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Register a new userPlasma diagnostic in eruptive prominences from SDO/AIA observations at 304 {AA}
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Context. Theoretical calculations have shown that when solar prominences move away from the surface of the Sun, their radiative output is affected via the Doppler dimming or brightening effects. Aims. In this paper we ask whether observational signatures of the changes in the radiative output of eruptive prominences can be found in EUV (extreme ultraviolet) observations of the first resonance line of ionised helium at 304 {AA}. We also investigate whether these observations can be used to perform a diagnostic of the plasma of the eruptive prominence. Methods. We first look for suitable events in the SDO/AIA database. The variation of intensity of arbitrarily selected features in the 304 channel is studied as a function of velocity in the plane of the sky. These results are then compared with new non-LTE radiative transfer calculations of the intensity of the He II 304 resonance line. Results. We find that observations of intensities in various parts of the four eruptive prominences studied here are sometimes consistent with the Doppler dimming effect on the He II 304 {AA} line. However, in some cases, one observes an increase in intensity in the 304 channel with velocity, in contradiction to what is expected from the Doppler dimming effect alone. The use of the non-LTE models allows us to explain the different behaviour of the intensity by changes in the plasma parameters inside the prominence, in particular the column mass of the plasma and its temperature. Conclusions. The non-LTE models used here are more realistic than what was used in previous calculations. They are able to reproduce qualitatively the range of observations from SDO/AIA analysed in this study. Thanks to non-LTE modelling, we can infer the plasma parameters in eruptive prominences from SDO/AIA observations at 304 {AA}.
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The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the {em Transition Region and Coronal Explorer} (TRACE) and {em Atmospheric Imaging Assembly} (AIA 1600 and 1700~AA) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without the knowledge of the spectral contribution to these UV filters, the use of these rich imaging datasets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300 to 1900~AA from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600~AA is { dominated by} the ion{C}{4} 1550~AA doublet (26%), ion{Si}{1} continua (20%), with smaller contributions from many other chromospheric lines such as ion{C}{1} 1561 and 1656~AA multiplets, ion{He}{2} 1640~AA, ion{Si}{2} 1526 and 1533~AA. For the AIA 1700~AA band, ion{C}{1} 1656~AA multiplet is the main contributor (38%), followed by ion{He}{2} 1640 (17%), and accompanied by a multitude of other, { weaker} chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.
Waves have long been thought to contribute to the heating of the solar corona and the generation of the solar wind. Recent observations have demonstrated evidence of quasi-periodic longitudinal disturbances and ubiquitous transverse wave propagation in many different coronal environments. This paper investigates signatures of different types of oscillatory behaviour, both above the solar limb and on-disk, by comparing findings from the Coronal Multi-channel Polarimeter (CoMP) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) for the same active region. We study both transverse and longitudinal motion by comparing and contrasting time-distance images of parallel and perpendicular cuts along/across active region fan loops. Comparisons between parallel space-time features in CoMP Doppler velocity and transverse oscillations in AIA images are made, together with space-time analysis of propagating quasi-periodic intensity features seen near the base of loops in AIA. Signatures of transverse motions are observed along the same magnetic structure using CoMP Doppler velocity (Vphase=600-750km/s, P=3-6mins) and in AIA/SDO above the limb (P=3-8mins). Quasi-periodic intensity features (Vphase=100-200km/s, P=6-11mins) also travel along the base of the same structure. On the disk, signatures of both transverse and longitudinal intensity features were observed by AIA; both show similar properties to signatures found along structures anchored in the same active region three days earlier above the limb. Correlated features are recovered by space-time analysis of neighbouring tracks over perpendicular distances of <2.6Mm.
We report an observation of a partially erupting prominence and associated dynamical plasma processes based on observations recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). The prominence first goes through a slow rise (SR) phase followed by a fast rise (FR). The slow rise phase started after a couple of small brightenings seen toward the footpoints. At the turning point from SR to FR, the prominence had already become kinked. The prominence shows strong brightening at the central kink location during the start of FR. We interpret this as internal magnetic reconnection occurring at a vertical current sheet forming between the two legs of the erupting prominence (flux-rope). The brightening at the central kink location is seen in all the EUV channels of AIA. The contributions of differential emission at higher temperatures are larger compared to that for typical coronal temperatures supporting a reconnection scenario at the central kink location. The plasma above the brightening location gets ejected as a hot plasmoid-like structure embedded in a CME, and those below drain down in the form of blobs moving towards the Suns surface. The unique time resolution of the AIA has allowed all of these eruptive aspects, including SR-to-FR, kinking, central current sheet formation, plasmoid-like eruption, and filament splitting, to be observed in a single event, providing strong and comprehensive evidence in favour of the model of partially erupting flux ropes.
We report on a statistical study of prominence eruptions (PEs) using a catalog of these events routinely imaged by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in the 304 r{A} pass band. Using an algorithm developed as part of an LWS project, we have detected PEs in 304 r{A} synoptic images with 2-min cadence since May 2010. A catalog of these PEs is made available online (https://cdaw.gsfc.nasa.gov/CME_list/autope/). The 304 r{A} images are polar-transformed and divided by a background map (pixels with minimum intensity during one day) to get the ratio maps above the limb. The prominence regions are defined as pixels with a ratio $ge$2. Two prominence regions with more than 50% of pixels overlapping are considered the same prominence. If the height of a prominence increases monotonically in 5 successive images, it is considered eruptive. All the PEs seen above the limb are detected by the routine, but only PEs with width $ge$15{deg} are included in the catalog to eliminate polar jets and other small-scale mass motions. The identifications are also cross-checked with the PEs identified in Nobeyama Radioheliograph images (http://solar.nro.nao.ac.jp/norh/html/prominence/). The catalog gives the date, time, central position angle, latitude, and width of the eruptive prominence. The catalog also provides links to JavaScript movies that combine SDO/AIA images with GOES soft X-ray data to identify the associated flares, and with SOHO/LASCO C2 images to identify the associated coronal mass ejections. We examined the statistical properties of the PEs and found that the high-latitude PE speed decreased with the decreasing of the average polar magnetic field strength of the previous cycle.
We report on the variability of rotation periods of solar coronal layers with respect to temperature (or, height). For this purpose, we have used the observations from Atmospheric Imaging Assembly (AIA) telescope on board Solar Dynamics Observatory (SDO) space mission. The images used are at the wavelengths 94 {AA}, 131 {AA}, 171 {AA}, 193 {AA}, 211 {AA}, and 335 {AA} for the period from 2012 to 2018. Analysis of solar full disk images obtained at these wavelengths by AIA is carried out using flux modulation method. Seventeen rectangular strips/bins at equal interval of 10 degrees (extending from 80 degree South to 80 degree North on the Sun) are selected to extract a time series of extreme ultraviolet (EUV) intensity variations to obtain auto-correlation coefficient. The peak of Gaussian fit to first secondary maxima in the autocorrelogram gives synodic rotation period. Our analysis shows the differential rotation with respect to latitude as well as temperature (or, height). In the present study, we find that the sidereal rotation periods of different coronal layers decrease with increasing temperature (or, height). Average sidereal rotation period at the lowest temperature (~ 600000 Kelvin) corresponding to AIA-171 {AA} which originates from the upper transition region/quiet corona is 27.03 days. The sidereal rotation period decreases with temperature (or, height) to 25.47 days at the higher temperature (~10 million Kelvin) corresponding to the flaring regions of solar corona as seen in AIA-131 {AA} observations.
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