Author name code: madjarska ADS astronomy entries on 2022-09-14 author:"Madjarska, Maria" ------------------------------------------------------------------------ Title: Mini-filament eruption, QSL reconnection, and reconnection-driven outflows: IRIS and AIA/HMI/SDO observations and modelling Authors: Madjarska, Maria S.; Mackay, Duncan H.; Galsgaard, Klaus; Xie, Haixia; Wiegelmann, Thomas Bibcode: 2022cosp...44.2533M Altcode: We will present unique observations of a mini-filament eruption associated with cancelling magnetic fluxes of a small-scale loop system known as a coronal bright point. The event is uniquely recorded in both the imaging and spectroscopic data taken with the Interface Region Imaging Spectrograph (IRIS). The study aims at providing a better understanding of the physical processes driving these ubiquitous small-scale eruptions. We also analysed images taken in the extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA) and line-of-sight magnetic-field data from the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamics Observatory. As the observations can only give an inkling about the possible physical processes at play, we also employed a non-linear force-free field (NLFFF) relaxation approach based on the HMI magnetogram time series. Furthermore, we computed the squashing factor, Q, in different horizontal planes of the NLFFF model. This allowed us to further investigate the evolution of the magnetic-field structures involved in the eruption process. Title: Eruptions from coronal bright points: A spectroscopic view by IRIS of a mini-filament eruption, QSL reconnection, and reconnection-driven outflows Authors: Madjarska, Maria S.; Mackay, Duncan H.; Galsgaard, Klaus; Wiegelmann, Thomas; Xie, Haixia Bibcode: 2022A&A...660A..45M Altcode: 2022arXiv220200370M Context. Our study investigates a mini-filament eruption associated with cancelling magnetic fluxes. The eruption originates from a small-scale loop complex commonly known as a coronal bright point (CBP). The event is uniquely recorded in both the imaging and spectroscopic data taken with the Interface Region Imaging Spectrograph (IRIS).
Aims: The investigation aims to gain a better understanding of the physical processes driving these ubiquitous small-scale eruptions.
Methods: We analysed IRIS spectroscopic and slit-jaw imaging observations as well as images taken in the extreme-ultraviolet channels of the Atmospheric Imaging Assembly (AIA) and line-of-sight magnetic-field data from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory. As the observations can only indicate the possible physical processes at play, we also employed a non-linear force-free field (NLFFF) relaxation approach based on the HMI magnetogram time series. This allowed us to further investigate the evolution of the magnetic-field structures involved in the eruption process.
Results: We identified a strong small-scale brightening as a micro-flare in a CBP, recorded in emission from chromospheric to flaring plasmas. The mini-eruption is manifested via the ejection of hot (CBP loops) and cool (mini-filament) plasma recorded in both the imaging and spectroscopic data. The micro-flare is preceded by the appearance of an elongated bright feature in the IRIS slit-jaw 1400 Å images, located above the polarity inversion line. The micro-flare starts with an IRIS pixel size brightening and propagates bi-directionally along the elongated feature. We detected, in both the spectral and imaging IRIS data and AIA data, strong flows along and at the edges of the elongated feature; we believe that these represent reconnection outflows. Both edges of the elongated feature that wrap around the edges of the erupting MF evolve into a J-type shape, creating a sigmoid appearance. A quasi-separatrix layer (QSL) is identified in the vicinity of the polarity inversion line by computing the squashing factor, Q, in different horizontal planes of the NLFFF model.
Conclusions: This CBP spectro-imaging study provides further evidence that CBPs represent downscaled active regions and, as such, they may make a significant contribution to the mass and energy balance of the solar atmosphere. They are the sources of all range of typical active-region features, including magnetic reconnection along QSLs, (mini-)filament eruptions, (micro-)flaring, reconnection outflows, etc. The QSL reconnection site has the same spectral appearance as the so-called explosive events identified by strong blue- and red-shifted emission, thus providing an answer to an outstanding question regarding the true nature of this spectral phenomenon.

Movies associated to Figs. A.1 and A.2 are available at https://www.aanda.org Title: Investigation of the subsurface structure of a sunspot based on the spatial distribution of oscillation centers inferred from umbral flashes Authors: Cho, Kyuhyoun; Chae, Jongchul; Madjarska, Maria S. Bibcode: 2021A&A...656A..86C Altcode: 2021arXiv210911185C The subsurface structure of a solar sunspot is important for the stability of the sunspot and the energy transport therein. Two subsurface structure models have been proposed, the monolithic and cluster models, but no clear observational evidence supporting a particular model has been found to date. To obtain clues about the subsurface structure of sunspots, we analyzed umbral flashes in merging sunspots registered by IRIS Mg II 2796 Å slit-jaw images. Umbral flashes are regarded as an observational manifestation of magnetohydrodynamic shock waves originating from convection cells below the photosphere. By tracking the motion of individual umbral flashes, we determined the position of the convection cells that are the oscillation centers located below the umbra. We found that the oscillation centers are preferentially located at dark nuclei in the umbral cores rather than in bright regions such as light bridges or umbral dots. Moreover, the oscillation centers tend to deviate from the convergent interface of the merging sunspots where vigorous convection is expected to occur. We also found that the inferred depths of the convection cells have no noticeable regional dependence. These results suggest that the subsurface of the umbra is an environment where convection can occur more easily than the convergent interface, and hence support the cluster model. For more concrete results, further studies based on umbral velocity oscillations in the lower atmosphere are required.

Movie is available at https://www.aanda.org Title: Coronal Hole Detection and Open Magnetic Flux Authors: Linker, Jon A.; Heinemann, Stephan G.; Temmer, Manuela; Owens, Mathew J.; Caplan, Ronald M.; Arge, Charles N.; Asvestari, Eleanna; Delouille, Veronique; Downs, Cooper; Hofmeister, Stefan J.; Jebaraj, Immanuel C.; Madjarska, Maria S.; Pinto, Rui F.; Pomoell, Jens; Samara, Evangelia; Scolini, Camilla; Vršnak, Bojan Bibcode: 2021ApJ...918...21L Altcode: 2021arXiv210305837L Many scientists use coronal hole (CH) detections to infer open magnetic flux. Detection techniques differ in the areas that they assign as open, and may obtain different values for the open magnetic flux. We characterize the uncertainties of these methods, by applying six different detection methods to deduce the area and open flux of a near-disk center CH observed on 2010 September 19, and applying a single method to five different EUV filtergrams for this CH. Open flux was calculated using five different magnetic maps. The standard deviation (interpreted as the uncertainty) in the open flux estimate for this CH ≍ 26%. However, including the variability of different magnetic data sources, this uncertainty almost doubles to 45%. We use two of the methods to characterize the area and open flux for all CHs in this time period. We find that the open flux is greatly underestimated compared to values inferred from in situ measurements (by 2.2-4 times). We also test our detection techniques on simulated emission images from a thermodynamic MHD model of the solar corona. We find that the methods overestimate the area and open flux in the simulated CH, but the average error in the flux is only about 7%. The full-Sun detections on the simulated corona underestimate the model open flux, but by factors well below what is needed to account for the missing flux in the observations. Under-detection of open flux in coronal holes likely contributes to the recognized deficit in solar open flux, but is unlikely to resolve it. Title: On the Nature of Propagating Intensity Disturbances in Polar Plumes during the 2017 Total Solar Eclipse Authors: Cho, Kyung-Suk; Cho, Il-Hyun; Madjarska, Maria S.; Nakariakov, Valery M.; Yang, Heesu; Choi, Seonghwan; Lim, Eun-Kyung; Lee, Kyung-Sun; Seough, Jung-Jun; Lee, Jaeok; Kim, Yeon-Han Bibcode: 2021ApJ...909..202C Altcode: 2021arXiv210202085C The propagating intensity disturbances (PIDs) in plumes are still poorly understood, and their identity (magnetoacoustic waves or flows) remains an open question. We investigate PIDs in five plumes located in the northern polar coronal hole observed during the 2017 total solar eclipse. Three plumes are associated with coronal bright points, jets, and macrospicules at their base (active plumes), and the other two plumes are not (quiet plumes). The electron temperature at the base of the plumes is obtained from the filter ratio of images taken with the X-ray Telescope on board Hinode and the passband ratio around 400 nm from an eclipse instrument, the Diagnostic Coronagraph Experiment. The phase speed (vr), frequency (ω), and wavenumber (k) of the PIDs in the plumes are obtained by applying a Fourier transformation to the spacetime (r - t plane) plots in images taken with the Atmospheric Imaging Assembly (AIA) in three different wavelength channels (171, 193, and 211 Å). We found that the PIDs in the higher-temperature AIA channels, 193 and 211 Å, are faster than that of the cooler AIA 171 Å channel. This tendency is more significant for the active plumes than the quiet ones. The observed speed ratio (∼1.3) between the AIA 171 and 193 Å channels is similar to the theoretical value (1.25) of a slow magnetoacoustic wave. Our results support the idea that PIDs in plumes represent a superposition of slow magnetoacoustic waves and plasma outflows that consist of dense cool flows and hot coronal jets. Title: The chromospheric component of coronal bright points. Coronal and chromospheric responses to magnetic-flux emergence Authors: Madjarska, Maria S.; Chae, Jongchul; Moreno-Insertis, Fernando; Hou, Zhenyong; Nóbrega-Siverio, Daniel; Kwak, Hannah; Galsgaard, Klaus; Cho, Kyuhyoun Bibcode: 2021A&A...646A.107M Altcode: 2020arXiv201209426M Context. We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating.
Aims: The aim of this study is to simultaneously investigate the chromospheric and coronal layers associated with a CBP, and in so doing, provide further understanding on the heating of plasmas confined in small-scale loops.
Methods: We used co-observations from the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager on board the Solar Dynamics Observatory, together with data from the Fast Imaging Solar Spectrograph taken in the Hα and Ca II 8542.1 Å lines. We also employed both linear force-free and potential field extrapolation models to investigate the magnetic topology of the CBP loops and the overlying corona, respectively. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the Hα loops (HLs).
Results: We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bundle of dark elongated features named in this work Hα loops, which constitute an integral part of the CBP loop magnetic structure. An increase in the photospheric magnetic flux due to flux emergence is accompanied by a rise of the coronal emission of the CBP loops, that is a heating episode. We also observe enhanced chromospheric activity associated with the occurrence of new HLs and mottles. While the coronal emission and magnetic flux increases appear to be co-temporal, the response of the Hα counterpart of the CBP occurs with a small delay of less than 3 min. A sharp temperature increase is found in one of the HLs and in one of the CBP footpoints estimated at 46% and 55% with respect to the pre-event values, also starting with a delay of less than 3 min following the coronal heating episode. The low-lying CBP loop structure remains non-potential for the entire observing period. The magnetic topological analysis of the overlying corona reveals the presence of a coronal null point at the beginning and towards the end of the heating episode.
Conclusions: The delay in the response of the chromospheric counterpart of the CBP suggests that the heating may have occurred at coronal heights.

Movies are available at https://www.aanda.org Title: Detection of Opposite Magnetic Polarity in a Light Bridge: Its Emergence and Cancellation in Association with LB Fan-shaped Jets Authors: Lim, Eun-Kyung; Yang, Heesu; Yurchyshyn, Vasyl; Chae, Jongchul; Song, Donguk; Madjarska, Maria S. Bibcode: 2020ApJ...904...84L Altcode: 2020arXiv201010713L Light bridges (LBs) are relatively bright structures that divide sunspot umbrae into two or more parts. Chromospheric LBs are known to be associated with various activities including fan-shaped jet-like ejections and brightenings. Although magnetic reconnection is frequently suggested to be responsible for such activities, not many studies present firm evidence to support the scenario. We carry out magnetic field measurements and imaging spectroscopy of an LB where fan-shaped jet-like ejections occur with co-spatial brightenings at their footpoints. We study LB fine structure and magnetic field changes using TiO images, Near-InfraRed Imaging Spectropolarimeter, and Hα data taken by the 1.6 m Goode Solar Telescope. We detect magnetic flux emergence in the LB that is of opposite polarity to that of the sunspot. The new magnetic flux cancels with the pre-existing flux at a rate of 5.6 × 1018 Mx hr-1. Both the recurrent jet-like ejections and their base brightenings are initiated at the vicinity of the magnetic flux cancellation, and show apparent horizontal extension along the LB at a projected speed of up to $18.4$ km s-1 to form a fan-shaped appearance. Based on these observations, we suggest that the fan-shaped ejections may have resulted from slipping reconnection between the new flux emerging in the LB and the ambient sunspot field. Title: Eruptions from coronal hole bright points: Observations and non-potential modelling Authors: Madjarska, Maria S.; Galsgaard, Klaus; Mackay, Duncan H.; Koleva, Kostadinka; Dechev, Momchil Bibcode: 2020A&A...643A..19M Altcode: 2020arXiv200904628M Context. We report on the third part of a series of studies on eruptions associated with small-scale loop complexes named coronal bright points (CBPs).
Aims: A single case study of a CBP in an equatorial coronal hole with an exceptionally large size is investigated to expand on our understanding of the formation of mini-filaments, their destabilisation, and the origin of the eruption triggering the formation of jet-like features recorded in extreme ultraviolet (EUV) and X-ray emission. We aim to explore the nature of the so-called micro-flares in CBPs associated with jets in coronal holes and mini coronal mass ejections in the quiet Sun.
Methods: Co-observations from the Atmospheric Imaging Assembly (AIA) and Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory as well as GONG Hα images are used together with a non-linear force free field (NLFFF) relaxation approach, where the latter is based on a time series of HMI line-of-sight magnetograms.
Results: A mini-filament (MF) that formed beneath the CBP arcade about 3-4 h before the eruption is seen in the Hα and EUV AIA images to lift up and erupt triggering the formation of an X-ray jet. No significant photospheric magnetic flux concentration displacement (convergence) is observed and neither is magnetic flux cancellation between the two main magnetic polarities forming the CBP in the time period leading to MF lift-off. The CBP micro-flare is associated with three flare kernels that formed shortly after the MF lift-off. No observational signature is found for magnetic reconnection beneath the erupting MF. The applied NLFFF modelling successfully reproduces both the CBP loop complex as well as the magnetic flux rope that hosts the MF during the build-up to the eruption.
Conclusions: The applied NLFFF modelling is able to clearly show that an initial potential field can be evolved into a non-potential magnetic field configuration that contains free magnetic energy in the region that observationally hosts the eruption. The comparison of the magnetic field structure shows that the magnetic NLFFF model contains many of the features that can explain the different observational signatures found in the evolution and eruption of the CBP. In the future, it may eventually indicate the location of destabilisation that results in the eruptions of flux ropes.

Movies associated to Figs. 9 and B.2 are available at https://www.aanda.org Title: Impulsive wave excitation by rapidly changing granules Authors: Kwak, Hannah; Chae, Jongchul; Madjarska, Maria S.; Cho, Kyuhyoun; Song, Donguk Bibcode: 2020A&A...642A.154K Altcode: 2020arXiv200812779K It is not yet fully understood how magnetohydrodynamic waves in the interior and atmosphere of the Sun are excited. Traditionally, turbulent convection in the interior is considered to be the source of wave excitation in the quiet Sun. Over the last few decades, acoustic events observed in the intergranular lanes in the photosphere have emerged as a strong candidate for a wave excitation source. Here we report our observations of wave excitation by a new type of event: rapidly changing granules. Our observations were carried out with the Fast Imaging Solar Spectrograph in the Hα and Ca II 8542 Å lines and the TiO 7057 Å broadband filter imager of the 1.6 m Goode Solar Telescope at the Big Bear Solar Observatory. We identify granules in the internetwork region that undergo rapid dynamic changes such as collapse (event 1), fragmentation (event 2), or submergence (event 3). In the photospheric images, these granules become significantly darker than neighboring granules. Following the granules' rapid changes, transient oscillations are detected in the photospheric and chromospheric layers. In the case of event 1, the dominant period of the oscillations is close to 4.2 min in the photosphere and 3.8 min in the chromosphere. Moreover, in the Ca II-0.5 Å raster image, we observe repetitive brightenings in the location of the rapidly changing granules that are considered the manifestation of shock waves. Based on our results, we suggest that dynamic changes of granules can generate upward-propagating acoustic waves in the quiet Sun that ultimately develop into shocks.

Movie attached to Fig. A.1 is available at https://www.aanda.org Title: Inference of chromospheric plasma parameters on the Sun. Multilayer spectral inversion of strong absorption lines Authors: Chae, Jongchul; Madjarska, Maria S.; Kwak, Hannah; Cho, Kyuhyoun Bibcode: 2020A&A...640A..45C Altcode: The solar chromosphere can be observed well through strong absorption lines. We infer the physical parameters of chromospheric plasmas from these lines using a multilayer spectral inversion. This is a new technique of spectral inversion. We assume that the atmosphere consists of a finite number of layers. In each layer the absorption profile is constant and the source function varies with optical depth with a constant gradient. Specifically, we consider a three-layer model of radiative transfer where the lowest layer is identified with the photosphere and the two upper layers are identified with the chromosphere. The absorption profile in the photosphere is described by a Voigt function, and the profile in the chromosphere by a Gaussian function. This three-layer model is fully specified by 13 parameters. Four parameters can be fixed to prescribed values, and one parameter can be determined from the analysis of a satellite photospheric line. The remaining 8 parameters are determined from a constrained least-squares fitting. We applied the multilayer spectral inversion to the spectral data of the Hα and the Ca II 854.21 nm lines taken in a quiet region by the Fast Imaging Solar Spectrograph (FISS) of the Goode Solar Telescope (GST). We find that our model successfully fits most of the observed profiles and produces regular maps of the model parameters. The combination of the inferred Doppler widths of the two lines yields reasonable estimates of temperature and nonthermal speed in the chromosphere. We conclude that our multilayer inversion is useful to infer chromospheric plasma parameters on the Sun. Title: Inference of chromospheric plasma parameters on the Sun Authors: Chae, Jongchul; Madjarska, Maria S.; Kwak, Hannah; Cho, Kyuhyoun Bibcode: 2020arXiv200611981C Altcode: The solar chromosphere can be observed well through strong absorption lines. We infer the physical parameters of chromospheric plasmas from these lines using a multilayer spectral inversion. This is a new technique of spectral inversion. We assume that the atmosphere consists of a finite number of layers. In each layer the absorption profile is constant and the source function varies with optical depth with a constant gradient. Specifically, we consider a three-layer model of radiative transfer where the lowest layer is identified with the photosphere and the two upper layers are identified with the chromosphere. The absorption profile in the photosphere is described by a Voigt function, and the profile in the chromosphere by a Gaussian function. This three-layer model is fully specified by 13 parameters. Four parameters can be fixed to prescribed values, and one parameter can be determined from the analysis of a satellite photospheric line. The remaining 8 parameters are determined from a constrained least-squares fitting. We applied the multilayer spectral inversion to the spectral data of the H$\alpha$ and the Ca II 854.21 nm lines taken in a quiet region by the Fast Imaging Solar Spectrograph (FISS) of the Goode Solar Telescope (GST). We find that our model successfully fits most of the observed profiles and produces regular maps of the model parameters. The combination of the inferred Doppler widths of the two lines yields reasonable estimates of temperature and nonthermal speed in the chromosphere. We conclude that our multilayer inversion is useful to infer chromospheric plasma parameters on the Sun. Title: Helium abundance and speed difference between helium ions and protons in the solar wind from coronal holes, active regions, and quiet Sun Authors: Fu, Hui; Madjarska, Maria S.; Li, Bo; Xia, Lidong; Huang, Zhenghua Bibcode: 2019EGUGA..21.3666F Altcode: Two main models have been developed to explain the mechanisms of release, heating, and acceleration of the nascent solar wind, the wave-turbulence-driven (WTD) models and reconnection-loop-opening (RLO) models, in which the plasma release processes are fundamentally different. Given that the statistical observational properties of helium ions produced in magnetically diverse solar regions could provide valuable information for the solar wind modelling, we examine the statistical properties of the helium abundance (A_He) and the speed difference between helium ions and protons (v_αp) for coronal holes (CHs), active regions (ARs), and the quiet Sun (QS). We find bimodal distributions in the space of A_He and v_αp/vA (where vA is the local Alfven speed) for the solar wind as a whole. The CH windmeasurements are concentrated at higher A_He and v_αp/vA values with a smaller A_He distribution range, while the AR and QS wind is associated with lower A_He and v_αp/v_A, and a larger A_He distribution range. The magnetic diversity of the source regions and the physical processes related to it are possibly responsible for the different properties of A_He and v_αp/v_A. The statistical results suggest that the two solar wind generation mechanisms, WTD and RLO, work in parallel in all solar wind source regions. In CH regions WTD plays a major role, whereas the RLO mechanism is more important in AR and QS. Title: Coronal bright points Authors: Madjarska, Maria S. Bibcode: 2019LRSP...16....2M Altcode: Coronal bright points (CBPs) are a fundamental class of solar activity. They represent a set of low-corona small-scale loops with enhanced emission in the extreme-ultraviolet and X-ray spectrum that connect magnetic flux concentrations of opposite polarities. CBPs are one of the main building blocks of the solar atmosphere outside active regions uniformly populating the solar atmosphere including active region latitudes and coronal holes. Their plasma properties classify them as downscaled active regions. Most importantly, their simple structure and short lifetimes of less than 20 h that allow to follow their full lifetime evolution present a unique opportunity to investigate outstanding questions in solar physics including coronal heating. The present Living Review is the first review of this essential class of solar phenomena and aims to give an overview of the current knowledge about the CBP general, plasma and magnetic properties. Several transient dynamic phenomena associated with CBPs are also briefly introduced. The observationally derived energetics and the theoretical modelling that aims at explaining the CBP formation and eruptive behaviour are reviewed. Title: Eruptions from quiet Sun coronal bright points. II. Non-potential modelling Authors: Galsgaard, Klaus; Madjarska, Maria S.; Mackay, Duncan H.; Mou, Chaozhou Bibcode: 2019A&A...623A..78G Altcode: 2019arXiv190109875G Context. Our recent observational study shows that the majority of coronal bright points (CBPs) in the quiet Sun are sources of one or more eruptions during their lifetime.
Aims: Here, we investigate the non-potential time-dependent structure of the magnetic field of the CBP regions with special emphasis on the time-evolving magnetic structure at the spatial locations where the eruptions are initiated.
Methods: The magnetic structure is evolved in time using a non-linear force-free field (NLFFF) relaxation approach based on a time series of helioseismic and magnetic imager (HMI) longitudinal magnetograms. This results in a continuous time series of NLFFFs. The time series is initiated with a potential field extrapolation based on a magnetogram taken well before the time of the eruptions. This initial field is then evolved in time in response to the observed changes in the magnetic field distribution at the photosphere. The local and global magnetic field structures from the time series of NLFFF field solutions are analysed in the vicinity of the eruption sites at the approximate times of the eruptions.
Results: The analysis shows that many of the CBP eruptions reported in a recent publication contain a twisted flux tube located at the sites of eruptions. The presence of flux ropes at these locations provides in many cases a direct link between the magnetic field structure, their eruption, and the observation of mini coronal mass ejections (mini-CMEs). It is found that all repetitive eruptions are homologous.
Conclusions: The NLFFF simulations show that twisted magnetic field structures are created at the locations hosting eruptions in CBPs. These twisted structures are produced by footpoint motions imposed by changes in the photospheric magnetic field observations. The true nature of the micro-flares remains unknown. Further 3D data-driven magnetohydrodynamic modelling is required to show how these twisted regions become unstable and erupt.

Movies associated to Figs. 1-5 are available at https://www.aanda.org Title: Solar Ultraviolet Bursts Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.; Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr Bibcode: 2018SSRv..214..120Y Altcode: 2018arXiv180505850Y The term "ultraviolet (UV) burst" is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016-2017. Title: Eruptions from quiet Sun coronal bright points: Observations & Modeling Authors: Madjarska, Maria S.; Galsgaard, Klaus; Mou, Chauzhou Bibcode: 2018csc..confE.122M Altcode: We present a two part study that aims first to observationally explore in full detail the morphological and dynamical evolution of eruptions from coronal bright points (CBPs) in the context of the full lifetime evolution of 11 CBPs. Next, we employ data-driven modelling based on a relaxation code to reproduce the time evolution of the magnetic field of these eruptive CBPs, and provide an insight on the possible causes for destabilisation and eruption. Observations of the full lifetime of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory in four passbands He II 304 Å, Fe IX/X 171 Å, Fe XII 193 Å, and Fe XVIII 94 Å are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions and mini coronal mass ejections (mini-CMEs). Data from the Helioseismic and Magnetic Imager are analysed to study the longitudinal photospheric magnetic field evolution associated with the CBPs and related eruptions. The magnetic structure of each CBP is then evolved in time using the relaxation approach, based on a time series of HMI magnetograms. This results in a series of Non-Linear Force Free Field Extrapolations (NLFFF). The time series is initiated with a potential field extrapolation based on a HMI magnetogram well before the eruptions, and evolved in time as a response to the changes in the magnetic field distribution in the photosphere. This time series of NLFFF field solutions is analysed for the local and global magnetic field structure in the vicinity of the eruption sites. Title: Eruptions from quiet Sun coronal bright points. I. Observations Authors: Mou, Chauzhou; Madjarska, Maria S.; Galsgaard, Klaus; Xia, Lidong Bibcode: 2018A&A...619A..55M Altcode: 2018arXiv180804541M Context. Eruptions from coronal bright points (CBPs) are investigated in a two-part study.
Aims: The present study aims to explore in full detail the morphological and dynamical evolution of these eruptions in the context of the full lifetime evolution of CBPs. A follow-up study employs data-driven modelling based on a relaxation code to reproduce the time evolution of the magnetic field of these eruptive CBPs, and provide insight into the possible causes for destabilisation and eruption.
Methods: Observations of the full lifetime of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory in four passbands, He II 304 Å, Fe IX/X 171 Å, Fe XII 193 Å, and Fe XVIII 94 Å are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions, and mini coronal-mass ejections (mini-CMEs). Data from the Helioseismic and Magnetic Imager are analysed to study the longitudinal photospheric magnetic field evolution associated with the CBPs and related eruptions.
Results: First and foremost, our study shows that the majority (76%) of quiet Sun CBPs (31 out of 42 CBPs) produce at least one eruption during their lifetime. From 21 eruptions in 11 CBPs, 18 of them occur, on average, ∼17 h after the CBP formation. The average lifetime of the CBPs in AIA 193 Å is ∼21 h. The time delay in the eruption occurrence coincides in each CBP with the convergence and cancellation phase of the CBP bipole evolution during which the CBPs become smaller until they fully disappear. The remaining three eruptions happen 4-6 h after the CBP formation. In 16 out of the 21 eruptions, the magnetic convergence and cancellation involve the CBP main bipoles, while in three eruptions, one of the BP magnetic fragments and a pre-existing fragment of opposite polarity converge and cancel. In one BP with two eruptions, cancellation was not observed. The CBP eruptions involve in most cases the expulsion of chromospheric material either as an elongated filamentary structure (mini-filament, MF) or a volume of cool material (cool plasma cloud, CPC), together with the CBP or higher overlying hot loops. Coronal waves were identified during three eruptions. A micro-flaring is observed beneath all erupting MFs/CPCs. Whether the destabilised MF causes the micro-flaring or the destabilisation and eruption of the MF is triggered by reconnection beneath the filament remains uncertain. In most eruptions, the cool erupting plasma either partially or fully obscures the micro-flare until the erupting material moves away from the CBP. From 21 eruptions, 11 are found to produce mini-CMEs. The dimming regions associated with the CMEs are found to be occupied by both the "dark" cool plasma and areas of weakened coronal emission caused by the depleted plasma density.
Conclusions: The present study demonstrates that the small-scale loop structures in the quiet Sun, the evolution of which is determined by their magnetic footpoint motions and/or ambient field topology, evolve into an eruptive phase that triggers the ejection of cool and hot plasma in the corona.

The movies associated to Figs 1, 3, 4, 6 are available at https://www.aanda.org Title: Helium abundance and speed difference between helium ions and protons in the solar wind from coronal holes, active regions, and quiet Sun Authors: Fu, Hui; Madjarska, Maria S.; Li, Bo; Xia, Lidong; Huang, Zhenghua Bibcode: 2018MNRAS.478.1884F Altcode: 2018arXiv180502880F; 2018MNRAS.tmp.1157F Two main models have been developed to explain the mechanisms of release, heating, and acceleration of the nascent solar wind, the wave-turbulence-driven (WTD) models and reconnection-loop-opening (RLO) models, in which the plasma release processes are fundamentally different. Given that the statistical observational properties of helium ions produced in magnetically diverse solar regions could provide valuable information for the solar wind modelling, we examine the statistical properties of the helium abundance (AHe) and the speed difference between helium ions and protons (vαp) for coronal holes (CHs), active regions (ARs), and the quiet Sun (QS). We find bimodal distributions in the space of AHe and vαp/vA (where vA is the local Alfvén speed) for the solar wind as a whole. The CH wind measurements are concentrated at higher AHe and vαp/vA values with a smaller AHe distribution range, while the AR and QS wind is associated with lower AHe and vαp/vA, and a larger AHe distribution range. The magnetic diversity of the source regions and the physical processes related to it are possibly responsible for the different properties of AHe and vαp/vA. The statistical results suggest that the two solar wind generation mechanisms, WTD and RLO, work in parallel in all solar wind source regions. In CH regions WTD plays a major role, whereas the RLO mechanism is more important in AR and QS. Title: Energetics of Hi-C EUV brightenings Authors: Subramanian, Srividya; Kashyap, Vinay L.; Tripathi, Durgesh; Madjarska, Maria S.; Doyle, John G. Bibcode: 2018A&A...615A..47S Altcode: 2018arXiv180309505S We study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings within a system of fan loops observed in the active region AR 11520. These brightenings were simultaneously observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA 193 Å light curves. The energetics of these brightenings were studied using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range log T(K) = 6.2-6.6 with radiative energies ≈1024-25 ergs and densities approximately equal to a few times 109 cm-3. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation. Title: Magnetic topological analysis of coronal bright points Authors: Galsgaard, K.; Madjarska, M. S.; Moreno-Insertis, F.; Huang, Z.; Wiegelmann, T. Bibcode: 2017A&A...606A..46G Altcode: 2017arXiv170704174G Context. We report on the first of a series of studies on coronal bright points which investigate the physical mechanism that generates these phenomena.
Aims: The aim of this paper is to understand the magnetic-field structure that hosts the bright points.
Methods: We use longitudinal magnetograms taken by the Solar Optical Telescope with the Narrowband Filter Imager. For a single case, magnetograms from the Helioseismic and Magnetic Imager were added to the analysis. The longitudinal magnetic field component is used to derive the potential magnetic fields of the large regions around the bright points. A magneto-static field extrapolation method is tested to verify the accuracy of the potential field modelling. The three dimensional magnetic fields are investigated for the presence of magnetic null points and their influence on the local magnetic domain.
Results: In nine out of ten cases the bright point resides in areas where the coronal magnetic field contains an opposite polarity intrusion defining a magnetic null point above it. We find that X-ray bright points reside, in these nine cases, in a limited part of the projected fan-dome area, either fully inside the dome or expanding over a limited area below which typically a dominant flux concentration resides. The tenth bright point is located in a bipolar loop system without an overlying null point.
Conclusions: All bright points in coronal holes and two out of three bright points in quiet Sun regions are seen to reside in regions containing a magnetic null point. An as yet unidentified process(es) generates the brigh points in specific regions of the fan-dome structure.

The movies are available at http://www.aanda.org Title: The Plasma Parameters and Geometry of Cool and Warm Active Region Loops Authors: Xie, Haixia; Madjarska, Maria S.; Li, Bo; Huang, Zhenghua; Xia, Lidong; Wiegelmann, Thomas; Fu, Hui; Mou, Chaozhou Bibcode: 2017ApJ...842...38X Altcode: 2017arXiv170502564X How the solar corona is heated to high temperatures remains an unsolved mystery in solar physics. In the present study we analyze observations of 50 whole active region loops taken with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode satellite. Eleven loops were classified as cool loops (<1 MK) and 39 as warm loops (1-2 MK). We study their plasma parameters, such as densities, temperatures, filling factors, nonthermal velocities, and Doppler velocities. We combine spectroscopic analysis with linear force-free magnetic field extrapolation to derive the 3D structure and positioning of the loops, their lengths and heights, and the magnetic field strength along the loops. We use density-sensitive line pairs from Fe xii, Fe xiii, Si x, and Mg vii ions to obtain electron densities by taking special care of intensity background subtraction. The emission measure loci method is used to obtain the loop temperatures. We find that the loops are nearly isothermal along the line of sight. Their filling factors are between 8% and 89%. We also compare the observed parameters with the theoretical Rosner-Tucker-Vaiana (RTV) scaling law. We find that most of the loops are in an overpressure state relative to the RTV predictions. In a follow-up study, we will report a heating model of a parallel-cascade-based mechanism and will compare the model parameters with the loop plasma and structural parameters derived here. Title: Charge States and FIP Bias of the Solar Wind from Coronal Holes, Active Regions, and Quiet Sun Authors: Fu, Hui; Madjarska, Maria S.; Xia, LiDong; Li, Bo; Huang, ZhengHua; Wangguan, Zhipeng Bibcode: 2017ApJ...836..169F Altcode: 2017arXiv170107610F Connecting in situ measured solar-wind plasma properties with typical regions on the Sun can provide an effective constraint and test to various solar wind models. We examine the statistical characteristics of the solar wind with an origin in different types of source regions. We find that the speed distribution of coronal-hole (CH) wind is bimodal with the slow wind peaking at ∼400 km s-1 and the fast at ∼600 km s-1. An anti-correlation between the solar wind speeds and the O7+/O6+ ion ratio remains valid in all three types of solar wind as well during the three studied solar cycle activity phases, I.e., solar maximum, decline, and minimum. The {N}{Fe}/{N}{{O}} range and its average values all decrease with the increasing solar wind speed in different types of solar wind. The {N}{Fe}/{N}{{O}} range (0.06-0.40, first ionization potential (FIP) bias range 1-7) for active region wind is wider than for CH wind (0.06-0.20, FIP bias range 1-3), while the minimum value of {N}{Fe}/{N}{{O}} (∼ 0.06) does not change with the variation of speed, and it is similar for all source regions. The two-peak distribution of CH wind and the anti-correlation between the speed and O7+/O6+ in all three types of solar wind can be explained qualitatively by both the wave-turbulence-driven and reconnection-loop-opening (RLO) models, whereas the distribution features of {N}{Fe}/{N}{{O}} in different source regions of solar wind can be explained more reasonably by the RLO models. Title: Explosive events in active region observed by IRIS and SST/CRISP Authors: Huang, Z.; Madjarska, M. S.; Scullion, E. M.; Xia, L. -D.; Doyle, J. G.; Ray, T. Bibcode: 2017MNRAS.464.1753H Altcode: 2016arXiv160907698H Transition-region explosive events (EEs) are characterized by non-Gaussian line profiles with enhanced wings at Doppler velocities of 50-150 km s-1. They are believed to be the signature of solar phenomena that are one of the main contributors to coronal heating. The aim of this study is to investigate the link of EEs to dynamic phenomena in the transition region and chromosphere in an active region. We analyse observations simultaneously taken by the Interface Region Imaging Spectrograph (IRIS) in the Si IV 1394 Å line and the slit-jaw (SJ) 1400 Å images, and the Swedish 1-m Solar Telescope in the Hα line. In total 24 events were found. They are associated with small-scale loop brightenings in SJ 1400 Å images. Only four events show a counterpart in the Hα-35 km s-1 and Hα+35 km s-1 images. Two of them represent brightenings in the conjunction region of several loops that are also related to a bright region (granular lane) in the Hα-35 km s-1 and Hα+35 km s-1 images. 16 are general loop brightenings that do not show any discernible response in the Hα images. Six EEs appear as propagating loop brightenings, from which two are associated with dark jet-like features clearly seen in the Hα-35 km s-1 images. We found that chromospheric events with jet-like appearance seen in the wings of the Hα line can trigger EEs in the transition region and in this case the IRIS Si IV 1394 Å line profiles are seeded with absorption components resulting from Fe II and Ni II. Our study indicates that EEs occurring in active regions have mostly upper-chromosphere/transition-region origin. We suggest that magnetic reconnection resulting from the braidings of small-scale transition region loops is one of the possible mechanisms of energy release that are responsible for the EEs reported in this paper. Title: Sources of the Slow Solar Wind During the Solar Cycle 23/24 Minimum Authors: Kilpua, E. K. J.; Madjarska, M. S.; Karna, N.; Wiegelmann, T.; Farrugia, C.; Yu, W.; Andreeova, K. Bibcode: 2016SoPh..291.2441K Altcode: 2016arXiv160605142K; 2016SoPh..tmp..149K We investigate the characteristics and the sources of the slow (<450 kms−1) solar wind during the four years (2006 - 2009) of low solar activity between Solar Cycles 23 and 24. We used a comprehensive set of in-situ observations in the near-Earth solar wind (Wind and ACE) and removed the periods when large-scale interplanetary coronal mass ejections were present. The investigated period features significant variations in the global coronal structure, including the frequent presence of low-latitude active regions in 2006 - 2007, long-lived low- and mid-latitude coronal holes in 2006 - mid-2008 and mostly the quiet Sun in 2009. We examined Carrington rotation averages of selected solar plasma, charge state, and compositional parameters and distributions of these parameters related to the quiet Sun, active region Sun, and the coronal hole Sun. While some of the investigated parameters (e.g. speed, the C+6/C+4 and He/H ratios) show clear variations over our study period and with solar wind source type, some (Fe/O) exhibit very little changes. Our results highlight the difficulty of distinguishing between the slow solar wind sources based on the inspection of solar wind conditions. Title: Narrow-line-width UV Bursts in the Transition Region above Sunspots Observed by IRIS Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S.; Fu, Hui; Mou, Chaozhou; Xie, Haixia Bibcode: 2016ApJ...829L..30H Altcode: 2016arXiv160804892H Various small-scale structures abound in the solar atmosphere above active regions, playing an important role in the dynamics and evolution therein. We report on a new class of small-scale transition region structures in active regions, characterized by strong emissions but extremely narrow Si IV line profiles as found in observations taken with the Interface Region Imaging Spectrograph (IRIS). Tentatively named as narrow-line-width UV bursts (NUBs), these structures are located above sunspots and comprise one or multiple compact bright cores at sub-arcsecond scales. We found six NUBs in two data sets (a raster and a sit-and-stare data set). Among these, four events are short-lived with a duration of ∼10 minutes, while two last for more than 36 minutes. All NUBs have Doppler shifts of 15-18 km s-1, while the NUB found in sit-and-stare data possesses an additional component at ∼50 km s-1 found only in the C II and Mg II lines. Given that these events are found to play a role in the local dynamics, it is important to further investigate the physical mechanisms that generate these phenomena and their role in the mass transport in sunspots. Title: Homologous prominence non-radial eruptions: A case study Authors: Duchlev, P.; Koleva, K.; Madjarska, M. S.; Dechev, M. Bibcode: 2016NewA...48...66D Altcode: 2016arXiv160502299D The present study provides important details on homologous eruptions of a solar prominence that occurred in active region NOAA 10904 on 2006 August 22. We report on the pre-eruptive phase of the homologous feature as well as the kinematics and the morphology of a forth from a series of prominence eruptions that is critical in defining the nature of the previous consecutive eruptions. The evolution of the overlying coronal field during homologous eruptions is discussed and a new observational criterion for homologous eruptions is provided. We find a distinctive sequence of three activation periods each of them containing pre-eruptive precursors such as a brightening and enlarging of the prominence body followed by small surge-like ejections from its southern end observed in the radio 17 GHz. We analyse a fourth eruption that clearly indicates a full reformation of the prominence after the third eruption. The fourth eruption although occurring 11 h later has an identical morphology, the same angle of propagation with respect to the radial direction, as well as similar kinematic evolution as the previous three eruptions. We find an important feature of the homologous eruptive prominence sequence that is the maximum height increase of each consecutive eruption. The present analysis establishes that all four eruptions observed in Hα are of confined type with the third eruption undergoing a thermal disappearance during its eruptive phase. We suggest that the observation of the same direction of the magnetic flux rope (MFR) ejections can be consider as an additional observational criterion for MFR homology. This observational indication for homologous eruptions is important, especially in the case of events of typical or poorly distinguishable morphology of eruptive solar phenomena. Title: Oscillatory Response of the Solar Chromosphere to a Strong Downflow Event above a Sunspot Authors: Kwak, Hannah; Chae, Jongchul; Song, Donguk; Kim, Yeon-Han; Lim, Eun-Kyung; Madjarska, Maria S. Bibcode: 2016ApJ...821L..30K Altcode: 2016arXiv160402252K We report three-minute oscillations in the solar chromosphere driven by a strong downflow event in a sunspot. We used the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope and the Interface Region Imaging Spectrograph (IRIS). The strong downflow event is identified in the chromospheric and transition region lines above the sunspot umbra. After the event, oscillations occur at the same region. The amplitude of the Doppler velocity oscillations is 2 km s-1 and gradually decreases with time. In addition, the period of the oscillations gradually increases from 2.7 to 3.3 minutes. In the IRIS 1330 Å slit-jaw images, we identify a transient brightening near the footpoint of the downflow detected in the Hα+0.5 Å image. The characteristics of the downflowing material are consistent with those of sunspot plumes. Based on our findings, we suggest that the gravitationally stratified atmosphere came to oscillate with a three-minute period in response to the impulsive downflow event as was theoretically investigated by Chae & Goode. Title: Transition region bright dots in active regions observed by the interface region imaging spectrograph Authors: Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S.; Fu, Hui Bibcode: 2016AIPC.1720b0001H Altcode: 2018arXiv180308294H The Interface Region Imaging Spectrograph (IRIS) reveals numerous small-scale (sub-arcsecond) brightenings that appear as bright dots sparkling the solar transition region in active regions. Here, we report a statistical study on these transition-region bright dots. We use an automatic approach to identify 2742 dots in a Si IV raster image. We find that the average spatial size of the dots is 0.8 arcsec2 and most of them are located in the faculae area. Their Doppler velocities obtained from the Si IV 1394 Å line range from -20 to 20 km s-1. Among these 2742 dots, 1224 are predominantly blue-shifted and 1518 are red-shifted. Their non-thermal velocities range from 4 to 50 km s-1 with an average of 24 km s-1. We speculate that the bright dots studied here are small-scale impulsive energetic events that can heat the active region corona. Title: Magnetic Flux Supplement to Coronal Bright Points Authors: Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong; Madjarska, Maria S.; Li, Bo; Fu, Hui; Jiao, Fangran; Hou, Zhenyong Bibcode: 2016ApJ...818....9M Altcode: 2015arXiv151109215M Coronal bright points (BPs) are associated with magnetic bipolar features (MBFs) and magnetic cancellation. Here we investigate how BP-associated MBFs form and how the consequent magnetic cancellation occurs. We analyze longitudinal magnetograms from the Helioseismic and Magnetic Imager to investigate the photospheric magnetic flux evolution of 70 BPs. From images taken in the 193 Å passband of the Atmospheric Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from 2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three processes, namely, emergence, convergence, and local coalescence of the magnetic fluxes. The formation of an MBF can involve more than one of these processes. Out of the 70 cases, flux emergence is the main process of an MBF buildup of 52 BPs, mainly convergence is seen in 28, and 14 cases are associated with local coalescence. For MBFs formed by bipolar emergence, the time difference between the flux emergence and the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr with an average of 1.3 hr. While magnetic cancellation is found in all 70 BPs, it can occur in three different ways: (I) between an MBF and small weak magnetic features (in 33 BPs); (II) within an MBF with the two polarities moving toward each other from a large distance (34 BPs); (III) within an MBF whose two main polarities emerge in the same place simultaneously (3 BPs). While an MBF builds up the skeleton of a BP, we find that the magnetic activities responsible for the BP heating may involve small weak fields. Title: Cool transition region loops observed by the Interface Region Imaging Spectrograph Authors: Huang, Z.; Xia, L.; Li, B.; Madjarska, M. S. Bibcode: 2015AGUFMSH31D..09H Altcode: An important class of loops in the solar atmosphere, cool transition region loops, have received little attention mainly due to instrumental limitations. We analyze a cluster of these loops in the on-disk active region NOAA 11934 recorded in a Si IV 1402.8 Å spectral raster and 1400Å slit-jaw (SJ) images taken by the Interface Region Imaging Spectrograph. We divide these loops into three groups and study their dynamics, evolution and interaction.The first group comprises geometrically relatively stable loops, which are finely scaled with 382~626 km cross-sections. Siphon flows in these loops are suggested by the Doppler velocities gradually changing from -10 km/s (blue-shifts) in one end to 20 km/s (red-shifts) in the other. Nonthermal velocities from 15 to 25 km/s were determined. The obtained physical properties suggest that these loops are impulsively heated by magnetic reconnection occurring at the blue-shifted footpoints where magnetic cancellation with a rate of 1015 Mx/s is found. The released magnetic energy is redistributed by the siphon flows. The second group corresponds to two active footpoints rooted in mixed-magnetic-polarity regions. Magnetic reconnection in both footpoints is suggested by explosive-event line profiles with enhanced wings up to 200 km/s and magnetic cancellation with a rate of ~1015 Mx/s. In the third group, an interaction between two cool loop systems is observed. Mixed-magnetic polarities are seen in their conjunction area where explosive-event line profiles and magnetic cancellation with a rate of 3×1015 Mx/s are found. This is a clear indication that magnetic reconnection occurs between these two loop systems. Our observations suggest that the cool transition region loops are heated impulsively most likely by sequences of magnetic reconnection events. Title: Active region upflows. I. Multi-instrument observations Authors: Vanninathan, K.; Madjarska, M. S.; Galsgaard, K.; Huang, Z.; Doyle, J. G. Bibcode: 2015A&A...584A..38V Altcode: 2015arXiv150905624V Context. We study upflows at the edges of active regions, called AR outflows, using multi-instrument observations.
Aims: This study intends to provide the first direct observational evidence of whether chromospheric jets play an important role in furnishing mass that could sustain coronal upflows. The evolution of the photospheric magnetic field, associated with the footpoints of the upflow region and the plasma properties of active region upflows is investigated with the aim of providing information for benchmarking data-driven modelling of this solar feature.
Methods: We spatially and temporally combine multi-instrument observations obtained with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode, the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager instruments on board the Solar Dynamics Observatory and the Interferometric BI-dimensional Spectro-polarimeter installed at the National Solar Observatory, Sac Peak, to study the plasma parameters of the upflows and the impact of the chromosphere on active region upflows.
Results: Our analysis shows that the studied active region upflow presents similarly to those studied previously, i.e. it displays blueshifted emission of 5-20 kms-1 in Fe xii and Fe xiii and its average electron density is 1.8 × 109 cm-3 at 1 MK. The time variation of the density is obtained showing no significant change (in a 3σ error). The plasma density along a single loop is calculated revealing a drop of 50% over a distance of ~20 000 km along the loop. We find a second velocity component in the blue wing of the Fe xii and Fe xiii lines at 105 kms-1 reported only once before. For the first time we study the time evolution of this component at high cadence and find that it is persistent during the whole observing period of 3.5 h with variations of only ±15 kms-1. We also, for the first time, study the evolution of the photospheric magnetic field at high cadence and find that magnetic flux diffusion is responsible for the formation of the upflow region. High cadence Hα observations are used to study the chromosphere at the footpoints of the upflow region. We find no significant jet-like (spicule/rapid blue excursion) activity to account for several hours/days of plasma upflow. The jet-like activity in this region is not continuous and blueward asymmetries are a bare minimum. Using an image enhancement technique for imaging and spectral data, we show that the coronal structures seen in the AIA 193 Å channel are comparable to the EIS Fe xii images, while images in the AIA 171 Å channel reveal additional loops that are a result of contribution from cooler emission to this channel.
Conclusions: Our results suggest that at chromospheric heights there are no signatures that support the possible contribution of spicules to active region upflows. We suggest that magnetic flux diffusion is responsible for the formation of the coronal upflows. The existence of two velocity components possibly indicates the presence of two different flows, which are produced by two different physical mechanisms, e.g. magnetic reconnection and pressure-driven jets.

Movies associated to Figs. A.1-A.3 are available in electronic form at http://www.aanda.org Title: Active region upflows. II. Data driven magnetohydrodynamic modelling Authors: Galsgaard, K.; Madjarska, M. S.; Vanninathan, K.; Huang, Z.; Presmann, M. Bibcode: 2015A&A...584A..39G Altcode: 2015arXiv150905639G Context. Observations of many active regions show a slow systematic outflow/upflow from their edges lasting from hours to days. At present no physical explanation has been proven, while several suggestions have been put forward.
Aims: This paper investigates one possible method for maintaining these upflows assuming, that convective motions drive the magnetic field to initiate them through magnetic reconnection.
Methods: We use Helioseismic and Magnetic Imager (HMI) data to provide an initial potential 3D magnetic field of the active region NOAA 11123 on 2010 November 13 where the characteristic upflow velocities are observed. A simple 1D hydrostatic atmospheric model covering the region from the photosphere to the corona is derived. Local correlation tracking of the magnetic features in the HMI data is used to derive a proxy for the time dependent velocity field. The time dependent evolution of the system is solved using a resistive 3D magnetohydrodynamic code.
Results: The magnetic field contains several null points located well above the photosphere, with their fan planes dividing the magnetic field into independent open and closed flux domains. The stressing of the interfaces between the different flux domains is expected to provide locations where magnetic reconnection can take place and drive systematic flows. In this case, the region between the closed and open flux is identified as the region where observations find the systematic upflows.
Conclusions: In the present experiment, the driving only initiates magneto-acoustic waves without driving any systematic upflows at any of the flux interfaces.

Movie is available in electronic form at http://www.aanda.org Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical, and near-infrared Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini, Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini, Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio, Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne; Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio; Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska, Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza, Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca; Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele; Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini, Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre, Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio; Zuccarello, Francesca Bibcode: 2015JATIS...1d4006B Altcode: Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept for a small solar and space weather mission with a budget compatible with an European Space Agency (ESA) S-class mission, including launch, and a fast development cycle. ADAHELI was submitted to the European Space Agency by a European-wide consortium of solar physics research institutes in response to the "Call for a small mission opportunity for a launch in 2017," of March 9, 2012. The ADAHELI project builds on the heritage of the former ADAHELI mission, which had successfully completed its phase-A study under the Italian Space Agency 2007 Small Mission Programme, thus proving the soundness and feasibility of its innovative low-budget design. ADAHELI is a solar space mission with two main instruments: ISODY: an imager, based on Fabry-Pérot interferometers, whose design is optimized to the acquisition of highest cadence, long-duration, multiline spectropolarimetric images in the visible/near-infrared region of the solar spectrum. XSPO: an x-ray polarimeter for solar flares in x-rays with energies in the 15 to 35 keV range. ADAHELI is capable of performing observations that cannot be addressed by other currently planned solar space missions, due to their limited telemetry, or by ground-based facilities, due to the problematic effect of the terrestrial atmosphere. Title: Coronal Response to an EUV Wave from DEM Analysis Authors: Vanninathan, K.; Veronig, A. M.; Dissauer, K.; Madjarska, M. S.; Hannah, I. G.; Kontar, E. P. Bibcode: 2015ApJ...812..173V Altcode: 2015arXiv150905269V Extreme-Ultraviolet (EUV) waves are globally propagating disturbances that have been observed since the era of the Solar and Heliospheric Observatory/Exteme-ultraviolet Imaging Telescope instrument. Although the kinematics of the wave front and secondary wave components have been widely studied, there is not much known about the generation and plasma properties of the wave. In this paper we discuss the effect of an EUV wave on the local plasma as it passes through the corona. We studied the EUV wave, generated during the 2011 February 15 X-class flare/coronal mass ejection event, using Differential Emission Measure diagnostics. We analyzed regions on the path of the EUV wave and investigated the local density and temperature changes. From our study we have quantitatively confirmed previous results that during wave passage the plasma visible in the Atmospheric Imaging Assembly (AIA) 171 Å channel is getting heated to higher temperatures corresponding to AIA 193 and 211 Å channels. We have calculated an increase of 6%-9% in density and 5%-6% in temperature during the passage of the EUV wave. We have compared the variation in temperature with the adiabatic relationship and have quantitatively demonstrated the phenomenon of heating due to adiabatic compression at the wave front. However, the cooling phase does not follow adiabatic relaxation but shows slow decay indicating slow energy release being triggered by the wave passage. We have also identified that heating is taking place at the front of the wave pulse rather than at the rear. Our results provide support for the case that the event under study here is a compressive fast-mode wave or a shock. Title: Cool Transition Region Loops Observed by the Interface Region Imaging Spectrograph Authors: Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S. Bibcode: 2015ApJ...810...46H Altcode: 2015arXiv150707594H We report on the first Interface Region Imaging Spectrograph (IRIS) study of cool transition region loops, a class of loops that has received little attention in the literature. A cluster of such loops was observed on the solar disk in active region NOAA11934, in the Si iv 1402.8 Å spectral raster and 1400 Å slit-jaw images. We divide the loops into three groups and study their dynamics. The first group comprises relatively stable loops, with 382-626 km cross-sections. Observed Doppler velocities are suggestive of siphon flows, gradually changing from -10 km s-1 at one end to 20 km s-1 at the other end of the loops. Nonthermal velocities of 15 ∼ 25 km s-1 were determined. Magnetic cancellation with a rate of 1015 Mx s-1 is found at the blueshifted footpoints. These physical properties suggest that these loops are impulsively heated by magnetic reconnection, and the siphon flows play an important role in the energy redistribution. The second group corresponds to two footpoints rooted in mixed-magnetic-polarity regions, where magnetic cancellation with a rate of 1015 Mx s-1 and explosive-event line profiles with enhanced wings of up to 200 km s-1 were observed. In the third group, interaction between two cool loop systems is observed. Evidence for magnetic reconnection between the two loop systems is reflected in the explosive-event line profiles and magnetic cancellation with a rate of 3× {10}15 Mx s-1 observed in the corresponding area. The IRIS has provided opportunity for in-depth investigations of cool transition region loops. Further numerical experiments are crucial for understanding their physics and their roles in the coronal heating processes. Title: A coronal wave and an asymmetric eruptive filament in SUMER, CDS, EIT, and TRACE co-observations Authors: Madjarska, M. S.; Doyle, J. G.; Shetye, J. Bibcode: 2015A&A...575A..39M Altcode: 2014arXiv1412.1984M Context. The investigation covers the complex subject of coronal waves and the phenomena contributing to and/or causing their formation.
Aims: The objectives of the present study is to provide a better physical understanding of the complex inter-relation and evolution of several solar coronal features comprising a double-peak flare, a coronal dimming caused by a coronal mass ejection (CME), a CME-driven compression, and a fast-mode wave. For the first time, the evolution of an asymmetric eruptive filament is analysed in simultaneous Solar Ultraviolet Measurement of Emitted Radiation (SUMER) spectroscopic and Transition Region and Coronal Explorer (TRACE) and Extreme-ultraviolet Imaging Telescope (EIT) imaging data.
Methods: We use imaging observations from EIT and TRACE in the 195 Å channel and spectroscopic observations from the Coronal Diagnostic Spectrometer (CDS) in a rastering and SUMER in a sit-and-stare observing mode. The SUMER spectra cover spectral lines with formation temperatures from log T(K) ~ 4.0 to 6.1.
Results: Although the event was already analysed in two previous studies, our analysis brings a wealth of new information on the dynamics and physical properties of the observed phenomena. We found that the dynamic event is related to a complex flare with two distinct impulsive peaks, one according to the Geostationary Operational Environmental Satellite (GOES) classification as C1.1 and the second - C1.9. The first energy release triggers a fast-mode wave and a CME with a clear CME driven compression ahead of it. This activity is related to, or possibly caused, by an asymmetric filament eruption. The filament is observed to rise with its leading edge moving at a speed of ~300 kms-1 detected both in the SUMER and CDS data. The rest of the filament body moves at only ~150 kms-1 while untwisting. No signature is found of the fast-mode wave in the SUMER data, suggesting that the plasma disturbed by the wave had temperatures above 600 000 K. The erupting filament material is found to emit only in spectral lines at transition region temperatures. Earlier identification of a coronal response detected in the Mg x 609.79 Å line is found to be caused by a blend from the O iv 609.83 Å line.
Conclusions: We present a unique analysis of the complex phenomenon called "EIT/coronal wave", confirming its bimodal nature. We suggest that the disintegration of the dimming/CME and the CME-driven compression are either caused by a CME-CME interaction taking place in the low solar atmosphere or by an impulsive CME cavity overexpansion in the low solar atmosphere.

A movie associated to Fig. A.1 is available in electronic form at http://www.aanda.org Title: Erratum: Erratum to: Off-limb (Spicule) DEM Distribution from SoHO/SUMER Observations Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G. Bibcode: 2014SoPh..289.4749V Altcode: 2014SoPh..tmp..127V No abstract at ADS Title: Explosive Events on a Subarcsecond Scale in IRIS Observations: A Case Study Authors: Huang, Zhenghua; Madjarska, Maria S.; Xia, Lidong; Doyle, J. G.; Galsgaard, Klaus; Fu, Hui Bibcode: 2014ApJ...797...88H Altcode: 2014arXiv1409.6425H We present a study of a typical explosive event (EE) at subarcsecond scale witnessed by strong non-Gaussian profiles with blue- and redshifted emission of up to 150 km s-1 seen in the transition region Si IV 1402.8 Å, and the chromospheric Mg II k 2796.4 Å and C II 1334.5 Å observed by the Interface Region Imaging Spectrograph (IRIS) at unprecedented spatial and spectral resolution. For the first time an EE is found to be associated with very small-scale (~120 km wide) plasma ejection followed by retraction in the chromosphere. These small-scale jets originate from a compact bright-point-like structure of ~1.''5 size as seen in the IRIS 1330 Å images. SDO/AIA and SDO/HMI co-observations show that the EE lies in the footpoint of a complex loop-like brightening system. The EE is detected in the higher temperature channels of AIA 171 Å, 193 Å, and 131 Å, suggesting that it reaches a higher temperature of log T = 5.36 ± 0.06 (K). Brightenings observed in the AIA channels with durations 90-120 s are probably caused by the plasma ejections seen in the chromosphere. The wings of the C II line behave in a similar manner to the Si IV'S, indicating close formation temperatures, while the Mg II k wings show additional Doppler-shifted emission. Magnetic convergence or emergence followed by cancellation at a rate of 5 × 1014 Mx s-1 is associated with the EE region. The combined changes of the locations and the flux of different magnetic patches suggest that magnetic reconnection must have taken place. Our results challenge several theories put forward in the past to explain non-Gaussian line profiles, i.e., EEs. Our case study on its own, however, cannot reject these theories; thus, further in-depth studies on the phenomena producing EEs are required. Title: Hα spectroscopy and multiwavelength imaging of a solar flare caused by filament eruption Authors: Huang, Z.; Madjarska, M. S.; Koleva, K.; Doyle, J. G.; Duchlev, P.; Dechev, M.; Reardon, K. Bibcode: 2014A&A...566A.148H Altcode: 2014arXiv1405.2194H Context. We study a sequence of eruptive events including filament eruption, a GOES C4.3 flare, and a coronal mass ejection.
Aims: We aim to identify the possible trigger(s) and precursor(s) of the filament destabilisation, investigate flare kernel characteristics, flare ribbons/kernels formation and evolution, study the interrelation of the filament-eruption/flare/coronal-mass-ejection phenomena as part of the integral active-region magnetic field configuration, and determine Hα line profile evolution during the eruptive phenomena.
Methods: Multi-instrument observations are analysed including Hα line profiles, speckle images at Hα - 0.8 Å and Hα + 0.8 Å from IBIS at DST/NSO, EUV images and magnetograms from the SDO, coronagraph images from STEREO, and the X-ray flux observations from Fermi and GOES.
Results: We establish that the filament destabilisation and eruption are the main triggers for the flaring activity. A surge-like event with a circular ribbon in one of the filament footpoints is determined as the possible trigger of the filament destabilisation. Plasma draining in this footpoint is identified as the precursor for the filament eruption. A magnetic flux emergence prior to the filament destabilisation followed by a high rate of flux cancellation of 1.34 × 1016 Mx s-1 is found during the flare activity. The flare X-ray lightcurves reveal three phases that are found to be associated with three different ribbons occurring consecutively. A kernel from each ribbon is selected and analysed. The kernel lightcurves and Hα line profiles reveal that the emission increase in the line centre is stronger than that in the line wings. A delay of around 5-6 min is found between the increase in the line centre and the occurrence of red asymmetry. Only red asymmetry is observed in the ribbons during the impulsive phases. Blue asymmetry is only associated with the dynamic filament.

Appendix A and movie associated to Fig. A.4 are available in electronic form at http://www.aanda.org Title: Intensity Enhancement of O VI Ultraviolet Emission Lines in Solar Spectra due to Opacity Authors: Keenan, F. P.; Doyle, J. G.; Madjarska, M. S.; Rose, S. J.; Bowler, L. A.; Britton, J.; McCrink, L.; Mathioudakis, M. Bibcode: 2014ApJ...784L..39K Altcode: 2014arXiv1403.1470K Opacity is a property of many plasmas. It is normally expected that if an emission line in a plasma becomes optically thick, then its intensity ratio to that of another transition that remains optically thin should decrease. However, radiative transfer calculations undertaken both by ourselves and others predict that under certain conditions the intensity ratio of an optically thick to an optically thin line can show an increase over the optically thin value, indicating an enhancement in the former. These conditions include the geometry of the emitting plasma and its orientation to the observer. A similar effect can take place between lines of differing optical depths. While previous observational studies have focused on stellar point sources, here we investigate the spatially resolved solar atmosphere using measurements of the I(1032 Å)/I(1038 Å) intensity ratio of O VI in several regions obtained with the Solar Ultraviolet Measurements of Emitted Radiation instrument on board the Solar and Heliospheric Observatory satellite. We find several I(1032 Å)/I(1038 Å) ratios observed on the disk to be significantly larger than the optically thin value of 2.0, providing the first detection (to our knowledge) of intensity enhancement in the ratio arising from opacity effects in the solar atmosphere. The agreement between observation and theory is excellent and confirms that the O VI emission originates from a slab-like geometry in the solar atmosphere, rather than from cylindrical structures. Title: Ellerman Bombs—Evidence for Magnetic Reconnection in the Lower Solar Atmosphere Authors: Nelson, C. J.; Shelyag, S.; Mathioudakis, M.; Doyle, J. G.; Madjarska, M. S.; Uitenbroek, H.; Erdélyi, R. Bibcode: 2013ApJ...779..125N Altcode: 2013arXiv1310.7756N The presence of photospheric magnetic reconnection has long been thought to give rise to short and impulsive events, such as Ellerman bombs (EBs) and Type II spicules. In this article, we combine high-resolution, high-cadence observations from the Interferometric BIdimensional Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments at the Dunn Solar Telescope, National Solar Observatory, New Mexico, with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly and Hinode Solar Optical Telescope (SOT) data to observe small-scale events situated within an active region. These data are then compared with state-of-the-art numerical simulations of the lower atmosphere made using the MURaM code. It is found that brightenings, in both the observations and the simulations, of the wings of the Hα line profile, interpreted as EBs, are often spatially correlated with increases in the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred from Hinode/SOT magnetic field data show evidence of flux cancellation associated, co-spatially, with these EBs, suggesting that magnetic reconnection could be a driver of these high-energy events. Through the analysis of similar events in the simulated lower atmosphere, we are able to infer that line profiles analogous to the observations occur co-spatially with regions of strong opposite-polarity magnetic flux. These observed events and their simulated counterparts are interpreted as evidence of photospheric magnetic reconnection at scales observable using current observational instrumentation. Title: Diagnosing transient ionization in dynamic events Authors: Doyle, J. G.; Giunta, A.; Madjarska, M. S.; Summers, H.; O'Mullane, M.; Singh, A. Bibcode: 2013A&A...557L...9D Altcode: 2013arXiv1307.8251D
Aims: The present study aims to provide a diagnostic line ratio that will enable the observer to determine whether a plasma is in a state of transient ionization.
Methods: We use the Atomic Data and Analysis Structure (ADAS) to calculate line contribution functions for two lines, Si iv 1394 Å and O iv 1401 Å, formed in the solar transition region. The generalized collisional-radiative theory is used. It includes all radiative and electron collisional processes, except for photon-induced processes. State-resolved direct ionization and recombination to and from the next ionization stage are also taken into account.
Results: For dynamic bursts with a decay time of a few seconds, the Si iv 1394 Å line can be enhanced by a factor of 2-4 in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature due to transient ionization compared to ionization equilibrium conditions. On the other hand, the O iv 1401 Å does not show such any enhancement. Thus the ratio of these two lines, which can be observed with the Interface Region Imaging Spectrograph, can be used as a diagnostic of transient ionization.
Conclusions: We show that simultaneous high-cadence observations of two lines formed in the solar transition region may be used as a direct diagnostic of whether the observed plasma is in transient ionization. The ratio of these two lines can change by a factor of four in a few seconds owing to transient ionization alone. Title: Evolution of magnetic field corresponding to X-ray brightening events in coronal holes and quiet Sun Authors: Huang, Zhenghua; Madjarska, Maria; Doyle, Gerry; Lamb, Derek Bibcode: 2013IAUS..294..155H Altcode: We study the magnetic field structure and evolution for 26 X-ray brightening events in coronal holes and quiet Sun regions, including bright points and jets. We found that all brightening events are associated with bipolar regions and caused by magnetic flux emergence followed by cancellation. The emission fluctuations seen in the X-ray bright points are associated with reoccurring magnetic cancellation in the footpoints. An X-ray jet presents similar magnetic behaviour in the footpoints but its magnetic flux cancellation rate is much higher than in the bright point. Comparing coronal holes and the quiet Sun, we do not find differences in their corresponding magnetic field behavior. Title: Jets from coronal holes - possible source of the slow solar wind Authors: Madjarska, Maria; Huang, Zhenghua; Subramanian, Srividya; Doyle, Gerry Bibcode: 2013EGUGA..15.2455M Altcode: We will report on statistical studies on the occurrence rate, plasma properties, dynamics and structural evolution, including the magnetic field evolution, of small-scale transients in and along the boundaries of equatorial coronal holes. A comparison is made with quiet-Sun transients. We use multi-instrument observations from the photosphere to the corona comprising imaging, magnetogram and imaging spectroscopy data from EIS, XRT and SOT on board Hinode and SUMER onboard SoHO. The visual analysis of these transients reveals that around 70% of them in equatorial, polar and transient coronal holes and their boundaries show expanding loop structures and/or collimated outflows, i.e. jets. In the quiet Sun only 30% of the brightenings show flows with most of them appearing to be contained in the solar corona by closed magnetic field lines. This strongly suggests that magnetic reconnection of co-spatial open and closed magnetic field lines creates the necessary conditions for plasma outflows to large distances. The ejected plasma always originates from preexisting or newly emerging (at X-ray temperatures) bright points. We will discuss in detail the evolution of individual jets and the possibility whether these phenomena could be one of the sources of the slow solar wind. Title: Statistical Analysis of Small Ellerman Bomb Events Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Huang, Z.; Madjarska, M. S.; Mathioudakis, M.; Mumford, S. J.; Reardon, K. Bibcode: 2013SoPh..283..307N Altcode: 2013arXiv1301.1351N The properties of Ellerman bombs (EBs), small-scale brightenings in the Hα line wings, have proved difficult to establish because their size is close to the spatial resolution of even the most advanced telescopes. Here, we aim to infer the size and lifetime of EBs using high-resolution data of an emerging active region collected using the Interferometric BIdimensional Spectrometer (IBIS) and Rapid Oscillations of the Solar Atmosphere (ROSA) instruments as well as the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We develop an algorithm to track EBs through their evolution, finding that EBs can often be much smaller (around 0.3″) and shorter-lived (less than one minute) than previous estimates. A correlation between G-band magnetic bright points and EBs is also found. Combining SDO/HMI and G-band data gives a good proxy of the polarity for the vertical magnetic field. It is found that EBs often occur both over regions of opposite polarity flux and strong unipolar fields, possibly hinting at magnetic reconnection as a driver of these events.The energetics of EB events is found to follow a power-law distribution in the range of a nanoflare (1022−25 ergs). Title: Ellerman bombs: small-scale brightenings in the photosphere Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Madjarska, M.; Mumford, S. J. Bibcode: 2013MmSAI..84..436N Altcode: Observations of small-scale events in the solar atmosphere are limited by the spatial and temporal resolutions of the current crop of observational instruments. Both high-cadence and high-resolution observations of the photosphere have shown the continued dynamics to extremely small-scales. Ellerman bombs, brightening events in the wings of the Halpha line profile, are one example of small-scale, short-lived events which have been widely studied due to their fast dynamics in recent years. By combining the Interferometric BIdimensional Spectrometer (IBIS) instrument with the Helioseismic and Magnetic Imager (HMI/SDO), we show the small-scale nature of these events, as well as their link to the background magnetic field. It is found that EBs can be much smaller and shorter-lived than previous estimates have stated, implying the continued dynamics of the solar atmosphere below current observational limits. Title: Nature of Quiet Sun Oscillations Using Data from the Hinode, TRACE, and SOHO Spacecraft Authors: Gupta, G. R.; Subramanian, S.; Banerjee, D.; Madjarska, M. S.; Doyle, J. G. Bibcode: 2013SoPh..282...67G Altcode: 2012arXiv1209.5252G; 2012SoPh..tmp..247G We study the nature of quiet-Sun oscillations using multi-wavelength observations from TRACE, Hinode, and SOHO. The aim is to investigate the existence of propagating waves in the solar chromosphere and the transition region by analyzing the statistical distribution of power in different locations, e.g. in bright magnetic (network), bright non-magnetic and dark non-magnetic (inter-network) regions, separately. We use Fourier power and phase-difference techniques combined with a wavelet analysis. Two-dimensional Fourier power maps were constructed in the period bands 2 - 4 minutes, 4 - 6 minutes, 6 - 15 minutes, and beyond 15 minutes. We detect the presence of long-period oscillations with periods between 15 and 30 minutes in bright magnetic regions. These oscillations were detected from the chromosphere to the transition region. The Fourier power maps show that short-period powers are mainly concentrated in dark regions whereas long-period powers are concentrated in bright magnetic regions. This is the first report of long-period waves in quiet-Sun network regions. We suggest that the observed propagating oscillations are due to magnetoacoustic waves, which can be important for the heating of the solar atmosphere. Title: Coronal hole boundaries at small scales. IV. SOT view. Magnetic field properties of small-scale transient brightenings in coronal holes Authors: Huang, Z.; Madjarska, M. S.; Doyle, J. G.; Lamb, D. A. Bibcode: 2012A&A...548A..62H Altcode: 2012arXiv1210.2009H Context. We study the magnetic properties of small-scale transients in coronal holes and a few in the quiet Sun identified in X-ray observations and spectroscopic data in two previous papers.
Aims: We aim to investigate the role of small-scale transients in the evolution of the magnetic field in an equatorial coronal hole.
Methods: Two sets of observations of an equatorial coronal hole and another two in quiet-Sun regions were analysed using longitudinal magnetograms taken by the Solar Optical Telescope. An automatic feature tracking program, SWAMIS, was used to identify and track the magnetic features. Each event was then visually analysed in detail.
Results: In both coronal holes and quiet-Sun regions, all brightening events are associated with bipolar regions and are caused by magnetic flux emergence followed by cancellation with the pre-existing and/or newly emerging magnetic flux. In the coronal hole, 19 of 22 events have a single stable polarity which does not change its position in time. In eleven cases this is the dominant polarity. In the coronal hole, the magnetic features with the largest flux are those of the dominant polarity, while the opposite polarity is distributed in weaker features. The number of magnetic features of the dominant polarity is four times grater than the opposite polarity. The supergranulation configuration appears to preserve its general shape during approximately nine hours of observations although the large concentrations (the dominant polarity) in the network did evolve and/or were slightly displaced, and their strength either increased or decreased. The emission fluctuations/radiance oscillations seen in the X-ray bright points are associated with recurring magnetic cancellation in the footpoints. Unique observations of an X-ray jet reveal similar magnetic behaviour in the footpoints, i.e. cancellation of the opposite polarity magnetic flux. We find that the magnetic flux cancellation rate during the jet is much higher than in bright points. Not all magnetic cancellations result in an X-ray enhancement, suggesting that there is a threshold of the amount of magnetic flux involved in a cancellation above which brightening would occur at X-ray temperatures.
Conclusions: Our study demonstrates that the magnetic flux in coronal holes is continuously processed through magnetic reconnection which is responsible for the formation of numerous small-scale transient events. The open magnetic flux forming the coronal-hole phenomenon is largely involved in these transient features. The question of whether this open flux is transported as a result of the formation and evolution of these transient events, however, still remains open.

Three movies and Appendix A are available in electronic form at http://www.aanda.org Title: Off-limb (Spicule) DEM Distribution from SoHO/SUMER Observations Authors: Vanninathan, K.; Madjarska, M. S.; Scullion, E.; Doyle, J. G. Bibcode: 2012SoPh..280..425V Altcode: 2012SoPh..tmp...88V; 2012arXiv1203.2073V In the present work we derive a Differential Emission Measure (DEM) distribution from a region dominated by spicules. We use spectral data from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on-board the Solar Heliospheric Observatory (SoHO) covering the entire SUMER wavelength range taken off-limb in the Northern polar coronal hole to construct this DEM distribution using the CHIANTI atomic database. This distribution is then used to study the thermal properties of the emission contributing to the 171 Å channel in the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). From our off-limb DEM we found that the radiance in the AIA 171 Å channel is dominated by emission from the Fe IX 171.07 Å line and has sparingly little contribution from other lines. The product of the Fe IX 171.07 Å line contribution function with the off-limb DEM was found to have a maximum at logTmax (K)=5.8 indicating that during spicule observations the emission in this line comes from plasma at transition region temperatures rather than coronal. For comparison, the same product with a quiet Sun and prominence DEM were found to have a maximum at logTmax (K)=5.9 and logTmax (K)=5.7, respectively. We point out that the interpretation of data obtained from the AIA 171 Å filter should be done with foreknowledge of the thermal nature of the observed phenomenon. For example, with an off-limb DEM we find that only 3.6 % of the plasma is above a million degrees, whereas using a quiet Sun DEM, this contribution rises to 15 %. Title: Coronal hole boundaries evolution at small scales. III. EIS and SUMER views Authors: Madjarska, M. S.; Huang, Z.; Doyle, J. G.; Subramanian, S. Bibcode: 2012A&A...545A..67M Altcode: 2012arXiv1207.1281M Context. We report on the plasma properties of small-scale transient events identified in the quiet Sun, coronal holes and their boundaries.
Aims: We aim at deriving the physical characteristics of events that were identified as small-scale transient brightenings in XRT images.
Methods: We used spectroscopic co-observations from SUMER/SoHO and EIS/Hinode combined with high-cadence imaging data from XRT/Hinode. We measured Doppler shifts using single and multiple Gaussian fits of the transition region and coronal lines as well as electron densities and temperatures. We combined co-temporal imaging and spectroscopy to separate brightening expansions from plasma flows.
Results: The transient brightening events in coronal holes and their boundaries were found to be very dynamical, producing high-density outflows at high speeds. Most of these events represent X-ray jets from pre-existing or newly emerging coronal bright points at X-ray temperatures. The average electron density of the jets is log10 Ne ≈ 8.76 cm-3 while in the flaring site it is log10 Ne ≈ 9.51 cm-3. The jet temperatures reach a maximum of 2.5 MK but in the majority of the cases the temperatures do not exceed 1.6 MK. The footpoints of jets have maximum temperatures of 2.5 MK, though in a single event scanned a minute after the flaring the measured temperature was 12 MK. The jets are produced by multiple microflaring in the transition region and corona. Chromospheric emission was only detected in their footpoints and was only associated with downflows. The Doppler shift measurements in the quiet Sun transient brightenings confirmed that these events do not produce jet-like phenomena. The plasma flows in these phenomena remain trapped in closed loops.
Conclusions: We can conclude that the dynamic day-by-day and even hour-by-hour small-scale evolution of coronal hole boundaries reported in Paper I is indeed related to coronal bright points. The XRT observations reported in Paper II revealed that these changes are associated with the dynamic evolution of coronal bright points producing multiple jets during their lifetime until their full disappearance. We demonstrate here through spectroscopic EIS and SUMER co-observations combined with high-cadence imaging information that the co-existence of open and closed magnetic fields results in multiple energy depositions, which propel high-density plasma along open magnetic field lines. We conclude from the physical characteristics obtained in this study that X-ray jets are important candidates for the source of the slow solar wind. This, however, does not exclude the possibility that these jets are also the microstreams observed in the fast solar wind, as recently suggested.

Figures A.1, A.2, and movies are available in electronic form at http://www.aanda.org Title: Solar Fine-Scale Structures. I. Spicules and Other Small-Scale, Jet-Like Events at the Chromospheric Level: Observations and Physical Parameters Authors: Tsiropoula, G.; Tziotziou, K.; Kontogiannis, I.; Madjarska, M. S.; Doyle, J. G.; Suematsu, Y. Bibcode: 2012SSRv..169..181T Altcode: 2012SSRv..tmp...65T; 2012arXiv1207.3956T Over the last two decades the uninterrupted, high resolution observations of the Sun, from the excellent range of telescopes aboard many spacecraft complemented with observations from sophisticated ground-based telescopes have opened up a new world producing significantly more complete information on the physical conditions of the solar atmosphere than before. The interface between the lower solar atmosphere where energy is generated by subsurface convection and the corona comprises the chromosphere, which is dominated by jet-like, dynamic structures, called mottles when found in quiet regions, fibrils when found in active regions and spicules when observed at the solar limb. Recently, space observations with Hinode have led to the suggestion that there should exist two different types of spicules called Type I and Type II which have different properties. Ground-based observations in the Ca ii H and K filtergrams reveal the existence of long, thin emission features called straws in observations close to the limb, and a class of short-lived events called rapid blue-shifted excursions characterized by large Doppler shifts that appear only in the blue wing of the Ca ii infrared line. It has been suggested that the key to understanding how the solar plasma is accelerated and heated may well be found in the studies of these jet-like, dynamic events. However, while these structures are observed and studied for more than 130 years in the visible, but also in the UV and EUV emission lines and continua, there are still many questions to be answered. Thus, despite their importance and a multitude of observations performed and theoretical models proposed, questions regarding their origin, how they are formed, their physical parameters, their association with the underlying photospheric magnetic field, how they appear in the different spectral lines, and the interrelationship between structures observed in quiet and active regions on the disk and at the limb, as well as their role in global processes has not yet received definitive answers. In addition, how they affect the coronal heating and solar wind need to be further explored. In this review we present observations and physical properties of small-scale jet-like chromospheric events observed in active and quiet regions, on the disk and at the limb and discuss their interrelationship. Title: The Diagnostic Potential of Transition Region Lines Undergoing Transient Ionization in Dynamic Events Authors: Doyle, J. G.; Giunta, A.; Singh, A.; Madjarska, M. S.; Summers, H.; Kellett, B. J.; O'Mullane, M. Bibcode: 2012SoPh..280..111D Altcode: 2012SoPh..tmp..118D; 2012arXiv1204.6598D We discuss the diagnostic potential of high cadence UV spectral data when transient ionization is considered. For this we use high cadence UV spectra taken during the impulsive phase of a solar flare (observed with instruments on-board the Solar Maximum Mission) which showed excellent correspondence with hard X-ray pulses. The ionization fraction of the transition region ion O V and, in particular, the contribution function for the O V 1371 Å line are computed within the Atomic Data and Analysis Structure, which is a collection of fundamental and derived atomic data and codes to manipulate them. Due to transient ionization, the O V 1371 Å line is enhanced in the first fraction of a second with the peak in the line contribution function occurring initially at a higher electron temperature than in ionization equilibrium. The rise time and enhancement factor depend mostly on the electron density. The fractional increase in the O V 1371 Å emissivity due to transient ionization can reach a factor of two-four and can explain the fast response in the line flux of transition regions ions during the impulsive phase of flares solely as a result of transient ionization. This technique can be used to diagnose the electron temperature and density of solar flares observed with the forthcoming Interface Region Imaging Spectrograph. Title: Kinematics and helicity evolution of a loop-like eruptive prominence Authors: Koleva, K.; Madjarska, M. S.; Duchlev, P.; Schrijver, C. J.; Vial, J. -C.; Buchlin, E.; Dechev, M. Bibcode: 2012A&A...540A.127K Altcode: 2012arXiv1202.4541K
Aims: We aim at investigating the morphology as well as kinematic and helicity evolution of a loop-like prominence during its eruption.
Methods: We used multi-instrument observations from AIA/SDO, EUVI/STEREO and LASCO/SoHO. The kinematic, morphological, geometrical, and helicity evolution of a loop-like eruptive prominence were studied in the context of the magnetic flux rope model of solar prominences.
Results: The prominence eruption evolved as a height-expanding twisted loop with both legs anchored in the chromosphere of a plage area. The eruption process consisted of a prominence activation, acceleration, and a phase of constant velocity. The prominence body was composed of counter-clockwise twisted threads around the main prominence axis. The twist during the eruption was estimated at 6π (3 turns). The prominence reached a maximum height of 526 Mm before contracting to its primary location and was partially reformed in the same place two days after the eruption. This ejection, however, triggered a coronal mass ejection (CME) observed in LASCO C2. The prominence was located in the northern periphery of the CME magnetic field configuration and, therefore, the background magnetic field was asymmetric with respect to the filament position. The physical conditions of the falling plasma blobs were analysed with respect to the prominence kinematics.
Conclusions: The same sign of the prominence body twist and writhe, as well as the amount of twisting above the critical value of 2π after the activation phase indicate that possibly conditions for kink instability were present. No signature of magnetic reconnection was observed anywhere in the prominence body and its surroundings. The filament/prominence descent following the eruption and its partial reformation at the same place two days later suggest a confined type of eruption. The asymmetric background magnetic field possibly played an important role in the failed eruption.

Movies showing the temporal evolution are available in electronic form at http://www.aanda.org Title: Multi-instrument study of chromospheric jets Authors: Vanninathan, Kamalam; Madjarska, Maria; Doyle, Gerry Bibcode: 2012decs.confE..21V Altcode: The contribution to coronal heating by jets of various kinds like spicules, mottles, surges etc. originating in the solar chromosphere is an issue which is being currently largely explored. We analyse multi-instrument data taken in the plage area of active regions during dedicated observing runs with ROSA, IBIS at Sac Peak, USA, SOT, EIS/XRT/Hinode and AIA/SDO. The high-resolution and high-cadence data allow us to track chromospheric jets through the solar atmosphere and thus helps us to understand the dynamics and plasma properties of these features. The study is a forward step towards the exploration of the forthcoming state-of-art IRIS observations. Title: Coronal hole boundaries and the slow solar wind from Hinode/EIS/XRT/SOT and SUMER/SoHO Authors: Madjarska, M. S.; Huang, Zh.; Doyle, J. G.; Subramanian, S. Bibcode: 2012decs.confE..16M Altcode: We present a statistical study on outflows at coronal hole boundaries and inside coronal holes and discuss their role in the slow solar wind formation in the low solar corona. The outflows are studied in XRT/Hinode image data taken with the Al_poly filter using an automatic identification method. A spectroscopic analysis is made using EIS and SUMER data of spectral lines with formation temperatures in the range from 10 000 K to 12 MK. The derived plasma parameters of about 60 phenomena will be reported. The longitudinal magnetic field data for each feature falling in the SOT/Hinode field-of-view (more than 25) are studied using a magnetic feature tracking procedure and a visual inspection. The mechanism of the outflow formation and acceleration will be discussed. Title: What is the true nature of blinkers? Authors: Subramanian, S.; Madjarska, M. S.; Doyle, J. G.; Bewsher, D. Bibcode: 2012A&A...538A..50S Altcode: 2011arXiv1111.2149S
Aims: The aim of this work is to identify the true nature of the transient EUV brightenings, called blinkers.
Methods: Co-spatial and co-temporal multi-instrument data, including imaging (EUVI/STEREO, XRT and SOT/Hinode), spectroscopic (CDS/SoHO and EIS/Hinode) and magnetogram (SOT/Hinode) data, of an isolated equatorial coronal hole were used. An automatic program for identifying transient brightenings in CDS O v 629 Å, EUVI 171 Å and XRT was applied.
Results: We identified 28 blinker groups in the CDS O v 629 Å raster images. All CDS O v 629 Å blinkers showed counterparts in EUVI 171 Å and 304 Å images. We classified these blinkers into two categories, one associated with coronal counterparts and other with no coronal counterparts as seen in XRT images and EIS Fe xii 195.12 Å raster images. Around two-thirds of the blinkers show coronal counterparts and correspond to various events like EUV/X-ray jets, brightenings in coronal bright points or foot-point brightenings of larger loops. These brightenings occur repetitively and have a lifetime of around 40 min at transition region temperatures. The remaining blinker groups with no coronal counterpart in XRT and EIS Fe xii 195.12 Å appear as point-like brightenings and have chromospheric/transition region origin. They take place only once and have a lifetime of around 20 min. In general, lifetimes of blinkers are different at different wavelengths, i.e. different temperatures, decreasing from the chromosphere to the corona.
Conclusions: This work shows that the term blinker covers a range of phenomena. Blinkers are the EUV response of various transient events originating at coronal, transition region and chromospheric heights. Hence, events associated with blinkers contribute to the formation and maintenance of the temperature gradient in the transition region and the corona. Title: Magnetic reconnection resulting from flux emergence: implications for jet formation in the lower solar atmosphere? Authors: Ding, J. Y.; Madjarska, M. S.; Doyle, J. G.; Lu, Q. M.; Vanninathan, K.; Huang, Z. Bibcode: 2011A&A...535A..95D Altcode: 2011arXiv1109.5606D
Aims: We aim at investigating the formation of jet-like features in the lower solar atmosphere, e.g. chromosphere and transition region, as a result of magnetic reconnection.
Methods: Magnetic reconnection as occurring at chromospheric and transition regions densities and triggered by magnetic flux emergence is studied using a 2.5D MHD code. The initial atmosphere is static and isothermal, with a temperature of 2 × 104 K. The initial magnetic field is uniform and vertical. Two physical environments with different magnetic field strength (25 G and 50 G) are presented. In each case, two sub-cases are discussed, where the environments have different initial mass density.
Results: In the case where we have a weaker magnetic field (25 G) and higher plasma density (Ne = 2 × 1011 cm-3), valid for the typical quiet Sun chromosphere, a plasma jet would be observed with a temperature of 2-3 × 104 K and a velocity as high as 40 kms-1. The opposite case of a medium with a lower electron density (Ne = 2 × 1010 cm-3), i.e. more typical for the transition region, and a stronger magnetic field of 50 G, up-flows with line-of-sight velocities as high as ~90 kms-1 and temperatures of 6 × 105 K, i.e. upper transition region - low coronal temperatures, are produced. Only in the latter case, the low corona Fe ix 171 Å shows a response in the jet which is comparable to the O v increase.
Conclusions: The results show that magnetic reconnection can be an efficient mechanism to drive plasma outflows in the chromosphere and transition region. The model can reproduce characteristics, such as temperature and velocity for a range of jet features like a fibril, a spicule, a hot X-ray jet or a transition region jet by changing either the magnetic field strength or the electron density, i.e. where in the atmosphere the reconnection occurs. Title: Can coronal hole spicules reach coronal temperatures? Authors: Madjarska, M. S.; Vanninathan, K.; Doyle, J. G. Bibcode: 2011A&A...532L...1M Altcode: 2011arXiv1105.1296M
Aims: The present study aims to provide observational evidence of whether coronal hole spicules reach coronal temperatures.
Methods: We combine multi-instrument co-observations obtained with the SUMER/SoHO and with the EIS/SOT/XRT/Hinode.
Results: The analysed three large spicules were found to be comprised of numerous thin spicules that rise, rotate, and descend simultaneously forming a bush-like feature. Their rotation resembles the untwisting of a large flux rope. They show velocities ranging from 50 to 250 kms-1. We clearly associated the red- and blue-shifted emissions in transition region lines not only with rotating but also with rising and descending plasmas. Our main result is that these spicules although very large and dynamic, are not present in the spectral lines formed at temperatures above 300 000 K.
Conclusions: In this paper we present the analysis of three Ca ii H large spicules that are composed of numerous dynamic thin spicules but appear as macrospicules in lower resolution EUV images. We found no coronal counterpart of these and smaller spicules. We believe that the identification of phenomena that have very different origins as macrospicules is due to the interpretation of the transition region emission, and especially the He ii emission, wherein both chromospheric large spicules and coronal X-ray jets are present. We suggest that the recent observation of spicules in the coronal AIA/SDO 171 Å and 211 Å channels probably comes from the existence of transition region emission there.

Movie is available in electronic form at http://www.aanda.org Title: Dynamics and plasma properties of an X-ray jet from SUMER, EIS, XRT, and EUVI A & B simultaneous observations Authors: Madjarska, M. S. Bibcode: 2011A&A...526A..19M Altcode: 2010arXiv1008.3983M Context. Small-scale transient phenomena in the quiet Sun are believed to play an important role in coronal heating and solar wind generation. One of them, called “X-ray jet”, is the subject of our study.
Aims: We intend to investigate the dynamics, evolution, and physical properties of this phenomenon.
Methods: We combine multi-instrument observations obtained simultaneously with the SUMER spectrometer onboard SoHO, with EIS and XRT onboard Hinode, and with EUVI/SECCHI onboard the Ahead and Behind STEREO spacecrafts. We derive plasma parameters such as temperatures and densities as well as dynamics by using spectral lines formed in the temperature range from 10 000 K to 12 MK. We also use an image difference technique to investigate the evolution of the complex structure of the studied phenomenon.
Results: With the available unique combination of data we were able to establish that the formation of a jet-like event is triggered by not one, but several energy depositions, which are most probably originating from magnetic reconnection. Each energy deposition is followed by the expulsion of pre-existing or newly reconnected loops and/or collimated flow along open magnetic field lines. We derived in great detail the dynamic process of X-ray jet formation and evolution. For the first time we also found spectroscopically a temperature of 12 MK (Fe xxiii 263.76 Å) and density of 4 × 1010 cm-3 in the quiet Sun, obtained from a pair of Fe xii lines with a maximum formation temperature of 1.3 × 106 K, in an energy deposition region. We point out a problem concerning an uncertainty in using the SUMER Mg x 624.9 Å line for coronal diagnostics. We clearly identified two types of up-flow: one collimated up-flow along open magnetic field lines and a plasma cloud formed from the expelled BP loops. We also report a cooler down-flow along closed magnetic field lines. A comparison is made with a model developed by Moreno-Insertis et al. (2008).

Figures 10-16 and movie are only available in electronic form at http://www.aanda.org Title: Coronal hole boundaries evolution at small scales. II. XRT view. Can small-scale outflows at CHBs be a source of the slow solar wind Authors: Subramanian, S.; Madjarska, M. S.; Doyle, J. G. Bibcode: 2010A&A...516A..50S Altcode: 2010arXiv1002.1675S
Aims: We aim to further explore the small-scale evolution of coronal hole boundaries using X-ray high-resolution and high-cadence images. We intend to determine the fine structure and dynamics of the events causing changes of coronal hole boundaries and to explore the possibility that these events are the source of the slow solar wind.
Methods: We developed an automated procedure for the identification of transient brightenings in images from the X-ray telescope on-board Hinode taken with an Al Poly filter in the equatorial coronal holes, polar coronal holes, and the quiet Sun with and without transient coronal holes.
Results: We found that in comparison to the quiet Sun, the boundaries of coronal holes are abundant with brightening events including areas inside the coronal holes where closed magnetic field structures are present. The visual analysis of these brightenings revealed that around 70% of them in equatorial, polar and transient coronal holes and their boundaries show expanding loop structures and/or collimated outflows. In the quiet Sun only 30% of the brightenings show flows with most of them appearing to be contained in the solar corona by closed magnetic field lines. This strongly suggests that magnetic reconnection of co-spatial open and closed magnetic field lines creates the necessary conditions for plasma outflows to large distances. The ejected plasma always originates from pre-existing or newly emerging (at X-ray temperatures) bright points.
Conclusions: The present study confirms our findings that the evolution of loop structures known as coronal bright points is associated with the small-scale changes of coronal hole boundaries. The loop structures show an expansion and eruption with the trapped plasma consequently escaping along the “quasi” open magnetic field lines. These ejections appear to be triggered by magnetic reconnection, e.g. the so-called interchange reconnection between the closed magnetic field lines (BPs) and the open magnetic field lines of the coronal holes. We suggest that these plasma outflows are possibly one of the sources of the slow solar wind.

4 movies are only available in electronic form at http://www.aanda.org Title: Chromospheric magnetic reconnection caused by photospheric flux emergence: implications for jet-like events formation Authors: Ding, J. Y.; Madjarska, M. S.; Doyle, J. G.; Lu, Q. M. Bibcode: 2010A&A...510A.111D Altcode: 2009arXiv0912.4449D Magnetic reconnection in the low atmosphere, e.g. chromosphere, is investigated in various physical environments. Its implications for the origination of explosive events (small-scale jets) are discussed. A 2.5-dimensional resistive magnetohydrodynamic (MHD) model in Cartesian coordinates is used. It is found that the temperature and velocity of the outflow jets as a result of magnetic reconnection are strongly dependent on the physical environments, e.g. the magnitude of the magnetic field strength and the plasma density. If the magnetic field strength is weak and the density is high, the temperature of the jets is very low (~104 K) as well as its velocity (~40 km s-1). However, if environments with stronger magnetic field strength (40 G) and smaller density (electron density N_e=2× 1010 cm-3) are considered, the outflow jets reach higher temperatures of up to 6× 10^5 K and a line-of-sight velocity of up to 130 km s-1 which is comparable with the observational values of jet-like events. Title: Fine Structure of a Coronal Bright Point as Seen with SoHO, TRACE, and Hinode Authors: Pérez-Suárez, D.; Maclean, R. C.; Doyle, J. G.; Madjarska, M. S. Bibcode: 2009ASPC..415..140P Altcode: We present a study of a Coronal Bright Point (BPs) where data from Hinode, SoHO and TRACE are analyzed. Covering a large temperature range, we study the variation of the BP from the surface to the corona investigating both the morphology and variation in physical parameters, such as electron density, Doppler-shift and magnetic field variability. We obtain excellent correlation between the X-ray light curve with the positive magnetic flux; also a good agreement is found between a potential extrapolated magnetic field and the loops seen in the X-ray images. Title: Coronal hole boundaries evolution at small scales. I. EIT 195 Å  and TRACE 171 Å view Authors: Madjarska, M. S.; Wiegelmann, T. Bibcode: 2009A&A...503..991M Altcode: 2009arXiv0906.2556M Aims: We aim to study the small-scale evolution at the boundaries of an equatorial coronal hole connected with a channel of open magnetic flux to the polar region and an “isolated” one in the extreme-ultraviolet spectral range. We determine the spatial and temporal scale of these changes.
Methods: Imager data from TRACE in the Fe ix/x 171 Å passband and EIT on-board Solar and Heliospheric Observatory in the Fe xii 195 Å passband were analysed.
Results: We found that small-scale loops known as bright points play an essential role in coronal hole boundary evolution at small scales. Their emergence and disappearance continuously expand or contract coronal holes. The changes appear to be random on a time scale comparable to the lifetime of the loops seen at these temperatures. No signature was found for a major energy release during the evolution of the loops.
Conclusions: Although coronal holes seem to maintain their general shape during a few solar rotations, a closer look at their day-by-day and even hour-by-hour evolution demonstrates significant dynamics. The small-scale loops (10´´-40´´ and smaller) which are abundant along coronal hole boundaries contribute to the small-scale evolution of coronal holes. Continuous magnetic reconnection of the open magnetic field lines of the coronal hole and the closed field lines of the loops in the quiet Sun is more likely to take place.

Movies are only available in electronic form at http://www.aanda.org Title: Explosive Events Associated with a Surge Authors: Madjarska, M. S.; Doyle, J. G.; de Pontieu, B. Bibcode: 2009ApJ...701..253M Altcode: 2009arXiv0906.2544M The solar atmosphere contains a wide variety of small-scale transient features. Here, we explore the interrelation between some of them such as surges, explosive events, and blinkers via simultaneous spectral and imaging data taken with the TRACE imager, the SUMER and Coronal Diagnostics Spectrometer (CDS) on board SOHO, and Swedish Vacuum Solar Telescope La Palma. The features were observed in spectral lines with formation temperatures from 10,000 K to 1 MK and with the TRACE Fe IX/X 171 Å filter. The Hα filtergrams were taken in the wings of the Hα 6365 Å line at ±700 mÅ and ±350 mÅ. The alignment of all data in both time and solar XY shows that SUMER line profiles, which are attributed to explosive events, are due to a surge phenomenon. The surge's up- and downflows, which often appear simultaneously, correspond to the blue- and redshifted emission of the transition region N V 1238.82 Å and O V 629.77 Å lines as well as radiance increases of the C I, S I, and S II and Si II chromospheric lines. Some parts of the surge are also visible in the TRACE 171 Å images which could suggest heating to coronal temperatures. The surge is triggered, most probably, by one or more Elerman bombs which are best visible in Hα ± 350 Å but were also registered by TRACE Fe IX/X 171 Å and correspond to a strong radiance increase in the CDS Mg IX 368.07 Å line. With the present study, we demonstrate that the division of small-scale transient events into a number of different subgroups, for instance explosive events, blinkers, spicules, surges or just brightenings, is ambiguous, implying that the definition of a feature based only on either spectroscopic or imaging characteristics as well as insufficient spectral and spatial resolution can be incomplete. Title: The structure and dynamics of a bright point as seen with Hinode, SoHO and TRACE Authors: Pérez-Suárez, D.; Maclean, R. C.; Doyle, J. G.; Madjarska, M. S. Bibcode: 2008A&A...492..575P Altcode: 2008arXiv0810.1020P Context: Solar coronal bright points have been studied for more than three decades, but some fundamental questions about their formation and evolution still remain unanswered.
Aims: Our aim is to determine the plasma properties of a coronal bright point and compare its magnetic topology extrapolated from magnetogram data with its appearance in X-ray images.
Methods: We analyse spectroscopic data obtained with EIS/Hinode, Ca ii H and G-band images from SOT/Hinode, UV images from TRACE, X-ray images from XRT/Hinode and high-resolution/high-cadence magnetogram data from MDI/SoHO.
Results: The BP comprises several coronal loops as seen in the X-ray images, while the chromospheric structure consists of tens of small bright points as seen in Ca ii H. An excellent correlation exists between the Ca ii H bright points and increases in the magnetic field strength, implying that the Ca ii H passband is a good indicator for the concentration of magnetic flux. Furthermore, some of the Ca ii H bright points are the locations of the loop foot-points as determined from a comparison between the extrapolated magnetic field configuration and the X-ray images. Doppler velocities between 6 and 15 km s-1 are derived from the Fe xii and Fe xiii lines for the bright point region, while for Fe xiv and Si vii they are in the range from -15 to +15 km s-1. The coronal electron density is 3.7 × 109 cm-3. An excellent correlation is found between the positive magnetic flux and the X-ray light-curves.
Conclusions: The remarkable agreement between the extrapolated magnetic field configuration and some of the loops composing the bright point as seen in the X-ray images suggests that a large fraction of the magnetic field in the bright point is close to potential. However, some loops in the X-ray images do not have a counterpart in the extrapolated magnetic field configuration implying a non-potential component. The close correlation between the positive magnetic flux and the X-ray emission suggests that energy released by magnetic reconnection is stimulated by flux emergence or cancellation. Title: EIS/ Hinode Observations of Doppler Flow Seen through the 40-Arcsec Wide-Slit Authors: Innes, D. E.; Attie, R.; Hara, H.; Madjarska, M. S. Bibcode: 2008SoPh..252..283I Altcode: 2008SoPh..tmp..174I; 2008arXiv0807.1185I The Extreme ultraviolet Imaging Spectrometer (EIS) onboard Hinode is the first solar telescope to obtain wide-slit spectral images that can be used for detecting Doppler flows in transition region and coronal lines on the Sun and to relate them to their surrounding small-scale dynamics. We select EIS lines covering the temperature range 6×104 to 2×106 K that give spectrally pure images of the Sun with the 40-arcsec slit. In these images Doppler shifts are seen as horizontal brightenings. Inside the image it is difficult to distinguish shifts from horizontal structures but emission beyond the image edge can be unambiguously identified as a line shift in several lines separated from others on their blue or red side by more than the width of the spectrometer slit (40 pixels). In the blue wing of He II, we find a large number of events with properties (size and lifetime) similar to the well-studied explosive events seen in the ultraviolet spectral range. Comparison with X-Ray Telescope (XRT) images shows many Doppler shift events at the footpoints of small X-ray loops. The most spectacular event observed showed a strong blue shift in the transition region and lower corona lines from a small X-ray spot that lasted less than 7 min. The emission appears to be near a cool coronal loop connecting an X-ray bright point to an adjacent region of quiet Sun. The width of the emission implies a line-of-sight velocity of 220 km s−1. In addition, we show an example of an Fe XV shift with a velocity of about 120 km s−1, coming from what looks like a narrow loop leg connecting a small X-ray brightening to a larger region of X-ray emission. Title: On the relation between DC current locations and an EUV bright point: A case study Authors: Santos, J. C.; Büchner, J.; Madjarska, M. S.; Alves, M. V. Bibcode: 2008A&A...490..345S Altcode: Context: Motion of the photospheric plasma forces the footpoints of magnetic flux tubes to move. This can give rise to electric currents in the solar atmosphere. The dissipation of these electric currents and the consequent heating of the solar plasma may be responsible for the formation of Extreme-UltraViolet (EUV) and X-ray bright points. Earlier bright point models usually consider either the emergence or the canceling of photospheric magnetic features as being responsible for reconnection causing the bright point.
Aims: We investigate the consequences of different patterns of horizontal photospheric plasma motion for the generation of electric currents in the solar atmosphere and locate them with respect to an observed EUV bright point. The goal is to find out whether these currents might be responsible for the heating of bright points.
Methods: To perform this study we use a “data driven” three dimensional magnetohydrodynamic model. The model solves an appropriate set of magnetohydrodynamic equations and uses, as initial condition, the magnetic field extrapolated from the line-of-sight component of the photospheric magnetic field observed by MDI/SoHO and the height-stratified, equilibrium density and temperature of the solar corona. We apply different patterns of horizontal photospheric plasma motion, derived from the temporal evolution of the photospheric magnetic structures in the course of the bright point lifetime, as boundary conditions of the model.
Results: All applied patterns of horizontal photospheric plasma motion (shearing, convergence and fragmentation) lead to the formation of electric currents in the chromosphere, transition region and corona. Currents do not develop everywhere in the region where the motion is applied but in specific places where the magnetic field connectivity changes significantly. An important result is that the position where the electric currents develop is independent of the motion pattern used as boundary condition of the model. A comparison with data obtained by TRACE in the 1550 Å channel and by the EIT in the 195 Å channel shows that the region where the strongest current concentrations are formed coincides with the region where the EUV bright point appears. Title: Explosive Events in the Quiet Sun as Seen by EIS and SUMER Authors: Madjarska, M. S.; Boutry, C.; Bewsher, D. Bibcode: 2008ASPC..397..180M Altcode: We present preliminary results on the capabilities of EIS to register explosive events in the quiet Sun. The events were registered with EIS/Hinode and SUMER/SoHO during the Hinode/SoHO observing campaign in April 2007. First results on the coronal response of these events are shown. Both SUMER and EIS were observing spectral lines from the widest possible temperature range from a few thousand to a few million degrees Kelvin. Title: Study of Transition Region Transient Events with Hinode Authors: Subramanian, S.; Madjarska, M.; Doyle, J. G. Bibcode: 2008ASPC..397..194S Altcode: We present preliminary results of a study of transient events in the solar transition region (TR), using observations taken at disk centre on 9 April, 2007 with SOT, XRT and EIS on-board Hinode; CDS and MDI on-board SoHO, plus TRACE covering the photosphere to corona. Title: Magnetic topology of blinkers Authors: Subramanian, S.; Madjarska, M. S.; Maclean, R. C.; Doyle, J. G.; Bewsher, D. Bibcode: 2008A&A...488..323S Altcode: Context: Co-spatial and co-temporal spectroscopic, imaging and magnetogram data enable us to better understand various solar transient phenomena. Here, we study brightening events in the transition region of the quiet Sun, also called “blinkers”.
Aims: We aim to investigate the physical mechanism responsible for blinkers.
Methods: An automated blinker identification procedure (BLIP) is used to identify blinker events in SoHO/CDS data. The 3D magnetic topology of the magnetic field in the blinker region is reconstructed based on SoHO/MDI magnetogram data.
Results: During 3 h of SoHO/CDS observations on 2006 January 18, 66 blinkers were identified in the O v 629 Å emission line. Out of them, a group comprising of 16 events were modelled here. They were found to be associated with the emergence of magnetic flux which gave rise to the appearance of, and multiple magnetic reconnection events across, an upper atmosphere (coronal) magnetic null point, along with a loop structure as observed with TRACE.
Conclusions: This blinker group results from the release of energy that was accumulated during flux emergence, although whether all blinkers follow the same formation scenario requires further investigation using additional multi-instrument/multi-mission studies.

2 movies are only available in electronic form at http://star.arm.ac.uk/preprints/ and http://www.aanda.org Title: Small-scale flows in SUMER and TRACE high-cadence co-observations Authors: Madjarska, M. S.; Doyle, J. G. Bibcode: 2008A&A...482..273M Altcode: 2008arXiv0802.2477M Context: We report on the physical properties of small-scale transient flows observed simultaneously at high cadence with the SUMER spectrometer and the TRACE imager in the plage area of an active region.
Aims: Our major objective is to provide a better understanding of the nature of transient phenomena in the solar atmosphere by using high-cadence imager and spectrometer co-observations at similar spatial and temporal resolution.
Methods: A sequence of TRACE Fe IX/X λ171 Å and high-resolution MDI images were analysed together with simultaneously obtained SUMER observations in spectral lines covering a temperature range from 10 000 K to 1 MK.
Results: We reveal the existence of numerous transient flows in small-scale loops (up to 30 Mm) observed in the plage area of an active region. These flows have temperatures from 10 000 K (the low temperature limit of our observations) to 250 000 K. The coronal response of these features is uncertain due to a blending of the observed coronal line Mg x λ624.85 Å. The duration of the events ranges from 60 s to 19 min depending on the loop size. Some of the flows reach supersonic velocities.
Conclusions: The Doppler shifts often associated with explosive events or bi-directional jets can actually be identified with flows (some of them reaching supersonic velocities) in small-scale loops. Additionally, we demonstrate how a line-of-sight effect can give misleading information on the nature of the observed phenomena if only either an imager or a spectrometer is used.

An animation of the TRACE λ171 Å images is only available in electronic form at http://www.aanda.org Title: Jets or High-Velocity Flows Revealed in High-Cadence Spectrometer and Imager Co-observations? Authors: Madjarska, M. S.; Doyle, J. G.; Innes, D. E.; Curdt, W. Bibcode: 2007ApJ...670L..57M Altcode: 2007arXiv0710.2199M We report on active region EUV dynamic events observed simultaneously at high cadence with SOHO SUMER and TRACE. Although the features appear in the TRACE Fe IX/X 171 Å images as jets seen in projection on the solar disk, the SUMER spectral line profiles suggest that the plasma has been driven along a curved large-scale magnetic structure, a preexisting loop. The SUMER observations were carried out in spectral lines covering a large temperature range from 104 to 106 K. The spectral analysis revealed that a sudden heating from an energy deposition is followed by a high-velocity plasma flow. The Doppler velocities were found to be in the range from 90 to 160 km s-1. The heating process has a duration which is below the SUMER exposure time of 25 s while the lifetime of the events is from 5 to 15 minutes. The additional check on soft X-ray Yohkoh images shows that the features most probably reach 3 MK (X-ray) temperatures. The spectroscopic analysis showed no existence of cold material during the events. Title: Evolution of coronal hole boundaries seen in EIT 195 Å and TRACE 171 Å images Authors: Madjarska, M. S.; Wiegelmann, T. Bibcode: 2007msfa.conf..249M Altcode: We aim at studying the spatial and temporal scales of the small-scale evolution of coronal hole boundaries using EUV observations from TRACE (171 Å) and EIT (195 Å) on-board SoHO with a spatial resolution of 1" and 5.5", respectively, and various time cadences. We found that small-scale loops known as bright points may play an essential role in coronal hole boundaries evolution. Their emergence and disappearance continuously expand or contract coronal holes. The changes appear to be random on a time scale comparable with the lifetime of the loops seen at these temperatures. No signature was found for a major energy release during the evolution of the loops. Title: Dynamic features in the solar atmosphere with unusual spectral line enhancements and Doppler-shifts Authors: Doyle, J. G.; Ishak, B.; Madjarska, M. S.; O'Shea, E.; Dzifćáková, E. Bibcode: 2006A&A...451L..35D Altcode: Context.The solar atmosphere contains a wide variety of transient features, here, we discuss data relating to one such feature.
Aims.To explore via simultaneous spectral and imaging data the nature of high-velocity flow events in the solar transition region.
Methods.High spectral and temporal resolution data from SUMER/SoHO plus high resolution images from TRACE are used.
Results.In the transient feature discussed, we see a factor of two enhancement in N v 1238, coupled with a factor of two decrease in O v 629 visible over 3''-4'' along the slit. Furthermore, the O v line shows a secondary component with a down-flow of ≈75 km s-1, while the N v line shows only a small additional broadening of the line.
Conclusions.Inclusion of an electron density dependent ionization calculation will increase the N v radiance over that of O v at large electron densities. We suggest this feature can be explained via a highly focused jet at the O v/Ovi formation temperature resulting from reconnection. Also, we believe that this event is not unique but that their detection depends on the availability of simultaneous spectral and imaging data of comparable spatial and temporal resolution. Title: Study of a transient siphon flow in a cold loop Authors: Doyle, J. G.; Taroyan, Y.; Ishak, B.; Madjarska, M. S.; Bradshaw, S. J. Bibcode: 2006A&A...452.1075D Altcode: Context: .The nature of loops is still a matter of debate with several explanations having been put forward. Simultaneous spectral and imaging data have the capacity to provide a new insight into mass motions, dynamics and energetics of loops.
Aims: .We report on spectral data taken with the Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) and imaging data from the Transition Region and Coronal Explorer (TRACE) of a transient event which occurred in a cold loop, lasting a few minutes.
Methods: .A sequence of TRACE images in the 1550 Å and 171 Å filters show a disturbance which originated at one foot-point and propagates along the loop. The SUMER slit was placed at the other foot-point of the loop. In order to interpret the results, numerical simulations were performed with the results then converted into observable quantities and compared with the data.
Results: .During the event a radiance increase and a relative red shift of ≈ 20~km s-1 was detected in the N v 1238.82 Å line. 1D numerical simulations are performed and observable quantities derived from the results of the simulations. The observed dynamic behaviour of the N v 1238.82 Å line profiles was recovered.
Conclusions: .The results suggest that the observations could be interpreted in terms of a short-lived siphon flow reaching a speed of 120~km s-1 and driven by a nonlinear heating pulse. The energies required to drive the observed red-shifts are estimated to be about 1025 erg. The absence of a significant blue-shift caused by the return flow is explained. Title: Macrospicules and blinkers as seen in Shutterless EIT 304 Å Authors: Madjarska, M. S.; Doyle, J. G.; Hochedez, J. -F.; Theissen, A. Bibcode: 2006A&A...452L..11M Altcode: Aims.Small-scale transient phenomena in the solar atmosphere are believed to play a crucial role in the coronal heating and solar wind generation. This study aims at providing new observational evidence on blinkers and macrospicules appearance in imager data and in doing so, establish the long disputed relationship between these phenomena.
Methods: .We analyse unique high-cadence images in the transition region He ii 304 Å line obtained in a shutterless mode of the Extreme-ultraviolet Imaging Telescope on board the Solar and Heliospheric Observatory. The data have a cadence of approximately 68 s and a pixel size of 2.62 arcsec. The events are identified through an automatic brightenings identification procedure. Features showing a jet-like structure seen in projection on the disk were selected and their light-curve further analysed.
Results: .The temporal evolution of the intensity in three events is shown, two of them seen on-disk as jet-like features and one above the limb. The flux increase, size and duration derived from the light-curve of the on-disk events show an identity with the blinker phenomenon.
Conclusions: .The light curves of these events suggest that the off-limb and on-disk features are in fact one and the same phenomenon and therefore that some blinkers are the on-disk counterparts of macrospicules. Title: Study of a Transient Siphon Flow in a Cold Loop Authors: Taroyan, Y.; Doyle, J. G.; Ishak, B.; Madjarska, M. S.; Bradshaw, S. J. Bibcode: 2005ESASP.600E..25T Altcode: 2005ESPM...11...25T; 2005dysu.confE..25T No abstract at ADS Title: Optical and EUV observations of solar flare kernels Authors: García-Alvarez, D.; Johns-Krull, C. M.; Doyle, J. G.; Ugarte-Urra, I.; Madjarska, M. S.; Butler, C. J. Bibcode: 2005A&A...444..593G Altcode: We present high-resolution spectral observations, covering the entire optical region (3800-9000 Å), of a solar flare observed during a multi-wavelength campaign. The flare, recorded on 2002 January 11, was a medium solar flare event (GOES class C7.5). The spectral observations were carried out using the Hamilton echelle spectrograph on the coudé auxiliary telescope at Lick Observatory and with the Coronal Diagnostic Spectrometer (CDS) on board SoHO. The high signal-to-noise optical spectra are analysed using the same techniques as we applied to stellar flare data. Hα images obtained at Big Bear Solar Observatory (BBSO), plus magnetograms obtained with the Michelson Doppler Imager (MDI) on board SoHO and Transition Region And Coronal Explorer (TRACE) 1600 Å were used in the flare analysis. We observe stellar-like behaviour in the main solar chromospheric activity indicators, which show either filling-in or emission during the flare. We find that the Balmer and Ca II lines show asymmetric profiles, with red-shifted wings and blue-shifted cores. This behaviour could be explained by material expanding. During the flare, the Mg i and Fe i lines show a filling-in of the line profile indicating that the flare affected the lower atmosphere. There is some evidence for pre-flare heating as seen in Fe xix 592 Å. Furthermore, O v 629 Å shows an increase in flux some 10 min. before the coronal lines, perhaps indicating particle beam heating in the initial stages of the flare. We have also determined the main physical parameters at flare maximum. The electron densities and electron temperatures found for the flare imply that the Balmer emitting plasma originates in the chromosphere. The physical parameters obtained for the modelled flare are consistent with previously derived values for solar flares. Title: Spicules and Blinkers as Seen in Shutterless EIT 304 Å Authors: Madjarska, M. S.; Doyle, J. G.; Hochedez, J. F.; Theissen, A. Bibcode: 2005ESASP.596E..73M Altcode: 2005ccmf.confE..73M No abstract at ADS Title: Electron density along a coronal loop observed with CDS/SOHO Authors: Ugarte-Urra, I.; Doyle, J. G.; Walsh, R. W.; Madjarska, M. S. Bibcode: 2005A&A...439..351U Altcode: The analysis of a coronal loop observed by CDS and EIT on board SOHO is presented. The loop was situated above the North-East limb at a latitude of ~48°, being clearly visible in the hottest lines of the dataset, Fe xvi 360.76 Å, i.e. greater than 2 000 000 K. The cooler lines in the sample (i.e. O v 629.73 Å and He i 584.35 Å) showed only a brightening at the footpoints location. Based on the Fe xiv 353.84/334.17 line ratio, the electron density along the loop was determined following three different approaches for the background subtraction. No differences, within the error bars, can be found between the three methods. At the apex, the density is 0.9×109 cm-3, while at the footpoint it is 50% greater, i.e. 1.4×109 cm-3. The inferred filling factor values along the loop, at the formation temperature of the lines, are in the range 0.2-0.9. One dimensional hydrodynamic modelling of the loop along a given field line, gravity neglected, was performed. A minimum χ2 analysis results in a best fit case where the total energy input is directed preferentially to the loop footpoint (the heating rate is three times larger at the base than at the apex). An isochoric solution can not be ruled out completely. The exercise illustrates the necessity of accurate spectral diagnostics in order to derive definite conclusions from theoretical models and suggests the need for simultaneous density and temperature diagnostics. Title: Line broadening of EUV lines across the Solar limb: A spicule contribution? Authors: Doyle, J. G.; Giannikakis, J.; Xia, L. D.; Madjarska, M. S. Bibcode: 2005A&A...431L..17D Altcode: Spectral lines formed in the solar transition region show an increase in the line width, peaking at ≈10 000 km above the limb. Looking at a region off-limb with no obvious spicules, the non-spicule region has a significantly smaller line width above 6000 km compared those taken in a spicule region. We suggest that this increase in line broadening is not due to small scale random motions but rather to unresolved line shifts due to spicules and/or macro-spicules activity. Title: Transition region small-scale dynamics as seen by SUMER on SOHO Authors: Teriaca, L.; Banerjee, D.; Falchi, A.; Doyle, J. G.; Madjarska, M. S. Bibcode: 2004A&A...427.1065T Altcode: High spectral, spatial and temporal resolution UV observations of the quiet Sun transition region show a highly structured and dynamical environment where transient supersonic flows are commonly observed. Strongly non-Gaussian line profiles are the spectral signatures of these flows and are known in the literature as explosive events. In this paper we present a high spatial resolution (≈ 1'') spectroheliogram of a 273''× 291'' area of the quiet Sun acquired with SUMER/SOHO in the O VI spectral line at λ103.193 nm. The extremely high quality of these observations allows us to identify tens of explosive events from which we estimate an average size of 1800 km and a birthrate of 2500 s-1 over the entire Sun. Estimates of the kinetic and enthalpy fluxes associated with these events show that explosive events are not important as far as solar coronal heating is concerned. The relationship with the underlying photospheric magnetic field is also studied, revealing that explosive events generally occur in regions with weak (and, very likely, mixed polarity) magnetic flux. By studying the structure of upward and downward flows exceeding those associated to average quiet Sun profiles, we find a clear correlation between the ``excess'' flows and the magnetic network. However, although explosive events are always associated with flow patterns often covering areas larger than the explosive event itself, the contrary is not true. In particular, almost all flows associated with the stronger concentrations of photospheric magnetic flux do not show non-Gaussian line profiles. In some cases, non-Gaussian line profiles are associated with supersonic flows in small magnetic loops. The case of a small loop showing a supersonic siphon-like flow of ≈130 km s-1 is studied in detail. This is, to our knowledge, the first detection of a supersonic siphon-like flow in a quiet Sun loop. In other cases, the flow patterns associated with explosive events may suggest a relation with UV spicules. Title: Coronal response of Bi-directional Jets Authors: Doyle, J. G.; Madjarska, M. S.; DzifČÁkovÁ, E.; Dammasch, I. E. Bibcode: 2004SoPh..221...51D Altcode: EUV bi-directional jets are a prominent class of phenomena characterizing the solar transition region. Using simultaneously obtained SUMER observations in the chromospheric Si ii 1251.16 Å and C i 1251.17 Å, transition region N v 1238.8 Å and coronal Mg x 625 Å lines we show an example of a bi-directional jet observed in the chromospheric and the transition region lines but not showing any detectable signature in the coronal line. The phenomenon, however, was also clearly detected by the TRACE imager with the 171 Å filter. This discrepancy is explained here with a non-Maxwellian electron distribution which makes a significant fraction of the plasma in the TRACE 171 Å pass-band to be derived from temperatures around ≈ 300 000 K, as opposed to ≈ 800 000 K. This could have implications for other phenomena observed in the TRACE pass-bands, including the transition region `moss' and the 3- and 5-min oscillations. Title: New insight into the blinker phenomenon and the dynamics of the solar transition region Authors: Doyle, J. G.; Roussev, I. I.; Madjarska, M. S. Bibcode: 2004A&A...418L...9D Altcode: We present, for the first time, blinker phenomena being associated with brightenings in pre-existing coronal loops registered by the Extreme-ultraviolet Imaging Telescope (EIT) in Fe XII 195 Å. The brightenings occur during the emergence of new magnetic flux as registered by the Big Bear Solar Observatory (BBSO) magnetograph. The blinkers were identified using simultaneous observations obtained with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrograph. In light of the new observational results, we present one possible theoretical interpretation of the blinker phenomenon. We suggest that the blinker activity we observe is triggered by interchange reconnection, serving to provide topological connectivity between newly emerging flux and pre-existing flux. The EIT images show the existence of loop structures prior to the onset of the blinker activity. Based on the available spatial resolution the blinker occurs within, or nearby, an existing coronal loop. The temperature interfaces created in the reconnection process between the cool plasma of the newly emerging loop and the hot plasma of the existing loop are what we suggest to causes the observed activity seen in both the SUMER and CDS data. As the temperature interfaces propagate with the characteristic speed of a conduction front, they heat up the cool chromospheric plasma to coronal temperatures, an increasing volume of which brightens at transition region temperatures. We believe this new interpretation gives further qualitative understanding about the evolution of newly emerging flux on the Sun. This also provides new insight into the dynamic nature of the solar transition region. Title: Signature of oscillations in coronal bright points Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E. Bibcode: 2004A&A...418..313U Altcode: A detailed study of two consecutive bright points observed simultaneously with the Coronal Diagnostic Spectrometer (CDS), the Extreme ultraviolet Imaging Telescope (EIT) and the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) is presented. The analysis of the evolution of the photospheric magnetic features and their coronal counterpart shows that there is a linear dependence between the EIT Fe XII 195 Å flux and the total magnetic flux of the photospheric bipolarity. The appearance of the coronal emission is associated with the emergence of new magnetic flux and the disappearance of coronal emission is associated with the cancellation of one of the polarities. In one of the cases the disappearance takes place ∼3-4 h before the full cancellation of the weakest polarity.

The spectral data obtained with CDS show that one of the bright points experienced short time variations in the flux on a time scale of 420-650 s, correlated in the transition region lines (O V 629.73 Å and O III 599.60 Å) and also the He I 584.34 Å line. The coronal line (Mg IX 368.07 Å) undergoes changes as well, but on a longer scale. The wavelet analysis of the temporal series reveals that many of these events appear in a random fashion and sometimes after periods of quietness. However, we have found two cases of an oscillatory behaviour. A sub-section of the O V temporal series of the second bright point shows a damped oscillation of five cycles peaking in the wavelet spectrum at 546 s, but showing in the latter few cycles a lengthening of that period. The period compares well with that detected in the S VI 933.40 Å oscillations seen in another bright point observed with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer, which has a period of 491 s. The derived electron density in the transition region was 3×1010 cm-3 with some small variability, while the coronal electron density was 5×108 cm-3. Title: Evidence of Magnetic Reconnection along Coronal Hole Boundaries Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L. Bibcode: 2004ApJ...603L..57M Altcode: The present study reveals for the first time the existence of bidirectional jets, which are a signature of magnetic reconnection, occurring along coronal hole boundaries. The Solar Ultraviolet Measurement of Emitted Radiation spectrometer observations obtained in the N IV 765.15 Å (1.3×105 K) and Ne VIII 770.42 Å (6×105 K) emission lines in an equatorial extension of a polar coronal hole, known as the ``Elephant's Trunk'' coronal hole, show small regions of a few arcseconds size with strong blue- and redshifted emission reaching Doppler shifts of up to 150 km s-1, i.e., bidirectional jets. The jets' number density along coronal hole boundaries was found to be about 4-5 times higher with respect to the quiet Sun. Title: Bi-Directional Jets at Coronal Hole Boundaries Authors: Madjarska, M. S.; Doyle, J. G.; van Driel-Gesztelyi, L. Bibcode: 2004ESASP.547..397M Altcode: 2004soho...13..397M Our study reveals, for the first time, the presence of bi-directional jets which are considered to be signatures of magnetic reconnection occurring along coronal hole boundaries. The SUMER observations obtained in Ne VIII 770.42 Å (6 10 K) and N IV 765.15 Å (1.3 10 K) show small regions of a few arcsec size with strong blueand red-shifted emission reaching Doppler shifts up to 150 km s which appear along the coronal hole boundaries where evolving loop systems are present. Title: Oscillations in Coronal Bright Points Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E. Bibcode: 2004ESASP.547..329U Altcode: 2004soho...13..329U No abstract at ADS Title: Coronal Oscillations above Sunspots? Authors: Doyle, J. G.; Dzifćáková, E.; Madjarska, M. S. Bibcode: 2003SoPh..218...79D Altcode: Observational data clearly indicate the presence of 3-min oscillations in sunspots in spectral lines covering a vast temperature range from the low chromosphere to those lines normally associated with coronal temperatures. We show that after folding in the sunspot plume emission measure distribution, the contribution functions for lines normally formed just below 1×106 K are shifted to lower temperatures. For example, the Fe ix 171 Å line is shifted to 6×105 K for a Maxwellian distribution and to less than 5×105 K with a non-Maxwellian distribution. Other lines such as Mg ix 368 Å will also be affected. This then questions some previous work regarding the suggested detection of 3-min oscillations in the corona above sunspots. Title: Line Shift Variations in Solar Transition Region Lines Authors: Doyle, J. G.; Madjarska, M.; Giamikakis, J.; Teriaca, L.; Roussev, I. Bibcode: 2003csss...12..619D Altcode: Two high time cadence datasets, taken in C III 977Å and O VI 1032Å were analysed in an effort to establish the extent of the variability in the Doppler-shift of typical mid-transition region lines. In C III, the shortest time-scale variability seems to occur in the network boundary regions where the line-shift can vary by 7-8 km s-1 in less than 1 min. The internetwork region also shows variability although this tends to be longer lived, ∼2-3 mins. The average C III line-shift in all regions is for a red-shift of ∼ 8 km s-1 in very good agreement with that derived by others. Furthermore, there does not seem to be any obvious difference in the average line-shift in network and internetwork regions. On a few rare occasions, the C III line was blue-shifted. The O VI line was also red-shifted with the network region showing evidence for a periodicity. These observations were compared to model line profiles based on the response of a 2D MHD environment representing the solar transition region to micro-scale energy depositions. A variety of temperatures at which the energy deposition takes place as well as the amount of energy deposited was examined. Title: Sunspot plume observations in the EUV. The gas pressure differential between the umbra and surrounding region Authors: Doyle, J. G.; Madjarska, M. S. Bibcode: 2003A&A...407L..29D Altcode: The electron density over a bright sunspot plume region was evaluated using lines within the O V 760 Å multiplet. The plume showed an intensity enhancement factor of ~9 in the O V lines compared to regions outside the sunspot umbra. Internal agreement between the various ratios is excellent which would suggest that the O V lines do not suffer from blending problems. The derived mean electron densities for the sunspot plume is log Ne/cm-3 ~ 9.9 compared to log Ne/cm-3 ~ 10.20-10.45 in the surrounding area. The derived gas pressure in the plume compared to that outside leads weight to the suggestion that it is plasma flowing from outside the spot into the umbra at transition region temperatures that is the main cause of the down-flows. The plume non-thermal velocities are 5 to 10 km ; s-1 smaller than those measured in regions external to the spot, suggesting significantly less turbulence within the umbra. Title: Simultaneous observations of solar transition region blinkers and explosive events by SUMER, CDS and BBSO. Are blinkers, explosive events and spicules the same phenomenon? Authors: Madjarska, M. S.; Doyle, J. G. Bibcode: 2003A&A...403..731M Altcode: The SoHO discovery of the new ``blinker'' phenomena focused our study on the search of its relation to already known phenomena such as explosive events and spicules. The study was performed using a specially planned joint observing program involving the Coronal Diagnostic Spectrometer (CDS), Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) and Big Bear Solar Observatory (BBSO) magnetograph. Within each blinker, the SUMER data reveal the presence of small-scale (3 arcsec-5 arcsec), short-lived (2-3 min) bright features not seen in the CDS data which has sometimes being interpreted as oscillations in SUMER data. With this data we have clearly identified UV explosive events in CDS data. The explosive events show a size close to the small-scale brightenings forming the blinker core. However, they appear in the SUMER data with their typical strong blue and red wings while the blinker shows at best only a small increase in the emission of the blue and red wings and in most instances the typical transition region red-shift in the center of the line. In all cases the explosive events cover one pixel in CDS corresponding to a size of 4arcsec x 4arcsec -6arcsec . All identified explosive events were located at the border of the bright network i.e. the blinker, in the network or even in the internetwork. From this data, we believe that blinkers and explosive events are two separate phenomena not directly related or triggering each other. In this study, the Doppler shift was derived in a blinker phenomenon for the first time. It ranges from -5 to 25 km ; s-1 and is predominantly red-shifted. The observed magnetic flux increase during the blinker phenomena seems to play a crucial role in the development of this event. We suggest that ``blinkers'' maybe the on-disk signature of spicules. Title: An EUV Bright Point as seen by SUMER, CDS, MDI and EIT on-board SoHO Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L.; Banerjee, D. Bibcode: 2003A&A...398..775M Altcode: This paper presents the formation, evolution and decay of a coronal bright point via a spectroscopic analysis of its transition region counterpart and the evolution of the underlying magnetic bipole during 3 days of almost continuous observations. The data were obtained with various instruments on-board SoHO, including the SUMER spectrograph in the transition region line S VI 933.40 Å, CDS in the He I 584.33, O V 629.73 and Mg IX 368.06 Å lines, plus MDI and EIT. The existence of the coronal feature is strongly correlated with the evolution of the underlying bipolar region. The lifetime of the bright point from the moment when it was first visible in the EIT images until its complete disappearance was ~ 18 hrs. Furthermore, the bright point only became visible at coronal temperatures when the two converging opposite magnetic polarities were ~ 7000 km apart. As far as the temporal coverage of the data permits, we found that the bright point disappeared at coronal temperatures after a full cancellation of one of the magnetic polarities. The spectroscopic analysis reveals the presence of small-scale ( ~ 6 arcsec) transient brightenings within the bright point with a periodicity of ~ 6 min. The Doppler shift in the bright point was found to be in the range of -10 to 10 km ; s-1 although it is dominated by a red-shifted emission which is associated with regions characterized by stronger ``quiet'' Sun photospheric magnetic flux. Small-scale brightenings within the bright point show velocity variations in the range 3-6 km ; s-1. In general the bright point has a radiance ~ 4 times higher than that of the network. No relation was found between the bright point and the UV explosive event phenomena. Title: Transition region small-scale dynamics: UV explosive events Authors: Teriaca, L.; Falchi, A.; Doyle, J. G.; Madjarska, M. S.; Banerjee, D. Bibcode: 2002ESASP.506..777T Altcode: 2002ESPM...10..777T; 2002svco.conf..777T High spectral, spatial and temporal resolution UV observations of the quiet Sun transition region show a highly structured and dynamical environment where transient events such as brightenings, blinkers and explosive events occur continuously. In particular explosive events are characterized by strongly non-Gaussian line profiles witnessing velocities up to 200 km s-1. The high kinetic and enthalpy fluxes associated with these events could be important in the energy balance of the transition region and, perhaps, of the whole corona. In this paper we present a high spatial resolution (~1") spectroheliogram of a 270×290 arcsec2 wide area of the quiet Sun acquired with SUMER/SoHO in the O VI 1032 spectral line. The extremely high quality of these observations allows us to identify tens of explosive events and to study their relationship with the underlying photospheric magnetic field. Moreover, the behaviour of lines emitted by plasma at chromospheric (2×104K) and coronal (106K) temperatures during transition region explosive events is investigated. We conclude that those events do not contribute significantly to the energy balance of the corona and seems typical of structure not obviously connected to the T≥106K corona. Title: Temporal variability in the Doppler-shift of solar transition region lines Authors: Doyle, J. G.; Madjarska, M. S.; Roussev, I.; Teriaca, L.; Giannikakis, J. Bibcode: 2002A&A...396..255D Altcode: High cadence datasets taken in C III 977 Å, O VI 1032 Å and Ne VIII 720 Å were analysed in an effort to establish the extent of the variability in the Doppler-shift of typical mid-transition region lines. The shortest time-scale variability seems to occur in the network boundary regions where the line-shift can vary by 7-8 km s-1 in less than 1 min. The internetwork region also shows variability although this tends to be longer lived, ~ 2-3 min. The average line-shift in C III is a red-shift which ranges from ~ 2 km s-1 to ~ 20 km s-1 with an average value for all regions selected being around 10 km s-1 in very good agreement with that derived by others. The red-shift values indicate a clear difference between network and internetwork regions, with the largest red-shift being present at the network boundary. For O VI, this gives an average red-shift ranging from 5 to 10 km s-1. For Ne VIII, there is a 13 km s-1 difference between internetwork and bright network plasma with the bright network being more red-shifted. This could imply that the bright network regions are dominated by spicule down-flow.\ In the second part we present results from 2-dimensional (2D) dissipative magnetohydrodynamic (MHD) simulations of the response of the solar transition region to micro-scale energy depositions. A variety of temperatures at which the energy deposition takes place as well as the amount of energy deposited are examined. This work is a continuation of previous related simulations where small-scale energy depositions were modelled in 1D hydrodynamics. The observable consequences of such transient events are then computed for three transition region lines, namely C IV 1548 Å, O VI 1032 Å, and Ne VIII 770 Å, under the consideration of non-equilibrium ionization. Title: The OIV and SIV intercombination lines in the ultraviolet spectra of astrophysical sources Authors: Keenan, F. P.; Ahmed, S.; Brage, T.; Doyle, J. G.; Espey, B. R.; Exter, K. M.; Hibbert, A.; Keenan, M. T. C.; Madjarska, M. S.; Mathioudakis, M.; Pollacco, D. L. Bibcode: 2002MNRAS.337..901K Altcode: New electron density diagnostic line ratios are presented for the OIV 2s22p 2P-2s2p24P and SIV 3s23p 2P-3s3p24P intercombination lines around 1400Å. A comparison of these with observational data for the symbiotic star RR Telescopii (RR Tel), obtained with the Space Telescope Imaging Spectrograph (STIS), reveals generally very good agreement between theory and observation. However the SIV2P3/2-4P1/2 transition at 1423.824Å is found to be blended with an unknown feature at 1423.774Å. The linewidth for the latter indicates that the feature arises from a species with a large ionization potential. In addition, the SIV2P1/2-4P3/2 transition at 1398.044Å is identified for the first time (to our knowledge) in an astrophysical source other than the Sun, and an improved wavelength of 1397.166 Å is measured for the OIV2P1/2-4P3/2 line. The OIV and SIV line ratios in a sunspot plume spectrum, obtained with the Solar Ultraviolet Measurements of the Emitted Radiation (SUMER) instrument on the Solar and Heliospheric Observatory, are found to be consistent, and remove discrepancies noted in previous comparisons of these two ions. Title: Magnetic properties of ultraviolet transient phenomena. Are blinkers and explosive events the same phenomenon? Authors: Madjarska, M. S.; Doyle, J. G. Bibcode: 2002ESASP.505..489M Altcode: 2002solm.conf..489M; 2002IAUCo.188..489M Simultaneous 'quiet' Sun observations were performed on 2001 October 23 with the SUMER and CDS spectrometers on-board SoHO together with the Big Bear Solar Observatory magnetograph. The aim was to study the magnetic properties and distinct nature of the transition region phenomena such as explosive events and blinkers. The different appearance of the two phenomena in both spectrometer observations was analysed. Blinker phenomena were clearly associated with bipolar magnetic regions with always one polarity stronger than the other one. Higher resolution observations are needed in order to associate explosive events with any particular magnetic field changes. Title: Electron density variation in off-limb solar corona structures Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S. Bibcode: 2002ESASP.505..595U Altcode: 2002IAUCo.188..595U; 2002solm.conf..595U We present a study of the electron density variation for off limb observations with the Coronal Diagnostic Spectrometer (CDS) on board SoHO using the density sensitive coronal line ratio Si X (356.0/347.4). The analysis is divided into three parts: the latitudinal variation from 1.01 < r/Rsolar < 1.09, the temporal variation in successive rasters, and the electron density along a hot coronal loop found in one of the rasters. Title: Transition region explosive events: Do they have a coronal counterpart? Authors: Teriaca, L.; Madjarska, M. S.; Doyle, J. G. Bibcode: 2002A&A...392..309T Altcode: EUV explosive events are a prominent class of phenomena characterizing the solar transition region. Their correct location in the wider frame-work of the outer solar atmosphere can provide important insight on the nature of the transition region itself and its relationship with the hotter corona and the cooler chromosphere. In this paper we present new high-cadence SUMER observations of the ``quiet'' Sun obtained simultaneously in the mid-transition region N V 1238.8 Å line (1.8x 105 K) and in the coronal Mg X 625 Å line (1.1x 106 K). These observations are aimed at providing information on the behaviour of the coronal plasma during EUV transition region explosive events detected in N V 1238.8 Å. None of the events observed in N V shows any detectable signature in the Mg X line profile or in its integrated intensity. The analysis of 1996 observations obtained simultaneously in N V 1238.8 Å and S II 1253.8 Å (3.5x 104 K) shows, instead, a weak but clear presence of enhanced wings in the S II line profile during a series of events observed in N V. These results suggest that EUV explosive events are not directly relevant in heating the corona and are characteristic of structures not obviously connected with the upper corona. The evidence of a chromospheric response suggests that, contrary to some previous suggestions, explosive events have a chromospheric origin. Title: Transition region counterpart of X-ray/EUV coronal bright points registered by SUMER, CDS, EIT and MDI/SOHO Authors: Madjarska, M. S.; Doyle, J. G. Bibcode: 2002ESASP.508..311M Altcode: 2002soho...11..311M We present a spectroscopic analysis of the transition region counterpart of Coronal Bright Points (BPs). Simultaneous observations obtained with the SUMER spectrometer in the S VI 933.38 Å and Ly 6 930.75 &Aring lines, CDS in the He I 584.33, O V 629.73 and Mg IX 368.06 Å MDI and EIT Fe XII 195 Å on-board SoHO were analysed. The dataset obtained on 1996 October 16, 17 & 18 reveals a complete picture of the formation, temporal evolution and decay of a bright point. The nature of the intensity variations in a BP, its Doppler velocities and its relation to transient phenomena such as explosive events and blinkers are discussed. Title: Dynamics and Diagnostics of Explosive Events and Blinkers Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L. Bibcode: 2002mwoc.conf...69M Altcode: The knowledge of the main physical parameters of UV explosive events and blinkers, such as density and temperature, is of great importance for the better understanding of the true nature of these transient events. In this context, density and temperature diagnostics based on lines belonging to O iv 1400Å and O iii multiplets is presented for both kind of events. The dynamics of the solar transient phenomena is revealed through their temporal and spatial evolution as observed in spectral lines covering a wide temperature range. The results are obtained using SUMER, CDS, MDI and EIT aboard SoHO, TRACE and Big Bear Solar Observatory observations and are aimed to give more information about the main properties of these phenomena. The events are also studied in connection with the evolution of the underlying magnetic field, searching for observational evidences of their further propagation higher in the solar corona. Title: Temporal evolution of different temperature plasma during explosive events Authors: Madjarska, M. S.; Doyle, J. G. Bibcode: 2002A&A...382..319M Altcode: High cadence observations (10 s exposure time) obtained with the SUMER spectrometer on-board SoHO in the Ly 6 (20 000 K) and S VI (200 000 K) lines reveal new insight on the nature of explosive events. A time delay in the response of the S VI line with respect to the Ly 6 line has been observed, with the Ly 6 line responding with about 20-40 s earlier. A temporal series obtained with 30 s exposure time and covering the entire Lyman series plus O I, C II and S VI (temperature range from 15 000 to 200 000 K) has also been explored showing the response of all these lines during transient phenomena. New common features linking explosive events and blinkers were found. During explosive events, the central intensity increases between 1.6 and 2.0 times the pre-event value while the same range of intensity increase was already reported during blinker phenomena. On the other hand the maximum intensity increase in Ly 6 was only 13%. Title: Temporal evolution of explosive events as observed in Lyman and S VI lines Authors: Madjarska, M. S.; Doyle, J. G. Bibcode: 2001ESASP.493..279M Altcode: 2001sefs.work..279M No abstract at ADS Title: Temporal Variability in Transition Region Line . Authors: Giannikakis, I.; Doyle, J. G.; Antonopoulou, E.; Madjarska, M. Bibcode: 2001hell.confE..41G Altcode: No abstract at ADS Title: Electron density variations during ultraviolet transient events Authors: Teriaca, L.; Madjarska, M. S.; Doyle, J. G. Bibcode: 2001SoPh..200...91T Altcode: % High-resolution temporal observations performed with the SUMER spectrometer on SOHO provide an opportunity to investigate the electron density variations in the `quiet-Sun' solar transition region due to UV transient events. Two datasets obtained in the density sensitive lines belonging to the O iv 1400 Å multiplet were searched for such events, leading to the identification of two explosive events, on 10 July 1996 and 31 May 1997. In both cases, the O iv 1401.16/1404.81 density-sensitive line intensity ratio shows a clear variation, corresponding to enhancements in the electron density by factors of ∼3. This is fully consistent with recent 2.5D MHD simulations. The 10 July 1996 dataset also provided us with the opportunity to monitor the behavior of the electron density through an UV blinker. Despite an increase of a factor of two in the line intensities, no variation of the electron density was found. This suggests that the intensity enhancement is due to an increase in the filling factor. Title: Electron Density Enhancement During an UV Explosive Event Authors: Madjarska, M. S.; Doyle, J. G.; Teriaca, L. Bibcode: 2001IAUS..203..407M Altcode: High resolution temporal observations performed with the SUMER spectrometer on SOHO provide us the opportunity to investigate the electron density variations in the solar mid transition region due to explosive event-like phenomena. The O IV 1401.16/1404.81 density sensitive line intensity ratio shows a clear increase during a strong explosive event, corresponding to an electron density enhancement of a factor of ~ 3.5 respect to pre-event values. This is consistent with recent MHD simulations (2.5 D) carried out by Karpen et al. (1998). Karpen J. T., Antiochos S. K., DeVore C. R. and Golub L., 1998, ApJ 495, 491. Title: Plasma Parameters of a Prominence Observed on October 16/17 1999 by SUMER and CDS/SOHO Authors: Madjarska, M. S.; Vial, J. -C.; Boccialini, K.; Dermendijiev, V. N. Bibcode: 2001IAUS..203..410M Altcode: The aim of our study was to confirm and enrich the results obtained so far on dynamics and diagnostics of solar prominences. A prominence observed on October 16/17, 1999 during MEDOC campaign # 4 in the frame of the updated joint observing programme 09 was studied. The main prominence plasma parameters like temperature and density were derived as well as their changes during 8 hours of observations. The relative line-of-sight velocities were obtained in the cool plasma material (SUMER, Si IV, 8 104 K) and prominence-corona transition region (SUMER, O IV, 2 105 K). Velocity and line width maps in both CDS He I 584 Å and O V 629.73 Å were derived. A study of the blend of O IV 1404.81 Å by Si IV 1404.77 Å and the second order line O III 702.31 Å was made. Title: Multi-wavelength study of the slow ``disparition brusque" of a filament observed with SOHO Authors: Schmieder, B.; Delannée, C.; Yong, Deng Yuan; Vial, J. C.; Madjarska, M. Bibcode: 2000A&A...358..728S Altcode: A mid-latitude filament was observed before and after its eruption with SOHO (EIT, SUMER, CDS and LASCO) and with ground based observatories (Meudon and Pic du Midi) in the context of a coordinated MEDOC campaign in Orsay. The eruption was followed by a large Coronal Mass Ejection well observed by LASCO. Few hours before its eruption, the filament is partially heated (as seen in 195 Ä with EIT). The physical conditions of the filament before its eruption have been investigated by spectroscopic analysis of SUMER (the Lyman series L4 to L9) and of CDS combined with the Multi-channel Subtractive Double Pass Spectrograph (MSDP) spectra of Hα . Five hours before the eruption, large broadenings of chromospheric and transition region lines (CDS) were observed in the main body of the filament suggesting strong turbulence as well as opposite Dopplershifts on each side of the filament (Hα and He I) which could be interpreted as twist motions. The optical thickness of the filament is rather large. During the eruption the twist is largely developed as observed in 304 Ä. The Doppler shifts of the filament estimated from Lyman lines are in good agreement with the velocity of the front edge of the CME bright loop. We notice that both, the filament and the bright loop, are deviated towards the equator. This implies that they belong to the same global expansion event constrained to remain in the equatorial streamer. An X-ray bright point observed close to a filament footpoint could be the signature of reconnection process linked to the destabilization of the filament. It is interpreted in the framework of new MHD modeling of lateral filament footpoints (Aulanier & Démoulin 1998). Title: Plasma Diagnostics Of A Solar Prominence Observed On 12 June 1997 by EIT, Sumer And CDS Authors: Madjarska, M. S.; Vial, J. -C.; Bocchialini, K.; Dermendjiev, V. N. Bibcode: 1999ESASP.446..467M Altcode: 1999soho....8..467M The plasma diagnostics of a quiescent prominence observed on June 12, 1997 with SUMER, CDS and EIT instruments aboard SOHO in the frame of Joint Observing Programme 9 has been made. Two sets of SUMER observations were taken in the four spectral lines Si IV 1393.755, 1402.770 (6-8 104 K) and O IV 1401.156, 1404.812 (1.7-2.0 105 K) at two different slit positions on the prominence body. The relative line-of-sight velocities using both Si IV 1393.755 and 1402.770 lines are derived. The electron density (derived from the intensity ratio of O IV 1401.156 to 1404.812 lines) in the prominence-corona interface is determined for both slit positions. CDS obtained 10 rasters in Si X 347.40, He I 584.33, Si X 356.04, Fe XVI 360.76, Mg IX 368.06, O V 629.73 lines covering a temperature range from 104 to 106 K. By analysing the CDS spectra in He I and O V ions the relative line-of-sight velocity maps with regards to the quiet sun are derived. Title: Behaviour of H-alpha and H CA II Emission Lines in a Prominence Before and During its Dynamic "Disparition Brusque" Authors: Madjarska, M. S.; Dermendjiev, V. N.; Mouradian, Z.; Kotrc, P. Bibcode: 1998ASPC..150..326M Altcode: 1998npsp.conf..326M; 1998IAUCo.167..326M No abstract at ADS Title: Small-Scale Structure in Loops and Prominence Threads Authors: Rudawy, P.; Madjarska, M. S. Bibcode: 1998ASPC..150...63R Altcode: 1998IAUCo.167...63R; 1998npsp.conf...63R No abstract at ADS Title: On a Possible Mechanism of Quiescent Prominence Destabilization Authors: Nenovski, P.; Dermendjiev, V. N.; Madjarska, M. S.; Vial, J. -C. Bibcode: 1998ASPC..150..354N Altcode: 1998IAUCo.167..354N; 1998npsp.conf..354N No abstract at ADS Title: Observation of the 1961 Total Solar Eclipse in Bulgaria Authors: Madjarska, M.; Dermendjiev, V. N. Bibcode: 1996RoAJ....6...13M Altcode: No abstract at ADS Title: Sudden Disappearance of a Quiescent Prominence on April 23, 1989. Morphology, Dynamics and MHD Interpretation Authors: Madjarska, M. S.; Dermendjiev, V. N.; Mouradian, Z.; Nenovski, P. Bibcode: 1996ApL&C..34..113M Altcode: No abstract at ADS Title: Possible preflare phase of the white light flares. Authors: Dermendjiev, V. N.; Dechev, M.; Madjarska, M. S. Bibcode: 1996joso.proc..152D Altcode: No abstract at ADS Title: Small-scale clusters of photospheric network bright points and their dependence on the solar cycle phase Authors: Dermendjev, V. N.; Muller, R.; Madjarska, M. S. Bibcode: 1994SoPh..155...45D Altcode: The tendency of network bright points (NBPs) to form in their surface distribution non-random, small-scale clusters is studied by a 2-D nearest-neighbours test, based on observational data for the distance between separate NBPs. High-resolution photographs taken from long time series obtained atλ4308 å with the 50-cm refractor of Pic du Midi Observatory are used. Three different epochs of the solar cycle were chosen. The results obtained suggest that the degree of clustering depends on the solar cycle phase. Supposing that the NBPs are good tracers of the kilogauss small-scale magnetic field, we use them to obtain information about the subphotospheric small-scale magnetic field organisation and its dependence on the solar cycle phase. Title: On the Dynamics of Surge Plasma Knots Authors: Dermendjiev, V. N.; Okten, A.; Madjarska, M. S. Bibcode: 1994scs..conf..369D Altcode: 1994IAUCo.144..369D Plasma knots of a high latitude surge, consisting of only one thin and very long jet are studied over long series of Hα filtergrams. An attempt to evaluate the influence of magnetic flux tube oscillation on the surge plasma was made. Title: Small-scale clusters of photospheric network bright points. Authors: Dermendjiev, V. N.; Muller, R.; Madjarska, M. S. Bibcode: 1993sova.conf...68D Altcode: The authors report the basic results of their study on the problem of NBP surface distribution obtained on the basis of Pic-du-Midi observations and using the processing and computer facilities of NAO-Rozhen.