Author name code: tziotziou ADS astronomy entries on 2022-09-14 author:"Tziotziou, K." ------------------------------------------------------------------------ Title: Short poster presentations Authors: Tziotziou, Kostas Bibcode: 2022cosp...44.2527T Altcode: Short presentations of posters related to event E2.4. Title: Automated detection of chromospheric swirls in the Halpha spectral line and statistical analysis of their parameters Authors: Dakanalis, Ioannis; Tziotziou, Kostas; Tsiropoula, Georgia; Kontogiannis, Ioannis Bibcode: 2022cosp...44.2519D Altcode: Ubiquitous vortical motions in the solar atmosphere have been recently revealed by high-resolution observations of both space-borne and ground-based observatories in quiet, as well as in active regions. In chromospheric observations obtained in spectral lines, such as the H$\alpha$ and Ca II IR, they manifest themselves as swirling dark spiral- and circular-shaped patches labelled as "chromospheric swirls". Their suggested contribution to the channelling of energy, mass and momentum from the sub-photospheric levels to the higher layers of the solar atmosphere places them amongst potential candidates for atmospheric heating. In this context, their detection and statistical information concerning their population and a number of significant physical parameters and properties are vital. To complement visual inspection and automated detection methods based on the velocity field derivation we developed a novel automated detection method, which is based on the morphological characteristics of these structures. The algorithm was applied to H$\alpha$ high-resolution observations obtained with the CRisp Imaging SpectroPolarimeter (CRISP) of the Swedish 1-m Solar Telescope (SST) and revealed the existence of a significantly larger number of chromospheric swirls compared to previous reports. We will be presenting a brief description of the automated detection algorithm, followed by the obtained results concerning their surface density, occurrence rate, spatial distribution and temporal evolution throughout the FOV, as well as a statistical analysis of some significant physical parameters, such as radii and lifetimes that were obtained by an unprecedented observational statistical sample of 577 swirls. Lifetimes have been derived by implementation of the survival analysis method that is extensively used in several scientific fields, but so far occasionally in Solar Physics, and provides more accurate estimates of the mean lifetime of swirls. Moreover, a hinted by the results linear correlation between lifetimes and radii is explored. Title: The European Solar Telescope Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.; Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein, C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados, M.; the EST team Bibcode: 2022arXiv220710905Q Altcode: The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope (DOT). With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems. Title: Chromospheric swirls. I. Automated detection in Hα observations and their statistical properties Authors: Dakanalis, I.; Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I. Bibcode: 2022A&A...663A..94D Altcode: 2022arXiv220507720D Context. Chromospheric swirls are related to convectively driven vortex flows and considered to play a significant role in the dynamics and heating of the upper solar atmosphere. It is important to automatically detect and track them in chromospheric observations and determine their properties.
Aims: We aim to detect and track chromospheric swirls both in space and time by applying a newly developed novel automated method on high quality time series of Hα observations and to conduct a statistical analysis to determine their properties.
Methods: We applied a recently developed automated chromospheric swirl detection method to time-series observations of a quiet region of the solar chromosphere obtained in the Hα-0.2 Å wavelength of the Hα spectral line by the CRISP instrument at the Swedish 1-m Solar Telescope. The algorithm exploits the morphological characteristics of swirling events in high contrast chromospheric observations and results in the detection of these structures in each frame of the time series and their tracking over time. We conducted a statistical analysis to determine their various properties, including a survival analysis for deriving the mean lifetime.
Results: A mean number of 146 ± 9 swirls was detected within the Hα-0.2 Å field of view at any given time. The mean surface density is found equal to ∼0.08 swirls Mm−2 and the occurrence rate is ∼10−2 swirls Mm−2 min−1. These values are much higher than those previously reported from chromospheric observations. The radii of the detected swirls range between 0.5 and 2.5 Mm, with a mean value equal to 1.3 ± 0.3 Mm, which is slightly higher than previous reports. The lifetimes range between 1.5 min and 33.7 min (equal to the duration of the observations) with an arithmetic mean value of ∼8.5 min. A survival analysis of the lifetimes, however, using the Kaplan-Meier estimator in combination with a parametric model results in a mean lifetime of 10.3 ± 0.6 min.
Conclusions: Swirls are ubiquitous in the solar chromosphere. An automated method sheds more light on their abundance than visual inspection, while higher cadence, higher resolution observations will most probably result in the detection of a higher number of such features on smaller scales and with shorter lifetimes.

Movies is available at https://www.aanda.org Title: 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. Bibcode: 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. Title: Automated Detection of Chromospheric Swirls Based on Their Morphological Characteristics Authors: Dakanalis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas; Koutroumbas, Konstantinos Bibcode: 2021SoPh..296...17D Altcode: High-resolution observations have revealed that rotating structures known as "chromospheric swirls" are ubiquitous in the solar chromosphere. These structures have circular or spiral shapes, are present across a broad range of spatial and temporal scales and are considered as viable candidates for providing an alternative mechanism for the heating of the chromosphere and corona. Therefore, an accurate determination of their number and a statistical study of their physical properties are deemed necessary. In this work we present a novel, automated swirl detection method, which utilizes image pre-processing, curved structure tracing and machine learning techniques that allow for the detection of swirling events based on their morphological features as they appear in chromosphere filtergrams. The method is applied to Hα chromospheric spectral line images obtained by the CRisp Imaging Spectropolarimeter (CRISP) at the Swedish 1-m Solar Telescope (SST). It is also tested on grayscale images of vortical sea current flows represented/visualized by synthetic streamlines from the NASA/Goddard Space Flight Center Scientific Visualization Studio. The results are rather encouraging since swirling events are successfully identified. Further improvements of the algorithm, its prospects for the detection and statistical studies of the properties of these events using a wide range of imaging data and its potential application in other scientific fields for the detection of rotating motions are discussed. Title: A persistent quiet-Sun small-scale tornado. III. Waves Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I. Bibcode: 2020A&A...643A.166T Altcode: 2020arXiv201006327T Context. Vortex flows can foster a variety of wave modes. A recent oscillatory analysis of a persistent 1.7 h vortex flow with a significant substructure has suggested the existence of various types of waves within it.
Aims: We investigate the nature and characteristics of waves within this quiet-Sun vortex flow, over the course of an uninterrupted 48-min observing time interval, in order to better understand its physics and dynamics.
Methods: We used a cross-wavelet spectral analysis between pairs of Hα and Ca II 8542 Å intensity time series at different wavelengths and, hence, atmospheric heights, acquired with the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope, as well as the derived Hα Doppler velocity and full width at half maximum time series. We constructed halftone frequency-phase difference plots and investigated the existence and propagation characteristics of different wave modes.
Results: Our analysis suggests the existence of Alfvénic type waves within the vortex flow that propagate upwards with phase speeds of ∼20-30 km s-1. The dominant wave mode seems to be the fast kink wave mode, however, our analysis also suggests the existence of localised Alfvénic torsional waves, which are related to the dynamics of individual chromospheric swirls that characterise the substructure of the vortex flow. The Hα V-I phase difference analysis seems to imply the existence of a standing wave pattern that is possibly arising from the interference of upwards propagating kink waves with downwards propagating ones that are reflected at the transition region or the corona. Moreover, the results provide further evidence that the central chromospheric swirl drives the dynamics of the vortex flow.
Conclusions: This is the first exhaustive phase difference analysis within a vortex flow that explores the nature and dynamics of different wave modes within it. The question, however, of whether, and how, the dissipation of the derived wave modes occurs remains open, and given that such structures are ubiquitous on the solar surface, it's also important to investigate whether they might ultimately play a significant role in the energy budget of the upper layers of the solar atmosphere. Title: The Solar Orbiter Science Activity Plan. Translating solar and heliospheric physics questions into action Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.; Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.; Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.; Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.; Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.; Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio, L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun, A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso, F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.; Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.; Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.; van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi, L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine, D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot, S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham, G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier, K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins, J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis, I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.; Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis, G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.; Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.; Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis, K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien, H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.; Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.; Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines, J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.; Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.; Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.; Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.; Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.; Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula, G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio, A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.; Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann, T.; Young, P. R.; Zhukov, A. N. Bibcode: 2020A&A...642A...3Z Altcode: 2020arXiv200910772Z Solar Orbiter is the first space mission observing the solar plasma both in situ and remotely, from a close distance, in and out of the ecliptic. The ultimate goal is to understand how the Sun produces and controls the heliosphere, filling the Solar System and driving the planetary environments. With six remote-sensing and four in-situ instrument suites, the coordination and planning of the operations are essential to address the following four top-level science questions: (1) What drives the solar wind and where does the coronal magnetic field originate?; (2) How do solar transients drive heliospheric variability?; (3) How do solar eruptions produce energetic particle radiation that fills the heliosphere?; (4) How does the solar dynamo work and drive connections between the Sun and the heliosphere? Maximising the mission's science return requires considering the characteristics of each orbit, including the relative position of the spacecraft to Earth (affecting downlink rates), trajectory events (such as gravitational assist manoeuvres), and the phase of the solar activity cycle. Furthermore, since each orbit's science telemetry will be downloaded over the course of the following orbit, science operations must be planned at mission level, rather than at the level of individual orbits. It is important to explore the way in which those science questions are translated into an actual plan of observations that fits into the mission, thus ensuring that no opportunities are missed. First, the overarching goals are broken down into specific, answerable questions along with the required observations and the so-called Science Activity Plan (SAP) is developed to achieve this. The SAP groups objectives that require similar observations into Solar Orbiter Observing Plans, resulting in a strategic, top-level view of the optimal opportunities for science observations during the mission lifetime. This allows for all four mission goals to be addressed. In this paper, we introduce Solar Orbiter's SAP through a series of examples and the strategy being followed. Title: 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 Bibcode: 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. Title: Emergence of small-scale magnetic flux in the quiet Sun Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Gontikakis, C.; Kuckein, C.; Verma, M.; Denker, C. Bibcode: 2020A&A...633A..67K Altcode: 2019arXiv191202496K Context. We study the evolution of a small-scale emerging flux region (EFR) in the quiet Sun, from its emergence in the photosphere to its appearance in the corona and its decay.
Aims: We track processes and phenomena that take place across all atmospheric layers; we explore their interrelations and compare our findings with those from recent numerical modelling studies.
Methods: We used imaging as well as spectral and spectropolarimetric observations from a suite of space-borne and ground-based instruments.
Results: The EFR appears in the quiet Sun next to the chromospheric network and shows all morphological characteristics predicted by numerical simulations. The total magnetic flux of the region exhibits distinct evolutionary phases, namely an initial subtle increase, a fast increase with a Co-temporal fast expansion of the region area, a more gradual increase, and a slow decay. During the initial stages, fine-scale G-band and Ca II H bright points coalesce, forming clusters of positive- and negative-polarity in a largely bipolar configuration. During the fast expansion, flux tubes make their way to the chromosphere, pushing aside the ambient magnetic field and producing pressure-driven absorption fronts that are visible as blueshifted chromospheric features. The connectivity of the quiet-Sun network gradually changes and part of the existing network forms new connections with the newly emerged bipole. A few minutes after the bipole has reached its maximum magnetic flux, the bipole brightens in soft X-rays forming a coronal bright point. The coronal emission exhibits episodic brightenings on top of a long smooth increase. These coronal brightenings are also associated with surge-like chromospheric features visible in Hα, which can be attributed to reconnection with adjacent small-scale magnetic fields and the ambient quiet-Sun magnetic field.
Conclusions: The emergence of magnetic flux even at the smallest scales can be the driver of a series of energetic phenomena visible at various atmospheric heights and temperature regimes. Multi-wavelength observations reveal a wealth of mechanisms which produce diverse observable effects during the different evolutionary stages of these small-scale structures. Title: 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. Bibcode: 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. Title: A persistent quiet-Sun small-scale tornado. II. Oscillations Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I. Bibcode: 2019A&A...623A.160T Altcode: 2019arXiv190304796T Context. Recently, the appearance, characteristics, and dynamics of a persistent 1.7 h vortex flow, resembling a small-scale tornado, have been investigated with observations both from the ground and from space in a quiet-Sun region in several lines and channels and for the first time in the Hα line centre. The vortex flow showed significant substructure in the form of several intermittent chromospheric swirls.
Aims: We investigate the oscillatory behaviour of various physical parameters in the vortex area in an attempt to better understand the physics of the reported vortex flow. This is the first analysis of this extent.
Methods: We used the same data set of high spatial and temporal resolution CRisp Imaging SpectroPolarimeter (CRISP) observations in several wavelengths along the Hα and Ca II 8542 Å line profiles, as well as Doppler velocities and full-width at half-maximum (FWHM) derived from the Hα line profiles. The spectral analysis of oscillations is based on a two-dimensional wavelet analysis performed within the vortex flow area and in a quiet-Sun region (used for comparison), as well as along line and circular slices.
Results: The vortex flow shows significant oscillatory power in the range of 3-5 min, peaking around 4 min. This power behaves differently than the reference quiet-Sun region. The derived oscillations reflect the cumulative action of different components such as swaying motions, rotation, and waves. The derived periods for swaying motions are in the range of 200-220 s, and the rotation periods are ∼270 s for Hα and ∼215 s for Ca II 8542 Å. Periods increase with atmospheric height and seem to decrease with radial distance from the vortex centre, suggesting a deviation from a rigid rotation. The behaviour of power within the vortex flow as a function of period and height implies the existence of evanescent waves. Moreover, considerable power is obtained even for periods as long as 10 min, not only at photospheric but also at chromospheric heights, while the formation of vortexes is related to turbulent convection or to twisting motions exercised in the magnetic field concentrations. These imply that different types of waves may be excited, such as magnetoacoustic (e.g. kink) or Alfvén waves.
Conclusions: The vortex flow seems to be dominated by two motions: a transverse (swaying) motion, and a rotational motion. The obtained oscillations point to the propagation of waves within it. Nearby fibril-like flows could play an important role in the rotational modulation of the vortex flow. There also exists indirect evidence that the structure is magnetically supported, and one of the swirls, close to its centre, seems to be acting as a "central engine" to the vortex flow. Title: A persistent quiet-Sun small-scale tornado. I. Characteristics and dynamics Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion, E.; Doyle, J. G. Bibcode: 2018A&A...618A..51T Altcode: Context. Vortex flows have been extensively observed over a wide range of spatial and temporal scales in different spectral lines, and thus layers of the solar atmosphere, and have been widely found in numerical simulations. However, signatures of vortex flows have only recently been reported in the wings of the Hα, but never so far in the Hα line centre.
Aims: We investigate the appearance, characteristics, substructure, and dynamics of a 1.7 h persistent vortex flow observed from the ground and from space in a quiet-Sun region in several lines/channels covering all atmospheric layers from the photosphere up to the low corona.
Methods: We use high spatial and temporal resolution CRisp Imaging SpectroPolarimeter (CRISP) observations in several wavelengths along the Hα and Ca II 8542 Å line profiles, simultaneous Atmospheric Imaging Assembly (AIA) observations in several Ultraviolet (UV) and Extreme ultraviolet (EUV) channels and Helioseismic and Magnetic Imager (HMI) magnetograms to study a persistent vortex flow located at the south solar hemisphere. Doppler velocities were derived from the Hα line profiles. Our analysis involves visual inspection and comparison of all available simultaneous/near-simultaneous observations and detailed investigation of the vortex appearance, characteristics and dynamics using time slices along linear and circular slits.
Results: The most important characteristic of the analysed clockwise rotating vortex flow is its long duration (at least 1.7 h) and its large radius ( 3″). The vortex flow shows different behaviours in the different wavelengths along the Hα and Ca II 8542 Å profiles reflecting the different formation heights and mechanisms of the two lines. Ground-based observations combined with AIA observations reveal the existence of a funnel-like structure expanding with height, possibly rotating rigidly or quasi-rigidly. However, there is no clear evidence that the flow is magnetically driven as no associated magnetic bright points have been observed in the photosphere. Hα and Ca II 8542 Å observations also reveal significant substructure within the flow, manifested as several individual intermittent chromospheric swirls with typical sizes and durations. They also exhibit a wide range of morphological patterns, appearing as dark absorbing features, associated mostly with mean upwards velocities around 3 km s-1 and up to 8 km s-1, and occupying on average 25% of the total vortex area. The radial expansion of the spiral flow occurs with a mean velocity of 3 km s-1, while its dynamics can be related to the dynamics of a clockwise rigidly rotating logarithmic spiral with a swinging motion that is, however, highly perturbed by nearby flows associated with fibril-like structures. A first rough estimate of the rotational period of the vortex falls in the range of 200-300 s.
Conclusions: The vortex flow resembles a small-scale tornado in contrast to previously reported short-lived swirls and in analogy to persistent giant tornadoes. It is unclear whether the observed substructure is indeed due to the physical presence of individual intermittent, recurring swirls or a manifestation of wave-related instabilities within a large vortex flow. Moreover, we cannot conclusively demonstrate that the long duration of the observed vortex is the result of a central swirl acting as an "engine" for the vortex flow, although there is significant supporting evidence inferred from its dynamics. It also cannot be excluded that this persistent vortex results from the combined action of several individual smaller swirls further assisted by nearby flows or that this is a new case in the literature of a hydrodynamically driven vortex flow.

The movie associated to Fig. 4 is available at https://www.aanda.org Title: Probing the Quiet Solar Atmosphere from the Photosphere to the Corona Authors: Kontogiannis, Ioannis; Gontikakis, Costis; Tsiropoula, Georgia; Tziotziou, Kostas Bibcode: 2018SoPh..293...56K Altcode: 2018arXiv180307934K We investigate the morphology and temporal variability of a quiet-Sun network region in different solar layers. The emission in several extreme ultraviolet (EUV) spectral lines through both raster and slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft is studied along with Hα observations and high-resolution spectropolarimetric observations of the photospheric magnetic field. The photospheric magnetic field is extrapolated up to the corona, showing a multitude of large- and small-scale structures. We show for the first time that the smallest magnetic structures at both the network and internetwork contribute significantly to the emission in EUV lines, with temperatures ranging from 8 ×104K to 6 ×105K. Two components of transition region emission are present, one associated with small-scale loops that do not reach coronal temperatures, and another component that acts as an interface between coronal and chromospheric plasma. Both components are associated with persistent chromospheric structures. The temporal variability of the EUV intensity at the network region is also associated with chromospheric motions, pointing to a connection between transition region and chromospheric features. Intensity enhancements in the EUV transition region lines are preferentially produced by Hα upflows. Examination of two individual chromospheric jets shows that their evolution is associated with intensity variations in transition region and coronal temperatures. Title: 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 Bibcode: 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. Bibcode: 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 (Beff) 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 Bibcode: 2017EGUGA..1913786T Altcode: Multi-spacecraft observations of solar energetic particle (SEP) events are important for understanding the acceleration processes and the interplanetary propagation of particles released during eruptive events. In this work, we have carefully studied 25 gamma-ray flare events observed by FERMI and investigated possible associations with SEP-related events observed with STEREO and L1 spacecraft in the heliosphere. A data-driven velocity dispersion analysis (VDA) and Time-Shifting Analysis (TSA) are used for deriving the release times of protons and electrons at the Sun and for comparing them with the respective times stemming from the gamma-ray event analysis and their X-ray signatures, in an attempt to interconnect the SEPs and Fermi events and better understand the physics involved. Acknowledgements: This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 637324. Title: Solar flares, coronal mass ejections and solar energetic particle event characteristics Authors: Papaioannou, Athanasios; Sandberg, Ingmar; Anastasiadis, Anastasios; Kouloumvakos, Athanasios; Georgoulis, Manolis K.; Tziotziou, Kostas; Tsiropoula, Georgia; Jiggens, Piers; Hilgers, Alain Bibcode: 2016JSWSC...6A..42P Altcode: A new catalogue of 314 solar energetic particle (SEP) events extending over a large time span from 1984 to 2013 has been compiled. The properties as well as the associations of these SEP events with their parent solar sources have been thoroughly examined. The properties of the events include the proton peak integral flux and the fluence for energies above 10, 30, 60 and 100 MeV. The associated solar events were parametrized by solar flare (SF) and coronal mass ejection (CME) characteristics, as well as related radio emissions. In particular, for SFs: the soft X-ray (SXR) peak flux, the SXR fluence, the heliographic location, the rise time and the duration were exploited; for CMEs the plane-of-sky velocity as well as the angular width were utilized. For radio emissions, type III, II and IV radio bursts were identified. Furthermore, we utilized element abundances of Fe and O. We found evidence that most of the SEP events in our catalogue do not conform to a simple two-class paradigm, with the 73% of them exhibiting both type III and type II radio bursts, and that a continuum of event properties is present. Although, the so-called hybrid or mixed events are found to be present in our catalogue, it was not possible to attribute each SEP event to a mixed/hybrid sub-category. Moreover, it appears that the start of the type III burst most often precedes the maximum of the SF and thus falls within the impulsive phase of the associated SF. At the same time, type III bursts take place within ≈5.22 min, on average, in advance from the time of maximum of the derivative of the SXR flux (Neupert effect). We further performed a statistical analysis and a mapping of the logarithm of the proton peak flux at E > 10 MeV, on different pairs of the parent solar source characteristics. This revealed correlations in 3-D space and demonstrated that the gradual SEP events that stem from the central part of the visible solar disk constitute a significant radiation risk. The velocity of the associated CMEs, as well as the SXR peak flux and fluence, are all fairly significantly correlated to both the proton peak flux and the fluence of the SEP events in our catalogue. The strongest correlation to SEP characteristics is manifested by the CME velocity. Title: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2016A&A...586A..25P Altcode: 2015arXiv151206032P Context. Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations.
Aims: We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated upflows through the photosphere and chromosphere of a quiet Sun internetwork region.
Methods: We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both Hα 6563 Å and Ca II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well as ultraviolet imaging and spectral data simultaneously obtained by the Interface Region Imaging Spectrograph (IRIS).
Results: A small-scale vortex is observed for the first time simultaneously in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the vortex, Hα narrowband images at -0.77 Å and Ca II 8542 Å narrowband images at -0.5 Å, and their corresponding Doppler signal maps, clearly show consecutive high-speed upflow events in the vortex region. These high-speed upflows with a size of 0.5-1 Mm appear in the shape of spiral arms and exhibit two distinctive apparent motions in the plane of sky for a few minutes: (1) a swirling motion with an average speed of 13 km s-1 and (2) an expanding motion at a rate of 4-6 km s-1. Furthermore, the spectral analysis of Mg II k and Mg II subordinate lines in the vortex region indicates an upward velocity of up to ~8 km s-1 along with a higher temperature compared to the nearby quiet Sun chromosphere.
Conclusions: The consecutive small-scale vortex events can heat the upper chromosphere by driving continuous high-speed upflows through the lower atmosphere.

Movies associated to Figs. 2 and 3 are available at http://www.aanda.org Title: 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. Bibcode: 2016ApJ...817...14P Altcode: During the interval 2012 March 7-11 the geospace experienced a barrage of intense space weather phenomena including the second largest geomagnetic storm of solar cycle 24 so far. Significant ultra-low-frequency wave enhancements and relativistic-electron dropouts in the radiation belts, as well as strong energetic-electron injection events in the magnetosphere were observed. These phenomena were ultimately associated with two ultra-fast (>2000 km s-1) 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⊙ 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. Bibcode: 2016A&A...585A.110K Altcode: 2015arXiv151108618K
Aims: We seek indications or evidence of transmission/conversion of magnetoacoustic waves at the magnetic canopy, as a result of its impact on the properties of the wave field of the photosphere and chromosphere.
Methods: We use cross-wavelet analysis to measure phase differences between intensity and Doppler signal oscillations in the Hα, Ca II h, and G-band. We use the height of the magnetic canopy to create appropriate masks to separate internetwork (IN) and magnetic canopy regions. We study wave propagation and differences between these two regions.
Results: The magnetic canopy affects wave propagation by lowering the phase differences of progressive waves and allowing the propagation of waves with frequencies lower than the acoustic cut-off. We also find indications in the Doppler signals of Hα of a response to the acoustic waves at the IN, observed in the Ca II h line. This response is affected by the presence of the magnetic canopy.
Conclusions: Phase difference analysis indicates the existence of a complicated wave field in the quiet Sun, which is composed of a mixture of progressive and standing waves. There are clear imprints of mode conversion and transmission due to the interaction between the p-modes and small-scale magnetic fields of the network and internetwork. Title: Energy and helicity injection in solar quiet regions Authors: Tziotziou, K.; Park, S. -H.; Tsiropoula, G.; Kontogiannis, I. Bibcode: 2015A&A...581A..61T Altcode:
Aims: We investigate the free magnetic energy and relative magnetic helicity injection in solar quiet regions.
Methods: We use the DAVE4VM method to infer the photospheric velocity field and calculate the free magnetic energy and relative magnetic helicity injection rates in 16 quiet-Sun vector magnetograms sequences.
Results: We find that there is no dominant sense of helicity injection in quiet-Sun regions, and that both helicity and energy injections are mostly due to surface shuffling motions that dominate the respective emergence by factors slightly larger than two. We, furthermore, estimate the helicity and energy rates per network unit area as well as the respective budgets over a complete solar cycle.
Conclusions: Derived helicity and energy budgets over the entire solar cycle are similar to respective budgets derived in a recent work from the instantaneous helicity and free magnetic energy budgets and higher than previously reported values that relied on similar approaches to this analysis. Free-energy budgets, mostly generated like helicity at the network, are high enough to power the dynamics of fine-scale structures residing at the network, such as mottles and spicules, while corresponding estimates of helicity budgets are provided, pending future verification from high-resolution magneto-hydrodynamic simulations and/or observations. Title: 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 Bibcode: 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. Bibcode: 2015SoPh..290..841D Altcode: 2014arXiv1410.6070D; 2015SoPh..tmp....1D A statistical analysis of the relationship between solar energetic particles (SEPs) and properties of solar flares and coronal mass ejections (CMEs) is presented. SEP events during Solar Cycle 23 are selected that are associated with solar flares originating in the visible hemisphere of the Sun and that are at least of magnitude M1. Taking into account all flares and CMEs that occurred during this period, the probability for the occurrence of an SEP event near Earth is determined. A strong rise of this probability is observed for increasing flare intensities, more western locations, higher CME speeds, and halo CMEs. The correlations between the proton peak flux and these solar parameters are derived for a low (> 10 MeV) and high (> 60 MeV) energy range excluding any flux enhancement due to the passage of fast interplanetary shocks. The obtained correlation coefficients are 0.55±0.07 (0.63±0.06) with flare intensity, and 0.56±0.08 (0.40±0.09) with CME speed for E>10 MeV (E>60 MeV). For both energy ranges, the correlations with flare longitude and CME width are very weak or non-existent. Furthermore, the occurrence probabilities, correlation coefficients, and mean peak fluxes are derived in multi-dimensional bins combining the aforementioned solar parameters. The correlation coefficients are also determined in different proton energy channels ranging from 5 to 200 MeV. The results show that the correlation between the proton peak flux and the CME speed decreases with energy, while the correlation with the flare intensity shows the opposite behaviour. Furthermore, the correlation with the CME speed is stronger than the correlation with the flare intensity below 15 MeV and becomes weaker above 20 MeV. When the enhancements in the flux profiles due to interplanetary shocks are not excluded, only a small but not very significant change is observed in the correlation coefficients between the proton peak flux below 7 MeV and the CME speed. Title: 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. Bibcode: 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. Bibcode: 2014A&A...570L...1T Altcode: 2014arXiv1409.8117T
Aims: We assess the validity of the free magnetic energy - relative magnetic helicity diagram for solar magnetic structures.
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.
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.
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. Bibcode: 2014A&A...569A..96P Altcode: The Solar Terrestrial Relations Observatory (STEREO) recordings provide an unprecedented opportunity to study the evolution of solar energetic particle (SEP) events from different observation points in the heliosphere, allowing one to identify the effects of the properties of the interplanetary magnetic field (IMF) and solar wind structures on the interplanetary transport and acceleration of SEPs. Two catalogues based on STEREO recordings, have been compiled as a part of the SEPServer project, a three-year collaborative effort of eleven European partners funded under the Seventh Framework Programme of the European Union (FP7/SPACE). In particular, two instruments on board STEREO have been used to identify all SEP events observed within the descending phase of solar cycle 23 and the rising phase of solar cycle 24 from 2007 to 2012, namely: the Low Energy Telescope (LET) and the Solar Electron Proton Telescope (SEPT). A scan of STEREO/LET protons within the energy range 6-10 MeV has been performed for each of the two STEREO spacecraft. We have tracked all enhancements that have been observed above the background level of this particular channel and cross-checked with available lists of interplanetary coronal mass ejections (ICMEs), stream interaction regions (SIRs), and shocks, as well as with the reported events in literature. Furthermore, parallel scanning of the STEREO near relativistic electrons has been performed in order to pinpoint the presence (or absence) of an electron event in the energy range of 55-85 keV, for all of the aforementioned proton events included in our lists. We provide the onset and peak time as well as the peak value of all events for both protons and electrons, the relevant solar associations in terms of electromagnetic emissions, soft and hard X-rays (SXRs and HXRs). Finally, a subset of events with clear recordings at both STEREO spacecraft is presented together with the parent solar events of these multispacecraft SEP events. Title: Transmission and conversion of magnetoacoustic waves on the magnetic canopy in a quiet Sun region Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2014A&A...567A..62K Altcode: 2014arXiv1406.5066K Context. We present evidence for the conversion and transmission of wave modes on the magnetic flux tubes that constitute mottles and form the magnetic canopy in a quiet Sun region.
Aims: Our aim is to highlight the details and the key parameters of the mechanism that produces power halos and magnetic shadows around the magnetic network observed in Hα.
Methods: We use our previous calculations of the magnetic field vector and the height of the magnetic canopy, and based on simple assumptions, we determine the turning height, i.e., the height at which the fast magnetoacoustic waves reflect at the chromosphere. We compare the variation of 3, 5, and 7 min power in the magnetic shadow and the power halo with the results of a two-dimensional model on mode conversion and transmission. The key parameter of the model is the attack angle, which is related to the inclination of the magnetic field vector at the canopy height. Our analysis takes also into account that 1) there are projection effects on the propagation of waves; 2) the magnetic canopy and the turning height are curved layers; 3) waves with periods longer than 3 min only reach the chromosphere in the presence of inclined magnetic fields (ramp effect); 4) mottles in Hα are canopy structures; and 5) the wings of Hα contain mixed signal from low- and high-β plasma.
Results: The dependence of the measured power on the attack angle follows the anticipated by the two-dimensional model very well. Long-period slow waves are channeled to the upper chromospheric layers following the magnetic field lines of mottles, while short-period fast waves penetrate the magnetic canopy and are reflected back higher, at the turning height.
Conclusions: Although both magnetoacoustic modes contribute to velocity signals, making the interpretation of observations a challenging task, we conclude that conversion and transmission of the acoustic waves into fast and slow magnetoacoustic waves are responsible for forming power halos and magnetic shadows in the quiet Sun region. Title: Energy and helicity budgets of solar quiet regions Authors: Tziotziou, K.; Tsiropoula, G.; Georgoulis, M. K.; Kontogiannis, I. Bibcode: 2014A&A...564A..86T Altcode: 2014arXiv1403.0730T
Aims: We investigate the free magnetic energy and relative magnetic helicity budgets of solar quiet regions.
Methods: Using a novel nonlinear force-free method that requires single solar vector magnetograms we calculated the instantaneous free magnetic energy and relative magnetic helicity budgets in 55 quiet-Sun vector magnetograms.
Results: As in a previous work on active regions, we constructed here for the first time the (free) energy-(relative) helicity diagram of quiet-Sun regions. We find that quiet-Sun regions have no dominant sense of helicity and show monotonic correlations a) between free magnetic energy/relative helicity and magnetic network area and, consequently, b) between free magnetic energy and helicity. Free magnetic energy budgets of quiet-Sun regions represent a rather continuous extension of respective active-region budgets towards lower values, but the corresponding helicity transition is discontinuous because of the incoherence of the helicity sense in contrast to active regions. We furthermore estimated the instantaneous free magnetic-energy and relative magnetic-helicity budgets of the entire quiet Sun, as well as the respective budgets over an entire solar cycle.
Conclusions: Derived instantaneous free magnetic energy budgets and, to a lesser extent, relative magnetic helicity budgets over the entire quiet Sun are similar to the respective budgets of a sizeable active region, while total budgets within a solar cycle are found to be higher than previously reported. Free-energy budgets are similar to the energy needed to power fine-scale structures residing at the network, such as mottles and spicules. Title: Free magnetic energy and relative magnetic helicity diagnostics for the quality of NLFF field extrapolations Authors: Moraitis, Kostas; Archontis, Vasilis; Tziotziou, Konstantinos; Georgoulis, Manolis K. Bibcode: 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 Bibcode: 2014cosp...40E3428T Altcode: We present a novel non-linear force-free method for the calculation of the instantaneous free magnetic energy and relative magnetic helicity budgets of a solar region from a single photospheric/chromospheric vector magnetogram. Our objective is to study the role of these quantities both in solar eruptions and in quiet-Sun dynamics. The validity of the method is tested using both observations and synthetic magnetohydrodynamical (MHD) models. The method is applied for the derivation of the energy-helicity (EH) diagram of solar active regions (ARs) from a sample of 162 vector magnetograms corresponding to 42 different ARs, suggesting the existence of 4×10(31) erg and 2×10(42) Mx(2) thresholds in free energy and relative helicity, respectively, for ARs to enter eruptive territory. Furthermore, the dynamical evolution of both quantities in eruptive NOAA AR 11158, using a high-cadence 5-day time series of vector magnetograms, suggests the formation of increasingly helical pre-eruption structures and a causal relation between flares and Coronal Mass Ejections (CMEs). The method is also used to derive helicity and energy budgets in quiet Sun regions and construct the respective EH diagram. Our results highlight the importance of both energy and helicity in AR evolution and quiet-Sun dynamics and instigate further research on the underlying physics with three-dimensional MHD models. This work is supported by EU's Seventh Framework Programme via a Marie Curie Fellowship. Title: Transmission and conversion of magneto-acoustic waves in the quiet solar chromosphere Authors: Kontogiannis, I., Tsiropoula, G.; Tziotziou, K. Bibcode: 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. Bibcode: 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. Bibcode: 2013hell.conf....6T Altcode: We present a novel nonlinear force-free method designed to calculate the instantaneous free magnetic energy and relative magnetic helicity budgets of a solar region from a single photospheric/chromospheric vector magnetogram of the region. Our objective is to study the role of these quantities in solar eruptions and quiet-Sun dynamics. We apply the method to (1) derive the energy/helicity diagram of solar active regions from a sample of 162 vector magnetograms corresponding to 42 different active regions (ARs), suggesting that there exist 4 1031 erg and 2 1042 Mx2 thresholds in free energy and relative helicity, respectively, for ARs to enter eruptive territory, (2) study the dynamics of eruptive NOAA AR 11158 using a high-cadence 5-day time series of vector magnetograms, suggesting the formation of increasingly helical pre-eruption structures and a causal relation between flares and Coronal Mass Ejections (CMEs) and, (3) derive helicity and energy budgets in quiet Sun regions and construct the respective energy/helicity diagram. Our results highlight the importance of these two parameters in AR evolution and quiet-Sun dynamics and instigate further research including detailed analysis with synthetic, magnetohydrodynamical models. This work is supported by EU's Seventh Framework Programme via a Marie Curie Fellowship and by the Hellenic National Space Weather Research Network (HNSWRN) via the THALIS Programme. Title: Solar Energetic Particles within the STEREO era: 2007-2012 Authors: Papaioannou, A.; Malandraki, O. E.; Heber, B.; Dresing, N.; Klein, K. L.; Vainio, R.; Rodriguez-Gasen, R.; Klassen, A.; Gomez-Herrero, R.; Vilmer, N.; Mewaldt, R. A.; Tziotziou, K.; Tsiropoula, G. Bibcode: 2013hell.conf....9P Altcode: STEREO (Solar TErrestrial RElations Observatory) recordings provide an unprecedented opportunity to identify the evolution of Solar Energetic Particles (SEPs) at different observing points in the heliosphere, which is expected to provide new insight on the physics of solar particle genesis, propagation and acceleration as well as on the properties of the interplanetary magnetic field that control these acceleration and propagation processes. In this work, two instruments onboard STEREO have been used in order to identify all SEP events observed within the rising phase of solar cycle 24 from 2007 to 2011, namely: the Low Energy Telescope (LET) and the Solar Electron Proton Telescope (SEPT). A scan over STEREO/LET protons within the energy range 6-10 MeV has been performed for each of the two STEREO spacecraft. We have tracked all enhancements that have been observed above the background level of this particular channel and cross checked with available lists on STEREO/ICMEs, SIRs and shocks as well as with the reported events in literature. Furthermore, parallel scanning of the STEREO/SEPT electrons in order to pinpoint the presence (or not) of an electron event has been performed in the energy range of 55-85 keV, for all of the aforementioned proton events, included in our lists. We provide the onset of all events for both protons and electrons, time-shifting analysis for near relativistic electrons which lead to the inferred solar release time and the relevant solar associations from radio spectrographs (Nancay Decametric Array; STEREO/WAVES) to GOES Soft X-rays and coronal mass ejections spotted by both SOHO/LASCO and STEREO Coronographs Title: 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. Bibcode: 2013hell.conf...10P Altcode: Transient expulsions of gigantic clouds of solar coronal plasma into the interplanetary space in the form of Coronal Mass Ejections (CMEs) and sudden, intense flashes of electromagnetic radiation, solar flares, are well-established drivers of the variable Space Weather. Given the innate, intricate links and connections between the solar drivers and their geomagnetic effects, synergistic efforts assembling all pieces of the puzzle along the Sun-Earth line are required to advance our understanding of the physics of Space Weather. This is precisely the focal point of the Hellenic National Space Weather Research Network (HNSWRN) under the THALIS Programme. Within the HNSWRN framework, we present here the first results from a coordinated multi-instrument case study of a major solar eruption (X5.4 and X1.3 flares associated with two ultra-fast (>2000 km/s) CMEs) which were launched early on 7 March 2012 and triggered an intense geomagnetic storm (min Dst =-147 nT) approximately two days afterwards. Several elements of the associated phenomena, such as the flare and CME, EUV wave, WL shock, proton and electron event, interplanetary type II radio burst, ICME and magnetic cloud and their spatiotemporal relationships and connections are studied all way from Sun to Earth. To this end, we make use of satellite data from a flotilla of solar, heliospheric and magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE, Herschel, Planck and INTEGRAL). We also present our first steps toward formulating a cohesive physical scenario to explain the string of the observables and to assess the various physical mechanisms than enabled and gave rise to the significant geoeffectiveness of the eruption. Title: Interpreting Eruptive Behavior in NOAA AR 11158 via the Region's Magnetic Energy and Relative-helicity Budgets Authors: Tziotziou, Kostas; Georgoulis, Manolis K.; Liu, Yang Bibcode: 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 Bibcode: 2013EGUGA..15..383K Altcode: We investigate the interaction between acoustic oscillations and the fine-scale structures found at the chromospheric network boundaries that form the magnetic canopy. We use high precision photospheric magnetograms obtained by SOT/SP on-board the Hinode satellite and time series of high spatial resolution filtergrams in five wavelengths along the Hα line profile taken by the Dutch Open Telescope. We extrapolate the photospheric magnetic field using the current-free hypothesis to calculate the vector of the magnetic field and reconstruct the magnetic configuration of the chromosphere. Assuming the VAL-C atmospheric model we are able to estimate the height of formation of the magnetic canopy. We use the wavelet analysis on the Ha observations and obtain the 2-D distribution of the oscillatory power at different atmospheric heights. We then compare the obtained distribution of power with the one predicted by the 2-D model of Schunker & Cally at various magnetic field inclination angles. Our results show that the magnetic shadow and power halo phenomena observed in network regions may be attributed to the conversion/transmission of magneto-acoustic waves on the magnetic canopy. The amount of transmission/conversion depends on the attack angle, i.e. the angle between the wave vector and magnetic field direction. Waves which experience mode conversion and/or transmission can propagate to greater atmospheric heights while some fraction of their energy escapes into the solar wind. Title: 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 Bibcode: 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 Bibcode: 2013JSWSC...3A..12V Altcode: SEPServer is a three-year collaborative project funded by the seventh framework programme (FP7-SPACE) of the European Union. The objective of the project is to provide access to state-of-the-art observations and analysis tools for the scientific community on solar energetic particle (SEP) events and related electromagnetic (EM) emissions. The project will eventually lead to better understanding of the particle acceleration and transport processes at the Sun and in the inner heliosphere. These processes lead to SEP events that form one of the key elements of space weather. In this paper we present the first results from the systematic analysis work performed on the following datasets: SOHO/ERNE, SOHO/EPHIN, ACE/EPAM, Wind/WAVES and GOES X-rays. A catalogue of SEP events at 1 AU, with complete coverage over solar cycle 23, based on high-energy (~68-MeV) protons from SOHO/ERNE and electron recordings of the events by SOHO/EPHIN and ACE/EPAM are presented. A total of 115 energetic particle events have been identified and analysed using velocity dispersion analysis (VDA) for protons and time-shifting analysis (TSA) for electrons and protons in order to infer the SEP release times at the Sun. EM observations during the times of the SEP event onset have been gathered and compared to the release time estimates of particles. Data from those events that occurred during the European day-time, i.e., those that also have observations from ground-based observatories included in SEPServer, are listed and a preliminary analysis of their associations is presented. We find that VDA results for protons can be a useful tool for the analysis of proton release times, but if the derived proton path length is out of a range of 1 AU < s ≲ 3 AU, the result of the analysis may be compromised, as indicated by the anti-correlation of the derived path length and release time delay from the associated X-ray flare. The average path length derived from VDA is about 1.9 times the nominal length of the spiral magnetic field line. This implies that the path length of first-arriving MeV to deka-MeV protons is affected by interplanetary scattering. TSA of near-relativistic electrons results in a release time that shows significant scatter with respect to the EM emissions but with a trend of being delayed more with increasing distance between the flare and the nominal footpoint of the Earth-connected field line. Title: The relation between Magnetic Energy and Helicity and their accumulation in Eruptive Solar Active Regions Authors: Tziotziou, K.; Georgoulis, M. K.; Raouafi, N. -E. Bibcode: 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 4×1031 erg and 2×1042 Mx2, 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 × 1031 erg and 2 × 1042 Mx2, 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. Bibcode: 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. Bibcode: 2012SSRv..169..181T Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T Over the last two decades the uninterrupted, high resolution observations of the Sun, from the excellent range of telescopes aboard many spacecraft complemented with observations from sophisticated ground-based telescopes have opened up a new world producing significantly more complete information on the physical conditions of the solar atmosphere than before. The interface between the lower solar atmosphere where energy is generated by subsurface convection and the corona comprises the chromosphere, which is dominated by jet-like, dynamic structures, called mottles when found in quiet regions, fibrils when found in active regions and spicules when observed at the solar limb. Recently, space observations with Hinode have led to the suggestion that there should exist two different types of spicules called Type I and Type II which have different properties. Ground-based observations in the Ca ii H and K filtergrams reveal the existence of long, thin emission features called straws in observations close to the limb, and a class of short-lived events called rapid blue-shifted excursions characterized by large Doppler shifts that appear only in the blue wing of the Ca ii infrared line. It has been suggested that the key to understanding how the solar plasma is accelerated and heated may well be found in the studies of these jet-like, dynamic events. However, while these structures are observed and studied for more than 130 years in the visible, but also in the UV and EUV emission lines and continua, there are still many questions to be answered. Thus, despite their importance and a multitude of observations performed and theoretical models proposed, questions regarding their origin, how they are formed, their physical parameters, their association with the underlying photospheric magnetic field, how they appear in the different spectral lines, and the interrelationship between structures observed in quiet and active regions on the disk and at the limb, as well as their role in global processes has not yet received definitive answers. In addition, how they affect the coronal heating and solar wind need to be further explored. In this review we present observations and physical properties of small-scale jet-like chromospheric events observed in active and quiet regions, on the disk and at the limb and discuss their interrelationship. Title: 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. Bibcode: 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. Bibcode: 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,

namely: 'SEPServer' and 'COMESEP'. 'SEPServer' focuses on the implementation of a comprehensive and up to date SEP analysis service including scientific data driven analysis both for 1 AU and for > 1 AU using data from the SOHO/ ERNE, SOHO/EPHIN, ACE/EPAM, ACE/SIS, WIND/3DP, Ulysses/HISCALE, Ulysses/COSPIN/LET and Ulysses/COSPIN/KET experiments. SEPServer will also provide for the first time the release of the HELIOS data set in a reasonable format and in full time resolution, thus making available data also for orbits inside 1 AU (down to 0.3 AU). Observational data-driven analysis methods such as: onset determination, velocity dispersion, and/or time-shifting analysis, direct comparison of observed SEP fluxes, spectra and abundance ratios with the associated electromagnetic emission data will be applied. 'SEPServer' will enhance our understanding of the source, acceleration and transport of SEPs which is directly related to space weather research progress. 'COMESEP' sets out to develop tools for forecasting SEP radiation storms and geomagnetic storms based on scientific data analysis and extensive modeling. It is foreseen that these forecasting tools will be incorporated into an automated operational European Space Weather Alert system, which is the 'COMESEP' primary goal. Basic research activities on Space Weather carried out at IAA/NOA within the framework of these two projects will be presented including the analysis of SEPs and the associated electromagnetic emissions for selected case studies, the detailed study of the so-called 'reservoir effect' in the heliosphere as well as the impact of the large-scale structure of the IMF on the SEP profiles and its space weather implications. These project-related activities will provide the basis for future solar missions such as Solar Orbiter - in which IAA/NOA participates as a Co-Investigator (EPD instrument). Title: Solar chromospheric fine scale structures: dynamics and energetics Authors: Tziotziou, K. Bibcode: 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. Bibcode: 2012hell.conf...11K Altcode: We use a dataset of simultaneous image sequences obtained by Hinode/SOT with the Ca II H filter, as well as in Ha+-0.2A. SOT was looking at the SW solar limb. The high temporal and spatial resolution allows us to study the structure and dynamics of spicules seen at the different filters. Individual spicules have been selected and intensity and velocity distributions at different heights along their central axes are examined along with transversal fluctuations. Title: Multi-wavelengths observations of oscillatory phenomena in a solar network region and their relation to the magnetic field Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2012hell.conf....6K Altcode: The chromosphere is an inhomogeneous and highly dynamic layer of the solar atmosphere. New high resolution observations have revealed that it consists mainly of fine-scale structures which are directly related to the magnetic field. In this work we use multi-wavelength observations to study oscillatory phenomena in the quiet Sun and their relation to the magnetic field and the chromospheric fine-scale structures. The observations were obtained during a coordinated campaign which included space-borne instruments (i.e. the Transition Region and Coronal Explorer, the Michelson Doppler Imager onboard SoHO, and the Specropolarimeter onboard the Hinode spacecraft) and a ground-based telescope (i.e. the Dutch Open Telescope). The analysed data consist of time series of filtergrams of a solar network region observed at different atmospheric layers from the photosphere through the temperature minimum region and well into the chromosphere and also of high resolution magnetograms. Using wavelet analysis we investigate the oscillatory power distribution in the 2D field-of-view, as well as its vertical distribution and its relation with the fine-scale chromospheric mottles, while through phase difference analysis we investigate wave propagation characteristics. Our results show that the oscillatory power has a fibrilar distribution and that chromospheric mottles are directly related to power enhancement (power halo) or suppression (magnetic shadow). This finding is attributed to the interaction between acoustic oscillations and mottles which outline inclined magnetic fields and clearly indicate that mottles are the loci of wave tranmission, reflection and refraction. It also leads to the conclusion that these structures are directly related to the formation of the magnetic canopy, i.e. the layer that divides the atmosphere into two components, a magnetized and a non magnetized one. Extrapolation of the photospheric magnetic field up to the chromosphere using the current-free assumption and use of the VAL C atmospheric model allows the determination of the height of formation of the magnetic canopy and provide the opportunity to highlight the details of the interaction between acoustic o scillations and the magnetic field. Title: 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. Bibcode: 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. Bibcode: 2011A&A...531A..66K Altcode:
Aims: We explore the differences in the measurement of the magnetic field of the quiet solar photosphere provided by the Michelson Doppler Imager (MDI) onboard SoHO and the SpectroPolarimeter (SOT/SP) onboard Hinode and the ensuing implications for the extrapolated chromospheric magnetic field and the determination of the location of the magnetic canopy.
Methods: We employ potential field extrapolation to reconstruct the chromospheric magnetic field using the magnetic field of the photosphere provided by the two instruments. We also calculate the plasma-β parameter using the VAL C model atmosphere of the quiet Sun to determine the height of the magnetic canopy.
Results: MDI underestimates the magnetic field of the quiet Sun sometimes by a factor of five, which leads to an overestimation of the height of the magnetic canopy by up to ~550 km. Although the overall magnetic field configuration does not differ significantly when calculated with either MDI or SOT/SP, the data of the latter lead to lower and more extended canopies. The difference in the resolution of the two instruments does not seem to affect the chromospheric magnetic field higher than 1000 km.
Conclusions: The height of the magnetic canopy is an important parameter to consider when investigating wave propagation and the oscillatory properties of the quiet Sun regions in the network and internetwork. The canopy height's derivation depends very much on the sensitivity of the instruments used to measure the photospheric magnetic field. Consequently precise measurements of the photospheric magnetic field are crucial to accurately reconstruct the chromospheric magnetic field and to distinguish between the various wave modes. Title: Oscillations in a network region observed in the Hα line and their relation to the magnetic field Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Georgoulis, M. K. Bibcode: 2010A&A...524A..12K Altcode:
Aims: Our aim is to gain a better understanding of the interaction between acoustic oscillations and the small-scale magnetic fields of the Sun. To this end, we examine the oscillatory properties of a network region and their relation to the magnetic configuration of the chromosphere. We link the oscillatory properties of a network region and their spatial variation with the variation of the parameters of the magnetic field. We investigate the effect of the magnetic canopy and the diverging flux tubes of the chromospheric network on the distribution of oscillatory power over the network and internetwork.
Methods: We use a time series of high resolution filtergrams at five wavelengths along the Hα profile observed with the Dutch Open Telescope, as well as high resolution magnetograms taken by the SOT/SP onboard HINODE. Using wavelet analysis, we construct power maps of the 3, 5 and 7 min oscillations of the Doppler signals calculated at ±0.35 Å and ±0.7 Å from the Hα line center. These represent velocities at chromospheric and photospheric levels respectively. Through a current-free (potential) field extrapolation we calculate the chromospheric magnetic field and compare its morphology with the Hα filtergrams. We calculate the plasma β and the magnetic field inclination angle and compare their distribution with the oscillatory power at the 3, 5 and 7 min period bands.
Results: Chromospheric mottles seem to outline the magnetic field lines. The Hα ± 0.35 Å Doppler signals are formed above the canopy, while the Hα ± 0.7 Å corresponding ones below it. The 3 min power is suppressed at the chromosphere around the network, where the canopy height is lower than 1600 km, while at the photosphere it is enhanced due to reflection. 3, 5 and 7 min oscillatory power is increased around the network at the photosphere due to reflection of waves on the overlying canopy, while increased 5 and 7 min power at the chromosphere is attributed mainly to wave refraction on the canopy. At these high periods, power is also increased due to p-mode leakage because of the high inclinations of the magnetic field.
Conclusions: Our high resolution Hα observations and photospheric magnetograms provide the opportunity to highlight the details of the interaction between acoustic oscillations and the magnetic field of a network region. We conclude that several mechanisms that have been proposed such as p-mode leakage, mode conversion, reflection and refraction of waves on the magnetic canopy may act together and result to the observed properties of network oscillations. Title: Estimating Fluxes of SEPs by Unfolding ESA/SREM Data Authors: Sandberg, I.; Daglis, I. A.; Anastasiadis, A.; Tziotziou, K.; Bühler, P.; Nieminen, P. Bibcode: 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. Bibcode: 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. Bibcode: 2010ASPC..424...31K Altcode: We analyze the temporal behavior of a solar quiet region using a set of multi-wavelength observations obtained during a coordinated campaign. The observations were acquired by the ground-based Dutch Open Telescope (DOT), the Michelson Doppler Imager (MDI) on-board SOHO and the UV filters of the Transition Region and Coronal Explorer (TRACE). A large range of height in the solar atmosphere, from the deep photosphere to the upper chromosphere is covered by these instruments. We investigate the oscillation properties of the intensities and velocities in distinct regions of the quiet Sun, i.e. internetwork, bright points (NBP) defining the network boundaries and dark mottles forming a well-defined rosette, as observed by the different instruments and in the different heights. The variations of the intensities and velocities are studied with wavelet analysis. The aim of our work is to find similarities and/or differences in the oscillatory phenomena observed in the different examined regions, as well as comprehensive information on the interaction of the oscillations and the magnetic field. Title: 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. Bibcode: 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.
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.
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.
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.
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. Bibcode: 2010A&A...510A..41K Altcode: Context. We investigate the oscillatory behavior of the quiet solar chromosphere and its discrete components in terms of oscillation properties, i.e. network and internetwork. For this purpose, we use a time series of high resolution filtergrams at five wavelengths along the Hα profile, obtained by the Dutch Open Telescope.
Aims: We aim to gain insight on the distribution of power in different period bands and its variation between network and internetwork. Our spectral resolution provides information on the vertical distribution of power, since the Hα line has both photospheric and chromospheric components. We investigate the effect of Hα mottles on chromospheric oscillations, since they are the most prominent feature of the Hα chromosphere and outline inclined magnetic fields.
Methods: We use wavelet and phase difference analyses of Hα intensities and Doppler signals. Two-dimensional power maps in the 3, 5 and 7 min period bands as well as coherence and phase difference maps were constructed.
Results: At photospheric heights, where the Hα ± 0.7 Å wing is formed, the 3 and 5 min power is enhanced around the network, and forms power halos. Higher in the chromosphere these areas are replaced by magnetic shadows, i.e. places of power suppression. Interestingly, the power maps show a filamentary structure in the network which correlates very well with mottles. These areas show positive phase differences at the 3 min period band. At the 5 min and 7 min period bands both positive and negative phase differences are obtained with an increased number of pixels with high coherence, indicating the existence of both upward and downward propagating waves.
Conclusions: We attribute our findings to the interaction between acoustic oscillations and the magnetic fields that constitute the magnetic network. The network flux tubes diverge at chromospheric levels and obtain a significant horizontal component, which is betrayed by the presence of mottles. The variation of power reveals the discrete role of the magnetic field at different heights, which guides or suppresses the oscillations, depending on its inclination. Spectral resolution in Hα provides useful information on the coupling between the acoustic sub-canopy atmosphere and the magnetized chromosphere. Title: 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. Bibcode: 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 Bibcode: 2010cosp...38.2918T Altcode: 2010cosp.meet.2918T This review focuses on the solar chromosphere, a very inhomogeneous and dynamic layer that exhibits phenomena on a large range of spatial and temporal scales. High-resolution observa-tions from existing telescopes (DST, SST, DOT), as well as long-duration observations with Hinode's SOT employing lines such as the Ca II infrared lines, the Ca II HK and above all the Hα line reveal an incredibly rich, dynamic and highly structured environment, both in quiet and active regions. The fine-structure chromosphere, is mainly constituted by fibrilar features that connect various parts of active regions or span across network cell interiors. We discuss this highly dynamical solar chromosphere, especially below the magnetic canopy, which is gov-erned by flows reflecting both the complex geometry and dynamics of the magnetic field and the propagation and dissipation of waves in the different atmospheric layers. A comprehensive view of the fine-structure chromosphere requires deep understanding of the physical processes involved, investigation of the intricate link with structures/processes at lower photospheric lev-els and analysis of its impact on the mass and energy transport to higher atmospheric layers through flows resulting from different physical processes such as magnetic reconnection and waves. Furthermore, we assess the challenges facing theory and numerical modelling which require the inclusion of several physical ingredients, such as non-LTE and three-dimensional numerical simulations. Title: Power halo and magnetic shadow observed in a network region by Hinode/SOT and the Dutch Open Telescope Authors: Tsiropoula, Georgia; Tziotziou, Konstantinos; Kontogiannis, Ioannis Bibcode: 2010cosp...38.2920T Altcode: 2010cosp.meet.2920T We use time series of G-band and Ca II H filtergrams obtained by SOT on-board Hinode, as well as Hα filtergrams in 5 wavelengths along the line profile obtained by the Dutch Open Telescope during a coordinated campaign. Our goal is to study the oscillatory behavior of a network region as seen at different heights of the solar atmosphere and to gain insight on the distribution of power in different period bands and its spatial variation. We use wavelet and phase difference analyses of intensities and doppler signals. Enhanced or suppressed power (power halo and magnetic shadow, respectively) is observed in the network region at the differ-ent heights. Interestingly, the power spatial distribution shows a filamentary structure, while a correlation analysis reveals that this structure is clearly related to the dark mottles. We at-tribute our findings to the interaction between acoustic oscillations and the inclined magnetic fields that outline the mottles and mark the presence of the magnetic canopy. Title: Oscillatory phenomena in a solar network region Authors: Tsiropoula, Georgia; Tziotziou, Kostas; Schwartz, Pavol; Heinzel, Petr Bibcode: 2009IAUS..257..181T Altcode: We examine oscillatory phenomena in a solar network region from multi-wavelength, observations obtained by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar and Heliospheric Observatory (SoHO). The observations were obtained during a coordinated observing campaign on October 14, 2005. The temporal variations of the intensities and velocities in two distinct regions of the quiet Sun were investigated: one containing several dark mottles and the other several bright points defining the network boundaries (NB). The aim is to find similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as propagation characteristics of waves. Title: A study of spicules from space observations Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia; Tziotziou, Kostas Bibcode: 2009IAUS..257..165K Altcode: We have studied spicules observed at the northern solar limb by using simultaneous high resolution image sequences. The images were obtained by Hinode/SOT (in the Ca II H passband) and TRACE (in the 1600 Å passband) during a coordinated campaign. Both data sets were reduced and then carefully co-aligned in order to compare the observed patterns in this highly dynamic region of the Sun. The identification of individual structures in both spectral bands allows us to trace their spatial and temporal behaviour. Persistent intensity variations at certain locations, indicate that at least some spicules have a recurrent behavior. Using wavelet analysis we investigate oscillatory phenomena along the axis of off-limb spicules and we construct 2-D maps of the solar limb with the observed oscillations. Title: Multiwavelength analysis of a solar quiet region Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P. Bibcode: 2009A&A...493..217T Altcode: Context: We examine oscillatory phenomena in a solar network region from multi-wavelength observations obtained by the ground-based Dutch Open Telescope (DOT) and by the Coronal Diagnostic Spectrometer (CDS) on the spacecraft Solar and Heliospheric Observatory (SoHO). The observations were obtained during a coordinated observing campaign in October 2005.
Aims: We investigate the temporal variations of the intensities and the velocities in two distinct regions of the quiet Sun, one containing several dark mottles and the other several bright points defining the network boundaries (NB). The aim is to find similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as the propagation characteristics of waves.
Methods: Intensity and velocity variations are studied with wavelet and phase difference analyses.
Results: Both regions (i.e. mottles and NB) show a periodicity of ~5 min in all considered lines. The V-V phase differences in the NB region point to an upward propagation of waves; in the region of mottles, for periods of 250-400 s, the phase difference is mainly negative, which suggests a downward propagation, in turn indicating a refraction of waves from the inclined magnetic field of mottles along the line-of-sight.
Conclusions: The phase differences at the NB arise from a predominance of upward propagating waves. In the mottles' region, the negative phase differences we found suggest that propagating waves encounter a boundary and are refracted and reflected. Of course, several limitations exist in the exact interpretation of the phase differences, e.g. the complex topology of the magnetic field, the formation conditions and heights of the examined spectral lines, and the low spatial resolution. Title: Influence of Seeing on Cloud Model Parameters Obtained from Hα Observations Authors: Tziotziou, K.; Tsiropoula, G.; Heinzel, P. Bibcode: 2008ASPC..397...63T Altcode: We study the influence of atmospheric seeing due to terrestrial atmospheric turbulence on cloud model parameters obtained from Hα observations with Beckers' cloud model. The analysis indicates that atmospheric seeing does not affect the velocity determination, but does influence significantly the determination of the Doppler width when velocity gradients are present, and hence, the determination of the temperature, while the optical thickness and source function are also quantitatively affected, especially for high values of atmospheric seeing. Title: Contrast of Fine-scale Structures in a Quiet Sun Network Region Authors: Schwartz, P.; Tziotziou, K.; Heinzel, P.; Tsiropoula, G. Bibcode: 2008ESPM...12.2.35S Altcode: We study the contrast of fine structures (mottles), found in a quiet-Sun network region and close to a filament, observed by the SOHO/SUMER spectrograph. The observations were made during August 29 -- 30, 1996, in several chromospheric, transition-region and coronal EUV lines. The contrasts of the fine-scale structures were obtained in the different spectral lines and compared to find whether they have any dependence on the inclination of the magnetic field lines and the line formation height. Also contributions of the absorption and emissivity blocking to the depression of brightness in these fine-scale structures are studied by comparing the observations in transition-region lines with wavelengths above and below 912 A (the head of the hydrogen Lyman continuum). Title: Study of H-alpha Spicule Profiles with Line Inversion Techniques Authors: Tziotziou, K.; Kontogiannis, I.; Tsiropoula, G.; Kotrc, P. Bibcode: 2008ESPM...12.2.42T Altcode: High resolution optical spectra of chromospheric spicules obtained in the H? line are studied together with slit-jaw filtergrams. The spectra were recorded along a vertical slit parallel to the solar limb with the HSFA2 (Horizontal-Sonnen-Forschungs-Anlage) Solar Spectrograph at Ondrejov Observatory on August 19, 2007 and show H? line profiles taken in spicules - due to the limb curvature - at different heights from the solar limb. A multi-cloud model that considers two or more spicules along the line-of-sight (LOS), together with a statistical approach that takes into account a large set of initial conditions for solving the radiative transfer equation, is used for the fitting of the observed profiles and the derivation of several parameters such as the LOS velocity, the source function, the optical thickness and the Doppler width that describe the respective spicules. The height-dependence of the shape of the observed profiles, as well as their dependence on the values of the derived parameters are studied in detail. The derived results are compared with the statistical theoretical results of a multi-cloud model where the aforementioned physical parameters, as well as a random number of spicules along the LOS were taken into account, in order to define the dependence of several spicule profile characteristics on them. Specific steps of the used procedures, as well as crucial problems are discussed. Title: Study of Spicules from Space Observations Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2008ESPM...12.2.43K Altcode: We present a study of the northern solar limb using simultaneous high resolution observations by HINODE/SOT (CaII H line) and TRACE (1600 Å) filtergrams, acquired during a coordinated campaign on October 15, 2007. Both data sets were reduced and then carefully coaligned in order to compare the observed patterns and topology in this highly dynamical region of the solar atmosphere. The identification of the same structures in both spectral bands allows us to trace their spatial and temporal variation. A multitude of spicules and small loops is revealed highlighting their association with magnetic field concentrations. Persistent plasma motions at certain locations, indicative of the recurrency of some structures, are visible throughout the entire time series. Cuts across and parallel to the limb provide information on these motions and their temporal evolution. Using wavelet and cross-correlation analyses we investigate oscillatory phenomena along the axis of off-limb spicules, as well as along lines parallel to the solar limb, and examine their interconnection with wave propagation. Title: Oscillatory Phenomena in a Solar Network Region Authors: Tziotziou, K.; Tsiropoula, G.; Schwartz, P.; Heinzel, P. Bibcode: 2008ESPM...12.2.41T Altcode: Multi-wavelength, multi-instrument observations, obtained during a coordinated observing campaign on October 2005 by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft Solar and Heliospheric Observatory (SoHO) and Transition Region and Coronal Explorer (TRACE), are used to study oscillatory phenomena in a solar network region. Temporal variations of the intensities and velocities in a region of the quiet Sun containing several dark mottles and in a region with several bright points defining the network boundaries (NB) are investigated with the aim of finding similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as propagation characteristics of waves. A wavelet, phase difference and coherence analyses were performed indicating a periodicity around 5 min in all considered lines for both regions. V-V phase differences in the NB region point to an upward propagation of, most probably, acoustic waves, while in the region of mottles they indicate a non vertical propagation of waves, due to the presence of several inclined mottles along the line-of-sight. In mottles, for periods of 250-400 s the phase difference is mainly negative suggesting that propagating waves encounter a boundary and are refracted and reflected. However, limitations arising from the complex topology of the magnetic field, the formation conditions and heights of the examined spectral lines and the low spatial resolution of the space instruments influence the exact interpretation of the phase differences. Title: Multi-wavelength Analysis of a Solar Network Region Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Heinzel, P. Bibcode: 2008CEAB...32..109T Altcode: We analyse co-temporal observations of a network region found near the solar disc centre, obtained by the Dutch Open Telescope (DOT) and the Coronal Diagnostic Spectrometer (CDS) on-board SOHO during a coordinated observing campaign in October 2005. DOT obtained images in 5 wavelengths along the ha\ profile, while CDS obtained sit-and-stare observations in several EUV spectral lines that span the upper solar atmosphere. After fitting the CDS spectral line profiles we obtained 2-D space-time maps of intensities, Doppler velocities and Doppler widths. We study the appearance of the network region in the different spectral lines and the temporal variations of the obtained physical parameters. We employ a wavelet analysis to examine the existence of oscillations at the network in the different solar layers. Title: Influence of seeing effects on cloud model inversions Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G. Bibcode: 2007A&A...472..287T Altcode: Context: Atmospheric seeing due to terrestrial atmospheric turbulence is a process that distorts solar ground-based observations.
Aims: We study the influence of atmospheric seeing on Hα cloud model inversions.
Methods: We use Beckers' cloud model which assumes a constant source function to obtain physical parameters from observed quiet-Sun Hα profiles, and profiles convolved with a Gaussian point spread function that simulates the effect of atmospheric seeing on solar observations.
Results: Our analysis indicates that atmospheric seeing does not affect the velocity determination, but does influence significantly the determination of the Doppler width when velocity gradients are present, and hence, the determination of the temperature, while the optical thickness and source function are also quantitatively affected, especially for high values of atmospheric seeing.
Conclusions: The effects of atmospheric seeing on cloud model inversions also depend on the actual size of the structures under study. For the presented observations, the derived cloud model parameter distributions do not change significantly for atmospheric seeing up to ∼0.5''. Title: Chromospheric Cloud-Model Inversion Techniques Authors: Tziotziou, K. Bibcode: 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. Bibcode: 2007ASPC..368..171T Altcode: 2007arXiv0704.1592T We present observations of a solar quiet region obtained by the ground-based Dutch Open Telescope (DOT), and by instruments on the spacecraft SOHO and TRACE. The observations were obtained during a coordinated observing campaign on October 2005. The aim of this work is to present the rich diversity of fine-scale structures that are found at the network boundaries and their appearance in different instruments and different spectral lines that span the photosphere to the corona. Detailed studies of these structures are crucial to understanding their dynamics in different solar layers, as well as the role such structures play in the mass balance and heating of the solar atmosphere. Title: Dual-line spectral and phase analysis of sunspot oscillations Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P. Bibcode: 2007A&A...463.1153T Altcode: Context: Sunspots exhibit a wide range of oscillatory phenomena within their umbrae and penumbrae.
Aims: We investigate the behavior of intensity and Doppler velocity oscillations in the umbra and the penumbra to study sunspot oscillations and their associations.
Methods: Simultaneous, high-cadence (8 s), two-dimensional, Ca II 8542 Å and Hα 6563 Å observations are used. Doppler velocity and intensity variations are studied with a wavelet spectral, phase difference and coherence analysis, both at distinct positions and within the whole umbra and the penumbra.
Results: The analysis reveals the presence of several umbral flashes (UFs) that seem to fill the whole umbra. The spectral analysis indicates oscillating elements of size 2.5'' to 5'' within the umbra with periods around the 3-min band and oscillation periods around the 5-min band within the penumbra. Two remarkable jumps of the oscillation period and the intensity-velocity phase difference are present at both umbra-penumbra and penumbra-superpenumbra boundaries reflecting a drastic change in physical and/or magnetic conditions. The intensity-velocity phase analysis shows a delay of the intensity response to the velocity variations in accordance with the physics of the observed sawtooth velocity behavior. Most of the UFs oscillate incoherently, while the calmest umbral area seems to be associated with velocity spreading from neighboring UFs. The derived incoherency among UFs in conjunction with the existence of coherently oscillating elements within the umbra suggests the presence of umbral areas with slightly different physical and/or magnetic field conditions.
Conclusions: .The presented analysis provides further important constraints for realistic models and theoretical interpretations describing sunspot oscillations. Title: Evolution of a Coronal Loop System Authors: Tsiropoula, G.; Tziotziou, K.; Wiegelmann, T.; Zachariadis, Th.; Gontikakis, C.; Dara, H. Bibcode: 2007SoPh..240...37T Altcode: The temporal variation of a loop system that appears to be changing rapidly is examined. The analyzed data were obtained on 15 May 1999, with the Transition Region and Coronal Explorer (TRACE) during an observing campaign and consist of observations in the Fe IX/Fe X 171 Å and Fe XII 195 Å passbands taken at a cadence of ∼10 min. The special interest in this loop system is that it looks like one expanding loop; however, careful examination reveals that the loop consists of several strands and that new loop strands become visible successively at higher altitudes and lower loop strands fade out during the one hour of our observations. These strands have different widths, densities, and temperatures and are most probably consisting of, at least, a few unresolved thinner threads. Several geometric and physical parameters are derived for two of the strands and an effort is made to determine their 3D structure based on the extrapolation of the magnetic field lines. Electron density estimates allow us to derive radiative and conductive cooling times and to conclude that these loop strands are cooling by radiation. Title: The fine-scale structure of the quiet solar chromosphere Authors: Tsiropoula, G.; Tziotziou, K. Bibcode: 2007MmSAI..78...32T Altcode: We present methods for estimating different physical properties of dark mottles from observations obtained with the MSDP spectrograph mounted on the 50 cm refractor of the Pic du Midi Observatory and on THEMIS (Tenerife). We also present studies of their dynamical evolution and estimates of the role they play in the mass balance and heating of the solar atmosphere. Title: Dual-line analysis of sunspot oscillations Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P. Bibcode: 2007MmSAI..78...98T Altcode: Umbral oscillations and running penumbral (RP) waves are studied with simultaneous, two-dimensional, high cadence (8 sec), dual-line sunspot observations in Ca II 8542 Å and Halpha , obtained with the MSDP spectrograph on the German VTT in Tenerife. Doppler velocity and intensity images are used to investigate the physical characteristics of umbral flashes (UFs) and RP waves while a wavelet spectral and phase analysis shows their temporal behaviour and permits us to elaborate on their nature and possible association. Title: Observational characteristics and association of umbral oscillations and running penumbral waves Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P. Bibcode: 2006A&A...456..689T Altcode: Context: .Umbral flashes (UFs) and running penumbral (RP) waves are believed to be closely related oscillatory phenomena of sunspots.
Aims: .We investigate the association of UFs and RP waves to see whether the latter are a visual pattern created by a common source with UFs or a trans-sunspot wave driven by UFs.
Methods: .Simultaneous, two-dimensional, dual-line observations in Ca II 8542 Å and Hα 6563 Å, obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph mounted on the German VTT at Teide Observatory on Tenerife, are used for this study. High-cadence 8 s Doppler velocity images, spectrograms, and spectral-analysis results are used to study the characteristics and the relationship of UFs and RP waves.
Results: .Several UFs were observed that seem to fill the whole umbra. Doppler velocity variations with time indicate a shock behaviour for UFs, as well as for umbral and RP waves and a smooth continuous propagation of the latter from the umbra through the umbra-penumbra boundary out to the edge of the penumbra. Furthermore, the spectral analysis shows a decreasing oscillatory frequency as we move from the umbra outwards and a jump at the umbra-penumbra boundary that could possibly reflect, apart from a change in physical conditions, a drastic change of the magnetic field inclination with respect to the vertical.
Conclusions: .The results do not permit us to convincingly support one scenario over the other (i.e. visual pattern vs. trans-sunspot wave) for RP waves; however, they do provide important constraints for future models of sunspot oscillations and RP waves. Title: Line Broadening of EUV Lines at the Solar Limb Observed with SUMER/SoHO. Relation to Spicules Authors: Giannikakis, J.; Tsiropoula, G.; Tziotziou, K.; Antonopoulou, E.; Doyle, J. G. Bibcode: 2006AIPC..848..115G Altcode: We study the broadening of EUV line widths as we move from the disk through and off the solar limb. This broadening maximizes at approximately 10 Mm above the limb. We use one raster scan and two time series obtained by SUMER/SoHO to examine a possible correlation between this phenomenon and spicule activity. It appears that spicule presence leads to even wider profiles whereas the appearance of macrospicules extends the broadening to even greater distances above the limb. We suggest that this correlation might imply that spicules are responsible for this disk-to-limb behavior even in regions where they cannot be observed. Title: Hα Chromospheric Mottles and their UV/EUV Counterparts Seen by SOHO/Sumer Authors: Tziotziou, K.; Heinzel, P.; Tsiropoula, G.; Schühle, U. Bibcode: 2006ESASP.617E.112T Altcode: 2006soho...17E.112T No abstract at ADS Title: Line broadening of EUV lines across the solar limb observed by SUMER/SOHO Authors: Tsiropoula, G.; Giannikakis, J.; Tziotziou, K.; Antonopoulou, E. Bibcode: 2006IAUS..233..183T Altcode: We analyze time series scans of the solar limb performed by the spectrometer SUMER on-board the SoHO satellite. The analyzed dataset consists of observations obtained in the C III 977 Å line. After applying the standard SUMER data reduction procedure, we perform a one line Gaussian fit to the profiles to obtain different parameters for each pixel within the scans. Studying the variations of the line width from the disk to the limb and off-limb we find that it increases off-limb and shows a peak at ∼15'' above the limb. We suggest that this increase is due to the random directions of several spicules found along the line of sight. Title: Chromospheric fine structure studies Authors: Tziotziou, Kostas; Tsiropoula, G. Bibcode: 2006IAUS..233..173T Altcode: Mottles and spicules are the most prominent, short-lived, dynamic features residing at the quiet Sun chromospheric network and constitute what is known as chromospheric fine structure. We are reporting a comprehensive study of the dynamical characteristics and physical properties of such structures, from multi-wavelength observations, using line inversion techniques and a wavelet spectral analysis. We are furthermore examining their dynamical evolution and their periodic bi-directional velocity behaviour, their interrelationship and their association with the underlying magnetic field which seems to be their forming and driving mechanism. These studies are crucial to understanding the dynamics of the solar chromosphere, as well as the role such structures play in the mass balance and heating of the overlying solar atmosphere. Title: Physical Parameters of Dark Mottles Derived from High Resolution Optical Spectra Authors: Tsiropoula, G.; Tziotziou, K.; Schwartz, P.; Kotrč, P.; Heinzel, P. Bibcode: 2005ESASP.600E..72T Altcode: 2005ESPM...11...72T; 2005dysu.confE..72T No abstract at ADS Title: Sunspot Umbral Oscillations and Running Waves Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P. Bibcode: 2005ESASP.600E..15T Altcode: 2005dysu.confE..15T; 2005ESPM...11...15T No abstract at ADS Title: DOT tomography of the solar atmosphere. V. Analysis of a surge from AR10486 Authors: Tziotziou, K.; Tsiropoula, G.; Sütterlin, P. Bibcode: 2005A&A...444..265T Altcode: We present an analysis of high temporal and spatial resolution CaII H chromospheric limb observations obtained with the Dutch Open Telescope (DOT). We focus on a solar surge observed both by the DOT in CaII H and the Transition Region and Coronal Explorer (TRACE) satellite in the 195 Å and 1600 Å passbands. The surge is observed in active region AR10486 located near the solar limb, a region which two hours later produced the largest X-flare ever recorded. It consists of relatively cold gas of about 104-105 K. In TRACE images the surge is followed for almost 2.5 h, shrinking and expanding at the same location several times. From DOT images we find outward propagating intensity disturbances, with velocities higher than 50 km s-1, indicative of upward material motion. The latter is also suggested by the good correlation between the DOT and TRACE surge apparent height curves, their apparent time delay and a phase difference analysis. A spectral wavelet analysis of the brightness variations within and along the surge shows a predominant period of ~6 min, the first ever reported for this kind of structures. Magnetic reconnection at the bottom of the surge as its driving mechanism is suggested by the observed inverted "Y" shape configuration and is further supported by a phase difference analysis. Title: Diagnostics of Dark Chromospheric Mottles Based on High Resolution Spectra I - Observational Data Authors: Kotrč, P.; Schwartz, P.; Heinzel, P.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2005HvaOB..29..289K Altcode: High resolution optical spectra of dark mottles in H and Ca lines were observed with the Echelle spectrograph of the VTT at Sacramento Peak Observatory. Until now, only Hα spectra and slit-jaw images were processed. Used methods of identification of the dark mottles in the slit-jaw images and in the spectra, as well as a calibration and correction on the scattered light are described. Individual steps of the procedure, as well as crucial problems are discussed. The finally processed line profiles

are comparable to the profiles of dark mottles obtained by other instruments including MSDP. Title: The role of chromospheric mottles in the mass balance and heating of the solar atmosphere Authors: Tsiropoula, G.; Tziotziou, K. Bibcode: 2004A&A...424..279T Altcode: High-resolution Hα observations of a solar region containing several mottles are analyzed. Mottles constitute the fine structure of the quiet solar chromosphere and are found at the boundaries of the network cells, where the magnetic field is mostly concentrated. The driving mechanism for mottles (as well as for spicules) is suggested to be magnetic flux cancellation which most likely involves magnetic reconnection. Magnetic reconnection explains the observed bi-directional flows and, furthermore, allows conversion of part of magnetic energy to heat. We estimate several physical parameters of mottles and report a detailed analysis of their temporal variations. We then consider their impact on the mass balance and the heating of the solar atmosphere. We find that less than 1% of the mass flux injected by these structures into the corona expands outward as solar wind. The major fraction of this flux returns back to the chromosphere and provides an explanation for the red-shifts observed in the transition region spectral lines. The energy released by magnetic dissipation is quantified in terms of different energy components. Using typical values for the parameters of these structures it is found that they can provide ∼20% to the energy budget of the solar corona, but only a small part of it goes to heating. This percentage, as well as the part of the energy that goes to heating, can be lower or higher depending on the relative frequency of these events and on their upward velocity. On the other hand, if one assumes that all the potential energy of the downflowing material is converted to heat the amount supplied to the chromosphere is really negligible. Title: On the nature of the chromospheric fine structure. II. Intensity and velocity oscillations of dark mottles and grains Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P. Bibcode: 2004A&A...423.1133T Altcode: We study periodicities of dark mottles and grains observed in high spatial and temporal resolution Hα 2-D intensity and velocity images, obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph at THEMIS in Tenerife, Canary Islands. Intensity and velocity variations of individual mottles and grains, as well as of large regions containing a substantial number of these structures are examined with a wavelet analysis which provides the temporal distribution of periods and with a randomization method that gives the respective probabilities associated with them. The wavelet analysis, which shows that velocity variations are the dominant ones, results in a wide range of periods, from 100 to 500 s, with variable probabilities. However, it strongly indicates the presence of a predominant period of ∼5 min seen in both dark mottle and grain oscillations. We suggest that differences in periods found in individual mottles as well as in averages of regions containing these structures are due to the topology of the local magnetic field which can affect oscillatory processes. We report for the first time oscillations of dark grains which are more likely vertical structures ``anchored" in the photosphere. The analysis supports further the suggestion that dark mottles and grains are the same structures, the only difference between them being their respective inclinations to the line-of-sight. Title: 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. Bibcode: 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. Bibcode: 2004IAUS..219..123T Altcode: 2003IAUS..219E..96T We investigate the role of chromospheric fine structures e.g. mottles (spicules) and dark grains in the mass balance and heating of the solar atmosphere by studying two-dimensional high-resolution Ha observations. The temporal and spatial variations of the line-of-sight velocity obtained with an inversion technique based on a cloud model provide strong indications that the mechanism responsible for the driving of the observed flows is magnetic reconnection. Apart from the line-of-sight velocity application of the cloud model enables the derivation of several other physical parameters like pressure temperature density etc. The temporal evolution of these parameters permits the estimation of the role of these structures in the mass balance of the solar atmosphere. Furthermore the energy balance between the released magnetic energy during reconnection and the associated kinetic and thermal energy provides a reasonable estimate of the energy available for the heating of the solar atmosphere. Title: Parameters of dark mottles based on high resolution optical spectra Authors: Kotrc, P.; Heinzel, P.; Tziotziou, K.; Tsiropoula, G. Bibcode: 2004IAUS..223..275K Altcode: 2005IAUS..223..275K High resolution optical spectra of hydrogen and calcium lines observed with the Echelle spectrograph of the VTT at Sacramento Peak Observatory were analyzed. The observed line profiles in some parts of dark chromospheric mottles are to be matched with theoretical ones using the cloud model and several parameters (e.g. the temperature, gas pressure, flow velocity) are to be derived. Individual steps of the procedure, as well as crucial problems are discussed. Title: On the Nature of Chromospheric Umbral Flashes And Running Penumbral Waves (Abstract) Authors: Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P. Bibcode: 2004hell.conf...50T Altcode: No abstract at ADS Title: The Role of Spicules in the Mass Balance and Energy Budget of the Solar Atmosphere (Abstract) Authors: Tsiropoula, G.; Tziotziou, K. Bibcode: 2004hell.confR..64T Altcode: No abstract at ADS Title: Spectroscopic diagnostics of an Hα and EUV filament observed with THEMIS and SOHO Authors: Schmieder, B.; Tziotziou, K.; Heinzel, P. Bibcode: 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. Bibcode: 2003A&A...402..361T Altcode: We analyze a time series of forty high spatial and temporal resolution two-dimensional intensity and Doppler velocity images at different wavelengths within the Hα line. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph at THEMIS. We study the morphology of dark mottles and grains as seen in different wavelengths and examine their relation to the MDI magnetic field topology. We determine some physical properties of dark mottles with an inversion technique based on an iterative cloud model method with constant source function, giving the optical thickness tau0, the Doppler width Delta lambdaD , the velocity v and the source function S distribution along a structure. The obtained global properties of mottles as well as the spatial and temporal evolution of several physical parameters along the axes of individual mottles are discussed. The derived velocities in mottles as a function of space and time (time slice images) exhibit a quasi-periodic, bi-directional pattern. It is suggested that magnetic reconnection is the mechanism responsible for their formation and dynamics. Furthermore, a similar quasi-periodic behaviour of the Doppler velocity variations in dark grains and their morphological characteristics both suggest the similarity of dark mottles and grains. Title: The role of chromospheric mottles in the mass balance and heating of the solar atmosphere Authors: Tziotziou, K.; Tsiropoula, G. Bibcode: 2002ESASP.506..787T Altcode: 2002svco.conf..787T; 2002ESPM...10..787T High-resolution Hα observations of a solar region containing several mottles were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph installed at the focus of THEMIS in Tenerife (Canary islands). Applications of the cloud model to measurements of the Hα contrast profiles enabled us to derive numerical values for several physcial parameters. A detailed analysis of the temporal and spatial variation of these parameters was performed. The variation of the line-of-sight velocity showing upflows at the tops and downflows at the footpoints of the structures provides an indication that the mechanism that drives the flow along them is magnetic reconnection. The derived parameters in combination with information concerning their number on the solar surface permitted us to make estimates for the mass flux curried upwards the solar atmosphere. Moreover, a rough estimate of the magnetic energy dissipated at the reconnection region provided us with an estimate of the energy content available for the heating of the solar atmosphere. Title: Chromospheric fine structure dynamics Authors: Tziotziou, K.; Tsiropoula, G.; Mein, P. Bibcode: 2002ESASP.505..163T Altcode: 2002solm.conf..163T; 2002IAUCo.188..163T We investigate the dynamics of chromospheric mottles observed with THEMIS. We study a half an hour time series of 2-D intensity and Doppler velocity images at different wavelengths within the Hα line, obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph with a cadence of 40.5 sec. We determine the physical parameters in dark mottles with an inversion technique which is based on an iterative cloud model method with constant source function. With this method we calculate the optical thickness τmax, the Doppler width ΔλD, the velocity v and the source function S describing the structure. We discuss the results of the inversion technique and show the spatial and temporal evolution of several physical parameters along the axes of individual mottles. The pattern of the derived velocities as a function of space and time (time slice images) suggests the presence of magnetic reconnection as the driving mechanism of their formation. Title: Theoretical hydrogen population relations for horizontal cloud-like solar structures Authors: Tziotziou, K.; Mein, N.; Mein, P.; Heinzel, P. Bibcode: 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. Bibcode: 2002A&A...381..279T Altcode: Oscillations in the umbra and the penumbra of an isolated sunspot located near the solar disk centre were investigated. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph operating in the Ca Ii 8542 Å line and installed at the focus of THEMIS (Tenerife). From the MSDP data, two-dimensional intensity and Doppler shift images were computed at different wavelengths within the line. Intensity and Doppler shift oscillations in the umbra and the penumbra of the sunspot showing up as umbral flashes and penumbral waves were analyzed using a 23 min time series with a cadence of 46 s. The Ca Ii umbral flash intensity profile shows an emission core in its blue wing. We investigate the relation between umbral flashes and running penumbral waves by a power spectrum analysis which shows a 6 mHz frequency for the standing umbral oscillations (flashes) which are observed only on the upper half part of the umbra. The running penumbral waves propagate with an average phase velocity of 16 km s-1 and their frequency is constant in the penumbra and equal to 3 mHz. Although the time slice images suggest that umbral flashes and running penumbral waves are probably due to the same resonator, the power analysis shows no direct relationship between the two phenomena. Based on observations made with the THEMIS telescope operated on the island of Tenerife by CNRS-CNR in the Spanish Observatorio del Teide of the Instituto de Astrof{ísica de Canarias. Title: Recent results from THEMIS/MSDP campaigns Authors: Tziotziou, K.; Mein, P. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 2 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 106 K and an emission measure of 1025.7 approximately 26.2 cm -5. 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.