Author name code: kontogiannis ADS astronomy entries on 2022-09-14 author:"Kontogiannis, Ioannis" ------------------------------------------------------------------------ Title: Coronal effects of small-scale dynamic phenomena and their traces in the lower solar atmosphere Authors: Kontogiannis, Ioannis Bibcode: 2022cosp...44.1339K Altcode: The magnetic field of the quiet Sun can produce complicated magnetic configurations, giving rise to various eruptive phenomena with profound effects in the corona. These often evade detection as they occur at the resolution limits of current observations and their study requires coordinated observations and synergies between space-borne and ground-based facilities. The aim of this contribution is to showcase recent detailed studies of small-scale activity, based on coordinated observations. Their analysis combined spectropolarimetry, spectroscopy in EUV, H$\alpha$ and H$\beta$, and photospheric flow-field measurements. A small-scale magnetic flux emergence event was observed by the Hinode instruments, the Michelson Doppler Imager onboard SoHO, and the ground-based Dutch Open Telescope (DOT). The granular-scale magnetic flux emergence led to a series of observable effects over all heights from the photosphere to the corona, producing miniature surges and intense variability at the smallest observable scales in EUV and soft X-rays. The formation and eruption of a minifilament were captured by the Solar Dynamics Observatory and the Vacuum Tower Telescope (VTT) and were monitored for the first time in detail. The minifilament formed above a group of small-scale photospheric magnetic concentrations and erupted, producing a small-scale dimming as it swept the nearby coronal magnetic structures. The size and abundance of these dynamic phenomena make them ideal targets for the new generation of ground-based telescopes and space missions. Synergies between observing facilities in ground and space, especially in light of the observations from the Solar Orbiter, can boost our understanding of fundamental processes and help trace the origins of the recently-revealed fine structure of the outer solar atmosphere. Title: Using sound and music in science shows to introduce fundamental physics concepts and modern research on space science Authors: Kontogiannis, Ioannis Bibcode: 2022cosp...44.1739K Altcode: This contribution presents an inventory of science demonstrations based on music and sound, which can be used to communicate concepts from fundamental physics and space science. They bring together fundamental physics, music history and recent results from space research. They were put together into interactive science shows, developed in the context of outreach activities in science centers, science festivals, schools and research institutes. The concepts include wave and sound characteristics (frequency/pitch and timbre), electromagnetism (working principles of speakers and microphones), waves in space plasmas, music and mathematics (Pythagoras and musical scales), waveforms, wavelets, musical notes and musical notation, oscillations on surfaces of musical instruments and helioseismology. The science demonstrations include, but are not limited to, oscilloscope and tone generator software, Faraday's experiment, the Pythagoras' monochord, and Chladni plates. Simple musical instruments and Boomwhackers are used to perform simple melodies with the audience. These science demonstrations and activities are seamed into a coherent show which relies heavily on the active participation of the audience, aiming to link their everyday experience with fundamental concepts, modern research and music, in the context of a fun narrative. The components of the described action can be used in different combinations in many contexts, depending on the specifics of the outreach activity and type of audience, illustrating the potential of using arts, and music in particular, to convey science-related information. 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: 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: Multiple Stokes I inversions for inferring magnetic fields in the spectral range around Cr I 5782 Å Authors: Kuckein, C.; Balthasar, H.; Quintero Noda, C.; Diercke, A.; Trelles Arjona, J. C.; Ruiz Cobo, B.; Felipe, T.; Denker, C.; Verma, M.; Kontogiannis, I.; Sobotka, M. Bibcode: 2021A&A...653A.165K Altcode: 2021arXiv210711116K
Aims: In this work, we explore the spectral window containing Fraunhofer lines formed in the solar photosphere, around the magnetically sensitive Cr I lines at 5780.9, 5781.1, 5781.7, 5783.0, and 5783.8 Å, with Landé g-factors between 1.6 and 2.5. The goal is to simultaneously analyze 15 spectral lines, comprising Cr I, Cu I, Fe I, Mn I, and Si I lines, without the use of polarimetry, to infer the thermodynamic and magnetic properties in strongly magnetized plasmas using an inversion code.
Methods: Our study is based on a new setup at the Vacuum Tower Telescope (VTT, Tenerife), which includes fast spectroscopic scans in the wavelength range around the Cr I 5781.75 Å line. The oscillator strengths log(gf) of all spectral lines, as well as their response functions to temperature, magnetic field, and Doppler velocity, were determined using the Stokes Inversion based on Response functions (SIR) code. Snapshot 385 of the enhanced network simulation from the Bifrost code serves to synthesize all the lines, which are, in turn, inverted simultaneously with SIR to establish the best inversion strategy. We applied this strategy to VTT observations of a sunspot belonging to NOAA 12723 on 2018 September 30 and compared the results to full-disk vector field data obtained with the Helioseismic and Magnetic Imager (HMI).
Results: The 15 simultaneously inverted intensity profiles (Stokes I) delivered accurate temperatures and Doppler velocities when compared with the simulations. The derived magnetic fields and inclinations achieve the best level of accuracy when the fields are oriented along the line-of-sight (LOS) and less accurate when the fields are transverse to the LOS. In general, the results appear similar to what is reported in the HMI vector-field data, although some discrepancies exist.
Conclusions: The analyzed spectral range has the potential to deliver thermal, dynamic, and magnetic information for strongly magnetized features on the Sun, such as pores and sunspots, even without the use of polarimetry. The highest sensitivity of the lines is found in the lower photosphere, on average, around log τ = −1. The multiple-line inversions provide smooth results across the whole field of view (FOV). The presented spectral range and inversion strategy will be used for future VTT observing campaigns. Title: The flare likelihood and region eruption forecasting (FLARECAST) project: flare forecasting in the big data & machine learning era Authors: Georgoulis, Manolis K.; Bloomfield, D. Shaun; Piana, Michele; Massone, Anna Maria; Soldati, Marco; Gallagher, Peter T.; Pariat, Etienne; Vilmer, Nicole; Buchlin, Eric; Baudin, Frederic; Csillaghy, Andre; Sathiapal, Hanna; Jackson, David R.; Alingery, Pablo; Benvenuto, Federico; Campi, Cristina; Florios, Konstantinos; Gontikakis, Constantinos; Guennou, Chloe; Guerra, Jordan A.; Kontogiannis, Ioannis; Latorre, Vittorio; Murray, Sophie A.; Park, Sung-Hong; von Stachelski, Samuelvon; Torbica, Aleksandar; Vischi, Dario; Worsfold, Mark Bibcode: 2021JSWSC..11...39G Altcode: 2021arXiv210505993G The European Union funded the FLARECAST project, that ran from January 2015 until February 2018. FLARECAST had a research-to-operations (R2O) focus, and accordingly introduced several innovations into the discipline of solar flare forecasting. FLARECAST innovations were: first, the treatment of hundreds of physical properties viewed as promising flare predictors on equal footing, extending multiple previous works; second, the use of fourteen (14) different machine learning techniques, also on equal footing, to optimize the immense Big Data parameter space created by these many predictors; third, the establishment of a robust, three-pronged communication effort oriented toward policy makers, space-weather stakeholders and the wider public. FLARECAST pledged to make all its data, codes and infrastructure openly available worldwide. The combined use of 170+ properties (a total of 209 predictors are now available) in multiple machine-learning algorithms, some of which were designed exclusively for the project, gave rise to changing sets of best-performing predictors for the forecasting of different flaring levels, at least for major flares. At the same time, FLARECAST reaffirmed the importance of rigorous training and testing practices to avoid overly optimistic pre-operational prediction performance. In addition, the project has (a) tested new and revisited physically intuitive flare predictors and (b) provided meaningful clues toward the transition from flares to eruptive flares, namely, events associated with coronal mass ejections (CMEs). These leads, along with the FLARECAST data, algorithms and infrastructure, could help facilitate integrated space-weather forecasting efforts that take steps to avoid effort duplication. In spite of being one of the most intensive and systematic flare forecasting efforts to-date, FLARECAST has not managed to convincingly lift the barrier of stochasticity in solar flare occurrence and forecasting: solar flare prediction thus remains inherently probabilistic. Title: Classification of High-resolution Solar Hα Spectra Using t-distributed Stochastic Neighbor Embedding Authors: Verma, Meetu; Matijevič, Gal; Denker, Carsten; Diercke, Andrea; Dineva, Ekaterina; Balthasar, Horst; Kamlah, Robert; Kontogiannis, Ioannis; Kuckein, Christoph; Pal, Partha S. Bibcode: 2021ApJ...907...54V Altcode: 2020arXiv201113214V The Hα spectral line is a well-studied absorption line revealing properties of the highly structured and dynamic solar chromosphere. Typical features with distinct spectral signatures in Hα include filaments and prominences, bright active-region plages, superpenumbrae around sunspots, surges, flares, Ellerman bombs, filigree, and mottles and rosettes, among others. This study is based on high-spectral resolution Hα spectra obtained with the Echelle spectrograph of the Vacuum Tower Telescope (VTT) located at Observatorio del Teide, Tenerife, Spain. The t-distributed stochastic neighbor embedding (t-SNE) is a machine-learning algorithm, which is used for nonlinear dimensionality reduction. In this application, it projects Hα spectra onto a two-dimensional map, where it becomes possible to classify the spectra according to results of cloud model (CM) inversions. The CM parameters optical depth, Doppler width, line-of-sight velocity, and source function describe properties of the cloud material. Initial results of t-SNE indicate its strong discriminatory power to separate quiet-Sun and plage profiles from those that are suitable for CM inversions. In addition, a detailed study of various t-SNE parameters is conducted, the impact of seeing conditions on the classification is assessed, results for various types of input data are compared, and the identified clusters are linked to chromospheric features. Although t-SNE proves to be efficient in clustering high-dimensional data, human inference is required at each step to interpret the results. This exploratory study provides a framework and ideas on how to tailor a classification scheme toward specific spectral data and science questions. 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: Differential Emission Measure Evolution as a Precursor of Solar Flares Authors: Gontikakis, C.; Kontogiannis, I.; Georgoulis, M. K.; Guennou, C.; Syntelis, P.; Park, S. H.; Buchlin, E. Bibcode: 2020arXiv201106433G Altcode: We analyse the temporal evolution of the Differential Emission Measure (DEM) of solar active regions and explore its usage in solar flare prediction. The DEM maps are provided by the Gaussian Atmospheric Imaging Assembly (GAIA-DEM) archive, calculated assuming a Gaussian dependence of the DEM on the logarithmic temperature. We analyse time-series of sixteen solar active regions and a statistically significant sample of 9454 point-in-time observations corresponding to hundreds of regions observed during solar cycle 24. The time-series analysis shows that the temporal derivatives of the Emission Measure dEM/dt and the maximum DEM temperature dTmax/dt frequently exhibit high positive values a few hours before M- and X-class flares, indicating that flaring regions become brighter and hotter as the flare onset approaches. From the point-in-time observations we compute the conditional probabilities of flare occurrences using the distributions of positive values of the dEM/dt, and dTmax/dt and compare them with corresponding flaring probabilities of the total unsigned magnetic flux, a conventionally used, standard flare predictor. For C-class flares, conditional probabilities have lower or similar values with the ones derived for the unsigned magnetic flux, for 24 and 12 hours forecast windows. For M- and X-class flares, these probabilities are higher than those of the unsigned flux for higher parameter values. Shorter forecast windows improve the conditional probabilities of dEM/dt, and dTmax/dt in comparison to those of the unsigned magnetic flux. We conclude that flare forerunner events such as preflare heating or small flare activity prior to major flares reflect on the temporal evolution of EM and Tmax. Of these two, the temporal derivative of the EM could conceivably be used as a credible precursor, or short-term predictor, of an imminent flare. Title: Observational study of chromospheric heating by acoustic waves Authors: Abbasvand, V.; Sobotka, M.; Švanda, M.; Heinzel, P.; García-Rivas, M.; Denker, C.; Balthasar, H.; Verma, M.; Kontogiannis, I.; Koza, J.; Korda, D.; Kuckein, C. Bibcode: 2020A&A...642A..52A Altcode: 2020arXiv200802688A
Aims: Our aim is to investigate the role of acoustic and magneto-acoustic waves in heating the solar chromosphere. Observations in strong chromospheric lines are analyzed by comparing the deposited acoustic-energy flux with the total integrated radiative losses.
Methods: Quiet-Sun and weak-plage regions were observed in the Ca II 854.2 nm and Hα lines with the Fast Imaging Solar Spectrograph (FISS) at the 1.6-m Goode Solar Telescope on 2019 October 3 and in the Hα and Hβ lines with the echelle spectrograph attached to the Vacuum Tower Telescope on 2018 December 11 and 2019 June 6. The deposited acoustic energy flux at frequencies up to 20 mHz was derived from Doppler velocities observed in line centers and wings. Radiative losses were computed by means of a set of scaled non-local thermodynamic equilibrium 1D hydrostatic semi-empirical models obtained by fitting synthetic to observed line profiles.
Results: In the middle chromosphere (h = 1000-1400 km), the radiative losses can be fully balanced by the deposited acoustic energy flux in a quiet-Sun region. In the upper chromosphere (h > 1400 km), the deposited acoustic flux is small compared to the radiative losses in quiet as well as in plage regions. The crucial parameter determining the amount of deposited acoustic flux is the gas density at a given height.
Conclusions: The acoustic energy flux is efficiently deposited in the middle chromosphere, where the density of gas is sufficiently high. About 90% of the available acoustic energy flux in the quiet-Sun region is deposited in these layers, and thus it is a major contributor to the radiative losses of the middle chromosphere. In the upper chromosphere, the deposited acoustic flux is too low, so that other heating mechanisms have to act to balance the radiative cooling. 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: SpaceGates Academy: Teaching science communication and outreach of Astronomy, Planetary and Space Science to Physics Students. Authors: Moutsouroufi, Konstantina; Tsilia, Styliani; Papadopoulos, Alexis; Stratigou-Psarra, Maria; Michalopoulou, Eleni; Kontogiannis, Ioannis; Dialynas, Kostas; Petakos, Dimitris; Andrikopoulou, Marilena; Poulis, Konstantinos; Anastasia Metallinou, Fiori; Daglis, Ioannis Bibcode: 2020EPSC...14..829M Altcode: Science Communication is a practice that is increasingly gaining ground among the STEM sciences as a practice that needs to be approached with the same scientific and robust methods as the sciences it aims to communicate. It has the potential to reach a wide variety of large audiences and increase the visibility and apprehension of Astronomy and Planetary science. The 20th century has regrettably witnessed the rise of pseudo-scientific practices and a lack of confidence in science, scientists, and scientific practices. It is therefore now, more important than ever, to diffuse and separate science from un-scientific practices and inform the non-specialist public in a concise, clear, and most importantly, scientific way. It is equally important, for young researchers, like physics students, to develop the ability to evaluate the quality of the overwhelming volume of scientific information in order for them to distill and communicate that, but also communicate their own work and research in an approachable way. To achieve this, the SpaceGates Team, an outreach team consisting of Physics Students with interest in Astronomy, Astrophysics and Space, decided to launch an ambitious initiative; the SpaceGates Academy. The Academy invited experts in different subjects with the aim to provide training on science communication to early career researchers (ECR) from undergraduate to PhD level. This training aimed to fill a gap in the core and optional academic curriculum that so far does not provide a course dedicated to the communication of science. The objective of the training was the development of communication skills of the participants with emphasis on Astronomy, Astrophysics and Space, and their application in a safe and scientifically robust environment. The Academy was delivered in the form of weekly, two-hour seminars organized by the SpaceGates team under the auspices of the Department of Astrophysics, Astronomy and Mechanics of the National and Kapodistrian University of Athens. This reflects the department's commitment to provide training for science communication. Highly experienced outreach professionals, educators and science communicators voluntarily shared their experience and expertise with the learners participating over a period of 15weeks. The topics covered were: creative writing, storytelling, public speaking, science performance, science communication, scientific research writing and communicating it with the public, communicating planetary science through music, teaching Astronomy using digital tools, STEM education, organizing outreach activities etc. The learners had to deliver a written or verbal project, design and co-develop a team outreach activity. They also participated in team building activities at the beginning of each session and were asked to fill google-forms evaluation questionnaires for every session. From the planned 17 sessions, 13 were delivered in person, 2 were delivered virtually and the last 2, affected by COVID-19 were cancelled. As the post pandemic phase is now developing, we are currently exploring ways to organize virtual team outreach activities and maybe some social distance safe ones, to facilitate the conclusion of the Academy, as per its original plan. SpaceGates Academy is a much needed, ambitious educational program that introduced the science of communication to the Greek ECR that participated in the program. This endeavor will be repeated next year and it is hoped that it will evolve in an established practice that covers both the needs of the learners but also the needs of the core and optional academic curriculum. the Academy logo was printed on the coton book bags shared to the learners Title: High-resolution Spectroscopy of an Erupting Minifilament and Its Impact on the Nearby Chromosphere Authors: Kontogiannis, I.; Dineva, E.; Diercke, A.; Verma, M.; Kuckein, C.; Balthasar, H.; Denker, C. Bibcode: 2020ApJ...898..144K Altcode: 2020arXiv200701564K We study the evolution of a minifilament eruption in a quiet region at the center of the solar disk and its impact on the ambient atmosphere. We used high spectral resolution imaging spectroscopy in Hα acquired by the echelle spectrograph of the Vacuum Tower Telescope, Tenerife, Spain; photospheric magnetic field observations from the Helioseismic Magnetic Imager; and UV/EUV imaging from the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. The Hα line profiles were noise-stripped using principal component analysis and then inverted to produce physical and cloud model parameter maps. The minifilament formed between small-scale, opposite-polarity magnetic features through a series of small reconnection events, and it erupted within an hour after its appearance in Hα. Its development and eruption exhibited similarities to large-scale erupting filaments, indicating the action of common mechanisms. Its eruption took place in two phases, namely, a slow rise and a fast expansion, and it produced a coronal dimming, before the minifilament disappeared. During its eruption, we detected a complicated velocity pattern, indicative of a twisted, thread-like structure. Part of its material returned to the chromosphere, producing observable effects on nearby low-lying magnetic structures. Cloud model analysis showed that the minifilament was initially similar to other chromospheric fine structures, in terms of optical depth, source function, and Doppler width, but it resembled a large-scale filament on its course to eruption. High spectral resolution observations of the chromosphere can provide a wealth of information regarding the dynamics and properties of minifilaments and their interactions with the surrounding atmosphere. Title: High-resolution spectroscopy of a surge in an emerging flux region Authors: Verma, M.; Denker, C.; Diercke, A.; Kuckein, C.; Balthasar, H.; Dineva, E.; Kontogiannis, I.; Pal, P. S.; Sobotka, M. Bibcode: 2020A&A...639A..19V Altcode: 2020arXiv200503966V
Aims: The regular pattern of quiet-Sun magnetic fields was disturbed by newly emerging magnetic flux, which led a day later to two homologous surges after renewed flux emergence, affecting all atmospheric layers. Hence, simultaneous observations in different atmospheric heights are needed to understand the interaction of rising flux tubes with the surrounding plasma, in particular by exploiting the important diagnostic capabilities provided by the strong chromospheric Hα line regarding morphology and energetic processes in active regions.
Methods: A newly emerged active region NOAA 12722 was observed with the Vacuum Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain, on 11 September 2018. High spectral resolution observations using the echelle spectrograph in the chromospheric Hαλ6562.8 Å line were obtained in the early growth phase. Noise-stripped Hα line profiles yield maps of line-core and bisector velocities, which were contrasted with velocities inferred from Cloud Model inversions. A high-resolution imaging system recorded simultaneously broad- and narrowband Hα context images. The Solar Dynamics Observatory provided additional continuum images, line-of-sight (LOS) magnetograms, and UV and extreme UV (EUV) images, which link the different solar atmospheric layers.
Results: The active region started as a bipolar region with continuous flux emergence when a new flux system emerged in the leading part during the VTT observations, resulting in two homologous surges. While flux cancellation at the base of the surges provided the energy for ejecting the cool plasma, strong proper motions of the leading pores changed the magnetic field topology making the region susceptible to surging. Despite the surge activity in the leading part, an arch filament system in the trailing part of the old flux remained stable. Thus, stable and violently expelled mass-loaded ascending magnetic structures can coexist in close proximity. Investigating the height dependence of LOS velocities revealed the existence of neighboring strong up- and downflows. However, downflows occur with a time lag. The opacity of the ejected cool plasma decreases with distance from the base of the surge, while the speed of the ejecta increases. The location at which the surge becomes invisible in Hα corresponds to the interface where the surge brightens in He IIλ304 Å. Broad-shouldered and dual-lobed Hα profiles suggests accelerated or decelerated and highly structured LOS plasma flows. Significantly broadened Hα profiles imply significant heating at the base of the surges, which is also supported by bright kernels in UV and EUV images uncovered by swaying motions of dark fibrils at the base of the surges.
Conclusions: The interaction of newly emerging flux with pre-existing flux concentrations of a young, diffuse active region provided suitable conditions for two homologous surges. High-resolution spectroscopy revealed broadened and dual-lobed Hα profiles tracing accelerated or decelerated flows of cool plasma along the multi-threaded structure of the surge.

Movies are available at https://www.aanda.org Title: Magnetic Flux Emergence in a Coronal Hole Authors: Palacios, Judith; Utz, Dominik; Hofmeister, Stefan; Krikova, Kilian; Gömöry, Peter; Kuckein, Christoph; Denker, Carsten; Verma, Meetu; González Manrique, Sergio Javier; Campos Rozo, Jose Iván; Koza, Július; Temmer, Manuela; Veronig, Astrid; Diercke, Andrea; Kontogiannis, Ioannis; Cid, Consuelo Bibcode: 2020SoPh..295...64P Altcode: 2020arXiv200611779P A joint campaign of various space-borne and ground-based observatories, comprising the Japanese Hinode mission (Hinode Observing Plan 338, 20 - 30 September 2017), the GREGOR solar telescope, and the Vacuum Tower Telescope (VTT), investigated numerous targets such as pores, sunspots, and coronal holes. In this study, we focus on the coronal hole region target. On 24 September 2017, a very extended non-polar coronal hole developed patches of flux emergence, which contributed to the decrease of the overall area of the coronal hole. These flux emergence patches erode the coronal hole and transform the area into a more quiet-Sun-like area, whereby bipolar magnetic structures play an important role. Conversely, flux cancellation leads to the reduction of opposite-polarity magnetic fields and to an increase in the area of the coronal hole. Title: The magnetic structure and dynamics of a decaying active region Authors: Kontogiannis, Ioannis; Kuckein, Christoph; González Manrique, Sergio Javier; Felipe, Tobias; Verma, Meetu; Balthasar, Horst; Denker, Carsten Bibcode: 2020IAUS..354...53K Altcode: We study the evolution of the decaying active region NOAA 12708, from the photosphere up to the corona using high resolution, multi-wavelength GREGOR observations taken on May 9, 2018. We utilize spectropolarimetric scans of the 10830 Å spectral range by the GREGOR Infrared Spectrograph (GRIS), spectral imaging time-series in the Na ID2 spectral line by the GREGOR Fabry-Pérot Interferometer (GFPI) and context imaging in the Ca IIH and blue continuum by the High-resolution Fast Imager (HiFI). Context imaging in the UV/EUV from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) complements our dataset. The region under study contains one pore with a light-bridge, a few micro-pores and extended clusters of magnetic bright points. We study the magnetic structure from the photosphere up to the upper chromosphere through the spectropolarimetric observations in He II and Si I and through the magnetograms provided by the Helioseismic and Magnetic Imager (HMI). The high-resolution photospheric images reveal the complex interaction between granular-scale convective motions and a range of scales of magnetic field concentrations in unprecedented detail. The pore itself shows a strong interaction with the convective motions, which eventually leads to its decay, while, under the influence of the photospheric flow field, micro-pores appear and disappear. Compressible waves are generated, which are guided towards the upper atmosphere along the magnetic field lines of the various magnetic structures within the field-of-view. Modelling of the He i absorption profiles reveals high velocity components, mostly associated with magnetic bright points at the periphery of the active region, many of which correspond to asymmetric Si I Stokes-V profiles revealing a coupling between upper photospheric and upper chromospheric dynamics. Time-series of Na ID2 spectral images reveal episodic high velocity components at the same locations. State-of-the-art multi-wavelength GREGOR observations allow us to track and understand the mechanisms at work during the decay phase of the active region. Title: Emergence of small-scale magnetic flux in the quiet Sun Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Gontikakis, C.; Kuckein, C.; Verma, M.; Denker, C. 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: Revisiting the building blocks of solar magnetic fields by GREGOR Authors: Utz, Dominik; Kuckein, Christoph; Campos Rozo, Jose Iván; González Manrique, Sergio Javier; Balthasar, Horst; Gömöry, Peter; Hernández, Judith Palacios; Denker, Carsten; Verma, Meetu; Kontogiannis, Ioannis; Krikova, Kilian; Hofmeister, Stefan; Diercke, Andrea Bibcode: 2020IAUS..354...38U Altcode: The Sun is our dynamic host star due to its magnetic fields causing plentiful of activity in its atmosphere. From high energetic flares and coronal mass ejections (CMEs) to lower energetic phenomena such as jets and fibrils. Thus, it is of crucial importance to learn about formation and evolution of solar magnetic fields. These fields cover a wide range of spatial and temporal scales, starting on the larger end with active regions harbouring complex sunspots, via isolated pores, down to the smallest yet resolved elements - so-called magnetic bright points (MBPs). Here, we revisit the various manifestations of solar magnetic fields by the largest European solar telescope in operation, the 1.5-meter GREGOR telescope. We show images from the High-resolution Fast Imager (HiFI) and spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS). Besides, we outline resolved convective features inside the larger structures - so-called light-bridges occurring on large to mid-sized scales. Title: Which Photospheric Characteristics Are Most Relevant to Active-Region Coronal Mass Ejections? Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Guerra, Jordan A.; Park, Sung-Hong; Bloomfield, D. Shaun Bibcode: 2019SoPh..294..130K Altcode: 2019arXiv190906088K We investigate the relation between characteristics of coronal mass ejections and parameterizations of the eruptive capability of solar active regions widely used in solar flare-prediction schemes. These parameters, some of which are explored for the first time, are properties related to topological features, namely, magnetic polarity-inversion lines (MPILs) that indicate large amounts of stored non-potential (i.e. free) magnetic energy. We utilize the Space Weather Database of Notifications, Knowledge, Information (DONKI) and the Large Angle and Spectrometric Coronograph (LASCO) databases to find flare-associated coronal mass ejections and their kinematic characteristics, while properties of MPILs are extracted from Helioseismic and Magnetic Imager (HMI) vector magnetic-field observations of active regions to extract the properties of source-region MPILs. The correlation between all properties and the characteristics of CMEs ranges from moderate to very strong. More significant correlations hold particularly for fast CMEs, which are most important in terms of adverse space-weather manifestations. Non-neutralized currents and the length of the main MPIL exhibit significantly stronger correlations than the rest of the properties. This finding supports a causal relationship between coronal mass ejections and non-neutralized electric currents in highly sheared, conspicuous MPILs. In addition, non-neutralized currents and MPIL length carry distinct, independent information as to the eruptive potential of active regions. The combined total amount of non-neutralized electric currents and the length of the main polarity-inversion line, therefore, reflect more efficiently than other parameters the eruptive capacity of solar active regions and the CME kinematic characteristics stemming from these regions. Title: A persistent quiet-Sun small-scale tornado. II. Oscillations Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I. 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: sTools - a software package for data reduction of GREGOR instruments and general data analysis Authors: Kuckein, Christoph; Denker, Carsten; Verma, Meetu; Balthasar, Horst; Diercke, Andrea; González Manrique, Sergio Javier; Dineva, Ekaterina; Kontogiannis, Ioannis; Shen, Zili Bibcode: 2018csc..confE.105K Altcode: The optical solar physics group at AIP is responsible for the GREGOR Fabry-Perot Interferometer (GFPI) and the large-format facility cameras (Blue Imaging Channel (BIC) and High-resolution Fast Imager (HiFI)) at the 1.5-meter GREGOR solar telescope (Tenerife, Spain). Since the »Early Science Phase« of the telescope in 2014, the group developed a data reduction pipeline for these two instruments. The pipeline »sTools« is based on the Interactive Data Language (IDL) and delivers reduced and image-restored data with a minimum of user interaction. Furthermore, it creates quick-look data and builds a webpage with an overview of the observations and their statistics (http://gregor.aip.de). However, during the last years, sTools continuously evolved and currently hosts many additional routines for data analysis: (1) A local correlation tracking (LCT) algorithm adapted for both high-resolution (GREGOR and Hinode) and synoptic full-disk (SDO) data. (2) A new quantitative tool, i.e., a Background-subtracted Solar Activity Map (BaSAM), to assess and visualize the temporal variation of the photospheric magnetic field and the EUV 160 nm intensity. This method utilizes SDO data and is applicable to both full-disk observations and regions-of-interest. (3) Calibration of synoptic full-disk data from the Chromospheric Telescope (ChroTel) including extraction of Doppler velocities from He I 1083 nm filtergrams. (4) Analysis tools for sun-as-a-star spectroscopy for the Solar Disk-Integrated (SDI) telescope of the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI). sTools is licensed under a creative commons license and is freely available, after registration, at the abovementioned website. Title: A persistent quiet-Sun small-scale tornado. I. Characteristics and dynamics Authors: Tziotziou, K.; Tsiropoula, G.; Kontogiannis, I.; Scullion, E.; Doyle, J. G. 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: Eruptive Flare Initiation and the CME Magnetic Field Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Kontogiannis, Ioannis Bibcode: 2018cosp...42E1180G Altcode: We recount very recent results on the correlation between photospheric characteristics of eruptive solar active regions and coronal mass ejection (CME) occurrence / characteristics. In particular, we argue that one of the most relevant parameters for CME occurrence is the non-neutralized electric currents appearing exclusively along intense, shear-ridden magnetic polarity-inversion lines (PILs) in the photosphere of eruptive active regions. These currents are simply lacking in the absence of strong PILs and shear. While the physics underlying non-neutralized currents is rich and shows far-reaching ramifications, we will focus on the injection of magnetic helicity due to non-neutralized currents in the pre-eruption phase, that will then be bodily transported via the CME. For a conductive plasma of high magnetic Reynolds number, such as that of the solar corona, we show how the fundamental helicity conservation principle can lead to estimates of, first, the CME's axial magnetic field strength and, second, the anticipated magnetic field strength of the interplanetary CME (ICME) on the verge of geospace. We discuss how this analysis can be viewed as a meaningful initial or boundary condition for more elaborate inner-heliospheric propagation models that further consider the orientation of the ICME magnetic field, thus leading to an improved understanding and prediction of ICME geoeffectiveness. Part of this work has been supported by the EU Horizon-2020 FLARECAST project (grant agreement no. 640216). Title: Testing and Improving a Set of Morphological Predictors of Flaring Activity Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park, Sung-Hong; Guerra, Jordan A. Bibcode: 2018SoPh..293...96K Altcode: 2018arXiv180706371K Efficient prediction of solar flares relies on parameters that quantify the eruptive capability of solar active regions. Several such quantitative predictors have been proposed in the literature, inferred mostly from photospheric magnetograms and/or white-light observations. Two of them are the Ising energy and the sum of the total horizontal magnetic field gradient. The former has been developed from line-of-sight magnetograms, while the latter uses sunspot detections and characteristics, based on continuum images. Aiming to include these parameters in an automated prediction scheme, we test their applicability on regular photospheric magnetic field observations provided by the Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO). We test their efficiency as predictors of flaring activity on a representative sample of active regions and investigate possible modifications of these quantities. The Ising energy appears to be an efficient predictor, and the efficiency is even improved if it is modified to describe interacting magnetic partitions or sunspot umbrae. The sum of the horizontal magnetic field gradient appears to be slightly more promising than the three variations of the Ising energy we implement in this article. The new predictors are also compared with two very promising predictors: the effective connected magnetic field strength and the total unsigned non-neutralized current. Our analysis shows that the efficiency of morphological predictors depends on projection effects in a nontrivial way. All four new predictors are found useful for inclusion in an automated flare forecasting facility, such as the Flare Likelihood and Region Eruption Forecasting (FLARECAST), but their utility, among others, will ultimately be determined by the validation effort underway in the framework of the FLARECAST project. Title: Probing the Quiet Solar Atmosphere from the Photosphere to the Corona Authors: Kontogiannis, Ioannis; Gontikakis, Costis; Tsiropoula, Georgia; Tziotziou, Kostas 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: Forecasting Solar Flares Using Magnetogram-based Predictors and Machine Learning Authors: Florios, Kostas; Kontogiannis, Ioannis; Park, Sung-Hong; Guerra, Jordan A.; Benvenuto, Federico; Bloomfield, D. Shaun; Georgoulis, Manolis K. Bibcode: 2018SoPh..293...28F Altcode: 2018arXiv180105744F We propose a forecasting approach for solar flares based on data from Solar Cycle 24, taken by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) mission. In particular, we use the Space-weather HMI Active Region Patches (SHARP) product that facilitates cut-out magnetograms of solar active regions (AR) in the Sun in near-realtime (NRT), taken over a five-year interval (2012 - 2016). Our approach utilizes a set of thirteen predictors, which are not included in the SHARP metadata, extracted from line-of-sight and vector photospheric magnetograms. We exploit several machine learning (ML) and conventional statistics techniques to predict flares of peak magnitude >M1 and >C1 within a 24 h forecast window. The ML methods used are multi-layer perceptrons (MLP), support vector machines (SVM), and random forests (RF). We conclude that random forests could be the prediction technique of choice for our sample, with the second-best method being multi-layer perceptrons, subject to an entropy objective function. A Monte Carlo simulation showed that the best-performing method gives accuracy ACC =0.93 (0.00 ), true skill statistic TSS =0.74 (0.02 ), and Heidke skill score HSS =0.49 (0.01 ) for >M1 flare prediction with probability threshold 15% and ACC =0.84 (0.00 ), TSS =0.60 (0.01 ), and HSS =0.59 (0.01 ) for >C1 flare prediction with probability threshold 35%. Title: Active Region Photospheric Magnetic Properties Derived from Line-of-Sight and Radial Fields Authors: Guerra, J. A.; Park, S. -H.; Gallagher, P. T.; Kontogiannis, I.; Georgoulis, M. K.; Bloomfield, D. S. Bibcode: 2018SoPh..293....9G Altcode: 2017arXiv171206902G The effect of using two representations of the normal-to-surface magnetic field to calculate photospheric measures that are related to the active region (AR) potential for flaring is presented. Several AR properties were computed using line-of-sight (Blos) and spherical-radial (Br) magnetograms from the Space-weather HMI Active Region Patch (SHARP) products of the Solar Dynamics Observatory, characterizing the presence and features of magnetic polarity inversion lines, fractality, and magnetic connectivity of the AR photospheric field. The data analyzed correspond to ≈4 ,000 AR observations, achieved by randomly selecting 25% of days between September 2012 and May 2016 for analysis at 6-hr cadence. Results from this statistical study include: i) the Br component results in a slight upwards shift of property values in a manner consistent with a field-strength underestimation by the Blos component; ii) using the Br component results in significantly lower inter-property correlation in one-third of the cases, implying more independent information as regards the state of the AR photospheric magnetic field; iii) flaring rates for each property vary between the field components in a manner consistent with the differences in property-value ranges resulting from the components; iv) flaring rates generally increase for higher values of properties, except the Fourier spectral power index that has flare rates peaking around a value of 5 /3 . These findings indicate that there may be advantages in using Br rather than Blos in calculating flare-related AR magnetic properties, especially for regions located far from central meridian. Title: The Next Level in Automated Solar Flare Forecasting: the EU FLARECAST Project Authors: Georgoulis, M. K.; Bloomfield, D.; Piana, M.; Massone, A. M.; Gallagher, P.; Vilmer, N.; Pariat, E.; Buchlin, E.; Baudin, F.; Csillaghy, A.; Soldati, M.; Sathiapal, H.; Jackson, D.; Alingery, P.; Argoudelis, V.; Benvenuto, F.; Campi, C.; Florios, K.; Gontikakis, C.; Guennou, C.; Guerra, J. A.; Kontogiannis, I.; Latorre, V.; Murray, S.; Park, S. H.; Perasso, A.; Sciacchitano, F.; von Stachelski, S.; Torbica, A.; Vischi, D. Bibcode: 2017AGUFMSA21C..07G Altcode: We attempt an informative description of the Flare Likelihood And Region Eruption Forecasting (FLARECAST) project, European Commission's first large-scale investment to explore the limits of reliability and accuracy achieved for the forecasting of major solar flares. We outline the consortium, top-level objectives and first results of the project, highlighting the diversity and fusion of expertise needed to deliver what was promised. The project's final product, featuring an openly accessible, fully modular and free to download flare forecasting facility will be delivered in early 2018. The project's three objectives, namely, science, research-to-operations and dissemination / communication, are also discussed: in terms of science, we encapsulate our close-to-final assessment on how close (or far) are we from a practically exploitable solar flare forecasting. In terms of R2O, we briefly describe the architecture of the FLARECAST infrastructure that includes rigorous validation for each forecasting step. From the three different communication levers of the project we finally focus on lessons learned from the two-way interaction with the community of stakeholders and governmental organizations. The FLARECAST project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 640216. Title: Non-neutralized Electric Currents in Solar Active Regions and Flare Productivity Authors: Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park, Sung-Hong; Guerra, Jordan A. Bibcode: 2017SoPh..292..159K Altcode: 2017arXiv170807087K We explore the association of non-neutralized currents with solar flare occurrence in a sizable sample of observations, aiming to show the potential of such currents in solar flare prediction. We used the high-quality vector magnetograms that are regularly produced by the Helioseismic Magnetic Imager, and more specifically, the Space weather HMI Active Region Patches (SHARP). Through a newly established method that incorporates detailed error analysis, we calculated the non-neutralized currents contained in active regions (AR). Two predictors were produced, namely the total and the maximum unsigned non-neutralized current. Both were tested in AR time-series and a representative sample of point-in-time observations during the interval 2012 - 2016. The average values of non-neutralized currents in flaring active regions are higher by more than an order of magnitude than in non-flaring regions and correlate very well with the corresponding flare index. The temporal evolution of these parameters appears to be connected to physical processes, such as flux emergence and/or magnetic polarity inversion line formation, that are associated with increased solar flare activity. Using Bayesian inference of flaring probabilities, we show that the total unsigned non-neutralized current significantly outperforms the total unsigned magnetic flux and other well-established current-related predictors. It therefore shows good prospects for inclusion in an operational flare-forecasting service. We plan to use the new predictor in the framework of the FLARECAST project along with other highly performing predictors. Title: Solar Magnetic Data Analysis for the FLARECAST Project Authors: Guerra, J. A.; Park, S. H.; Kontogiannis, I.; Bloomfield, D.; Gallagher, P.; Georgoulis, M. K. Bibcode: 2016AGUFMSH11C2234G Altcode: The Flare Likelihood And Region Eruption foreCASTing (FLARECAST) project is an EU H2020-funded consortium project aiming to develop an advanced solar flare forecasting system by implementing state-of-the-art solar data analysis and flare prediction algorithms. The Solar Physics Group at Trinity College Dublin is in charge of the analysis of observational data to extract solar active region properties that serve as input for the prediction algorithms. The calculated active region properties correspond to a non-exhaustive list of parameters that have demonstrated a strong flare association, such as Schrijver's R-value, the Fourier power spectrum exponent, the effective connected magnetic field (Beff), the horizontal field decay index, and the weighted length of strong-gradient polarity inversion lines (WLSG). Parameters were calculated from Spaceweather HMI Active Region Patch (SHARP) magnetograms, a data product of the Helioseismic and Magnetic Imager (HMI) magnetograph on the Solar Dynamics Observatory (SDO). SHARPs provide photospheric vector-magnetic field (B) images in near-realtime. For this study, results from a statistical study performed on a robust subsample of the entire SHARP dataset will be presented. In the framework of the FLARECAST predictor component, this study focuses, for the first time, on differences between parameter values found when the radial magnetic field component, Br, is used instead of the line-of-sight component, Blos. The effect of active region longitudinal position is discussed, as well as the flare association of the properties. Title: Enabling Solar Flare Forecasting at an Unprecedented Level: the FLARECAST Project Authors: Georgoulis, Manolis K.; Pariat, Etienne; Massone, Anna Maria; Vilmer, Nicole; Jackson, David; Buchlin, Eric; Csillaghy, Andre; Bommier, Veronique; Kontogiannis, Ioannis; Gallagher, Peter; Gontikakis, Costis; Guennou, Chloé; Murray, Sophie; Bloomfield, D. Shaun; Alingery, Pablo; Baudin, Frederic; Benvenuto, Federico; Bruggisser, Florian; Florios, Konstantinos; Guerra, Jordan; Park, Sung-Hong; Perasso, Annalisa; Piana, Michele; Sathiapal, Hanna; Soldati, Marco; Von Stachelski, Samuel; Argoudelis, Vangelis; Caminade, Stephane Bibcode: 2016cosp...41E.657G Altcode: We attempt a brief but informative description of the Flare Likelihood And Region Eruption Forecasting (FLARECAST) project, European Commission's first large-scale investment to explore the limits of reliability and accuracy for the forecasting of major solar flares. The consortium, objectives, and first results of the project - featuring an openly accessible, interactive flare forecasting facility by the end of 2017 - will be outlined. In addition, we will refer to the so-called "explorative research" element of project, aiming to connect solar flares with coronal mass ejections (CMEs) and possibly pave the way for CME, or eruptive flare, prediction. We will also emphasize the FLARECAST modus operandi, namely the diversity of expertise within the consortium that independently aims to science, infrastructure development and dissemination, both to stakeholders and to the general public. Concluding, we will underline that the FLARECAST project responds squarely to the joint COSPAR - ILWS Global Roadmap to shield society from the adversities of space weather, addressing its primary goal and, in particular, its Research Recommendations 1, 2 and 4, Teaming Recommendations II and III, and Collaboration Recommendations A, B, and D. The FLARECAST project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 640216. Title: The New Solar Telescope at the National Observatory of Athens Authors: Kontogiannis, I.; Tsiropoula, G. Bibcode: 2016ASPC..504..317K Altcode: In the context of a new space weather facility, the National Observatory of Athens has installed a small full-disk solar telescope. Its aim is to provide full disk images of the Sun and active region cut-outs in the Hα line. Here, we describe the specificiations of the telescope and the data reduction procedure. Title: First simultaneous SST/CRISP and IRIS observations of a small-scale quiet Sun vortex Authors: Park, S. -H.; Tsiropoula, G.; Kontogiannis, I.; Tziotziou, K.; Scullion, E.; Doyle, J. G. Bibcode: 2016A&A...586A..25P Altcode: 2015arXiv151206032P Context. Ubiquitous small-scale vortices have recently been found in the lower atmosphere of the quiet Sun in state-of-the-art solar observations and in numerical simulations.
Aims: We investigate the characteristics and temporal evolution of a granular-scale vortex and its associated upflows through the photosphere and chromosphere of a quiet Sun internetwork region.
Methods: We analyzed high spatial and temporal resolution ground- and spaced-based observations of a quiet Sun region. The observations consist of high-cadence time series of wideband and narrowband images of both Hα 6563 Å and Ca II 8542 Å lines obtained with the CRisp Imaging SpectroPolarimeter (CRISP) instrument at the Swedish 1-m Solar Telescope (SST), as well as ultraviolet imaging and spectral data simultaneously obtained by the Interface Region Imaging Spectrograph (IRIS).
Results: A small-scale vortex is observed for the first time simultaneously in Hα, Ca II 8542 Å, and Mg II k lines. During the evolution of the vortex, Hα narrowband images at -0.77 Å and Ca II 8542 Å narrowband images at -0.5 Å, and their corresponding Doppler signal maps, clearly show consecutive high-speed upflow events in the vortex region. These high-speed upflows with a size of 0.5-1 Mm appear in the shape of spiral arms and exhibit two distinctive apparent motions in the plane of sky for a few minutes: (1) a swirling motion with an average speed of 13 km s-1 and (2) an expanding motion at a rate of 4-6 km s-1. Furthermore, the spectral analysis of Mg II k and Mg II subordinate lines in the vortex region indicates an upward velocity of up to ~8 km s-1 along with a higher temperature compared to the nearby quiet Sun chromosphere.
Conclusions: The consecutive small-scale vortex events can heat the upper chromosphere by driving continuous high-speed upflows through the lower atmosphere.

Movies associated to Figs. 2 and 3 are available at http://www.aanda.org Title: Building a new space weather facility at the National Observatory of Athens Authors: Kontogiannis, Ioannis; Belehaki, Anna; Tsiropoula, Georgia; Tsagouri, Ioanna; Anastasiadis, Anastasios; Papaioannou, Athanasios Bibcode: 2016AdSpR..57..418K Altcode: The PROTEAS project has been initiated at the Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing (IAASARS) of the National Observatory of Athens (NOA). One of its main objectives is to provide observations, processed data and space weather nowcasting and forecasting products, designed to support the space weather research community and operators of commercial and industrial systems. The space weather products to be released by this facility, will be the result of the exploitation of ground-based, as well as space-borne observations and of model results and tools already available or under development by IAASARS researchers. The objective will be achieved through: (a) the operation of a small full-disk solar telescope to conduct regular observations of the Sun in the H-alpha line; (b) the construction of a database with near real-time solar observations which will be available to the community through a web-based facility (HELIOSERVER); (c) the development of a tool for forecasting Solar Energetic Particle (SEP) events in relation to observed solar eruptive events; (d) the upgrade of the Athens Digisonde with digital transceivers and the capability of operating in bi-static link mode and (e) the sustainable operation of the European Digital Upper Atmosphere Server (DIAS) upgraded with additional data sets integrated in an interface with the HELIOSERVER and with improved models for the real-time quantification of the effects of solar eruptive events in the ionosphere. Title: Wave propagation in a solar quiet region and the influence of the magnetic canopy Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2016A&A...585A.110K Altcode: 2015arXiv151108618K
Aims: We seek indications or evidence of transmission/conversion of magnetoacoustic waves at the magnetic canopy, as a result of its impact on the properties of the wave field of the photosphere and chromosphere.
Methods: We use cross-wavelet analysis to measure phase differences between intensity and Doppler signal oscillations in the Hα, Ca II h, and G-band. We use the height of the magnetic canopy to create appropriate masks to separate internetwork (IN) and magnetic canopy regions. We study wave propagation and differences between these two regions.
Results: The magnetic canopy affects wave propagation by lowering the phase differences of progressive waves and allowing the propagation of waves with frequencies lower than the acoustic cut-off. We also find indications in the Doppler signals of Hα of a response to the acoustic waves at the IN, observed in the Ca II h line. This response is affected by the presence of the magnetic canopy.
Conclusions: Phase difference analysis indicates the existence of a complicated wave field in the quiet Sun, which is composed of a mixture of progressive and standing waves. There are clear imprints of mode conversion and transmission due to the interaction between the p-modes and small-scale magnetic fields of the network and internetwork. Title: Energy and helicity injection in solar quiet regions Authors: Tziotziou, K.; Park, S. -H.; Tsiropoula, G.; Kontogiannis, I. Bibcode: 2015A&A...581A..61T Altcode:
Aims: We investigate the free magnetic energy and relative magnetic helicity injection in solar quiet regions.
Methods: We use the DAVE4VM method to infer the photospheric velocity field and calculate the free magnetic energy and relative magnetic helicity injection rates in 16 quiet-Sun vector magnetograms sequences.
Results: We find that there is no dominant sense of helicity injection in quiet-Sun regions, and that both helicity and energy injections are mostly due to surface shuffling motions that dominate the respective emergence by factors slightly larger than two. We, furthermore, estimate the helicity and energy rates per network unit area as well as the respective budgets over a complete solar cycle.
Conclusions: Derived helicity and energy budgets over the entire solar cycle are similar to respective budgets derived in a recent work from the instantaneous helicity and free magnetic energy budgets and higher than previously reported values that relied on similar approaches to this analysis. Free-energy budgets, mostly generated like helicity at the network, are high enough to power the dynamics of fine-scale structures residing at the network, such as mottles and spicules, while corresponding estimates of helicity budgets are provided, pending future verification from high-resolution magneto-hydrodynamic simulations and/or observations. Title: Transmission and conversion of magnetoacoustic waves on the magnetic canopy in a quiet Sun region Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2014A&A...567A..62K Altcode: 2014arXiv1406.5066K Context. We present evidence for the conversion and transmission of wave modes on the magnetic flux tubes that constitute mottles and form the magnetic canopy in a quiet Sun region.
Aims: Our aim is to highlight the details and the key parameters of the mechanism that produces power halos and magnetic shadows around the magnetic network observed in Hα.
Methods: We use our previous calculations of the magnetic field vector and the height of the magnetic canopy, and based on simple assumptions, we determine the turning height, i.e., the height at which the fast magnetoacoustic waves reflect at the chromosphere. We compare the variation of 3, 5, and 7 min power in the magnetic shadow and the power halo with the results of a two-dimensional model on mode conversion and transmission. The key parameter of the model is the attack angle, which is related to the inclination of the magnetic field vector at the canopy height. Our analysis takes also into account that 1) there are projection effects on the propagation of waves; 2) the magnetic canopy and the turning height are curved layers; 3) waves with periods longer than 3 min only reach the chromosphere in the presence of inclined magnetic fields (ramp effect); 4) mottles in Hα are canopy structures; and 5) the wings of Hα contain mixed signal from low- and high-β plasma.
Results: The dependence of the measured power on the attack angle follows the anticipated by the two-dimensional model very well. Long-period slow waves are channeled to the upper chromospheric layers following the magnetic field lines of mottles, while short-period fast waves penetrate the magnetic canopy and are reflected back higher, at the turning height.
Conclusions: Although both magnetoacoustic modes contribute to velocity signals, making the interpretation of observations a challenging task, we conclude that conversion and transmission of the acoustic waves into fast and slow magnetoacoustic waves are responsible for forming power halos and magnetic shadows in the quiet Sun region. Title: Energy and helicity budgets of solar quiet regions Authors: Tziotziou, K.; Tsiropoula, G.; Georgoulis, M. K.; Kontogiannis, I. Bibcode: 2014A&A...564A..86T Altcode: 2014arXiv1403.0730T
Aims: We investigate the free magnetic energy and relative magnetic helicity budgets of solar quiet regions.
Methods: Using a novel nonlinear force-free method that requires single solar vector magnetograms we calculated the instantaneous free magnetic energy and relative magnetic helicity budgets in 55 quiet-Sun vector magnetograms.
Results: As in a previous work on active regions, we constructed here for the first time the (free) energy-(relative) helicity diagram of quiet-Sun regions. We find that quiet-Sun regions have no dominant sense of helicity and show monotonic correlations a) between free magnetic energy/relative helicity and magnetic network area and, consequently, b) between free magnetic energy and helicity. Free magnetic energy budgets of quiet-Sun regions represent a rather continuous extension of respective active-region budgets towards lower values, but the corresponding helicity transition is discontinuous because of the incoherence of the helicity sense in contrast to active regions. We furthermore estimated the instantaneous free magnetic-energy and relative magnetic-helicity budgets of the entire quiet Sun, as well as the respective budgets over an entire solar cycle.
Conclusions: Derived instantaneous free magnetic energy budgets and, to a lesser extent, relative magnetic helicity budgets over the entire quiet Sun are similar to the respective budgets of a sizeable active region, while total budgets within a solar cycle are found to be higher than previously reported. Free-energy budgets are similar to the energy needed to power fine-scale structures residing at the network, such as mottles and spicules. Title: Free magnetic energy and relative magnetic helicity in active and quiet solar regions and their role in solar dynamics Authors: Tziotziou, Konstantinos; Archontis, Vasilis; Tsiropoula, Georgia; Georgoulis, Manolis K.; Moraitis, Kostas; Kontogiannis, Ioannis Bibcode: 2014cosp...40E3428T Altcode: We present a novel non-linear force-free method for the calculation of the instantaneous free magnetic energy and relative magnetic helicity budgets of a solar region from a single photospheric/chromospheric vector magnetogram. Our objective is to study the role of these quantities both in solar eruptions and in quiet-Sun dynamics. The validity of the method is tested using both observations and synthetic magnetohydrodynamical (MHD) models. The method is applied for the derivation of the energy-helicity (EH) diagram of solar active regions (ARs) from a sample of 162 vector magnetograms corresponding to 42 different ARs, suggesting the existence of 4×10(31) erg and 2×10(42) Mx(2) thresholds in free energy and relative helicity, respectively, for ARs to enter eruptive territory. Furthermore, the dynamical evolution of both quantities in eruptive NOAA AR 11158, using a high-cadence 5-day time series of vector magnetograms, suggests the formation of increasingly helical pre-eruption structures and a causal relation between flares and Coronal Mass Ejections (CMEs). The method is also used to derive helicity and energy budgets in quiet Sun regions and construct the respective EH diagram. Our results highlight the importance of both energy and helicity in AR evolution and quiet-Sun dynamics and instigate further research on the underlying physics with three-dimensional MHD models. This work is supported by EU's Seventh Framework Programme via a Marie Curie Fellowship. Title: Free Magnetic Energy and Helicity in Active and Quiet Solar Regions and their role in Solar Authors: Tziotziou, K.; Georgoulis, M. K.; Tsiropoula, G.; Moraitis, K.; Kontogiannis, I. Bibcode: 2013hell.conf....6T Altcode: We present a novel nonlinear force-free method designed to calculate the instantaneous free magnetic energy and relative magnetic helicity budgets of a solar region from a single photospheric/chromospheric vector magnetogram of the region. Our objective is to study the role of these quantities in solar eruptions and quiet-Sun dynamics. We apply the method to (1) derive the energy/helicity diagram of solar active regions from a sample of 162 vector magnetograms corresponding to 42 different active regions (ARs), suggesting that there exist 4 1031 erg and 2 1042 Mx2 thresholds in free energy and relative helicity, respectively, for ARs to enter eruptive territory, (2) study the dynamics of eruptive NOAA AR 11158 using a high-cadence 5-day time series of vector magnetograms, suggesting the formation of increasingly helical pre-eruption structures and a causal relation between flares and Coronal Mass Ejections (CMEs) and, (3) derive helicity and energy budgets in quiet Sun regions and construct the respective energy/helicity diagram. Our results highlight the importance of these two parameters in AR evolution and quiet-Sun dynamics and instigate further research including detailed analysis with synthetic, magnetohydrodynamical models. This work is supported by EU's Seventh Framework Programme via a Marie Curie Fellowship and by the Hellenic National Space Weather Research Network (HNSWRN) via the THALIS Programme. Title: 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: Μελέτη του ρόλου της λεπτής υφής της χρωμόσφαιρας στο σχηματισμό του μαγνητικού θόλου και στη διάδοση των κυμάτων Title: Μελέτη του ρόλου της λεπτής υφής της χρωμόσφαιρας στο σχηματισμό του μαγνητικού θόλου και στη διάδοση των κυμάτων Title: The role of chromospheric fine structure on the formation of the magnetic canopy and the propagation of waves; Authors: Kontogiannis, Ioannis Bibcode: 2013PhDT.......694K Altcode: No abstract at ADS Title: Solar Fine-Scale Structures. I. Spicules and Other Small-Scale, Jet-Like Events at the Chromospheric Level: Observations and Physical Parameters Authors: Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.; Madjarska, M. S.; Doyle, J. G.; Suematsu, Y. Bibcode: 2012SSRv..169..181T Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T Over the last two decades the uninterrupted, high resolution observations of the Sun, from the excellent range of telescopes aboard many spacecraft complemented with observations from sophisticated ground-based telescopes have opened up a new world producing significantly more complete information on the physical conditions of the solar atmosphere than before. The interface between the lower solar atmosphere where energy is generated by subsurface convection and the corona comprises the chromosphere, which is dominated by jet-like, dynamic structures, called mottles when found in quiet regions, fibrils when found in active regions and spicules when observed at the solar limb. Recently, space observations with Hinode have led to the suggestion that there should exist two different types of spicules called Type I and Type II which have different properties. Ground-based observations in the Ca ii H and K filtergrams reveal the existence of long, thin emission features called straws in observations close to the limb, and a class of short-lived events called rapid blue-shifted excursions characterized by large Doppler shifts that appear only in the blue wing of the Ca ii infrared line. It has been suggested that the key to understanding how the solar plasma is accelerated and heated may well be found in the studies of these jet-like, dynamic events. However, while these structures are observed and studied for more than 130 years in the visible, but also in the UV and EUV emission lines and continua, there are still many questions to be answered. Thus, despite their importance and a multitude of observations performed and theoretical models proposed, questions regarding their origin, how they are formed, their physical parameters, their association with the underlying photospheric magnetic field, how they appear in the different spectral lines, and the interrelationship between structures observed in quiet and active regions on the disk and at the limb, as well as their role in global processes has not yet received definitive answers. In addition, how they affect the coronal heating and solar wind need to be further explored. In this review we present observations and physical properties of small-scale jet-like chromospheric events observed in active and quiet regions, on the disk and at the limb and discuss their interrelationship. Title: Study of spicules observed in the CaII H and Ha lines with Hinode/SOT Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2012hell.conf...11K Altcode: We use a dataset of simultaneous image sequences obtained by Hinode/SOT with the Ca II H filter, as well as in Ha+-0.2A. SOT was looking at the SW solar limb. The high temporal and spatial resolution allows us to study the structure and dynamics of spicules seen at the different filters. Individual spicules have been selected and intensity and velocity distributions at different heights along their central axes are examined along with transversal fluctuations. Title: Multi-wavelengths observations of oscillatory phenomena in a solar network region and their relation to the magnetic field Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2012hell.conf....6K Altcode: The chromosphere is an inhomogeneous and highly dynamic layer of the solar atmosphere. New high resolution observations have revealed that it consists mainly of fine-scale structures which are directly related to the magnetic field. In this work we use multi-wavelength observations to study oscillatory phenomena in the quiet Sun and their relation to the magnetic field and the chromospheric fine-scale structures. The observations were obtained during a coordinated campaign which included space-borne instruments (i.e. the Transition Region and Coronal Explorer, the Michelson Doppler Imager onboard SoHO, and the Specropolarimeter onboard the Hinode spacecraft) and a ground-based telescope (i.e. the Dutch Open Telescope). The analysed data consist of time series of filtergrams of a solar network region observed at different atmospheric layers from the photosphere through the temperature minimum region and well into the chromosphere and also of high resolution magnetograms. Using wavelet analysis we investigate the oscillatory power distribution in the 2D field-of-view, as well as its vertical distribution and its relation with the fine-scale chromospheric mottles, while through phase difference analysis we investigate wave propagation characteristics. Our results show that the oscillatory power has a fibrilar distribution and that chromospheric mottles are directly related to power enhancement (power halo) or suppression (magnetic shadow). This finding is attributed to the interaction between acoustic oscillations and mottles which outline inclined magnetic fields and clearly indicate that mottles are the loci of wave tranmission, reflection and refraction. It also leads to the conclusion that these structures are directly related to the formation of the magnetic canopy, i.e. the layer that divides the atmosphere into two components, a magnetized and a non magnetized one. Extrapolation of the photospheric magnetic field up to the chromosphere using the current-free assumption and use of the VAL C atmospheric model allows the determination of the height of formation of the magnetic canopy and provide the opportunity to highlight the details of the interaction between acoustic o scillations and the magnetic field. Title: Hinode SOT/SP and SoHO/MDI quiet Sun magnetic field. Implications of their differences on the extrapolated chromospheric field and the height of the magnetic canopy Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2011A&A...531A..66K Altcode:
Aims: We explore the differences in the measurement of the magnetic field of the quiet solar photosphere provided by the Michelson Doppler Imager (MDI) onboard SoHO and the SpectroPolarimeter (SOT/SP) onboard Hinode and the ensuing implications for the extrapolated chromospheric magnetic field and the determination of the location of the magnetic canopy.
Methods: We employ potential field extrapolation to reconstruct the chromospheric magnetic field using the magnetic field of the photosphere provided by the two instruments. We also calculate the plasma-β parameter using the VAL C model atmosphere of the quiet Sun to determine the height of the magnetic canopy.
Results: MDI underestimates the magnetic field of the quiet Sun sometimes by a factor of five, which leads to an overestimation of the height of the magnetic canopy by up to ~550 km. Although the overall magnetic field configuration does not differ significantly when calculated with either MDI or SOT/SP, the data of the latter lead to lower and more extended canopies. The difference in the resolution of the two instruments does not seem to affect the chromospheric magnetic field higher than 1000 km.
Conclusions: The height of the magnetic canopy is an important parameter to consider when investigating wave propagation and the oscillatory properties of the quiet Sun regions in the network and internetwork. The canopy height's derivation depends very much on the sensitivity of the instruments used to measure the photospheric magnetic field. Consequently precise measurements of the photospheric magnetic field are crucial to accurately reconstruct the chromospheric magnetic field and to distinguish between the various wave modes. Title: Oscillations in a network region observed in the Hα line and their relation to the magnetic field Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K.; Georgoulis, M. K. Bibcode: 2010A&A...524A..12K Altcode:
Aims: Our aim is to gain a better understanding of the interaction between acoustic oscillations and the small-scale magnetic fields of the Sun. To this end, we examine the oscillatory properties of a network region and their relation to the magnetic configuration of the chromosphere. We link the oscillatory properties of a network region and their spatial variation with the variation of the parameters of the magnetic field. We investigate the effect of the magnetic canopy and the diverging flux tubes of the chromospheric network on the distribution of oscillatory power over the network and internetwork.
Methods: We use a time series of high resolution filtergrams at five wavelengths along the Hα profile observed with the Dutch Open Telescope, as well as high resolution magnetograms taken by the SOT/SP onboard HINODE. Using wavelet analysis, we construct power maps of the 3, 5 and 7 min oscillations of the Doppler signals calculated at ±0.35 Å and ±0.7 Å from the Hα line center. These represent velocities at chromospheric and photospheric levels respectively. Through a current-free (potential) field extrapolation we calculate the chromospheric magnetic field and compare its morphology with the Hα filtergrams. We calculate the plasma β and the magnetic field inclination angle and compare their distribution with the oscillatory power at the 3, 5 and 7 min period bands.
Results: Chromospheric mottles seem to outline the magnetic field lines. The Hα ± 0.35 Å Doppler signals are formed above the canopy, while the Hα ± 0.7 Å corresponding ones below it. The 3 min power is suppressed at the chromosphere around the network, where the canopy height is lower than 1600 km, while at the photosphere it is enhanced due to reflection. 3, 5 and 7 min oscillatory power is increased around the network at the photosphere due to reflection of waves on the overlying canopy, while increased 5 and 7 min power at the chromosphere is attributed mainly to wave refraction on the canopy. At these high periods, power is also increased due to p-mode leakage because of the high inclinations of the magnetic field.
Conclusions: Our high resolution Hα observations and photospheric magnetograms provide the opportunity to highlight the details of the interaction between acoustic oscillations and the magnetic field of a network region. We conclude that several mechanisms that have been proposed such as p-mode leakage, mode conversion, reflection and refraction of waves on the magnetic canopy may act together and result to the observed properties of network oscillations. Title: Comparative Analysis of Oscillations of a Solar Quiet Region Using Multi-Wavelength Observations Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2010ASPC..424...31K Altcode: We analyze the temporal behavior of a solar quiet region using a set of multi-wavelength observations obtained during a coordinated campaign. The observations were acquired by the ground-based Dutch Open Telescope (DOT), the Michelson Doppler Imager (MDI) on-board SOHO and the UV filters of the Transition Region and Coronal Explorer (TRACE). A large range of height in the solar atmosphere, from the deep photosphere to the upper chromosphere is covered by these instruments. We investigate the oscillation properties of the intensities and velocities in distinct regions of the quiet Sun, i.e. internetwork, bright points (NBP) defining the network boundaries and dark mottles forming a well-defined rosette, as observed by the different instruments and in the different heights. The variations of the intensities and velocities are studied with wavelet analysis. The aim of our work is to find similarities and/or differences in the oscillatory phenomena observed in the different examined regions, as well as comprehensive information on the interaction of the oscillations and the magnetic field. Title: Power halo and magnetic shadow in a solar quiet region observed in the Hα line Authors: Kontogiannis, I.; Tsiropoula, G.; Tziotziou, K. Bibcode: 2010A&A...510A..41K Altcode: Context. We investigate the oscillatory behavior of the quiet solar chromosphere and its discrete components in terms of oscillation properties, i.e. network and internetwork. For this purpose, we use a time series of high resolution filtergrams at five wavelengths along the Hα profile, obtained by the Dutch Open Telescope.
Aims: We aim to gain insight on the distribution of power in different period bands and its variation between network and internetwork. Our spectral resolution provides information on the vertical distribution of power, since the Hα line has both photospheric and chromospheric components. We investigate the effect of Hα mottles on chromospheric oscillations, since they are the most prominent feature of the Hα chromosphere and outline inclined magnetic fields.
Methods: We use wavelet and phase difference analyses of Hα intensities and Doppler signals. Two-dimensional power maps in the 3, 5 and 7 min period bands as well as coherence and phase difference maps were constructed.
Results: At photospheric heights, where the Hα ± 0.7 Å wing is formed, the 3 and 5 min power is enhanced around the network, and forms power halos. Higher in the chromosphere these areas are replaced by magnetic shadows, i.e. places of power suppression. Interestingly, the power maps show a filamentary structure in the network which correlates very well with mottles. These areas show positive phase differences at the 3 min period band. At the 5 min and 7 min period bands both positive and negative phase differences are obtained with an increased number of pixels with high coherence, indicating the existence of both upward and downward propagating waves.
Conclusions: We attribute our findings to the interaction between acoustic oscillations and the magnetic fields that constitute the magnetic network. The network flux tubes diverge at chromospheric levels and obtain a significant horizontal component, which is betrayed by the presence of mottles. The variation of power reveals the discrete role of the magnetic field at different heights, which guides or suppresses the oscillations, depending on its inclination. Spectral resolution in Hα provides useful information on the coupling between the acoustic sub-canopy atmosphere and the magnetized chromosphere. Title: Study of spicules observed in the Ca II H and Ha lines with Hinode/SOT Authors: Kontogiannis, Ioannis; Tsiropoula, Georgia Bibcode: 2010cosp...38.2949K Altcode: 2010cosp.meet.2949K We use a dataset of simultaneous image sequences obtained by Hinode/SOT with the Ca II H filter, as well as in Hα ±0.2 ˚. SOT was looking at the SW solar limb. The high temporal A and spatial resolution allows us to study the structure and dynamics of spicules seen at the different filters. Individual spicules have been selected and intensity and velocity distributions at different heights along their central axes are examined along with transversal fluctuations. Their temporal variations are also examined through wavelet and phase difference analyses Title: 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: 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: 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.