dimensional nonlinear force-free (NLFF) magnetic
structure extending above a single known lower-boundary magnetic field
vector. The proposed method does not rely on the detailed knowledge
of the three-dimensional field configuration but is general enough to
employ only a magnetic connectivity matrix on the lower boundary. The
calculation yields a minimum free magnetic energy and a relative
magnetic helicity consistent with this free magnetic energy. The
method is directly applicable to photospheric or chromospheric vector
magnetograms of solar active regions. Upon validation, it basically
reproduces magnetic energies and helicities obtained by well known,
but computationally more intensive and non-unique, methods relying on
the extrapolated three-dimensional magnetic field vector. We apply
the method to three active regions, calculating the photospheric
connectivity matrices by means of simulated annealing, rather than a
model-dependent NLFF extrapolation. For two of these regions we correct
for the inherent LFF overestimation in free energy and relative helicity
that is larger for larger, more eruptive, active regions. In the third
region studied, our calculation can lead to a physical interpretation of
observed eruptive manifestations. We conclude that the proposed method,
including the proposed inference of the magnetic connectivity matrix,
is practical enough to contribute to a physical interpretation of the
dynamical evolution of solar active regions.
---------------------------------------------------------
Title: The Magnetic Energy-Helicity Diagram of Solar Active Regions
Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Raouafi,
Nour-Eddine
2012ApJ...759L...4T Altcode: 2012arXiv1209.5612T
Using a recently proposed nonlinear force-free method designed for
single-vector magnetograms of solar active regions, we calculate
the instantaneous free magnetic energy and relative magnetic helicity
budgets in 162 vector magnetograms corresponding to 42 different active
regions. We find a statistically robust, monotonic correlation between
the free magnetic energy and the relative magnetic helicity in the
studied regions. This correlation implies that magnetic helicity, in
addition to free magnetic energy, may be an essential ingredient for
major solar eruptions. Eruptive active regions appear well segregated
from non-eruptive ones in both free energy and relative helicity with
major (at least M-class) flares occurring in active regions with free
energy and relative helicity exceeding 4 × 10<SUP>31</SUP> erg and 2
× 10<SUP>42</SUP> Mx<SUP>2</SUP>, respectively. The helicity threshold
agrees well with estimates of the helicity contents of typical coronal
mass ejections.
---------------------------------------------------------
Title: Scientific Analysis within SEPServer - New Perspectives in
Solar Energetic Particle Research: The Case Study of the 13 July
2005 Event
Authors: Malandraki, O. E.; Agueda, N.; Papaioannou, A.; Klein, K. -L.;
Valtonen, E.; Heber, B.; Dröge, W.; Aurass, H.; Nindos, A.; Vilmer,
N.; Sanahuja, B.; Kouloumvakos, A.; Braune, S.; Preka-Papadema, P.;
Tziotziou, K.; Hamadache, C.; Kiener, J.; Tatischeff, V.; Riihonen,
E.; Kartavykh, Y.; Rodríguez-Gasén, R.; Vainio, R.
2012SoPh..281..333M Altcode: 2012SoPh..tmp..287M; 2012SoPh..tmp..267M
Solar energetic particle (SEP) events are a key ingredient of
solar-terrestrial physics both for fundamental research and space
weather applications. Multi-satellite observations are an important
and incompletely exploited tool for studying the acceleration and the
coronal and interplanetary propagation of the particles. While STEREO
uses for this diagnostic two identical sets of instrumentation, there
are many earlier observations carried out with different spacecraft. It
is the aim of the SEPServer project to make these data and analysis
tools available to a broad user community. The consortium will carry
out data-driven analysis and simulation-based data analysis capable
of deconvolving the effects of interplanetary transport and solar
injection from SEP observations, and will compare the results with the
electromagnetic signatures. The tools and results will be provided on
the web server of the project in order to facilitate further analysis
by the research community. This paper describes the data products and
analysis strategies with one specific event, the case study of 13 July
2005. The release time of protons and electrons are derived using
data-driven and simulation-based analyses, and compared with hard
X-ray and radio signatures. The interconnection of the experimental
and the simulation-based results are discussed in detail.
---------------------------------------------------------
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: Scientific analysis within SEPServer: the 13 July 2005 SEP
event case study
Authors: Malandraki, O. E.; Valtonen, E.; Agueda, N.; Papaioannou, A.;
Klein, K. -L.; Heber, B.; Droege, W.; Aurass, H.; Nindos, A.; Vilmer,
N.; Sanahuja, B.; Kouloumvakos, A.; Braune, S.; Preka-Papadema, P.;
Tziotziou, K.; Hamadache, C.; Kiener, J.; Tatischeff, V.; Kartavykh,
J.; Vainio, R.
2012EGUGA..14.9001M Altcode:
SEPServer is set out to make the first database of particle and
corresponding EM observations of solar energetic particle (SEP) events
over roughly three solar cycles. It will also provide users with results
from the scientific analysis of multiple datasets using different
observational and simulation based methods. Therefore, SEPServer
will lead to new perspectives of scientific analysis and will serve
as a new asset valuable for SEP and Space Weather research. In this
contribution, the event of 13 July 2005 has been used as a case study,
which is a proxy for the overall information that the SEPServer will
include and at the same time it reveals the capabilities offered to
the future users of SEPServer. The analysis of the 13 July 2005 event
- focusing on the data driven analysis, i.e., onset and release time
determination from SOHO/ERNE, SOHO/EPHIN and ACE/EPAM together with
pitch angle distributions from ACE/EPAM, simulations based on WIND/3DP
and ACE/EPAM electrons as well as direct comparison of the observed SEP
fluxes with the associated electromagnetic emissions - is performed. The
physical interpretation and the interconnection of the experimental and
the simulation based results are discussed in detail. The 13 July 2005
case study exemplifies the future usage of SEPServer, which will provide
a comprehensive and up to date SEP analysis service. Acknowledgements:
The research leading to these results has received funding from the
European Union's Seventh Framework Programme (FP7/2007-2013) under
grant agreement No 262773 (SEPServer).
---------------------------------------------------------
Title: Space Weather Research at IAA/NOA: Solar Energetic Particle
Investigations
Authors: Malandraki, O.; Tylka, A. J.; Ng, C. K.; Marsden, R. G.;
Tranquille, C.; Klein, K. L.; Patterson, J. D.; Armstrong, T. P.;
Lanzerotti, L. J.; Papaioannou, A.; Marhavilas, P. K.; Tziotziou,
K.; Crosby, N.; Vainio, R.
2012hell.conf....7M Altcode:
During an eleven year cycle the Sun goes from quiet conditions at
minimum to levels of high activity at maximum. In the latter case,
energetic phenomena such as coronal mass ejections (CMEs) and solar
flares (SFs) accompanied by explosive releases of mass, magnetic flux
and solar energetic particles (SEPs) are common. Damaging effects,
as a result of these phenomena, have been recorded on satellites,
on-board detectors and in extreme cases on ground based systems
(e.g. oil and natural gas pipelines, communication systems, aircraft
electronics, power-grids). Furthermore, the intense SEP radiation can
damage human DNA and cause cell replications. To this end, ensuring
the safety of astronauts working in the extreme conditions of space,
especially the energetic particle environments, is a key goal for both
ESA and NASA. The analysis, the risk assessment and management and the
possible forecasting of such events constitutes the scientific field of
Space Weather. The Institute of Astronomy and Astrophysics (IAA) of the
National Observatory of Athens (NOA) is currently strongly involved in
two collaborative projects funded by the seventh framework program of
the European Union, <P />namely: 'SEPServer' and 'COMESEP'. 'SEPServer'
focuses on the implementation of a comprehensive and up to date SEP
analysis service including scientific data driven analysis both for
1 AU and for > 1 AU using data from the SOHO/ ERNE, SOHO/EPHIN,
ACE/EPAM, ACE/SIS, WIND/3DP, Ulysses/HISCALE, Ulysses/COSPIN/LET and
Ulysses/COSPIN/KET experiments. SEPServer will also provide for the
first time the release of the HELIOS data set in a reasonable format
and in full time resolution, thus making available data also for orbits
inside 1 AU (down to 0.3 AU). Observational data-driven analysis methods
such as: onset determination, velocity dispersion, and/or time-shifting
analysis, direct comparison of observed SEP fluxes, spectra and
abundance ratios with the associated electromagnetic emission data
will be applied. 'SEPServer' will enhance our understanding of
the source, acceleration and transport of SEPs which is directly
related to space weather research progress. 'COMESEP' sets out to
develop tools for forecasting SEP radiation storms and geomagnetic
storms based on scientific data analysis and extensive modeling. It
is foreseen that these forecasting tools will be incorporated into an
automated operational European Space Weather Alert system, which is the
'COMESEP' primary goal. Basic research activities on Space Weather
carried out at IAA/NOA within the framework of these two projects
will be presented including the analysis of SEPs and the associated
electromagnetic emissions for selected case studies, the detailed study
of the so-called 'reservoir effect' in the heliosphere as well as the
impact of the large-scale structure of the IMF on the SEP profiles and
its space weather implications. These project-related activities will
provide the basis for future solar missions such as Solar Orbiter -
in which IAA/NOA participates as a Co-Investigator (EPD instrument).
---------------------------------------------------------
Title: Solar chromospheric fine scale structures: dynamics and
energetics
Authors: Tziotziou, K.
2012hell.conf....5T Altcode:
The solar chromosphere is a very inhomogeneous and dynamic layer of
the solar atmosphere that exhibits several phenomena on a wide range
of spatial and temporal scales. High-resolution and long-duration
observations, employing mostly lines, such as Halpha, the Ca II infrared
lines and the Ca II H and K lines, obtained both from ground-based
telescope facilities (e.g. DST, VTT, THEMIS, SST, DOT), as well
as state-of-the-art satellites (e.g. SOHO, TRACE, HINODE) reveal
an incredibly rich, dynamic and highly structured chromospheric
environment. What is known in literature as the chromospheric
fine-scale structure mainly consists of small fibrilar-like features
that connect various parts of quiet/active regions or span across
the chromospheric network cell interiors, showing a large diversity
of both physical and dynamic characteristics. The highly dynamic,
fine-scale chromospheric structures are mostly governed by flows
which reflect the complex geometry and dynamics of the local magnetic
field and play an important role in the propagation and dissipation
of waves. A comprehensive study of these structures requires deep
understanding of the physical processes involved and investigation of
their intricate link with structures/processes at lower photospheric
levels. Furthermore, due to their large number present on the solar
surface, it is essential to investigate their impact on the mass and
energy transport to higher atmospheric layers through processes such
as magnetic reconnection and propagation of waves. The in-depth study
of all aforementioned characteristics and processes, with the further
addition of non-LTE physics, as well as the use of three-dimensional
numerical simulations poses a fascinating challenge for both theory
and numerical modeling of chromospheric fine-scale structures.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Solar Energetic Particles (SEPs) on a heliospheric scale - an
attempt to compile the complete Ulysses event list over solar cycle 23
Authors: Papaioannou, A.; Malandraki, O. E.; Tziotziou, K.
2012hell.conf...12P Altcode:
The intensities of Solar Energetic Particles (SEPs) are strongly
affected by the variations in the level of solar activity,
the characteristics of the solar wind and the properties of the
interplanetary magnetic field that enable the acceleration and
propagation of SEPs throughout the heliosphere. The study of SEPs at
different latitudes and under different heliospheric conditions provides
useful information about the global structure of the heliosphere
during solar minimum and solar maximum, as well as on the mechanisms
and the physics of solar particle propagation and acceleration. Due to
its eccentric orbit over the solar poles and its continuous presence
in space for 18 years, Ulysses spacecraft has been the only solar
mission so far that allowed us to study the characteristics of SEPs at
low and high latitudes and their distribution over a solar cycle. In
this work, the Heliosphere Instrument for Spectra, Composition and
Anisotropy in Low-Energies (HI-SCALE) and the Low-Energy Telescope
(LET) of the Cosmic Ray and Solar Particle Investigation (COSPIN)
onboard Ulysses have been used in order to identify all SEPs observed
in and out of the ecliptic plane over solar cycle 23. A scan has been
performed on the recordings of the low-energy protons of COSPIN/LET
(energy range: 0.9-8.0 MeV) and the Deflected Electrons (DEs) of
HI-SCALE (energy range: 38-315 keV). As a result, a list of about 150
well-defined events has been compiled. A part of this list, together
with the analysis of case studies is being discussed. Furthermore,
ongoing work includes the single treatment of each event and the
possible identification of its solar source which could also be used
as the basis for future solar missions such as Solar Orbiter in which
IAA/NOA participates as a Co-Investigator (EPD instrument).
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Estimating Fluxes of SEPs by Unfolding ESA/SREM Data
Authors: Sandberg, I.; Daglis, I. A.; Anastasiadis, A.; Tziotziou,
K.; Bühler, P.; Nieminen, P.
2010ASPC..424...43S Altcode:
The Standard Radiation Environment Monitor (SREM) belongs to a second
generation of instruments in a program established by the European
Research and Technology Centre (ESTEC) of the European Space Agency
(ESA) to provide minimum intrusive particle radiation detectors on ESA
spacecrafts for space weather applications. SREM detects high-energy
electrons and protons and bins the measurements in overlapping energy
channels. In order to estimate the particle fluxes associated with
Solar Particle Events (SPEs), a method based on the Singular Value
Decomposition (SVD) analysis was developed. This method does not
require any assumption on the spectral form of the particle fluxes
and includes proper schemes treating issues related to several
characteristic properties of the detector. As an example, we present
results associated to the January 20, 2005 SPE.
---------------------------------------------------------
Title: Solar Origin of Solar Particle Events Detected by the Standard
Radiation Environment Monitor of ESA
Authors: Tziotziou, K.; Sandberg, I.; Anastasiadis, A.; Daglis, I. A.;
Panagopoulos, I.; Mavromichalaki, H.; Papaioannou, A.; Gerontidou,
M.; Nieminen, P.; Glover, A.
2010ASPC..424...47T Altcode:
Solar Particle Events (SPEs) of the 23rd Solar Cycle detected by the
ESA Standard Radiation Environment Monitor (SREM) onboard the INTEGRAL
satellite have been studied in order to find their connection to
solar sources. X-ray, optical and radio data of solar flares that were
observed by several space-based instruments during the aforementioned
solar cycle have been selected. The data were reduced and thoroughly
analyzed in order to establish the corresponding solar origin of
the selected SPEs. The extensive scientific analysis has produced
clear correlations with X class solar flares for the events of the
October-November 2003, January 2005 and December 2006 periods while
for the events that occurred during September 2005, correlations with X
class flares are possible but not straightforward due to the complexity
of the registered solar particle fluxes.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Using a new set of space-borne particle monitors to investigate
solar-terrestrial relations
Authors: Tziotziou, K.; Sandberg, I.; Anastasiadis, A.; Daglis, I. A.;
Nieminen, P.
2010A&A...514A..21T Altcode:
Context. We investigated the solar origin of Solar Particle Events
(SPEs) which occurred during four time periods of the 23rd solar cycle
with intense solar activity and were detected by the Standard Radiation
Environment Monitor (SREM) onboard the INTEGRAL satellite. SREM is
a second generation ESA particle radiation monitor, already flying
onboard seven spacecraft. <BR /> Aims: The present study attempts
to establish the association of recorded SPEs by INTEGRAL/SREM with
their solar sources and hence evaluate the potential of SREM units as
an alarm system for hazardous SPEs. <BR /> Methods: X-ray, optical and
radio data of solar flares and coronal mass ejections (CMEs) that were
observed by several space-based instruments during the aforementioned
solar cycle were reduced and thoroughly analyzed to establish the
corresponding solar origin of the selected SPEs. <BR /> Results: The
analysis produced clear associations with X-class solar flares and
respective CMEs for the events of the October-November 2003, January
2005 and December 2006 periods, while for the events that occurred
during September 2005, associations with X-class flares are possible
but not straightforward due to the complexity of the registered solar
particle fluxes. <BR /> Conclusions: SREM proves to be a new valuable
asset for a comprehensive study of SPEs and a useful alert instrument
for explosive geoeffective solar events.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Status of the ESA Standard Radiation Environment Monitor
(SREM) products
Authors: Nieminen, Petteri; Anastasiadis, A.; Bühler, P.; Daglis, I.;
Daly, E.; Desorgher, L.; Evans, H.; Hajdas, W.; Lyons, J.; Marinov,
D.; Nieminen, P.; Sandberg, I.; Siegl, M.; Tziotziou, K.; Zadeh, A.
2010cosp...38.4188N Altcode: 2010cosp.meet.4188N
The ESA Standard Radiation Environment Monitor (SREM) is thus far
succesfully flying and producing radiation data on Proba-1, INTEGRAL,
Rosetta, Giove-B, Herschel and Planck missions, with the environments
covering LEO, MEO, highly elliptical orbit, L2, and the in-terplanetary
space. This presentation will outline the main SREM results to date
from these various missions, and will give an overview of the present
efforts taken to process the SREM data from raw particle count rates to
proton and electron fluxes. Interfaces to various envi-ronment modelling
activities and other higher level products are also discussed. Lessons
learnt from the SREM programme will be summarised with the aim of
facilitating future radiation monitor development and data processing /
utilisation efforts.
---------------------------------------------------------
Title: The dynamic solar chromosphere: recent advances from high
resolution telescopes
Authors: Tziotziou, Konstantinos; Tsiropoula, Georgia
2010cosp...38.2918T Altcode: 2010cosp.meet.2918T
This review focuses on the solar chromosphere, a very inhomogeneous
and dynamic layer that exhibits phenomena on a large range of spatial
and temporal scales. High-resolution observa-tions from existing
telescopes (DST, SST, DOT), as well as long-duration observations
with Hinode's SOT employing lines such as the Ca II infrared lines,
the Ca II HK and above all the Hα line reveal an incredibly rich,
dynamic and highly structured environment, both in quiet and active
regions. The fine-structure chromosphere, is mainly constituted by
fibrilar features that connect various parts of active regions or
span across network cell interiors. We discuss this highly dynamical
solar chromosphere, especially below the magnetic canopy, which is
gov-erned by flows reflecting both the complex geometry and dynamics of
the magnetic field and the propagation and dissipation of waves in the
different atmospheric layers. A comprehensive view of the fine-structure
chromosphere requires deep understanding of the physical processes
involved, investigation of the intricate link with structures/processes
at lower photospheric lev-els and analysis of its impact on the mass and
energy transport to higher atmospheric layers through flows resulting
from different physical processes such as magnetic reconnection and
waves. Furthermore, we assess the challenges facing theory and numerical
modelling which require the inclusion of several physical ingredients,
such as non-LTE and three-dimensional numerical simulations.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Oscillatory phenomena in a solar network region
Authors: Tsiropoula, Georgia; Tziotziou, Kostas; Schwartz, Pavol;
Heinzel, Petr
2009IAUS..257..181T Altcode:
We examine oscillatory phenomena in a solar network region from
multi-wavelength, observations obtained by the ground-based Dutch
Open Telescope (DOT), and by instruments on the spacecraft Solar and
Heliospheric Observatory (SoHO). The observations were obtained during
a coordinated observing campaign on October 14, 2005. The temporal
variations of the intensities and velocities in two distinct regions of
the quiet Sun were investigated: one containing several dark mottles
and the other several bright points defining the network boundaries
(NB). The aim is to find similarities and/or differences in the
oscillatory phenomena observed in these two regions and in different
spectral lines formed from the chromosphere to the transition region,
as well as propagation characteristics of waves.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Multiwavelength analysis of a solar quiet region
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P.
2009A&A...493..217T Altcode:
Context: We examine oscillatory phenomena in a solar network region
from multi-wavelength observations obtained by the ground-based Dutch
Open Telescope (DOT) and by the Coronal Diagnostic Spectrometer (CDS)
on the spacecraft Solar and Heliospheric Observatory (SoHO). The
observations were obtained during a coordinated observing campaign in
October 2005. <BR />Aims: We investigate the temporal variations of the
intensities and the velocities in two distinct regions of the quiet Sun,
one containing several dark mottles and the other several bright points
defining the network boundaries (NB). The aim is to find similarities
and/or differences in the oscillatory phenomena observed in these two
regions and in different spectral lines formed from the chromosphere
to the transition region, as well as the propagation characteristics
of waves. <BR />Methods: Intensity and velocity variations are
studied with wavelet and phase difference analyses. <BR />Results:
Both regions (i.e. mottles and NB) show a periodicity of ~5 min in all
considered lines. The V-V phase differences in the NB region point to
an upward propagation of waves; in the region of mottles, for periods
of 250-400 s, the phase difference is mainly negative, which suggests
a downward propagation, in turn indicating a refraction of waves from
the inclined magnetic field of mottles along the line-of-sight. <BR
/>Conclusions: The phase differences at the NB arise from a predominance
of upward propagating waves. In the mottles' region, the negative phase
differences we found suggest that propagating waves encounter a boundary
and are refracted and reflected. Of course, several limitations exist
in the exact interpretation of the phase differences, e.g. the complex
topology of the magnetic field, the formation conditions and heights
of the examined spectral lines, and the low spatial resolution.
---------------------------------------------------------
Title: Influence of Seeing on Cloud Model Parameters Obtained from
Hα Observations
Authors: Tziotziou, K.; Tsiropoula, G.; Heinzel, P.
2008ASPC..397...63T Altcode:
We study the influence of atmospheric seeing due to terrestrial
atmospheric turbulence on cloud model parameters obtained from Hα
observations with Beckers' cloud model. The analysis indicates that
atmospheric seeing does not affect the velocity determination, but
does influence significantly the determination of the Doppler width
when velocity gradients are present, and hence, the determination of
the temperature, while the optical thickness and source function are
also quantitatively affected, especially for high values of atmospheric
seeing.
---------------------------------------------------------
Title: Contrast of Fine-scale Structures in a Quiet Sun Network Region
Authors: Schwartz, P.; Tziotziou, K.; Heinzel, P.; Tsiropoula, G.
2008ESPM...12.2.35S Altcode:
We study the contrast of fine structures (mottles), found in a quiet-Sun
network region and close to a filament, observed by the SOHO/SUMER
spectrograph. The observations were made during August 29 -- 30, 1996,
in several chromospheric, transition-region and coronal EUV lines. The
contrasts of the fine-scale structures were obtained in the different
spectral lines and compared to find whether they have any dependence
on the inclination of the magnetic field lines and the line formation
height. Also contributions of the absorption and emissivity blocking
to the depression of brightness in these fine-scale structures are
studied by comparing the observations in transition-region lines
with wavelengths above and below 912 A (the head of the hydrogen
Lyman continuum).
---------------------------------------------------------
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.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Oscillatory Phenomena in a Solar Network Region
Authors: Tziotziou, K.; Tsiropoula, G.; Schwartz, P.; Heinzel, P.
2008ESPM...12.2.41T Altcode:
Multi-wavelength, multi-instrument observations, obtained during a
coordinated observing campaign on October 2005 by the ground-based
Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar
and Heliospheric Observatory (SoHO) and Transition Region and Coronal
Explorer (TRACE), are used to study oscillatory phenomena in a solar
network region. Temporal variations of the intensities and velocities
in a region of the quiet Sun containing several dark mottles and in a
region with several bright points defining the network boundaries (NB)
are investigated with the aim of finding similarities and/or differences
in the oscillatory phenomena observed in these two regions and in
different spectral lines formed from the chromosphere to the transition
region, as well as propagation characteristics of waves. A wavelet,
phase difference and coherence analyses were performed indicating a
periodicity around 5 min in all considered lines for both regions. V-V
phase differences in the NB region point to an upward propagation of,
most probably, acoustic waves, while in the region of mottles they
indicate a non vertical propagation of waves, due to the presence
of several inclined mottles along the line-of-sight. In mottles, for
periods of 250-400 s the phase difference is mainly negative suggesting
that propagating waves encounter a boundary and are refracted and
reflected. However, limitations arising from the complex topology
of the magnetic field, the formation conditions and heights of the
examined spectral lines and the low spatial resolution of the space
instruments influence the exact interpretation of the phase differences.
---------------------------------------------------------
Title: Multi-wavelength Analysis of a Solar Network Region
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P.
2008CEAB...32..109T Altcode:
We analyse co-temporal observations of a network region found near
the solar disc centre, obtained by the Dutch Open Telescope (DOT)
and the Coronal Diagnostic Spectrometer (CDS) on-board SOHO during a
coordinated observing campaign in October 2005. DOT obtained images in
5 wavelengths along the ha\ profile, while CDS obtained sit-and-stare
observations in several EUV spectral lines that span the upper solar
atmosphere. After fitting the CDS spectral line profiles we obtained
2-D space-time maps of intensities, Doppler velocities and Doppler
widths. We study the appearance of the network region in the different
spectral lines and the temporal variations of the obtained physical
parameters. We employ a wavelet analysis to examine the existence of
oscillations at the network in the different solar layers.
---------------------------------------------------------
Title: Influence of seeing effects on cloud model inversions
Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G.
2007A&A...472..287T Altcode:
Context: Atmospheric seeing due to terrestrial atmospheric turbulence
is a process that distorts solar ground-based observations. <BR
/>Aims: We study the influence of atmospheric seeing on Hα cloud
model inversions. <BR />Methods: We use Beckers' cloud model which
assumes a constant source function to obtain physical parameters from
observed quiet-Sun Hα profiles, and profiles convolved with a Gaussian
point spread function that simulates the effect of atmospheric seeing
on solar observations. <BR />Results: Our analysis indicates that
atmospheric seeing does not affect the velocity determination, but
does influence significantly the determination of the Doppler width
when velocity gradients are present, and hence, the determination of
the temperature, while the optical thickness and source function are
also quantitatively affected, especially for high values of atmospheric
seeing. <BR />Conclusions: The effects of atmospheric seeing on cloud
model inversions also depend on the actual size of the structures
under study. For the presented observations, the derived cloud model
parameter distributions do not change significantly for atmospheric
seeing up to ∼0.5”.
---------------------------------------------------------
Title: Chromospheric Cloud-Model Inversion Techniques
Authors: Tziotziou, K.
2007ASPC..368..217T Altcode: 2007arXiv0704.1558T
Spectral inversion techniques based on the cloud model are extremely
useful for the study of properties and dynamics of various chromospheric
cloud-like structures. Several inversion techniques are reviewed based
on simple (constant source function) and more elaborated cloud models,
as well as on grids of synthetic line profiles produced for a wide range
of physical parameters by different NLTE codes. Several examples are
shown of how such techniques can be used in different chromospheric
lines, for the study of structures of the quiet chromosphere, such
as mottles/spicules, as well as for active region structures such as
fibrils, arch filament systems (AFS), filaments and flares.
---------------------------------------------------------
Title: Multi-wavelength Analysis of a Quiet Solar Region
Authors: Tsiropoula, G.; Tziotziou, K.; Giannikakis, J.; Young, P.;
Schühle, U.; Heinzel, P.
2007ASPC..368..171T Altcode: 2007arXiv0704.1592T
We present observations of a solar quiet region obtained by the
ground-based Dutch Open Telescope (DOT), and by instruments on the
spacecraft SOHO and TRACE. The observations were obtained during a
coordinated observing campaign on October 2005. The aim of this work
is to present the rich diversity of fine-scale structures that are
found at the network boundaries and their appearance in different
instruments and different spectral lines that span the photosphere
to the corona. Detailed studies of these structures are crucial to
understanding their dynamics in different solar layers, as well as
the role such structures play in the mass balance and heating of the
solar atmosphere.
---------------------------------------------------------
Title: Dual-line spectral and phase analysis of sunspot oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2007A&A...463.1153T Altcode:
Context: Sunspots exhibit a wide range of oscillatory phenomena within
their umbrae and penumbrae. <BR />Aims: We investigate the behavior
of intensity and Doppler velocity oscillations in the umbra and the
penumbra to study sunspot oscillations and their associations. <BR
/>Methods: Simultaneous, high-cadence (8 s), two-dimensional, Ca
II 8542 Å and Hα 6563 Å observations are used. Doppler velocity
and intensity variations are studied with a wavelet spectral, phase
difference and coherence analysis, both at distinct positions and
within the whole umbra and the penumbra. <BR />Results: The analysis
reveals the presence of several umbral flashes (UFs) that seem to
fill the whole umbra. The spectral analysis indicates oscillating
elements of size 2.5” to 5” within the umbra with periods around
the 3-min band and oscillation periods around the 5-min band within
the penumbra. Two remarkable jumps of the oscillation period and the
intensity-velocity phase difference are present at both umbra-penumbra
and penumbra-superpenumbra boundaries reflecting a drastic change in
physical and/or magnetic conditions. The intensity-velocity phase
analysis shows a delay of the intensity response to the velocity
variations in accordance with the physics of the observed sawtooth
velocity behavior. Most of the UFs oscillate incoherently, while the
calmest umbral area seems to be associated with velocity spreading
from neighboring UFs. The derived incoherency among UFs in conjunction
with the existence of coherently oscillating elements within the umbra
suggests the presence of umbral areas with slightly different physical
and/or magnetic field conditions. <BR />Conclusions: .The presented
analysis provides further important constraints for realistic models
and theoretical interpretations describing sunspot oscillations.
---------------------------------------------------------
Title: Evolution of a Coronal Loop System
Authors: Tsiropoula, G.; Tziotziou, K.; Wiegelmann, T.; Zachariadis,
Th.; Gontikakis, C.; Dara, H.
2007SoPh..240...37T Altcode:
The temporal variation of a loop system that appears to be changing
rapidly is examined. The analyzed data were obtained on 15 May 1999,
with the Transition Region and Coronal Explorer (TRACE) during an
observing campaign and consist of observations in the Fe IX/Fe X 171
Å and Fe XII 195 Å passbands taken at a cadence of ∼10 min. The
special interest in this loop system is that it looks like one expanding
loop; however, careful examination reveals that the loop consists of
several strands and that new loop strands become visible successively
at higher altitudes and lower loop strands fade out during the one hour
of our observations. These strands have different widths, densities,
and temperatures and are most probably consisting of, at least, a few
unresolved thinner threads. Several geometric and physical parameters
are derived for two of the strands and an effort is made to determine
their 3D structure based on the extrapolation of the magnetic field
lines. Electron density estimates allow us to derive radiative and
conductive cooling times and to conclude that these loop strands are
cooling by radiation.
---------------------------------------------------------
Title: The fine-scale structure of the quiet solar chromosphere
Authors: Tsiropoula, G.; Tziotziou, K.
2007MmSAI..78...32T Altcode:
We present methods for estimating different physical properties of dark
mottles from observations obtained with the MSDP spectrograph mounted
on the 50 cm refractor of the Pic du Midi Observatory and on THEMIS
(Tenerife). We also present studies of their dynamical evolution and
estimates of the role they play in the mass balance and heating of
the solar atmosphere.
---------------------------------------------------------
Title: Dual-line analysis of sunspot oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2007MmSAI..78...98T Altcode:
Umbral oscillations and running penumbral (RP) waves are studied
with simultaneous, two-dimensional, high cadence (8 sec), dual-line
sunspot observations in Ca II 8542 Å and Halpha , obtained with the
MSDP spectrograph on the German VTT in Tenerife. Doppler velocity and
intensity images are used to investigate the physical characteristics
of umbral flashes (UFs) and RP waves while a wavelet spectral and phase
analysis shows their temporal behaviour and permits us to elaborate
on their nature and possible association.
---------------------------------------------------------
Title: Observational characteristics and association of umbral
oscillations and running penumbral waves
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2006A&A...456..689T Altcode:
Context: .Umbral flashes (UFs) and running penumbral (RP) waves are
believed to be closely related oscillatory phenomena of sunspots.<BR />
Aims: .We investigate the association of UFs and RP waves to see whether
the latter are a visual pattern created by a common source with UFs
or a trans-sunspot wave driven by UFs.<BR /> Methods: .Simultaneous,
two-dimensional, dual-line observations in Ca II 8542 Å and Hα
6563 Å, obtained with the Multichannel Subtractive Double Pass (MSDP)
spectrograph mounted on the German VTT at Teide Observatory on Tenerife,
are used for this study. High-cadence 8 s Doppler velocity images,
spectrograms, and spectral-analysis results are used to study the
characteristics and the relationship of UFs and RP waves.<BR /> Results:
.Several UFs were observed that seem to fill the whole umbra. Doppler
velocity variations with time indicate a shock behaviour for UFs, as
well as for umbral and RP waves and a smooth continuous propagation
of the latter from the umbra through the umbra-penumbra boundary
out to the edge of the penumbra. Furthermore, the spectral analysis
shows a decreasing oscillatory frequency as we move from the umbra
outwards and a jump at the umbra-penumbra boundary that could possibly
reflect, apart from a change in physical conditions, a drastic change
of the magnetic field inclination with respect to the vertical.<BR />
Conclusions: .The results do not permit us to convincingly support one
scenario over the other (i.e. visual pattern vs. trans-sunspot wave)
for RP waves; however, they do provide important constraints for future
models of sunspot oscillations and RP waves.
---------------------------------------------------------
Title: Line Broadening of EUV Lines at the Solar Limb Observed with
SUMER/SoHO. Relation to Spicules
Authors: Giannikakis, J.; Tsiropoula, G.; Tziotziou, K.; Antonopoulou,
E.; Doyle, J. G.
2006AIPC..848..115G Altcode:
We study the broadening of EUV line widths as we move from the
disk through and off the solar limb. This broadening maximizes at
approximately 10 Mm above the limb. We use one raster scan and two
time series obtained by SUMER/SoHO to examine a possible correlation
between this phenomenon and spicule activity. It appears that spicule
presence leads to even wider profiles whereas the appearance of
macrospicules extends the broadening to even greater distances above
the limb. We suggest that this correlation might imply that spicules
are responsible for this disk-to-limb behavior even in regions where
they cannot be observed.
---------------------------------------------------------
Title: Hα Chromospheric Mottles and their UV/EUV Counterparts Seen
by SOHO/Sumer
Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G.; Schühle, U.
2006ESASP.617E.112T Altcode: 2006soho...17E.112T
No abstract at ADS
---------------------------------------------------------
Title: Line broadening of EUV lines across the solar limb observed
by SUMER/SOHO
Authors: Tsiropoula, G.; Giannikakis, J.; Tziotziou, K.; Antonopoulou,
E.
2006IAUS..233..183T Altcode:
We analyze time series scans of the solar limb performed by the
spectrometer SUMER on-board the SoHO satellite. The analyzed dataset
consists of observations obtained in the C III 977 Å line. After
applying the standard SUMER data reduction procedure, we perform a
one line Gaussian fit to the profiles to obtain different parameters
for each pixel within the scans. Studying the variations of the line
width from the disk to the limb and off-limb we find that it increases
off-limb and shows a peak at ∼15” above the limb. We suggest that
this increase is due to the random directions of several spicules
found along the line of sight.
---------------------------------------------------------
Title: Chromospheric fine structure studies
Authors: Tziotziou, Kostas; Tsiropoula, G.
2006IAUS..233..173T Altcode:
Mottles and spicules are the most prominent, short-lived, dynamic
features residing at the quiet Sun chromospheric network and constitute
what is known as chromospheric fine structure. We are reporting a
comprehensive study of the dynamical characteristics and physical
properties of such structures, from multi-wavelength observations,
using line inversion techniques and a wavelet spectral analysis. We
are furthermore examining their dynamical evolution and their periodic
bi-directional velocity behaviour, their interrelationship and their
association with the underlying magnetic field which seems to be
their forming and driving mechanism. These studies are crucial to
understanding the dynamics of the solar chromosphere, as well as
the role such structures play in the mass balance and heating of the
overlying solar atmosphere.
---------------------------------------------------------
Title: Physical Parameters of Dark Mottles Derived from High
Resolution Optical Spectra
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Kotrč, P.;
Heinzel, P.
2005ESASP.600E..72T Altcode: 2005ESPM...11...72T; 2005dysu.confE..72T
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Umbral Oscillations and Running Waves
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2005ESASP.600E..15T Altcode: 2005dysu.confE..15T; 2005ESPM...11...15T
No abstract at ADS
---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. V. Analysis of a
surge from AR10486
Authors: Tziotziou, K.; Tsiropoula, G.; Sütterlin, P.
2005A&A...444..265T Altcode:
We present an analysis of high temporal and spatial resolution CaII H
chromospheric limb observations obtained with the Dutch Open Telescope
(DOT). We focus on a solar surge observed both by the DOT in CaII H and
the Transition Region and Coronal Explorer (TRACE) satellite in the
195 Å and 1600 Å passbands. The surge is observed in active region
AR10486 located near the solar limb, a region which two hours later
produced the largest X-flare ever recorded. It consists of relatively
cold gas of about 10<SUP>4</SUP>-10<SUP>5</SUP> K. In TRACE images
the surge is followed for almost 2.5 h, shrinking and expanding at
the same location several times. From DOT images we find outward
propagating intensity disturbances, with velocities higher than 50
km s<SUP>-1</SUP>, indicative of upward material motion. The latter
is also suggested by the good correlation between the DOT and TRACE
surge apparent height curves, their apparent time delay and a phase
difference analysis. A spectral wavelet analysis of the brightness
variations within and along the surge shows a predominant period of
~6 min, the first ever reported for this kind of structures. Magnetic
reconnection at the bottom of the surge as its driving mechanism is
suggested by the observed inverted "Y" shape configuration and is
further supported by a phase difference analysis.
---------------------------------------------------------
Title: Diagnostics of Dark Chromospheric Mottles Based on High
Resolution Spectra I - Observational Data
Authors: Kotrč, P.; Schwartz, P.; Heinzel, P.; Tsiropoula, G.;
Tziotziou, K.
2005HvaOB..29..289K Altcode:
High resolution optical spectra of dark mottles in H and Ca lines
were observed with the Echelle spectrograph of the VTT at Sacramento
Peak Observatory. Until now, only Hα spectra and slit-jaw images
were processed. Used methods of identification of the dark mottles in
the slit-jaw images and in the spectra, as well as a calibration and
correction on the scattered light are described. Individual steps of
the procedure, as well as crucial problems are discussed. The finally
processed line profiles <P />are comparable to the profiles of dark
mottles obtained by other instruments including MSDP.
---------------------------------------------------------
Title: The role of chromospheric mottles in the mass balance and
heating of the solar atmosphere
Authors: Tsiropoula, G.; Tziotziou, K.
2004A&A...424..279T Altcode:
High-resolution Hα observations of a solar region containing several
mottles are analyzed. Mottles constitute the fine structure of the
quiet solar chromosphere and are found at the boundaries of the
network cells, where the magnetic field is mostly concentrated. The
driving mechanism for mottles (as well as for spicules) is suggested
to be magnetic flux cancellation which most likely involves magnetic
reconnection. Magnetic reconnection explains the observed bi-directional
flows and, furthermore, allows conversion of part of magnetic energy to
heat. We estimate several physical parameters of mottles and report a
detailed analysis of their temporal variations. We then consider their
impact on the mass balance and the heating of the solar atmosphere. We
find that less than 1% of the mass flux injected by these structures
into the corona expands outward as solar wind. The major fraction of
this flux returns back to the chromosphere and provides an explanation
for the red-shifts observed in the transition region spectral lines. The
energy released by magnetic dissipation is quantified in terms of
different energy components. Using typical values for the parameters
of these structures it is found that they can provide ∼20% to the
energy budget of the solar corona, but only a small part of it goes
to heating. This percentage, as well as the part of the energy that
goes to heating, can be lower or higher depending on the relative
frequency of these events and on their upward velocity. On the other
hand, if one assumes that all the potential energy of the downflowing
material is converted to heat the amount supplied to the chromosphere
is really negligible.
---------------------------------------------------------
Title: On the nature of the chromospheric fine
structure. II. Intensity and velocity oscillations of dark mottles
and grains
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2004A&A...423.1133T Altcode:
We study periodicities of dark mottles and grains observed in
high spatial and temporal resolution Hα 2-D intensity and velocity
images, obtained with the Multichannel Subtractive Double Pass (MSDP)
spectrograph at THEMIS in Tenerife, Canary Islands. Intensity and
velocity variations of individual mottles and grains, as well as of
large regions containing a substantial number of these structures
are examined with a wavelet analysis which provides the temporal
distribution of periods and with a randomization method that gives
the respective probabilities associated with them. The wavelet
analysis, which shows that velocity variations are the dominant
ones, results in a wide range of periods, from 100 to 500 s, with
variable probabilities. However, it strongly indicates the presence
of a predominant period of ∼5 min seen in both dark mottle and grain
oscillations. We suggest that differences in periods found in individual
mottles as well as in averages of regions containing these structures
are due to the topology of the local magnetic field which can affect
oscillatory processes. We report for the first time oscillations of
dark grains which are more likely vertical structures “anchored"
in the photosphere. The analysis supports further the suggestion that
dark mottles and grains are the same structures, the only difference
between them being their respective inclinations to the line-of-sight.
---------------------------------------------------------
Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
K.; de Wijn, A. G.
2004IAUS..223..597R Altcode: 2005IAUS..223..597R
The Dutch Open Telescope (DOT) on La Palma is an innovative solar
telescope combining open telescope structure and an open support tower
with a multi-wavelength imaging assembly and with synchronous speckle
cameras to generate high-resolution movies which sample different
layers of the solar atmosphere simultaneously and co-spatially at high
resolution over long durations. The DOT test and development phase is
nearly concluded. The installation of an advanced speckle processor
enables full science utilization including "Open-DOT" time allocation
to the international community. Co-pointing with spectropolarimeters
at other Canary Island telescopes and with TRACE furnishes valuable
Solar-B precursor capabilities.
---------------------------------------------------------
Title: Mass and Energy Supply of Fine Structure to the Solar Corona
Authors: Tziotziou, K.; Tsiropoula, G.
2004IAUS..219..123T Altcode: 2003IAUS..219E..96T
We investigate the role of chromospheric fine structures e.g. mottles
(spicules) and dark grains in the mass balance and heating of the
solar atmosphere by studying two-dimensional high-resolution Ha
observations. The temporal and spatial variations of the line-of-sight
velocity obtained with an inversion technique based on a cloud model
provide strong indications that the mechanism responsible for the
driving of the observed flows is magnetic reconnection. Apart from
the line-of-sight velocity application of the cloud model enables
the derivation of several other physical parameters like pressure
temperature density etc. The temporal evolution of these parameters
permits the estimation of the role of these structures in the mass
balance of the solar atmosphere. Furthermore the energy balance between
the released magnetic energy during reconnection and the associated
kinetic and thermal energy provides a reasonable estimate of the energy
available for the heating of the solar atmosphere.
---------------------------------------------------------
Title: Parameters of dark mottles based on high resolution optical
spectra
Authors: Kotrc, P.; Heinzel, P.; Tziotziou, K.; Tsiropoula, G.
2004IAUS..223..275K Altcode: 2005IAUS..223..275K
High resolution optical spectra of hydrogen and calcium lines
observed with the Echelle spectrograph of the VTT at Sacramento Peak
Observatory were analyzed. The observed line profiles in some parts
of dark chromospheric mottles are to be matched with theoretical ones
using the cloud model and several parameters (e.g. the temperature,
gas pressure, flow velocity) are to be derived. Individual steps of
the procedure, as well as crucial problems are discussed.
---------------------------------------------------------
Title: On the Nature of Chromospheric Umbral Flashes And Running
Penumbral Waves (Abstract)
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2004hell.conf...50T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Role of Spicules in the Mass Balance and Energy Budget
of the Solar Atmosphere (Abstract)
Authors: Tsiropoula, G.; Tziotziou, K.
2004hell.confR..64T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spectroscopic diagnostics of an Hα and EUV filament observed
with THEMIS and SOHO
Authors: Schmieder, B.; Tziotziou, K.; Heinzel, P.
2003A&A...401..361S Altcode:
A long filament has been observed with THEMIS/MSDP and SOHO/CDS -
SUMER, during a coordinated campaign (JOPs 131/95) on May 5, 2000. The
data were (a) 2-D Hα spectra, observed using THEMIS, (b) Lyman series
spectra and Lyman continuum, observed using SOHO/SUMER, and (c) EUV
spectra (in O V 629 Å, Mg X 624 Å, Si Xii 520 Å, Ca X 557 Å and
He I 584 Å) observed using SOHO/CDS. A large depression of the line
emissions in CDS images represents the EUV filament. A computed model
shows that the EUV filament consists of an extended in height cloud of
low gas pressure at an altitude lower than the top of the Hα filament,
volume-blocking and absorbing coronal emission and absorbing transition
region line emission. The optical thickness of the Lyman continuum is
estimated by using the ratio of O V intensity inside and outside the
EUV filament, while the optical thickness of Hα is computed from the
Hα line profile by using an inversion technique. Using simultaneous
Hα , Lyman lines and Lyman continuum spectroscopic data, we performed
detailed, non-LTE radiative transfer diagnostics of the filament plasma
conditions. The optical thickness of the Lyman continuum is larger than
that of the Hα line by one to two orders of magnitude. This could be
of a great importance for filament formation modeling, if we consider
that more cool material exists in filament channels but is optically
too thin to be visible in Hα images.
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Title: On the nature of the chromospheric fine structure. I. Dynamics
of dark mottles and grains
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2003A&A...402..361T Altcode:
We analyze a time series of forty high spatial and temporal resolution
two-dimensional intensity and Doppler velocity images at different
wavelengths within the Hα line. The observations were obtained with the
Multichannel Subtractive Double Pass (MSDP) spectrograph at THEMIS. We
study the morphology of dark mottles and grains as seen in different
wavelengths and examine their relation to the MDI magnetic field
topology. We determine some physical properties of dark mottles with
an inversion technique based on an iterative cloud model method with
constant source function, giving the optical thickness tau<SUB>0</SUB>,
the Doppler width Delta lambda<SUB>D</SUB> , the velocity v and the
source function S distribution along a structure. The obtained global
properties of mottles as well as the spatial and temporal evolution of
several physical parameters along the axes of individual mottles are
discussed. The derived velocities in mottles as a function of space
and time (time slice images) exhibit a quasi-periodic, bi-directional
pattern. It is suggested that magnetic reconnection is the mechanism
responsible for their formation and dynamics. Furthermore, a similar
quasi-periodic behaviour of the Doppler velocity variations in dark
grains and their morphological characteristics both suggest the
similarity of dark mottles and grains.
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Title: The role of chromospheric mottles in the mass balance and
heating of the solar atmosphere
Authors: Tziotziou, K.; Tsiropoula, G.
2002ESASP.506..787T Altcode: 2002svco.conf..787T; 2002ESPM...10..787T
High-resolution Hα observations of a solar region containing several
mottles were obtained with the Multichannel Subtractive Double Pass
(MSDP) spectrograph installed at the focus of THEMIS in Tenerife
(Canary islands). Applications of the cloud model to measurements of
the Hα contrast profiles enabled us to derive numerical values for
several physcial parameters. A detailed analysis of the temporal and
spatial variation of these parameters was performed. The variation of
the line-of-sight velocity showing upflows at the tops and downflows
at the footpoints of the structures provides an indication that the
mechanism that drives the flow along them is magnetic reconnection. The
derived parameters in combination with information concerning their
number on the solar surface permitted us to make estimates for the mass
flux curried upwards the solar atmosphere. Moreover, a rough estimate
of the magnetic energy dissipated at the reconnection region provided
us with an estimate of the energy content available for the heating
of the solar atmosphere.
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Title: Chromospheric fine structure dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2002ESASP.505..163T Altcode: 2002solm.conf..163T; 2002IAUCo.188..163T
We investigate the dynamics of chromospheric mottles observed with
THEMIS. We study a half an hour time series of 2-D intensity and
Doppler velocity images at different wavelengths within the Hα
line, obtained with the Multichannel Subtractive Double Pass (MSDP)
spectrograph with a cadence of 40.5 sec. We determine the physical
parameters in dark mottles with an inversion technique which is based
on an iterative cloud model method with constant source function. With
this method we calculate the optical thickness τ<SUB>max</SUB>,
the Doppler width Δλ<SUB>D</SUB>, the velocity v and the source
function S describing the structure. We discuss the results of the
inversion technique and show the spatial and temporal evolution of
several physical parameters along the axes of individual mottles. The
pattern of the derived velocities as a function of space and time
(time slice images) suggests the presence of magnetic reconnection as
the driving mechanism of their formation.
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Title: Theoretical hydrogen population relations for horizontal
cloud-like solar structures
Authors: Tziotziou, K.; Mein, N.; Mein, P.; Heinzel, P.
2002ESASP.477..183T Altcode: 2002scsw.conf..183T
A large set of parameterized NLTE models has been computed for a 1D
horizontal cloud-like structure standing above the solar surface. The
used input model parameters are temperature, velocity, microturbulence,
electronic density and geometrical thickness of the structure. From
the output of our computations which is the hydrogen level populations
as a function of the line center optical depth, we calculate several
relations between the hydrogen population levels and the considered
electron density. These relations are important for the study of
prominence-like structures from observations.
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Title: Ca II 8542 Å sunspot oscillations observed with THEMIS
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2002A&A...381..279T Altcode:
Oscillations in the umbra and the penumbra of an isolated sunspot
located near the solar disk centre were investigated. The observations
were obtained with the Multichannel Subtractive Double Pass (MSDP)
spectrograph operating in the Ca Ii 8542 Å line and installed at
the focus of THEMIS (Tenerife). From the MSDP data, two-dimensional
intensity and Doppler shift images were computed at different
wavelengths within the line. Intensity and Doppler shift oscillations
in the umbra and the penumbra of the sunspot showing up as umbral
flashes and penumbral waves were analyzed using a 23 min time series
with a cadence of 46 s. The Ca Ii umbral flash intensity profile shows
an emission core in its blue wing. We investigate the relation between
umbral flashes and running penumbral waves by a power spectrum analysis
which shows a 6 mHz frequency for the standing umbral oscillations
(flashes) which are observed only on the upper half part of the
umbra. The running penumbral waves propagate with an average phase
velocity of 16 km s<SUP>-1</SUP> and their frequency is constant in the
penumbra and equal to 3 mHz. Although the time slice images suggest
that umbral flashes and running penumbral waves are probably due to
the same resonator, the power analysis shows no direct relationship
between the two phenomena. Based on observations made with the THEMIS
telescope operated on the island of Tenerife by CNRS-CNR in the Spanish
Observatorio del Teide of the Instituto de Astrof{ísica de Canarias.
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Title: Recent results from THEMIS/MSDP campaigns
Authors: Tziotziou, K.; Mein, P.
2002joso.book..129T Altcode:
We present recent results based on observations of the 2000 campaign
with the Multichannel Subtractive Double Pass (MSDP) spectrograph of the
solar telescope THEMIS. The MSDP spectrograph permits the simultaneous
recording of line profiles at every pixel of a two-dimensional solar
image. We show results based on inversion methods developed for the
study of THEMIS observations, either with the use of a non-LTE grid of
line profiles or with the use of response functions. We also discuss
results concerning sunspot observations and in particular a study
of magnetic field gradients in the umbra of sunspots and a study of
oscillatory phenomena like umbral flashes and running penumbral waves.
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Title: Why Are Solar Filaments More Extended in Extreme-Ultraviolet
Lines than in Hα?
Authors: Heinzel, P.; Schmieder, B.; Tziotziou, K.
2001ApJ...561L.223H Altcode:
A long solar filament was observed simultaneously in the Hα line
by THEMIS/MSDP and in selected EUV lines by the Coronal Diagnostic
Spectrometer on SOHO. Co-alignment of optical and EUV images reveals
that the dark EUV filament is much more extended than the Hα
filament. Assuming that the EUV filament represents Lyman continuum
absorption of the background EUV-line radiation, a straightforward
explanation of this effect is suggested. Based on non-LTE filament
models, we demonstrate that the ratio of the Lyman continuum to Hα
opacity can reach a factor of 50-100, and thus the EUV filament is
still well visible while the Hα line contrast diminishes below the
detection limit. This kind of interpretation leads to an important
conclusion that the cool filament material in which the Lyman continuum
absorption takes place is more abundant than one would expect from
Hα disk observations. This then may have significant consequences
on the filament structure and on formation models, as well as on mass
considerations related to coronal mass ejections.
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Title: 2D spectroscopy and science with THEMIS
Authors: Tziotziou, K.; Mein, P.; Tsiropoula, G.; Eibe, T.
2001hell.confE..25T Altcode:
No abstract at ADS
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Title: Non-LTE inversion of chromospheric {\Ca Ii} cloud-like features
Authors: Tziotziou, K.; Heinzel, P.; Mein, P.; Mein, N.
2001A&A...366..686T Altcode:
A chromospheric cloud-like feature observed in the 8542 Å {{Ca Ii}
line is studied by a two step inversion procedure which provides
estimates of its temperature, electronic density, microturbulence,
geometrical thickness and bulk velocity. The first step involves the
computation of a large grid of models by a multi-level non-LTE transfer
code which gives the {{Ca Ii} line depth-dependent mean intensity
inside an isolated, isothermal cloud lying above the chromosphere. The
second step involves the inversion of the observed profiles with the
grid of computed synthetic {{Ca Ii} profiles. A searching and matching
chi <SUP>2</SUP> algorithm is implemented followed by an interpolation
algorithm which permits a more accurate determination of the parameters
on which the profiles depend. The five grid parameters are reduced to
four by defining the emission measure from the geometrical thickness
and electronic density. We show that this inversion procedure gives
accurate results for some of our inversion parameters when dealing
with solar filaments and is complementary to a previous study of the
same object in the {{Hα }} line. The main advantages, problems and
future extension of the inversion approach are also discussed.
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Title: Study of Chromospheric Ca II Cloud-like Structures
Authors: Tziotziou, K.; Heinzel, P.; Mein, P.; Mein, N.
2000ESASP.463..443T Altcode: 2000sctc.proc..443T
No abstract at ADS
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Title: Energy and momentum deposition in coronal holes. Solar
coronal hole simulations compared with interpretations of YOHKOH
SXT observations
Authors: Tziotziou, K.; Martens, P. C. H.; Hearn, A. G.
1998A&A...340..203T Altcode:
A grid of 74 coronal models with parameterized heating distribution,
representing a wide range of physical parameters, has been
calculated. We find that three of these models reproduce the recent
observations made by Hara et al. (\cite{hara:tsun}) with the soft
X-ray telescope aboard the Japanese satellite Yohkoh, which indicate
a temperature of 1.8 ~ 2.4 x es 10(6) { K with an emission measure
of 10(25.5) to 10(26.2) cm^{-5}, while other solutions reproduce the
more standard Yohkoh and Skylab observations, which have a temperature
of about 1.4 x es 10(6) { K The best fit for the coronal temperature
and emission measure gives a velocity at the Earth's orbit of only
10 {km s^{-1}. A model including acceleration by Alfven waves gives
a final velocity of 630 km s^{-1} which is in agreement with the
observations. The mechanical heating flux at the transition region
is 2.1 x es 10(5) ergcms with a weighted average dissipation scale
length of 0.1 R_{\odot}. The flux of Alfven waves is 1 x es 10(5)
ergcms . In our models the velocity of the solar wind from coronal
holes is completely determined by the Alfven wave acceleration, in
contrast to previous models in which the Alfven wave acceleration
increased the velocity of the purely thermal model only by a factor
2. Observations of the non thermal broadening of the coronal red and
green lines are consistent with this model.
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Title: Dynamics of stellar coronae
Authors: Tziotziou, Konstantinos
1997PhDT.......223T Altcode:
No abstract at ADS
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Title: Solar coronal hole simulations compared with interpretations
of YOHKOH SXT observations
Authors: Tziotziou, K.; Hearn, A. G.
1995sowi.conf...63T Altcode:
Recent observations of coronal holes made with the soft X-ray telescope
aboard Yohkoh have indicated a temperature of 1.8 approximately 2.1 x
10<SUP>6</SUP> K and an emission measure of 10<SUP>25.7 approximately
26.2</SUP> cm <SUP>-5</SUP>. This is almost the same as in quiet
regions of the Sun. Numerical simulations of the temperature density
and velocity structure in a coronal hole. using a parameterized
heating distribution have been used for a comparison with the Yohkoh
observations. Models are obtained which fit the observed temperature
and emission measure. with heating fluxes which are consistent with
other measurements. However, the final velocity of the solar wind
is very slow which indicates the necessity of another acceleration
mechanism such as alfven waves.