Author name code: patsourakos ADS astronomy entries on 2022-09-14 author:"Patsourakos, Spiros" ------------------------------------------------------------------------ Title: The Low-Corona Evolution of Coronal Mass Ejections: Solar Truth and Implications for Stellar Coronal Mass Ejections Authors: Patsourakos, Spiros; Vourlidas, Angelos; Balmaceda, Laura Bibcode: 2022cosp...44.1407P Altcode: Once a Coronal Mass Ejection (CME) is underway, it sparks a variety of phenomena in the low corona including dimmings, waves and shocks. An important finding of multi-viewpoint and high-cadence imaging observations of the initial stages of CMEs from STEREO and SDO is that they evolve differently in the lateral compared to the radial direction. The CME lateral expansion in the low corona is of particular interest to solar-stellar studies because it occurs in the region that dominates the emission in stellar observations, and triggers wave and shock phenomena. With this presentation we will discuss: i) basic observational aspects of the lateral expansion of CMEs in the solar corona, and ii) how these may contribute to the hunt for stellar CMEs. We will show how our understanding of the low lateral expansion of CMEs in the solar corona may help into deciphering and eventually modeling of the light-curves of dimmings presumably associated with stellar CMEs. Title: The lower solar atmosphere inside and outside coronal holes and the base of the Solar Wind Authors: Gontikakis, Costis; Patsourakos, Spiros; Tsinganos, Kanaris; Koletti, Myrto Bibcode: 2022cosp...44.1336G Altcode: In this review, we will present the crucial observations that gave rise to current concepts on the formation of the solar wind, low in the solar atmosphere. We will discuss the differences between the fast solar wind originating from coronal holes and the slow solar wind emanating around solar streamers and closed solar magnetic structures. Observations from remote spectrographs that may constitute critical tests for the different solar wind acceleration models will be emphasized. Phenomena such as plumes and jets will also be examined. Finally, we will introduce the most recent SolO and PSP results on the origins and early stages of the solar wind. Title: The impact of virtual mass and magnetic erosion on the propagation of fast ICMEs Authors: Stamkos, Sotiris; Patsourakos, Spiros; Daglis, Ioannis A.; Vourlidas, Angelos Bibcode: 2022cosp...44.1406S Altcode: In order to enhance our understanding of the dynamic interactions of Interplanetary Coronal Mass Ejections (ICMEs) with the solar wind and interplanetary magnetic field, we investigate the effect of magnetic erosion on the well-known aerodynamic drag force acting on ICMEs. In particular, we generate empirical equations for the basic parameters of an ICME assuming a cylindrical morphology. Furthermore, we examine the impact of the virtual mass on the equation of motion by essentially studying a variable mass system. We quantify the effect of the reconnection process, which erodes part of the ICME's magnetic flux and outer-shell mass, on the drag acting on ICMEs and, eventually, we determine its impact on the time and speed of arrival of those transients at 1 AU. Title: Assessment of near sun axial CME magnetic field. Authors: Koya, Shifana; Patsourakos, Spiros; Georgoulis, Manolis K.; Nindos, Alexander Bibcode: 2022cosp...44.1405K Altcode: The magnetic origin and the role of magnetic helicity in solar eruptions are known for several years. Here we present a survey of near-Sun axial coronal mass ejection (CME) magnetic fields that are obtained by applying a semi-analytical method that calculates the magnetic helicity of the source active region relying primarily on photospheric vector magnetograms. The geometrical parameters of CMEs observed by STEREO/SECCHI and SOHO/LASCO are obtained by fitting the GCS magnetic flux rope model. We use the estimated near-Sun CME magnetic fields to infer ICME magnetic fields and to validate them with existing in-situ magnetometer observation at L1. We conclude that the proposed method, including the proposed inferences from the survey, is useful for CME magnetic field forecasting purposes, solar-stellar connection and projecting towards potential properties of stellar CMEs. Title: When do solar erupting hot magnetic flux ropes form? Authors: Nindos, Alexander; Zhang, Jie; Patsourakos, Spiros; Cheng, Xin; Vourlidas, Angelos Bibcode: 2022cosp...44.2419N Altcode: We investigate the formation times of eruptive magnetic flux ropes relative to the onset of solar eruptions, which is important for constraining models of coronal mass ejection (CME) initiation. We inspected uninterrupted sequences of 131 A images that spanned more than eight hours and were obtained by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory to identify the formation times of hot flux ropes that erupted in CMEs from locations close to the limb. The appearance of the flux ropes as well as their evolution toward eruptions were determined using morphological criteria. Two-thirds (20/30) of the flux ropes were formed well before the onset of the eruption (from 51 min to more than eight hours), and their formation was associated with the occurrence of a confined flare. We also found four events with preexisting hot flux ropes whose formations occurred a matter of minutes (from three to 39) prior to the eruptions without any association with distinct confined flare activity. Six flux ropes were formed once the eruptions were underway. However, in three of them, prominence material could be seen in 131 Å images, which may indicate the presence of preexisting flux ropes that were not hot. The formation patterns of the last three groups of hot flux ropes did not show significant differences. For the whole population of events, the mean and median values of the time difference between the onset of the eruptive flare and the appearance of the hot flux rope were 151 and 98 min, respectively. Our results provide, on average, indirect support for CME models that involve preexisting flux ropes; on the other hand, for a third of the events, models in which the ejected flux rope is formed during the eruption appear more appropriate. Title: Identifying the Terrestrial Exoplanets which Deserve More Scrutiny for Atmosphere Viability: the mASC method Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis K. Bibcode: 2022cosp...44.1395S Altcode: We introduce a practical and physically intuitive method to assess whether a given exoplanet is a viable candidate for the existence of an atmosphere, thanks to an efficient magnetospheric shielding from intense space weather activity from its host star. Our proposed mASC (magnetic Atmosphere Sustainability Constraint) relies on a best-case scenario for a dynamo-generated planetary magnetic field and subsequent magnetic pressure, and a worst-case scenario for the magnetic pressure of stellar CMEs. The method estimates a dimensionless ratio R whose excursion from unity implies accordingly an "atmosphere likely" (R < 1) or an "atmosphere unlikely" (R > 1) scenario. In this work, we implement our mASC on six "famous" exoplanets whose discovery was greeted with praise and hopes of habitability. These are Kepler-438b, Proxima-Centauri b, and Trappist-1d, -1e, -1f, -1g. We conclude that for none of them the existence of an atmosphere is likely while our findings are robust for five out of six cases. We conclude that the mASC ratio could help set observing priorities and suggest which exoplanets deserve further scrutiny, possibly toward the ultimate search of potential biosignatures, among other objectives. Title: Investigating possible EUV precursors of major solar flares Authors: AndrÉ-Hoffmann, Augustin; Patsourakos, Spiros; Georgoulis, Manolis K.; Nindos, Alexander Bibcode: 2022cosp...44.2481A Altcode: Large-scale solar eruptions that produce major flares and fast coronal mass ejections are often associated with precursor activity that may start several hours before the main event. Such activity may be observed from the photosphere all the way to the transition region and corona but it is not clear whether it plays an essential role in the eruption initiation. To investigate this question we search for precursor activity in Extreme Ultra-violet (EUV) images obtained by the Atmospheric Imaging Assembly (AIA) instrument on board Solar Dynamics Observatory (SDO) within a 24-hour window prior to large eruptive events and investigate whether they contribute to the restructuring and overall evolution of the magnetic field that leads to eruptions. We cross-check our findings by performing the same search in relatively quiet active regions. By comparing the results from the eruptive and quiet active regions we attempt to identify possible signatures that could be useful in both the short-term prediction of major flare events and an enhanced physical understanding of the preflare phase. Title: First detection of metric emission from a solar surge Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bouratzis, C.; Hillaris, A. Bibcode: 2022A&A...662A..14A Altcode: 2022arXiv220301043A We report the first detection of metric radio emission from a surge, observed with the Nançay Radioheliograph (NRH), STEREO, and other instruments. The emission was observed during the late phase of the M9 complex event SOL2010-02-012T11:25:00, described in a previous publication. It was associated with a secondary energy release, also observed in STEREO 304 Å images, and there was no detectable soft X-ray emission. The triangulation of the STEREO images allowed for the identification of the surge with NRH sources near the central meridian. The radio emission of the surge occurred in two phases and consisted of two sources, one located near the base of the surge, apparently at or near the site of energy release, and another in the upper part of the surge; these were best visible in the frequency range of 445.0 to about 300 MHz, whereas a spectral component of a different nature was observed at lower frequencies. Sub-second time variations were detected in both sources during both phases, with a 0.2-0.3 s delay of the upper source with respect to the lower, suggesting superluminal velocities. This effect can be explained if the emission of the upper source was due to scattering of radiation from the source at the base of the surge. In addition, the radio emission showed signs of pulsations and spikes. We discuss possible emission mechanisms for the slow time variability component of the lower radio source. Gyrosynchrotron emission reproduced the characteristics of the observed total intensity spectrum at the start of the second phase of the event fairly well, but failed to reproduce the high degree of the observed circular polarization or the spectra at other instances. On the other hand, type IV-like plasma emission from the fundamental could explain the high polarization and the fine structure in the dynamic spectrum; moreover, it gives projected radio source positions on the plane of the sky, as seen from STEREO-A, near the base of the surge. Taking all the properties into consideration, we suggest that type IV-like plasma emission with a low-intensity gyrosynchrotron component is the most plausible mechanism.

Movie associated to Fig. A.2 is available at https://www.aanda.org Title: Earth-affecting solar transients: a review of progresses in solar cycle 24 Authors: Zhang, Jie; Temmer, Manuela; Gopalswamy, Nat; Malandraki, Olga; Nitta, Nariaki V.; Patsourakos, Spiros; Shen, Fang; Vršnak, Bojan; Wang, Yuming; Webb, David; Desai, Mihir I.; Dissauer, Karin; Dresing, Nina; Dumbović, Mateja; Feng, Xueshang; Heinemann, Stephan G.; Laurenza, Monica; Lugaz, Noé; Zhuang, Bin Bibcode: 2021PEPS....8...56Z Altcode: 2020arXiv201206116Z This review article summarizes the advancement in the studies of Earth-affecting solar transients in the last decade that encompasses most of solar cycle 24. It is a part of the effort of the International Study of Earth-affecting Solar Transients (ISEST) project, sponsored by the SCOSTEP/VarSITI program (2014-2018). The Sun-Earth is an integrated physical system in which the space environment of the Earth sustains continuous influence from mass, magnetic field, and radiation energy output of the Sun in varying timescales from minutes to millennium. This article addresses short timescale events, from minutes to days that directly cause transient disturbances in the Earth's space environment and generate intense adverse effects on advanced technological systems of human society. Such transient events largely fall into the following four types: (1) solar flares, (2) coronal mass ejections (CMEs) including their interplanetary counterparts ICMEs, (3) solar energetic particle (SEP) events, and (4) stream interaction regions (SIRs) including corotating interaction regions (CIRs). In the last decade, the unprecedented multi-viewpoint observations of the Sun from space, enabled by STEREO Ahead/Behind spacecraft in combination with a suite of observatories along the Sun-Earth lines, have provided much more accurate and global measurements of the size, speed, propagation direction, and morphology of CMEs in both 3D and over a large volume in the heliosphere. Many CMEs, fast ones, in particular, can be clearly characterized as a two-front (shock front plus ejecta front) and three-part (bright ejecta front, dark cavity, and bright core) structure. Drag-based kinematic models of CMEs are developed to interpret CME propagation in the heliosphere and are applied to predict their arrival times at 1 AU in an efficient manner. Several advanced MHD models have been developed to simulate realistic CME events from the initiation on the Sun until their arrival at 1 AU. Much progress has been made on detailed kinematic and dynamic behaviors of CMEs, including non-radial motion, rotation and deformation of CMEs, CME-CME interaction, and stealth CMEs and problematic ICMEs. The knowledge about SEPs has also been significantly improved. An outlook of how to address critical issues related to Earth-affecting solar transients concludes this article. Title: Which Terrestrial Exoplanets Deserve More Scrutiny for Atmosphere Viability? Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis Bibcode: 2021AGUFM.U44B..05S Altcode: We introduce a practical and physically intuitive method to assess whether a given exoplanet is a viable candidate for the existence of an atmosphere thanks to an efficient magnetospheric shielding from intense space weather activity originating from its host star. Our proposed mASC (magnetic Atmosphere Sustainability Constraint) relies on a best-case scenario for the dynamo-generated planetary magnetic field and subsequent magnetic pressure, and a worst-case scenario for the magnetic pressure of stellar CMEs. It provides a dimensionless ratio R whose excursion from unity implies accordingly an atmosphere likely (R < 1) or an atmosphere unlikely (R > 1) scenario. In this work, we implement our mASC on six famous exoplanets whose discovery was greeted with praise and hopes of habitability. These are Kepler-438b, Proxima-Centauri b, and Trappist-1d, -1e, -1f, -1g. The results show that for none of them the existence of an atmosphere is likely while our findings are robust for five out of six cases. We conclude that the mASC ratio could help set observing priorities and suggest which exoplanets deserve further scrutiny, possibly toward the ultimate search of potential biosignatures, among other objectives. Title: Multiwavelength observations of a metric type-II event Authors: Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.; Hillaris, A. Bibcode: 2021A&A...654A.112A Altcode: 2021arXiv210802855A We have studied a complex metric radio event that originated in a compact flare, observed with the ARTEMIS-JLS radiospectrograph on February 12, 2010. The event was associated with a surge observed at 195 and 304 Å and with a coronal mass ejection observed by instruments on board STEREO A and B near the eastern and western limbs respectively. On the disk the event was observed at ten frequencies by the Nançay Radioheliograph (NRH), in Hα by the Catania observatory, in soft X-rays by GOES SXI and Hinode XRT, and in hard X-rays by RHESSI. We combined these data, together with MDI longitudinal magnetograms, to get as complete a picture of the event as possible. Our emphasis is on two type-II bursts that occurred near respective maxima in the GOES light curves. The first, associated with the main peak of the event, showed an impressive fundamental-harmonic structure, while the emission of the second consisted of three well-separated bands with superposed pulsations. Using positional information for the type-IIs from the NRH and triangulation from STEREO A and B, we found that the type-IIs were associated neither with the surge nor with the disruption of a nearby streamer, but rather with an extreme ultraviolet (EUV) wave probably initiated by the surge. The fundamental-harmonic structure of the first type-II showed a band split corresponding to a magnetic field strength of 18 G, a frequency ratio of 1.95 and a delay of 0.23−0.65 s of the fundamental with respect to the harmonic; moreover it became stationary shortly after its start and then drifted again. The pulsations superposed on the second type-II were broadband and had started before the burst. In addition, we detected another pulsating source, also before the second type-II, polarized in the opposite sense; the pulsations in the two sources were out of phase and hence hardly detectable in the dynamic spectrum. The pulsations had a measurable reverse frequency drift of about 2 s−1. Title: ALMA observations of the variability of the quiet Sun at millimeter wavelengths Authors: Nindos, A.; Patsourakos, S.; Alissandrakis, C. E.; Bastian, T. S. Bibcode: 2021A&A...652A..92N Altcode: 2021arXiv210604220N
Aims: We address the variability of the quiet solar chromosphere at 1.26 mm and 3 mm with a focus on the study of spatially resolved oscillations and transient brightenings, which are small, weak events of energy release. Both phenomena may have a bearing on the heating of the chromosphere.
Methods: We used Atacama Large Millimeter/submillimeter Array (ALMA) observations of the quiet Sun at 1.26 mm and 3 mm. The spatial and temporal resolution of the data were 1 − 2″ and 1 s, respectively. The concatenation of light curves from different scans yielded a frequency resolution in spectral power of 0.5−0.6 mHz. At 1.26 mm, in addition to power spectra of the original data, we degraded the images to the spatial resolution of the 3 mm images and used fields of view that were equal in area for both data sets. The detection of transient brightenings was made after the effect of oscillations was removed.
Results: At both frequencies, we detected p-mode oscillations in the range 3.6−4.4 mHz. The corrections for spatial resolution and field of view at 1.26 mm decreased the root mean square (rms) of the oscillations by a factor of 1.6 and 1.1, respectively. In the corrected data sets, the oscillations at 1.26 mm and 3 mm showed brightness temperature fluctuations of ∼1.7 − 1.8% with respect to the average quiet Sun, corresponding to 137 and 107 K, respectively. We detected 77 transient brightenings at 1.26 mm and 115 at 3 mm. Although their majority occurred in the cell interior, the occurrence rate per unit area of the 1.26 mm events was higher than that of the 3 mm events; this conclusion does not change if we take into account differences in spatial resolution and noise levels. The energy associated with the transient brightenings ranged from 1.8 × 1023 to 1.1 × 1026 erg and from 7.2 × 1023 to 1.7 × 1026 erg for the 1.26 mm and 3 mm events, respectively. The corresponding power-law indices of the energy distribution were 1.64 and 1.73. We also found that ALMA bright network structures corresponded to dark mottles or spicules that can be seen in broadband Hα images from the GONG network.
Conclusions: The fluctuations associated with the p-mode oscillations represent a fraction of 0.55−0.68 of the full power spectrum. Their energy density at 1.26 mm is 3 × 10−2 erg cm−3. The computed low-end energy of the 1.26 mm transient brightenings is among the smallest ever reported, irrespective of the wavelength of the observation. Although the occurrence rate per unit area of the 1.26 mm transient brightenings was higher than that of the 3 mm events, their power per unit area is smaller likely due to the detection of many weak 1.26 mm events. Title: Tracking solar wind flows from rapidly varying viewpoints by the Wide-field Imager for Parker Solar Probe Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Liewer, P. C.; Penteado, P.; Hall, J. R. Bibcode: 2021A&A...650A..30N Altcode: 2020arXiv201013140N
Aims: Our goal is to develop methodologies to seamlessly track transient solar wind flows viewed by coronagraphs or heliospheric imagers from rapidly varying viewpoints.
Methods: We constructed maps of intensity versus time and elongation (J-maps) from Parker Solar Probe (PSP) Wide-field Imager (WISPR) observations during the fourth encounter of PSP. From the J-map, we built an intensity on impact-radius-on-Thomson-surface map (R-map). Finally, we constructed a latitudinal intensity versus time map (Lat-map). Our methodology satisfactorily addresses the challenges associated with the construction of such maps from data taken from rapidly varying viewpoint observations.
Results: Our WISPR J-map exhibits several tracks, corresponding to transient solar wind flows ranging from a coronal mass ejection down to streamer blobs. The latter occurrence rate is about 4-5 per day, which is similar to the occurrence rate in a J-map made from ~1 AU data obtained with the Heliospheric Imager-1 (HI-1) on board the Solar Terrestrial Relations Observatory Ahead spacecraft (STEREO-A). STEREO-A was radially aligned with PSP during the study period. The WISPR J-map tracks correspond to angular speeds of 2.28 ± 0.7°/h (2.49 ± 0.95°/h), for linear (quadratic) time-elongation fittings, and radial speeds of about 150-300 km s−1. The analysis of the Lat-map reveals a bifurcating streamer, which implies that PSP was flying through a slightly folded streamer during perihelion.
Conclusions: We developed a framework to systematically capture and characterize transient solar wind flows from space platforms with rapidly varying vantage points. The methodology can be applied to PSP WISPR observations as well as to upcoming observations from instruments on board the Solar Orbiter mission.

Movie associated to Fig. 8 is available at https://www.aanda.org Title: Relative field line helicity of a large eruptive solar active region Authors: Moraitis, K.; Patsourakos, S.; Nindos, A. Bibcode: 2021A&A...649A.107M Altcode: 2021arXiv210303643M Context. Magnetic helicity is a physical quantity of great importance in the study of astrophysical and natural plasmas. Although a density for helicity cannot be defined, a good proxy for this quantity is field line helicity. The appropriate quantity for use in solar conditions is relative field line helicity (RFLH).
Aims: This work aims to study in detail the behaviour of RFLH, for the first time, in a solar active region (AR).
Methods: The target AR is the large, eruptive AR 11158. In order to compute RFLH and all other quantities of interest, we used a non-linear force-free reconstruction of the AR coronal magnetic field of excellent quality.
Results: We find that the photospheric morphology of RFLH is very different than that of the magnetic field or electrical current, and this morphology is not sensitive to the chosen gauge in the computation of RFLH. The value of helicity experiences a large decrease, that is ∼25% of its pre-flare value, during an X-class flare of the AR; this change is also depicted in the photospheric morphology of RFLH. Moreover, the area of this change coincides with the area that encompasses the flux rope, which is the magnetic structure that later erupted.
Conclusions: The use of RFLH can provide important information about the value and location of the magnetic helicity expelled from the solar atmosphere during eruptive events. Title: A Readily Implemented Atmosphere Sustainability Constraint for Terrestrial Exoplanets Orbiting Magnetically Active Stars Authors: Samara, Evangelia; Patsourakos, Spiros; Georgoulis, Manolis K. Bibcode: 2021ApJ...909L..12S Altcode: 2021arXiv210207837S With more than 4300 confirmed exoplanets and counting, the next milestone in exoplanet research is to determine which of these newly found worlds could harbor life. Coronal mass ejections (CMEs), spawned by magnetically active, superflare-triggering dwarf stars, pose a direct threat to the habitability of terrestrial exoplanets, as they can deprive them of their atmospheres. Here we develop a readily implementable atmosphere sustainability constraint for terrestrial exoplanets orbiting active dwarfs, relying on the magnetospheric compression caused by CME impacts. Our constraint focuses on an understanding of CMEs propagation in our own Sun-heliosphere system that, applied to a given exoplanet requires as key input the observed bolometric energy of flares emitted by its host star. Application of our constraint to six famous exoplanets, Kepler-438b, Proxima Centauri b, and Trappist-1d, -1e, -1f, and -1g, within or in the immediate proximity of their stellar host's habitable zones showed that only for Kepler-438b might atmospheric sustainability against stellar CMEs be likely. This seems to align with some recent studies that, however, may require far more demanding computational resources and observational inputs. Our physically intuitive constraint can be readily and en masse applied, as is or generalized, to large-scale exoplanet surveys to detect planets that warrant further scrutiny for atmospheres and, perhaps, possible biosignatures at higher priority by current and future instrumentation. Title: Properties Determining Eruption Initiation and Planeto-Effectiveness of Eruptive Transients in Magnetically Active Stars Authors: Georgoulis, Manolis K.; Patsourakos, Spiros; Zhang, Hongqi; Nindos, Alexander; Samara, Evangelia; Sadykov, Viacheslav M. Bibcode: 2021cosp...43E.993G Altcode: We present a combined theoretical and data analysis approach to, first, understand why magnetic eruptions and corresponding ejecta are triggered in strong-field regions of the Sun and magnetically active stars and, second, assess the key physical parameters responsible for the planeto-effectiveness of these eruptions, both on Earth and in other (exo-)planets. This approach converges on one physical parameter besides magnetic energy, at least for stellar coronae of high magnetic Reynolds numbers allowing this parameter to be conserved even under confined energy release: magnetic helicity. Helicity, via the magnetic energy-helicity diagram, should be treated equally with magnetic energy. Due to magnetic helicity accumulation in solar active regions and its inverse cascading, solar - and stellar, correspondingly - eruptions may become inevitable after a certain 'point-of-no-return' is reached. We identify this critical instant as the time when magnetic polarity inversion lines in active-region photospheres accumulate fluxes that generate fields stronger than local equipartition values. Furthermore, using the conserved helicity budgets we abstractly model post-eruption flux ropes and their transit through astrospheres, reaching exoplanets and compressing their magnetospheres via magnetic pressure effects. A rudimentary validation between the near-Sun and L1 axial magnetic field values of these data-constrained flux ropes is encouraging and allows us to further constrain scaling laws appropriate for the astrospheric transit of these ropes. Importantly, we also find that exoplanets orbiting magnetically active dwarf stars at orbital radii that are fractions of an astronomical unit seem to be strong contenders for eruption-driven atmospheric erosion that may gradually even deprive them from their atmospheres. Some famous exoplanet cases are examined under this prism. Future improvements are expected by widely anticipated space- (Parker Solar Probe and Solar Orbiter) and ground-based (Daniel K. Inouye Solar Telescope) observations. Title: Investigating the circumsolar wind with Parker Solar Probe near-imaging and in-situ high cadence observations Authors: Patsourakos, Spiros; Liewer, Paulett; Stenborg, Guillermo; Howard, Russell; Hess, Phillip; Stevens, Michael; Vourlidas, Angelos; Kasper, Justin; Nindos, Alexander; Penteado, Paulo; Korreck, Kelly; Case, Anthony Bibcode: 2021cosp...43E.940P Altcode: The proposition of the existence of the solar wind and its subsequent discovery were major milestones at the dawn of the Space Age. Since then, the solar wind has been extensively observed by in-situ instruments at various locations in the inner and outer heliosphere but mainly at 1 AU, and by remote sensing instruments at 1 AU. Despite significant progress in the characterization and understanding of the solar wind, important questions about the nature of the solar wind remain unsettled. These questions include the nature of the launch and acceleration of the solar wind and whether it is steady, quasi-steady, periodic or intermittent. The recently launched Parker Solar Probe (PSP) mission, which has been already plunged several times in the solar corona, is ideally suited to shed more light into these lingering questions. We present a coordinated analysis of up-close and high-cadence imaging observations of the solar wind taken by WISPR and of in-situ solar-wind observations taken inside the solar corona by SWEAP during the first solar encounters of PSP. A discussion of instrumental and orbital aspects of the WISPR observations pertinent to our analysis is also included. Imaging data of the solar wind from ~ 1 AU by COR2 on STEREO-A spacecraft is also analyzed. We submit the time-series of the imaging and in-situ solar wind data to an array of methods aiming to map their properties. We conclude with a discussion of future PSP (WISPR and SWEAP) and Solar Orbiter (SoloHI) observing and analysis strategies pertinent to our science questions. Title: Lower atmospheric consequences of Coronal Mass Ejections: waves, shocks and dimmings Authors: Patsourakos, Spiros Bibcode: 2021cosp...43E1735P Altcode: Coronal Mass Ejections (CMEs) is a multi-facet phenomenon significantly perturbing and interacting with the solar, heliospheric and geospace environments. As far as the CME impact on the solar atmosphere is concerned, CMEs are intimately linked with a diverse array of large-scale and multi-wavelength phenomena including chromospheric and coronal waves, shocks and coronal dimmings. Characterizing and understanding these phenomena has important implications for not only CME physics, but also for coronal physics. We hereby supply a discussion of the state-of-the art regarding the atmospheric consequences of CMEs as resulting from observations of chromospheric and coronal waves and shocks and coronal dimmings. We will cover topics including their physical properties, their connection with CME expansion and evolution in the low solar atmosphere, their association with particle acceleration in the low corona, their use as a diagnostic probe of the properties of the ambient solar atmosphere, and their potential use for space-weather applications. Moving to stellar contexts, we discuss recent work on how coronal dimmings in active dwarfs may be be used in the detection of stellar CMEs. We finally close with a discussion of new areas in the research of the solar consequences of CMEs that could be possible with new instrumentation coming recently on-line including SolO and DKIST. Title: Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections Authors: Patsourakos, S.; Vourlidas, A.; Török, T.; Kliem, B.; Antiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis, M. K.; Green, L. M.; Leake, J. E.; Moore, R.; Nindos, A.; Syntelis, P.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J. Bibcode: 2020SSRv..216..131P Altcode: 2020arXiv201010186P A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation). Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images. Title: When do solar erupting hot magnetic flux ropes form? Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Cheng, X.; Zhang, J. Bibcode: 2020A&A...642A.109N Altcode: 2020arXiv200804380N
Aims: We investigate the formation times of eruptive magnetic flux ropes relative to the onset of solar eruptions, which is important for constraining models of coronal mass ejection (CME) initiation.
Methods: We inspected uninterrupted sequences of 131 Å images that spanned more than eight hours and were obtained by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory to identify the formation times of hot flux ropes that erupted in CMEs from locations close to the limb. The appearance of the flux ropes as well as their evolution toward eruptions were determined using morphological criteria.
Results: Two-thirds (20/30) of the flux ropes were formed well before the onset of the eruption (from 51 min to more than eight hours), and their formation was associated with the occurrence of a confined flare. We also found four events with preexisting hot flux ropes whose formations occurred a matter of minutes (from three to 39) prior to the eruptions without any association with distinct confined flare activity. Six flux ropes were formed once the eruptions were underway. However, in three of them, prominence material could be seen in 131 Å images, which may indicate the presence of preexisting flux ropes that were not hot. The formation patterns of the last three groups of hot flux ropes did not show significant differences. For the whole population of events, the mean and median values of the time difference between the onset of the eruptive flare and the appearance of the hot flux rope were 151 and 98 min, respectively.
Conclusions: Our results provide, on average, indirect support for CME models that involve preexisting flux ropes; on the other hand, for a third of the events, models in which the ejected flux rope is formed during the eruption appear more appropriate.

Movies attached to Figs. 2, 5, 8, and 10 are available at http://www.aanda.org 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: The Solar Orbiter Heliospheric Imager (SoloHI) Authors: Howard, R. A.; Vourlidas, A.; Colaninno, R. C.; Korendyke, C. M.; Plunkett, S. P.; Carter, M. T.; Wang, D.; Rich, N.; Lynch, S.; Thurn, A.; Socker, D. G.; Thernisien, A. F.; Chua, D.; Linton, M. G.; Koss, S.; Tun-Beltran, S.; Dennison, H.; Stenborg, G.; McMullin, D. R.; Hunt, T.; Baugh, R.; Clifford, G.; Keller, D.; Janesick, J. R.; Tower, J.; Grygon, M.; Farkas, R.; Hagood, R.; Eisenhauer, K.; Uhl, A.; Yerushalmi, S.; Smith, L.; Liewer, P. C.; Velli, M. C.; Linker, J.; Bothmer, V.; Rochus, P.; Halain, J. -P.; Lamy, P. L.; Auchère, F.; Harrison, R. A.; Rouillard, A.; Patsourakos, S.; St. Cyr, O. C.; Gilbert, H.; Maldonado, H.; Mariano, C.; Cerullo, J. Bibcode: 2020A&A...642A..13H Altcode:
Aims: We present the design and pre-launch performance of the Solar Orbiter Heliospheric Imager (SoloHI) which is an instrument prepared for inclusion in the ESA/NASA Solar Orbiter mission, currently scheduled for launch in 2020.
Methods: The goal of this paper is to provide details of the SoloHI instrument concept, design, and pre-flight performance to give the potential user of the data a better understanding of how the observations are collected and the sources that contribute to the signal.
Results: The paper discusses the science objectives, including the SoloHI-specific aspects, before presenting the design concepts, which include the optics, mechanical, thermal, electrical, and ground processing. Finally, a list of planned data products is also presented.
Conclusions: The performance measurements of the various instrument parameters meet or exceed the requirements derived from the mission science objectives. SoloHI is poised to take its place as a vital contributor to the science success of the Solar Orbiter mission. Title: Modeling the quiet Sun cell and network emission with ALMA Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T. S.; Patsourakos, S. Bibcode: 2020A&A...640A..57A Altcode: 2020arXiv200609886A Observations of the Sun at millimeter wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity to investigate the temperature structure of the solar chromosphere. In this article we expand our previous work on modeling the chromospheric temperature of the quiet Sun, by including measurements of the brightness temperature in the network and cell interiors, from high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We also examine the absolute calibration of ALMA full-disk images. We suggest that the brightness temperature at the center of the solar disk in Band 6 is ∼440 K above the value recommended by White et al. (2017, Sol. Phys., 292, 88). In addition, we give improved results for the electron temperature variation of the average quiet Sun with optical depth and the derived spectrum at the center of the disk. We found that the electron temperature in the network is considerably lower than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319) and that of the cell interior considerably higher than predicted by model A. Depending on the network/cell segregation scheme, the electron temperature difference between network and cell at τ = 1 (100 GHz) ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted by the models; similarly, the electron temperature, Te ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model prediction. We also found that the network/cell Te(τ) curves diverge as τ decreases, indicating an increase of contrast with height and possibly a steeper temperature rise in the network than in the cell interior. Title: Transient brightenings in the quiet Sun detected by ALMA at 3 mm Authors: Nindos, A.; Alissandrakis, C. E.; Patsourakos, S.; Bastian, T. S. Bibcode: 2020A&A...638A..62N Altcode: 2020arXiv200407591N
Aims: We investigate transient brightenings, that is, weak, small-scale episodes of energy release, in the quiet solar chromosphere; these episodes can provide insights into the heating mechanism of the outer layers of the solar atmosphere.
Methods: Using Atacama Large Millimeter/submillimeter Array (ALMA) observations, we performed the first systematic survey for quiet Sun transient brightenings at 3 mm. Our dataset included images of six 87″ × 87″ fields of view of the quiet Sun obtained with angular resolution of a few arcsec at a cadence of 2 s. The transient brightenings were detected as weak enhancements above the average intensity after we removed the effect of the p-mode oscillations. A similar analysis, over the same fields of view, was performed for simultaneous 304 and 1600 Å data obtained with the Atmospheric Imaging Assembly.
Results: We detected 184 3 mm transient brightening events with brightness temperatures from 70 K to more than 500 K above backgrounds of ∼7200 - 7450 K. All events showed light curves with a gradual rise and fall, strongly suggesting a thermal origin. Their mean duration and maximum area were 51.1 s and 12.3 Mm2, respectively, with a weak preference of appearing at network boundaries rather than in cell interiors. Both parameters exhibited power-law behavior with indices of 2.35 and 2.71, respectively. Only a small fraction of ALMA events had either 304 or 1600 Å counterparts but the properties of these events were not significantly different from those of the general population except that they lacked their low-end energy values. The total thermal energies of the ALMA transient brightenings were between 1.5 × 1024 and 9.9 × 1025 erg and their frequency distribution versus energy was a power law with an index of 1.67 ± 0.05. We found that the power per unit area provided by the ALMA events could account for only 1% of the chromospheric radiative losses (10% of the coronal ones).
Conclusions: We were able to detect, for the first time, a significant number of weak 3 mm quiet Sun transient brightenings. However, their energy budget falls short of meeting the requirements for the heating of the upper layers of the solar atmosphere and this conclusion does not change even if we use the least restrictive criteria possible for the detection of transient brightenings. Title: Modeling of the Brightness of the Chromospheric Network Based on ALMA High Resolution Observations of the Quiet Sun Authors: Alissandrakis, C. E.; Nindos, A.; Bastian, T.; Patsourakos, S. Bibcode: 2020AAS...23610607A Altcode: ALMA observations of the Sun at mm-λ offer a unique opportunity to investigate the temperature/density structure of the solar chromosphere. In a previous work (Alissandrakis et al 2017, A&A 605, A78) we measured the center-to-limb variation of the brightness temperature, Tb, using low resolution ALMA full-disk observations in Band 3 (3mm) and Band 6 (1.26 mm), together with data at 0.85 mm from Bastian et al. 1993 (ApJ, 415, 364). Combining all data and inverting the solution of the transfer equation we found that the electron temperature, Te, in the range of 0.34 < τ100 < 12, where τ100 is the optical depth at 100 GHz, was ~5% (~300 K) below the one predicted by model C (average quiet sun) of FAL93 (Fontenla, Avrett, & Loeser, 1993, ApJ, 406, 319). Here we expand that work by including measurements of the brightness temperature in the network and cell interiors, from high resolution ALMA images in Bands 3 and 6. We found that the observed Tb in the network is considerably lower than predicted by the FAL93 model F and that of the cell interior considerably higher than predicted by the FAL93 model A. The observed network/cell difference of brightness temperature at the center of the disk, at 100 GHz is about 920 K, compared to ~3250 K predicted by the FAL93 models; similarly, the Tb, ratio is ~1.14, against ~1.51 of the model prediction. After inversion of the observed data, the electron temperature of cell interior at τ100=1 is ~390 K below the average (~600 K above model A) and of the network ~400 K above the average (~1800 K below model A). The implications of these results will be discussed. We will also discuss the question of the normalization of brightness temperature observed by ALMA. Title: Interplanetary Coronal Mass Ejections as the Driver of Non-recurrent Forbush Decreases Authors: Papaioannou, Athanasios; Belov, Anatoly; Abunina, Maria; Eroshenko, Eugenia; Abunin, Artem; Anastasiadis, Anastasios; Patsourakos, Spiros; Mavromichalaki, Helen Bibcode: 2020ApJ...890..101P Altcode: Interplanetary coronal mass ejections (ICMEs) are the counterparts of coronal mass ejections (CMEs) that extend in the interplanetary (IP) space and interact with the underlying solar wind (SW). ICMEs and their corresponding shocks can sweep out galactic cosmic rays (GCRs) and thus modulate their intensity, resulting in non-recurrent Forbush decreases (FDs). In this work, we selected all FDs that were associated with a sudden storm commencement (SSC) at Earth, and a solar driver (e.g., CME) was clearly identified as the ICME's source. We introduce and employ the tH parameter, which is the time delay (in hours) of the maximum strength of the interplanetary magnetic field from the FD onset (as is marked via the SSC), and consequently derive three groups of FD events (I.e., the early, medium, and late ones). For each of these we examine the mean characteristics of the FDs and the associated IP variations per group, as well as the resulting correlations. In addition, we demonstrate the outputs of a superposed epoch analysis, which led to an average time profile of the resulting FDs and the corresponding IP variations, per group. Finally, we interpret our results based on the theoretical expectations for the FD phenomenon. We find that both the shock sheath and the ejecta are necessary for deep GCR depressions and that the FD amplitude (A0) is larger for faster-propagating ICMEs. Additionally, we note the importance of the turbulent shock-sheath region across all groups. Finally, we present empirical relations connecting A0 to SW properties. Title: Observations of solar chromospheric oscillations at 3 mm with ALMA Authors: Patsourakos, S.; Alissandrakis, C. E.; Nindos, A.; Bastian, T. S. Bibcode: 2020A&A...634A..86P Altcode: 2019arXiv191203480P
Aims: We aim to study spatially resolved chromospheric oscillations of the quiet Sun (QS) in the mm-domain at a resolution of a few arcsec, typically 2.4″ × 4.5″.
Methods: We used Atacama Large millimeter and submillimeter Array (ALMA) time series of interferometric observations of the QS obtained at 3 mm with a 2-s cadence and a spatial resolution of a few arcsec. The observations were performed on March 16, 2017 and seven 80″ × 80″ fields of view (FoV) going from disk center to limb were covered, each one observed for 10 min, therefore limiting the frequency resolution of the power spectra to 1.7 mHz. For each FoV, masks for cell and network were derived, and the averaged power spectral densities (PSDs) for the entire FoV, cell, and network were computed. The resulting power spectra were fit with an analytical function in order to derive the frequency and the root-mean-square (rms) power associated with the peaks. The same analysis, over the same FoVs and for the same intervals, was performed for simultaneous Atmospheric Imaging Assembly (AIA) image sequences in 1600 Å.
Results: Spatially resolved chromospheric oscillations at 3 mm, with frequencies of 4.2 ± 1.7 mHz are observed in the QS, in both cell and network. The coherence length-scale of the oscillations is commensurate with the spatial resolution of our ALMA observations. Brightness-temperature fluctuations in individual pixels could reach up to a few hundred K, while the spatially averaged PSDs yield rms in the range ≈55-75 K, i.e., up to ≈1% of the averaged brightness temperatures and exhibit a moderate increase towards the limb. For AIA 1600 Å, the oscillation frequency is 3.7 ± 1.7 mHz. The relative rms is up to 6% of the background intensity, with a weak increase towards the disk center (cell, average). ALMA 3 mm time-series lag AIA 1600 Å by ≈100 s, which corresponds to a formation-height difference of ≈1200 km, representing a novel determination of this important parameter.
Conclusions: The ALMA oscillations that we detected exhibit higher amplitudes than those derived from previous lower (≈10″) resolution observations at 3.5 mm by the Berkeley-Illinois-Maryland Array. Chromospheric oscillations are, therefore, not fully resolved at the length-scale of the chromospheric network, and possibly not even at the spatial resolution of our ALMA observations. Any study of transient brightenings in the mm-domain should take into account the oscillations. Title: Magnetic Impact of Propagating Interplanetary Coronal Mass Ejections in the Solar and Stellar Habitability Zones Authors: Georgoulis, M. K.; Samara, E.; Patsourakos, S. Bibcode: 2019AGUFMSH43A..05G Altcode: We recount recent results of a statistical method that assigns an axial magnetic field to CME flux ropes, inferred via the fundamental conservation principle of magnetic helicity in solar active region sources. We then extrapolate the near-Sun CME magnetic field to 1 AU, juxtaposing the extrapolation with tens of magnetic-cloud observations. Uncertainties given, we manage to statistically reproduce observations, thereby proposing a simple method that alleviates unnecessary complexity, while featuring applicability on a case-by-case basis. At a second level, we generalize CME magnetic configurations and stellar activity, expanding to flaring M-dwarf and Sun-like stars. We correlate the magnetic energy of stellar, assumed eruptive, flares with their helicity and extrapolate again to stellar habitable zones. From assumed planetary equatorial magnetic fields we predict atmospheric erosion by CME activity for a number of recently discovered exoplanets (Keppler 438b; Proxima b; the TRAPPIST system), thought promising for harboring life. Preliminary results show that knowledge of the planetary equatorial magnetic field can impose a valuable constraint for exoplanet habitability. Meanwhile, (1) terrestrial atmospheric erosion seems unlikely even for unrealistically intense solar eruptions and (2) the likelihood of absence of atmosphere due to CME-induced erosion in many of the studied exoplanets seems high. Title: Predicting the geoeffective properties of coronal mass ejections: current status, open issues and path forward Authors: Vourlidas, A.; Patsourakos, S.; Savani, N. P. Bibcode: 2019RSPTA.37780096V Altcode: Much progress has been made in the study of coronal mass ejections (CMEs), the main drivers of terrestrial space weather thanks to the deployment of several missions in the last decade. The flow of energy required to power solar eruptions is beginning to be understood. The initiation of CMEs is routinely observed with cadences of tens of seconds with arc-second resolution. Their inner heliospheric evolution can now be imaged and followed routinely. Yet relatively little progress has been made in predicting the geoeffectiveness of a particular CME. Why is that? What are the issues holding back progress in medium-term forecasting of space weather? To answer these questions, we review, here, the measurements, status and open issues on the main CME geoeffective parameters; namely, their entrained magnetic field strength and configuration, their Earth arrival time and speed, and their mass (momentum). We offer strategies for improving the accuracy of the measurements and their forecasting in the near and mid-term future. To spark further discussion, we incorporate our suggestions into a top-level draft action plan that includes suggestions for sensor deployment, technology development and modelling/theory improvements.

This article is part of the theme issue `Solar eruptions and their space weather impact'. Title: Sheared Magnetic Arcades and the Pre-eruptive Magnetic Configuration of Coronal Mass Ejections: Diagnostics, Challenges and Future Observables Authors: Patsourakos, Spiros; Vourlidas, A.; Anthiochos, S. K.; Archontis, V.; Aulanier, G.; Cheng, X.; Chintzoglou, G.; Georgoulis, M. K.; Green, L. M.; Kliem, B.; Leake, J.; Moore, R. L.; Nindos, A.; Syntelis, P.; Torok, T.; Yardley, S. L.; Yurchyshyn, V.; Zhang, J. Bibcode: 2019shin.confE.194P Altcode: Our thinking about the pre-eruptive magnetic configuration of Coronal Mass Ejections has been effectively dichotomized into two opposing and often fiercely contested views: namely, sheared magnetic arcades and magnetic flux ropes. Finding a solution to this issue will have important implications for our understanding of CME initiation. We first discuss the very value of embarking into the arcade vs. flux rope dilemma and illustrate the corresponding challenges and difficulties to address it. Next, we are compiling several observational diagnostics of pre-eruptive sheared magnetic arcades stemming from theory/modeling, discuss their merits, and highlight potential ambiguities that could arise in their interpretation. We finally conclude with a discussion of possible new observables, in the frame of upcoming or proposed instrumentation, that could help to circumvent the issues we are currently facing. Title: Deriving the Near-Sun Magnetic Field of Coronal Mass Ejections from Magnetic Helicity Conservation Authors: Patsourakos, Spiros; Georgoulis, M. K.; Petroulea, G.; Vourlidas, A.; Nieves-Chinchilla, T. Bibcode: 2019shin.confE.222P Altcode: The near-Sun magnetic field of Coronal Mass Ejections represents a key parameter for assessing their energetics and structuring, and additionally, it is a major element of methods/applications/simulations aiming to predict the magnetic field of Earth-directed CMEs upon impact at geospace. Diagnostics of CME magnetic fields in the corona can be achieved via observations in the radio domain, which however, are currently not available on a regular basis. Therefore, several methods to infer the CME magnetic field in the corona have recently emerged. We developed one such method which is based on the magnetic helicity conservation principle applied to flux rope CMEs. Its input parameters could be readily retrieved from the analysis of HMI magnetograms and SOHO/STEREO WL coronagraph images. We present parametric and case-study applications of this method, and discuss how it be could be used to predict the CME magnetic field magnitude at 1 AU. Title: ICSF: Intensity Conserving Spectral Fitting Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh Bibcode: 2019ascl.soft03007K Altcode: ICSF (Intensity Conserving Spectral Fitting) "corrects" (x,y) data in which the ordinate represents the average of a quantity over a finite interval in the abscissa. A typical example is spectral data, where the average intensity over a wavelength bin (the measured quantity) is assigned to the center of the bin. If the profile is curved, the average will be different from the discrete value at the bin center location. ICSF, written in IDL and available separately and as part of SolarSoft (ascl:1208.013), corrects the intensity using an iterative procedure and cubic spline. The corrected intensity equals the "true" intensity at bin center, rather than the average over the bin. Unlike other methods that are restricted to a single fitting function, typically a spline, ICSF can be used with any function, such as a cubic spline or a Gaussian, with slight changes to the code. Title: Modeling of the Sunspot-Associated Microwave Emission Using a New Method of DEM Inversion Authors: Alissandrakis, C. E.; Bogod, V. M.; Kaltman, T. I.; Patsourakos, S.; Peterova, N. G. Bibcode: 2019SoPh..294...23A Altcode: 2018arXiv181205751A We develope a method to compute the temperature and density structure along the line of sight by inversion of the differential emission measure (DEM), under the assumptions of stratification and hydrostatic equilibrium. We apply this method to the DEM obtained from the Atmospheric Imaging Assembly (AIA) observations and use the results, together with potential extrapolations of the photospheric magnetic field, to compute the microwave emission of three sunspots, which we compare with observations from the Academy of Sciences Radio Telescope - 600 (RATAN-600) radio telescope and the Nobeyama Radioheliograph (NoRH). Our DEM-based models reproduce very well the observations of the moderate-size spot on October 2011 and within 25% the data of a similar sized spot on March 2016, but predict too low values for the big spot of 14 April 2016. The latter is better fitted by a constant conductive flux atmospheric model which, however, cannot reproduce the peak brightness temperature of 4.7 ×106K and the shape of the source at the NoRH frequency. We propose that these deviations are due to the low intensity non-thermal emission associated to a moving pore and to an opposite polarity light bridge. We also find that the double structure of the big spot at high RATAN-600 frequencies can be interpreted in terms of the variation of the angle between the magnetic field and the line of sight along the sunspot. Title: First high-resolution look at the quiet Sun with ALMA at 3mm Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos, S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu, T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V. Bibcode: 2018A&A...619L...6N Altcode: 2018arXiv181005223N We present an overview of high-resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun regions were observed at a resolution of up to 2.5″ by 4.5″. We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full-disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by ∼305 K while the intranetwork is less bright by ∼280 K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 Å images, with somewhat larger size. We detect, for the first time, spicular structures, rising up to 15″ above the limb with a width down to the image resolution and brightness temperature of ∼1800 K above the local background. No trace of spicules, either in emission or absorption, is found on the disk. Our results highlight the potential of ALMA for the study of the quiet chromosphere. 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: A New Spin to Exoplanet Habitability Criteria Authors: Georgoulis, M. K.; Patsourakos, S. Bibcode: 2017AGUFM.P53E2676G Altcode: We describe a physically- and statistically-based method to infer the near-Sun magnetic field of coronal mass ejections (CMEs) and then extrapolate it to the inner heliosphere and beyond. Besides a ballpark agreement with in-situ observations of interplanetary CMEs (ICMEs) at L1, we use our estimates to show that Earth does not seem to be at risk of an extinction-level atmospheric erosion or stripping by the magnetic pressure of extreme solar eruptions, even way above a Carrington-type event. This does not seem to be the case with exoplanets, however, at least those orbiting in the classically defined habitability zones of magnetically active dwarf stars at orbital radii of a small fraction of 1 AU. We show that the combination of stellar ICMEs and the tidally locking zone of mother stars, that quite likely does not allow these exoplanets to attain Earth-like magnetic fields to shield themselves, probably render the existence of a proper atmosphere in them untenable. We propose, therefore, a critical revision of habitability criteria in these cases that would limit the number of target exoplanets considered as potential biosphere hosts. Title: Center-to-limb observations of the Sun with ALMA . Implications for solar atmospheric models Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian, T. S. Bibcode: 2017A&A...605A..78A Altcode:
Aims: We seek to derive information on the temperature structure of the solar chromosphere and compare these results with existing models.
Methods: We measured the center-to-limb variation of the brightness temperature, Tb, from ALMA full-disk images at two frequencies and inverted the solution of the transfer equation to obtain the electron temperature, Te as a function of optical depth, τ.
Results: The ALMA images are very similar to AIA images at 1600 Å. The brightness temperature at the center of the disk is 6180 and 7250 K at 239 and 100 GHz, respectively, with dispersions of 100 and 170 K. Plage regions stand out clearly in the 239/100 GHz intensity ratio, while faculae and filament lanes do not. The solar disk radius, reduced to 1 AU, is 961.1 ± 2.5'' and 964.1 ± 4.5'' at 239 and 100 GHz, respectively. A slight but statistically significant limb brightening is observed at both frequencies.
Conclusions: The inversion of the center-to-limb curves shows that Te varies linearly with the logarithm of optical depth for 0.34 <τ100 GHz< 12, with a slope dTe/ dlnτ = -608 K. Our results are 5% lower than predicted by the average quiet Sun model C of Fontenla et al. (1993, ApJ. 406, 319), but do not confirm previous reports that the mm-λ solar spectrum is better fitted with models of the cell interior. Title: A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability Authors: Patsourakos, S.; Georgoulis, M. K. Bibcode: 2017SoPh..292...89P Altcode: 2017arXiv170703579P Patsourakos et al. (Astrophys. J.817, 14, 2016) and Patsourakos and Georgoulis (Astron. Astrophys.595, A121, 2016) introduced a method to infer the axial magnetic field in flux-rope coronal mass ejections (CMEs) in the solar corona and farther away in the interplanetary medium. The method, based on the conservation principle of magnetic helicity, uses the relative magnetic helicity of the solar source region as input estimates, along with the radius and length of the corresponding CME flux rope. The method was initially applied to cylindrical force-free flux ropes, with encouraging results. We hereby extend our framework along two distinct lines. First, we generalize our formalism to several possible flux-rope configurations (linear and nonlinear force-free, non-force-free, spheromak, and torus) to investigate the dependence of the resulting CME axial magnetic field on input parameters and the employed flux-rope configuration. Second, we generalize our framework to both Sun-like and active M-dwarf stars hosting superflares. In a qualitative sense, we find that Earth may not experience severe atmosphere-eroding magnetospheric compression even for eruptive solar superflares with energies ≈104 times higher than those of the largest Geostationary Operational Environmental Satellite (GOES) X-class flares currently observed. In addition, the two recently discovered exoplanets with the highest Earth-similarity index, Kepler 438b and Proxima b, seem to lie in the prohibitive zone of atmospheric erosion due to interplanetary CMEs (ICMEs), except when they possess planetary magnetic fields that are much higher than that of Earth. Title: Evidence for two-loop interaction from IRIS and SDO observations of penumbral brightenings Authors: Alissandrakis, C. E.; Koukras, A.; Patsourakos, S.; Nindos, A. Bibcode: 2017A&A...603A..95A Altcode: 2017arXiv170407344A
Aims: We investigate small scale energy release events which can provide clues on the heating mechanism of the solar corona.
Methods: We analyzed spectral and imaging data from the Interface Region Imaging Spectrograph (IRIS), images from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamics Observatoty (SDO), and magnetograms from the Helioseismic and Magnetic Imager (HMI) aboard SDO.
Results: We report observations of small flaring loops in the penumbra of a large sunspot on July 19, 2013. Our main event consisted of a loop spanning 15'', from the umbral-penumbral boundary to an opposite polarity region outside the penumbra. It lasted approximately 10 min with a two minute impulsive peak and was observed in all AIA/SDO channels, while the IRIS slit was located near its penumbral footpoint. Mass motions with an apparent velocity of 100 km s-1 were detected beyond the brightening, starting in the rise phase of the impulsive peak; these were apparently associated with a higher-lying loop. We interpret these motions in terms of two-loop interaction. IRIS spectra in both the C II and Si iv lines showed very extended wings, up to about 400 km s-1, first in the blue (upflows) and subsequently in the red wing. In addition to the strong lines, emission was detected in the weak lines of Cl I, O I and C I, as well as in the Mg II triplet lines. Absorption features in the profiles of the C II doublet, the Si iv doublet and the Mg II h and k lines indicate the existence of material with a lower source function between the brightening and the observer. We attribute this absorption to the higher loop and this adds further credibility to the two-loop interaction hypothesis. Tilts were detected in the absorption spectra, as well as in the spectra of Cl I, O I, and C I lines, possibly indicating rotational motions from the untwisting of magnetic flux tubes.
Conclusions: We conclude that the absorption features in the C II, Si iv and Mg II profiles originate in a higher-lying, descending loop; as this approached the already activated lower-lying loop, their interaction gave rise to the impulsive peak, the very broad line profiles and the mass motions.

Movies associated to Figs. A.1-A.3 are available at http://www.aanda.org Title: Center-to-limb observations of the Sun with ALMA Authors: Alissandrakis, C. E.; Patsourakos, S.; Nindos, A.; Bastian, T. S. Bibcode: 2017arXiv170509008A Altcode: We measured the center-to-limb variation of the brightness temperature, $T_b$, from ALMA full-disk images at two frequencies and inverted the solution of the transfer equation to obtain the electron temperature, $T_e$ as a function of optical depth, $\tau$. The ALMA images are very similar to AIA images at 1600Å. The brightness temperature at the center of the disk is 6180 and 7250 K at 239 and 100 GHz respectively, with dispersions of 100 and 170 K. Plage regions stand out clearly in the 239/100 GHz intensity ratio, while faculae and filament lanes do not. The solar disk radius, reduced to 1 AU, is $961.1\pm2.5$ arcsec and $964.1\pm4.5$ arcsec at 239 and 100 GHz respectively. A slight but statistically significant limb brightening is observed at both frequencies. The inversion of the center-to-limb curves shows that $T_e$ varies linearly with the logarithm of optical depth for $0.34<\tau_{100\,GHz}<12$, with a slope $d\ln T_e/d\tau=-608$ K. Our results are 5% lower than predicted by the average quiet sun model C of Fontenla et al. (1993), but do not confirm previous reports that the mm-$\lambda$ solar spectrum is better fitted with models of the cell interior. Title: Near-Sun and 1 AU magnetic field of coronal mass ejections: a parametric study Authors: Patsourakos, S.; Georgoulis, M. K. Bibcode: 2016A&A...595A.121P Altcode: 2016arXiv160900134P
Aims: The magnetic field of coronal mass ejections (CMEs) determines their structure, evolution, and energetics, as well as their geoeffectiveness. However, we currently lack routine diagnostics of the near-Sun CME magnetic field, which is crucial for determining the subsequent evolution of CMEs.
Methods: We recently presented a method to infer the near-Sun magnetic field magnitude of CMEs and then extrapolate it to 1 AU. This method uses relatively easy to deduce observational estimates of the magnetic helicity in CME-source regions along with geometrical CME fits enabled by coronagraph observations. We hereby perform a parametric study of this method aiming to assess its robustness. We use statistics of active region (AR) helicities and CME geometrical parameters to determine a matrix of plausible near-Sun CME magnetic field magnitudes. In addition, we extrapolate this matrix to 1 AU and determine the anticipated range of CME magnetic fields at 1 AU representing the radial falloff of the magnetic field in the CME out to interplanetary (IP) space by a power law with index αB.
Results: The resulting distribution of the near-Sun (at 10 R⊙) CME magnetic fields varies in the range [0.004, 0.02] G, comparable to, or higher than, a few existing observational inferences of the magnetic field in the quiescent corona at the same distance. We also find that a theoretically and observationally motivated range exists around αB = -1.6 ± 0.2, thereby leading to a ballpark agreement between our estimates and observationally inferred field magnitudes of magnetic clouds (MCs) at L1.
Conclusions: In a statistical sense, our method provides results that are consistent with observations. Title: Solar Coronal Jets: Observations, Theory, and Modeling Authors: Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.; Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.; DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.; Meyer, K.; Dalmasse, K.; Matsui, Y. Bibcode: 2016SSRv..201....1R Altcode: 2016arXiv160702108R; 2016SSRv..tmp...31R Coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of "nominal" solar flares and coronal mass ejections (CMEs), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar-heliospheric problems. Title: A Robust Method to Predict the Near-Sun and Interplanetary Magnetic Field Strength of Coronal Mass Ejections: Parametric and Case Studies Authors: Patsourakos, Spiros; Georgoulis, Manolis K. Bibcode: 2016cosp...41E1531P Altcode: Predicting the near-Sun, and particularly the Interplanetary (IP), magnetic field structure of Coronal Mass Ejections (CMEs) and interplanetary counterparts (ICMEs) is a topic of intense research activity. This is because Earth-directed CMEs with strong southward magnetic fields are responsible for the most powerful geomagnetic storms. We have recently developed a simple two-tier method to predict the magnetic field strength of CMEs in the outer corona and in the IP medium, using as input the magnetic-helicity budget of the source solar active region and stereoscopic coronagraphic observations. Near-Sun CME magnetic fields are obtained by utilizing the principle of magnetic helicity conservation of flux-rope CMEs for coronagraphic observations. Interplanetary propagation of the inferred values is achieved by employing power-law prescriptions of the radial evolution of the CME-ICME magnetic fields. We hereby present a parametric study of our method, based on the observed statistics of input parameters, to infer the anticipated range of values for the near-Sun and interplanetary CME-ICME magnetic fields. This analysis is complemented by application of our method to several well-observed major CME-ICME events. Title: The 3D structure of Coronal Mass Ejections Authors: Patsourakos, Spiros Bibcode: 2016cosp...41E1532P Altcode: Coronal Mass Ejections (CMEs) represent one of the most powerful energy release phenomena in the entire solar system and are a major driver of space weather. Prior to 2006, our observational access to CMEs was limited to single viewpoint remote sensing observations in the inner/outer corona, and in-situ observations further away, e.g. at 1 AU. Taking all these factors together, turned out to be a major obstacle in our understanding and characterizing of the 3D structure and evolution of CMEs. The situation improved dramatically with the availability of multi-viewpoint imaging observations of CMEs, all way through from the Sun to 1 AU, from the STEREO mission since 2006, combined with observations from other missions (SOHO, Hinode, SDO, IRIS). With this talk we will discuss several key recent results in CME science resulting from the analysis of multi-viewpoint observations. This includes: (1) shape and structure; (2) kinematics and energetics; (3) trajectories, deflections and rotations; (4) arrival times and velocities at 1 AU; (5) magnetic field structure; (6) relationships with coronal and interplanetary shocks and solar energetic particles. The implications of these results in terms of CME theories and models will be also addressed. We will conclude with a discussion of important open issues in our understanding of CMEs and how these could be addressed with upcoming (Solar Orbiter, Solar Probe Plus) and under-study missions (e.g., L5). Title: Coronal Mass Ejections: From Sun to Earth Authors: Patsourakos, S. Bibcode: 2016Hipp....2m..17P Altcode: Coronal Mass Ejections (CMEs) are gigantic expulsions of magnetized plasmas from the solar corona into the interplanetary (IP) space. CMEs spawn ~ 1015 gr of mass and reach speeds ranging between several hundred to a few thousand km/s (e.g., Gopalswamy et al. 2009; Vourlidas et al. 2010). It takes 1-5 days for a CME to reach Earth. CMEs are one of the most energetic eruptive manifestations in the solar system and are major drivers of space weather via their magnetic fields and energetic particles, which are accelerated by CME-driven shocks. In this review we give a short account of recent, mainly observational, results on CMEs from the STEREO and SDO missions which include the nature of their pre-eruptive and eruptive configurations and the CME propagation from Sun to Earth. We conclude with a discussion of the exciting capabilities in CME studies that will soon become available from new solar and heliospheric instrumentation. Title: Multi-viewpoint Observations of a Widely distributed Solar Energetic Particle Event: The Role of EUV Waves and White-light Shock Signatures Authors: Kouloumvakos, A.; Patsourakos, S.; Nindos, A.; Vourlidas, A.; Anastasiadis, A.; Hillaris, A.; Sandberg, I. Bibcode: 2016ApJ...821...31K Altcode: On 2012 March 7, two large eruptive events occurred in the same active region within 1 hr from each other. Each consisted of an X-class flare, a coronal mass ejection (CME), an extreme-ultraviolet (EUV) wave, and a shock wave. The eruptions gave rise to a major solar energetic particle (SEP) event observed at widely separated (∼120°) points in the heliosphere. From multi-viewpoint energetic proton recordings we determine the proton release times at STEREO B and A (STB, STA) and the first Lagrange point (L1) of the Sun-Earth system. Using EUV and white-light data, we determine the evolution of the EUV waves in the low corona and reconstruct the global structure and kinematics of the first CME’s shock, respectively. We compare the energetic proton release time at each spacecraft with the EUV waves’ arrival times at the magnetically connected regions and the timing and location of the CME shock. We find that the first flare/CME is responsible for the SEP event at all three locations. The proton release at STB is consistent with arrival of the EUV wave and CME shock at the STB footpoint. The proton release time at L1 was significantly delayed compared to STB. Three-dimensional modeling of the CME shock shows that the particle release at L1 is consistent with the timing and location of the shock’s western flank. This indicates that at L1 the proton release did not occur in low corona but farther away from the Sun. However, the extent of the CME shock fails to explain the SEP event observed at STA. A transport process or a significantly distorted interplanetary magnetic field may be responsible. Title: The spectroscopic imprint of the pre-eruptive configuration resulting into two major coronal mass ejections Authors: Syntelis, P.; Gontikakis, C.; Patsourakos, S.; Tsinganos, K. Bibcode: 2016A&A...588A..16S Altcode: 2016arXiv160203680S
Aims: We present a spectroscopic analysis of the pre-eruptive configuration of active region NOAA 11429, prior to two very fast coronal mass ejections (CMEs) on March 7, 2012 that are associated with this active region. We study the thermal components and the dynamics associated with the ejected flux ropes.
Methods: Using differential emission measure (DEM) analysis of Hinode/EIS and SDO/AIA observations, we identify the emission components of both the flux rope and the host active region. We then follow the time evolution of the flux rope emission components by using AIA observations. The plasma density and the Doppler and non-thermal velocities associated with the flux ropes are also calculated from the EIS data.
Results: The eastern and western parts of the active region, in which the two different fast CMEs originated during two X-class flares, were studied separately. In both regions we identified an emission component in the temperature range of log T = 6.8-7.1 associated with the presence of flux ropes. The time evolution of the eastern region showed an increase in the mean DEM in this temperature range by an order of magnitude, 5 h prior to the first CME. This was associated with a gradual rise and heating of the flux rope as manifested by blue-shifts and increased non-thermal velocities in Ca xv 200.97 Å, respectively. An overall upward motion of the flux ropes was measured (relative blue-shifts of ~ 12 km s-1). The measured electron density was found to be 4 × 109-2 × 1010 cm-3 (using the ratio of Ca xv 181.90 Å over Ca xv 200.97 Å). We compare our findings with other works on the same AR to provide a unified picture of its evolution. Title: Predicting the near-Sun and Interplanetary Magnetic Field of CMEs using photospheric magnetograms and coronagraph images Authors: Patsourakos, Spiros; Georgoulis, Manolis Bibcode: 2016EGUGA..18.4784P Altcode: Earth-directed Coronal Mass Ejections (CMEs) containing a strong southward magnetic-field component upon arrival at 1 AU statistically account for the most powerful geomagnetic storms. Unfortunately, though, we currently lack routine diagnostics of the magnetic field of CMEs and its evolution in the inner heliosphere and the interplanetary (IP) medium. We hereby present a simple, yet powerful and easy-to-implement, method to deduce the near-Sun and IP magnetic field entrained in CMEs, by using photospheric magnetograms of the solar source regions and multi-viewpoint coronagraph images of the corresponding CMEs. The method relies on the principle of magnetic-helicity conservation in low plasma-beta, flux-rope CMEs and a power-law prescription of the radial evolution of the CME magnetic field in the IP medium. We outline a parametric study based on the observed statistics of input parameters to calculate a matrix of magnetic-field solutions for 10000 synthetic CMEs. The robustness and possible limitations / ramifications of the method are deduced by a comparison with the distributions of the predicted CME-ICME magnetic fields at 0.3 and 1 AU using actual Messenger and ACE published observations. Title: The Major Geoeffective Solar Eruptions of 2012 March 7: Comprehensive Sun-to-Earth Analysis Authors: Patsourakos, S.; Georgoulis, M. K.; Vourlidas, A.; Nindos, A.; Sarris, T.; Anagnostopoulos, G.; Anastasiadis, A.; Chintzoglou, G.; Daglis, I. A.; Gontikakis, C.; Hatzigeorgiu, N.; Iliopoulos, A. C.; Katsavrias, C.; Kouloumvakos, A.; Moraitis, K.; Nieves-Chinchilla, T.; Pavlos, G.; Sarafopoulos, D.; Syntelis, P.; Tsironis, C.; Tziotziou, K.; Vogiatzis, I. I.; Balasis, G.; Georgiou, M.; Karakatsanis, L. P.; Malandraki, O. E.; Papadimitriou, C.; Odstrčil, D.; Pavlos, E. G.; Podlachikova, O.; Sandberg, I.; Turner, D. L.; Xenakis, M. N.; Sarris, E.; Tsinganos, K.; Vlahos, L. Bibcode: 2016ApJ...817...14P Altcode: During the interval 2012 March 7-11 the geospace experienced a barrage of intense space weather phenomena including the second largest geomagnetic storm of solar cycle 24 so far. Significant ultra-low-frequency wave enhancements and relativistic-electron dropouts in the radiation belts, as well as strong energetic-electron injection events in the magnetosphere were observed. These phenomena were ultimately associated with two ultra-fast (>2000 km s-1) coronal mass ejections (CMEs), linked to two X-class flares launched on early 2012 March 7. Given that both powerful events originated from solar active region NOAA 11429 and their onsets were separated by less than an hour, the analysis of the two events and the determination of solar causes and geospace effects are rather challenging. Using satellite data from a flotilla of solar, heliospheric and magnetospheric missions a synergistic Sun-to-Earth study of diverse observational solar, interplanetary and magnetospheric data sets was performed. It was found that only the second CME was Earth-directed. Using a novel method, we estimated its near-Sun magnetic field at 13 R⊙ to be in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun CME magnetic field are required to match the magnetic fields of the corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream solar-wind conditions, as resulting from the shock associated with the Earth-directed CME, offer a decent description of its kinematics. The magnetospheric compression caused by the arrival at 1 AU of the shock associated with the ICME was a key factor for radiation-belt dynamics. Title: Intensity Conserving Spectral Fitting Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D. Bibcode: 2016SoPh..291...55K Altcode: 2015SoPh..tmp..180K The detailed shapes of spectral-line profiles provide valuable information about the emitting plasma, especially when the plasma contains an unresolved mixture of velocities, temperatures, and densities. As a result of finite spectral resolution, the intensity measured by a spectrometer is the average intensity across a wavelength bin of non-zero size. It is assigned to the wavelength position at the center of the bin. However, the actual intensity at that discrete position will be different if the profile is curved, as it invariably is. Standard fitting routines (spline, Gaussian, etc.) do not account for this difference, and this can result in significant errors when making sensitive measurements. We have developed an iterative procedure that corrects for this effect. It converges rapidly and is very flexible in that it can be used with any fitting function. We present examples of cubic-spline and Gaussian fits and give special attention to measurements of blue-red asymmetries of coronal emission lines. Title: EUV Coronal Waves: Atmospheric and Heliospheric Connections and Energetics Authors: Patsourakos, S. Bibcode: 2015AGUFMSH22A..03P Altcode: Since their discovery in late 90's by EIT on SOHO, the study EUV coronal waves has been a fascinating andfrequently strongly debated research area. While it seems as ifan overall consensus has been reached about the nurture and nature of this phenomenon,there are still several important questions regarding EUV waves. By focusing on the most recentobservations, we will hereby present our current understanding about the nurture and nature of EUV waves,discuss their connections with other atmospheric and heliospheric phenomena (e.g.,flares and CMEs, Moreton waves, coronal shocks, coronal oscillations, SEP events) and finallyassess their possible energetic contribution to the overall budget of relatederuptive phenomena. Title: North-south asymmetry in the magnetic deflection of polar coronal hole jets Authors: Nisticò, G.; Zimbardo, G.; Patsourakos, S.; Bothmer, V.; Nakariakov, V. M. Bibcode: 2015A&A...583A.127N Altcode: 2015arXiv150801072N Context. Measurements of the sunspots area, of the magnetic field in the interplanetary medium, and of the heliospheric current sheet (HCS) position, reveal a possible north-south (N-S) asymmetry in the magnetic field of the Sun. This asymmetry could cause the bending of the HCS of the order of 5-10 deg in the southward direction, and it appears to be a recurrent characteristic of the Sun during the minima of solar activity.
Aims: We study the N-S asymmetry as inferred from measurements of the deflection of polar coronal hole jets when they propagate throughout the corona.
Methods: Since the corona is an environment where the magnetic pressure is greater than the kinetic pressure (β ≪ 1), we can assume that the magnetic field controls the dynamics of plasma. On average, jets follow magnetic field lines during their propagation, highlighting their local direction. We measured the position angles at 1 R⊙ and at 2 R⊙ of 79 jets, based on the Solar TErrestrial RElations Observatory (STEREO) ultraviolet and white-light coronagraph observations during the solar minimum period March 2007-April 2008. The average jet deflection is studied both in the plane perpendicular to the line of sight and, for a reduced number of jets, in 3D space. The observed jet deflection is studied in terms of an axisymmetric magnetic field model comprising dipole (g1), quadrupole (g2), and esapole (g3) moments.
Results: We found that the propagation of the jets is not radial, which is in agreement with the deflection due to magnetic field lines. Moreover, the amount of the deflection is different between jets over the north and those from the south pole. A comparison of jet deflections and field line tracing shows that a ratio g2/g1 ≃ -0.5 for the quadrupole and a ratio g3/g1 ≃ 1.6-2.0 for the esapole can describe the field. The presence of a non-negligible quadrupole moment confirms the N-S asymmetry of the solar magnetic field for the considered period.
Conclusions: We find that the magnetic deflection of jets is larger in the north than in the south of the order of 25-40%, with an asymmetry that is consistent with a southward deflection of the heliospheric current sheet of the order of 10 deg, consistent with that inferred from other independent datasets and instruments. Title: A tiny event producing an interplanetary type III burst Authors: Alissandrakis, C. E.; Nindos, A.; Patsourakos, S.; Kontogeorgos, A.; Tsitsipis, P. Bibcode: 2015A&A...582A..52A Altcode: 2015arXiv150708423A
Aims: We investigate the conditions under which small-scale energy release events in the low corona gave rise to strong interplanetary (IP) type III bursts.
Methods: We analyzed observations of three tiny events, detected by the Nançay Radio Heliograph (NRH), two of which produced IP type III bursts. We took advantage of the NRH positioning information and of the high cadence of AIA/SDO data to identify the associated extreme-UV (EUV) emissions. We measured positions and time profiles of the metric and EUV sources.
Results: We found that the EUV events that produced IP type III bursts were located near a coronal hole boundary, while the one that did not was located in a closed magnetic field region. In all three cases tiny flaring loops were involved, without any associated mass eruption. In the best observed case, the radio emission at the highest frequency (435 MHz) was displaced by ~55'' with respect to the small flaring loop. The metric type III emission shows a complex structure in space and in time, indicative of multiple electron beams, despite the low intensity of the events. From the combined analysis of dynamic spectra and NRH images, we derived the electron beam velocity as well as the height, ambient plasma temperature, and density at the level of formation of the 160 MHz emission. From the analysis of the differential emission measure derived from the AIA images, we found that the first evidence of energy release was at the footpoints, and this was followed by the development of flaring loops and subsequent cooling.
Conclusions: Even small energy release events can accelerate enough electrons to give rise to powerful IP type III bursts. The proximity of the electron acceleration site to open magnetic field lines facilitates the escape of the electrons into the interplanetary space. The offset between the site of energy release and the metric type III location warrants further investigation.

The movie is available in electronic form at http://www.aanda.org Title: Formation of Magnetic Flux Ropes during a Confined Flaring Well before the Onset of a Pair of Major Coronal Mass Ejections Authors: Chintzoglou, Georgios; Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2015ApJ...809...34C Altcode: 2015arXiv150701165C NOAA active region (AR) 11429 was the source of twin super-fast coronal mass ejections (CMEs). The CMEs took place within an hour from each other, with the onset of the first taking place in the beginning of 2012 March 7. This AR fulfills all the requirements for a “super active region” namely, Hale's law incompatibility and a δ-spot magnetic configuration. One of the biggest storms of Solar Cycle 24 to date ({D}{st}=-143 nT) was associated with one of these events. Magnetic flux ropes (MFRs) are twisted magnetic structures in the corona, best seen in ∼10 MK hot plasma emission and are often considered the core of erupting structures. However, their “dormant” existence in the solar atmosphere (i.e., prior to eruptions), is an open question. Aided by multi-wavelength observations by the Solar Dynamics Observatory (SDO) and by the Solar Terrestrial Relations Observatory (STEREO) and a nonlinear force-free model for the coronal magnetic field, our work uncovers two separate, weakly twisted magnetic flux systems which suggest the existence of pre-eruption MFRs that eventually became the seeds of the two CMEs. The MFRs could have been formed during confined (i.e., not leading to major CMEs) flaring and sub-flaring events which took place the day before the two CMEs in the host AR 11429. Title: How Common Are Hot Magnetic Flux Ropes in the Low Solar Corona? A Statistical Study of EUV Observations Authors: Nindos, A.; Patsourakos, S.; Vourlidas, A.; Tagikas, C. Bibcode: 2015ApJ...808..117N Altcode: 2015arXiv150703766N We use data at 131, 171, and 304 Å from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory to search for hot flux ropes in 141 M-class and X-class solar flares that occurred at solar longitudes equal to or larger than 50°. Half of the flares were associated with coronal mass ejections. The goal of our survey is to assess the frequency of hot flux ropes in large flares irrespective of their formation time relative to the onset of eruptions. The flux ropes were identified in 131 Å images using morphological criteria and their high temperatures were confirmed by their absence in the cooler 171 and 304 Å passbands. We found hot flux ropes in 45 of our events (32% of the flares); 11 of them were associated with confined flares while the remaining 34 were associated with eruptive flares. Therefore almost half (49%) of the eruptive events involved a hot flux rope configuration. The use of supplementary Hinode X-Ray Telescope data indicates that these percentages should be considered as lower limits of the actual rates of occurrence of hot flux ropes in large flares. Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool for Spectroscopic Analysis Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh Bibcode: 2015TESS....120309K Altcode: 2015arXiv150608102K Spectroscopy is an extremely powerful tool for diagnosing astrophysical and other plasmas. For example, the shapes of line profiles provide valuable information on the distribution of velocities along an optically thin line-of-sight and across the finite area of a resolution element. A number of recent studies have measured the asymmetries of line profiles in order to detect faint high-speed upflows, perhaps associated with coronal nanoflares or perhaps associated with chromospheric nanoflares and type II spicules. Over most of the Sun, these asymmetries are very subtle, so great care must be taken. A common technique is to perform a spline fit of the points in the profile in order to extract information at a spectral resolution higher than that of the original data. However, a fundamental problem is that the fits do not conserve intensity. We have therefore developed an iterative procedure called Intensity Conserving Spline Interpolation that does preserve the observed intensity within each wavelength bin. It improves the measurement of line asymmetries and can also help with the determination of line blends. Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool for Spectroscopic Analysis Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D. Bibcode: 2014AGUFMSH13B4109K Altcode: Spectroscopy is an extremely powerful tool for diagnosing astrophysical and other plasmas. For example, the shapes of line profiles provide valuable information on the distribution of velocities along an optically thin line-of-sight and across the finite area of a resolution element. A number of recent studies have measured the asymmetries of line profiles in order to detect faint high-speed upflows, perhaps associated with coronal nanoflares or perhaps associated with chromospheric nanoflares and type II spicules. Over most of the Sun, these asymmetries are very subtle, so great care must be taken. A common technique is to perform a spline fit of the points in the profile in order to extract information at a spectral resolution higher than that of the original data. However, a fundamental problem is that the fits do not conserve intensity. We have therefore developed an iterative procedure called Intensity Conserving Spline Interpolation that does preserve the observed intensity within each wavelength bin. It improves the measurement of line asymmetries and can also help with the determination of line blends. Title: CME Expansion as the Driver of Metric Type II Shock Emission as Revealed by Self-consistent Analysis of High-Cadence EUV Images and Radio Spectrograms Authors: Kouloumvakos, A.; Patsourakos, S.; Hillaris, A.; Vourlidas, A.; Preka-Papadema, P.; Moussas, X.; Caroubalos, C.; Tsitsipis, P.; Kontogeorgos, A. Bibcode: 2014SoPh..289.2123K Altcode: 2013arXiv1311.5159K On 13 June 2010, an eruptive event occurred near the solar limb. It included a small filament eruption and the onset of a relatively narrow coronal mass ejection (CME) surrounded by an extreme ultraviolet (EUV) wave front recorded by the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) at high cadence. The ejection was accompanied by a GOES M1.0 soft X-ray flare and a Type-II radio burst; high-resolution dynamic spectra of the latter were obtained by the Appareil de Routine pour le Traitement et l'Enregistrement Magnetique de l'Information Spectral (ARTEMIS IV) radio spectrograph. The combined observations enabled a study of the evolution of the ejecta and the EUV wave front and its relationship with the coronal shock manifesting itself as metric Type-II burst. By introducing a novel technique, which deduces a proxy of the EUV compression ratio from AIA imaging data and compares it with the compression ratio deduced from the band-split of the Type-II metric radio burst, we are able to infer the potential source locations of the radio emission of the shock on that AIA images. Our results indicate that the expansion of the CME ejecta is the source for both EUV and radio shock emissions. Early in the CME expansion phase, the Type-II burst seems to originate in the sheath region between the EUV bubble and the EUV shock front in both radial and lateral directions. This suggests that both the nose and the flanks of the expanding bubble could have driven the shock. Title: Rapid CME Cavity Formation and Expansion Authors: Kliem, Bernhard; Forbes, Terry G.; Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2014AAS...22421206K Altcode: A cavity is supposed to be a general feature of well-developed CMEs at the stage they can be imaged by white-light coronagraphs (in the outer corona and solar wind). The cavity is interpreted as the cross section of the CME flux rope in the plane of sky. Preexisting cavities are observed around some quiescent erupting prominences, but usually not in active regions. Observations of CME cavities in the inner corona, where most of them appear to form, have become possible only with the STEREO and SDO missions. These reveal a very rapid formation and expansion of "EUV cavities" in fast and impulsively commencing eruptions early in the phase of main CME acceleration and impulsive flare rise. Different from the white-light observations, the EUV cavity initially appears to be larger than the CME flux rope. However, it evolves into the white-light cavity subsequently. MHD simulations of flux rope eruptions conform to this picture of initially larger cavity but subsequently approaching cavity and flux rope size. The initial expansion of ambient flux can be understood as a "reverse pinch effect", driven by decreasing flux rope current as the rope rises. Title: Independent CMEs from a Single Solar Active Region - The Case of the Super-Eruptive NOAA AR11429 Authors: Chintzoglou, Georgios; Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2014AAS...22432328C Altcode: In this investigation we study AR 11429, the origin of the twin super-fast CME eruptions of 07-Mar-2012. This AR fulfills all the requirements for the 'perfect storm'; namely, Hale's law incompatibility and a delta-magnetic configuration. In fact, during its limb-to-limb transit, AR 11429 spawned several eruptions which caused geomagnetic storms, including the biggest in Cycle 24 so far. Magnetic Flux Ropes (MFRs) are twisted magnetic structures in the corona, best seen in ~10MK hot plasma emission and are often considered as the culprit causing such super-eruptions. However, their 'dormant' existence in the solar atmosphere (i.e. prior to eruptions), is a matter of strong debate. Aided by multi-wavelength and multi-spacecraft observations (SDO/HMI & AIA, HINODE/SOT/SP, STEREO B/EUVI) and by using a Non-Linear Force-Free (NLFFF) model for the coronal magnetic field, our work shows two separate, weakly-twisted magnetic flux systems which suggest the existence of possible pre-eruption MFRs. Title: Core and Wing Densities of Asymmetric Coronal Spectral Profiles: Implications for the Mass Supply of the Solar Corona Authors: Patsourakos, S.; Klimchuk, J. A.; Young, P. R. Bibcode: 2014ApJ...781...58P Altcode: 2013arXiv1312.4842P Recent solar spectroscopic observations have shown that coronal spectral lines can exhibit asymmetric profiles, with enhanced emissions at their blue wings. These asymmetries correspond to rapidly upflowing plasmas at speeds exceeding ≈50 km s-1. Here, we perform a study of the density of the rapidly upflowing material and compare it with that of the line core that corresponds to the bulk of the plasma. For this task, we use spectroscopic observations of several active regions taken by the Extreme Ultraviolet Imaging Spectrometer of the Hinode mission. The density sensitive ratio of the Fe XIV lines at 264.78 and 274.20 Å is used to determine wing and core densities. We compute the ratio of the blue wing density to the core density and find that most values are of order unity. This is consistent with the predictions for coronal nanoflares if most of the observed coronal mass is supplied by chromospheric evaporation driven by the nanoflares. However, much larger blue wing-to-core density ratios are predicted if most of the coronal mass is supplied by heated material ejected with type II spicules. Our measurements do not rule out a spicule origin for the blue wing emission, but they argue against spicules being a primary source of the hot plasma in the corona. We note that only about 40% of the pixels where line blends could be safely ignored have blue wing asymmetries in both Fe XIV lines. Anticipated sub-arcsecond spatial resolution spectroscopic observations in future missions could shed more light on the origin of blue, red, and mixed asymmetries. Title: North-South Asymmetry in the Magnetic Deflection of Polar Coronal Jets Authors: Nisticò, Giuseppe; Zimbardo, Gaetano; Bothmer, Volker; Patsourakos, Spiros Bibcode: 2014cosp...40E2295N Altcode: Solar jets observed with the Extreme Ultra-Violet Imager (EUVI) and CORonagraphs (COR) instruments aboard the STEREO mission provide a tool to probe and understand the magnetic structure of the corona. Since the corona is an environment where the magnetic pressure is greater than the kinetic pressure, the magnetic field controls the dynamics of plasma and, on average, jets during their propagation trace the magnetic field lines. We discuss the North-South asymmetry of the magnetic field of the Sun as inferred from measurements of the deflection of polar coronal hole jets when they propagate throughout the corona. We measured the position angle at 1 and at 2 solar radii for the 79 jets of the catalogue of Nisticò et al. (2009), based on the STEREO ultraviolet and visible observations, and we found that the propagation is not radial. The average jet deflection is studied both in the plane perpendicular to the line of sight, and, for a reduced number of jets in the three dimensional (3D) space. We find that the magnetic deflection of jets is larger in the North than in the South, with an asymmetry which is consistent with the N-S asymmetry of the heliospheric magnetic field inferred from the Ulysses in situ measurements, and gives clues to the study of the large scale solar magnetic field. Title: Observations of CMEs-ICMEs: Results from Current Space Missions and Expectations from Future Instrumentation Authors: Patsourakos, Spiros Bibcode: 2014cosp...40E2464P Altcode: Our understanding of the physics of CMEs and ICMEs has been substantially improved over the last 20 years, thanks particularly to a stream of space missions. While many questions regarding CMEs and ICMEs have been resolved there are still some important pending questions. With this talk we will focus on two important problems of CME and ICME physics, namely the determination of the CME pre-erupting structures and the physical processes behind their initiation as well as the properties of CME-ICME propagation in the IP medium. We will supply a review of recent results related to these two areas and discuss specific examples of how progress from future instrumentation may be expected. Title: Sun-to-Earth Analysis of a Major Solar Eruption Authors: Patsourakos, Spiros Bibcode: 2014cosp...40E2465P Altcode: During the interval of 7-10 March 2012, Earth's space environment experienced a barrage of space weather phenomena. Early during 7 March 2012, the biggest proton event of 2012 took place, while on 8 March 2012, an interplanetary shock and coronal mass ejection (CME) arrived at 1 AU. This sequence trigerred the biggest geomagnetic storm of cycle 24 so far. The solar source of these activities was a pair of homologous, eruptive X-class flares associated with two ultra-fast CMEs. The two eruptions originated from NOAA active region 11429 during the early hours of 7 March 2012 and within an hour from each other. Using satellite data from a flotilla of solar, heliospheric and magnetospheric missions and monitors, we perform a synergistic Sun-to-Earth study of various observational aspects of the event sequences. We will present an attempt to formulate a cohesive scenario which couples the eruption initiation, interplanetary propagation, and geospace consequences. Our main focus is on building a framework that starting from solar and near-Sun estimates of the magnetic and dynamic content and properties of the Earth-directed CME assess in advance the subsequent geomagnetic response expected, once the associated interplanetary CME reaches 1 AU. This research has been co-financed by the European Union (European Social Fund - ESF) and Greek national funds through the Operational Program "Education and Lifelong Learning" of the National Strategic Reference Framework (NSRF) - Research Funding Program: Thales. Investing in knowledge society through the European Social Fund. Title: Microwave and EUV Observations of an Erupting Filament and Associated Flare and Coronal Mass Ejections Authors: Alissandrakis, Costas E.; Kochanov, Alexey A.; Patsourakos, Spiros; Altyntsev, Alexander T.; Lesovoi, Sergey V.; Lesovoya, Nadya N. Bibcode: 2013PASJ...65S...8A Altcode: 2013arXiv1309.1703A A filament eruption was observed with the Siberian Solar Radio Telescope (SSRT) on 2012 June 23, starting at around 06:40 UT, beyond the west limb. The filament could be followed in SSRT images to heights above 1 R⊙, and coincided with the core of the CME, seen in LASCO C2 images. We briefly discuss the dynamics of the eruption: the top of the filament showed a smooth acceleration up to an apparent velocity of ∼ 1100 km s-1. Images behind the limb from STEREO-A show a two-ribbon flare and the interaction of the main filament, located along the primary neutral line, with an arch-like structure, oriented in the perpendicular direction. The interaction was accompanied by strong emission and twisting motions. The microwave images show a low-temperature component, a high-temperature component associated with the interaction of the two filaments and another high-temperature component apparently associated with the top of flare loops. We computed the differential emission measure from the high-temperature AIA bands and from this the expected microwave brightness temperature; for emission associated with the top of the flare loops, the computed brightness was 35% lower than the observed value. Title: Parametric study of drag force acting on interplanetary CME Authors: Podladchikova, O.; Patsourakos, S.; Nindos, A. Bibcode: 2013hell.confR..22P Altcode: The interaction of an interplanetary coronal mass ejection (ICME) with the solar wind leads to an equalisation of the ICME and solar wind velocities at 1 AU. The forces acting on ICMEs have been evaluated so far in terms of an empirical drag coefficient C_D ~ 1 that describes the aerodynamic drag experienced by a typical ICME due to its interaction with the ambient solar wind. The consideration of viscous drag coefficients due to proton-magnetic kink encounters is more realistic for solar wind turbulence. We compare aerodynamic and viscous drag description and their impact on ICME propagation in solar wind. We also consider the impact of ICME distortions to their kinematics as they propagate in the inner heliosphere. Title: The spatial relationship between coronal mass ejections and solar flares Authors: Nikou, E.; Nindos, A.; Patsourakos, S. Bibcode: 2013hell.conf...21N Altcode: Using 19 well-observed eruptions that gave both coronal mass ejections (CMEs) and flares, we quantified the spatial relationship between pairs of CMEs and associated flares. The flare and CME source locations were identified using images obtained at 174 A by the SWAP instrument aboard PROBA 2 satellite. The SWAP data are suitable for this study because flare emission does not saturate much. To reduce saturation even more, our database did not contain any M-class or X-class flare events. We selected eruptions that occurred close to disk center, as viewed from Earth, whereas they appeared as limb events in images obtained by the EUV Imagers (EUVI) aboard the SECCHI/STEREO spacecraft. The centroids of the CME-associated EUV dimmings in the SWAP images were used as proxies for the CME source locations. For each event, we compared the location of the flare brightenings with the location of the dimmings' centroid at the time of CME initiation which was determined from the EUVI data. In six cases the CME location was cospatial with flare brightenings while in the remaining cases the distance between each pair of flare-CME locations varied from 4 to 191 arcsecs with a median value of 71 arcsecs. Furthermore, we investigated the CME source locations with respect to the underlying magnetic field structures. Title: Particle acceleration and nanoflare heating in coronal loops Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.; Anastasiadis, A.; Georgoulis, M. Bibcode: 2013hell.conf...18G Altcode: We model nanoflare heating of extrapolated active-region coronal loops via the acceleration of electrons and protons in Harris-type current sheets. The kinetic energy of the accelerated particles is estimated using semi-analytical and test-particle-tracing approaches. Vector magnetograms and photospheric Doppler velocity maps of NOAA active region 09114, recorded by the Imaging Vector Magnetograph (IVM), were used for this analysis in order to compute a current-free field extrapolation of the active-region corona. The corresponding Poynting fluxes at the footpoints of 5000 extrapolated coronal loops were then calculated. Assuming that reconnecting current sheets develop along these loops, we utilized previous results to estimate the kinetic-energy gain of the accelerated particles and we related this energy to nanoflare heating and macroscopic loop characteristics. Kinetic energies of 0.1 to 8~keV (for electrons) and 0.3 to 470~keV (for protons) were found to cause heating rates ranging from 10^-6 to 1 erg s^-1 cm^-3. Hydrodynamic simulations show that such heating rates can sustain plasma in coronal conditions inside the loops and generate plasma thermal distributions which are consistent with active region observations. We concluded the analysis by computing the form of Xray spectra generated by the accelerated electrons using the thick target approach that were found to be in agreement with observed X-ray spectra, thus supporting the plausibility of our nanoflare-heating scenario. 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: Sun-to-Earth Analysis of a Major Geoeffective Solar Eruption within the Framework of the Authors: Patsourakos, S.; Vlahos, L.; Georgoulis, M.; Tziotziou, K.; Nindos, A.; Podladchikova, O.; Vourlidas, A.; Anastasiadis, A.; Sandberg, I.; Tsinganos, K.; Daglis, I.; Hillaris, A.; Preka-Papadema, P.; Sarris, M.; Sarris, T. Bibcode: 2013hell.conf...10P Altcode: Transient expulsions of gigantic clouds of solar coronal plasma into the interplanetary space in the form of Coronal Mass Ejections (CMEs) and sudden, intense flashes of electromagnetic radiation, solar flares, are well-established drivers of the variable Space Weather. Given the innate, intricate links and connections between the solar drivers and their geomagnetic effects, synergistic efforts assembling all pieces of the puzzle along the Sun-Earth line are required to advance our understanding of the physics of Space Weather. This is precisely the focal point of the Hellenic National Space Weather Research Network (HNSWRN) under the THALIS Programme. Within the HNSWRN framework, we present here the first results from a coordinated multi-instrument case study of a major solar eruption (X5.4 and X1.3 flares associated with two ultra-fast (>2000 km/s) CMEs) which were launched early on 7 March 2012 and triggered an intense geomagnetic storm (min Dst =-147 nT) approximately two days afterwards. Several elements of the associated phenomena, such as the flare and CME, EUV wave, WL shock, proton and electron event, interplanetary type II radio burst, ICME and magnetic cloud and their spatiotemporal relationships and connections are studied all way from Sun to Earth. To this end, we make use of satellite data from a flotilla of solar, heliospheric and magnetospheric missions and monitors (e.g., SDO, STEREO, WIND, ACE, Herschel, Planck and INTEGRAL). We also present our first steps toward formulating a cohesive physical scenario to explain the string of the observables and to assess the various physical mechanisms than enabled and gave rise to the significant geoeffectiveness of the eruption. Title: Hot coronal loops associated with umbral brightenings Authors: Alissandrakis, C. E.; Patsourakos, S. Bibcode: 2013A&A...556A..79A Altcode: 2013arXiv1307.3392A
Aims: We aim to investigate the association of umbral brightenings with coronal structures.
Methods: We analyzed AIA/SDO high-cadence images in all bands, HMI/SDO data, soft X-ray images from SXI/GOES-15, and Hα images from the GONG network.
Results: We detected umbral brightenings that were visible in all AIA bands as well as in Hα. Moreover, we identified hot coronal loops that connected the brightenings with nearby regions of opposite magnetic polarity. These loops were initially visible in the 94 Å band, subsequently in the 335 Å band, and in one case in the 211 Å band. A differential emission measure analysis revealed plasma with an average temperature of about 6.5 × 106 K. This behavior suggests cooling of impulsively heated loops.

Two movies are available in electronic from at http://www.aanda.org Title: Where is Coronal Plasma Heated? Authors: Klimchuk, James A.; Bradshaw, S.; Patsourakos, S.; Tripathi, D. Bibcode: 2013SPD....4420006K Altcode: The coupling between the chromosphere and corona is a question of great current interest. It has long been understood that coronal mass originates in the chromosphere and that the energy which powers the corona flows up through the chromosphere. However, the details of how this happens are now being questioned. In the traditional view, “mechanical” energy flows into the corona in the form of waves or gradually increasing magnetic stresses. The waves and stresses dissipate and heat the plasma. The resulting downward thermal conduction flux causes material to evaporate from the chromosphere and fill the corona. If the heating is steady, an equilibrium is established whereby radiation and thermal conduction balance the energy input. If the heating is impulsive (a nanoflare), the evaporated plasma cools and drains, only to reappear during the next event. In either case, the heating occurs in the corona. A new idea is that the heating occurs instead in the chromosphere. Cold plasma is directly heated to coronal temperatures and then flows upward due to expansion and perhaps also an ejection process. The hot tips of type II spicules are one example, though spicules need not be involved. I will discuss these two fundamentally different scenarios and the observational predictions that they make. A comparison with actual observations leads to the conclusion that only a small fraction of the hot plasma in the corona comes from chromospheric heating. Most coronal plasma is a consequence of heating that occurs in the corona itself. Title: Combining Particle Acceleration and Coronal Heating via Data-constrained Calculations of Nanoflares in Coronal Loops Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.; Anastasiadis, A.; Georgoulis, M. K. Bibcode: 2013ApJ...771..126G Altcode: 2013arXiv1305.5195G We model nanoflare heating of extrapolated active-region coronal loops via the acceleration of electrons and protons in Harris-type current sheets. The kinetic energy of the accelerated particles is estimated using semi-analytical and test-particle-tracing approaches. Vector magnetograms and photospheric Doppler velocity maps of NOAA active region 09114, recorded by the Imaging Vector Magnetograph, were used for this analysis. A current-free field extrapolation of the active-region corona was first constructed. The corresponding Poynting fluxes at the footpoints of 5000 extrapolated coronal loops were then calculated. Assuming that reconnecting current sheets develop along these loops, we utilized previous results to estimate the kinetic energy gain of the accelerated particles. We related this energy to nanoflare heating and macroscopic loop characteristics. Kinetic energies of 0.1-8 keV (for electrons) and 0.3-470 keV (for protons) were found to cause heating rates ranging from 10-6 to 1 erg s-1 cm-3. Hydrodynamic simulations show that such heating rates can sustain plasma in coronal conditions inside the loops and generate plasma thermal distributions that are consistent with active-region observations. We concluded the analysis by computing the form of X-ray spectra generated by the accelerated electrons using the thick-target approach. These spectra were found to be in agreement with observed X-ray spectra, thus supporting the plausibility of our nanoflare-heating scenario. Title: Spectral diagnostic of a microflare. Evidences of resonant scattering in C IV 1548 Å, 1550 Å lines Authors: Gontikakis, C.; Winebarger, A. R.; Patsourakos, S. Bibcode: 2013A&A...550A..16G Altcode:
Aims: We study a microflare, classified as a GOES-A1 after background subtraction, which was observed in active region NOAA 8541 on May 15, 1999.
Methods: We used TRACE filtergrams to study the morphology and time evolution. SUMER spectral lines were used to diagnose the chromospheric plasma (Si ii 1533 Å), transition region plasma (C iv 1548, 1550 Å), and coronal plasma (Ne viii 770 Å).
Results: In the 171 Å and 195 Å filtergrams, we measure apparent mass motions along two small loops that compose the microflare from the eastern toward the western footpoints. In SUMER, the microflare is detected as a small (47 Mm2), bright area at the western footpoints of the TRACE loops. The spectral profiles recorded over the bright area are complex. The Si ii 1533 Å line is self-reversed owing to opacity, and the coronal Ne viii line profile is composed of two Gaussian components, one of them systematically redshifted. The C iv 1548 Å and 1550 Å profiles are badly distorted because of the temporary depression of the detector local gain caused by the very high count rates reached in the flaring region and we can only confirm the presence of strong blueshifts of ≃ -200 km s-1. Few, unaffected C iv profiles show two spectral components. In the northern part of the bright area, all SUMER spectral lines have at least one blueshifted spectral component. In the southern region of the bright area the spectral lines are redshifted. Adjacent to the microflare we measure, for the first time on the solar disk, an intensity ratio of the 1548 Å line to 1550 Å line with values of three to four, indicating that resonance scattering prevails in the lines formation. Moreover, the scattering region is found to be cospatial to a solar pore.
Conclusions: The blueshifts in the footpoints of the microflare and the apparent mass motions observed with TRACE can be explained by a gentle chromospheric evaporation triggered by the microflare. The redshifted spectral components can be explained as cooling material that is falling back on the solar surface. The presence of resonant scattering can be explained by the low electron density expected in the transition region of a solar pore, combined with the high photon flux coming from the nearby microflare. We estimate that the lower limit of the electron density in the pore lies in the range 108 cm-3 to 109 cm-3. Title: Direct Evidence for a Fast Coronal Mass Ejection Driven by the Prior Formation and Subsequent Destabilization of a Magnetic Flux Rope Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G. Bibcode: 2013ApJ...764..125P Altcode: 2012arXiv1211.7211P Magnetic flux ropes play a central role in the physics of coronal mass ejections (CMEs). Although a flux-rope topology is inferred for the majority of coronagraphic observations of CMEs, a heated debate rages on whether the flux ropes pre-exist or whether they are formed on-the-fly during the eruption. Here, we present a detailed analysis of extreme-ultraviolet observations of the formation of a flux rope during a confined flare followed about 7 hr later by the ejection of the flux rope and an eruptive flare. The two flares occurred during 2012 July 18 and 19. The second event unleashed a fast (>1000 km s-1) CME. We present the first direct evidence of a fast CME driven by the prior formation and destabilization of a coronal magnetic flux rope formed during the confined flare on July 18. Title: On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode (Invited Review) Authors: Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2012SoPh..281..187P Altcode: 2012SoPh..tmp...93P; 2012arXiv1203.1135P A major, albeit serendipitous, discovery of the SOlar and Heliospheric Observatory mission was the observation by the Extreme Ultraviolet Telescope (EIT) of large-scale extreme ultraviolet (EUV) intensity fronts propagating over a significant fraction of the Sun's surface. These so-called EIT or EUV waves are associated with eruptive phenomena and have been studied intensely. However, their wave nature has been challenged by non-wave (or pseudo-wave) interpretations and the subject remains under debate. A string of recent solar missions has provided a wealth of detailed EUV observations of these waves bringing us closer to resolving the question of their nature. With this review, we gather the current state-of-the-art knowledge in the field and synthesize it into a picture of an EUV wave driven by the lateral expansion of the CME. This picture can account for both wave and pseudo-wave interpretations of the observations, thus resolving the controversy over the nature of EUV waves to a large degree but not completely. We close with a discussion on several remaining open questions in the field of EUV waves research. Title: LEMUR: Large European module for solar Ultraviolet Research. European contribution to JAXA's Solar-C mission Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric; Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len; Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green, Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem, Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet, Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto, Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu, Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele; Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas; Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann, Thomas; Winter, Berend; Young, Peter Bibcode: 2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T The solar outer atmosphere is an extremely dynamic environment characterized by the continuous interplay between the plasma and the magnetic field that generates and permeates it. Such interactions play a fundamental role in hugely diverse astrophysical systems, but occur at scales that cannot be studied outside the solar system. Understanding this complex system requires concerted, simultaneous solar observations from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at high spatial resolution (between 0.1'' and 0.3''), at high temporal resolution (on the order of 10 s, i.e., the time scale of chromospheric dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the chromosphere to the flaring corona), and the capability of measuring magnetic fields through spectropolarimetry at visible and near-infrared wavelengths. Simultaneous spectroscopic measurements sampling the entire temperature range are particularly important. These requirements are fulfilled by the Japanese Solar-C mission (Plan B), composed of a spacecraft in a geosynchronous orbit with a payload providing a significant improvement of imaging and spectropolarimetric capabilities in the UV, visible, and near-infrared with respect to what is available today and foreseen in the near future. The Large European Module for solar Ultraviolet Research (LEMUR), described in this paper, is a large VUV telescope feeding a scientific payload of high-resolution imaging spectrographs and cameras. LEMUR consists of two major components: a VUV solar telescope with a 30 cm diameter mirror and a focal length of 3.6 m, and a focal-plane package composed of VUV spectrometers covering six carefully chosen wavelength ranges between 170 Å and 1270 Å. The LEMUR slit covers 280'' on the Sun with 0.14'' per pixel sampling. In addition, LEMUR is capable of measuring mass flows velocities (line shifts) down to 2 km s - 1 or better. LEMUR has been proposed to ESA as the European contribution to the Solar C mission. Title: On the Role of the Background Overlying Magnetic Field in Solar Eruptions Authors: Nindos, A.; Patsourakos, S.; Wiegelmann, T. Bibcode: 2012ApJ...748L...6N Altcode: The primary constraining force that inhibits global solar eruptions is provided by the overlying background magnetic field. Using magnetic field data from both the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory and the spectropolarimeter of the Solar Optical Telescope aboard Hinode, we study the long-term evolution of the background field in active region AR11158 that produced three major coronal mass ejections (CMEs). The CME formation heights were determined using EUV data. We calculated the decay index -(z/B)(∂B/∂z) of the magnetic field B (i.e., how fast the field decreases with height, z) related to each event from the time of the active region emergence until well after the CMEs. At the heights of CME formation, the decay indices were 1.1-2.1. Prior to two of the events, there were extended periods (of more than 23 hr) where the related decay indices at heights above the CME formation heights either decreased (up to -15%) or exhibited small changes. The decay index related to the third event increased (up to 118%) at heights above 20 Mm within an interval that started 64 hr prior to the CME. The magnetic free energy and the accumulated helicity into the corona contributed the most to the eruptions by their increase throughout the flux emergence phase (by factors of more than five and more than two orders of magnitude, respectively). Our results indicate that the initiation of eruptions does not depend critically on the temporal evolution of the variation of the background field with height. Title: EBTEL: Enthalpy-Based Thermal Evolution of Loops Authors: Klimchuk, J. A.; Patsourakos, S.; Cargill, P. J. Bibcode: 2012ascl.soft03007K Altcode: Observational and theoretical evidence suggests that coronal heating is impulsive and occurs on very small cross-field spatial scales. A single coronal loop could contain a hundred or more individual strands that are heated quasi-independently by nanoflares. It is therefore an enormous undertaking to model an entire active region or the global corona. Three-dimensional MHD codes have inadequate spatial resolution, and 1D hydro codes are too slow to simulate the many thousands of elemental strands that must be treated in a reasonable representation. Fortunately, thermal conduction and flows tend to smooth out plasma gradients along the magnetic field, so "0D models" are an acceptable alternative. We have developed a highly efficient model called Enthalpy-Based Thermal Evolution of Loops (EBTEL) that accurately describes the evolution of the average temperature, pressure, and density along a coronal strand. It improves significantly upon earlier models of this type-in accuracy, flexibility, and capability. It treats both slowly varying and highly impulsive coronal heating; it provides the differential emission measure distribution, DEM(T), at the transition region footpoints; and there are options for heat flux saturation and nonthermal electron beam heating. EBTEL gives excellent agreement with far more sophisticated 1D hydro simulations despite using four orders of magnitude less computing time. It promises to be a powerful new tool for solar and stellar studies. Title: Nanoflare heating of coronal loops in an active region triggered by reconnecting current sheets Authors: Gontikakis, C.; Patsourakos, S.; Efthymiopoulos, C.; Anastasiadis, A.; Georgoulis, M. Bibcode: 2012hell.conf....7G Altcode: The purpose of this work is to study the heating of coronal loops, produced by the acceleration of particles inside reconnecting current sheets (RCS) which represent nanoflares. We also study the hydrodynamic response of the loops atmosphere to such a heating event. The RCS are formed as discontinuities of the loop magnetic field caused by the photospheric shuffling motions. The coronal loops are represented by the closed magnetic lines of force calculated by the magnetic field extrapolation of the active region NOAA 9114 magnetogram. The photospheric motions at the loops footpoints are measured using local correlation tracking. The magnetic and electric fields accelerating particles at the RCS are computed using the loop magnetic fields and the photospheric motions. We further discuss the question of energy conservation inside the current sheet, and we present the statistical distributions of quantities relevant for particles acceleration and coronal heating for a number of the active region's coronal loops. Title: Arrival Times of Interplanetary CMEs and Shocks into the Earth's Vicinity: STEREO Observations and Analytical Modeling Authors: Ontiveros, V.; Patsourakos, S.; Corona-Romero, P.; Gonzalez-Esparza, J. A. Bibcode: 2012hell.conf....9O Altcode: Interplanetary Coronal Mass Ejections (ICMEs) are one of the largest disturbances in the solar system. ICMEs and their associated shocks are the main cause of intense geomagnetic perturbations, that might affect satellite orbits and telecommunications among other systems. These important repercussions in the Space Weather have lead to a continuous effort to predict the arrival times of the ICMEs and their shocks into the Earth's vicinity, but still the current accuracy in their arrival time to Earth of few hours needs further ramification, in particular for operational purposes. White light images from the STEREO coronagraphs and heliospheric imagers provide an early detection of coronal mass ejections (CMEs) and ICMEs. In February 6, 2011, spacecrafts A and B were 180 degrees apart, each one looking down on a different hemisphere of the Sun and therefore they view from the side Earth-directed events, allowing a better determination of the physical parameters of the events and their kinematics in particular. We take advantage of this configuration and determine the kinematics of the CMEs and ICMEs of Feb 15th (01:56), March 7th (19:43) and June 21st (16:03 UT), 2011. These events have an interplanetary counterpart with Earth arrivals in Feb 18th (00:40 UT), March 10th (05:45 UT) and Jun 23rd (02:18 UT) respectively, as observed by the ACE spacecraft. We perform 3D fittings of the CME-ICME-shock systems viewed by COR1, COR2 HI1 and HI2 to deduce their kinematics and we use our measurements to constrain an analytical model of ICME and shock propagation from the Sun to Earth and compare with the in-situ arrival times to Earth's orbit. This model is applied where the dynamic pressure parameter dominates the solar wind dynamics and it is focused on the role of the transmission of momentum in the ICME-shock system. Title: Multi-wavelength Observations of a Metric Type-II Event Authors: Alissandrakis, C.; Nindos, A.; Patsourakos, S.; Hillaris, Al.; Artemis Group Bibcode: 2012hell.conf....6A Altcode: We have studied a complex metric radio event,observed with the ARTEMIS radiospectrogarph on February 12, 2010. The event was associated with a surge observed at 195 and 304 A and with a coronal mass ejection observed by STEREO A and B instruments near the East wnd West limbs respectively. On the disk the event was observed at 10 frequencies by the Nancay Radioheliograph (NRH), in H-alpha by the Catania observatory and in soft x-rays by GOES SXI. We combined these data, together with MDI longitudinal magnetic field, to get as complete a picture of the event as possible. Our emphasis is on two type-II bursts that occured near respective maxima in the GOES light curves. The first, associated with the main peak of the event, showed a clear foundamental-harmonic structure, while the emission of the second consisted of three well-separated bands. Using positional infornation for the type-IIs from the NRH we explore their possible association with the surge, the coronal front and the CME. We also studied fine structured and foundamental harmonic structure in the metric dynamic spectrum. Title: Constraining a Model for EUV Wave Formation with SDO and STEREO Quadrature Observations Authors: Patsourakos, S.; Vourlidas, A.; Olmedo, O. Bibcode: 2012hell.conf....7P Altcode: The generation mechanism(s) of large-scale propagating intensity fronts seen in the EUV, often called EUV waves, in association with impulsive Coronal Mass Ejection (CMEs) is currently a matter of debate. The strong lateral expansion which some impulsive CMEs undergo during their early phases, when they are observed in the inner corona by EUV imagers, is one possible mechanism for the generation of EUV waves. One impulsive CME - EUV wave pair was observed during 15 February 2011 in quadrature by SDO and STEREO. The source active region was close to disk center as seen by SDO and at the limb as seen by STEREO. This configuration allowed us to determine the kinematics of the EUV wave and of the early EUV CME by AIA/SDO and EUVI/STEREO respectively. The detailed kinematics of the early EUV CME (height and radius evolution of the erupting flux) were then used to constrain a simple model of EUV wave formation, invoking the erupting flux as the wave driver. The ground tracks of the EUV wave as predicted by this data-driven model were then compared with those of the observed wave. Title: Determination of temperature maps of EUV coronal hole jets Authors: Nisticò, Giuseppe; Patsourakos, Spiros; Bothmer, Volker; Zimbardo, Gaetano Bibcode: 2011AdSpR..48.1490N Altcode: Coronal hole jets are fast ejections of plasma occurring within coronal holes, observed at Extreme-UltraViolet (EUV) and X-ray wavelengths. Recent observations of jets by the STEREO and Hinode missions show that they are transient phenomena which occur at much higher rates than large-scale impulsive phenomena like flares and Coronal Mass Ejections (CMEs). In this paper we describe some typical characteristics of coronal jets observed by the SECCHI instruments of STEREO spacecraft. We show an example of 3D reconstruction of the helical structure for a south pole jet, and present how the angular distribution of the jet position angles changes from the Extreme-UltraViolet-Imager (EUVI) field of view to the CORonagraph1 (COR1) (height ∼2.0 R⊙ heliocentric distance) field of view. Then we discuss a preliminary temperature determination for the jet plasma by using the filter ratio method at 171 and 195 Å and applying a technique for subtracting the EUV background radiation. The results show that jets are characterized by electron temperatures ranging between 0.8 and 1.3 MK. We present the thermal structure of the jet as temperature maps and we describe its thermal evolution. Title: Euv Imaging Of Shock Formation In The Low Corona With Sdo/aia Authors: Vourlidas, Angelos; Patsourakos, S.; Kouloumvakos, T. Bibcode: 2011SPD....42.0907V Altcode: 2011BAAS..43S.0907V Shock generation in the low corona has long been inferred by spectral observations of drifting so-called type-II radio emission in the metric wavelengths. Type-IIs occur with coronal mass ejections (CMEs) and/or flares but not consistently. Therefore, the exact relationship has been difficult to pin down, mostly because of the lack of radio imaging capability and of the low cadence of EUV observations in the low corona during the flare/CME formation. The advent of ultra-high observations from the AIA imagers has changed all that. In this talk, we present several direct observations of shock formation in the EUV and their association to the accompanying type-IIs. We will show that the coronal expansion driven by the formation of the CME ejecta is responsible for both EUV and radio emissions. Title: Erratum: "Comprehensive Analysis of Coronal Mass Ejection Mass and Energy Properties Over a Full Solar Cycle" (2010, ApJ, 722, 1522) Authors: Vourlidas, A.; Howard, R. A.; Esfandiari, E.; Patsourakos, S.; Yashiro, S.; Michalek, G. Bibcode: 2011ApJ...730...59V Altcode: No abstract at ADS Title: Evidence for a current sheet forming in the wake of a coronal mass ejection from multi-viewpoint coronagraph observations Authors: Patsourakos, S.; Vourlidas, A. Bibcode: 2011A&A...525A..27P Altcode: 2010arXiv1010.0323P Context. Ray-like features observed by coronagraphs in the wake of coronal mass ejections (CMEs) are sometimes interpreted as the white light counterparts of current sheets (CSs) produced by the eruption. The 3D geometry of these ray-like features is largely unknown and its knowledge should clarify their association to the CS and place constraints on CME physics and coronal conditions.
Aims: If these rays are related to field relaxation behind CMEs, therefore representing current sheets, then they should be aligned to the CME axis. With this study we test these important implications for the first time.
Methods: An example of such a post-CME ray was observed by various coronagraphs, including these of the Sun Earth Connection Coronal and Heliospheric investigation (SECCHI) onboard the Solar Terrestrial Relations Observatory (STEREO) twin spacecraft and the Large Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). The ray was observed in the aftermath of a CME which occurred on 9 April 2008. The twin STEREO spacecraft were separated by about 48° on that day. This significant separation combined with a third “eye” view supplied by LASCO allow for a truly multi-viewpoint observation of the ray and of the CME. We applied 3D forward geometrical modeling to the CME and to the ray as simultaneously viewed by SECCHI-A and B and by SECCHI-A and LASCO, respectively.
Results: We found that the ray can be approximated by a rectangular slab, nearly aligned with the CME axis, and much smaller than the CME in both terms of thickness and depth (≈0.05 and 0.15 R⊙ respectively). The ray electron density and temperature were substantially higher than their values in the ambient corona. We found that the ray and CME are significantly displaced from the associated post-CME flaring loops.
Conclusions: The properties and location of the ray are fully consistent with the expectations of the standard CME theories for post-CME current sheets. Therefore, our multi-viewpoint observations supply strong evidence that the observed post-CME ray is indeed related to a post-CME current sheet.

Movies are only available in electronic form at http://www.aanda.org Title: Constraining the Initiation and Early Evolution of CMEs Authors: Patsourakos, Spiros Bibcode: 2011sswh.book...73P Altcode: No abstract at ADS Title: The Genesis of an Impulsive CME observed by AIA on SDO Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G. Bibcode: 2010AGUFMSH14A..03P Altcode: Understanding the first moments in the life-time of Coronal Mass Ejections (CMEs), i.e. their genesis, represents possibly the key to unlock the physical processes responsible for their initiation. After this critical interval, which could last as little as few minutes for the most impulsive events, differences between various CME models become minimal. The recent launch of the SDO mission and the availability of high-quality EUV imaging from AIA in particular, opened a new avenue into CME initiation investigations with its unprecedented image cadence and multi-wavelength simultaneous coverage. We here report on AIA observations of an impulsive CME-flare-EUV wave event which took place during 13 June 2010. All the important dynamics (e.g., rise phase of the flare, impulsive acceleration of the CME) had a duration of only 10 minutes making this event a perfect showcase event for AIA. Taking advantage of the unique aspects of AIA data (12 sec cadence and 7 different EUV channels) we present a detailed analysis of this event which includes: (1) its kinematic behavior (acceleration profile); (2) radial and expansion speeds; (3) relationships between (1) and (2) with the flare energy release; (4) multi-temperature evolution of the early CME. All the above supply new strong constraints for the physics of impulsive CMEs. Title: The Genesis of an Impulsive Coronal Mass Ejection Observed at Ultra-high Cadence by AIA on SDO Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G. Bibcode: 2010ApJ...724L.188P Altcode: 2010arXiv1010.5234P The study of fast, eruptive events in the low solar corona is one of the science objectives of the Atmospheric Imaging Assembly (AIA) imagers on the recently launched Solar Dynamics Observatory (SDO), which take full disk images in 10 wavelengths with arcsecond resolution and 12 s cadence. We study with AIA the formation of an impulsive coronal mass ejection (CME) which occurred on 2010 June 13 and was associated with an M1.0 class flare. Specifically, we analyze the formation of the CME EUV bubble and its initial dynamics and thermal evolution in the low corona using AIA images in three wavelengths (171 Å, 193 Å, and 211 Å). We derive the first ultra-high cadence measurements of the temporal evolution of the CME bubble aspect ratio (=bubble height/bubble radius). Our main result is that the CME formation undergoes three phases: it starts with a slow self-similar expansion followed by a fast but short-lived (~70 s) period of strong lateral overexpansion which essentially creates the CME. Then the CME undergoes another phase of self-similar expansion until it exits the AIA field of view. During the studied interval, the CME height-time profile shows a strong, short-lived, acceleration followed by deceleration. The lateral overexpansion phase coincides with the deceleration phase. The impulsive flare heating and CME acceleration are closely coupled. However, the lateral overexpansion of the CME occurs during the declining phase and is therefore not linked to flare reconnection. In addition, the multi-thermal analysis of the bubble does not show significant evidence of temperature change. Title: Simulations of Overexpanding CME Cavities Authors: Kliem, B.; Forbes, T.; Vourlidas, A.; Patsourakos, S. Bibcode: 2010AGUFMSH51A1661K Altcode: Coronal mass ejection (CME) cavities seen in white-light coronagraphs expand nearly self similarly in the outer corona and inner solar wind. Little is known about their initial expansion in the inner corona. A two-phase evolution, consisting of an initial overexpansion up to a heliocentric front height of about 1.5 solar radii, followed by nearly self-similar expansion, was recently discovered in STEREO/SECCHI observations of a fast CME (Patsourakos et al. 2010). The overexpansion is expressed as a decrease of the cavity aspect ratio (center height by radius) by at least a factor of 2 during the rise phase of the main CME acceleration. We present MHD simulations of erupting flux ropes that show the initial overexpansion of a cavity in line with the observed evolution. The contributions of ideal-MHD expansion and of magnetic reconnection to the growth of the flux rope and cavity in the simulations will be quantified to identify the primary cause of the overexpansion. This assesses the diagnostic potential of the overexpansion for the change of flux rope current and the role of magnetic reconnection in the early evolution of CMEs. Title: The Birth of Coronal Mass Ejections As Seen by STEREO and SDO Authors: Vourlidas, A.; Patsourakos, S. Bibcode: 2010AGUFMSH21C..07V Altcode: Despite observations of thousands of coronal mass ejections (CMEs), the details of their formation still elude us. Impulsive CMEs, in particular, originate low in the corona, and form within 10-15 mins while accelerating rapidly. This region of the corona is regularly observed by EUV imagers but the rapid CME evolution requires high cadence and relatively large fields of view. Thanks to the operation of the STEREO and SDO missions, we are currently in a unique position to address the problem of CME formation. The two missions provide almost simultaneous observations from three viewpoints with 3 EUV imagers. The EUV instruments observe in the same (or similar) channels and have highly complimentary cadences and fields of view. In this paper, we discuss a coherent picture of the birth of CMEs based on a study of the first few-minute evolution of several impulsive CMEs. These CMEs seem to first undergo an non-linear expansion followed by a self-similar phase. We discuss the implication for CME initiation models. Title: Toward understanding the early stages of an impulsively accelerated coronal mass ejection. SECCHI observations Authors: Patsourakos, S.; Vourlidas, A.; Kliem, B. Bibcode: 2010A&A...522A.100P Altcode: 2010arXiv1008.1171P Context. The expanding magnetic flux in coronal mass ejections (CMEs) often forms a cavity. Studies of CME cavities have so far been limited to the pre-event configuration to evolved CMEs at great heights, and to two-dimensional imaging data.
Aims: Quantitative analysis of three-dimensional cavity evolution at CME onset can reveal information that is relevant to the genesis of the eruption.
Methods: A spherical model was simultaneously fit to Solar Terrestrial Relations Observatory (STEREO) Extreme Ultraviolet Imager (EUVI) and Inner Coronagraph (COR1) data of an impulsively accelerated CME on 25 March 2008, which displays a well-defined extreme ultraviolet (EUV) and white-light cavity of nearly circular shape already at low heights h ≈ 0.2 R_⊙. The center height h(t) and radial expansion r(t) of the cavity were obtained in the whole height range of the main acceleration. We interpret them as the axis height and as a quantity proportional to the minor radius of a flux rope.
Results: The three-dimensional expansion of the CME exhibits two phases in the course of its main upward acceleration. From the first h and r data points, taken shortly after the onset of the main acceleration, the erupting flux shows an overexpansion compared to its rise, as expressed by the decrease in the aspect ratio from κ = h/r ≈ 3 to κ ≈ (1.5-2). This phase is approximately coincident with the impulsive rise in the acceleration and is followed by a phase of very gradual change in the aspect ratio (a nearly self-similar expansion) toward κ ~ 2.5 at h ~ 10 R_⊙. The initial overexpansion of the CME cavity can be caused by flux conservation around a rising flux rope of decreasing axial current and by the addition of flux to a growing, or by even newly formed, flux rope by magnetic reconnection. Further analysis will be required to decide which of these contributions is dominant. The data also suggest that the horizontal component of the impulsive cavity expansion (parallel to the solar surface) triggers the associated EUV wave, which subsequently detaches from the CME volume. Title: Comprehensive Analysis of Coronal Mass Ejection Mass and Energy Properties Over a Full Solar Cycle Authors: Vourlidas, A.; Howard, R. A.; Esfandiari, E.; Patsourakos, S.; Yashiro, S.; Michalek, G. Bibcode: 2010ApJ...722.1522V Altcode: 2010arXiv1008.3737V The LASCO coronagraphs, in continuous operation since 1995, have observed the evolution of the solar corona and coronal mass ejections (CMEs) over a full solar cycle with high-quality images and regular cadence. This is the first time that such a data set becomes available and constitutes a unique resource for the study of CMEs. In this paper, we present a comprehensive investigation of the solar cycle dependence on the CME mass and energy over a full solar cycle (1996-2009) including the first in-depth discussion of the mass and energy analysis methods and their associated errors. Our analysis provides several results worthy of further studies. It demonstrates the possible existence of two event classes: "normal" CMEs reaching constant mass for >10 R sun and "pseudo"-CMEs which disappear in the C3 field of view. It shows that the mass and energy properties of CME reach constant levels and therefore should be measured only above ~10 R sun. The mass density (g/R 2 sun) of CMEs varies relatively little (< order of magnitude) suggesting that the majority of the mass originates from a small range in coronal heights. We find a sudden reduction in the CME mass in mid-2003 which may be related to a change in the electron content of the large-scale corona and we uncover the presence of a 6 month periodicity in the ejected mass from 2003 onward. Title: Observational features of equatorial coronal hole jets Authors: Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G. Bibcode: 2010AnGeo..28..687N Altcode: 2010arXiv1002.2181N Collimated ejections of plasma called "coronal hole jets" are commonly observed in polar coronal holes. However, such coronal jets are not only a specific features of polar coronal holes but they can also be found in coronal holes appearing at lower heliographic latitudes. In this paper we present some observations of "equatorial coronal hole jets" made up with data provided by the STEREO/SECCHI instruments during a period comprising March 2007 and December 2007. The jet events are selected by requiring at least some visibility in both COR1 and EUVI instruments. We report 15 jet events, and we discuss their main features. For one event, the uplift velocity has been determined as about 200 km s-1, while the deceleration rate appears to be about 0.11 km s-2, less than solar gravity. The average jet visibility time is about 30 min, consistent with jet observed in polar regions. On the basis of the present dataset, we provisionally conclude that there are not substantial physical differences between polar and equatorial coronal hole jets. Title: Extreme Ultraviolet Observations and Analysis of Micro-Eruptions and Their Associated Coronal Waves Authors: Podladchikova, O.; Vourlidas, A.; Van der Linden, R. A. M.; Wülser, J. -P.; Patsourakos, S. Bibcode: 2010ApJ...709..369P Altcode: The Solar Terrestrial Relations Observatory EUV telescopes have uncovered small-scale eruptive events, tentatively referred to as "mini-CMEs" because they exhibit morphologies similar to large-scale coronal mass ejections (CMEs). Coronal waves and widespread diffuse dimmings followed by the expansion of the coronal waves are the most brightly manifestations of large-scale CMEs. The high temporal and spatial resolution of the EUV data allows us to detect and analyze these eruptive events, to resolve their fine structure, and to show that the observed "mini-waves" have a strong similarity to the large-scale "EIT' waves. Here, we analyze a micro-event observed on 2007 October 17 by the Sun Earth Connection Coronal and Heliospheric Investigation EUV Imager (EUVI) in 171 Å (Fe IX) with a 2.5 minute cadence. The mini-CME differs from its large-scale counterparts by having smaller geometrical size, a shorter lifetime, and reduced intensity of coronal wave and dimmings. The small-scale coronal wave develops from micro-flaring sites and propagate up to a distance of 40,000 km in a wide angular sector of the quiet Sun over 20 minutes. The area of the small-scale dimming is two orders of magnitude smaller than for large-scale events. The average speed of the small-scale coronal wave studied is 14 km s-1. Our observations give strong indications that small-scale EUV coronal waves associated with the micro-eruptions propagate in the form of slow mode waves almost perpendicular to the background magnetic field. Title: The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations Authors: Vourlidas, A.; Sanchez Andrade-Nuño, B.; Landi, E.; Patsourakos, S.; Teriaca, L.; Schühle, U.; Korendyke, C. M.; Nestoras, I. Bibcode: 2010SoPh..261...53V Altcode: 2009arXiv0912.2272V The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding rocket payload built to study the crucial interface between the solar chromosphere and the corona by observing the strongest line in the solar spectrum, the Ly α line at 1216 Å. In two flights, VAULT succeeded in obtaining the first ever subarcsecond ( 0.5\hbox{$^''$} ) images of this region with high sensitivity and cadence. Detailed analyses of those observations contributed significantly to new ideas about the nature of the transition region. Here, we present a broad overview of the Ly α atmosphere as revealed by the VAULT observations and bring together past results and new analyses from the second VAULT flight to create a synthesis of our current knowledge of the high-resolution Ly α Sun. We hope that this work will serve as a good reference for the design of upcoming Ly α telescopes and observing plans. Title: The nature of micro CMEs within coronal holes Authors: Bothmer, Volker; Nistico, Giuseppe; Zimbardo, Gaetano; Patsourakos, Spiros; Bosman, Eckhard Bibcode: 2010cosp...38.2840B Altcode: 2010cosp.meet.2840B Whilst investigating the origin and characteristics of coronal jets and large-scale CMEs identi-fied in data from the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) instrument suites on board the two STEREO satellites, we discovered transient events that originated in the low corona with a morphology resembling that of typical three-part struc-tured coronal mass ejections (CMEs). However, the CMEs occurred on considerably smaller spatial scales. In this presentation we show evidence for the existence of small-scale CMEs from inside coronal holes and present quantitative estimates of their speeds and masses. We interprete the origin and evolution of micro CMEs as a natural consequence of the emergence of small-scale magnetic bipoles related to the Sun's ever changing photospheric magnetic flux on various scales and their interactions with the ambient plasma and magnetic field. The analysis of CMEs is performed within the framework of the EU Erasmus and FP7 SOTERIA projects. Title: Heatwaves on the Sun Authors: Robbrecht, Eva; Wang, Yi-Ming; Vourlidas, Angelos; Patsourakos, Spiros Bibcode: 2010cosp...38.1791R Altcode: 2010cosp.meet.1791R Dimmings have been observed for several years now, but their interpretation is still problematic. A dimming is an observational effect of diminished brightness with respect to pre-event images, which is usually interpreted as a density depletion. But not all dimmings are what they appear to be. In this paper we report on an unusual "dimming wave" which is not a density depletion but rather a heat wave. Thanks to the stereoscopic view from the SECCHI/EUVI imagers we are able not only to uncover the nature of the wave, but also to understand its three dimensional evolution and its relationship to a quiet sun CME. Title: What Is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models Authors: Patsourakos, S.; Vourlidas, A.; Wang, Y. M.; Stenborg, G.; Thernisien, A. Bibcode: 2009SoPh..259...49P Altcode: 2009arXiv0905.2189P One of the major discoveries of the Extreme ultraviolet Imaging Telescope (EIT) on SOHO was the intensity enhancements propagating over a large fraction of the solar surface. The physical origin(s) of the so-called EIT waves is still strongly debated with either wave (primarily fast-mode MHD waves) or nonwave (pseudo-wave) interpretations. The difficulty in understanding the nature of EUV waves lies in the limitations of the EIT observations that have been used almost exclusively for their study. They suffer from low cadence and single temperature and viewpoint coverage. These limitations are largely overcome by the SECCHI/EUVI observations onboard the STEREO mission. The EUVI telescopes provide high-cadence, simultaneous multitemperature coverage and two well-separated viewpoints. We present here the first detailed analysis of an EUV wave observed by the EUVI disk imagers on 7 December 2007 when the STEREO spacecraft separation was ≈ 45°. Both a small flare and a coronal mass ejection (CME) were associated with the wave. We also offer the first comprehensive comparison of the various wave interpretations against the observations. Our major findings are as follows: (1) High-cadence (2.5-minute) 171 Å images showed a strong association between expanding loops and the wave onset and significant differences in the wave appearance between the two STEREO viewpoints during its early stages; these differences largely disappeared later; (2) the wave appears at the active region periphery when an abrupt disappearance of the expanding loops occurs within an interval of 2.5 minutes; (3) almost simultaneous images at different temperatures showed that the wave was most visible in the 1 - 2 MK range and almost invisible in chromospheric/transition region temperatures; (4) triangulations of the wave indicate it was rather low lying (≈ 90 Mm above the surface); (5) forward-fitting of the corresponding CME as seen by the COR1 coronagraphs showed that the projection of the best-fit model on the solar surface was inconsistent with the location and size of the co-temporal EUV wave; and (6) simulations of a fast-mode wave were found in good agreement with the overall shape and location of the observed wave. Our findings give significant support for a fast-mode interpretation of EUV waves and indicate that they are probably triggered by the rapid expansion of the loops associated with the CME. Title: Characteristics of EUV Coronal Jets Observed with STEREO/SECCHI Authors: Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G. Bibcode: 2009SoPh..259...87N Altcode: 2009arXiv0906.4407N In this paper we present the first comprehensive statistical study of EUV coronal jets observed with the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suites of the two STEREO spacecraft. A catalogue of 79 polar jets is presented, identified from simultaneous EUV and white-light coronagraph observations, taken during the time period March 2007 to April 2008, when solar activity was at a minimum. The twin spacecraft angular separation increased during this time interval from 2 to 48 degrees. The appearances of the coronal jets were always correlated with underlying small-scale chromospheric bright points. A basic characterization of the morphology and identification of the presence of helical structure were established with respect to recently proposed models for their origin and temporal evolution. Though each jet appeared morphologically similar in the coronagraph field of view, in the sense of a narrow collimated outward flow of matter, at the source region in the low corona the jet showed different characteristics, which may correspond to different magnetic structures. A classification of the events with respect to previous jet studies shows that amongst the 79 events there were 37 Eiffel tower-type jet events, commonly interpreted as a small-scale (∼35 arc sec) magnetic bipole reconnecting with the ambient unipolar open coronal magnetic fields at its loop tops, and 12 lambda-type jet events commonly interpreted as reconnection with the ambient field happening at the bipole footpoints. Five events were termed micro-CME-type jet events because they resembled the classical coronal mass ejections (CMEs) but on much smaller scales. The remaining 25 cases could not be uniquely classified. Thirty-one of the total number of events exhibited a helical magnetic field structure, indicative for a torsional motion of the jet around its axis of propagation. A few jets are also found in equatorial coronal holes. In this study we present sample events for each of the jet types using both, STEREO A and STEREO B, perspectives. The typical lifetimes in the SECCHI/EUVI (Extreme UltraViolet Imager) field of view between 1.0 to 1.7 R⊙ and in SECCHI/COR1 field of view between 1.4 to 4 R⊙ are obtained, and the derived speeds are roughly estimated. In summary, the observations support the assumption of continuous small-scale reconnection as an intrinsic feature of the solar corona, with its role for the heating of the corona, particle acceleration, structuring and acceleration of the solar wind remaining to be explored in more detail in further studies. Title: Estimating the Chromospheric Absorption of Transition Region Moss Emission Authors: De Pontieu, Bart; Hansteen, Viggo H.; McIntosh, Scott W.; Patsourakos, Spiros Bibcode: 2009ApJ...702.1016D Altcode: 2009arXiv0907.1883D Many models for coronal loops have difficulty explaining the observed EUV brightness of the transition region, which is often significantly less than theoretical models predict. This discrepancy has been addressed by a variety of approaches including filling factors and time-dependent heating, with varying degrees of success. Here, we focus on an effect that has been ignored so far: the absorption of EUV light with wavelengths below 912 Å by the resonance continua of neutral hydrogen and helium. Such absorption is expected to occur in the low-lying transition region of hot, active region loops that is colocated with cool chromospheric features and called "moss" as a result of the reticulated appearance resulting from the absorption. We use cotemporal and cospatial spectroheliograms obtained with the Solar and Heliospheric Observatory/SUMER and Hinode/EIS of Fe XII 1242 Å, 195 Å, and 186.88 Å, and compare the density determination from the 186/195 Å line ratio to that resulting from the 195/1242 Å line ratio. We find that while coronal loops have compatible density values from these two line pairs, upper transition region moss has conflicting density determinations. This discrepancy can be resolved by taking into account significant absorption of 195 Å emission caused by the chromospheric inclusions in the moss. We find that the amount of absorption is generally of the order of a factor of 2. We compare to numerical models and show that the observed effect is well reproduced by three-dimensional radiative MHD models of the transition region and corona. We use STEREO A/B data of the same active region and find that increased angles between line of sight and local vertical cause additional absorption. Our determination of the amount of chromospheric absorption of TR emission can be used to better constrain coronal heating models. Title: No Trace Left Behind: STEREO Observation of a Coronal Mass Ejection Without Low Coronal Signatures Authors: Robbrecht, Eva; Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2009ApJ...701..283R Altcode: 2009arXiv0905.2583R The availability of high-quality synoptic observations of the extreme-ultraviolet (EUV) and visible corona during the SOHO mission has advanced our understanding of the low corona manifestations of coronal mass ejections (CMEs). The EUV imager/white light coronagraph connection has been proven so powerful, it is routinely assumed that if no EUV signatures are present when a CME is observed by a coronagraph, then the event must originate behind the visible limb. This assumption carries strong implications for space weather forecasting but has not been put to the test. This paper presents the first detailed analysis of a frontside, large-scale CME that has no obvious counterparts in the low corona as observed in EUV and Hα wavelengths. The event was observed by the SECCHI instruments onboard the STEREO mission. The COR2A coronagraph observed a slow flux-rope-type CME, while an extremely faint partial halo was observed in COR2B. The event evolved very slowly and is typical of the streamer-blowout CME class. EUVI A 171 Å images show a concave feature above the east limb, relatively stable for about two days before the eruption, when it rises into the coronagraphic fields and develops into the core of the CME. None of the typical low corona signatures of a CME (flaring, EUV dimming, filament eruption, waves) were observed in the EUVI B images, which we attribute to the unusually large height from which the flux rope lifted off. This interpretation is supported by the CME mass measurements and estimates of the expected EUV dimming intensity. Only thanks to the availability of the two viewpoints we were able to identify the likely source region. The event originated along a neutral line over the quiet-Sun. No active regions were present anywhere on the visible (from STEREO B) face of the disk. Leaving no trace behind on the solar disk, this observation shows unambiguously that a CME eruption does not need to have clear on-disk signatures. Also it sheds light on the question of "mystery" geomagnetic storms, storms without clear solar origin (formerly called problem storms). We discuss the implications for space weather monitoring. Preliminary inspection of STEREO data indicates that events like this are not uncommon, particularly during the ongoing period of deep solar minimum. Title: "Extreme Ultraviolet Waves" are Waves: First Quadrature Observations of an Extreme Ultraviolet Wave from STEREO Authors: Patsourakos, Spiros; Vourlidas, Angelos Bibcode: 2009ApJ...700L.182P Altcode: 2009arXiv0905.2164P The nature of coronal mass ejection (CME)-associated low corona propagating disturbances, "extreme ultraviolet (EUV) waves," has been controversial since their discovery by EIT on SOHO. The low-cadence, single-viewpoint EUV images and the lack of simultaneous inner corona white-light observations have hindered the resolution of the debate on whether they are true waves or just projections of the expanding CME. The operation of the twin EUV imagers and inner corona coronagraphs aboard STEREO has improved the situation dramatically. During early 2009, the STEREO Ahead (STA) and Behind (STB) spacecrafts observed the Sun in quadrature having a ≈90° angular separation. An EUV wave and CME erupted from active region 11012, on February 13, when the region was exactly at the limb for STA and hence at disk center for STB. The STEREO observations capture the development of a CME and its accompanying EUV wave not only with high cadence but also in quadrature. The resulting unprecedented data set allowed us to separate the CME structures from the EUV wave signatures and to determine without doubt the true nature of the wave. It is a fast-mode MHD wave after all. Title: Spectroscopic Observations of Hot Lines Constraining Coronal Heating in Solar Active Regions Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2009ApJ...696..760P Altcode: 2009arXiv0903.3880P Extreme-ultraviolet observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared with static equilibrium) when it cools into the 1-2MK range. If this interpretation is correct, then very hot emission should be present outside of proper flares. It is predicted to be very faint, however. A critical element for proving or refuting this hypothesis is the existence of hot, yet faint plasmas which should be at amounts predicted by impulsive heating models. We report on the first comprehensive spectroscopic study of hot plasmas in active regions (ARs). Data from the Extreme-ultraviolet Imaging Spectrometer on Hinode were used to construct emission measure (EM) distributions in quiescent ARs in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that AR models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature. Title: Spectroscopic Observations of Hot Lines Constraining Coronal Heating in Solar Active Regions Authors: Patsourakos, Spiros; Klimchuk, J. A. Bibcode: 2009SPD....40.1211P Altcode: EUV observations of warm coronal loops suggest that they are bundles of unresolved strands that are heated impulsively to high temperatures by nanoflares. The plasma would then have the observed properties (e.g., excess density compared to static equilibrium) when it cools into the 1-2 MK range. If this interpretation is correct, then very hot emission should be present outside of proper flares. It is predicted to be vey faint, however. A critical element for proving or refuting this hypothesis is the existence of hot, very faint plasmas which should be at amounts predicted by impulsive heating. We report on the first comprehensive spectroscopic study of hot plasmas in active regions. Data from the EIS spectrometer on Hinode were used to construct emission measure distributions in quiescent active regions in the 1-5 MK temperature range. The distributions are flat or slowly increasing up to approximately 3 MK and then fall off rapidly at higher temperatures. We show that active region models based on impulsive heating can reproduce the observed EM distributions relatively well. Our results provide strong new evidence that coronal heating is impulsive in nature. Title: No trace left behind: STEREO Observation of a Coronal Mass Ejection Lacking Low Coronal Signatures Authors: Vourlidas, Angelos; Robbrecht, E.; Patsourakos, S. Bibcode: 2009SPD....40.2104V Altcode: The availability of high quality synoptic observations of the EUV and visible corona during the SOHO mission has advanced our understanding of the low corona manifestations of CMEs. The EUV imager/White light coronagraph connection has been proven so powerful, it is routinely assumed that if no EUV signatures are present when a CME is observed by a coronagraph, then the event must originate behind the visible limb. This assumption carries strong implications for space weather forecasting but has not been put to the test. This paper presents the first detailed analysis of a frontside, large-scale CME that has no obvious counterparts in the low corona. The event was observed by the SECCHI instruments on the STEREO mission. The COR2A coronagraph observed the event as a typical flux-rope type CME, while an extremely faint partial halo was observed in COR2B. The event evolved very slowly and is typical of the streamer-blowout CME class. EUVI-A 171A images show a concave feature above the east limb, relatively stable for about two days before the eruption, when it rises into the coronagraphic fields and develops into the core of the CME. None of the typical low corona signatures of a CME (flaring, EUV dimming, filament eruption, waves) were observed. Thanks to the two STEREO viewpoints we were able to identify the likely source region. The event originated along a quiet sun neutral line. No active regions were present anywhere on the visible face of the disk. Leaving no trace behind, this observation shows unambiguously that a CME eruption does not need to have clear on-disk signatures. Also it sheds light on the question of `mystery' geomagnetic storms; storms without clear solar origin. Preliminary inspection of STEREO data indicates that events like this are not uncommon, particularly during the ongoing period of deep solar minimum. Title: Quadrature STEREO Observations Determine the Nature of EUV Waves Authors: Kliem, Bernhard; Patsourakos, S.; Vourlidas, A.; Ontiveros, V. Bibcode: 2009SPD....40.2603K Altcode: One of the major discoveries of EIT on SOHO was the observation of large-scale EUV intensity disturbances which travel over significant fractions of the solar disk. These `EUV waves' are associated with CME onsets and can be either an MHD wave triggered by the eruption or the footprints of the associated CME, which currently is a subject of intense debate. EUV waves are better observed when their source region is close to disk center, whereas CME onsets and CMEs in general are better observed off-limb. Therefore, simultaneous multi-viewpoint observations of EUV waves are best suited to clarify the nature of these transients and to determine their true relationship with CMEs.

We present here the first quadrature STEREO observations of an EUV wave. The wave was observed on 2009 February 13 by both satellites, which were at a separation of 90 degrees. The wave originated from an erupting active region near disk center as seen from SC B and propagated over almost the entire visible solar disk. For SC A the active region was at the east limb and showed a small erupting bubble, expanding impulsively in both radial and lateral directions and inducing deflections of nearby and remote coronal structures. We present high cadence EUVI and COR1 measurements of both the wave (SC B), and the expanding EUV bubble (SC A), and of the resulting white-light CME (SC A; COR1). These would allow to quantify for the first time the true sizes and expansion characteristics of both the EUV wave and the associated CME.

Finally, we search for wave-associated features in 3D MHD simulations of CME onsets based on ideal MHD instabilities. These are compared with the STEREO observations. Title: STEREO Observations of a post-CME Current Sheet Authors: Patsourakos, S.; Vourlidas, A.; Stenborg, G. Bibcode: 2008AGUFMSH13B1552P Altcode: Ray-like features in the wake of Coronal Mass Ejections (CMEs) are often interpreted as current sheets produced by the eruption. The 3D geometry of such post-CME current sheets is largely unknown and its knowledge should place important constraints on CME physics and coronal conditions. An example of a post-CME current sheet was observed on April 9th 2008, in the aftermath of the 'cartwheel' CME, which was observed by Hinode, SoHO, STEREO and TRACE. The CME and the corresponding current sheet were well-observed by both STEREO spacecraft, which were separated by about 48 degrees the day of the event. We present here an analysis of the 3D morphology of the current sheet using data from the COR1 and COR2 coronagraphs from both STEREO spacecraft. We will attempt various forward models (e.g., slabs, cylinders) of the current sheet as seen by the COR1 and COR2 coronagraphs from both STEREO spacecraft. This will characterize the 3D geometry of the current sheet and more precisely its shape and its real width and length. Our forward modeling will also supply the radial variation of the density along the current sheet. This information will supply some estimates of the temperature and magnetic field distributions in and out the current sheet respectively. Title: First STEREO observation of a quiet sun CME Authors: Robbrecht, E.; Patsourakos, S.; Vourlidas, A. Bibcode: 2008AGUFMSH13B1560R Altcode: Streamer-blowouts form a particular class of CMEs characterized by a slow rise and swelling of the streamer that can last for days. While they are more massive than the average CME, their slow development complicates their association with features/activity in the low corona and hampers studies on their initiation mechanism(s). This paper reports on the first observation from 2 viewpoints of a streamer blowout CME. The event was observed by the SECCHI/COR2 A instrument as a typical flux-rope type CME, while a very faint partial halo was observed in COR2-B. The CME erupted from the east limb in the COR2 A field of view. EUVI-171 A images show a bright feature above the limb, traveling from the southern hemisphere towards the equator after which it slowly rises into the coronagraphic fields of view developing into the flux-rope structure CME. At the time of eruption the separation between the two STEREO spacecraft is sufficiently large (54 deg) to observe the source region face-on in STEREO-B. However, inspection of EUVI B data didn't reveal any particular source region, other than the quiet sun. No flaring activity could be related to the eruption. This observation shows unambiguously that a CME eruption does not necessarily have clear on-disk signature. Also it sheds light on the long-standing question of the necessity of having a flare for producing a CME. This result supplies strong constraints for CME initiation models. This type of observation could not have been achieved without the multi-viewpoint observations by STEREO. Title: Comparison of Automated Flare Location Algorithm Results to Solar Truth Authors: Plunkett, S. P.; Newmark, J. S.; Kunkel, V.; Patsourakos, S.; McMullin, D. R.; Hill, S. M. Bibcode: 2008AGUFMSA51A1534P Altcode: Accurate and timely detection of solar flares and determination of their heliocentric coordinates are key requirements for space weather forecasting. We report the results of a study to compare the results of multiple algorithms for automated determination of flare locations to "solar truth". The XFL algorithm determines flare locations in near real-time using GOES-12 SXI image data, and is triggered by GOES-12 XRS flare detections. We also consider H-alpha flare locations reported in the FLA data set, and the Latest Events (LEV) locations produced by LMSAL, based on GOES-12 SXI or SOHO EIT observations. We compare the results of each of these algorithms to solar truth heliocentric flare locations determined from analysis of GOES-12 SXI images of several hundred flares of C class and higher, during periods of high, moderate, and low solar activity between 2003 and 2006. We also compare the relative effectiveness of each of these algorithms for determining flare locations in near real-time, considering both timeliness and accuracy of the reported flare locations. Title: Observations and analysis of the April 9, 2008 CME using STEREO, Hinode TRACE and SoHO data Authors: Reeves, K. K.; Patsourakos, S.; Stenborg, G.; Miralles, M.; Deluca, E.; Forbes, T.; Golub, L.; Kasper, J.; Landi, E.; McKenzie, D.; Narukage, N.; Raymond, J.; Savage, S.; Su, Y.; van Ballegooijen, A.; Vourlidas, A.; Webb, D. Bibcode: 2008AGUFMSH12A..04R Altcode: On April 9, 2008 a CME originating from an active region behind the limb was well-observed by STEREO, Hinode, TRACE and SoHO. Several interesting features connected to this eruption were observed. (1) The interaction of the CME with open field lines from a nearby coronal hole appeared to cause an abrupt change in the direction of the CME ejecta. (2) The prominence material was heated, as evidenced by a change from absorption to emission in the EUV wavelengths. (3) Because the active region was behind the limb, the X-Ray Telescope on Hinode was able to take long enough exposure times to observe a faint current- sheet like structure, and it was able to monitor the dynamics of the plasma surrounding this structure. This event is also being studied in the context of activity that occurred during the Whole Heliosphere Interval (WHI). Title: Static and Impulsive Models of Solar Active Regions Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2008ApJ...689.1406P Altcode: 2008arXiv0808.2745P The physical modeling of active regions (ARs) and of the global corona is receiving increasing interest lately. Recent attempts to model ARs using static equilibrium models were quite successful in reproducing AR images of hot soft X-ray (SXR) loops. They however failed to predict the bright extreme-ultraviolet (EUV) warm loops permeating ARs: the synthetic images were dominated by intense footpoint emission. We demonstrate that this failure is due to the very weak dependence of loop temperature on loop length which cannot simultaneously account for both hot and warm loops in the same AR. We then consider time-dependent AR models based on nanoflare heating. We demonstrate that such models can simultaneously reproduce EUV and SXR loops in ARs. Moreover, they predict radial intensity variations consistent with the localized core and extended emissions in SXR and EUV AR observations, respectively. We finally show how the AR morphology can be used as a gauge of the properties (duration, energy, spatial dependence, and repetition time) of the impulsive heating. Title: 3D Numerical Simulation of a New Model for Coronal Jets Authors: Pariat, E.; Antiochos, S.; DeVore, C. R.; Patsourakos, S. Bibcode: 2008ESPM...12.3.28P Altcode: Recent solar observations with STEREO and HINODE have revealed evidence of twisting motions during the evolution of coronal jets. Furthermore, the observations indicate that some jets achieve near-Alfvenic velocities. Most models of jet are not capable of explaining these new observational features. In addition, the impulsiveness of jets, manifested as a brief, violent energy release phase in contrast to a slow, quasi-static energy storage phase storage, is an issue not easily addressed.

We will present the results of 3D numerical simulations of our model for coronal jets. The simulations were performed with our state-of-art adaptive mesh MHD solver ARMS. The basic idea of the model is that a jet is due to the release of magnetic twist when a closed field region undergoes interchange reconnection with surrounding open field. The fast reconnection between open and closed field results in the generation of nonlinear Alfven waves that propagate along the open field, accelerating plasma upward. We will show how the new stereoscopically-observed features of jets can be explained by the results of our numerical simulations Title: Highly Efficient Modeling of Dynamic Coronal Loops Authors: Klimchuk, J. A.; Patsourakos, S.; Cargill, P. J. Bibcode: 2008ApJ...682.1351K Altcode: 2007arXiv0710.0185K Observational and theoretical evidence suggests that coronal heating is impulsive and occurs on very small cross-field spatial scales. A single coronal loop could contain a hundred or more individual strands that are heated quasi-independently by nanoflares. It is therefore an enormous undertaking to model an entire active region or the global corona. Three-dimensional MHD codes have inadequate spatial resolution, and one-dimensional (1D) hydrodynamic codes are too slow to simulate the many thousands of elemental strands that must be treated in a reasonable representation. Fortunately, thermal conduction and flows tend to smooth out plasma gradients along the magnetic field, so zero-dimensional (0D) models are an acceptable alternative. We have developed a highly efficient model called "enthalpy-based thermal evolution of loops" (EBTEL), which accurately describes the evolution of the average temperature, pressure, and density along a coronal strand. It improves significantly on earlier models of this type—in accuracy, flexibility, and capability. It treats both slowly varying and highly impulsive coronal heating; it provides the time-dependent differential emission measure distribution, DEM(T), at the transition region footpoints; and there are options for heat flux saturation and nonthermal electron beam heating. EBTEL gives excellent agreement with far more sophisticated 1D hydrodynamic simulations despite using 4 orders of magnitude less computing time. It promises to be a powerful new tool for solar and stellar studies. Title: STEREO SECCHI Stereoscopic Observations Constraining the Initiation of Polar Coronal Jets Authors: Patsourakos, S.; Pariat, E.; Vourlidas, A.; Antiochos, S. K.; Wuelser, J. P. Bibcode: 2008ApJ...680L..73P Altcode: 2008arXiv0804.4862P We report on the first stereoscopic observations of polar coronal jets made by the EUVI/SECCHI imagers on board the twin STEREO spacecraft. The significantly separated viewpoints (~11°) allowed us to infer the 3D dynamics and morphology of a well-defined EUV coronal jet for the first time. Triangulations of the jet's location in simultaneous image pairs led to the true 3D position and thereby its kinematics. Initially the jet ascends slowly at ≈10-20 km s-1 and then, after an apparent "jump" takes place, it accelerates impulsively to velocities exceeding 300 km s-1 with accelerations exceeding the solar gravity. Helical structure is the most important geometrical feature of the jet which shows evidence of untwisting. The jet structure appears strikingly different from each of the two STEREO viewpoints: face-on in one viewpoint and edge-on in the other. This provides conclusive evidence that the observed helical structure is real and does not result from possible projection effects of single-viewpoint observations. The clear demonstration of twisted structure in polar jets compares favorably with synthetic images from a recent MHD simulation of jets invoking magnetic untwisting as their driving mechanism. Therefore, the latter can be considered as a viable mechanism for the initiation of polar jets. Title: Hot Spectral Emissions in Quiescent Active Regions and Nanoflare Heating Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2008AGUSMSP43C..02P Altcode: A leading candidate for the heating of active region (AR) coronal loops is the nanoflare model. This model treats coronal loops as collections of impulsively heated sub-resolution strands and explains several key observational aspects of warm (1-2 MK) coronal loops. However, the basic requirement of this model is that the strands initially reach very high temperatures of several MK before they cool down to canonical coronal temperatures. Therefore, the detection of hot plasmas in AR loops represents a stringest test of the nanoflare model. Previous work has shown that the best way to observe the postulated hot plasmas is by the means of spectroscopic observations in hot lines (T > 3 MK). The emission is predicted to be quite faint, but the EIS spectrometer onboard Hinode has sufficient sensitivity to allow us to perform such a test for the first time. We will present an analysis of the emission characteristics of quiescent coronal loops in a number of hot lines spanning approximately 3-12 MK (Ni XVII, Ca XV, Fe XVII, Ca XVII, Fe XXIII). We will show that hot plasmas are ubiquitous over entire active regions, and we will compare the measured intensities of both hot and warm lines with predictions of nanoflare models. Title: 3D Numerical Simulation and Stereoscopic Observations of Coronal Jets Authors: Pariat, E.; Antiochos, S. K.; Patsourakos, S.; DeVore, C. R. Bibcode: 2008AGUSMSP53A..05P Altcode: Recent solar observations have revealed that coronal jets are a more frequent phenomenon than previously believed. It is widely accepted that magnetic reconnection is the fundamental mechanism that gives rise to the jets. The improved spatial and temporal resolution of the STEREO observations in combination with stereoscopy yields new insights into the origins of coronal jets, and provides detailed data that can be used to test and refine models. We present the results of 3D numerical simulations of our model for coronal jets. The simulations were performed with our state-of-art adaptive mesh MHD solver ARMS. The basic idea of the model is that a jet is due to the release of twist as a closed field region undergoes interchange reconnection with surrounding open field. The photospheric driven evolution of the structure results in the generation of a non linear Alfven wave along the open fields. Using stereoscopic EUVI images, we reveal the presence of such twisted structure in a coronal jet event. This work was supported, in part, by NASA and ONR. Title: Understanding the Initiation of Polar Coronal Jets with STEREO/SECCHI Stereoscopic Observations Authors: Vourlidas, A.; Patsourakos, S.; Pariat, E.; Antiochos, S. Bibcode: 2008AGUSMSH23A..02V Altcode: Polar coronal jets are collimated transient ejections of plasma occurring in polar coronal holes. The kinematics and mostly the 3D morphology of jets place strong constraints on the physical mechanism(s) responsible for their initiation, and were not accessible before the STEREO mission. We report on the first stereoscopic observations of polar coronal jets made by the EUVI/SECCHI imagers on-board the twin STEREO spacecraft at spacecraft separations of ~ 11° and ~ 45°. Triangulations of the jet locations in simultaneous image pairs led to the true 3D position and thereby their kinematics. The most important geometrical feature of the observed jets is helical structures showing evidence of untwisting. The jet structure appear strikingly different from each of the two STEREO viewpoints: face-on in the one viewpoint and edge-on in the other. This provides solid evidence that the observed helical structure is real and not resulting from possible projection effects of single viewpoint observations. The clear demonstration of twisted structure in polar jets compares favorably with synthetic images from a recent MHD simulation of jets invoking magnetic untwisting as their driving mechanism. Title: Understanding Warm Coronal Loops Authors: Klimchuk, J. A.; Karpen, J. T.; Patsourakos, S. Bibcode: 2007AGUFMSH51C..05K Altcode: One of the great mysteries of coronal physics that has come to light in the last few years is the discovery that warm (~ 1 MK) coronal loops are much denser than expected for quasi-static equilibrium. It has been shown that the excess density can be explained if loops are bundles of unresolved strands that are heated impulsively and quasi-randomly to very high temperatures. This picture of nanoflare heating predicts that neighboring strands of different temperature should coexist and therefore that loops should have multi-thermal cross sections. In particular, emission should be produced at temperatures hotter than 2 MK. Such emission is sometimes but not always seen, however. We offer two possible explanations for the existence of over-dense warm loops without corresponding hot emission: (1) loops are bundles of nanoflare heated strands, but a significant fraction of the nanoflare energy takes the form of a nonthermal electron beam rather then direct heating; (2) loops are bundles of strands that undergo thermal nonequilibrium that results when steady heating is sufficiently concentrated near the footpoints. We verify these possibilities with numerical hydro simulations. Time permitting, we will show FeXVII line profile observations from EIS/Hinode that support the existence of nanoflare heating. Work supported by NASA and ONR. Title: Comparison of 3D Numerical Simulations with STEREO Observations of Coronal Jets Authors: Pariat, E.; Patsourakos, S.; Antiochos, S. K.; DeVore, C. R. Bibcode: 2007AGUFMSH41B..03P Altcode: Recent solar observations have revealed that coronal jets are a more frequent phenomenon than previously believed. It is widely accepted that magnetic reconnection is the fundamental mechanism that gives rise to the jets. The improved spatial and temporal resolution of the STEREO observations in combination with stereoscopy yields new insights into the origins of coronal jets, and provides detailed data that can be used to test and refine models. We present the results of a 3D numerical simulation of our model for coronal jets. The simulations were performed with our state-of-art adaptive mesh MHD solver ARMS. The basic idea of the model is that a jet is due to the release of twist as a closed field region undergoes interchange reconnection with surrounding open field. We compare the structure and dynamics of the simulated jet with actual EUVI observations, focusing on how the reconfiguration of the 3D magnetic field explains observed properties of the jet. We also discuss possible signatures for STEREO of twisted structures within jets. Finally, we discuss the implications of our simulations for future stereoscopic observations with STEREO. This work was supported, in part, by NASA and ONR. Title: Towards a Better Understanding of CME Onsets with SECCHI on STEREO Authors: Patsourakos, S.; Vourlidas, A. Bibcode: 2007AGUFMSH32A0779P Altcode: Observations of the first minutes in the life of Coronal Mass Ejections (CMEs) represent the main key into identifying the physical mechanism(s) behind them. Previous observations of CME onsets were limited by factors such as low cadence, small field of view, single-temperature coverage, and lack of 3D information. These limitations are significantly mitigated by the availability of SECCHI observations onboard the STEREO mission. We analyze a series of high-cadence, multi-temperature observations of CME onsets taken with the EUVI/SECCHI imagers tied with high-cadence coronagraphic COR1/SECCHI observations. We discuss how our perception of well-known features pertinent to CME onsets such as dimmings, EIT waves and cavities is shaped by the unique characteristics of SECCHI observations, and of the 3D information available in STEREO obervations in particular. We finally discuss how the generic elements of our observations compare with the expectations of CME models in an attempt to place some constraints on them. Title: The Cross-Field Thermal Structure of Coronal Loops from Triple-Filter TRACE Observations Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2007ApJ...667..591P Altcode: The highly suppressed thermal transport across the magnetic field in the solar corona makes the determination of the cross-field thermal distribution within coronal loops a powerful diagnostic of the properties of the heating process itself. The cross-field thermal structure is currently being strongly debated. Spectroscopic observations with high temperature fidelity but low spatial resolution indicate that some observed loops are multithermal, whereas imaging observations with high spatial resolution but low temperature fidelity indicate more isothermal conditions. We report here on triple filter observations of coronal loops made by the Transition Region and Coronal Explorer (TRACE), which has the best spatial resolution currently available. We tested the isothermal hypothesis using the emission measure loci technique and found that the loops are consistent with an isothermal plasma near 1.5 MK only if a generous estimate of the photometric uncertainties is used. A more restrictive estimate based on discussions with the TRACE experimenters rules out the isothermal hypothesis. The observations are much better explained by a multithermal plasma with significant emission measure throughout the range 1-3 MK. The details of the emission measure distribution are not well defined, however. Future subarcsecond spectroscopic observations covering a wide range of temperatures are the most promising means of unlocking the thermal structure of the corona. Title: The Quiet Sun Network at Subarcsecond Resolution: VAULT Observations and Radiative Transfer Modeling of Cool Loops Authors: Patsourakos, S.; Gouttebroze, P.; Vourlidas, A. Bibcode: 2007ApJ...664.1214P Altcode: One of the most enigmatic regions of the solar atmosphere is the transition region (TR), corresponding to plasmas with temperatures intermediate of the cool, few thousand K, chromosphere and the hot, few million K, corona. The traditional view is that the TR emission originates from a thin thermal interface in hot coronal structures, connecting their chromosphere with their corona. This paradigm fails badly for cool plasmas (~T<105 K), since it predicts emission orders of magnitude less than what it is observed. It was therefore proposed that the ``missing'' TR emission could originate from tiny, isolated from the hot corona, cool loops at TR temperatures. A major problem in investigating this proposal is the very small sizes of the hypothesized cool loops. Here, we report the first spatially resolved observations of subarcsecond-scale looplike structures seen in the Lyα line made by the Very High Angular Resolution Ultraviolet Telescope (VAULT). The subarcsecond (~0.3") resolution of VAULT allows us to directly view and resolve looplike structures in the quiet Sun network. We compare the observed intensities of these structures with simplified radiative transfer models of cool loops. The reasonable agreement between the models and the observations indicates that an explanation of the observed fine structure in terms of cool loops is plausible. Title: Modeling Active Regions with Steady and Impulsive Heating Authors: Patsourakos, Spiros; Klimchuk, J. Bibcode: 2007AAS...210.9124P Altcode: 2007BAAS...39..208P There has been considerable recent interest in constructing physical models of active regions (ARs) and the global coronal. Models based on static equilibrium theory are quite successful at reproducing soft X-ray (SXR) images of active regions. They however fail to predict the warm ( 1 MK) loops that are seen to permeate ARs in the EUV. Instead, the synthetic EUV images are dominated by intense footpoint emission. We demonstrate that the failure of static models to predict EUV loops is associated with the very weak dependence of loop temperature on loop length in models that are based on a single heating mechanism and that match the SXR observations. The models predict either SXR loops or EUV loops, but not both. We therefore consider time-dependent AR models based on nanoflare heating. We demonstrate that such models can simultaneously reproduce both SXR and EUV loops. Moreover, they explain the general tendency for SXR emission to dominate in the cores of ARs and EUV emission to dominate in the periphery. We finally show how the properties of nanoflares (energy, duration, spatial dependence, repetition time) can affect the AR morphology.

Research supported by NASA and ONR. Title: Impulsive Coronal Heating At Sub- Arcsecond Scales: What Is The Best Diagnostic? Authors: Patsourakos, S.; Klimchik, J. A. Bibcode: 2007ESASP.641E..22P Altcode: Significant observational and theoretical evidence suggests that coronal heating operates at sub- rcsecond, currently unresolved, spatial scales and is impulsive in time. We demonstrate that the most sensitive diagnostic for this type of heating is provided by spectroscopic observations in the early phase of such events. We demonstrate that the spectra of hot lines ( 5 MK), observed at arcsecond resolution with the EIS spectrometer onboard the recently launched Hinode mission, hold the signature of the impulsive heating process via the development of asymmetric profiles. Solar Orbiter (SolO) will provide a unique opportunity to directly view the postulated sub-arcsecond impulsive energy releases. We demonstrate that the superior spatial resolution of the Orbiter EUV remote sensing instrumentation should be tuned to high temperature plasmas in order to resolve the individual strands. Title: Nonthermal Spectral Line Broadening and the Nanoflare Model Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2006ApJ...647.1452P Altcode: A number of theoretical and observational considerations suggest that coronal loops are bundles of unresolved, impulsively heated strands. This ``nanoflare'' model, as it is sometimes called, predicts high-speed evaporative upflows, which might be revealed as nonthermal broadening of spectral line profiles. We have therefore generated synthetic line profile observations based on one-dimensional hydrodynamic simulations for comparison with actual observations. The predicted profiles for Ne VIII (770.4 Å), a transition region line, and Mg X (624.9 Å), a warm coronal line, have modest broadening that agrees well with existing observations. The predicted profiles for Fe XVII (254.87 Å), a hot line that will be observed by the Extreme Ultraviolet Imaging Spectrometer (EIS) on the Solar-B mission, are somewhat broader and are also consistent with the limited number of hot line observations that are currently available. Moreover, depending on the properties of the assumed nanoflare and other parameters of the simulation, the Fe XVII profile can have distinctive enhancements in the line wing. This indicates a powerful diagnostic capability that can be exploited once Solar-B is launched. Title: Testing Nanoflare Heating in Coronal Loops With Observations From the Extreme Ultraviolet Imaging Spectrometer On-board the SOLAR-B Mission Authors: Patsourakos, Spiros; Klimchuk, J. A. Bibcode: 2006SPD....37.0124P Altcode: 2006BAAS...38..219P A number of theoretical and observational considerations suggest that coronal loops are bundles of unresolved, impulsively heated strands. This "nanoflare" model, as it is sometimes called, predicts high-speed evaporative upflows, which might be revealed as non-thermal broadening of spectral line profiles. We have therefore generated synthetic line profile observations based on 1D hydrodynamic simulations of nanoflare heated loop bundles.We will show that hot lines (T>5MK) hold the imprints of the heating process via the development of distinct enhancements in the line wings. These signatures do not appear in the profiles of cooler lines, which is fully consistent with existing observations. We will demonstrate how the spectra of hot lines from the Extreme Ultraviolet Imaging Spectrometer (EIS) on-board the upcoming SOLAR-B mission can be used to test the basic nanoflare picture and perhaps even to pinpoint the properties of the nanoflares, such as their energy content, duration, and spatial dependence. We will present sample observing programs for studying nanoflare heating in coronal loops that utilize EIS and other instrumentation on-board SOLAR-B and STEREO.Research supported by NASA and ONR. Title: Coronal Loop Heating by Nanoflares: The Impact of the Field-aligned Distribution of the Heating on Loop Observations Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2005ApJ...628.1023P Altcode: Nanoflares occurring at subresolution strands with repetition times longer than the coronal cooling time are a promising candidate for coronal loop heating. To investigate the impact of the spatial distribution of the nanoflare heating on loop observables, we compute hydrodynamic simulations with several different spatial distributions (uniform, loop top, randomly localized, and footpoint). The outputs of the simulations are then used to calculate density and temperature diagnostics from synthetic TRACE and SXT observations. We find that the diagnostics depend only weakly on the spatial distribution of the heating and therefore are not especially useful for distinguishing among the different possibilities. Observations of the very high temperature plasmas that are present only in the earliest stages of nanoflares can shed more light on the field-aligned distribution of the heating. Title: Coronal Loop Heating by Nanoflares: Non-thermal Velocities Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2005AGUSMSP41A..06P Altcode: Spectroscopic observations show non-negligible non-thermal velocities under coronal conditions. These motions place tight constraints on any coronal heating mechanism that should be able to reproduce them. We calculate the non-thermal velocities predicted by the nanoflare model. We perform 1D time-dependent hydrodynamic simulations of nanoflares occurring at sub-resolution strands, that make up the observed coronal loops and calculate profiles for representative spectral lines. We show that: (1) the calculated non-thermal velocities compare favorably with observations of cool and warm spectral lines and (2) the profiles of hot lines, that would be available in observations from the Extreme Ultraviolet Imaging Spectrometer (EIS) spectrometer onboard the SOLAR-B mission, can exhibit significant blue-wing asymmetries which can be used as a monitor of nanoflare properties. Research supported by NASA and ONR. Title: Coronal Loop Heating by Nanoflares: The Influence of the Field-aligned Distribution of the Heating on Observables Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2005AGUSMSP41A..05P Altcode: We investigate the effect of the spatial distribution of nanoflare heating on loop observables. We perform 1D time-dependent hydrodynamic simulations of nanoflares occurring at sub-resolution strands, that make up the observed coronal loops. The simulations use different spatial forms for the nanoflare heating (randomly localized, footpoint, uniform loop top). The outputs of the simulations are then used to calculate diagnostics from synthetic TRACE and SXT observations. We find that the diagnostics depend only weakly on the spatial distribution of the heating, and therefore are not especially useful for distinguishing among the different possibilities. We propose that the best way to study the field-aligned spatial distribution of nanoflare heating is to observe the very high temperature plasmas that are present only in the earliest stages of an event. Research supported by NASA and ONR. Title: Highly Efficient Modeling of Dynamic Coronal Loops Authors: Klimchuk, J. A.; Patsourakos, S.; Cargill, P. J. Bibcode: 2005AGUSMSP14A..03K Altcode: It now seems clear that many coronal loops, especially those observed by TRACE and EIT, are inherently dynamic and composed of large numbers of impulsively-heated strands. Modeling these loops in full detail is extremely challenging, and modeling entire active regions or the whole Sun is completely out of the question unless approximate techniques are used. We have developed a simplified set of equations that is remarkably accurate at describing the evolution of the thermodynamic variables (T, P, n, v) averaged along the magnetic field of an individual strand. The equations can be solved ten thousand times more quickly than the full 1D hydro equations. This "0D" model relaxes two key assumptions of Cargill's (1994) nanoflare model: (1) the heating can have any time-dependent profile and need not be instantaneous; and (2) thermal conduction cooling and radiation cooling occur together at all times, in varying proportions. We here describe the essential features of the model and show examples of how well it works. Title: The Effect of the Spatial Distribution of Nanoflare Heating on Loop Observables Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2004ESASP.575..297P Altcode: 2004soho...15..297P No abstract at ADS Title: A Model for Bright Extreme-Ultraviolet Knots in Solar Flare Loops Authors: Patsourakos, S.; Antiochos, S. K.; Klimchuk, J. A. Bibcode: 2004ApJ...614.1022P Altcode: EUV observations often indicate the presence of bright knots in flare loops. The temperature of the knot plasma is of the order of 1 MK, and the knots themselves are usually localized somewhere near the loop tops. We propose a model in which the formation of EUV knots is due to the spatial structure of the nonflare active region heating. We present the results of a series of one-dimensional hydrodynamic, flare-loop simulations, which include both an impulsive flare heating and a background, active region heating. The simulations demonstrate that the formation of the observed knots depends critically on the spatial distribution of the background heating during the decay phase. In particular, the heating must be localized far from the loop apex and have a magnitude comparable to the local radiative losses of the cooling loop. Our results, therefore, provide strong constraints on both coronal heating and postflare conditions. Title: Bright EUV Knots in Solar Flare Loops: Constraints on Coronal Heating Authors: Patsourakos, S.; Antiochos, S.; Klimchuk, J. Bibcode: 2004AAS...204.8705P Altcode: 2004BAAS...36Q.819P EUV observations often indicate the presence of bright knots in flare loops. The temperature of the knot plasma is of order 1MK, and the knots themselves are usually localized somewhere near the loop tops. We propose a model in which the formation of EUV knots is due to the spatial structure of the non-flare active region heating. We present the results of a series of 1D hydrodynamic, flare-loop simulations, which include both an impulsive flare heating and a background, active region heating. The simulations demonstrate that the formation of the observed knots depends critically on the spatial distribution of the background heating during the decay phase. In particular, the heating must: (1) be localized, (2) be situated far from the loop apex and (3) have a magnitude comparable with the local radiative losses of the cooling loop. Our results, therefore, provide strong constraints on both coronal heating and post-flare conditions.

Research supported by NASA and ONR. Title: Mass and Kinetic Energy Distributions of Coronal Mass Ejections in 1996-2002 Authors: Vourlidas, A.; Patsourakos, S. Bibcode: 2004AAS...204.7303V Altcode: 2004BAAS...36..800V We present the mass and kinetic energy distributions of coronal mass ejections observed by LASCO between 1996 and 2002. The sample includes more than 4000 events. Events with projected widths larger than 120 deg were excluded because of uncertainties in the calculation of the mass and speed for such large events.

We compare the LASCO mass and energy distribution to similar distributions from Solwind and soft x-ray flares. In particular, we find that the CME kinetic energy distribution follows a power law similar to the one found for solar flares. The implications of our findings are discussed in the paper. Title: The Inability of Steady-Flow Models to Explain the Extreme-Ultraviolet Coronal Loops Authors: Patsourakos, S.; Klimchuk, J. A.; MacNeice, P. J. Bibcode: 2004ApJ...603..322P Altcode: Recent observations from the Transition Region and Coronal Explorer (TRACE) and the EUV Imaging Telescope (EIT) show that warm (T~1-1.5 MK) EUV coronal loops in active regions generally have enhanced densities, enhanced pressure scale heights, and flat filter ratio (temperature) profiles in comparison with the predictions of static-equilibrium theory. It has been suggested that mass flows may explain these discrepancies. We investigate this conjecture using one-dimensional hydrodynamic simulations of steady flows in coronal loops. The flows are driven by asymmetric heating that decreases exponentially along the loop from one footpoint to the other. We find that a sufficiently large heating asymmetry can produce density enhancements consistent with a sizable fraction of the observed loops, but that the pressure scale heights are smaller than the corresponding gravitational scale heights, and that the filter ratio profiles are highly structured, in stark contrast to the observations. We conclude that most warm EUV loops cannot be explained by steady flows. It is thus likely that the heating in these loops is time dependent. Title: Solar Physics from Space for the Next Solar Cycle Authors: Vourlidas, Angelos; Patsourakos, Spiros Bibcode: 2004hell.conf...78V Altcode: No abstract at ADS Title: Coronal Loop Heating by Nanoflares: Some Observational Implications Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2004hell.conf...35P Altcode: No abstract at ADS Title: Are All Coronal Loops Heated by Nanoflares? Authors: Klimchuk, J. A.; Patsourakos, S.; Winebarger, A. R. Bibcode: 2003SPD....34.1006K Altcode: 2003BAAS...35R.825K Observations from TRACE, SOHO, and Yohkoh have revealed new details of coronal loops that make them more mysterious than ever. One of the biggest puzzles concerns the loop density. Hot (> 2 MK) loops observed by Yohkoh tend to be under dense compared to the predictions of equilibrium theory, while warm ( 1 MK) loops observed by TRACE and EIT tend to be over dense. Some over dense loops can be explained by steady heating that is concentrated near one or both of the loop legs, but a majority of these loops cannot.

We here consider the possibility that observed loops are comprised of large numbers of unresolved strands that are heated impulsively and randomly by nanoflares. The loops appear quasi-steady even though the individual sub-strands are highly time dependent. When the strands are hot, they cool primarily by thermal conduction and are under dense, but when they are warm, they cool primarily by radiation and are over dense. Since Yohkoh and TRACE are sensitive to different strands, we might expect them to observe the under and over densities that they do.

To evaluate the feasibility of this universal model of coronal loops, we have performed 1D hydrodynamic simulations of impulsively heated strands and compared them with observations from Yohkoh and TRACE. The results are encouraging in many respects, but difficulties remain. In this presentation, we discuss the successes and failures of the model.

This work was supported by NASA and ONR. Title: Can Steady-state Mass Flows Explain the Non-hydrostatic Cool EUV Coronal Loops in Active Regions? Authors: Patsourakos, S.; Klimchuk, J. A. Bibcode: 2003SPD....34.1009P Altcode: 2003BAAS...35..826P Recent EIT/TRACE observations of cool (≈ 1-1.5 MK) EUV coronal loops in active regions showed that these loops are very often characterized by greatly enhanced pressure scale-heights and densities compared to the predictions of static equilibrium theory. It has been suggested that mass flows may explain these over-dense and over-pressure loops. We investigate this conjecture by the means of 1D hydrodynamic simulations of steady-state mass flows in coronal loops. The mass flows in our calculations are driven by asymmetric heating that decreases exponentially along the loop from one footpoint all way to the other. By considering several representative cases for the magnitude and the length scale of the applied asymmetric heating, we determine how steady-state mass flows affect the thermodynamic structure of coronal loops and assess whether they can lead to enhanced pressure scale-heights and densities. Research supported in part by NASA and ONR. Title: Bright Knots in EUV Post-flare Loops : TRACE Observations and 1D Hydrodynamic Modeling Authors: Patsourakos, S.; Antiochos, S. K.; Klimchuk, J. A. Bibcode: 2002AGUFMSH21C..04P Altcode: EUV post-flare loops often possess bright knots along them. Some examples of such post-flare loops seen by TRACE will be shown, along with a brief outline of their properties. We will then present the results of a series of 1D hydrodynamic simulations of flaring loops, which employ different heating functions for the impulsive and decay phase of the simulated flares. It will be demonstrated that the creation of these knots depends crucially on the spatio-temporal distribution of the heating during the decay phase. This provides strong constraints on both post-flaring conditions and AR loop heating. We will finally briefly outline how SDO instrumentation could improve our knowledge of this topic. Research supported in part by NASA and ONR. Title: Ion Effective Temperatures in Polar Coronal Holes: Observations versus Ion-Cyclotron Resonance Authors: Patsourakos, S.; Habbal, S. R.; Hu, Y. Q. Bibcode: 2002ApJ...581L.125P Altcode: The resonant cyclotron interaction between ion-cyclotron waves and solar wind species is considered nowadays to be a strong candidate for heating and acceleration of protons, α-particles, and heavy ions. A crucial physical parameter for determining the amount and the location of significant heating and acceleration, which the different solar wind ions receive from the waves in the frame of the ion-cyclotron mechanism, is their charge-to-mass ratio q/m. Therefore, comparisons of ion temperatures derived from spectroscopic observations and calculated by ion-cyclotron models, for ions that span a broad range in q/m, would provide a rigorous test for such models. By using an ion-cyclotron model, we calculate the effective temperatures for 10 different ions that cover the range 0.16-0.37 in q/m. Effective temperatures correspond to unresolved thermal motions and wave motions. The good agreement between our calculations, based on the specific mechanism that we employed here (ion-cyclotron resonance) and on spectroscopic observations of effective temperatures in polar coronal holes, provides support that the above mechanism accounts for the energetics and kinematics of fast solar wind heavy ions. However, such an agreement does not prove that other potential mechanisms can be excluded. Title: Fuzzy hot post-flare loops versus sharp cool post-flare loops Authors: Patsourakos, S.; Antiochos, S. K.; Klimchuk, J. A. Bibcode: 2002ESASP.505..207P Altcode: 2002solm.conf..207P; 2002IAUCo.188..207P By using high spatial resolution TRACE EUV observations we show that hot (≍2 MK) post-flare loops are fuzzier than the cooler (≍1 MK) ones. A simple 0d model of a cooling loop arcade, where different loops in the arcade start to cool down at slightly different initial conditions, is sufficient to reproduce qualitatively the observed behavior of the EUV post-flare loops. Title: Soho Contribution to Prominence Science Authors: Patsourakos, Spiros; Vial, Jean-Claude Bibcode: 2002SoPh..208..253P Altcode: We present the main current issues concerning prominence studies. We recall the large range of plasma parameters found in prominences which makes the work of the MHD modeler more difficult. We also summarize the capabilities of the SOHO instrumentation. We present and discuss the most recent SOHO results concerning the determination of temperature, densities, and velocities. We put some emphasis on the different morphologies observed, the diagnostic capabilities of the Lyman lines profiles when accompanied by improved non-LTE modeling, and the information gathered from the first prominence oscillations measured from space. We also make an account of eruptive prominences. We finally discuss what could be done with present and future SOHO data to improve our understanding of prominences. Title: Solar cycle variation of the temperature structure within the cores of coronal streamers Authors: Culhane, J. L.; Foley, C. R.; Patsourakos, S.; Mackay, D. Bibcode: 2002ESASP.508..371C Altcode: 2002soho...11..371C We use the Coronal Diagnostic Spectrometer onboard the Solar and Heliospheric Observatory (SOHO) to analyze conditions in coronal streamer structures observed close to solar minimum (1996, July 8) and near maximum (1999, August 5). From emission line intensities (Fe IX-XV ions), the line ratio method gives the radial temperature behaviour. The solar minimum peak values were about 1.4 MK at 1.3 R0, while near solar maximum values were consistent with Yohkoh observations at the last maximum, displaying an asymptotic temperature of around 2.2 MK above 1.2 R0. We discuss the observations in relation to possible mechanisms for energy deposition in large coronal structures. Title: Hot versus cool coronal loops Authors: Patsourakos, S.; Klimchuk, J. A.; Antiochos, S. K. Bibcode: 2002AAS...200.0209P Altcode: 2002BAAS...34..640P EUV and SXR observations show respectively that cool (1 MK) loops are finer and maybe more dynamic than hotter (2 MK) ones. Whether this reflects a fundamental difference in the properties of the heating mechanism in action in each loop class is not yet clear. We will address some aspects of this issue by combining EUV and SXR observations of such loops with eventually hydrodynamic simulations of a nano-flare heated corona. Research supported in part by ONR and NASA. Title: Intermittent behavior in the transition region and the low corona of the quiet Sun Authors: Patsourakos, S.; Vial, J. -C. Bibcode: 2002A&A...385.1073P Altcode: We present an analysis of light-curves obtained in the O IV and Ne VIII transition region and low corona lines, that were simultaneously recorded in a quiet Sun region by SUMER/SOHO. By using the flatness spectrum of the observed light-curves we searched for intermittency signatures. It was found that a significant proportion of points in the observed area exhibit clear indications of intermittency, irrespectively of their intrinsic intensity. Our findings give favor to an impulsively heated transition region and corona via intermittent-type MHD turbulence. Title: What are the Origins of Quiescent Coronal Soft X-Rays? Authors: Foley, C. R.; Culhane, J. L.; Patsourakos, S.; Yurow, R.; Moroney, C.; Mackay, D. Bibcode: 2002mwoc.conf..341F Altcode: We have examined the evolution and modulation of the Sun's atmosphere from the photosphere up to the outer corona through the decline and rise of solar cycles 22, and 23 respectfully. For this we have used Yohkoh soft X-ray telescope (SXT) images, Kitt peak magnetograms and EUV spectra provided by the Coronal Diagnostic Spectrometer (CDS). We find as Hara (1996, 1997) found, that there is a modulation of the coronal brightness which varies annually in the high latitude activity zones, and that this is linked to the presence and disappearance of active regions on the sun's disk. We interpret our results with regards to the emergence and diffusion of magnetic flux. We find that the appearance of high latitude activity zones may be explained simply by the decay of diffused active region flux, We also find evidence for a positive temperature gradient within the corona from the emission profiles in the different lines. Title: Solar cycle variation of the temperature structure within the cores of coronal streamers Authors: Foley, C. R.; Patsourakos, S.; Culhane, J. L.; MacKay, D. Bibcode: 2002A&A...381.1049F Altcode: We use the Coronal Diagnostic Spectrometer onboard the Solar and Heliospheric Observatory (SOHO) to analyze conditions in coronal streamer structures observed close to solar minimum (1996 July 8) and near maximum (1999 August 5). We measured the intensities of emission lines from Fe IX-XV ions and found the most intense emission to be from Fe XI at solar minimum and from Fe XV at solar maximum. We then used the line ratio method with transitions in selected ions to extract the radial temperature behavior in the structures. The solar minimum peak values were about 1.4 MK at 1.3 Rsun, while values derived close to solar maximum were consistent with the Yohkoh observations at the last maximum, displaying an apparently asymptotic temperature of around 2.2 MK above 1.2 Rsun. We discuss the observations in relation to possible mechanisms for energy deposition in large coronal structures at different phases of the solar cycle. Title: The polar coronal holes and the fast solar wind: Some recent results Authors: Patsourakos, S.; Habbal, S. -R.; Vial, J. -C.; Hu, Y. Q. Bibcode: 2001AIPC..598..299P Altcode: 2001sgc..conf..299P We report on recent results on the source regions of the fast solar wind: the Polar Coronal Holes (PCH). They concern a comparison between the effective temperatures for a large set of different ions obtained from observations in the inner corona of PCH and from a fast wind numerical model based on the ion-cyclotron resonant dissipation of high-frequency Alfvén waves. We also report on some preliminary results from our modeling concerning the Fe/O ratio in the inner corona in PCH. . Title: Analysis of a UV Event in a Polar Coronal Hole Authors: Patsourakos, Spiros; Vial, Jean-Claude Bibcode: 2001SoPh..203...39P Altcode: We present observations of a UV event which occurred in a polar coronal hole. They were obtained by SUMER on SOHO in several chromospheric and transition region spectral lines. Its birth site was about 50 arc sec inside the limb and in a network lane showing a net outflow before its initiation. The event had an extension of about 5 arc sec along the slit, a duration of about 3 min and was characterized by a large increase of intensity together with a significant line broadening with, however, downflows of about 50 km s−1 being dominant. Proper motions with a velocity of about 10 km s−1 were also observed. The event appeared at middle transition (O vi) temperatures and it simultaneously showed up in chromospheric (O i, Ly β) and low transition region (C ii) temperatures. We discuss this event in view of different scenarios to account for it. Our event could be a part of the large family of quiet-Sun explosive events observed by Ryutova and Tarbell (2000) taking place in polar coronal holes that are triggered by magnetic reconnection in the low solar atmosphere. Title: High-resolution EUV imaging and spectroscopy of the corona Authors: Patsourakos, Spiros; Vial, J. -C. Bibcode: 2001ESASP.493...13P Altcode: 2001sefs.work...13P We present a set of imagers and spectrometer which have been proposed as a strawman payload on board the Solar Orbiter mission. The scientific requirements of the mission are put in the context of the main issues presently discussed in solar physics. The on-going successful space solar missions have evidenced a very fine structuring of the solar atmosphere and its role in various processes at work for coronal heating, wind acceleration, flaring activity, etc. This is especially true for magnetic reconnection which seems to proceed at many different scales. These results point at the need of observations substantially improving both the spatial resolution and the multi-temperature (multi-wavelength) coverage. Solar Orbiter offers a unique opportunity to analyze this fine structure (e.g. the internal structure of the thin loops observed by TRACE) in closed and open fields. It will allow for a diagnostic of regions such as the magnetic network which seems to play a major role in the wind acceleration, in conjunction with in-situ observations of the ejected plasma. Title: Searching the source regions of the fast solar wind in polar coronal holes: some recent SOHO/eclipse results and the potential of the Solar Orbiter Authors: Patsourakos, Spiros; Vial, J. -C. Bibcode: 2001ESASP.493..321P Altcode: 2001sefs.work..321P No abstract at ADS Title: Outflow velocity of interplume regions at the base of Polar Coronal Holes Authors: Patsourakos, S.; Vial, J. -C. Bibcode: 2000A&A...359L...1P Altcode: We report on SUMER/SOHO observations at 1.05 Rsun of a well identified interplume region in a South Pole Coronal Hole. Combination of Doppler shifts and Doppler dimming measurements allowed to determine, for the first time, the total wind outflow velocity (~ 67 km s-1) at this height. Our calculations of the outflow velocity benefit from co-spatial and almost co-temporal observations. This large outflow velocity is a strong argument in favour of the interplumes being the main source of the fast solar wind. We find that the mass flux density through the observed interplume is 4.8 10-10 g cm-2s-1 which yields 10-15 g cm-2s-1 at 1 AU with an expansion factor of 11. Title: Contribution a l'etude du chauffage de la couronne solaire et de l'acceleration du vent solaire dans les trous coronaux Title: Contribution a l'etude du chauffage de la couronne solaire et de l'acceleration du vent solaire dans les trous coronaux Title: Investigation of coronal heating and solar wind acceleration in coronal holes; Authors: Patsourakos, Spiros Bibcode: 2000PhDT.......234P Altcode: No abstract at ADS Title: Transition-Region Network Boundaries in the Quiet Sun: Width Variation with Temperature as Observed with CDS on SOHO Authors: Patsourakos, S.; Vial, J. -C.; Gabriel, A. H.; Bellamine, N. Bibcode: 1999ApJ...522..540P Altcode: We report here the results of a study of the temperature variation of the network boundary thicknesses in the quiet-Sun transition region. A Fourier-based two-dimensional autocorrelation method has been applied to 240''×240'' rasters obtained in several transition-region lines by the CDS spectrometer on SOHO. The quantitative variation of the network boundary width with temperature has been obtained for the first time in a full two-dimensional field. It appears that network boundaries have an almost constant width up to a temperature of about 105.4 K and then fan out rapidly at coronal temperatures. This expansion of the transition-region network boundaries with temperature is found to be quantitatively in agreement with earlier theoretical models of the transition region. Title: Coordinated observations between SOHO/SUMER and ground during the 1998 total eclipse: Non-thermal line broadenings and electron densities in a polar coronal hole Authors: Patsourakos, S.; Vial, J. -C.; Gabryl, J. -R.; Koutchmy, S.; Schühle, U. Bibcode: 1999AIPC..471..285P Altcode: 1999sowi.conf..285P Alfvén waves represent one of the most prominent ways of heating the solar corona and accelerating the solar wind. One of their signatures is to broaden the spectral lines in excess of their thermal width. Here we aim to combine observations of non-thermal broadenings measured by SUMER in OVI (1037.6 Å) line and electronic densities derived from white-light observations during the 1998 total eclipse. After checking the validity of the frequently-used assumption of equal ion and electron temperatures, we compute the variation of the non-thermal velocity as a function of height in an interplume region within the south polar coronal hole. Title: Outflow Velocities at the Base of a Polar Coronal Hole During the 1998 Total Eclipse Authors: Patsourakos, S.; Vial, J. -C.; Gabryl, J. -R.; Koutchmy, S.; Schühle, U. Bibcode: 1999SSRv...87..291P Altcode: Polar coronal holes represent the most convincing site from which the high-speed solar wind originates. Here we report high-accuracy Doppler shifts measured in the O VI (1037.6 Å) line obtained by SUMER on SOHO inside an interplume region within the south polar coronal hole. We infer limits on the outflow velocity and draw hints about the flow geometry. Title: Solar chromospheric structures observed in UV ressonance lines : a multivariate analysis approach Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C. Bibcode: 1999CR2...322..337P Altcode: We present the results of a statistical analysis carried out from a data base of 6 solar chromospheric emission lines recorded simultaneously and with high spectral resolution. An empirical and a clustering method for separating the different solar structures contributions have been used and been found in a good agreement. Mean profiles corresponding to the different populations have been built. Correlations of different parameters for each profile allowed us to deduce different properties of the solar chromosphere, such as the existence of magnetic canopies and downflows in active regions. Title: Solar chromospheric structures observed in UV resonance lines: a multivariate analysis approach. Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C. Bibcode: 1998CRASB.326..337P Altcode: The authors present the results of a statistical analysis carried out from a data base of six solar chromospheric emission lines recorded simultaneously and with high spectral resolution. An empirical and a clustering method for separating the different solar structure contributions have been used and found to be in good agreement. Mean profiles corresponding to the different populations have been built. Correlations of different parameters for each profile allowed one to deduce different properties of the solar chromosphere, such as the existence of magnetic canopies and downflows in active regions. Title: Simulated white-light images of coronal structures as obtained by the CORI imager on-board a solar probe Authors: Patsourakos, S.; Vial, J. -C. Bibcode: 1997AIPC..385..129P Altcode: 1997recs.conf..129P A white-light coronal imager called CORI to be implemented on a solar probe has been proposed by Habbal et al. (1995). Its scientific objectives concern the investigation of the solar corona and the source of the solar wind. It is aimed as a complement to the in-situ instruments. This paper presents some simulations of the images that will be recorded when observing solar structures of increasing complexity during the close encounter phase of the trajectory. These attempts should be considered as a first step towards the assessment of the full scientific capabilities of CORI and the definition of the observing strategy. Title: Low Transition-Region Characteristics of Equatorial Coronal Holes Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C. Bibcode: 1997ESASP.404..577P Altcode: 1997cswn.conf..577P No abstract at ADS Title: First Results of SOHO's Joint Observing Programme 40 Authors: Patsourakos, S.; Bocchialini, K.; Vial, J. -C. Bibcode: 1997IAUJD..19E..38P Altcode: The first results of SOHO's JOP 40 are presented. This program proposes to study the chromospheric to transition region of equatorial coronal holes in order to derive parameters such as the temperature, the density, using different lines formed at different altitudes, in different places: the boundary of a coronal hole or the central region, on the disk. The two components of the chromospheric quiet Sun, network and internetwork, should be observed, in and out of an equatorial coronal hole.