Author name code: tsiropoula
ADS astronomy entries on 2022-09-14
author:"Tsiropoula, Georgia"
------------------------------------------------------------------------
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
Bibcode: 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.
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
Bibcode: 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.
Title: Chromospheric swirls. I. Automated detection in Hα
observations and their statistical properties
Authors: Dakanalis, I.; Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.
Bibcode: 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.
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.
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.
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−2 and the occurrence rate is ∼10−2 swirls
Mm−2 min−1. 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.
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. Movies is available at https://www.aanda.org
Title: Automated Detection of Chromospheric Swirls Based on Their
Morphological Characteristics
Authors: Dakanalis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas;
Koutroumbas, Konstantinos
Bibcode: 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.
Title: A persistent quiet-Sun small-scale tornado. III. Waves
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.
Bibcode: 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.
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.
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.
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-1. 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.
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.
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.
Bibcode: 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.
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.
Bibcode: 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.
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.
Methods: We used imaging
as well as spectral and spectropolarimetric observations from a suite
of space-borne and ground-based instruments.
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.
Conclusions:
The emergence of magnetic flux even at the smallest scales can be the
driver of a series of energetic phenomena visible at various atmospheric
heights and temperature regimes. Multi-wavelength observations reveal
a wealth of mechanisms which produce diverse observable effects during
the different evolutionary stages of these small-scale structures.
Title: A persistent quiet-Sun small-scale tornado. II. Oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.
Bibcode: 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.
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.
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.
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.
Conclusions: The vortex flow seems to be dominated by two motions:
a transverse (swaying) motion, and a rotational motion. The obtained
oscillations point to the propagation of waves within it. Nearby
fibril-like flows could play an important role in the rotational
modulation of the vortex flow. There also exists indirect evidence that
the structure is magnetically supported, and one of the swirls, close to
its centre, seems to be acting as a "central engine" to the vortex flow.
Title: A persistent quiet-Sun small-scale tornado. I. Characteristics
and dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion,
E.; Doyle, J. G.
Bibcode: 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.
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.
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.
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-1 and
up to 8 km s-1, 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-1, 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.
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. The movie associated to Fig. 4 is available at https://www.aanda.org
Title: Probing the Quiet Solar Atmosphere from the Photosphere to
the Corona
Authors: Kontogiannis, Ioannis; Gontikakis, Costis; Tsiropoula,
Georgia; Tziotziou, Kostas
Bibcode: 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 ×104K to
6 ×105K. 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: Solar Particle Radiation Storms Forecasting and Analysis
within the Framework of the `HESPERIA' HORIZON 2020 Project
Authors: Posner, A.; Malandraki, O.; Nunez, M.; Heber, B.; Labrenz,
J.; Kühl, P.; Milas, N.; Tsiropoula, G.; Pavlos, E.
Bibcode: 2017AGUFMSH21A2638P
Altcode:
Two prediction tools that have been developed in the
framework of HESPERIA based upon the proven concepts UMASEP and
REleASE. Near-relativistic (NR) electrons traveling faster than
ions (30 MeV protons have 0.25c) are used to forecast the arrival
of protons of Solar Energetic Particle (SEP) events with real-time
measurements of NR electrons. The faster electrons arrive at L1
30 to 90 minutes before the slower protons. REleASE (Relativistic
Electron Alert System for Exploration, Posner, 2007) uses this effect
to predict the proton flux by utilizing actual electron fluxes and
their most recent increases. Through HESPERIA, a clone of REleASE
was built in open source programming language. The same forecasting
principle was adapted to real-time data from ACE/EPAM. It is shown
that HESPERIA REleASE forecasting works with any NR electron flux
measurements. >500 MeV solar protons are so energetic that they
usually have effects on the ground, producing Ground Level Enhancement
(GLE) events. Within HESPERIA, a predictor of >500 SEP proton events
near earth (geostationary orbit) has been developed. In order to predict
these events, UMASEP (Núñez, 2011, 2015) has been used. UMASEP makes
a lag-correlation of solar electromagnetic (EM) flux with the particle
flux near earth. If the correlation is high, the model infers that
there is a magnetic connection through which particles are arriving. If,
additionally, the intensity of the flux of the associated solar event
is also high, then UMASEP issues a SEP prediction. In the case of
the prediction of >500 MeV SEP events, the implemented system,
called HESPERIA UMASEP-500, correlates X-ray flux with differential
proton fluxes by GOES, and with fluxes collected by neutron monitor
stations around the world. When the correlation estimation and flare
surpasses thresholds, a >500 MeV SEP forecast is issued. These
findings suggest that a synthesis of the various approaches may improve
over the status quo. Both forecasting tools are operational on the
HESPERIA server maintained at the National Observatory of Athens
(https://www.hesperia.astro.noa.gr/). This project received funding
from the EU's Horizon 2020 research and innovation programme under
grant No 637324.
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
Bibcode: 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
Bibcode: 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: The New Solar Telescope at the National Observatory of Athens
Authors: Kontogiannis, I.; Tsiropoula, G.
Bibcode: 2016ASPC..504..317K
Altcode:
In the context of a new space weather facility, the National Observatory
of Athens has installed a small full-disk solar telescope. Its aim is
to provide full disk images of the Sun and active region cut-outs in
the Hα line. Here, we describe the specificiations of the telescope
and the data reduction procedure.
Title: First simultaneous SST/CRISP and IRIS observations of a
small-scale quiet Sun vortex
Authors: Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.; Tziotziou,
K.; Scullion, E.; Doyle, J. G.
Bibcode: 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.
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.
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).
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-1 and (2) an expanding motion at a rate of
4-6 km s-1. 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-1 along with a higher temperature
compared to the nearby quiet Sun chromosphere.
Conclusions:
The consecutive small-scale vortex events can heat the upper
chromosphere by driving continuous high-speed upflows through the lower
atmosphere. Movies associated to Figs. 2 and 3 are available at http://www.aanda.org
Title: Building a new space weather facility at the National
Observatory of Athens
Authors: Kontogiannis, Ioannis; Belehaki, Anna; Tsiropoula, Georgia;
Tsagouri, Ioanna; Anastasiadis, Anastasios; Papaioannou, Athanasios
Bibcode: 2016AdSpR..57..418K
Altcode:
The PROTEAS project has been initiated at the Institute of Astronomy,
Astrophysics, Space Applications and Remote Sensing (IAASARS) of the
National Observatory of Athens (NOA). One of its main objectives is to
provide observations, processed data and space weather nowcasting and
forecasting products, designed to support the space weather research
community and operators of commercial and industrial systems. The space
weather products to be released by this facility, will be the result of
the exploitation of ground-based, as well as space-borne observations
and of model results and tools already available or under development
by IAASARS researchers. The objective will be achieved through: (a)
the operation of a small full-disk solar telescope to conduct regular
observations of the Sun in the H-alpha line; (b) the construction of a
database with near real-time solar observations which will be available
to the community through a web-based facility (HELIOSERVER); (c) the
development of a tool for forecasting Solar Energetic Particle (SEP)
events in relation to observed solar eruptive events; (d) the upgrade
of the Athens Digisonde with digital transceivers and the capability
of operating in bi-static link mode and (e) the sustainable operation
of the European Digital Upper Atmosphere Server (DIAS) upgraded with
additional data sets integrated in an interface with the HELIOSERVER
and with improved models for the real-time quantification of the
effects of solar eruptive events in the ionosphere.
Title: Wave propagation in a solar quiet region and the influence
of the magnetic canopy
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
Bibcode: 2016A&A...585A.110K
Altcode: 2015arXiv151108618K
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.
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.
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.
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.
Bibcode: 2015A&A...581A..61T
Altcode:
Aims: We investigate the free magnetic energy and relative
magnetic helicity injection in solar quiet regions.
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.
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.
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: 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.
Bibcode: 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: 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.
Bibcode: 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.
Bibcode: 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.
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.
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.
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.
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.
Bibcode: 2014A&A...564A..86T
Altcode: 2014arXiv1403.0730T
Aims: We investigate the free magnetic energy and relative
magnetic helicity budgets of solar quiet regions.
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.
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.
Conclusions: Derived instantaneous free magnetic energy
budgets and, to a lesser extent, relative magnetic helicity budgets
over the entire quiet Sun are similar to the respective budgets of a
sizeable active region, while total budgets within a solar cycle are
found to be higher than previously reported. Free-energy budgets are
similar to the energy needed to power fine-scale structures residing
at the network, such as mottles and spicules.
Title: Free magnetic energy and relative magnetic helicity in active
and quiet solar regions and their role in solar dynamics
Authors: Tziotziou, Konstantinos; Archontis, Vasilis; Tsiropoula,
Georgia; Georgoulis, Manolis K.; Moraitis, Kostas; Kontogiannis,
Ioannis
Bibcode: 2014cosp...40E3428T
Altcode:
We present a novel non-linear force-free method for the calculation of
the instantaneous free magnetic energy and relative magnetic helicity
budgets of a solar region from a single photospheric/chromospheric
vector magnetogram. Our objective is to study the role of these
quantities both in solar eruptions and in quiet-Sun dynamics. The
validity of the method is tested using both observations and synthetic
magnetohydrodynamical (MHD) models. The method is applied for the
derivation of the energy-helicity (EH) diagram of solar active regions
(ARs) from a sample of 162 vector magnetograms corresponding to 42
different ARs, suggesting the existence of 4×10(31) erg and 2×10(42)
Mx(2) thresholds in free energy and relative helicity, respectively, for
ARs to enter eruptive territory. Furthermore, the dynamical evolution
of both quantities in eruptive NOAA AR 11158, using a high-cadence
5-day time series of vector magnetograms, suggests the formation of
increasingly helical pre-eruption structures and a causal relation
between flares and Coronal Mass Ejections (CMEs). The method is
also used to derive helicity and energy budgets in quiet Sun regions
and construct the respective EH diagram. Our results highlight the
importance of both energy and helicity in AR evolution and quiet-Sun
dynamics and instigate further research on the underlying physics with
three-dimensional MHD models. This work is supported by EU's Seventh
Framework Programme via a Marie Curie Fellowship.
Title: Free Magnetic Energy and Helicity in Active and Quiet Solar
Regions and their role in Solar
Authors: Tziotziou, K.; Georgoulis, M. K.; Tsiropoula, G.; Moraitis,
K.; Kontogiannis, I.
Bibcode: 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.
Bibcode: 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: Mode conversion and transmission of waves in quiet solar
regions
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia; Tziotziou,
Konstantinos
Bibcode: 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: Compiling a STEREO SEP event list: 2007-2011
Authors: Papaioannou, Athanasios; Malandraki, Olga E.; Heber, Bernd;
Dresing, Nina; Klein, Karl-Ludwig; Tsiropoula, Georgia; Gomez-Herrero,
Raoul; Mewaldt, Richard A.; Vainio, Rami
Bibcode: 2013EGUGA..15.7792P
Altcode:
The STEREO (Solar TErrestrial RElations Observatory) mission employs
two nearly identical space-based observatories - one ahead of Earth in
its orbit (STEREO-A: STA), the other trailing behind (STEREO-B: STB)
aiming at providing the first-ever stereoscopic measurements of the
Sun. STEREO 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 to GOES Soft X-rays and coronal
mass ejections spotted by both SOHO/LASCO and STEREO Coronographs.
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.
Bibcode: 2012SSRv..169..181T
Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T
Over the last two decades the uninterrupted, high resolution
observations of the Sun, from the excellent range of telescopes aboard
many spacecraft complemented with observations from sophisticated
ground-based telescopes have opened up a new world producing
significantly more complete information on the physical conditions of
the solar atmosphere than before. The interface between the lower solar
atmosphere where energy is generated by subsurface convection and the
corona comprises the chromosphere, which is dominated by jet-like,
dynamic structures, called mottles when found in quiet regions,
fibrils when found in active regions and spicules when observed at
the solar limb. Recently, space observations with Hinode have led to
the suggestion that there should exist two different types of spicules
called Type I and Type II which have different properties. Ground-based
observations in the Ca ii H and K filtergrams reveal the existence of
long, thin emission features called straws in observations close to
the limb, and a class of short-lived events called rapid blue-shifted
excursions characterized by large Doppler shifts that appear only
in the blue wing of the Ca ii infrared line. It has been suggested
that the key to understanding how the solar plasma is accelerated
and heated may well be found in the studies of these jet-like,
dynamic events. However, while these structures are observed and
studied for more than 130 years in the visible, but also in the UV
and EUV emission lines and continua, there are still many questions
to be answered. Thus, despite their importance and a multitude of
observations performed and theoretical models proposed, questions
regarding their origin, how they are formed, their physical parameters,
their association with the underlying photospheric magnetic field, how
they appear in the different spectral lines, and the interrelationship
between structures observed in quiet and active regions on the disk
and at the limb, as well as their role in global processes has not
yet received definitive answers. In addition, how they affect the
coronal heating and solar wind need to be further explored. In this
review we present observations and physical properties of small-scale
jet-like chromospheric events observed in active and quiet regions,
on the disk and at the limb and discuss their interrelationship.
Title: Study of spicules observed in the CaII H and Ha lines with
Hinode/SOT
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
Bibcode: 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.
Bibcode: 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: 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.
Bibcode: 2011A&A...531A..66K
Altcode:
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.
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.
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.
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.
Bibcode: 2010A&A...524A..12K
Altcode:
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.
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.
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.
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: Comparative Analysis of Oscillations of a Solar Quiet Region
Using Multi-Wavelength Observations
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
Bibcode: 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: Power halo and magnetic shadow in a solar quiet region observed
in the Hα line
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
Bibcode: 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.
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.
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.
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.
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: Study of spicules observed in the Ca II H and Ha lines with
Hinode/SOT
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia
Bibcode: 2010cosp...38.2949K
Altcode: 2010cosp.meet.2949K
We use a dataset of simultaneous image sequences obtained by Hinode/SOT
with the Ca II H filter, as well as in Hα ±0.2 ˚. SOT was looking at
the SW solar limb. The high temporal A and spatial resolution allows us
to study the structure and dynamics of spicules seen at the different
filters. Individual spicules have been selected and intensity and
velocity distributions at different heights along their central axes are
examined along with transversal fluctuations. Their temporal variations
are also examined through wavelet and phase difference analyses
Title: The dynamic solar chromosphere: recent advances from high
resolution telescopes
Authors: Tziotziou, Konstantinos; Tsiropoula, Georgia
Bibcode: 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
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
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.
Methods: Intensity and velocity variations are
studied with wavelet and phase difference analyses.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 2007A&A...472..287T
Altcode:
Context: Atmospheric seeing due to terrestrial atmospheric turbulence
is a process that distorts solar ground-based observations.
Aims: We study the influence of atmospheric seeing on Hα cloud
model inversions.
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.
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.
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: Multi-wavelength Analysis of a Quiet Solar Region
Authors: Tsiropoula, G.; Tziotziou, K.; Giannikakis, J.; Young, P.;
Schühle, U.; Heinzel, P.
Bibcode: 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.
Bibcode: 2007A&A...463.1153T
Altcode:
Context: Sunspots exhibit a wide range of oscillatory phenomena within
their umbrae and penumbrae.
Aims: We investigate the behavior
of intensity and Doppler velocity oscillations in the umbra and the
penumbra to study sunspot oscillations and their associations.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 2006A&A...456..689T
Altcode:
Context: .Umbral flashes (UFs) and running penumbral (RP) waves are
believed to be closely related oscillatory phenomena of sunspots.
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.
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.
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.
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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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: Multiwavelength Analysis of an Active Region
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th. G.;
Alissandrakis, C. E.; Nindos, A.; Vial, J. -C.; Tsiropoula, G.
Bibcode: 2006SoPh..233...57G
Altcode:
We study active region NOAA 8541, observed with instruments on board
SOHO, as well as with TRACE. The data set mainly covers the transition
region and the low corona. In selected loops studied with SUMER on SOHO,
the VIII 770 Å line is systematically redshifted. In order to estimate
the plasma velocity, we combine the Doppler shifts with proper motions
(TRACE) along these loops. In the case of an ejection, apparently
caused by the emergence of a parasitic polarity, proper motions and
Doppler shifts give consistent results for the velocity. A cooler loop,
observed in the same active region with CDS, shows a unidirectional
motion reminiscent of a siphon flow. The derived electron temperature
and density along a large steady loop confirm that it cannot be
described by hydrostatic models.
Title: Physical Parameters of Dark Mottles Derived from High
Resolution Optical Spectra
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Kotrč, P.;
Heinzel, P.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 104-105 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-1, 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: October/November 2003 interplanetary coronal mass ejections:
ACE/EPAM solar energetic particle observations
Authors: Malandraki, O. E.; Lario, D.; Lanzerotti, L. J.; Sarris,
E. T.; Geranios, A.; Tsiropoula, G.
Bibcode: 2005JGRA..110.9S06M
Altcode: 2005JGRA..11009S06M
In late October and early November 2003 the ACE spacecraft at 1 AU
detected two shock-associated interplanetary coronal mass ejections
(ICMEs). In the sheath region formed in front of both ICMEs, some
of the highest speeds ever directly measured in the solar wind were
observed. We analyze in detail the energetic particle signatures
measured at 1 AU by the EPAM experiment on board ACE during the passage
and in the vicinity of these ICMEs. Solar energetic particles (SEPs)
are utilized as diagnostic tracers of the large-scale structure and
topology of the interplanetary magnetic field (IMF) embedded within
both ICME events. In order to explain the bidirectional particle
flows observed within both ICMEs, we have examined two candidate
scenarios for these ICMEs in terms of open and closed magnetic field
configurations. In the context of an open field configuration, the
enhanced magnetic field regions associated with the CME-driven shocks
mirror the energetic particles and hence the observed bidirectional
flows. In the context of a closed field configuration, bidirectional
flows result from particle circulation and reflection in a looped
field configuration. Furthermore, we use the ACE/EPAM observations to
reassess the leading and trailing boundaries of the ICMEs with respect
to those previously proposed based upon ACE/SWEPAM solar wind plasma,
suprathermal electron measurements, and ACE/MAG magnetic field data.
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.
Bibcode: 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 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.
Bibcode: 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.
Bibcode: 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: Mass and Energy Supply of Fine Structure to the Solar Corona
Authors: Tziotziou, K.; Tsiropoula, G.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 2004hell.confR..64T
Altcode:
No abstract at ADS
Title: Tracing the Magnetic Topology of the July 2000 Coronal Mass
Ejection Event at 62% South Heliolatitude By Means of ULYSSES/HI-SCALE
> 38 KeV Electron Observations
Authors: Malandraki, O. E.; Sarris, E. T.; Trochoutsos, P.;
Tsiropoula, G.
Bibcode: 2004hell.conf...51M
Altcode:
No abstract at ADS
Title: Magnetic topology of coronal mass ejection events out of the
ecliptic: Ulysses/HI-SCALE energetic particle observations
Authors: Malandraki, O. E.; Sarris, E. T.; Tsiropoula, G.
Bibcode: 2003AnGeo..21.1249M
Altcode:
Solar energetic particle fluxes (Ee > 38 keV) observed by the
ULYSSES/HI-SCALE experiment are utilized as diagnostic tracers of the
large-scale structure and topology of the Interplanetary Magnetic Field
(IMF) embedded within two well-identified Interplanetary Coronal Mass
Ejections (ICMEs) detected at 56° and 62° south heliolatitudes by
ULYSSES during the solar maximum southern high-latitude pass. On the
basis of the energetic solar particle observations it is concluded that:
(A) the high-latitude ICME magnetic structure observed in May 2000
causes a depression in the solar energetic electron intensities which
can be accounted for by either a detached or an attached magnetic field
topology for the ICME; (B) during the traversal of the out-of-ecliptic
ICME event observed in July 2000 energetic electrons injected at the
Sun are channeled by the ICME and propagate freely along the ICME
magnetic field lines to 62° S heliolatitude.
Title: On the nature of the chromospheric fine structure. I. Dynamics
of dark mottles and grains
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
Bibcode: 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 tau0,
the Doppler width Delta lambdaD , 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.
Title: Signatures of solar activity variability in meteorological
parameters
Authors: Tsiropoula, G.
Bibcode: 2003JASTP..65..469T
Altcode: 2003JATP...65..469T
Solar radiation (both total and in various wavelengths) varies
at different time scales-from seconds to decades or centuries-as
a consequence of solar activity. The energy received from the Sun
is one of the natural driving forces of the Earth's atmosphere and
since this energy is not constant, it has been argued that there must
be some non-zero climate response to it. This response must be fully
specified in order to improve our understanding of the climate system
and the impact of anthropogenic activities on it. However, despite
all the efforts, if and how subtle variations of solar radiation
affect climate and weather still remains an unsolved puzzle. One key
element that is very often taken as evidence of a response, is the
similarity of periodicities between several solar activity indices
and different meteorological parameters. The literature contains a
long history of positive or negative correlations between weather and
climate parameters like temperature, rainfall, droughts, etc. and
solar activity cycles like the 27-day cycle, the prominent 11-year
sunspot cycle, the 22-year Hale cycle and the Gleissberg cycle of 80-90
years. A review of these different cycles is provided as well as some
of the correlative analyses between them and several stratospheric
parameters (like stratospheric geopotential heights, temperature and
ozone concentration) and tropospheric parameters (like temperature,
rainfall, water level in lakes and river flooding, clouds) that
point to a relationship of some kind. However, the suspicion on these
relationships will remain as long as an indisputable physical mechanism,
which might act to produce these correlations, is not available.
Title: The role of chromospheric mottles in the mass balance and
heating of the solar atmosphere
Authors: Tziotziou, K.; Tsiropoula, G.
Bibcode: 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.
Title: Study of coronal loops using TRACE and SOHO
Authors: Gontikakis, C.; Dara, H. C.; Zachariadis, Th.; Nindos, A.;
Alissandrakis, C.; Tsiropoula, G.; Vial, J. -C.
Bibcode: 2002ESASP.505..417G
Altcode: 2002solm.conf..417G; 2002IAUCo.188..417G
We analysed coronal loops observed in many spectral lines from TRACE and
SUMER, at the active region NOAA 8541, on May 15, 1999. For the loops,
which are identified in a number of wavelengths, we try to combine
the good temporal and spatial resolution of TRACE with the spectral
information obtained by the SUMER rasters, in order to determine some
physical parameters such as temperature, flow velocity and electron
density. The morphology of the magnetic field of the loops is also
approximated by a force-free extrapolation of the photospheric magnetic
field, measured with MDI, and is compared to the loop morphology.
Title: Preface (SOLMAG 2002)
Authors: Tsiropoula, Georgia; Schühle, Udo
Bibcode: 2002ESASP.505D..13T
Altcode: 2002IAUCo.188D..13T; 2002solm.confD..13T
No abstract at ADS
Title: Chromospheric fine structure dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
Bibcode: 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 τmax,
the Doppler width ΔλD, 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.
Title: Multiwavelength analysis of an active region observed with
SOHO and TRACE
Authors: Dara, H. C.; Gontikakis, C.; Zachariadis, Th.; Tsiropoula,
G.; Alissandrakis, C. E.; Vial, J. -C.
Bibcode: 2002ESASP.477...95D
Altcode: 2002scsw.conf...95D
We study the solar active region NOAA 8541, observed on May 15, 1999,
from 13:00 to 15:00 UT, with the instruments aboard SOHO (SUMER,
CDS, MDI) and TRACE. The SOHO observations produced a set of raster
scans of the region with a field of view of 159"×120" for SUMER and
of 244"×240" for CDS. TRACE gave a sequence of high time resolution
images for a much larger (510"×510") field of view, in several spectral
passbands, while MDI gave the photospheric full disk longitudinal
magnetic field. The data set mainly covers the transition region and
the low corona. We have used the data to construct intensity, velocity
and magnetic field maps of the region. The comparison of the intensity
images in various wavelengths with the velocity images, as well as
with the magnetic field, gives us information about the dynamical
characteristics of the observed features and their relationship to
the photospheric magnetic field.
Title: Cooling and evacuation of an active region loop complex
observed with TRACE
Authors: Tsiropoula, G.; Gontikakis, C.; Dara, H. C.; Zachariadis,
Th.; Alissandrakis, C.; Vial, J. -C.
Bibcode: 2002ESASP.477..179T
Altcode: 2002scsw.conf..179T
We analyse the temporal variation of temperature and emission measure
at the top of a coronal loop system observed with the Transition
Region and Coronal Explorer (TRACE). Loops delineate regions of highly
localized heating and are thus typically the focus of coronal heating
theories. The analyzed data consist of observations in the 171 Å and
195 Å passbands taken at a cadence of ~10 min obtained on May 15,
1999 during an observing campaign. The temperature and emission measure
diagnostic is based in the 171 Å / 195 Å filter-ratio technique. The
loop system evacuates after the plasma at the top of the loops has
cooled. Estimates of the timescales of energy losses by radiation
and by conduction clearly suggest that the cooling is mainly due to
radiation losses.
Title: Solar energetic particles inside a coronal mass ejection
event observed with the ACE spacecraft
Authors: Malandraki, O. E.; Sarris, E. T.; Lanzerotti, L. J.;
Trochoutsos, P.; Tsiropoula, G.; Pick, M.
Bibcode: 2002JASTP..64..517M
Altcode: 2002JATP...64..517M
In this work, solar flare energetic particle fluxes
(Ee>=38keV) observed by the EPAM experiment aboard ACE are
utilized as diagnostics of the large-scale structure and topology of the
interplanetary magnetic field (IMF) embedded within a well-identified
interplanetary coronal mass ejection (ICME). The still controversial
question of whether the detected ICME structure has been detached
from the solar corona or is still magnetically anchored to it is
addressed. The observation of two impulsive solar flare electron events
inside the ICME suggests that field lines in this ICME are rooted at
the Sun. From the time evolution of the angular distributions of the
particle intensities we infer that the observations are consistent
with the magnetic topology of a magnetic bottle between a magnetic
mirror located at the Sun and a magnetic constriction upstream from
ACE formed by the convergence of open field lines that reflects the
outgoing electrons. The magnetic mirror strength is calculated in one
case based upon the local IMF observations and the electron event onset
characteristics. A magnetic field enhancement observed by ACE in the
downstream region of the CME-driven shock is identified as the agent
responsible for the mirroring of the energetic electrons.
Title: Ca II 8542 Å sunspot oscillations observed with THEMIS
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
Bibcode: 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-1 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.
Title: Multi-wavelength analysis of a solar active region loop system
with SOHO, TRACE and ground-based telescopes
Authors: Tsiropoula, G.; Gontikakis, C.; Dara, H. C.; Zachariadis,
Th. G.; Alissandrakis, C.; Vial, J. -C.
Bibcode: 2001hell.confE..40T
Altcode:
No abstract at ADS
Title: 2D spectroscopy and science with THEMIS
Authors: Tziotziou, K.; Mein, P.; Tsiropoula, G.; Eibe, T.
Bibcode: 2001hell.confE..25T
Altcode:
No abstract at ADS
Title: Tracing the magnetic topology of coronal mass ejection events
by Ulysses/HI-SCALE energetic particle observations in and out of
the ecliptic
Authors: Malandraki, O. E.; Sarris, E. T.; Lanzerotti, L. J.;
Maclennan, C. G.; Pick, M.; Tsiropoula, G.
Bibcode: 2001SSRv...97..263M
Altcode:
In January 2000, the Ulysses spacecraft observed an ICME event
at 43° S heliographic latitude and ∼ 4.1 AU. We use electron
(E e>38 keV) observations to trace the topology of
the IMF embedded within the ICME. The still controversial issue of
whether ICMEs have been detached from the solar corona or are still
magnetically anchored to it when they arrive at the spacecraft is
tackled. An in ecliptic ICME event is also presented.
Title: Physical parameters and flows along chromospheric penumbral
fibrils
Authors: Tsiropoula, G.
Bibcode: 2000A&A...357..735T
Altcode:
High resolution observations of a sunspot region were obtained on
October 3, 1994 with the Multichannel Subtractive Double Pass (MSDP)
spectrograph. This instrument installed at the focus of the Vacuum
Tower Telescope (VTT) at Tenerife (Canary Islands) operated in the
Hα line. Intensity fluctuations and Doppler shift velocities at
several wavelengths were derived over a two dimensional field of
view. The observed intensity profiles were matched with theoretical
ones using a technique proposed by Tsiropoula et al. 1999, which
enables the variation of the source function inside the structures
and the derivation of some physical parameters like the source
function, the Doppler width, the optical depth and the line-of-sight
velocity. This technique was applied to the dark fibrils surrounding
the sunspot umbra. Once these parameters are estimated several other
parameters can be determined like population densities at levels 1,
2, 3 (N1, N2, N3), total particle
density of hydrogen, NH, electron density, Ne,
electron temperature, Te, gas pressure, p, total column mass,
m, mass density, rho , sound speed, cs etc. Furthermore,
using a simple geometrical model we estimated from the line-of-sight
velocity the flow velocity along the dark fibrils assuming different
sets of inclination angles of the velocity vector with respect to
the vertical. We found that there is a flow from the outer edge of
the fibrils (in the side of the penumbra), to their inner edge (umbra
side), which is consistent to the siphon flow. Moreover, we found a
subsonic flow for the entire extent of two of the fibrils considered
and for all inclination angle sets, while for one fibril we found a
subsonic flow in the outer edge and supersonic velocity in the inner
edge for some of the inclination angle sets.
Title: Determination of the line-of-sight velocities in the dark
penumbral fibrils
Authors: Tsiropoula, G.
Bibcode: 2000NewA....5....1T
Altcode:
High resolution observations of an isolated sunspot located near the
centre of the solar disk (NOAA/AR 7783) were obtained on October 3,
1994. They were performed with the Multichannel Subtractive Double Pass
(MSDP) Spectrograph installed at the focus of the VTT at Tenerife and
operating in the H α line. The penumbra and superpenumbra are made up
of an apparently well-ordered pattern of elongated dark fibrils. Line
profiles were reconstructed and monochromatic images and Doppler shift
velocities were derived at several depths in the H α line over a two
dimensional field of view. Apart from the Doppler velocities the H
α line profiles are used for the computation of the line-of-sight
velocities of the dark fibrils by two other methods. The first
one involves the well-known Beckers' cloud model. The second is the
photographic subtraction method based on the cloud model and expressing
the "Doppler signal". This method using the monochromatic intensities
at two wavelengths on either side of the H α line profile can give,
in the general case, a quantitative picture of the velocity field,
but under some assumptions, values of the velocities at different
depths can be obtained. The values of the velocities obtained by this
method are compared to those given by the Doppler shift method and
by the cloud model, while comparison of the velocities at different
depths can give a picture of the gradient of the velocity inside the
dark penumbral fibrils.
Title: Association of chromospheric sunspot umbral oscillations and
running penumbral waves. I. Morphological study
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Mein, P.
Bibcode: 2000A&A...355..375T
Altcode:
Observations of a sunspot region located near the center of the solar
disk were obtained on October 3, 1994, with the Multichannel Subtractive
Double Pass Spectrograph (MSDP). This instrument, operating in Hα ,
was installed at the focus of the VTT at Tenerife (Canary Islands)
and provided Hα intensity profiles at every pixel of the field of
view. Reconstruction of the Hα profile allowed the computation of
two dimensional intensity and Doppler velocity images at different
wavelengths within the line. We analyse a time series of 1 hour and
8 min, obtained with a cadence of 36 sec and investigate the relation
between umbral oscillations and running penumbral waves. The Doppler
velocity as a function of time, along radial cuts through the center of
the spot, shows several clear cases where waves that originate inside
the umbra continue to propagate in the penumbra. In one case we were
able to follow the evolution of an oscillating element for 216 sec,
from the inner part of the umbra to the penumbra and we describe the
propagation characteristics. We confirm the close association between
sunspot oscillations and running penumbral waves and suggest that they
are probably due to the same resonator.
Title: Estimation of a `Clear' Sky Atmosphere using Ground and
Satellite Measurements of the Solar Radiation
Authors: Tsiropoula, G.; Argiriou, A.
Bibcode: 2000ESASP.463..551T
Altcode: 2000sctc.proc..551T
No abstract at ADS
Title: Association between Umbral Oscillations and Running Penumbral
Waves
Authors: Alissandrakis, C. E.; Tsiropoula, G.; Mein, P.
Bibcode: 1999ESASP.448..217A
Altcode: 1999ESPM....9..217A; 1999mfsp.conf..217A
No abstract at ADS
Title: Physical State of Dark Penumbral Fibrils
Authors: Tsiropoula, G.
Bibcode: 1999ESASP.448..395T
Altcode: 1999mfsp.conf..395T; 1999ESPM....9..395T
No abstract at ADS
Title: Derivation of physical parameters of chromospheric structures
assuming a constant and a varying source function
Authors: Tsiropoula, G.; Madi, C.; Schmieder, B.
Bibcode: 1999SoPh..187...11T
Altcode:
Hα profiles of a rosette region consisting of several bright and dark
mottles were obtained with the Multichannel Subtractive Double Pass
(MSDP) spectrograph mounted on the 50 cm 'Tourelle' refractor of the
Pic du Midi Observatory. These profiles have been analysed in terms
of the classical cloud model which assumes a constant source function
and holds only for optically thin structures. A new technique is also
described which enables the determination of various physical parameters
of chromospheric features taking into account the variation of the
source function with the optical depth. This method can be applied, in
contrast to the classical cloud model, to all lines whether optically
thin or optically thick and gives a good fit to the entire profile
from the core to the wings. A comparison of the results given by the
two different methods is also performed.
Title: Gradient of the line-of-sight velocities in the dark
superpenumbral fibrils.
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Mein, P.; Mein, N.
Bibcode: 1999joso.proc..116T
Altcode:
An isolated sunspot located near the centre of the solar disk was
observed on October 3, 1994. The present high resolution observations
were obtained with the Multichannel Subtractive Double Pass Spectrograph
(MSDP) operating in Hα. Two dimensional intensity and Doppler velocity
maps at several depths in the Hα line were computed. The monochromatic
intensities at two wavelengths on either side of the line are used in
terms of the photographic subtraction method expressing the "Doppler
signal" to give, under some assumptions, the velocities at different
depths in the Hα line. The values of the velocities obtained by
this method are compared to those given by the bisector method while
comparison of the velocities at different depths can give a picture
of the gradient of the velocity in the dark superpenumbral fibrils.
Title: Analysis of H profiles. Physical parameters of chromospheric
mottles: A case study
Authors: Tsiropoula, G.; Madi, C.; Schmieder, B.; Preka-Papadema, P.
Bibcode: 1999A&AT...18..455T
Altcode:
Observations of a well-defined rosette region which consisted of
several bright and dark mottles and located almost at the solar disc
centre (N5, W5) were made with the Multichannel Double Pass (MSDP)
spectrograph mounted on the 50 cm "Tourelle" refractor of the Pic
Du Midi Observatory, on June 17, 1986. This instrument records a
two-dimensional field on the solar surface and having 11 channels
provides at every pixel of the field of view the profile of the H
line. We have used these profiles to derive several physical parameters
of the chromospheric mottles. The basic assumption of the method we used
is that the source function is not constant inside the structures, but
has a parabolic variation with the optical depth. By using an iterative
least square procedure for non-linear functions, five parameters of
chromospheric mottles were computed: the optical depth, the Doppler
width, the line-of-sight velocity, the source function at the middle
of the structure, and the source function's variation factor.
Title: Umbral and Penumbral Waves in a Chromospheric Sunspot
Authors: Alissandrakis, C. E.; Tsiropoula, G.; Mein, P.
Bibcode: 1998ASPC..155...49A
Altcode: 1998sasp.conf...49A
No abstract at ADS
Title: Structures and Flows in the Solar Active Photosphere and
Chromosphere (Invited review)
Authors: Tsiropoula, G.
Bibcode: 1998ASPC..155...24T
Altcode: 1998sasp.conf...24T
No abstract at ADS
Title: A method for determining physical parameters in chromospheric
mottles
Authors: Tsiropoula, G.; Madi, C.; Schmieder, B.
Bibcode: 1998ESASP.421..341T
Altcode: 1998sjcp.conf..341T
No abstract at ADS
Title: Observations of flux rope - associated particle bursts with
GEOTAIL in the distant tail
Authors: Belehaki, A.; Sarris, E. T.; Tsiropoula, G.; McEntire, R. W.;
Kokubun, S.; Yamamoto, T.
Bibcode: 1997AnGeo..15.1515B
Altcode:
Geotail energetic particle, magnetic field data and plasma observations
(EPIC, MGF and CPI experiments) have been examined for a number of
energetic particle bursts in the distant tail (120Re<|XGSM|<
130 Re), associated with moving magnetic field structures, following
substorm onsets. The features obtained from this data analysis are
consistent with the distant magnetotail dynamics determined first
by ISEE3 observations and explained in terms of the neutral line
model. At the onset of the bursts, before plasma sheet entrance,
energetic electrons appear as a field-aligned beam flowing in the
tailward direction, followed by anisotropic ions. Within the flux
rope region, suprathermal ions exhibit a convective anisotropy, which
allows determination of the plasma flow velocity, assuming that the
anisotropy arises from the Compton-Getting effect. The velocities thus
determined in the plasma sheet are estimated to be 200-650 km/s, and
compare favourably with the velocities derived from the CPI electron
and proton experiment. The estimated length of magnetic field structures
varies between 28 and 56 Re and depends on the strength of the westward
electrojet intensification. Finally, the three structures reported
here show clear magnetic field signatures of flux rope topology. The
existence of a strong magnetic field aligned approximately along the
Y-axis and centred on the north-to-south excursion of the field, and
the bipolar signature in both By and/or Bz components, is consistent
with the existence of closed field lines extending from Earth and
wrapping around the core of the flux rope structure.
Title: Determination of physical parameters in dark mottles.
Authors: Tsiropoula, G.; Schmieder, B.
Bibcode: 1997A&A...324.1183T
Altcode:
The application of the cloud model to measurements of the contrast as
a function of wavelength in the Hα line has recently enabled us to
derive numerical values for various parameters (such as velocity, source
function, Doppler width and optical depth) of dark mottles observed near
the center of the solar disk. The values of these parameters are used
together with the calculations of Poland et al. (1971SPh....18..391P)
and Yakovkin and Zel'dina (1975SPh....45..319Y) in order to determine
the physical conditions in these structures. Thus population densities
at levels 1, 2, 3 (N_1_, N_2_, N_3_), total particle density of hydrogen
N_H_, electron density N_e_, electron temperature T_e_, gas pressure,
total column mass, mass density and degree of hydrogen ionization
can be determined. The values obtained are comparable with estimates
obtained for spicules and mottles by different authors in the past and,
furthermore, offer the prospect of putting observational constraints
on non-LTE two-dimensional modelling of dark mottles observed in the
Hα line which is currently in progress.
Title: Evolution in Space and Time of Superpenumbral Chromospheric
Fibrils
Authors: Tsiropoula, G.; Dialetis, D.; Alissandrakis, C. E.; Mein,
P.; Mein, N.
Bibcode: 1997SoPh..172..139T
Altcode: 1997ESPM....8..139T
We have studied the spatial structure and temporal evolution of the
intensity and Doppler velocity of dark fibrils forming the superpenumbra
of an isolated regular sunspot. The observations were obtained with the
Multichannel Subtractive Double Pass (MSDP) spectrograph which operates
in Hα and is installed at the focus of the Vacuum Tower Telescope (VTT)
at Tenerife (Canary Islands). The fibril pattern shows a remarkable
stability during the period of our observations (64 min). Moreover,
almost all individual fibrils are identifiable in all frames, but they
undergo continual changes in contrast, shape and size. Investigating the
temporal evolution of intensity and velocity of individual fibrils,
fluctuations were found which have a quasi periodic behavior. As
mechanisms for these changes we may suggest (a) change of the Doppler
shift due to a wave, (b) periodic changes of the density of the Hα
absorbing material, (c) disappearance and reappearance of fibrils,
in more or less the same magnetic flux tube, at regular intervals.
Title: Solar Flare Electrons Propagation in Converging Interplanetary
Magnetic Structures
Authors: Malandraki, O.; Kasotakis, G.; Sarris, E. T.; Trochoutsos,
P.; Dialetis, D.; Tsiropoula, G.
Bibcode: 1997ICRC....1..281M
Altcode: 1997ICRC...25a.281M
No abstract at ADS
Title: Two dimensional distribution of physical parameters in dark
mottles assuming constant and non-constant source function
Authors: Tsiropoula, G.; Madi, G.; Christopoulou, E.; Alissandrakis,
G.; Schmieder, B.; Preka-Papadema, P.
Bibcode: 1997jena.confE..60T
Altcode:
Observations of a rosette region consisting of several dark mottles
located almost at the solar disk centre (N5, W5) were made with the
Multichannel Double Pass (MSDP) spectrograph mounted on the 50 cm
``Tourelle'' refractor of the Pic du Midi Observatory, on June 17,
1986. The MSDP having 11 channels provides at every point of the field
of view the profile of the H-alpha line, which is reconstructed from
11 values. The observed contrast profiles of the dark features as a
function of the wavelength are used in terms of Beckers' cloud model
(e.g. assuming that the source function is constant throughout the
feature) in order to derive 4 parameters: the line-of-sight velocity,
the optical depth at line centre, the Doppler width and the source
function. The computation of the four parameters was carried out by an
iterative least square procedure for non linear functions. Allowing
the source function to have a parabolic variation with the optical
depth and using the same iteration procedure the source function at
the centre of the feature and the source function variation factor
are determined. Comparison of the values of the physical parameters
derived under these two different assumptions concerning the source
function is performed. These values are also compared with the values
obtained from multilevel non-LTE models.
Title: Comparison of line-of-sight velocities of chromospheric
structures derived by three different methods
Authors: Tsiropoula, G.; Christopoulou, E.; Madi, C.; Dialetis, D.;
Mein, P.; Mein, N.
Bibcode: 1997jena.confE..61T
Altcode:
We have used three different methods to derive line-of-sight velocities
in dark fibrils forming the superpenumbra of an isolated regular sunspot
located near the centre of the solar disk (NOOA/AR 7783). The present
observations were obtained on October 3, 1994. They were performed
with the Multichannel Subtractive Double Pass (MSDP) spectrograph which
operates in H-alpha and it is installed at the focus of the Vacuum Tower
Telescope (VTT) at Tenerife (Canary Islands). This instrument records
a two dimensional field of view on the solar surface with good spatial
and temporal resolution. The observations were made simultaneously in 9
wavelengts, 0.3AA apart in the H-alpha profile. At every pixel of the
2D field of view the line profile can be restored from the measured
values of the intensity in the 9 channels and a third degree spline
interpolation. These profiles were used for the computation of the
line-of-sight velocity by three different methods: (a) the Doppler
shift method, (b) the photographic subtraction method expressing the
``Doppler signal'' and (c) the classical Beckers' cloud model. 2D
maps of the velocity are computed, comparison of the values derived
by the 3 different methods is performed and the conditions governing
the validity of the 3 methods are stated.
Title: Flux rope signatures in the distant plasma sheet boundary
layer observed by Geotail: a case study
Authors: Belehaki, A.; Sarris, E. T.; Tsiropoula, G.; McEntire, R. W.;
Kokubun, S.; Yamamoto, T.
Bibcode: 1996ESASP.389..507B
Altcode: 1996icss.conf..507B
No abstract at ADS
Title: Energetic particle bursts detected by Geotail in the distant
tail
Authors: Belehaki, A.; Sarris, E. T.; Tsiropoula, G.; McEntire, R. W.;
Kokubun, S.; Yamamoto, T.
Bibcode: 1996ESASP.389..487B
Altcode: 1996icss.conf..487B
No abstract at ADS
Title: Periodic and Non-Periodic Phenomena in a Sunspot Region
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Dialetis, D.; Mein, P.
Bibcode: 1996SoPh..167...79T
Altcode:
We have studied running penumbral waves, the homogeneous Evershed
effect, and the spatial relation between intensity and Doppler velocity
penumbral features of a chromospheric sunspot. The observations were
obtained with the multichannel subtractive double-pass spectrograph
(MSDP) operating in Hα at the Vacuum Tower Telescope (VTT) installed
at Tenerife (Canary Islands). We derived intensity and Doppler velocity
maps at Hα ± 0.3 Å over a two-dimensional field of view. We have
computed the components of the velocity vector (radial, azimuthal,
vertical) as a function of distance from the center of the spot under
the assumption of axial symmetry. The results show the well-known,
from previous observations, general large-scale characteristics of the
chromospheric Evershed flow. Our measurements show that the axes along
the discrete structures, where the Evershed flow is confined, are not
spatially related to the axes along Hα ± 0.3 Å intensity features,
and we suggest that either the flow is confined in flow channels or that
it takes place along sheared magnetic field lines. We also detected,
for the first time in velocity images, running penumbral waves, which
started in the outer 0.3 of the umbral radius and propagated through
the penumbra with propagation velocities 13-24 km s−1. The
propagation velocity, as well as the velocity amplitude, is greater
for the waves closer to the center of the spot and diminishes as one
moves outward.
Title: Running Penumbral Waves in a chromospheric Sunspot
Authors: Tsiropoula, G.; Dialetis, D.; Alissandrakis, C. E.; Mein, P.
Bibcode: 1996hell.conf...37T
Altcode:
No abstract at ADS
Title: The fine scale Structure of the velocity Field in the
chromospheric Penumbra of a solar Sunspot
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Dialetis, D.; Mein, P.
Bibcode: 1996hell.conf...32T
Altcode:
No abstract at ADS
Title: Dynamical fine structures of the chromosphere
Authors: Tsiropoula, G.; Schmieder, B.; Alissandrakis, C. E.
Bibcode: 1994SSRv...70...65T
Altcode:
We have studied the spatial structure and temporal evolution of a
chromospheric region with chains of mottles at the junction of three
supergranules. The observations were obtained with the Multichannel
Subtractive Double Pass spectrograph operating in Hα at the Pic du
Midi Observatory. From a statistical point of view the fine structures
were stable in intensity over the observation period (15 min), while the
line of sight velocity showed remarkable changes within a few minutes. A
detailed analysis shows that the predominant pattern of bulk motion in
the dark mottles is that of downflow at their footpoints and upflow at
their tops, which is followed by downflows along the whole structure and
that this process repeats itself several times during their lifetime.
Title: Time evolution of fine structures in the solar chromosphere.
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Schmieder, B.
Bibcode: 1994A&A...290..285T
Altcode:
We have studied the temporal evolution of two quiet chromospheric
regions, one with a typical rosette and another with chains of
mottles at the junction of three supergranules. The observations
were obtained during 15 minutes with the Multichannel Subtractive
Double Pass spectrograph (MSDP) operating in Hα at the Pic du Midi
Observatory. We derived intensity maps and Doppler shift velocities at
different wavelengths along the Hα profile over a two dimensional
field of view. The observed contrast profiles were matched with
theoretical contrast profiles using Beckers' cloud model for a more
accurate determination of the line of sight velocity. A statistical
analysis with cross correlation functions showed that the fine
structures were stable in intensity over the observation period (15
min), but the line of sight velocity showed important changes within
a few minutes. A detailed analysis of the velocities along the axes
of dark mottles showed that the predominant pattern of bulk motion is
that of downflow at their footpoints and alternating phases of upflow
and downflow at their tops. This motion is consistent with Pikel'ner's
model for spicules, which attributes this pattern to the reconnection of
opposite magnetic filed lines. This picture is also consistent with the
velocity reversals with time observed in spicules and may be associated
to the systematic downflows observed in the transition region. Doppler
shift velocities in dark mottles are too low compared to those derived
with the cloud model; the latter are comparable to those reported for
spicules, strengthening the view that these structures are identical.
Title: Fine structures of the solar chromosphere
Authors: Schmieder, B.; Heinzel, P.; Tsiropoula, G.; Alessandrakis,
C. E.
Bibcode: 1994ASIC..433..151S
Altcode:
No abstract at ADS
Title: Time Evolution of Chromospheric Fine Structures
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Schmieder, B.
Bibcode: 1994emsp.conf..111T
Altcode:
No abstract at ADS
Title: The fine structure of a chromospheric rosette
Authors: Tsiropoula, G.; Alissandrakis, C. E.; Schmieder, B.
Bibcode: 1993A&A...271..574T
Altcode:
We have studied the spatial behaviour of the physical properties
of dark mottles forming a well-defined rosette. The observations
were obtained with the Multichannel Subtractive Double Pass (MSDP)
spectrograph, operating in Hα at the Pic du Midi Observatory. From
these observations, intensity fluctuations and Doppler shift velocities
at different wavelengths were derived over a two dimensional field of
view. The observed contrast profiles were matched with theoretical
contrast profiles using Beckers' cloud model and 4 parameters were
derived for the dark mottles: the source function, the line-of-sight
velocity, the Doppler width and the optical depth. From these parameters
a range for the temperature and electron density can be derived using
Vernazza's et al. (1981) model D. We detected strong downflows at
the roots of the mottles, while their upper part is ascending with
velocities sometimes greater than 10 km s-1. The values of
the cloud parameters are consistent with values given by other authors
for this kind of features. Consistency was also found between cloud
parameters and the values given for spicules, leading to the conclusion
for the identity of these structures.
Title: Time evolution of arch filaments
Authors: Tsiropoula, G.; Georgakilas, A. A.; Alissandrakis, C. E.;
Mein, P.
Bibcode: 1992A&A...262..587T
Altcode:
We have studied the spatial structure and the temporal evolution of the
velocity in active region arch filaments. The observations were obtained
with the Multichannel Double Pass Spectrograph operating in H-alpha
at the Pic du Midi Observatory. Line profiles were reconstructed and
monochromatic images and Doppler shift velocities were derived over a 2D
FOV. Using Beckers' (1964) cloud model we derived physical parameters,
in particular the line of sight velocity. The arches showed the
'classical' type of motion, with material moving towards the observer
near the apex and away from the observer near the footpoints. Assuming
a symmetric loop, we reconstructed the velocity vector along the arch
filaments. The results are consistent with the picture where material is
draining out of the filament, while the whole structure is ascending. In
one case we observed changes in the geometry and the velocity vector;
however, other arch filaments did not change appreciably in a time
period of about 13.5 min.
Title: Physical parameters of solar H-alpha absorption features
derived with the cloud model
Authors: Alissandrakis, C. E.; Tsiropoula, G.; Mein, P.
Bibcode: 1990A&A...230..200A
Altcode:
Observations of a fibril region and of an arch filament region
obtained by the Multichannel Subtractive Double Pass Spectrograph
(MSDP) operating in H-alpha at the Pic du Midi Observatory are
presented. Intensity fluctuations and Doppler shift velocities were
derived over two dimensional fields of view. The observed contrast
profiles have been matched with theoretical contrast profiles based on
the cloud model which has four parameters: the line-of-sight velocity,
the source function, the optical depth, and the Doppler width. Contour
maps and histograms of the 4 parameters were made for these regions,
and a comparison of the velocities given by 3 different methods (cloud
model, Doppler shift, and the '3-optical depths' method of Mein and
Mein, 1988) is made.
Title: Helicoidal material motion in a prominence.
Authors: Prokakis, T.; Tsiropoula, G.
Bibcode: 1988dssp.conf...21P
Altcode:
Good quality photos taken in Athens Observatory with the Hα filter
are used for the study of the motion of bright material into an active
prominence. A strong activation with dynamic expansion of the prominence
appeared during the observations. The trajectory of the brightest point
into the prominence has been found during the evolution of the whole
phenomenon. The aim of this work is to find the real motion of the
brightest point, based on the shape of the observed trajectory and to
give some explanations on the cause of formation of this kind of motion.
Title: Determination of the mean lifetime of solar features from
photographic observations
Authors: Alissandrakis, C. E.; Dialetis, D.; Tsiropoula, G.
Bibcode: 1987A&A...174..275A
Altcode:
Two approaches, one based on a lifetime distribution and the second
based on survival functions, are combined in order to determine the
mean lifetimes of solar features. The relations between the lifetime
distributions and the survival and probability density functions
are derived. This method is applied to the determination of the mean
lifetimes of solar granules. The accuracy of the method is evaluated by
comparing the calculated lifetimes with data obtained using different
methods. It is determined that the proposed method provides accurate
lifetime data, and a mean lifetime value of 16 min with a standard
deviation of about 5 min was obtained for the solar granules.
Title: Helicoidal Material Motion in a Prominence
Authors: Prokakis, T.; Tsiropoula, G.
Bibcode: 1987dssp.work...21P
Altcode: 1987ASSL..150...21P
No abstract at ADS
Title: On the long-lived photospheric granules.
Authors: Dialetis, D.; Prokakis, Th.; Sarris, E.; Tsiropoula, G.
Bibcode: 1987PAICz..66...25D
Altcode: 1987eram....1...25D
The authors have studied the spatial distribution of the long-lived
granules from a population of 346 granules located in a photospheric
region 37arcsec×37arcsec. The study is based on an exceptional sequence
of photos taken by R. Muller at the Pic-du-Midi Observatory on May 16,
1979. The authors have determined the lifetime of all the granules
situated in this rectangular photospheric region.
Title: Emission of Lyman-α radiation by solar coronal
loops. II. Filtergram analysis.
Authors: Tsiropoula, G.; Alissandrakis, C.; Bonnet, R. M.; Gouttebroze,
P.
Bibcode: 1986A&A...167..351T
Altcode:
The authors study active region loops, observed on Lα high resolution
filtergrams obtained with a rocket borne instrument. Some formulae or
diagrams are given for the computations of Lα and Hα intensities
emitted by homogeneous loop models. The dimensions and emitted
intensities of the observed loops being known, the authors determine
the variations of temperature, pressure and density inside these
objects under the assumption of constant temperature and hydrostatic
equilibrium. The influence of temperature gradient and mass flow
on the results is discussed, and an alternative model with radial
temperature increase is envisaged. The case of an isolated loop with
a larger diameter is also discussed.
Title: Emission of Lyman alpha radiation by solar coronal loops. I -
General synopsis
Authors: Gouttebroze, P.; Vial, J. C.; Tsiropoula, G.
Bibcode: 1986A&A...154..154G
Altcode:
The processes of emission of Lyman-alpha radiation by loop-like
structures embedded in the solar corona are investigated, for
a large range of physical conditions within these objects. The
coupled set of equations for radiative transfer, and hydrogen atom
level populations, ionization and pressure equilibria is solved
to obtain the emitted L-alpha intensities as functions of pressure,
temperature and size. Three different cases are treated: (1) optically
thin structures with arbitrary geometry. (2) plane-parallel slabs,
either horizontal or vertical, with arbitrary optical depth. (3)
cylindrical loops with horizontal axis, for moderate optical depths
(au is less than 1000). The importance of geometry, as well as that of
partial frequency redistribution and of the hydrogen atom's model, are
evaluated. Empirical formulae and diagrams of intensity as a function
of physical state parameters are given. The diagnostic possibilities of
Lyman-alpha filtergrams alone or in conjunction with other observations,
are discussed.
Title: Transfer of Lyman-α radiation in solar coronal loops.
Authors: Gouttebroze, P.; Vial, J. -C.; Tsiropoula, G.
Bibcode: 1985ASIC..152..359G
Altcode: 1985pssl.proc..359G
The emission and scattering of Lyman-α radiation within the loop-like
structures of the solar corona are investigated, for a large range
of physical conditions within these objects. Results from partial
and complete redistribution computations are compared. A series of
predictions, concerning line profiles, integrated intensities, and
directional diagrams are given for observation diagnosis.
Title: Μελέτη της εκπομπής στη γραμμή
Ly-α του υδρογόνου σχηματισμών της
ηλιακής ατμόσφαιρας Title: Μελέτη της
εκπομπής στη γραμμή Ly-α του υδρογόνου
σχηματισμών της ηλιακής ατμόσφαιρας
Title: A study of the Lyman-α emission in the solar atmosphere;
Authors: Tsiropoula, Georgia
Bibcode: 1985PhDT........63T
Altcode:
No abstract at ADS
Title: Density and temperature determination of neutral hydrogen in
coronal structures
Authors: Bonnet, R. M.; Tsiropoula, G.
Bibcode: 1982SoPh...75..139B
Altcode:
High-resolution filtergrams in Lα have been obtained with a rocket
borne instrument and evidence several loop shaped structures which
can be seen as absorption features over the solar surface. The optical
thickness of these coronal structures is measured with respect to nearby
unabsorbed disk features. Their shape and dimension being known from
the images, the determination of the neutral hydrogen temperature and
density is possible. It is found that temperatures below 105
K and densities of a few 104 hydrogen atoms cm−3
are compatible with the opacities observed in the structures.