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Author name code: tziotziou
ADS astronomy entries on 2022-09-14
author:"Tziotziou, K." 

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Title: Short poster presentations
Authors: Tziotziou, Kostas
2022cosp...44.2527T    Altcode:
  Short presentations of posters related to event E2.4.

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Title: Automated detection of chromospheric swirls in the Halpha
    spectral line and statistical analysis of their parameters
Authors: Dakanalis, Ioannis; Tziotziou, Kostas; Tsiropoula, Georgia;
   Kontogiannis, Ioannis
2022cosp...44.2519D    Altcode:
  Ubiquitous vortical motions in the solar atmosphere have been recently
  revealed by high-resolution observations of both space-borne and
  ground-based observatories in quiet, as well as in active regions. In
  chromospheric observations obtained in spectral lines, such as
  the H$\alpha$ and Ca II IR, they manifest themselves as swirling
  dark spiral- and circular-shaped patches labelled as "chromospheric
  swirls". Their suggested contribution to the channelling of energy,
  mass and momentum from the sub-photospheric levels to the higher layers
  of the solar atmosphere places them amongst potential candidates for
  atmospheric heating. In this context, their detection and statistical
  information concerning their population and a number of significant
  physical parameters and properties are vital. To complement visual
  inspection and automated detection methods based on the velocity field
  derivation we developed a novel automated detection method, which is
  based on the morphological characteristics of these structures. The
  algorithm was applied to H$\alpha$ high-resolution observations
  obtained with the CRisp Imaging SpectroPolarimeter (CRISP) of the
  Swedish 1-m Solar Telescope (SST) and revealed the existence of a
  significantly larger number of chromospheric swirls compared to previous
  reports. We will be presenting a brief description of the automated
  detection algorithm, followed by the obtained results concerning their
  surface density, occurrence rate, spatial distribution and temporal
  evolution throughout the FOV, as well as a statistical analysis of some
  significant physical parameters, such as radii and lifetimes that were
  obtained by an unprecedented observational statistical sample of 577
  swirls. Lifetimes have been derived by implementation of the survival
  analysis method that is extensively used in several scientific fields,
  but so far occasionally in Solar Physics, and provides more accurate
  estimates of the mean lifetime of swirls. Moreover, a hinted by the
  results linear correlation between lifetimes and radii is explored.

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Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
   Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
   C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
   Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
   M.; the EST team
2022arXiv220710905Q    Altcode:
  The European Solar Telescope (EST) is a project aimed at studying
  the magnetic connectivity of the solar atmosphere, from the deep
  photosphere to the upper chromosphere. Its design combines the knowledge
  and expertise gathered by the European solar physics community during
  the construction and operation of state-of-the-art solar telescopes
  operating in visible and near-infrared wavelengths: the Swedish 1m Solar
  Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
  the French Télescope Héliographique pour l'Étude du Magnétisme
  et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
  (DOT). With its 4.2 m primary mirror and an open configuration, EST will
  become the most powerful European ground-based facility to study the Sun
  in the coming decades in the visible and near-infrared bands. EST uses
  the most innovative technological advances: the first adaptive secondary
  mirror ever used in a solar telescope, a complex multi-conjugate
  adaptive optics with deformable mirrors that form part of the optical
  design in a natural way, a polarimetrically compensated telescope design
  that eliminates the complex temporal variation and wavelength dependence
  of the telescope Mueller matrix, and an instrument suite containing
  several (etalon-based) tunable imaging spectropolarimeters and several
  integral field unit spectropolarimeters. This publication summarises
  some fundamental science questions that can be addressed with the
  telescope, together with a complete description of its major subsystems.

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Title: Chromospheric swirls. I. Automated detection in Hα
    observations and their statistical properties
Authors: Dakanalis, I.; Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.
2022A&A...663A..94D    Altcode: 2022arXiv220507720D
  Context. Chromospheric swirls are related to convectively driven vortex
  flows and considered to play a significant role in the dynamics and
  heating of the upper solar atmosphere. It is important to automatically
  detect and track them in chromospheric observations and determine their
  properties. <BR /> Aims: We aim to detect and track chromospheric
  swirls both in space and time by applying a newly developed novel
  automated method on high quality time series of Hα observations and
  to conduct a statistical analysis to determine their properties. <BR
  /> Methods: We applied a recently developed automated chromospheric
  swirl detection method to time-series observations of a quiet region
  of the solar chromosphere obtained in the Hα-0.2 Å wavelength of
  the Hα spectral line by the CRISP instrument at the Swedish 1-m Solar
  Telescope. The algorithm exploits the morphological characteristics of
  swirling events in high contrast chromospheric observations and results
  in the detection of these structures in each frame of the time series
  and their tracking over time. We conducted a statistical analysis
  to determine their various properties, including a survival analysis
  for deriving the mean lifetime. <BR /> Results: A mean number of 146
  ± 9 swirls was detected within the Hα-0.2 Å field of view at any
  given time. The mean surface density is found equal to ∼0.08 swirls
  Mm<SUP>−2</SUP> and the occurrence rate is ∼10<SUP>−2</SUP> swirls
  Mm<SUP>−2</SUP> min<SUP>−1</SUP>. These values are much higher
  than those previously reported from chromospheric observations. The
  radii of the detected swirls range between 0.5 and 2.5 Mm, with a
  mean value equal to 1.3 ± 0.3 Mm, which is slightly higher than
  previous reports. The lifetimes range between 1.5 min and 33.7 min
  (equal to the duration of the observations) with an arithmetic mean
  value of ∼8.5 min. A survival analysis of the lifetimes, however,
  using the Kaplan-Meier estimator in combination with a parametric model
  results in a mean lifetime of 10.3 ± 0.6 min. <BR /> Conclusions:
  Swirls are ubiquitous in the solar chromosphere. An automated method
  sheds more light on their abundance than visual inspection, while
  higher cadence, higher resolution observations will most probably
  result in the detection of a higher number of such features on smaller
  scales and with shorter lifetimes. <P />Movies is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202243236/olm">https://www.aanda.org</A>

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Title: A Diligent Analysis of the Flash and Coronal Spectrum of the
    Total Solar Eclipse of 20 March 2015
Authors: Voulgaris, Aristeidis G.; Mouratidis, C.; Tziotziou, K.;
   Seiradakis, J. H.; Pasachoff, J. M.
2022SoPh..297...49V    Altcode:
  During totality of the solar eclipse of 20 March 2015, at Svalbard,
  Norway, the emission spectra of the solar chromosphere and corona were
  captured with a slitless spectrograph. A very lucky coincidence of a
  large number of sunspots and Active Regions (ARs) around the solar limb
  allowed us to observe a number of different spectroscopic effects. This
  eclipse took place about one year after the second solar maximum of the
  double-peaked Solar Cycle 24, which produced less activity than the
  previous stronger solar maxima. The spectra taken during the eclipse
  show strong and high activity of the green coronal line Fe XIV (5303 Å)
  and the lower intensity of the red coronal line Fe X (6374 Å). After
  subtraction of the emitted continuum of K+(F) corona, the detection
  and identification of several extremely weak emission lines, including
  the two forbidden emission lines of Ca XV (5694 Å and 5446 Å) and
  also Ni XIII (5116 Å) and Ni XV (6702 Å), was possible. The large
  number of ARs also led to the observation of a continuum brightening
  in ARs and a continuum darkening in surrounding areas.

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Title: Automated Detection of Chromospheric Swirls Based on Their
    Morphological Characteristics
Authors: Dakanalis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas;
   Koutroumbas, Konstantinos
2021SoPh..296...17D    Altcode:
  High-resolution observations have revealed that rotating structures
  known as "chromospheric swirls" are ubiquitous in the solar
  chromosphere. These structures have circular or spiral shapes, are
  present across a broad range of spatial and temporal scales and are
  considered as viable candidates for providing an alternative mechanism
  for the heating of the chromosphere and corona. Therefore, an accurate
  determination of their number and a statistical study of their physical
  properties are deemed necessary. In this work we present a novel,
  automated swirl detection method, which utilizes image pre-processing,
  curved structure tracing and machine learning techniques that allow
  for the detection of swirling events based on their morphological
  features as they appear in chromosphere filtergrams. The method is
  applied to Hα chromospheric spectral line images obtained by the
  CRisp Imaging Spectropolarimeter (CRISP) at the Swedish 1-m Solar
  Telescope (SST). It is also tested on grayscale images of vortical
  sea current flows represented/visualized by synthetic streamlines
  from the NASA/Goddard Space Flight Center Scientific Visualization
  Studio. The results are rather encouraging since swirling events are
  successfully identified. Further improvements of the algorithm, its
  prospects for the detection and statistical studies of the properties
  of these events using a wide range of imaging data and its potential
  application in other scientific fields for the detection of rotating
  motions are discussed.

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Title: A persistent quiet-Sun small-scale tornado. III. Waves
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.
2020A&A...643A.166T    Altcode: 2020arXiv201006327T
  Context. Vortex flows can foster a variety of wave modes. A recent
  oscillatory analysis of a persistent 1.7 h vortex flow with a
  significant substructure has suggested the existence of various
  types of waves within it. <BR /> Aims: We investigate the nature and
  characteristics of waves within this quiet-Sun vortex flow, over the
  course of an uninterrupted 48-min observing time interval, in order to
  better understand its physics and dynamics. <BR /> Methods: We used a
  cross-wavelet spectral analysis between pairs of Hα and Ca II 8542 Å
  intensity time series at different wavelengths and, hence, atmospheric
  heights, acquired with the CRisp Imaging SpectroPolarimeter at the
  Swedish Solar Telescope, as well as the derived Hα Doppler velocity
  and full width at half maximum time series. We constructed halftone
  frequency-phase difference plots and investigated the existence and
  propagation characteristics of different wave modes. <BR /> Results:
  Our analysis suggests the existence of Alfvénic type waves within the
  vortex flow that propagate upwards with phase speeds of ∼20-30 km
  s<SUP>-1</SUP>. The dominant wave mode seems to be the fast kink wave
  mode, however, our analysis also suggests the existence of localised
  Alfvénic torsional waves, which are related to the dynamics of
  individual chromospheric swirls that characterise the substructure
  of the vortex flow. The Hα V-I phase difference analysis seems to
  imply the existence of a standing wave pattern that is possibly
  arising from the interference of upwards propagating kink waves
  with downwards propagating ones that are reflected at the transition
  region or the corona. Moreover, the results provide further evidence
  that the central chromospheric swirl drives the dynamics of the vortex
  flow. <BR /> Conclusions: This is the first exhaustive phase difference
  analysis within a vortex flow that explores the nature and dynamics
  of different wave modes within it. The question, however, of whether,
  and how, the dissipation of the derived wave modes occurs remains open,
  and given that such structures are ubiquitous on the solar surface,
  it's also important to investigate whether they might ultimately play
  a significant role in the energy budget of the upper layers of the
  solar atmosphere.

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Title: The Solar Orbiter Science Activity Plan. Translating solar
    and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
   Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
   A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
   Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
   Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
   Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
   Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
   Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
   L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
   A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
   F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
   Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
   Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
   van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
   L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
   D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
   S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
   G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
   D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
   K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
   J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
   I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
   Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
   G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
   Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
   Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
   K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
   H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
   Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
   Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
   J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
   Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
   Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
   Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
   Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
   Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
   G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
   A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
   Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
   T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z    Altcode: 2020arXiv200910772Z
  Solar Orbiter is the first space mission observing the solar plasma
  both in situ and remotely, from a close distance, in and out of the
  ecliptic. The ultimate goal is to understand how the Sun produces
  and controls the heliosphere, filling the Solar System and driving
  the planetary environments. With six remote-sensing and four in-situ
  instrument suites, the coordination and planning of the operations are
  essential to address the following four top-level science questions:
  (1) What drives the solar wind and where does the coronal magnetic field
  originate?; (2) How do solar transients drive heliospheric variability?;
  (3) How do solar eruptions produce energetic particle radiation that
  fills the heliosphere?; (4) How does the solar dynamo work and drive
  connections between the Sun and the heliosphere? Maximising the
  mission's science return requires considering the characteristics
  of each orbit, including the relative position of the spacecraft
  to Earth (affecting downlink rates), trajectory events (such
  as gravitational assist manoeuvres), and the phase of the solar
  activity cycle. Furthermore, since each orbit's science telemetry
  will be downloaded over the course of the following orbit, science
  operations must be planned at mission level, rather than at the level
  of individual orbits. It is important to explore the way in which those
  science questions are translated into an actual plan of observations
  that fits into the mission, thus ensuring that no opportunities are
  missed. First, the overarching goals are broken down into specific,
  answerable questions along with the required observations and the
  so-called Science Activity Plan (SAP) is developed to achieve this. The
  SAP groups objectives that require similar observations into Solar
  Orbiter Observing Plans, resulting in a strategic, top-level view of
  the optimal opportunities for science observations during the mission
  lifetime. This allows for all four mission goals to be addressed. In
  this paper, we introduce Solar Orbiter's SAP through a series of
  examples and the strategy being followed.

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Title: An overview of methodologies for real-time detection,
    characterisation and tracking of traveling ionospheric disturbances
    developed in the TechTIDE project
Authors: Belehaki, Anna; Tsagouri, Ioanna; Altadill, David; Blanch,
   Estefania; Borries, Claudia; Buresova, Dalia; Chum, Jaroslav; Galkin,
   Ivan; Juan, José Miguel; Segarra, Antoni; Timoté, Cristhian Camilo;
   Tziotziou, Kostas; Verhulst, Tobias G. W.; Watermann, Jurgen
2020JSWSC..10...42B    Altcode:
  The main objective of the TechTIDE project (warning and mitigation
  technologies for travelling ionospheric disturbances effects) is the
  development of an identification and tracking system for travelling
  ionospheric disturbances (TIDs) which will issue warnings of electron
  density perturbations over large world regions. The TechTIDE project has
  put in operation a real-time warning system that provides the results of
  complementary TID detection methodologies and many potential drivers to
  help users assess the risks and develop mitigation techniques tailored
  to their applications. The TechTIDE methodologies are able to detect
  in real time activity caused by both large-scale and medium-scale TIDs
  and characterize background conditions and external drivers, as an
  additional information required by the users to assess the criticality
  of the ongoing disturbances in real time. TechTIDE methodologies
  are based on the exploitation of data collected in real time from
  Digisondes, Global Navigation Satellite System (GNSS) receivers and
  Continuous Doppler Sounding System (CDSS) networks. The results are
  obtained and provided to users in real time. The paper presents the
  achievements of the project and discusses the challenges faced in the
  development of the final TechTIDE warning system.

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Title: Emergence of small-scale magnetic flux in the quiet Sun
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Gontikakis,
   C.; Kuckein, C.; Verma, M.; Denker, C.
2020A&A...633A..67K    Altcode: 2019arXiv191202496K
  Context. We study the evolution of a small-scale emerging flux region
  (EFR) in the quiet Sun, from its emergence in the photosphere to
  its appearance in the corona and its decay. <BR /> Aims: We track
  processes and phenomena that take place across all atmospheric layers;
  we explore their interrelations and compare our findings with those from
  recent numerical modelling studies. <BR /> Methods: We used imaging
  as well as spectral and spectropolarimetric observations from a suite
  of space-borne and ground-based instruments. <BR /> Results: The EFR
  appears in the quiet Sun next to the chromospheric network and shows all
  morphological characteristics predicted by numerical simulations. The
  total magnetic flux of the region exhibits distinct evolutionary phases,
  namely an initial subtle increase, a fast increase with a Co-temporal
  fast expansion of the region area, a more gradual increase, and a slow
  decay. During the initial stages, fine-scale G-band and Ca II H bright
  points coalesce, forming clusters of positive- and negative-polarity
  in a largely bipolar configuration. During the fast expansion, flux
  tubes make their way to the chromosphere, pushing aside the ambient
  magnetic field and producing pressure-driven absorption fronts that
  are visible as blueshifted chromospheric features. The connectivity
  of the quiet-Sun network gradually changes and part of the existing
  network forms new connections with the newly emerged bipole. A few
  minutes after the bipole has reached its maximum magnetic flux, the
  bipole brightens in soft X-rays forming a coronal bright point. The
  coronal emission exhibits episodic brightenings on top of a long
  smooth increase. These coronal brightenings are also associated
  with surge-like chromospheric features visible in Hα, which can
  be attributed to reconnection with adjacent small-scale magnetic
  fields and the ambient quiet-Sun magnetic field. <BR /> Conclusions:
  The emergence of magnetic flux even at the smallest scales can be the
  driver of a series of energetic phenomena visible at various atmospheric
  heights and temperature regimes. Multi-wavelength observations reveal
  a wealth of mechanisms which produce diverse observable effects during
  the different evolutionary stages of these small-scale structures.

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Title: Quantifying Ionospheric Disturbances for User Oriented
    Applications as a Contribution of the ISWAT Ionosphere Variability
    Cluster
Authors: Belehaki, A.; Tsagouri, I.; Tziotziou, K.; Xenaki, I.; Juan,
   J. M.; Magdaleno, S.
2019AGUFMSM31C3184B    Altcode:
  The reliable identification of space weather effects on the Earth's
  ionosphere and the effective communication of ionospheric alerts and
  warnings in support of technological systems' operations are always
  considered key users' requirements. The requirements differ for
  different applications and effects of different temporal and spatial
  scales (i.e. large-scale and small-scale ionospheric effects) and
  therefore, the close collaboration with users for the development of
  really actionable products is necessary. This is a challenging task,
  involving coordination at international level such as the Ionosphere
  Variability ISWAT Cluster that anticipates and embraces relevant
  activities. To help the efforts, this work takes advantage of the
  European TechTIDE network (http://www.tech-tide.eu/) to report results
  regarding the quantification of the ionospheric activity level with
  respect to relevant systems' performances (e.g. EGNOS). To this effect,
  the deviations of observed ionospheric characteristics from their
  background values are statistically analyzed during quiet and disturbed
  conditions to indicate quantitative criteria for the determination of
  significant ionospheric disturbances. The sophisticated representation
  of the background conditions by running averages with variable time
  windows (ranging from 60 minutes to 30-days) allows the distinction of
  ionospheric disturbances at different scales (e.g. ionospheric storm
  effects and travelling ionospheric disturbances, TIDs) in real time
  mode, while the comparison of the results with ionosphere activity
  indicators related to users' requirements, such as the AATR (Along
  Track TEC Rate) index supports fine tuning of different ionospheric
  activity levels in conjunction to the relevance of each level in
  systems' underperformances. The analysis applies to electron densities
  at various altitudes in the bottomside and topside ionosphere and
  the critical frequency foF2, aiming to cover the needs in the middle
  latitude ionosphere.

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Title: A persistent quiet-Sun small-scale tornado. II. Oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.
2019A&A...623A.160T    Altcode: 2019arXiv190304796T
  Context. Recently, the appearance, characteristics, and dynamics of
  a persistent 1.7 h vortex flow, resembling a small-scale tornado,
  have been investigated with observations both from the ground and from
  space in a quiet-Sun region in several lines and channels and for the
  first time in the Hα line centre. The vortex flow showed significant
  substructure in the form of several intermittent chromospheric
  swirls. <BR /> Aims: We investigate the oscillatory behaviour of
  various physical parameters in the vortex area in an attempt to better
  understand the physics of the reported vortex flow. This is the first
  analysis of this extent. <BR /> Methods: We used the same data set of
  high spatial and temporal resolution CRisp Imaging SpectroPolarimeter
  (CRISP) observations in several wavelengths along the Hα and Ca II
  8542 Å line profiles, as well as Doppler velocities and full-width at
  half-maximum (FWHM) derived from the Hα line profiles. The spectral
  analysis of oscillations is based on a two-dimensional wavelet analysis
  performed within the vortex flow area and in a quiet-Sun region (used
  for comparison), as well as along line and circular slices. <BR />
  Results: The vortex flow shows significant oscillatory power in the
  range of 3-5 min, peaking around 4 min. This power behaves differently
  than the reference quiet-Sun region. The derived oscillations reflect
  the cumulative action of different components such as swaying motions,
  rotation, and waves. The derived periods for swaying motions are in the
  range of 200-220 s, and the rotation periods are ∼270 s for Hα and
  ∼215 s for Ca II 8542 Å. Periods increase with atmospheric height
  and seem to decrease with radial distance from the vortex centre,
  suggesting a deviation from a rigid rotation. The behaviour of power
  within the vortex flow as a function of period and height implies the
  existence of evanescent waves. Moreover, considerable power is obtained
  even for periods as long as 10 min, not only at photospheric but also
  at chromospheric heights, while the formation of vortexes is related to
  turbulent convection or to twisting motions exercised in the magnetic
  field concentrations. These imply that different types of waves may be
  excited, such as magnetoacoustic (e.g. kink) or Alfvén waves. <BR />
  Conclusions: The vortex flow seems to be dominated by two motions:
  a transverse (swaying) motion, and a rotational motion. The obtained
  oscillations point to the propagation of waves within it. Nearby
  fibril-like flows could play an important role in the rotational
  modulation of the vortex flow. There also exists indirect evidence that
  the structure is magnetically supported, and one of the swirls, close to
  its centre, seems to be acting as a "central engine" to the vortex flow.

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Title: A persistent quiet-Sun small-scale tornado. I. Characteristics
    and dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion,
   E.; Doyle, J. G.
2018A&A...618A..51T    Altcode:
  Context. Vortex flows have been extensively observed over a wide range
  of spatial and temporal scales in different spectral lines, and thus
  layers of the solar atmosphere, and have been widely found in numerical
  simulations. However, signatures of vortex flows have only recently
  been reported in the wings of the Hα, but never so far in the Hα line
  centre. <BR /> Aims: We investigate the appearance, characteristics,
  substructure, and dynamics of a 1.7 h persistent vortex flow observed
  from the ground and from space in a quiet-Sun region in several
  lines/channels covering all atmospheric layers from the photosphere up
  to the low corona. <BR /> Methods: We use high spatial and temporal
  resolution CRisp Imaging SpectroPolarimeter (CRISP) observations in
  several wavelengths along the Hα and Ca II 8542 Å line profiles,
  simultaneous Atmospheric Imaging Assembly (AIA) observations in several
  Ultraviolet (UV) and Extreme ultraviolet (EUV) channels and Helioseismic
  and Magnetic Imager (HMI) magnetograms to study a persistent vortex flow
  located at the south solar hemisphere. Doppler velocities were derived
  from the Hα line profiles. Our analysis involves visual inspection and
  comparison of all available simultaneous/near-simultaneous observations
  and detailed investigation of the vortex appearance, characteristics
  and dynamics using time slices along linear and circular slits. <BR />
  Results: The most important characteristic of the analysed clockwise
  rotating vortex flow is its long duration (at least 1.7 h) and its
  large radius ( 3″). The vortex flow shows different behaviours in
  the different wavelengths along the Hα and Ca II 8542 Å profiles
  reflecting the different formation heights and mechanisms of the two
  lines. Ground-based observations combined with AIA observations reveal
  the existence of a funnel-like structure expanding with height, possibly
  rotating rigidly or quasi-rigidly. However, there is no clear evidence
  that the flow is magnetically driven as no associated magnetic bright
  points have been observed in the photosphere. Hα and Ca II 8542 Å
  observations also reveal significant substructure within the flow,
  manifested as several individual intermittent chromospheric swirls
  with typical sizes and durations. They also exhibit a wide range of
  morphological patterns, appearing as dark absorbing features, associated
  mostly with mean upwards velocities around 3 km s<SUP>-1</SUP> and
  up to 8 km s<SUP>-1</SUP>, and occupying on average 25% of the total
  vortex area. The radial expansion of the spiral flow occurs with
  a mean velocity of 3 km s<SUP>-1</SUP>, while its dynamics can be
  related to the dynamics of a clockwise rigidly rotating logarithmic
  spiral with a swinging motion that is, however, highly perturbed by
  nearby flows associated with fibril-like structures. A first rough
  estimate of the rotational period of the vortex falls in the range of
  200-300 s. <BR /> Conclusions: The vortex flow resembles a small-scale
  tornado in contrast to previously reported short-lived swirls and
  in analogy to persistent giant tornadoes. It is unclear whether
  the observed substructure is indeed due to the physical presence
  of individual intermittent, recurring swirls or a manifestation of
  wave-related instabilities within a large vortex flow. Moreover,
  we cannot conclusively demonstrate that the long duration of
  the observed vortex is the result of a central swirl acting as an
  "engine" for the vortex flow, although there is significant supporting
  evidence inferred from its dynamics. It also cannot be excluded that
  this persistent vortex results from the combined action of several
  individual smaller swirls further assisted by nearby flows or that
  this is a new case in the literature of a hydrodynamically driven
  vortex flow. <P />The movie associated to Fig. 4 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201833101/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Probing the Quiet Solar Atmosphere from the Photosphere to
    the Corona
Authors: Kontogiannis, Ioannis; Gontikakis, Costis; Tsiropoula,
   Georgia; Tziotziou, Kostas
2018SoPh..293...56K    Altcode: 2018arXiv180307934K
  We investigate the morphology and temporal variability of a quiet-Sun
  network region in different solar layers. The emission in several
  extreme ultraviolet (EUV) spectral lines through both raster and
  slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on
  board the Hinode spacecraft is studied along with Hα observations and
  high-resolution spectropolarimetric observations of the photospheric
  magnetic field. The photospheric magnetic field is extrapolated up to
  the corona, showing a multitude of large- and small-scale structures. We
  show for the first time that the smallest magnetic structures at both
  the network and internetwork contribute significantly to the emission
  in EUV lines, with temperatures ranging from 8 ×10<SUP>4</SUP>K to
  6 ×10<SUP>5</SUP>K. Two components of transition region emission
  are present, one associated with small-scale loops that do not reach
  coronal temperatures, and another component that acts as an interface
  between coronal and chromospheric plasma. Both components are associated
  with persistent chromospheric structures. The temporal variability
  of the EUV intensity at the network region is also associated with
  chromospheric motions, pointing to a connection between transition
  region and chromospheric features. Intensity enhancements in the
  EUV transition region lines are preferentially produced by Hα
  upflows. Examination of two individual chromospheric jets shows that
  their evolution is associated with intensity variations in transition
  region and coronal temperatures.

---------------------------------------------------------
Title: X-Ray, Radio and SEP Observations of Relativistic Gamma-Ray
    Events
Authors: Klein, Karl-Ludwig; Tziotziou, Kostas; Zucca, Pietro;
   Valtonen, Eino; Vilmer, Nicole; Malandraki, Olga E.; Hamadache,
   Clarisse; Heber, Bernd; Kiener, Jürgen
2018ASSL..444..133K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Predicting Flares and Solar Energetic Particle Events: The
    FORSPEF Tool
Authors: Anastasiadis, A.; Papaioannou, A.; Sandberg, I.; Georgoulis,
   M.; Tziotziou, K.; Kouloumvakos, A.; Jiggens, P.
2017SoPh..292..134A    Altcode:
  A novel integrated prediction system for solar flares (SFs) and solar
  energetic particle (SEP) events is presented here. The tool called
  forecasting solar particle events and flares (FORSPEF) provides
  forecasts of solar eruptive events, such as SFs with a projection
  to occurrence and velocity of coronal mass ejections (CMEs), and
  the likelihood of occurrence of an SEP event. In addition, the
  tool provides nowcasting of SEP events based on actual SF and CME
  near real-time data, as well as the SEP characteristics (e.g. peak
  flux, fluence, rise time, and duration) per parent solar event. The
  prediction of SFs relies on the effective connected magnetic field
  strength (B<SUB>eff</SUB>) metric, which is based on an assessment
  of potentially flaring active-region (AR) magnetic configurations,
  and it uses a sophisticated statistical analysis of a large number
  of AR magnetograms. For the prediction of SEP events, new statistical
  methods have been developed for the likelihood of the SEP occurrence
  and the expected SEP characteristics. The prediction window in the
  forecasting scheme is 24 hours with a refresh rate of 3 hours, while
  the respective prediction time for the nowcasting scheme depends on
  the availability of the near real-time data and ranges between 15 - 20
  minutes for solar flares and 6 hours for CMEs. We present the modules
  of the FORSPEF system, their interconnection, and the operational
  setup. Finally, we demonstrate the validation of the modules of the
  FORSPEF tool using categorical scores constructed on archived data,
  and we also discuss independent case studies.

---------------------------------------------------------
Title: Multi-spacecraft solar energetic particle analysis of FERMI
    gamma-ray flare events within the HESPERIA H2020 project
Authors: Tziotziou, Kostas; Malandraki, Olga; Valtonen, Eino; Heber,
   Bernd; Zucca, Pietro; Klein, Karl-Ludwig; Vainio, Rami; Tsiropoula,
   Georgia; Share, Gerald
2017EGUGA..1913786T    Altcode:
  Multi-spacecraft observations of solar energetic particle (SEP)
  events are important for understanding the acceleration processes and
  the interplanetary propagation of particles released during eruptive
  events. In this work, we have carefully studied 25 gamma-ray flare
  events observed by FERMI and investigated possible associations with
  SEP-related events observed with STEREO and L1 spacecraft in the
  heliosphere. A data-driven velocity dispersion analysis (VDA) and
  Time-Shifting Analysis (TSA) are used for deriving the release times
  of protons and electrons at the Sun and for comparing them with the
  respective times stemming from the gamma-ray event analysis and their
  X-ray signatures, in an attempt to interconnect the SEPs and Fermi
  events and better understand the physics involved. Acknowledgements:
  This project has received funding from the European Union's Horizon
  2020 research and innovation program under grant agreement No 637324.

---------------------------------------------------------
Title: Solar flares, coronal mass ejections and solar energetic
    particle event characteristics
Authors: Papaioannou, Athanasios; Sandberg, Ingmar; Anastasiadis,
   Anastasios; Kouloumvakos, Athanasios; Georgoulis, Manolis K.;
   Tziotziou, Kostas; Tsiropoula, Georgia; Jiggens, Piers; Hilgers, Alain
2016JSWSC...6A..42P    Altcode:
  A new catalogue of 314 solar energetic particle (SEP) events extending
  over a large time span from 1984 to 2013 has been compiled. The
  properties as well as the associations of these SEP events with their
  parent solar sources have been thoroughly examined. The properties of
  the events include the proton peak integral flux and the fluence for
  energies above 10, 30, 60 and 100 MeV. The associated solar events
  were parametrized by solar flare (SF) and coronal mass ejection (CME)
  characteristics, as well as related radio emissions. In particular,
  for SFs: the soft X-ray (SXR) peak flux, the SXR fluence, the
  heliographic location, the rise time and the duration were exploited;
  for CMEs the plane-of-sky velocity as well as the angular width were
  utilized. For radio emissions, type III, II and IV radio bursts were
  identified. Furthermore, we utilized element abundances of Fe and
  O. We found evidence that most of the SEP events in our catalogue
  do not conform to a simple two-class paradigm, with the 73% of them
  exhibiting both type III and type II radio bursts, and that a continuum
  of event properties is present. Although, the so-called hybrid or mixed
  events are found to be present in our catalogue, it was not possible
  to attribute each SEP event to a mixed/hybrid sub-category. Moreover,
  it appears that the start of the type III burst most often precedes
  the maximum of the SF and thus falls within the impulsive phase of the
  associated SF. At the same time, type III bursts take place within
  ≈5.22 min, on average, in advance from the time of maximum of the
  derivative of the SXR flux (Neupert effect). We further performed
  a statistical analysis and a mapping of the logarithm of the proton
  peak flux at E &gt; 10 MeV, on different pairs of the parent solar
  source characteristics. This revealed correlations in 3-D space and
  demonstrated that the gradual SEP events that stem from the central part
  of the visible solar disk constitute a significant radiation risk. The
  velocity of the associated CMEs, as well as the SXR peak flux and
  fluence, are all fairly significantly correlated to both the proton peak
  flux and the fluence of the SEP events in our catalogue. The strongest
  correlation to SEP characteristics is manifested by the CME velocity.

---------------------------------------------------------
Title: Solar Flare Prediction Science-to-Operations: the ESA/SSA
    SWE A-EFFort Service
Authors: Georgoulis, Manolis K.; Tziotziou, Konstantinos; Themelis,
   Konstantinos; Magiati, Margarita; Angelopoulou, Georgia
2016cosp...41E.656G    Altcode:
  We attempt a synoptical overview of the scientific origins of the
  Athens Effective Solar Flare Forecasting (A-EFFort) utility and
  the actions taken toward transitioning it into a pre-operational
  service of ESA's Space Situational Awareness (SSA) Programme. The
  preferred method for solar flare prediction, as well as key efforts
  to make it function in a fully automated environment by coupling
  calculations with near-realtime data-downloading protocols (from the
  Solar Dynamics Observatory [SDO] mission), pattern recognition (solar
  active-region identification) and optimization (magnetic connectivity
  by simulated annealing) will be highlighted. In addition, the entire
  validation process of the service will be described, with its results
  presented. We will conclude by stressing the need for across-the-board
  efforts and synergistic work in order to bring science of potentially
  limited/restricted interest into realizing a much broader impact
  and serving the best public interests. The above presentation was
  partially supported by the ESA/SSA SWE A-EFFort project, ESA Contract
  No. 4000111994/14/D/MRP. Special thanks go to the ESA Project Officers
  R. Keil, A. Glover, and J.-P. Luntama (ESOC), M. Bobra and C. Balmer
  of the SDO/HMI team at Stanford University, and M. Zoulias at the
  RCAAM of the Academy of Athens for valuable technical help.

---------------------------------------------------------
Title: Quiet Sun and its Dynamics as Viewed from the Ground and
    from Space
Authors: Tziotziou, K.
2016ASPC..504....3T    Altcode:
  Over the last years, state-of-the-art ground-based and/or space-based
  observations using imaging, spectroscopic and spectropolarimetric
  instruments, at a wide range of wavelengths, reveal that the quiet
  Sun, just like active regions, is a highly inhomogeneous and dynamic
  environment that plays an important role in the dynamics of the
  entire solar atmosphere. This dynamic quiet Sun is manifested through
  a number of different types of features and phenomena that occur
  in a large range of spatial and temporal scales and are nowadays
  believed to be mostly driven by the local magnetic field and its
  dynamics. Ground-based observations processed with state-of-the-art,
  post-processing reconstruction techniques, often combined with
  simultaneous space-based observations from a variety of instruments on
  different spacecraft, offer a unique opportunity to investigate and
  understand the physical conditions of the local plasma, the nature,
  formation mechanisms and evolution of quiet Sun phenomena and possible
  interrelationships between quiet Sun phenomena occurring at different
  heights of the quiet Sun solar atmosphere, from the photosphere and
  chromosphere to the transition region and low corona. We provide a
  comprehensive review of our latest understanding of quiet Sun and
  its dynamics as viewed from the ground and from space and discuss the
  advantages/disadvantages of ground- and space-based observations and
  future advents in solar observations with new solar instruments.

---------------------------------------------------------
Title: First simultaneous SST/CRISP and IRIS observations of a
    small-scale quiet Sun vortex
Authors: Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.; Tziotziou,
   K.; Scullion, E.; Doyle, J. G.
2016A&A...586A..25P    Altcode: 2015arXiv151206032P
  Context. Ubiquitous small-scale vortices have recently been found
  in the lower atmosphere of the quiet Sun in state-of-the-art solar
  observations and in numerical simulations. <BR /> Aims: We investigate
  the characteristics and temporal evolution of a granular-scale vortex
  and its associated upflows through the photosphere and chromosphere
  of a quiet Sun internetwork region. <BR /> Methods: We analyzed high
  spatial and temporal resolution ground- and spaced-based observations
  of a quiet Sun region. The observations consist of high-cadence time
  series of wideband and narrowband images of both Hα 6563 Å and Ca
  II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter
  (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well
  as ultraviolet imaging and spectral data simultaneously obtained by
  the Interface Region Imaging Spectrograph (IRIS). <BR /> Results:
  A small-scale vortex is observed for the first time simultaneously
  in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the
  vortex, Hα narrowband images at -0.77 Å and Ca II 8542 Å narrowband
  images at -0.5 Å, and their corresponding Doppler signal maps, clearly
  show consecutive high-speed upflow events in the vortex region. These
  high-speed upflows with a size of 0.5-1 Mm appear in the shape of
  spiral arms and exhibit two distinctive apparent motions in the plane
  of sky for a few minutes: (1) a swirling motion with an average speed
  of 13 km s<SUP>-1</SUP> and (2) an expanding motion at a rate of
  4-6 km s<SUP>-1</SUP>. Furthermore, the spectral analysis of Mg II k
  and Mg II subordinate lines in the vortex region indicates an upward
  velocity of up to ~8 km s<SUP>-1</SUP> along with a higher temperature
  compared to the nearby quiet Sun chromosphere. <BR /> Conclusions:
  The consecutive small-scale vortex events can heat the upper
  chromosphere by driving continuous high-speed upflows through the lower
  atmosphere. <P />Movies associated to Figs. 2 and 3 are available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201527440/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: The Major Geoeffective Solar Eruptions of 2012 March 7:
    Comprehensive Sun-to-Earth Analysis
Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos,
   A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou,
   G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.;
   Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.;
   Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou,
   K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.;
   Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.;
   Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris,
   E.; Tsinganos, K.; Vlahos, L.
2016ApJ...817...14P    Altcode:
  During the interval 2012 March 7-11 the geospace experienced a
  barrage of intense space weather phenomena including the second
  largest geomagnetic storm of solar cycle 24 so far. Significant
  ultra-low-frequency wave enhancements and relativistic-electron dropouts
  in the radiation belts, as well as strong energetic-electron injection
  events in the magnetosphere were observed. These phenomena were
  ultimately associated with two ultra-fast (&gt;2000 km s<SUP>-1</SUP>)
  coronal mass ejections (CMEs), linked to two X-class flares launched
  on early 2012 March 7. Given that both powerful events originated from
  solar active region NOAA 11429 and their onsets were separated by less
  than an hour, the analysis of the two events and the determination
  of solar causes and geospace effects are rather challenging. Using
  satellite data from a flotilla of solar, heliospheric and magnetospheric
  missions a synergistic Sun-to-Earth study of diverse observational
  solar, interplanetary and magnetospheric data sets was performed. It was
  found that only the second CME was Earth-directed. Using a novel method,
  we estimated its near-Sun magnetic field at 13 R<SUB>⊙</SUB> to be
  in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun
  CME magnetic field are required to match the magnetic fields of the
  corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream
  solar-wind conditions, as resulting from the shock associated with the
  Earth-directed CME, offer a decent description of its kinematics. The
  magnetospheric compression caused by the arrival at 1 AU of the shock
  associated with the ICME was a key factor for radiation-belt dynamics.

---------------------------------------------------------
Title: Wave propagation in a solar quiet region and the influence
    of the magnetic canopy
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2016A&A...585A.110K    Altcode: 2015arXiv151108618K
  <BR /> Aims: We seek indications or evidence of transmission/conversion
  of magnetoacoustic waves at the magnetic canopy, as a result of its
  impact on the properties of the wave field of the photosphere and
  chromosphere. <BR /> Methods: We use cross-wavelet analysis to measure
  phase differences between intensity and Doppler signal oscillations
  in the Hα, Ca II h, and G-band. We use the height of the magnetic
  canopy to create appropriate masks to separate internetwork (IN) and
  magnetic canopy regions. We study wave propagation and differences
  between these two regions. <BR /> Results: The magnetic canopy affects
  wave propagation by lowering the phase differences of progressive waves
  and allowing the propagation of waves with frequencies lower than the
  acoustic cut-off. We also find indications in the Doppler signals of
  Hα of a response to the acoustic waves at the IN, observed in the Ca
  II h line. This response is affected by the presence of the magnetic
  canopy. <BR /> Conclusions: Phase difference analysis indicates
  the existence of a complicated wave field in the quiet Sun, which
  is composed of a mixture of progressive and standing waves. There
  are clear imprints of mode conversion and transmission due to the
  interaction between the p-modes and small-scale magnetic fields of
  the network and internetwork.

---------------------------------------------------------
Title: Energy and helicity injection in solar quiet regions
Authors: Tziotziou, K.; Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.
2015A&A...581A..61T    Altcode:
  <BR /> Aims: We investigate the free magnetic energy and relative
  magnetic helicity injection in solar quiet regions. <BR /> Methods:
  We use the DAVE4VM method to infer the photospheric velocity field
  and calculate the free magnetic energy and relative magnetic helicity
  injection rates in 16 quiet-Sun vector magnetograms sequences. <BR />
  Results: We find that there is no dominant sense of helicity injection
  in quiet-Sun regions, and that both helicity and energy injections are
  mostly due to surface shuffling motions that dominate the respective
  emergence by factors slightly larger than two. We, furthermore,
  estimate the helicity and energy rates per network unit area as
  well as the respective budgets over a complete solar cycle. <BR />
  Conclusions: Derived helicity and energy budgets over the entire solar
  cycle are similar to respective budgets derived in a recent work from
  the instantaneous helicity and free magnetic energy budgets and higher
  than previously reported values that relied on similar approaches to
  this analysis. Free-energy budgets, mostly generated like helicity
  at the network, are high enough to power the dynamics of fine-scale
  structures residing at the network, such as mottles and spicules,
  while corresponding estimates of helicity budgets are provided,
  pending future verification from high-resolution magneto-hydrodynamic
  simulations and/or observations.

---------------------------------------------------------
Title: The European Ionosonde Service: nowcasting and forecasting
    ionospheric conditions over Europe for the ESA Space Situational
    Awareness services
Authors: Belehaki, Anna; Tsagouri, Ioanna; Kutiev, Ivan; Marinov,
   Pencho; Zolesi, Bruno; Pietrella, Marco; Themelis, Kostas; Elias,
   Panagiotis; Tziotziou, Kostas
2015JSWSC...5A..25B    Altcode:
  The Earth's ionosphere is a magnetoionic medium imbedded in a background
  neutral atmosphere, exhibiting very interesting refractive properties,
  including anisotropy, dispersion, and dissipation. As such, it poses a
  challenge for several radio systems that make use of signal transmission
  through all or some portion of the medium. It is important therefore to
  develop prediction systems able to inform the operators of such systems
  about the current state of the ionosphere, about the expected effects
  of forthcoming space weather disturbances and about support long-term
  planning of operations and data post-processing projects for improving
  modelling and mitigation techniques. The European Space Agency (ESA)
  in the framework of the Space Situational Awareness (SSA) Programme has
  supported the development of the European Ionosonde Service (EIS) that
  releases a set of products to characterise the bottomside and topside
  ionosphere over Europe. The Service is based on a set of prediction
  models driven by data from ground-based ionosondes and supportive data
  from satellites and spacecraft. The service monitors the foF2 and the
  electron density profile up to the height of the Global Navigation
  Satellite System (GNSS) at European middle and high latitudes and
  provides estimates for forthcoming disturbances mainly triggered by
  geo-effective Coronal Mass Ejections (CMEs). The model's performance
  has been validated and based on these results, it was possible to issue
  together with the products, quality metrics characterizing the product's
  reliability. The EIS products meet the requirements of various SSA
  service domains, especially the transionospheric radio link and the
  spacecraft operations. Currently, the service is freely available to
  all interested users, and access is possible upon registration.

---------------------------------------------------------
Title: Relationship between Solar Energetic Particles and Properties
of Flares and CMEs: Statistical Analysis of Solar Cycle 23 Events
Authors: Dierckxsens, M.; Tziotziou, K.; Dalla, S.; Patsou, I.; Marsh,
   M. S.; Crosby, N. B.; Malandraki, O.; Tsiropoula, G.
2015SoPh..290..841D    Altcode: 2014arXiv1410.6070D; 2015SoPh..tmp....1D
  A statistical analysis of the relationship between solar energetic
  particles (SEPs) and properties of solar flares and coronal mass
  ejections (CMEs) is presented. SEP events during Solar Cycle 23 are
  selected that are associated with solar flares originating in the
  visible hemisphere of the Sun and that are at least of magnitude
  M1. Taking into account all flares and CMEs that occurred during
  this period, the probability for the occurrence of an SEP event near
  Earth is determined. A strong rise of this probability is observed
  for increasing flare intensities, more western locations, higher
  CME speeds, and halo CMEs. The correlations between the proton peak
  flux and these solar parameters are derived for a low (&gt; 10 MeV)
  and high (&gt; 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&gt;10 MeV
  (E&gt;60 MeV). For both energy ranges, the correlations with flare
  longitude and CME width are very weak or non-existent. Furthermore, the
  occurrence probabilities, correlation coefficients, and mean peak fluxes
  are derived in multi-dimensional bins combining the aforementioned
  solar parameters. The correlation coefficients are also determined in
  different proton energy channels ranging from 5 to 200 MeV. The results
  show that the correlation between the proton peak flux and the CME speed
  decreases with energy, while the correlation with the flare intensity
  shows the opposite behaviour. Furthermore, the correlation with the CME
  speed is stronger than the correlation with the flare intensity below
  15 MeV and becomes weaker above 20 MeV. When the enhancements in the
  flux profiles due to interplanetary shocks are not excluded, only a
  small but not very significant change is observed in the correlation
  coefficients between the proton peak flux below 7 MeV and the CME speed.

---------------------------------------------------------
Title: Validation and Benchmarking of a Practical Free Magnetic
    Energy and Relative Magnetic Helicity Budget Calculation in Solar
    Magnetic Structures
Authors: Moraitis, K.; Tziotziou, K.; Georgoulis, M. K.; Archontis, V.
2014SoPh..289.4453M    Altcode: 2014arXiv1406.5381M; 2014SoPh..tmp..122M
  In earlier works we introduced and tested a nonlinear force-free
  (NLFF) method designed to self-consistently calculate the coronal
  free magnetic energy and the relative magnetic helicity budgets of
  observed solar magnetic structures. In principle, the method requires
  only a single, photospheric or low-chromospheric, vector magnetogram
  of a quiet-Sun patch or an active region and performs calculations
  without three-dimensional magnetic and velocity-field information. In
  this work we strictly validate this method using three-dimensional
  coronal magnetic fields. Benchmarking employs both synthetic,
  three-dimensional magnetohydrodynamic simulations and nonlinear
  force-free field extrapolations of the active-region solar corona. Our
  time-efficient NLFF method provides budgets that differ from those of
  more demanding semi-analytical methods by a factor of approximately
  three, at most. This difference is expected to come from the physical
  concept and the construction of the method. Temporal correlations show
  more discrepancies that are, however, soundly improved for more complex,
  massive active regions, reaching correlation coefficients on the order
  of, or exceeding, 0.9. In conclusion, we argue that our NLFF method
  can be reliably used for a routine and fast calculation of the free
  magnetic energy and relative magnetic helicity budgets in targeted
  parts of the solar magnetized corona. As explained in this article and
  in previous works, this is an asset that can lead to valuable insight
  into the physics and triggering of solar eruptions.

---------------------------------------------------------
Title: Validation of the magnetic energy vs. helicity scaling in
    solar magnetic structures
Authors: Tziotziou, K.; Moraitis, K.; Georgoulis, M. K.; Archontis, V.
2014A&A...570L...1T    Altcode: 2014arXiv1409.8117T
  <BR /> Aims: We assess the validity of the free magnetic energy -
  relative magnetic helicity diagram for solar magnetic structures. <BR />
  Methods: We used two different methods of calculating the free magnetic
  energy and the relative magnetic helicity budgets: a classical,
  volume-calculation nonlinear force-free (NLFF) method applied to
  finite coronal magnetic structures and a surface-calculation NLFF
  derivation that relies on a single photospheric or chromospheric vector
  magnetogram. Both methods were applied to two different data sets,
  namely synthetic active-region cases obtained by three-dimensional
  magneto-hydrodynamic (MHD) simulations and observed active-region cases,
  which include both eruptive and noneruptive magnetic structures. <BR
  /> Results: The derived energy-helicity diagram shows a consistent
  monotonic scaling between relative helicity and free energy with
  a scaling index 0.84 ± 0.05 for both data sets and calculation
  methods. It also confirms the segregation between noneruptive and
  eruptive active regions and the existence of thresholds in both free
  energy and relative helicity for active regions to enter eruptive
  territory. <BR /> Conclusions: We consider the previously reported
  energy-helicity diagram of solar magnetic structures as adequately
  validated and envision a significant role of the uncovered scaling in
  future studies of solar magnetism.

---------------------------------------------------------
Title: SEPServer catalogues of solar energetic particle events at
1 AU based on STEREO recordings: 2007-2012
Authors: Papaioannou, A.; Malandraki, O. E.; Dresing, N.; Heber, B.;
   Klein, K. -L.; Vainio, R.; Rodríguez-Gasén, R.; Klassen, A.; Nindos,
   A.; Heynderickx, D.; Mewaldt, R. A.; Gómez-Herrero, R.; Vilmer, N.;
   Kouloumvakos, A.; Tziotziou, K.; Tsiropoula, G.
2014A&A...569A..96P    Altcode:
  The Solar Terrestrial Relations Observatory (STEREO) recordings
  provide an unprecedented opportunity to study the evolution of
  solar energetic particle (SEP) events from different observation
  points in the heliosphere, allowing one to identify the effects of
  the properties of the interplanetary magnetic field (IMF) and solar
  wind structures on the interplanetary transport and acceleration of
  SEPs. Two catalogues based on STEREO recordings, have been compiled as
  a part of the SEPServer project, a three-year collaborative effort of
  eleven European partners funded under the Seventh Framework Programme
  of the European Union (FP7/SPACE). In particular, two instruments on
  board STEREO have been used to identify all SEP events observed within
  the descending phase of solar cycle 23 and the rising phase of solar
  cycle 24 from 2007 to 2012, namely: the Low Energy Telescope (LET)
  and the Solar Electron Proton Telescope (SEPT). A scan of STEREO/LET
  protons within the energy range 6-10 MeV has been performed for each of
  the two STEREO spacecraft. We have tracked all enhancements that have
  been observed above the background level of this particular channel
  and cross-checked with available lists of interplanetary coronal mass
  ejections (ICMEs), stream interaction regions (SIRs), and shocks, as
  well as with the reported events in literature. Furthermore, parallel
  scanning of the STEREO near relativistic electrons has been performed
  in order to pinpoint the presence (or absence) of an electron event in
  the energy range of 55-85 keV, for all of the aforementioned proton
  events included in our lists. We provide the onset and peak time as
  well as the peak value of all events for both protons and electrons,
  the relevant solar associations in terms of electromagnetic emissions,
  soft and hard X-rays (SXRs and HXRs). Finally, a subset of events with
  clear recordings at both STEREO spacecraft is presented together with
  the parent solar events of these multispacecraft SEP events.

---------------------------------------------------------
Title: Transmission and conversion of magnetoacoustic waves on the
    magnetic canopy in a quiet Sun region
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2014A&A...567A..62K    Altcode: 2014arXiv1406.5066K
  Context. We present evidence for the conversion and transmission of
  wave modes on the magnetic flux tubes that constitute mottles and form
  the magnetic canopy in a quiet Sun region. <BR /> Aims: Our aim is
  to highlight the details and the key parameters of the mechanism that
  produces power halos and magnetic shadows around the magnetic network
  observed in Hα. <BR /> Methods: We use our previous calculations of
  the magnetic field vector and the height of the magnetic canopy, and
  based on simple assumptions, we determine the turning height, i.e.,
  the height at which the fast magnetoacoustic waves reflect at the
  chromosphere. We compare the variation of 3, 5, and 7 min power in the
  magnetic shadow and the power halo with the results of a two-dimensional
  model on mode conversion and transmission. The key parameter of the
  model is the attack angle, which is related to the inclination of the
  magnetic field vector at the canopy height. Our analysis takes also
  into account that 1) there are projection effects on the propagation of
  waves; 2) the magnetic canopy and the turning height are curved layers;
  3) waves with periods longer than 3 min only reach the chromosphere
  in the presence of inclined magnetic fields (ramp effect); 4) mottles
  in Hα are canopy structures; and 5) the wings of Hα contain mixed
  signal from low- and high-β plasma. <BR /> Results: The dependence of
  the measured power on the attack angle follows the anticipated by the
  two-dimensional model very well. Long-period slow waves are channeled
  to the upper chromospheric layers following the magnetic field lines of
  mottles, while short-period fast waves penetrate the magnetic canopy and
  are reflected back higher, at the turning height. <BR /> Conclusions:
  Although both magnetoacoustic modes contribute to velocity signals,
  making the interpretation of observations a challenging task, we
  conclude that conversion and transmission of the acoustic waves into
  fast and slow magnetoacoustic waves are responsible for forming power
  halos and magnetic shadows in the quiet Sun region.

---------------------------------------------------------
Title: Energy and helicity budgets of solar quiet regions
Authors: Tziotziou, K.; Tsiropoula, G.; Georgoulis, M. K.;
   Kontogiannis, I.
2014A&A...564A..86T    Altcode: 2014arXiv1403.0730T
  <BR /> Aims: We investigate the free magnetic energy and relative
  magnetic helicity budgets of solar quiet regions. <BR /> Methods:
  Using a novel nonlinear force-free method that requires single solar
  vector magnetograms we calculated the instantaneous free magnetic
  energy and relative magnetic helicity budgets in 55 quiet-Sun vector
  magnetograms. <BR /> Results: As in a previous work on active regions,
  we constructed here for the first time the (free) energy-(relative)
  helicity diagram of quiet-Sun regions. We find that quiet-Sun regions
  have no dominant sense of helicity and show monotonic correlations
  a) between free magnetic energy/relative helicity and magnetic
  network area and, consequently, b) between free magnetic energy and
  helicity. Free magnetic energy budgets of quiet-Sun regions represent
  a rather continuous extension of respective active-region budgets
  towards lower values, but the corresponding helicity transition is
  discontinuous because of the incoherence of the helicity sense in
  contrast to active regions. We furthermore estimated the instantaneous
  free magnetic-energy and relative magnetic-helicity budgets of the
  entire quiet Sun, as well as the respective budgets over an entire solar
  cycle. <BR /> Conclusions: Derived instantaneous free magnetic energy
  budgets and, to a lesser extent, relative magnetic helicity budgets
  over the entire quiet Sun are similar to the respective budgets of a
  sizeable active region, while total budgets within a solar cycle are
  found to be higher than previously reported. Free-energy budgets are
  similar to the energy needed to power fine-scale structures residing
  at the network, such as mottles and spicules.

---------------------------------------------------------
Title: Free magnetic energy and relative magnetic helicity diagnostics
    for the quality of NLFF field extrapolations
Authors: Moraitis, Kostas; Archontis, Vasilis; Tziotziou, Konstantinos;
   Georgoulis, Manolis K.
2014cosp...40E2169M    Altcode:
  We calculate the instantaneous free magnetic energy and relative
  magnetic helicity of solar active regions using two independent
  approaches: a) a non-linear force-free (NLFF) method that requires
  only a single photospheric vector magnetogram, and b) well known
  semi-analytical formulas that require the full three-dimensional (3D)
  magnetic field structure. The 3D field is obtained either from MHD
  simulations, or from observed magnetograms via respective NLFF field
  extrapolations. We find qualitative agreement between the two methods
  and, quantitatively, a discrepancy not exceeding a factor of 4. The
  comparison of the two methods reveals, as a byproduct, two independent
  tests for the quality of a given force-free field extrapolation. We find
  that not all extrapolations manage to achieve the force-free condition
  in a valid, divergence-free, magnetic configuration. This research has
  been co-financed by the European Union (European Social Fund - ESF)
  and Greek national funds through the Operational Program "Education
  and Lifelong Learning" of the National Strategic Reference Framework
  (NSRF) - Research Funding Program: Thales. Investing in knowledge
  society through the European Social Fund.

---------------------------------------------------------
Title: Free magnetic energy and relative magnetic helicity in active
    and quiet solar regions and their role in solar dynamics
Authors: Tziotziou, Konstantinos; Archontis, Vasilis; Tsiropoula,
   Georgia; Georgoulis, Manolis K.; Moraitis, Kostas; Kontogiannis,
   Ioannis
2014cosp...40E3428T    Altcode:
  We present a novel non-linear force-free method for the calculation of
  the instantaneous free magnetic energy and relative magnetic helicity
  budgets of a solar region from a single photospheric/chromospheric
  vector magnetogram. Our objective is to study the role of these
  quantities both in solar eruptions and in quiet-Sun dynamics. The
  validity of the method is tested using both observations and synthetic
  magnetohydrodynamical (MHD) models. The method is applied for the
  derivation of the energy-helicity (EH) diagram of solar active regions
  (ARs) from a sample of 162 vector magnetograms corresponding to 42
  different ARs, suggesting the existence of 4×10(31) erg and 2×10(42)
  Mx(2) thresholds in free energy and relative helicity, respectively, for
  ARs to enter eruptive territory. Furthermore, the dynamical evolution
  of both quantities in eruptive NOAA AR 11158, using a high-cadence
  5-day time series of vector magnetograms, suggests the formation of
  increasingly helical pre-eruption structures and a causal relation
  between flares and Coronal Mass Ejections (CMEs). The method is
  also used to derive helicity and energy budgets in quiet Sun regions
  and construct the respective EH diagram. Our results highlight the
  importance of both energy and helicity in AR evolution and quiet-Sun
  dynamics and instigate further research on the underlying physics with
  three-dimensional MHD models. This work is supported by EU's Seventh
  Framework Programme via a Marie Curie Fellowship.

---------------------------------------------------------
Title: Transmission and conversion of magneto-acoustic waves in the
    quiet solar chromosphere
Authors: Kontogiannis, I., Tsiropoula, G.; Tziotziou, K.
2013hell.conf....6K    Altcode:
  We investigate the interaction between acoustic oscillations and the
  fine-scale structures found at the chromospheric network boundaries
  that form the magnetic canopy. To this end, high precision photospheric
  magnetograms obtained by SOT/SP on-board the Hinode space mission and
  time series of high spatial-resolution filtergrams in five wavelengths
  along the Hα line profile taken by the Dutch Open Telescope are
  utilized. We extrapolate the photospheric magnetic field using the
  current-free assumption to calculate the vector of the magnetic field
  and reconstruct the magnetic configuration of the chromosphere. Assuming
  the VAL-C atmospheric model we calculate the height of the magnetic
  canopy. Through wavelet analysis on the Hα observations we obtain
  the 2-D distribution of the oscillatory power at different atmospheric
  heights. We then compare the obtained distribution of power with the
  one predicted by a 2-D theoretical model at various magnetic field
  inclination angles. Our results show that the magnetic shadow and
  power halo phenomena observed in network regions may be attributed to
  the conversion/transmission of magneto-acoustic waves in the magnetic
  canopy. The amount of transmission/conversion depends on the frequency
  of the waves and the "attack" angle, i.e. the angle between the wave
  vector and magnetic field direction. This mechanism allows transmitted
  waves to propagate to greater atmospheric heights.

---------------------------------------------------------
Title: Magnetic helicity and free energy in solar active regions
Authors: Moraitis, K.; Georgoulis, M.; Tziotziou, K.; Archontis, V.
2013hell.confS..21M    Altcode:
  We study the evolution of the non-potential free magnetic energy
  and relative magnetic helicity budgets in solar active regions
  (ARs). For this we use a time-series of a three-dimensional, synthetic
  AR produced by magnetohydrodynamical (MHD) simulations. As a first
  step, we calculate the potential magnetic field that has the same
  normal components with the MHD field along all boundaries of the AR,
  by solving Laplace's equation. The free magnetic energy of the AR is
  then easily derived. From the two fields, MHD and potential one, we
  calculate the corresponding vector potentials with a recently proposed
  integration method. The knowledge of both fields and their respective
  vector potentials throughout the AR, allows us to estimate the relative
  magnetic helicity budget of the AR. Following this procedure for each
  snapshot of the AR, we reconstruct the evolution of free energy and
  helicity in the AR. Our method reproduces, for a synthetic AR, the
  energy/helicity relations known to hold in real active regions.

---------------------------------------------------------
Title: Free Magnetic Energy and Helicity in Active and Quiet Solar
    Regions and their role in Solar
Authors: Tziotziou, K.; Georgoulis, M. K.; Tsiropoula, G.; Moraitis,
   K.; Kontogiannis, I.
2013hell.conf....6T    Altcode:
  We present a novel nonlinear force-free method designed to calculate
  the instantaneous free magnetic energy and relative magnetic helicity
  budgets of a solar region from a single photospheric/chromospheric
  vector magnetogram of the region. Our objective is to study the role of
  these quantities in solar eruptions and quiet-Sun dynamics. We apply the
  method to (1) derive the energy/helicity diagram of solar active regions
  from a sample of 162 vector magnetograms corresponding to 42 different
  active regions (ARs), suggesting that there exist 4 1031 erg and 2 1042
  Mx2 thresholds in free energy and relative helicity, respectively, for
  ARs to enter eruptive territory, (2) study the dynamics of eruptive NOAA
  AR 11158 using a high-cadence 5-day time series of vector magnetograms,
  suggesting the formation of increasingly helical pre-eruption structures
  and a causal relation between flares and Coronal Mass Ejections (CMEs)
  and, (3) derive helicity and energy budgets in quiet Sun regions and
  construct the respective energy/helicity diagram. Our results highlight
  the importance of these two parameters in AR evolution and quiet-Sun
  dynamics and instigate further research including detailed analysis
  with synthetic, magnetohydrodynamical models. This work is supported by
  EU's Seventh Framework Programme via a Marie Curie Fellowship and by
  the Hellenic National Space Weather Research Network (HNSWRN) via the
  THALIS Programme.

---------------------------------------------------------
Title: Solar Energetic Particles within the STEREO era: 2007-2012
Authors: Papaioannou, A.; Malandraki, O. E.; Heber, B.; Dresing,
   N.; Klein, K. L.; Vainio, R.; Rodriguez-Gasen, R.; Klassen, A.;
   Gomez-Herrero, R.; Vilmer, N.; Mewaldt, R. A.; Tziotziou, K.;
   Tsiropoula, G.
2013hell.conf....9P    Altcode:
  STEREO (Solar TErrestrial RElations Observatory) recordings provide an
  unprecedented opportunity to identify the evolution of Solar Energetic
  Particles (SEPs) at different observing points in the heliosphere, which
  is expected to provide new insight on the physics of solar particle
  genesis, propagation and acceleration as well as on the properties of
  the interplanetary magnetic field that control these acceleration and
  propagation processes. In this work, two instruments onboard STEREO
  have been used in order to identify all SEP events observed within
  the rising phase of solar cycle 24 from 2007 to 2011, namely: the
  Low Energy Telescope (LET) and the Solar Electron Proton Telescope
  (SEPT). A scan over STEREO/LET protons within the energy range 6-10
  MeV has been performed for each of the two STEREO spacecraft. We have
  tracked all enhancements that have been observed above the background
  level of this particular channel and cross checked with available
  lists on STEREO/ICMEs, SIRs and shocks as well as with the reported
  events in literature. Furthermore, parallel scanning of the STEREO/SEPT
  electrons in order to pinpoint the presence (or not) of an electron
  event has been performed in the energy range of 55-85 keV, for all of
  the aforementioned proton events, included in our lists. We provide
  the onset of all events for both protons and electrons, time-shifting
  analysis for near relativistic electrons which lead to the inferred
  solar release time and the relevant solar associations from radio
  spectrographs (Nancay Decametric Array; STEREO/WAVES) to GOES Soft
  X-rays and coronal mass ejections spotted by both SOHO/LASCO and
  STEREO Coronographs

---------------------------------------------------------
Title: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption
    within the Framework of the
Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou,
   K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.;
   Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema,
   P.; Sarris, M.; Sarris, T.
2013hell.conf...10P    Altcode:
  Transient expulsions of gigantic clouds of solar coronal plasma into
  the interplanetary space in the form of Coronal Mass Ejections (CMEs)
  and sudden, intense flashes of electromagnetic radiation, solar flares,
  are well-established drivers of the variable Space Weather. Given the
  innate, intricate links and connections between the solar drivers and
  their geomagnetic effects, synergistic efforts assembling all pieces
  of the puzzle along the Sun-Earth line are required to advance our
  understanding of the physics of Space Weather. This is precisely the
  focal point of the Hellenic National Space Weather Research Network
  (HNSWRN) under the THALIS Programme. Within the HNSWRN framework,
  we present here the first results from a coordinated multi-instrument
  case study of a major solar eruption (X5.4 and X1.3 flares associated
  with two ultra-fast (&gt;2000 km/s) CMEs) which were launched early
  on 7 March 2012 and triggered an intense geomagnetic storm (min Dst
  =-147 nT) approximately two days afterwards. Several elements of
  the associated phenomena, such as the flare and CME, EUV wave, WL
  shock, proton and electron event, interplanetary type II radio burst,
  ICME and magnetic cloud and their spatiotemporal relationships and
  connections are studied all way from Sun to Earth. To this end, we
  make use of satellite data from a flotilla of solar, heliospheric and
  magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE,
  Herschel, Planck and INTEGRAL). We also present our first steps toward
  formulating a cohesive physical scenario to explain the string of the
  observables and to assess the various physical mechanisms than enabled
  and gave rise to the significant geoeffectiveness of the eruption.

---------------------------------------------------------
Title: Interpreting Eruptive Behavior in NOAA AR 11158 via the
    Region's Magnetic Energy and Relative-helicity Budgets
Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Liu, Yang
2013ApJ...772..115T    Altcode: 2013arXiv1306.2135T
  In previous works, we introduced a nonlinear force-free method
  that self-consistently calculates the instantaneous budgets of free
  magnetic energy and relative magnetic helicity in solar active regions
  (ARs). Calculation is expedient and practical, using only a single
  vector magnetogram per computation. We apply this method to a time
  series of 600 high-cadence vector magnetograms of the eruptive NOAA
  AR 11158 acquired by the Helioseismic and Magnetic Imager on board the
  Solar Dynamics Observatory over a five-day observing interval. Besides
  testing our method extensively, we use it to interpret the dynamical
  evolution in the AR, including eruptions. We find that the AR builds
  large budgets of both free magnetic energy and relative magnetic
  helicity, sufficient to power many more eruptions than the ones it gave
  within the interval of interest. For each of these major eruptions,
  we find eruption-related decreases and subsequent free-energy and
  helicity budgets that are consistent with the observed eruption (flare
  and coronal mass ejection (CME)) sizes. In addition, we find that (1)
  evolution in the AR is consistent with the recently proposed (free)
  energy-(relative) helicity diagram of solar ARs, (2) eruption-related
  decreases occur before the flare and the projected CME-launch times,
  suggesting that CME progenitors precede flares, and (3) self terms of
  free energy and relative helicity most likely originate from respective
  mutual terms, following a progressive mutual-to-self conversion pattern
  that most likely stems from magnetic reconnection. This results in the
  non-ideal formation of increasingly helical pre-eruption structures
  and instigates further research on the triggering of solar eruptions
  with magnetic helicity firmly placed in the eruption cadre.

---------------------------------------------------------
Title: Mode conversion and transmission of waves in quiet solar
    regions
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia; Tziotziou,
   Konstantinos
2013EGUGA..15..383K    Altcode:
  We investigate the interaction between acoustic oscillations and the
  fine-scale structures found at the chromospheric network boundaries
  that form the magnetic canopy. We use high precision photospheric
  magnetograms obtained by SOT/SP on-board the Hinode satellite and time
  series of high spatial resolution filtergrams in five wavelengths
  along the Hα line profile taken by the Dutch Open Telescope. We
  extrapolate the photospheric magnetic field using the current-free
  hypothesis to calculate the vector of the magnetic field and reconstruct
  the magnetic configuration of the chromosphere. Assuming the VAL-C
  atmospheric model we are able to estimate the height of formation of
  the magnetic canopy. We use the wavelet analysis on the Ha observations
  and obtain the 2-D distribution of the oscillatory power at different
  atmospheric heights. We then compare the obtained distribution of power
  with the one predicted by the 2-D model of Schunker &amp; Cally at
  various magnetic field inclination angles. Our results show that the
  magnetic shadow and power halo phenomena observed in network regions
  may be attributed to the conversion/transmission of magneto-acoustic
  waves on the magnetic canopy. The amount of transmission/conversion
  depends on the attack angle, i.e. the angle between the wave vector
  and magnetic field direction. Waves which experience mode conversion
  and/or transmission can propagate to greater atmospheric heights while
  some fraction of their energy escapes into the solar wind.

---------------------------------------------------------
Title: Statistical analysis of solar energetic particle events and
    related solar activity
Authors: Dierckxsens, Mark; Patsou, Ioanna; Tziotziou, Kostas; Marsh,
   Michael; Lygeros, Nik; Crosby, Norma; Dalla, Silvia; Malandraki, Olga
2013EGUGA..15.8865D    Altcode:
  The FP7 COMESEP (COronal Mass Ejections and Solar Energetic Particles:
  forecasting the space weather impact) project is developing tools
  for forecasting geomagnetic storms and solar energetic particle
  (SEP) radiation storms. Here we present preliminary results on a
  statistical analysis of SEP events and their parent solar activity
  during Solar Cycle 23. The work aims to identify correlations between
  solar events and SEP events relevant for space weather, as well as
  to quantify SEP event probabilities for use within the COMESEP alert
  system. The data sample covers the SOHO era and is based on the SEPEM
  reference event list [http://dev.sepem.oma.be/]. Events are subdivided
  if separate enhancements are observed in higher energy channels as
  defined for the list of Cane et al (2010). Energetic Storm Particle
  (ESP) enhancements during these events are identified by associating
  ESP-like increases in the proton channels with shocks detected in ACE
  and WIND data. Their contribution has been estimated and subtracted from
  the proton fluxes. Relationships are investigated between solar flare
  parameters such as X-ray intensity and heliographic location on the
  one hand, and the probability of occurrence and strength of energetic
  proton flux increases on the other hand. The same exercise is performed
  using the velocity and width of coronal mass ejections to examine their
  SEP productiveness. Relationships between solar event characteristics
  and SEP event spectral indices and fluences are also studied, as well
  as enhancements in heavy ion fluxes measured by the SIS instrument
  on board the ACE spacecraft during the same event periods. This work
  has received funding from the European Commission FP7 Project COMESEP
  (263252).

---------------------------------------------------------
Title: The first SEPServer event catalogue ~68-MeV solar proton
    events observed at 1 AU in 1996-2010
Authors: Vainio, Rami; Valtonen, Eino; Heber, Bernd; Malandraki, Olga
   E.; Papaioannou, Athanasios; Klein, Karl-Ludwig; Afanasiev, Alexander;
   Agueda, Neus; Aurass, Henry; Battarbee, Markus; Braune, Stephan;
   Dröge, Wolfgang; Ganse, Urs; Hamadache, Clarisse; Heynderickx, Daniel;
   Huttunen-Heikinmaa, Kalle; Kiener, Jürgen; Kilian, Patrick; Kopp,
   Andreas; Kouloumvakos, Athanasios; Maisala, Sami; Mishev, Alexander;
   Miteva, Rositsa; Nindos, Alexander; Oittinen, Tero; Raukunen, Osku;
   Riihonen, Esa; Rodríguez-Gasén, Rosa; Saloniemi, Oskari; Sanahuja,
   Blai; Scherer, Renate; Spanier, Felix; Tatischeff, Vincent; Tziotziou,
   Kostas; Usoskin, Ilya G.; Vilmer, Nicole
2013JSWSC...3A..12V    Altcode:
  SEPServer is a three-year collaborative project funded by the seventh
  framework programme (FP7-SPACE) of the European Union. The objective
  of the project is to provide access to state-of-the-art observations
  and analysis tools for the scientific community on solar energetic
  particle (SEP) events and related electromagnetic (EM) emissions. The
  project will eventually lead to better understanding of the particle
  acceleration and transport processes at the Sun and in the inner
  heliosphere. These processes lead to SEP events that form one of the key
  elements of space weather. In this paper we present the first results
  from the systematic analysis work performed on the following datasets:
  SOHO/ERNE, SOHO/EPHIN, ACE/EPAM, Wind/WAVES and GOES X-rays. A catalogue
  of SEP events at 1 AU, with complete coverage over solar cycle 23,
  based on high-energy (~68-MeV) protons from SOHO/ERNE and electron
  recordings of the events by SOHO/EPHIN and ACE/EPAM are presented. A
  total of 115 energetic particle events have been identified and analysed
  using velocity dispersion analysis (VDA) for protons and time-shifting
  analysis (TSA) for electrons and protons in order to infer the SEP
  release times at the Sun. EM observations during the times of the
  SEP event onset have been gathered and compared to the release time
  estimates of particles. Data from those events that occurred during
  the European day-time, i.e., those that also have observations from
  ground-based observatories included in SEPServer, are listed and a
  preliminary analysis of their associations is presented. We find that
  VDA results for protons can be a useful tool for the analysis of proton
  release times, but if the derived proton path length is out of a range
  of 1 AU &lt; s ≲ 3 AU, the result of the analysis may be compromised,
  as indicated by the anti-correlation of the derived path length and
  release time delay from the associated X-ray flare. The average path
  length derived from VDA is about 1.9 times the nominal length of
  the spiral magnetic field line. This implies that the path length of
  first-arriving MeV to deka-MeV protons is affected by interplanetary
  scattering. TSA of near-relativistic electrons results in a release
  time that shows significant scatter with respect to the EM emissions
  but with a trend of being delayed more with increasing distance between
  the flare and the nominal footpoint of the Earth-connected field line.

---------------------------------------------------------
Title: The relation between Magnetic Energy and Helicity and their
    accumulation in Eruptive Solar Active Regions
Authors: Tziotziou, K.; Georgoulis, M. K.; Raouafi, N. -E.
2013ASPC..470...59T    Altcode:
  Magnetic free energy and relative magnetic helicity are two important
  quantities characterizing solar active regions (ARs). Although the
  importance of free magnetic energy storage for solar eruptions is
  widely accepted, the role of magnetic helicity, that quantifies the
  stress and distortion of the magnetic field compared to its lowest
  (potential) energy state, is still under debate. A new nonlinear
  force-free method designed to calculate the instantaneous free magnetic
  energy and relative magnetic helicity budgets of a solar active region
  from a single vector magnetogram is presented. A sample of 40 vector
  magnetograms corresponding to different eruptive and non-eruptive ARs
  is used to calculate their free magnetic energy and relative magnetic
  helicity budgets, aiming to find a statistically robust correlation
  between them. The derived correlation implies that magnetic helicity,
  besides free magnetic energy, is a crucial ingredient for active
  regions hosting major (M-class and higher) solar eruptions. Eruptive
  active regions appear well segregated from non-eruptive ones in both
  free energy and relative helicity with eruptive major flares occurring
  in ARs with free energy and helicity exceeding 4×10<SUP>31</SUP>
  erg and 2×10<SUP>42</SUP> Mx<SUP>2</SUP>, respectively. Helicity is
  expelled from ARs mainly in the form of coronal mass ejections (CMEs)
  and the above helicity threshold agrees well with estimates of typical
  helicity contents of CMEs.

---------------------------------------------------------
Title: Magnetic Energy and Helicity Properties of Eruptive Solar
    Active Regions
Authors: Georgoulis, M. K.; Tziotziou, K.; Raouafi, N.
2012AGUFMSH53B..02G    Altcode:
  We outline a new nonlinear force-free method designed to
  self-consistently calculate the magnetic energy and the relative
  magnetic helicity budgets of solar active regions using only
  a single vector magnetogram at the lower atmospheric boundary
  of these regions. The method is fast and has been successfully
  validated with well-known magnetic-energy and relative-helicity
  formulas that, however, are model-dependent and more computationally
  demanding. Application of the method to a sizable sample of vector
  magnetograms reveals that eruptive active regions exceed well-defined,
  physically meaningful thresholds in both their magnetic free-energy
  and relative magnetic-helicity budgets. Moreover, application to
  a high-cadence vector-magnetogram timeseries of an eruptive region
  observed by the Helioseismic and Magnetic Imager onboard the Solar
  Dynamics Observatory leads to a physical interpretation of the region's
  dynamical evolution and reveals eruption-related energy and helicity
  changes. Several intriguing possibilities suggesting promising research
  avenues emerge from this analysis and are briefly discussed.

---------------------------------------------------------
Title: Magnetic Energy and Helicity Budgets in the Active-region
    Solar Corona. II. Nonlinear Force-free Approximation
Authors: Georgoulis, Manolis K.; Tziotziou, Kostas; Raouafi,
   Nour-Eddine
2012ApJ...759....1G    Altcode: 2012arXiv1209.5606G
  Expanding on an earlier work that relied on linear force-free (LFF)
  magnetic fields, we self-consistently derive the instantaneous
  free magnetic energy and relative magnetic helicity budgets of
  an unknown three-dimensional nonlinear force-free (NLFF) magnetic
  structure extending above a single known lower-boundary magnetic field
  vector. The proposed method does not rely on the detailed knowledge
  of the three-dimensional field configuration but is general enough to
  employ only a magnetic connectivity matrix on the lower boundary. The
  calculation yields a minimum free magnetic energy and a relative
  magnetic helicity consistent with this free magnetic energy. The
  method is directly applicable to photospheric or chromospheric vector
  magnetograms of solar active regions. Upon validation, it basically
  reproduces magnetic energies and helicities obtained by well known,
  but computationally more intensive and non-unique, methods relying on
  the extrapolated three-dimensional magnetic field vector. We apply
  the method to three active regions, calculating the photospheric
  connectivity matrices by means of simulated annealing, rather than a
  model-dependent NLFF extrapolation. For two of these regions we correct
  for the inherent LFF overestimation in free energy and relative helicity
  that is larger for larger, more eruptive, active regions. In the third
  region studied, our calculation can lead to a physical interpretation of
  observed eruptive manifestations. We conclude that the proposed method,
  including the proposed inference of the magnetic connectivity matrix,
  is practical enough to contribute to a physical interpretation of the
  dynamical evolution of solar active regions.

---------------------------------------------------------
Title: The Magnetic Energy-Helicity Diagram of Solar Active Regions
Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Raouafi,
   Nour-Eddine
2012ApJ...759L...4T    Altcode: 2012arXiv1209.5612T
  Using a recently proposed nonlinear force-free method designed for
  single-vector magnetograms of solar active regions, we calculate
  the instantaneous free magnetic energy and relative magnetic helicity
  budgets in 162 vector magnetograms corresponding to 42 different active
  regions. We find a statistically robust, monotonic correlation between
  the free magnetic energy and the relative magnetic helicity in the
  studied regions. This correlation implies that magnetic helicity, in
  addition to free magnetic energy, may be an essential ingredient for
  major solar eruptions. Eruptive active regions appear well segregated
  from non-eruptive ones in both free energy and relative helicity with
  major (at least M-class) flares occurring in active regions with free
  energy and relative helicity exceeding 4 × 10<SUP>31</SUP> erg and 2
  × 10<SUP>42</SUP> Mx<SUP>2</SUP>, respectively. The helicity threshold
  agrees well with estimates of the helicity contents of typical coronal
  mass ejections.

---------------------------------------------------------
Title: Scientific Analysis within SEPServer - New Perspectives in
Solar Energetic Particle Research: The Case Study of the 13 July
    2005 Event
Authors: Malandraki, O. E.; Agueda, N.; Papaioannou, A.; Klein, K. -L.;
   Valtonen, E.; Heber, B.; Dröge, W.; Aurass, H.; Nindos, A.; Vilmer,
   N.; Sanahuja, B.; Kouloumvakos, A.; Braune, S.; Preka-Papadema, P.;
   Tziotziou, K.; Hamadache, C.; Kiener, J.; Tatischeff, V.; Riihonen,
   E.; Kartavykh, Y.; Rodríguez-Gasén, R.; Vainio, R.
2012SoPh..281..333M    Altcode: 2012SoPh..tmp..287M; 2012SoPh..tmp..267M
  Solar energetic particle (SEP) events are a key ingredient of
  solar-terrestrial physics both for fundamental research and space
  weather applications. Multi-satellite observations are an important
  and incompletely exploited tool for studying the acceleration and the
  coronal and interplanetary propagation of the particles. While STEREO
  uses for this diagnostic two identical sets of instrumentation, there
  are many earlier observations carried out with different spacecraft. It
  is the aim of the SEPServer project to make these data and analysis
  tools available to a broad user community. The consortium will carry
  out data-driven analysis and simulation-based data analysis capable
  of deconvolving the effects of interplanetary transport and solar
  injection from SEP observations, and will compare the results with the
  electromagnetic signatures. The tools and results will be provided on
  the web server of the project in order to facilitate further analysis
  by the research community. This paper describes the data products and
  analysis strategies with one specific event, the case study of 13 July
  2005. The release time of protons and electrons are derived using
  data-driven and simulation-based analyses, and compared with hard
  X-ray and radio signatures. The interconnection of the experimental
  and the simulation-based results are discussed in detail.

---------------------------------------------------------
Title: Solar Fine-Scale Structures. I. Spicules and Other Small-Scale,
Jet-Like Events at the Chromospheric Level: Observations and Physical
    Parameters
Authors: Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.; Madjarska,
   M. S.; Doyle, J. G.; Suematsu, Y.
2012SSRv..169..181T    Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T
  Over the last two decades the uninterrupted, high resolution
  observations of the Sun, from the excellent range of telescopes aboard
  many spacecraft complemented with observations from sophisticated
  ground-based telescopes have opened up a new world producing
  significantly more complete information on the physical conditions of
  the solar atmosphere than before. The interface between the lower solar
  atmosphere where energy is generated by subsurface convection and the
  corona comprises the chromosphere, which is dominated by jet-like,
  dynamic structures, called mottles when found in quiet regions,
  fibrils when found in active regions and spicules when observed at
  the solar limb. Recently, space observations with Hinode have led to
  the suggestion that there should exist two different types of spicules
  called Type I and Type II which have different properties. Ground-based
  observations in the Ca ii H and K filtergrams reveal the existence of
  long, thin emission features called straws in observations close to
  the limb, and a class of short-lived events called rapid blue-shifted
  excursions characterized by large Doppler shifts that appear only
  in the blue wing of the Ca ii infrared line. It has been suggested
  that the key to understanding how the solar plasma is accelerated
  and heated may well be found in the studies of these jet-like,
  dynamic events. However, while these structures are observed and
  studied for more than 130 years in the visible, but also in the UV
  and EUV emission lines and continua, there are still many questions
  to be answered. Thus, despite their importance and a multitude of
  observations performed and theoretical models proposed, questions
  regarding their origin, how they are formed, their physical parameters,
  their association with the underlying photospheric magnetic field, how
  they appear in the different spectral lines, and the interrelationship
  between structures observed in quiet and active regions on the disk
  and at the limb, as well as their role in global processes has not
  yet received definitive answers. In addition, how they affect the
  coronal heating and solar wind need to be further explored. In this
  review we present observations and physical properties of small-scale
  jet-like chromospheric events observed in active and quiet regions,
  on the disk and at the limb and discuss their interrelationship.

---------------------------------------------------------
Title: Scientific analysis within SEPServer: the 13 July 2005 SEP
    event case study
Authors: Malandraki, O. E.; Valtonen, E.; Agueda, N.; Papaioannou, A.;
   Klein, K. -L.; Heber, B.; Droege, W.; Aurass, H.; Nindos, A.; Vilmer,
   N.; Sanahuja, B.; Kouloumvakos, A.; Braune, S.; Preka-Papadema, P.;
   Tziotziou, K.; Hamadache, C.; Kiener, J.; Tatischeff, V.; Kartavykh,
   J.; Vainio, R.
2012EGUGA..14.9001M    Altcode:
  SEPServer is set out to make the first database of particle and
  corresponding EM observations of solar energetic particle (SEP) events
  over roughly three solar cycles. It will also provide users with results
  from the scientific analysis of multiple datasets using different
  observational and simulation based methods. Therefore, SEPServer
  will lead to new perspectives of scientific analysis and will serve
  as a new asset valuable for SEP and Space Weather research. In this
  contribution, the event of 13 July 2005 has been used as a case study,
  which is a proxy for the overall information that the SEPServer will
  include and at the same time it reveals the capabilities offered to
  the future users of SEPServer. The analysis of the 13 July 2005 event
  - focusing on the data driven analysis, i.e., onset and release time
  determination from SOHO/ERNE, SOHO/EPHIN and ACE/EPAM together with
  pitch angle distributions from ACE/EPAM, simulations based on WIND/3DP
  and ACE/EPAM electrons as well as direct comparison of the observed SEP
  fluxes with the associated electromagnetic emissions - is performed. The
  physical interpretation and the interconnection of the experimental and
  the simulation based results are discussed in detail. The 13 July 2005
  case study exemplifies the future usage of SEPServer, which will provide
  a comprehensive and up to date SEP analysis service. Acknowledgements:
  The research leading to these results has received funding from the
  European Union's Seventh Framework Programme (FP7/2007-2013) under
  grant agreement No 262773 (SEPServer).

---------------------------------------------------------
Title: Space Weather Research at IAA/NOA: Solar Energetic Particle
    Investigations
Authors: Malandraki, O.; Tylka, A. J.; Ng, C. K.; Marsden, R. G.;
   Tranquille, C.; Klein, K. L.; Patterson, J. D.; Armstrong, T. P.;
   Lanzerotti, L. J.; Papaioannou, A.; Marhavilas, P. K.; Tziotziou,
   K.; Crosby, N.; Vainio, R.
2012hell.conf....7M    Altcode:
  During an eleven year cycle the Sun goes from quiet conditions at
  minimum to levels of high activity at maximum. In the latter case,
  energetic phenomena such as coronal mass ejections (CMEs) and solar
  flares (SFs) accompanied by explosive releases of mass, magnetic flux
  and solar energetic particles (SEPs) are common. Damaging effects,
  as a result of these phenomena, have been recorded on satellites,
  on-board detectors and in extreme cases on ground based systems
  (e.g. oil and natural gas pipelines, communication systems, aircraft
  electronics, power-grids). Furthermore, the intense SEP radiation can
  damage human DNA and cause cell replications. To this end, ensuring
  the safety of astronauts working in the extreme conditions of space,
  especially the energetic particle environments, is a key goal for both
  ESA and NASA. The analysis, the risk assessment and management and the
  possible forecasting of such events constitutes the scientific field of
  Space Weather. The Institute of Astronomy and Astrophysics (IAA) of the
  National Observatory of Athens (NOA) is currently strongly involved in
  two collaborative projects funded by the seventh framework program of
  the European Union, <P />namely: 'SEPServer' and 'COMESEP'. 'SEPServer'
  focuses on the implementation of a comprehensive and up to date SEP
  analysis service including scientific data driven analysis both for
  1 AU and for &gt; 1 AU using data from the SOHO/ ERNE, SOHO/EPHIN,
  ACE/EPAM, ACE/SIS, WIND/3DP, Ulysses/HISCALE, Ulysses/COSPIN/LET and
  Ulysses/COSPIN/KET experiments. SEPServer will also provide for the
  first time the release of the HELIOS data set in a reasonable format
  and in full time resolution, thus making available data also for orbits
  inside 1 AU (down to 0.3 AU). Observational data-driven analysis methods
  such as: onset determination, velocity dispersion, and/or time-shifting
  analysis, direct comparison of observed SEP fluxes, spectra and
  abundance ratios with the associated electromagnetic emission data
  will be applied. 'SEPServer' will enhance our understanding of
  the source, acceleration and transport of SEPs which is directly
  related to space weather research progress. 'COMESEP' sets out to
  develop tools for forecasting SEP radiation storms and geomagnetic
  storms based on scientific data analysis and extensive modeling. It
  is foreseen that these forecasting tools will be incorporated into an
  automated operational European Space Weather Alert system, which is the
  'COMESEP' primary goal. Basic research activities on Space Weather
  carried out at IAA/NOA within the framework of these two projects
  will be presented including the analysis of SEPs and the associated
  electromagnetic emissions for selected case studies, the detailed study
  of the so-called 'reservoir effect' in the heliosphere as well as the
  impact of the large-scale structure of the IMF on the SEP profiles and
  its space weather implications. These project-related activities will
  provide the basis for future solar missions such as Solar Orbiter -
  in which IAA/NOA participates as a Co-Investigator (EPD instrument).

---------------------------------------------------------
Title: Solar chromospheric fine scale structures: dynamics and
    energetics
Authors: Tziotziou, K.
2012hell.conf....5T    Altcode:
  The solar chromosphere is a very inhomogeneous and dynamic layer of
  the solar atmosphere that exhibits several phenomena on a wide range
  of spatial and temporal scales. High-resolution and long-duration
  observations, employing mostly lines, such as Halpha, the Ca II infrared
  lines and the Ca II H and K lines, obtained both from ground-based
  telescope facilities (e.g. DST, VTT, THEMIS, SST, DOT), as well
  as state-of-the-art satellites (e.g. SOHO, TRACE, HINODE) reveal
  an incredibly rich, dynamic and highly structured chromospheric
  environment. What is known in literature as the chromospheric
  fine-scale structure mainly consists of small fibrilar-like features
  that connect various parts of quiet/active regions or span across
  the chromospheric network cell interiors, showing a large diversity
  of both physical and dynamic characteristics. The highly dynamic,
  fine-scale chromospheric structures are mostly governed by flows
  which reflect the complex geometry and dynamics of the local magnetic
  field and play an important role in the propagation and dissipation
  of waves. A comprehensive study of these structures requires deep
  understanding of the physical processes involved and investigation of
  their intricate link with structures/processes at lower photospheric
  levels. Furthermore, due to their large number present on the solar
  surface, it is essential to investigate their impact on the mass and
  energy transport to higher atmospheric layers through processes such
  as magnetic reconnection and propagation of waves. The in-depth study
  of all aforementioned characteristics and processes, with the further
  addition of non-LTE physics, as well as the use of three-dimensional
  numerical simulations poses a fascinating challenge for both theory
  and numerical modeling of chromospheric fine-scale structures.

---------------------------------------------------------
Title: Study of spicules observed in the CaII H and Ha lines with
    Hinode/SOT
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2012hell.conf...11K    Altcode:
  We use a dataset of simultaneous image sequences obtained by Hinode/SOT
  with the Ca II H filter, as well as in Ha+-0.2A. SOT was looking at
  the SW solar limb. The high temporal and spatial resolution allows us
  to study the structure and dynamics of spicules seen at the different
  filters. Individual spicules have been selected and intensity and
  velocity distributions at different heights along their central axes
  are examined along with transversal fluctuations.

---------------------------------------------------------
Title: Multi-wavelengths observations of oscillatory phenomena in
    a solar network region and their relation to the magnetic field
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2012hell.conf....6K    Altcode:
  The chromosphere is an inhomogeneous and highly dynamic layer of
  the solar atmosphere. New high resolution observations have revealed
  that it consists mainly of fine-scale structures which are directly
  related to the magnetic field. In this work we use multi-wavelength
  observations to study oscillatory phenomena in the quiet Sun and
  their relation to the magnetic field and the chromospheric fine-scale
  structures. The observations were obtained during a coordinated
  campaign which included space-borne instruments (i.e. the Transition
  Region and Coronal Explorer, the Michelson Doppler Imager onboard
  SoHO, and the Specropolarimeter onboard the Hinode spacecraft) and a
  ground-based telescope (i.e. the Dutch Open Telescope). The analysed
  data consist of time series of filtergrams of a solar network region
  observed at different atmospheric layers from the photosphere through
  the temperature minimum region and well into the chromosphere and also
  of high resolution magnetograms. Using wavelet analysis we investigate
  the oscillatory power distribution in the 2D field-of-view, as well
  as its vertical distribution and its relation with the fine-scale
  chromospheric mottles, while through phase difference analysis we
  investigate wave propagation characteristics. Our results show that the
  oscillatory power has a fibrilar distribution and that chromospheric
  mottles are directly related to power enhancement (power halo) or
  suppression (magnetic shadow). This finding is attributed to the
  interaction between acoustic oscillations and mottles which outline
  inclined magnetic fields and clearly indicate that mottles are the loci
  of wave tranmission, reflection and refraction. It also leads to the
  conclusion that these structures are directly related to the formation
  of the magnetic canopy, i.e. the layer that divides the atmosphere into
  two components, a magnetized and a non magnetized one. Extrapolation
  of the photospheric magnetic field up to the chromosphere using the
  current-free assumption and use of the VAL C atmospheric model allows
  the determination of the height of formation of the magnetic canopy
  and provide the opportunity to highlight the details of the interaction
  between acoustic o scillations and the magnetic field.

---------------------------------------------------------
Title: Solar Energetic Particles (SEPs) on a heliospheric scale - an
    attempt to compile the complete Ulysses event list over solar cycle 23
Authors: Papaioannou, A.; Malandraki, O. E.; Tziotziou, K.
2012hell.conf...12P    Altcode:
  The intensities of Solar Energetic Particles (SEPs) are strongly
  affected by the variations in the level of solar activity,
  the characteristics of the solar wind and the properties of the
  interplanetary magnetic field that enable the acceleration and
  propagation of SEPs throughout the heliosphere. The study of SEPs at
  different latitudes and under different heliospheric conditions provides
  useful information about the global structure of the heliosphere
  during solar minimum and solar maximum, as well as on the mechanisms
  and the physics of solar particle propagation and acceleration. Due to
  its eccentric orbit over the solar poles and its continuous presence
  in space for 18 years, Ulysses spacecraft has been the only solar
  mission so far that allowed us to study the characteristics of SEPs at
  low and high latitudes and their distribution over a solar cycle. In
  this work, the Heliosphere Instrument for Spectra, Composition and
  Anisotropy in Low-Energies (HI-SCALE) and the Low-Energy Telescope
  (LET) of the Cosmic Ray and Solar Particle Investigation (COSPIN)
  onboard Ulysses have been used in order to identify all SEPs observed
  in and out of the ecliptic plane over solar cycle 23. A scan has been
  performed on the recordings of the low-energy protons of COSPIN/LET
  (energy range: 0.9-8.0 MeV) and the Deflected Electrons (DEs) of
  HI-SCALE (energy range: 38-315 keV). As a result, a list of about 150
  well-defined events has been compiled. A part of this list, together
  with the analysis of case studies is being discussed. Furthermore,
  ongoing work includes the single treatment of each event and the
  possible identification of its solar source which could also be used
  as the basis for future solar missions such as Solar Orbiter in which
  IAA/NOA participates as a Co-Investigator (EPD instrument).

---------------------------------------------------------
Title: Hinode SOT/SP and SoHO/MDI quiet Sun magnetic
    field. Implications of their differences on the extrapolated
    chromospheric field and the height of the magnetic canopy
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2011A&A...531A..66K    Altcode:
  <BR /> Aims: We explore the differences in the measurement of the
  magnetic field of the quiet solar photosphere provided by the Michelson
  Doppler Imager (MDI) onboard SoHO and the SpectroPolarimeter (SOT/SP)
  onboard Hinode and the ensuing implications for the extrapolated
  chromospheric magnetic field and the determination of the location
  of the magnetic canopy. <BR /> Methods: We employ potential field
  extrapolation to reconstruct the chromospheric magnetic field
  using the magnetic field of the photosphere provided by the two
  instruments. We also calculate the plasma-β parameter using the VAL
  C model atmosphere of the quiet Sun to determine the height of the
  magnetic canopy. <BR /> Results: MDI underestimates the magnetic
  field of the quiet Sun sometimes by a factor of five, which leads
  to an overestimation of the height of the magnetic canopy by up
  to ~550 km. Although the overall magnetic field configuration does
  not differ significantly when calculated with either MDI or SOT/SP,
  the data of the latter lead to lower and more extended canopies. The
  difference in the resolution of the two instruments does not seem
  to affect the chromospheric magnetic field higher than 1000 km. <BR
  /> Conclusions: The height of the magnetic canopy is an important
  parameter to consider when investigating wave propagation and the
  oscillatory properties of the quiet Sun regions in the network and
  internetwork. The canopy height's derivation depends very much on
  the sensitivity of the instruments used to measure the photospheric
  magnetic field. Consequently precise measurements of the photospheric
  magnetic field are crucial to accurately reconstruct the chromospheric
  magnetic field and to distinguish between the various wave modes.

---------------------------------------------------------
Title: Oscillations in a network region observed in the Hα line
    and their relation to the magnetic field
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Georgoulis,
   M. K.
2010A&A...524A..12K    Altcode:
  <BR /> Aims: Our aim is to gain a better understanding of the
  interaction between acoustic oscillations and the small-scale magnetic
  fields of the Sun. To this end, we examine the oscillatory properties
  of a network region and their relation to the magnetic configuration of
  the chromosphere. We link the oscillatory properties of a network region
  and their spatial variation with the variation of the parameters of the
  magnetic field. We investigate the effect of the magnetic canopy and the
  diverging flux tubes of the chromospheric network on the distribution
  of oscillatory power over the network and internetwork. <BR /> Methods:
  We use a time series of high resolution filtergrams at five wavelengths
  along the Hα profile observed with the Dutch Open Telescope, as
  well as high resolution magnetograms taken by the SOT/SP onboard
  HINODE. Using wavelet analysis, we construct power maps of the 3,
  5 and 7 min oscillations of the Doppler signals calculated at ±0.35
  Å and ±0.7 Å from the Hα line center. These represent velocities
  at chromospheric and photospheric levels respectively. Through
  a current-free (potential) field extrapolation we calculate the
  chromospheric magnetic field and compare its morphology with the
  Hα filtergrams. We calculate the plasma β and the magnetic field
  inclination angle and compare their distribution with the oscillatory
  power at the 3, 5 and 7 min period bands. <BR /> Results: Chromospheric
  mottles seem to outline the magnetic field lines. The Hα ± 0.35
  Å Doppler signals are formed above the canopy, while the Hα ± 0.7
  Å corresponding ones below it. The 3 min power is suppressed at the
  chromosphere around the network, where the canopy height is lower than
  1600 km, while at the photosphere it is enhanced due to reflection. 3,
  5 and 7 min oscillatory power is increased around the network at the
  photosphere due to reflection of waves on the overlying canopy, while
  increased 5 and 7 min power at the chromosphere is attributed mainly
  to wave refraction on the canopy. At these high periods, power is also
  increased due to p-mode leakage because of the high inclinations of the
  magnetic field. <BR /> Conclusions: Our high resolution Hα observations
  and photospheric magnetograms provide the opportunity to highlight
  the details of the interaction between acoustic oscillations and the
  magnetic field of a network region. We conclude that several mechanisms
  that have been proposed such as p-mode leakage, mode conversion,
  reflection and refraction of waves on the magnetic canopy may act
  together and result to the observed properties of network oscillations.

---------------------------------------------------------
Title: Estimating Fluxes of SEPs by Unfolding ESA/SREM Data
Authors: Sandberg, I.; Daglis, I. A.; Anastasiadis, A.; Tziotziou,
   K.; Bühler, P.; Nieminen, P.
2010ASPC..424...43S    Altcode:
  The Standard Radiation Environment Monitor (SREM) belongs to a second
  generation of instruments in a program established by the European
  Research and Technology Centre (ESTEC) of the European Space Agency
  (ESA) to provide minimum intrusive particle radiation detectors on ESA
  spacecrafts for space weather applications. SREM detects high-energy
  electrons and protons and bins the measurements in overlapping energy
  channels. In order to estimate the particle fluxes associated with
  Solar Particle Events (SPEs), a method based on the Singular Value
  Decomposition (SVD) analysis was developed. This method does not
  require any assumption on the spectral form of the particle fluxes
  and includes proper schemes treating issues related to several
  characteristic properties of the detector. As an example, we present
  results associated to the January 20, 2005 SPE.

---------------------------------------------------------
Title: Solar Origin of Solar Particle Events Detected by the Standard
    Radiation Environment Monitor of ESA
Authors: Tziotziou, K.; Sandberg, I.; Anastasiadis, A.; Daglis, I. A.;
   Panagopoulos, I.; Mavromichalaki, H.; Papaioannou, A.; Gerontidou,
   M.; Nieminen, P.; Glover, A.
2010ASPC..424...47T    Altcode:
  Solar Particle Events (SPEs) of the 23rd Solar Cycle detected by the
  ESA Standard Radiation Environment Monitor (SREM) onboard the INTEGRAL
  satellite have been studied in order to find their connection to
  solar sources. X-ray, optical and radio data of solar flares that were
  observed by several space-based instruments during the aforementioned
  solar cycle have been selected. The data were reduced and thoroughly
  analyzed in order to establish the corresponding solar origin of
  the selected SPEs. The extensive scientific analysis has produced
  clear correlations with X class solar flares for the events of the
  October-November 2003, January 2005 and December 2006 periods while
  for the events that occurred during September 2005, correlations with X
  class flares are possible but not straightforward due to the complexity
  of the registered solar particle fluxes.

---------------------------------------------------------
Title: Comparative Analysis of Oscillations of a Solar Quiet Region
    Using Multi-Wavelength Observations
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2010ASPC..424...31K    Altcode:
  We analyze the temporal behavior of a solar quiet region using a
  set of multi-wavelength observations obtained during a coordinated
  campaign. The observations were acquired by the ground-based Dutch
  Open Telescope (DOT), the Michelson Doppler Imager (MDI) on-board
  SOHO and the UV filters of the Transition Region and Coronal
  Explorer (TRACE). A large range of height in the solar atmosphere,
  from the deep photosphere to the upper chromosphere is covered by
  these instruments. We investigate the oscillation properties of
  the intensities and velocities in distinct regions of the quiet Sun,
  i.e. internetwork, bright points (NBP) defining the network boundaries
  and dark mottles forming a well-defined rosette, as observed by the
  different instruments and in the different heights. The variations of
  the intensities and velocities are studied with wavelet analysis. The
  aim of our work is to find similarities and/or differences in the
  oscillatory phenomena observed in the different examined regions, as
  well as comprehensive information on the interaction of the oscillations
  and the magnetic field.

---------------------------------------------------------
Title: Using a new set of space-borne particle monitors to investigate
    solar-terrestrial relations
Authors: Tziotziou, K.; Sandberg, I.; Anastasiadis, A.; Daglis, I. A.;
   Nieminen, P.
2010A&A...514A..21T    Altcode:
  Context. We investigated the solar origin of Solar Particle Events
  (SPEs) which occurred during four time periods of the 23rd solar cycle
  with intense solar activity and were detected by the Standard Radiation
  Environment Monitor (SREM) onboard the INTEGRAL satellite. SREM is
  a second generation ESA particle radiation monitor, already flying
  onboard seven spacecraft. <BR /> Aims: The present study attempts
  to establish the association of recorded SPEs by INTEGRAL/SREM with
  their solar sources and hence evaluate the potential of SREM units as
  an alarm system for hazardous SPEs. <BR /> Methods: X-ray, optical and
  radio data of solar flares and coronal mass ejections (CMEs) that were
  observed by several space-based instruments during the aforementioned
  solar cycle were reduced and thoroughly analyzed to establish the
  corresponding solar origin of the selected SPEs. <BR /> Results: The
  analysis produced clear associations with X-class solar flares and
  respective CMEs for the events of the October-November 2003, January
  2005 and December 2006 periods, while for the events that occurred
  during September 2005, associations with X-class flares are possible
  but not straightforward due to the complexity of the registered solar
  particle fluxes. <BR /> Conclusions: SREM proves to be a new valuable
  asset for a comprehensive study of SPEs and a useful alert instrument
  for explosive geoeffective solar events.

---------------------------------------------------------
Title: Power halo and magnetic shadow in a solar quiet region observed
    in the Hα line
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2010A&A...510A..41K    Altcode:
  Context. We investigate the oscillatory behavior of the quiet solar
  chromosphere and its discrete components in terms of oscillation
  properties, i.e. network and internetwork. For this purpose, we use a
  time series of high resolution filtergrams at five wavelengths along
  the Hα profile, obtained by the Dutch Open Telescope. <BR /> Aims:
  We aim to gain insight on the distribution of power in different
  period bands and its variation between network and internetwork. Our
  spectral resolution provides information on the vertical distribution
  of power, since the Hα line has both photospheric and chromospheric
  components. We investigate the effect of Hα mottles on chromospheric
  oscillations, since they are the most prominent feature of the Hα
  chromosphere and outline inclined magnetic fields. <BR /> Methods: We
  use wavelet and phase difference analyses of Hα intensities and Doppler
  signals. Two-dimensional power maps in the 3, 5 and 7 min period bands
  as well as coherence and phase difference maps were constructed. <BR
  /> Results: At photospheric heights, where the Hα ± 0.7 Å wing is
  formed, the 3 and 5 min power is enhanced around the network, and forms
  power halos. Higher in the chromosphere these areas are replaced by
  magnetic shadows, i.e. places of power suppression. Interestingly, the
  power maps show a filamentary structure in the network which correlates
  very well with mottles. These areas show positive phase differences at
  the 3 min period band. At the 5 min and 7 min period bands both positive
  and negative phase differences are obtained with an increased number
  of pixels with high coherence, indicating the existence of both upward
  and downward propagating waves. <BR /> Conclusions: We attribute our
  findings to the interaction between acoustic oscillations and the
  magnetic fields that constitute the magnetic network. The network
  flux tubes diverge at chromospheric levels and obtain a significant
  horizontal component, which is betrayed by the presence of mottles. The
  variation of power reveals the discrete role of the magnetic field
  at different heights, which guides or suppresses the oscillations,
  depending on its inclination. Spectral resolution in Hα provides
  useful information on the coupling between the acoustic sub-canopy
  atmosphere and the magnetized chromosphere.

---------------------------------------------------------
Title: Status of the ESA Standard Radiation Environment Monitor
    (SREM) products
Authors: Nieminen, Petteri; Anastasiadis, A.; Bühler, P.; Daglis, I.;
   Daly, E.; Desorgher, L.; Evans, H.; Hajdas, W.; Lyons, J.; Marinov,
   D.; Nieminen, P.; Sandberg, I.; Siegl, M.; Tziotziou, K.; Zadeh, A.
2010cosp...38.4188N    Altcode: 2010cosp.meet.4188N
  The ESA Standard Radiation Environment Monitor (SREM) is thus far
  succesfully flying and producing radiation data on Proba-1, INTEGRAL,
  Rosetta, Giove-B, Herschel and Planck missions, with the environments
  covering LEO, MEO, highly elliptical orbit, L2, and the in-terplanetary
  space. This presentation will outline the main SREM results to date
  from these various missions, and will give an overview of the present
  efforts taken to process the SREM data from raw particle count rates to
  proton and electron fluxes. Interfaces to various envi-ronment modelling
  activities and other higher level products are also discussed. Lessons
  learnt from the SREM programme will be summarised with the aim of
  facilitating future radiation monitor development and data processing /
  utilisation efforts.

---------------------------------------------------------
Title: The dynamic solar chromosphere: recent advances from high
    resolution telescopes
Authors: Tziotziou, Konstantinos; Tsiropoula, Georgia
2010cosp...38.2918T    Altcode: 2010cosp.meet.2918T
  This review focuses on the solar chromosphere, a very inhomogeneous
  and dynamic layer that exhibits phenomena on a large range of spatial
  and temporal scales. High-resolution observa-tions from existing
  telescopes (DST, SST, DOT), as well as long-duration observations
  with Hinode's SOT employing lines such as the Ca II infrared lines,
  the Ca II HK and above all the Hα line reveal an incredibly rich,
  dynamic and highly structured environment, both in quiet and active
  regions. The fine-structure chromosphere, is mainly constituted by
  fibrilar features that connect various parts of active regions or
  span across network cell interiors. We discuss this highly dynamical
  solar chromosphere, especially below the magnetic canopy, which is
  gov-erned by flows reflecting both the complex geometry and dynamics of
  the magnetic field and the propagation and dissipation of waves in the
  different atmospheric layers. A comprehensive view of the fine-structure
  chromosphere requires deep understanding of the physical processes
  involved, investigation of the intricate link with structures/processes
  at lower photospheric lev-els and analysis of its impact on the mass and
  energy transport to higher atmospheric layers through flows resulting
  from different physical processes such as magnetic reconnection and
  waves. Furthermore, we assess the challenges facing theory and numerical
  modelling which require the inclusion of several physical ingredients,
  such as non-LTE and three-dimensional numerical simulations.

---------------------------------------------------------
Title: Power halo and magnetic shadow observed in a network region
    by Hinode/SOT and the Dutch Open Telescope
Authors: Tsiropoula, Georgia; Tziotziou, Konstantinos; Kontogiannis,
   Ioannis
2010cosp...38.2920T    Altcode: 2010cosp.meet.2920T
  We use time series of G-band and Ca II H filtergrams obtained by
  SOT on-board Hinode, as well as Hα filtergrams in 5 wavelengths
  along the line profile obtained by the Dutch Open Telescope during a
  coordinated campaign. Our goal is to study the oscillatory behavior of
  a network region as seen at different heights of the solar atmosphere
  and to gain insight on the distribution of power in different period
  bands and its spatial variation. We use wavelet and phase difference
  analyses of intensities and doppler signals. Enhanced or suppressed
  power (power halo and magnetic shadow, respectively) is observed in
  the network region at the differ-ent heights. Interestingly, the
  power spatial distribution shows a filamentary structure, while a
  correlation analysis reveals that this structure is clearly related
  to the dark mottles. We at-tribute our findings to the interaction
  between acoustic oscillations and the inclined magnetic fields that
  outline the mottles and mark the presence of the magnetic canopy.

---------------------------------------------------------
Title: Oscillatory phenomena in a solar network region
Authors: Tsiropoula, Georgia; Tziotziou, Kostas; Schwartz, Pavol;
   Heinzel, Petr
2009IAUS..257..181T    Altcode:
  We examine oscillatory phenomena in a solar network region from
  multi-wavelength, observations obtained by the ground-based Dutch
  Open Telescope (DOT), and by instruments on the spacecraft Solar and
  Heliospheric Observatory (SoHO). The observations were obtained during
  a coordinated observing campaign on October 14, 2005. The temporal
  variations of the intensities and velocities in two distinct regions of
  the quiet Sun were investigated: one containing several dark mottles
  and the other several bright points defining the network boundaries
  (NB). The aim is to find similarities and/or differences in the
  oscillatory phenomena observed in these two regions and in different
  spectral lines formed from the chromosphere to the transition region,
  as well as propagation characteristics of waves.

---------------------------------------------------------
Title: A study of spicules from space observations
Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas
2009IAUS..257..165K    Altcode:
  We have studied spicules observed at the northern solar limb by
  using simultaneous high resolution image sequences. The images were
  obtained by Hinode/SOT (in the Ca II H passband) and TRACE (in the
  1600 Å passband) during a coordinated campaign. Both data sets were
  reduced and then carefully co-aligned in order to compare the observed
  patterns in this highly dynamic region of the Sun. The identification
  of individual structures in both spectral bands allows us to trace
  their spatial and temporal behaviour. Persistent intensity variations
  at certain locations, indicate that at least some spicules have a
  recurrent behavior. Using wavelet analysis we investigate oscillatory
  phenomena along the axis of off-limb spicules and we construct 2-D
  maps of the solar limb with the observed oscillations.

---------------------------------------------------------
Title: Multiwavelength analysis of a solar quiet region
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P.
2009A&A...493..217T    Altcode:
  Context: We examine oscillatory phenomena in a solar network region
  from multi-wavelength observations obtained by the ground-based Dutch
  Open Telescope (DOT) and by the Coronal Diagnostic Spectrometer (CDS)
  on the spacecraft Solar and Heliospheric Observatory (SoHO). The
  observations were obtained during a coordinated observing campaign in
  October 2005. <BR />Aims: We investigate the temporal variations of the
  intensities and the velocities in two distinct regions of the quiet Sun,
  one containing several dark mottles and the other several bright points
  defining the network boundaries (NB). The aim is to find similarities
  and/or differences in the oscillatory phenomena observed in these two
  regions and in different spectral lines formed from the chromosphere
  to the transition region, as well as the propagation characteristics
  of waves. <BR />Methods: Intensity and velocity variations are
  studied with wavelet and phase difference analyses. <BR />Results:
  Both regions (i.e. mottles and NB) show a periodicity of ~5 min in all
  considered lines. The V-V phase differences in the NB region point to
  an upward propagation of waves; in the region of mottles, for periods
  of 250-400 s, the phase difference is mainly negative, which suggests
  a downward propagation, in turn indicating a refraction of waves from
  the inclined magnetic field of mottles along the line-of-sight. <BR
  />Conclusions: The phase differences at the NB arise from a predominance
  of upward propagating waves. In the mottles' region, the negative phase
  differences we found suggest that propagating waves encounter a boundary
  and are refracted and reflected. Of course, several limitations exist
  in the exact interpretation of the phase differences, e.g. the complex
  topology of the magnetic field, the formation conditions and heights
  of the examined spectral lines, and the low spatial resolution.

---------------------------------------------------------
Title: Influence of Seeing on Cloud Model Parameters Obtained from
    Hα Observations
Authors: Tziotziou, K.; Tsiropoula, G.; Heinzel, P.
2008ASPC..397...63T    Altcode:
  We study the influence of atmospheric seeing due to terrestrial
  atmospheric turbulence on cloud model parameters obtained from Hα
  observations with Beckers' cloud model. The analysis indicates that
  atmospheric seeing does not affect the velocity determination, but
  does influence significantly the determination of the Doppler width
  when velocity gradients are present, and hence, the determination of
  the temperature, while the optical thickness and source function are
  also quantitatively affected, especially for high values of atmospheric
  seeing.

---------------------------------------------------------
Title: Contrast of Fine-scale Structures in a Quiet Sun Network Region
Authors: Schwartz, P.; Tziotziou, K.; Heinzel, P.; Tsiropoula, G.
2008ESPM...12.2.35S    Altcode:
  We study the contrast of fine structures (mottles), found in a quiet-Sun
  network region and close to a filament, observed by the SOHO/SUMER
  spectrograph. The observations were made during August 29 -- 30, 1996,
  in several chromospheric, transition-region and coronal EUV lines. The
  contrasts of the fine-scale structures were obtained in the different
  spectral lines and compared to find whether they have any dependence
  on the inclination of the magnetic field lines and the line formation
  height. Also contributions of the absorption and emissivity blocking
  to the depression of brightness in these fine-scale structures are
  studied by comparing the observations in transition-region lines
  with wavelengths above and below 912 A (the head of the hydrogen
  Lyman continuum).

---------------------------------------------------------
Title: Study of H-alpha Spicule Profiles with Line Inversion
    Techniques
Authors: Tziotziou, K.; Kontogiannis, I.; Tsiropoula, G.; Kotrc, P.
2008ESPM...12.2.42T    Altcode:
  High resolution optical spectra of chromospheric spicules obtained in
  the H? line are studied together with slit-jaw filtergrams. The spectra
  were recorded along a vertical slit parallel to the solar limb with
  the HSFA2 (Horizontal-Sonnen-Forschungs-Anlage) Solar Spectrograph
  at Ondrejov Observatory on August 19, 2007 and show H? line profiles
  taken in spicules - due to the limb curvature - at different heights
  from the solar limb. A multi-cloud model that considers two or more
  spicules along the line-of-sight (LOS), together with a statistical
  approach that takes into account a large set of initial conditions for
  solving the radiative transfer equation, is used for the fitting of the
  observed profiles and the derivation of several parameters such as the
  LOS velocity, the source function, the optical thickness and the Doppler
  width that describe the respective spicules. The height-dependence
  of the shape of the observed profiles, as well as their dependence
  on the values of the derived parameters are studied in detail. The
  derived results are compared with the statistical theoretical results
  of a multi-cloud model where the aforementioned physical parameters,
  as well as a random number of spicules along the LOS were taken into
  account, in order to define the dependence of several spicule profile
  characteristics on them. Specific steps of the used procedures, as
  well as crucial problems are discussed.

---------------------------------------------------------
Title: Study of Spicules from Space Observations
Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.
2008ESPM...12.2.43K    Altcode:
  We present a study of the northern solar limb using simultaneous high
  resolution observations by HINODE/SOT (CaII H line) and TRACE (1600
  Å) filtergrams, acquired during a coordinated campaign on October
  15, 2007. Both data sets were reduced and then carefully coaligned
  in order to compare the observed patterns and topology in this
  highly dynamical region of the solar atmosphere. The identification
  of the same structures in both spectral bands allows us to trace
  their spatial and temporal variation. A multitude of spicules and
  small loops is revealed highlighting their association with magnetic
  field concentrations. Persistent plasma motions at certain locations,
  indicative of the recurrency of some structures, are visible throughout
  the entire time series. Cuts across and parallel to the limb provide
  information on these motions and their temporal evolution. Using wavelet
  and cross-correlation analyses we investigate oscillatory phenomena
  along the axis of off-limb spicules, as well as along lines parallel to
  the solar limb, and examine their interconnection with wave propagation.

---------------------------------------------------------
Title: Oscillatory Phenomena in a Solar Network Region
Authors: Tziotziou, K.; Tsiropoula, G.; Schwartz, P.; Heinzel, P.
2008ESPM...12.2.41T    Altcode:
  Multi-wavelength, multi-instrument observations, obtained during a
  coordinated observing campaign on October 2005 by the ground-based
  Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar
  and Heliospheric Observatory (SoHO) and Transition Region and Coronal
  Explorer (TRACE), are used to study oscillatory phenomena in a solar
  network region. Temporal variations of the intensities and velocities
  in a region of the quiet Sun containing several dark mottles and in a
  region with several bright points defining the network boundaries (NB)
  are investigated with the aim of finding similarities and/or differences
  in the oscillatory phenomena observed in these two regions and in
  different spectral lines formed from the chromosphere to the transition
  region, as well as propagation characteristics of waves. A wavelet,
  phase difference and coherence analyses were performed indicating a
  periodicity around 5 min in all considered lines for both regions. V-V
  phase differences in the NB region point to an upward propagation of,
  most probably, acoustic waves, while in the region of mottles they
  indicate a non vertical propagation of waves, due to the presence
  of several inclined mottles along the line-of-sight. In mottles, for
  periods of 250-400 s the phase difference is mainly negative suggesting
  that propagating waves encounter a boundary and are refracted and
  reflected. However, limitations arising from the complex topology
  of the magnetic field, the formation conditions and heights of the
  examined spectral lines and the low spatial resolution of the space
  instruments influence the exact interpretation of the phase differences.

---------------------------------------------------------
Title: Multi-wavelength Analysis of a Solar Network Region
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P.
2008CEAB...32..109T    Altcode:
  We analyse co-temporal observations of a network region found near
  the solar disc centre, obtained by the Dutch Open Telescope (DOT)
  and the Coronal Diagnostic Spectrometer (CDS) on-board SOHO during a
  coordinated observing campaign in October 2005. DOT obtained images in
  5 wavelengths along the ha\ profile, while CDS obtained sit-and-stare
  observations in several EUV spectral lines that span the upper solar
  atmosphere. After fitting the CDS spectral line profiles we obtained
  2-D space-time maps of intensities, Doppler velocities and Doppler
  widths. We study the appearance of the network region in the different
  spectral lines and the temporal variations of the obtained physical
  parameters. We employ a wavelet analysis to examine the existence of
  oscillations at the network in the different solar layers.

---------------------------------------------------------
Title: Influence of seeing effects on cloud model inversions
Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G.
2007A&A...472..287T    Altcode:
  Context: Atmospheric seeing due to terrestrial atmospheric turbulence
  is a process that distorts solar ground-based observations. <BR
  />Aims: We study the influence of atmospheric seeing on Hα cloud
  model inversions. <BR />Methods: We use Beckers' cloud model which
  assumes a constant source function to obtain physical parameters from
  observed quiet-Sun Hα profiles, and profiles convolved with a Gaussian
  point spread function that simulates the effect of atmospheric seeing
  on solar observations. <BR />Results: Our analysis indicates that
  atmospheric seeing does not affect the velocity determination, but
  does influence significantly the determination of the Doppler width
  when velocity gradients are present, and hence, the determination of
  the temperature, while the optical thickness and source function are
  also quantitatively affected, especially for high values of atmospheric
  seeing. <BR />Conclusions: The effects of atmospheric seeing on cloud
  model inversions also depend on the actual size of the structures
  under study. For the presented observations, the derived cloud model
  parameter distributions do not change significantly for atmospheric
  seeing up to ∼0.5”.

---------------------------------------------------------
Title: Chromospheric Cloud-Model Inversion Techniques
Authors: Tziotziou, K.
2007ASPC..368..217T    Altcode: 2007arXiv0704.1558T
  Spectral inversion techniques based on the cloud model are extremely
  useful for the study of properties and dynamics of various chromospheric
  cloud-like structures. Several inversion techniques are reviewed based
  on simple (constant source function) and more elaborated cloud models,
  as well as on grids of synthetic line profiles produced for a wide range
  of physical parameters by different NLTE codes. Several examples are
  shown of how such techniques can be used in different chromospheric
  lines, for the study of structures of the quiet chromosphere, such
  as mottles/spicules, as well as for active region structures such as
  fibrils, arch filament systems (AFS), filaments and flares.

---------------------------------------------------------
Title: Multi-wavelength Analysis of a Quiet Solar Region
Authors: Tsiropoula, G.; Tziotziou, K.; Giannikakis, J.; Young, P.;
   Schühle, U.; Heinzel, P.
2007ASPC..368..171T    Altcode: 2007arXiv0704.1592T
  We present observations of a solar quiet region obtained by the
  ground-based Dutch Open Telescope (DOT), and by instruments on the
  spacecraft SOHO and TRACE. The observations were obtained during a
  coordinated observing campaign on October 2005. The aim of this work
  is to present the rich diversity of fine-scale structures that are
  found at the network boundaries and their appearance in different
  instruments and different spectral lines that span the photosphere
  to the corona. Detailed studies of these structures are crucial to
  understanding their dynamics in different solar layers, as well as
  the role such structures play in the mass balance and heating of the
  solar atmosphere.

---------------------------------------------------------
Title: Dual-line spectral and phase analysis of sunspot oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2007A&A...463.1153T    Altcode:
  Context: Sunspots exhibit a wide range of oscillatory phenomena within
  their umbrae and penumbrae. <BR />Aims: We investigate the behavior
  of intensity and Doppler velocity oscillations in the umbra and the
  penumbra to study sunspot oscillations and their associations. <BR
  />Methods: Simultaneous, high-cadence (8 s), two-dimensional, Ca
  II 8542 Å and Hα 6563 Å observations are used. Doppler velocity
  and intensity variations are studied with a wavelet spectral, phase
  difference and coherence analysis, both at distinct positions and
  within the whole umbra and the penumbra. <BR />Results: The analysis
  reveals the presence of several umbral flashes (UFs) that seem to
  fill the whole umbra. The spectral analysis indicates oscillating
  elements of size 2.5” to 5” within the umbra with periods around
  the 3-min band and oscillation periods around the 5-min band within
  the penumbra. Two remarkable jumps of the oscillation period and the
  intensity-velocity phase difference are present at both umbra-penumbra
  and penumbra-superpenumbra boundaries reflecting a drastic change in
  physical and/or magnetic conditions. The intensity-velocity phase
  analysis shows a delay of the intensity response to the velocity
  variations in accordance with the physics of the observed sawtooth
  velocity behavior. Most of the UFs oscillate incoherently, while the
  calmest umbral area seems to be associated with velocity spreading
  from neighboring UFs. The derived incoherency among UFs in conjunction
  with the existence of coherently oscillating elements within the umbra
  suggests the presence of umbral areas with slightly different physical
  and/or magnetic field conditions. <BR />Conclusions: .The presented
  analysis provides further important constraints for realistic models
  and theoretical interpretations describing sunspot oscillations.

---------------------------------------------------------
Title: Evolution of a Coronal Loop System
Authors: Tsiropoula, G.; Tziotziou, K.; Wiegelmann, T.; Zachariadis,
   Th.; Gontikakis, C.; Dara, H.
2007SoPh..240...37T    Altcode:
  The temporal variation of a loop system that appears to be changing
  rapidly is examined. The analyzed data were obtained on 15 May 1999,
  with the Transition Region and Coronal Explorer (TRACE) during an
  observing campaign and consist of observations in the Fe IX/Fe X 171
  Å and Fe XII 195 Å passbands taken at a cadence of ∼10 min. The
  special interest in this loop system is that it looks like one expanding
  loop; however, careful examination reveals that the loop consists of
  several strands and that new loop strands become visible successively
  at higher altitudes and lower loop strands fade out during the one hour
  of our observations. These strands have different widths, densities,
  and temperatures and are most probably consisting of, at least, a few
  unresolved thinner threads. Several geometric and physical parameters
  are derived for two of the strands and an effort is made to determine
  their 3D structure based on the extrapolation of the magnetic field
  lines. Electron density estimates allow us to derive radiative and
  conductive cooling times and to conclude that these loop strands are
  cooling by radiation.

---------------------------------------------------------
Title: The fine-scale structure of the quiet solar chromosphere
Authors: Tsiropoula, G.; Tziotziou, K.
2007MmSAI..78...32T    Altcode:
  We present methods for estimating different physical properties of dark
  mottles from observations obtained with the MSDP spectrograph mounted
  on the 50 cm refractor of the Pic du Midi Observatory and on THEMIS
  (Tenerife). We also present studies of their dynamical evolution and
  estimates of the role they play in the mass balance and heating of
  the solar atmosphere.

---------------------------------------------------------
Title: Dual-line analysis of sunspot oscillations
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2007MmSAI..78...98T    Altcode:
  Umbral oscillations and running penumbral (RP) waves are studied
  with simultaneous, two-dimensional, high cadence (8 sec), dual-line
  sunspot observations in Ca II 8542 Å and Halpha , obtained with the
  MSDP spectrograph on the German VTT in Tenerife. Doppler velocity and
  intensity images are used to investigate the physical characteristics
  of umbral flashes (UFs) and RP waves while a wavelet spectral and phase
  analysis shows their temporal behaviour and permits us to elaborate
  on their nature and possible association.

---------------------------------------------------------
Title: Observational characteristics and association of umbral
    oscillations and running penumbral waves
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2006A&A...456..689T    Altcode:
  Context: .Umbral flashes (UFs) and running penumbral (RP) waves are
  believed to be closely related oscillatory phenomena of sunspots.<BR />
  Aims: .We investigate the association of UFs and RP waves to see whether
  the latter are a visual pattern created by a common source with UFs
  or a trans-sunspot wave driven by UFs.<BR /> Methods: .Simultaneous,
  two-dimensional, dual-line observations in Ca II 8542 Å and Hα
  6563 Å, obtained with the Multichannel Subtractive Double Pass (MSDP)
  spectrograph mounted on the German VTT at Teide Observatory on Tenerife,
  are used for this study. High-cadence 8 s Doppler velocity images,
  spectrograms, and spectral-analysis results are used to study the
  characteristics and the relationship of UFs and RP waves.<BR /> Results:
  .Several UFs were observed that seem to fill the whole umbra. Doppler
  velocity variations with time indicate a shock behaviour for UFs, as
  well as for umbral and RP waves and a smooth continuous propagation
  of the latter from the umbra through the umbra-penumbra boundary
  out to the edge of the penumbra. Furthermore, the spectral analysis
  shows a decreasing oscillatory frequency as we move from the umbra
  outwards and a jump at the umbra-penumbra boundary that could possibly
  reflect, apart from a change in physical conditions, a drastic change
  of the magnetic field inclination with respect to the vertical.<BR />
  Conclusions: .The results do not permit us to convincingly support one
  scenario over the other (i.e. visual pattern vs. trans-sunspot wave)
  for RP waves; however, they do provide important constraints for future
  models of sunspot oscillations and RP waves.

---------------------------------------------------------
Title: Line Broadening of EUV Lines at the Solar Limb Observed with
    SUMER/SoHO. Relation to Spicules
Authors: Giannikakis, J.; Tsiropoula, G.; Tziotziou, K.; Antonopoulou,
   E.; Doyle, J. G.
2006AIPC..848..115G    Altcode:
  We study the broadening of EUV line widths as we move from the
  disk through and off the solar limb. This broadening maximizes at
  approximately 10 Mm above the limb. We use one raster scan and two
  time series obtained by SUMER/SoHO to examine a possible correlation
  between this phenomenon and spicule activity. It appears that spicule
  presence leads to even wider profiles whereas the appearance of
  macrospicules extends the broadening to even greater distances above
  the limb. We suggest that this correlation might imply that spicules
  are responsible for this disk-to-limb behavior even in regions where
  they cannot be observed.

---------------------------------------------------------
Title: Hα Chromospheric Mottles and their UV/EUV Counterparts Seen
    by SOHO/Sumer
Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G.; Schühle, U.
2006ESASP.617E.112T    Altcode: 2006soho...17E.112T
  No abstract at ADS

---------------------------------------------------------
Title: Line broadening of EUV lines across the solar limb observed
    by SUMER/SOHO
Authors: Tsiropoula, G.; Giannikakis, J.; Tziotziou, K.; Antonopoulou,
   E.
2006IAUS..233..183T    Altcode:
  We analyze time series scans of the solar limb performed by the
  spectrometer SUMER on-board the SoHO satellite. The analyzed dataset
  consists of observations obtained in the C III 977 Å line. After
  applying the standard SUMER data reduction procedure, we perform a
  one line Gaussian fit to the profiles to obtain different parameters
  for each pixel within the scans. Studying the variations of the line
  width from the disk to the limb and off-limb we find that it increases
  off-limb and shows a peak at ∼15” above the limb. We suggest that
  this increase is due to the random directions of several spicules
  found along the line of sight.

---------------------------------------------------------
Title: Chromospheric fine structure studies
Authors: Tziotziou, Kostas; Tsiropoula, G.
2006IAUS..233..173T    Altcode:
  Mottles and spicules are the most prominent, short-lived, dynamic
  features residing at the quiet Sun chromospheric network and constitute
  what is known as chromospheric fine structure. We are reporting a
  comprehensive study of the dynamical characteristics and physical
  properties of such structures, from multi-wavelength observations,
  using line inversion techniques and a wavelet spectral analysis. We
  are furthermore examining their dynamical evolution and their periodic
  bi-directional velocity behaviour, their interrelationship and their
  association with the underlying magnetic field which seems to be
  their forming and driving mechanism. These studies are crucial to
  understanding the dynamics of the solar chromosphere, as well as
  the role such structures play in the mass balance and heating of the
  overlying solar atmosphere.

---------------------------------------------------------
Title: Physical Parameters of Dark Mottles Derived from High
    Resolution Optical Spectra
Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Kotrč, P.;
   Heinzel, P.
2005ESASP.600E..72T    Altcode: 2005ESPM...11...72T; 2005dysu.confE..72T
  No abstract at ADS

---------------------------------------------------------
Title: Sunspot Umbral Oscillations and Running Waves
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2005ESASP.600E..15T    Altcode: 2005dysu.confE..15T; 2005ESPM...11...15T
  No abstract at ADS

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. V. Analysis of a
    surge from AR10486
Authors: Tziotziou, K.; Tsiropoula, G.; Sütterlin, P.
2005A&A...444..265T    Altcode:
  We present an analysis of high temporal and spatial resolution CaII H
  chromospheric limb observations obtained with the Dutch Open Telescope
  (DOT). We focus on a solar surge observed both by the DOT in CaII H and
  the Transition Region and Coronal Explorer (TRACE) satellite in the
  195 Å and 1600 Å passbands. The surge is observed in active region
  AR10486 located near the solar limb, a region which two hours later
  produced the largest X-flare ever recorded. It consists of relatively
  cold gas of about 10<SUP>4</SUP>-10<SUP>5</SUP> K. In TRACE images
  the surge is followed for almost 2.5 h, shrinking and expanding at
  the same location several times. From DOT images we find outward
  propagating intensity disturbances, with velocities higher than 50
  km s<SUP>-1</SUP>, indicative of upward material motion. The latter
  is also suggested by the good correlation between the DOT and TRACE
  surge apparent height curves, their apparent time delay and a phase
  difference analysis. A spectral wavelet analysis of the brightness
  variations within and along the surge shows a predominant period of
  ~6 min, the first ever reported for this kind of structures. Magnetic
  reconnection at the bottom of the surge as its driving mechanism is
  suggested by the observed inverted "Y" shape configuration and is
  further supported by a phase difference analysis.

---------------------------------------------------------
Title: Diagnostics of Dark Chromospheric Mottles Based on High
    Resolution Spectra I - Observational Data
Authors: Kotrč, P.; Schwartz, P.; Heinzel, P.; Tsiropoula, G.;
   Tziotziou, K.
2005HvaOB..29..289K    Altcode:
  High resolution optical spectra of dark mottles in H and Ca lines
  were observed with the Echelle spectrograph of the VTT at Sacramento
  Peak Observatory. Until now, only Hα spectra and slit-jaw images
  were processed. Used methods of identification of the dark mottles in
  the slit-jaw images and in the spectra, as well as a calibration and
  correction on the scattered light are described. Individual steps of
  the procedure, as well as crucial problems are discussed. The finally
  processed line profiles <P />are comparable to the profiles of dark
  mottles obtained by other instruments including MSDP.

---------------------------------------------------------
Title: The role of chromospheric mottles in the mass balance and
    heating of the solar atmosphere
Authors: Tsiropoula, G.; Tziotziou, K.
2004A&A...424..279T    Altcode:
  High-resolution Hα observations of a solar region containing several
  mottles are analyzed. Mottles constitute the fine structure of the
  quiet solar chromosphere and are found at the boundaries of the
  network cells, where the magnetic field is mostly concentrated. The
  driving mechanism for mottles (as well as for spicules) is suggested
  to be magnetic flux cancellation which most likely involves magnetic
  reconnection. Magnetic reconnection explains the observed bi-directional
  flows and, furthermore, allows conversion of part of magnetic energy to
  heat. We estimate several physical parameters of mottles and report a
  detailed analysis of their temporal variations. We then consider their
  impact on the mass balance and the heating of the solar atmosphere. We
  find that less than 1% of the mass flux injected by these structures
  into the corona expands outward as solar wind. The major fraction of
  this flux returns back to the chromosphere and provides an explanation
  for the red-shifts observed in the transition region spectral lines. The
  energy released by magnetic dissipation is quantified in terms of
  different energy components. Using typical values for the parameters
  of these structures it is found that they can provide ∼20% to the
  energy budget of the solar corona, but only a small part of it goes
  to heating. This percentage, as well as the part of the energy that
  goes to heating, can be lower or higher depending on the relative
  frequency of these events and on their upward velocity. On the other
  hand, if one assumes that all the potential energy of the downflowing
  material is converted to heat the amount supplied to the chromosphere
  is really negligible.

---------------------------------------------------------
Title: On the nature of the chromospheric fine
    structure. II. Intensity and velocity oscillations of dark mottles
    and grains
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2004A&A...423.1133T    Altcode:
  We study periodicities of dark mottles and grains observed in
  high spatial and temporal resolution Hα 2-D intensity and velocity
  images, obtained with the Multichannel Subtractive Double Pass (MSDP)
  spectrograph at THEMIS in Tenerife, Canary Islands. Intensity and
  velocity variations of individual mottles and grains, as well as of
  large regions containing a substantial number of these structures
  are examined with a wavelet analysis which provides the temporal
  distribution of periods and with a randomization method that gives
  the respective probabilities associated with them. The wavelet
  analysis, which shows that velocity variations are the dominant
  ones, results in a wide range of periods, from 100 to 500 s, with
  variable probabilities. However, it strongly indicates the presence
  of a predominant period of ∼5 min seen in both dark mottle and grain
  oscillations. We suggest that differences in periods found in individual
  mottles as well as in averages of regions containing these structures
  are due to the topology of the local magnetic field which can affect
  oscillatory processes. We report for the first time oscillations of
  dark grains which are more likely vertical structures “anchored"
  in the photosphere. The analysis supports further the suggestion that
  dark mottles and grains are the same structures, the only difference
  between them being their respective inclinations to the line-of-sight.

---------------------------------------------------------
Title: The Dutch Open Telescope on La Palma
Authors: Rutten, R. J.; Bettonvil, F. C. M.; Hammerschlag, R. H.;
   Jägers, A. P. L.; Leenaarts, J.; Snik, F.; Sütterlin, P.; Tziotziou,
   K.; de Wijn, A. G.
2004IAUS..223..597R    Altcode: 2005IAUS..223..597R
  The Dutch Open Telescope (DOT) on La Palma is an innovative solar
  telescope combining open telescope structure and an open support tower
  with a multi-wavelength imaging assembly and with synchronous speckle
  cameras to generate high-resolution movies which sample different
  layers of the solar atmosphere simultaneously and co-spatially at high
  resolution over long durations. The DOT test and development phase is
  nearly concluded. The installation of an advanced speckle processor
  enables full science utilization including "Open-DOT" time allocation
  to the international community. Co-pointing with spectropolarimeters
  at other Canary Island telescopes and with TRACE furnishes valuable
  Solar-B precursor capabilities.

---------------------------------------------------------
Title: Mass and Energy Supply of Fine Structure to the Solar Corona
Authors: Tziotziou, K.; Tsiropoula, G.
2004IAUS..219..123T    Altcode: 2003IAUS..219E..96T
  We investigate the role of chromospheric fine structures e.g. mottles
  (spicules) and dark grains in the mass balance and heating of the
  solar atmosphere by studying two-dimensional high-resolution Ha
  observations. The temporal and spatial variations of the line-of-sight
  velocity obtained with an inversion technique based on a cloud model
  provide strong indications that the mechanism responsible for the
  driving of the observed flows is magnetic reconnection. Apart from
  the line-of-sight velocity application of the cloud model enables
  the derivation of several other physical parameters like pressure
  temperature density etc. The temporal evolution of these parameters
  permits the estimation of the role of these structures in the mass
  balance of the solar atmosphere. Furthermore the energy balance between
  the released magnetic energy during reconnection and the associated
  kinetic and thermal energy provides a reasonable estimate of the energy
  available for the heating of the solar atmosphere.

---------------------------------------------------------
Title: Parameters of dark mottles based on high resolution optical
    spectra
Authors: Kotrc, P.; Heinzel, P.; Tziotziou, K.; Tsiropoula, G.
2004IAUS..223..275K    Altcode: 2005IAUS..223..275K
  High resolution optical spectra of hydrogen and calcium lines
  observed with the Echelle spectrograph of the VTT at Sacramento Peak
  Observatory were analyzed. The observed line profiles in some parts
  of dark chromospheric mottles are to be matched with theoretical ones
  using the cloud model and several parameters (e.g. the temperature,
  gas pressure, flow velocity) are to be derived. Individual steps of
  the procedure, as well as crucial problems are discussed.

---------------------------------------------------------
Title: On the Nature of Chromospheric Umbral Flashes And Running
    Penumbral Waves (Abstract)
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.
2004hell.conf...50T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Role of Spicules in the Mass Balance and Energy Budget
    of the Solar Atmosphere (Abstract)
Authors: Tsiropoula, G.; Tziotziou, K.
2004hell.confR..64T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Spectroscopic diagnostics of an Hα  and EUV filament observed
    with THEMIS and SOHO
Authors: Schmieder, B.; Tziotziou, K.; Heinzel, P.
2003A&A...401..361S    Altcode:
  A long filament has been observed with THEMIS/MSDP and SOHO/CDS -
  SUMER, during a coordinated campaign (JOPs 131/95) on May 5, 2000. The
  data were (a) 2-D Hα spectra, observed using THEMIS, (b) Lyman series
  spectra and Lyman continuum, observed using SOHO/SUMER, and (c) EUV
  spectra (in O V 629 Å, Mg X 624 Å, Si Xii 520 Å, Ca X 557 Å and
  He I 584 Å) observed using SOHO/CDS. A large depression of the line
  emissions in CDS images represents the EUV filament. A computed model
  shows that the EUV filament consists of an extended in height cloud of
  low gas pressure at an altitude lower than the top of the Hα filament,
  volume-blocking and absorbing coronal emission and absorbing transition
  region line emission. The optical thickness of the Lyman continuum is
  estimated by using the ratio of O V intensity inside and outside the
  EUV filament, while the optical thickness of Hα is computed from the
  Hα line profile by using an inversion technique. Using simultaneous
  Hα , Lyman lines and Lyman continuum spectroscopic data, we performed
  detailed, non-LTE radiative transfer diagnostics of the filament plasma
  conditions. The optical thickness of the Lyman continuum is larger than
  that of the Hα line by one to two orders of magnitude. This could be
  of a great importance for filament formation modeling, if we consider
  that more cool material exists in filament channels but is optically
  too thin to be visible in Hα images.

---------------------------------------------------------
Title: On the nature of the chromospheric fine structure. I. Dynamics
    of dark mottles and grains
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2003A&A...402..361T    Altcode:
  We analyze a time series of forty high spatial and temporal resolution
  two-dimensional intensity and Doppler velocity images at different
  wavelengths within the Hα line. The observations were obtained with the
  Multichannel Subtractive Double Pass (MSDP) spectrograph at THEMIS. We
  study the morphology of dark mottles and grains as seen in different
  wavelengths and examine their relation to the MDI magnetic field
  topology. We determine some physical properties of dark mottles with
  an inversion technique based on an iterative cloud model method with
  constant source function, giving the optical thickness tau<SUB>0</SUB>,
  the Doppler width Delta lambda<SUB>D</SUB> , the velocity v and the
  source function S distribution along a structure. The obtained global
  properties of mottles as well as the spatial and temporal evolution of
  several physical parameters along the axes of individual mottles are
  discussed. The derived velocities in mottles as a function of space
  and time (time slice images) exhibit a quasi-periodic, bi-directional
  pattern. It is suggested that magnetic reconnection is the mechanism
  responsible for their formation and dynamics. Furthermore, a similar
  quasi-periodic behaviour of the Doppler velocity variations in dark
  grains and their morphological characteristics both suggest the
  similarity of dark mottles and grains.

---------------------------------------------------------
Title: The role of chromospheric mottles in the mass balance and
    heating of the solar atmosphere
Authors: Tziotziou, K.; Tsiropoula, G.
2002ESASP.506..787T    Altcode: 2002svco.conf..787T; 2002ESPM...10..787T
  High-resolution Hα observations of a solar region containing several
  mottles were obtained with the Multichannel Subtractive Double Pass
  (MSDP) spectrograph installed at the focus of THEMIS in Tenerife
  (Canary islands). Applications of the cloud model to measurements of
  the Hα contrast profiles enabled us to derive numerical values for
  several physcial parameters. A detailed analysis of the temporal and
  spatial variation of these parameters was performed. The variation of
  the line-of-sight velocity showing upflows at the tops and downflows
  at the footpoints of the structures provides an indication that the
  mechanism that drives the flow along them is magnetic reconnection. The
  derived parameters in combination with information concerning their
  number on the solar surface permitted us to make estimates for the mass
  flux curried upwards the solar atmosphere. Moreover, a rough estimate
  of the magnetic energy dissipated at the reconnection region provided
  us with an estimate of the energy content available for the heating
  of the solar atmosphere.

---------------------------------------------------------
Title: Chromospheric fine structure dynamics
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2002ESASP.505..163T    Altcode: 2002solm.conf..163T; 2002IAUCo.188..163T
  We investigate the dynamics of chromospheric mottles observed with
  THEMIS. We study a half an hour time series of 2-D intensity and
  Doppler velocity images at different wavelengths within the Hα
  line, obtained with the Multichannel Subtractive Double Pass (MSDP)
  spectrograph with a cadence of 40.5 sec. We determine the physical
  parameters in dark mottles with an inversion technique which is based
  on an iterative cloud model method with constant source function. With
  this method we calculate the optical thickness τ<SUB>max</SUB>,
  the Doppler width Δλ<SUB>D</SUB>, the velocity v and the source
  function S describing the structure. We discuss the results of the
  inversion technique and show the spatial and temporal evolution of
  several physical parameters along the axes of individual mottles. The
  pattern of the derived velocities as a function of space and time
  (time slice images) suggests the presence of magnetic reconnection as
  the driving mechanism of their formation.

---------------------------------------------------------
Title: Theoretical hydrogen population relations for horizontal
    cloud-like solar structures
Authors: Tziotziou, K.; Mein, N.; Mein, P.; Heinzel, P.
2002ESASP.477..183T    Altcode: 2002scsw.conf..183T
  A large set of parameterized NLTE models has been computed for a 1D
  horizontal cloud-like structure standing above the solar surface. The
  used input model parameters are temperature, velocity, microturbulence,
  electronic density and geometrical thickness of the structure. From
  the output of our computations which is the hydrogen level populations
  as a function of the line center optical depth, we calculate several
  relations between the hydrogen population levels and the considered
  electron density. These relations are important for the study of
  prominence-like structures from observations.

---------------------------------------------------------
Title: Ca II 8542 Å sunspot oscillations observed with THEMIS
Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P.
2002A&A...381..279T    Altcode:
  Oscillations in the umbra and the penumbra of an isolated sunspot
  located near the solar disk centre were investigated. The observations
  were obtained with the Multichannel Subtractive Double Pass (MSDP)
  spectrograph operating in the Ca Ii 8542 Å line and installed at
  the focus of THEMIS (Tenerife). From the MSDP data, two-dimensional
  intensity and Doppler shift images were computed at different
  wavelengths within the line. Intensity and Doppler shift oscillations
  in the umbra and the penumbra of the sunspot showing up as umbral
  flashes and penumbral waves were analyzed using a 23 min time series
  with a cadence of 46 s. The Ca Ii umbral flash intensity profile shows
  an emission core in its blue wing. We investigate the relation between
  umbral flashes and running penumbral waves by a power spectrum analysis
  which shows a 6 mHz frequency for the standing umbral oscillations
  (flashes) which are observed only on the upper half part of the
  umbra. The running penumbral waves propagate with an average phase
  velocity of 16 km s<SUP>-1</SUP> and their frequency is constant in the
  penumbra and equal to 3 mHz. Although the time slice images suggest
  that umbral flashes and running penumbral waves are probably due to
  the same resonator, the power analysis shows no direct relationship
  between the two phenomena. Based on observations made with the THEMIS
  telescope operated on the island of Tenerife by CNRS-CNR in the Spanish
  Observatorio del Teide of the Instituto de Astrof{ísica de Canarias.

---------------------------------------------------------
Title: Recent results from THEMIS/MSDP campaigns
Authors: Tziotziou, K.; Mein, P.
2002joso.book..129T    Altcode:
  We present recent results based on observations of the 2000 campaign
  with the Multichannel Subtractive Double Pass (MSDP) spectrograph of the
  solar telescope THEMIS. The MSDP spectrograph permits the simultaneous
  recording of line profiles at every pixel of a two-dimensional solar
  image. We show results based on inversion methods developed for the
  study of THEMIS observations, either with the use of a non-LTE grid of
  line profiles or with the use of response functions. We also discuss
  results concerning sunspot observations and in particular a study
  of magnetic field gradients in the umbra of sunspots and a study of
  oscillatory phenomena like umbral flashes and running penumbral waves.

---------------------------------------------------------
Title: Why Are Solar Filaments More Extended in Extreme-Ultraviolet
    Lines than in Hα?
Authors: Heinzel, P.; Schmieder, B.; Tziotziou, K.
2001ApJ...561L.223H    Altcode:
  A long solar filament was observed simultaneously in the Hα line
  by THEMIS/MSDP and in selected EUV lines by the Coronal Diagnostic
  Spectrometer on SOHO. Co-alignment of optical and EUV images reveals
  that the dark EUV filament is much more extended than the Hα
  filament. Assuming that the EUV filament represents Lyman continuum
  absorption of the background EUV-line radiation, a straightforward
  explanation of this effect is suggested. Based on non-LTE filament
  models, we demonstrate that the ratio of the Lyman continuum to Hα
  opacity can reach a factor of 50-100, and thus the EUV filament is
  still well visible while the Hα line contrast diminishes below the
  detection limit. This kind of interpretation leads to an important
  conclusion that the cool filament material in which the Lyman continuum
  absorption takes place is more abundant than one would expect from
  Hα disk observations. This then may have significant consequences
  on the filament structure and on formation models, as well as on mass
  considerations related to coronal mass ejections.

---------------------------------------------------------
Title: 2D spectroscopy and science with THEMIS
Authors: Tziotziou, K.; Mein, P.; Tsiropoula, G.; Eibe, T.
2001hell.confE..25T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Non-LTE inversion of chromospheric {\Ca Ii} cloud-like features
Authors: Tziotziou, K.; Heinzel, P.; Mein, P.; Mein, N.
2001A&A...366..686T    Altcode:
  A chromospheric cloud-like feature observed in the 8542 Å {{Ca Ii}
  line is studied by a two step inversion procedure which provides
  estimates of its temperature, electronic density, microturbulence,
  geometrical thickness and bulk velocity. The first step involves the
  computation of a large grid of models by a multi-level non-LTE transfer
  code which gives the {{Ca Ii} line depth-dependent mean intensity
  inside an isolated, isothermal cloud lying above the chromosphere. The
  second step involves the inversion of the observed profiles with the
  grid of computed synthetic {{Ca Ii} profiles. A searching and matching
  chi <SUP>2</SUP> algorithm is implemented followed by an interpolation
  algorithm which permits a more accurate determination of the parameters
  on which the profiles depend. The five grid parameters are reduced to
  four by defining the emission measure from the geometrical thickness
  and electronic density. We show that this inversion procedure gives
  accurate results for some of our inversion parameters when dealing
  with solar filaments and is complementary to a previous study of the
  same object in the {{Hα }} line. The main advantages, problems and
  future extension of the inversion approach are also discussed.

---------------------------------------------------------
Title: Study of Chromospheric Ca II Cloud-like Structures
Authors: Tziotziou, K.; Heinzel, P.; Mein, P.; Mein, N.
2000ESASP.463..443T    Altcode: 2000sctc.proc..443T
  No abstract at ADS

---------------------------------------------------------
Title: Energy and momentum deposition in coronal holes. Solar
    coronal hole simulations compared with interpretations of YOHKOH
    SXT observations
Authors: Tziotziou, K.; Martens, P. C. H.; Hearn, A. G.
1998A&A...340..203T    Altcode:
  A grid of 74 coronal models with parameterized heating distribution,
  representing a wide range of physical parameters, has been
  calculated. We find that three of these models reproduce the recent
  observations made by Hara et al. (\cite{hara:tsun}) with the soft
  X-ray telescope aboard the Japanese satellite Yohkoh, which indicate
  a temperature of 1.8 ~ 2.4 x es 10(6) { K with an emission measure
  of 10(25.5) to 10(26.2) cm^{-5}, while other solutions reproduce the
  more standard Yohkoh and Skylab observations, which have a temperature
  of about 1.4 x es 10(6) { K The best fit for the coronal temperature
  and emission measure gives a velocity at the Earth's orbit of only
  10 {km s^{-1}. A model including acceleration by Alfven waves gives
  a final velocity of 630 km s^{-1} which is in agreement with the
  observations. The mechanical heating flux at the transition region
  is 2.1 x es 10(5) ergcms with a weighted average dissipation scale
  length of 0.1 R_{\odot}. The flux of Alfven waves is 1 x es 10(5)
  ergcms . In our models the velocity of the solar wind from coronal
  holes is completely determined by the Alfven wave acceleration, in
  contrast to previous models in which the Alfven wave acceleration
  increased the velocity of the purely thermal model only by a factor
  2. Observations of the non thermal broadening of the coronal red and
  green lines are consistent with this model.

---------------------------------------------------------
Title: Dynamics of stellar coronae
Authors: Tziotziou, Konstantinos
1997PhDT.......223T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Solar coronal hole simulations compared with interpretations
    of YOHKOH SXT observations
Authors: Tziotziou, K.; Hearn, A. G.
1995sowi.conf...63T    Altcode:
  Recent observations of coronal holes made with the soft X-ray telescope
  aboard Yohkoh have indicated a temperature of 1.8 approximately 2.1 x
  10<SUP>6</SUP> K and an emission measure of 10<SUP>25.7 approximately
  26.2</SUP> cm <SUP>-5</SUP>. This is almost the same as in quiet
  regions of the Sun. Numerical simulations of the temperature density
  and velocity structure in a coronal hole. using a parameterized
  heating distribution have been used for a comparison with the Yohkoh
  observations. Models are obtained which fit the observed temperature
  and emission measure. with heating fluxes which are consistent with
  other measurements. However, the final velocity of the solar wind
  is very slow which indicates the necessity of another acceleration
  mechanism such as alfven waves.