Author name code: joshi-anand ADS astronomy entries on 2022-09-14 =author: "Joshi, Anand D." ------------------------------------------------------------------------ Title: A Solar Magnetic-fan Flaring Arch Heated by Nonthermal Particles and Hot Plasma from an X-Ray Jet Eruption Authors: Lee, Kyoung-Sun; Hara, Hirohisa; Watanabe, Kyoko; Joshi, Anand D.; Brooks, David H.; Imada, Shinsuke; Prasad, Avijeet; Dang, Phillip; Shimizu, Toshifumi; Savage, Sabrina L.; Moore, Ronald; Panesar, Navdeep K.; Reep, Jeffrey W. Bibcode: 2020ApJ...895...42L Altcode: 2020arXiv200509875L We have investigated an M1.3 limb flare, which develops as a magnetic loop/arch that fans out from an X-ray jet. Using Hinode/EIS, we found that the temperature increases with height to a value of over 107 K at the loop top during the flare. The measured Doppler velocity (redshifts of 100-500 km s-1) and the nonthermal velocity (≥100 km s-1) from Fe XXIV also increase with loop height. The electron density increases from 0.3 × 109 cm-3 early in the flare rise to 1.3 × 109 cm-3 after the flare peak. The 3D structure of the loop derived with Solar TErrestrial RElations Observatory/EUV Imager indicates that the strong redshift in the loop-top region is due to upflowing plasma originating from the jet. Both hard X-ray and soft X-ray emission from the Reuven Ramaty High Energy Solar Spectroscopic Imager were only seen as footpoint brightenings during the impulsive phase of the flare, then, soft X-ray emission moved to the loop top in the decay phase. Based on the temperature and density measurements and theoretical cooling models, the temperature evolution of the flare arch is consistent with impulsive heating during the jet eruption followed by conductive cooling via evaporation and minor prolonged heating in the top of the fan loop. Investigating the magnetic field topology and squashing factor map from Solar Dynamics Observatory/HMI, we conclude that the observed magnetic-fan flaring arch is mostly heated from low atmospheric reconnection accompanying the jet ejection, instead of from reconnection above the arch as expected in the standard flare model. Title: Structure and dynamics of the hot flaring loop-top source observed by Hinode, SDO, RHESSI, and STEREO Authors: Lee, Kyoung-Sun; Hara, Hirohisa; Watanabe, Kyoko; Joshi, Anand D.; Imada, Shinsuke; Brooks, David H.; Dang, Phillip; Shimizu, Toshifumi; Savage, Sabrina Bibcode: 2019AAS...23421605L Altcode: We have investigated an M1.3 flare on 2014 January 13 around 21:48 UT observed at the west limb using the Hinode, SDO, RHESSI, and STEREO. Especially, the Hinode/EIS scanned the flaring loop covering the loop-top region over the limb, which is a good target to investigate the dynamics of the flaring loop with their height. Using the multi-wavelength observations from the Hinode/EIS and SDO/AIA, we found a very hot emission above the loop-top observed in Fe XXIV and 131Å channel. Measuring the intensity, Doppler velocity and line width for the flaring loop, we found that hot emission observed at the cusp-like shape of the loop-top region which shows strong redshift about 500 km s-1 in Doppler velocity and strong enhancement of the non-thermal velocity (line width enhancement) larger than 100 km s-1. Combining with the STEREO observation, we have examined the 3D structure with loop tilt angle and have investigated the velocity distribution of the loop-top region. With the loop tilt angle, we could identify the strong redshift at the loop-top region may indicate an up-flow along the loop-top region. From RHESSI hard X-ray (HXR), and soft X-ray (SXR) emission, we found that the footpoint brightening region at the beginning of the flare has a both HXR (25-50 keV) and SXR (12-25 keV) emission in which imply that the region has non-thermal emission or accelerated particles. Then, within 10 minutes the soft X-ray (SXR) emission observed near the cusp shape region at loop top. The temporal variation of the HXR and SXR emissions and the Doppler velocity variation of the hot plasma component at the loop-top imply that the strong flow in a hot component near loop-top could be the evaporation flows which detected at the corona along the tilted loop. Moreover, The temporal evolution of the temperature observed by SDO/AIA and Hinode/EIS also shows the cooling process of the flare plasma which is consistent with the impulsively heated flare model. Title: Statistical Study of Eruptive Filaments using Automated Detection and Tracking Technique Authors: Joshi, Anand D.; Hanaoka, Yoichiro Bibcode: 2017SPD....4811507J Altcode: Solar filaments are dense and cool material suspended in the low solar corona. They are found to be on the Sun for periods up to a few weeks, and they end their lifetime either as a gradual disappearance or an eruption. We have developed an automated detection and tracking technique to study such filament eruptions using full-disc Hα images. Various processing steps are used before subjecting an image to segmentation, that would extract only the filaments. Further steps track the filaments between successive images, label them uniquely, and generate output that can be used for a comparative study. In this poster, we would use this technique to carry out a statistical study of several erupting filaments through which the common underlying properties of such eruptions can be derived. Details of the technique will also be discussed in brief. Filament eruptions are found to be closely associated with coronal mass ejections (CMEs) wherein a large mass from corona is ejected into the interplanetary space. If such a CME hits the Earth with a favourable orientation of magnetic field a geomagnetic storm can result adversely affecting electronic infrastructure in space as well as ground. The properties of filament eruptions derived can be used in future to predict an eruption in an almost real-time basis, thereby giving a warning of imminent storm. Title: Pre-eruption Oscillations in Thin and Long Features in a Quiescent Filament Authors: Joshi, Anand D.; Hanaoka, Yoichiro; Suematsu, Yoshinori; Morita, Satoshi; Yurchyshyn, Vasyl; Cho, Kyung-Suk Bibcode: 2016ApJ...833..243J Altcode: 2016arXiv161204917J We investigate the eruption of a quiescent filament located close to an active region. Large-scale activation was observed in only half of the filament in the form of pre-eruption oscillations. Consequently only this half erupted nearly 30 hr after the oscillations commenced. Time-slice diagrams of 171 Å images from the Atmospheric Imaging Assembly were used to study the oscillations. These were observed in several thin and long features connecting the filament spine to the chromosphere below. This study traces the origin of such features and proposes their possible interpretation. Small-scale magnetic flux cancellation accompanied by a brightening was observed at the footpoint of the features shortly before their appearance, in images recorded by the Helioseismic and Magnetic Imager. A slow rise of the filament was detected in addition to the oscillations, indicating a gradual loss of equilibrium. Our analysis indicates that a change in magnetic field connectivity between two neighbouring active regions and the quiescent filament resulted in a weakening of the overlying arcade of the filament, leading to its eruption. It is also suggested that the oscillating features are filament barbs, and the oscillations are a manifestation during the pre-eruption phase of the filaments. Title: Pre-Eruption Oscillations in Quiescent Filament Observed in AIA 171 Å Authors: Joshi, Anand D.; Yurchyshyn, Vasyl; Cho, Kyung-Suk Bibcode: 2016usc..confE..62J Altcode: A large quiescent filament located near the south-west limb of the Sun underwent an eruption on 14 August 2013. Shortly before the eruption two flares occur in NOAA Active Region (AR) 11817, located near the filament. The temporal and spatial proximity suggests that the flares caused the filament to erupt. However, there is no extreme ultraviolet (EUV) wave or ejection which seemed to cause this. We use 171 Å images for over two days before the eruption from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) to investigate this event. We observe oscillations in the western portion of the quiescent filament almost 40 hours prior to eruption, but not so much in the eastern portion. For several hours prior to eruption, the western portion is seen to undergo a slow rise. Subsequently, it is this western portion which erupts, while the eastern portion does not. We also use Helioseismic and Magnetic Imager (HMI) to study changes in the active region, and find that along with a continuous emergence of magnetic flux in the region, there was also a migration of polarity producing a large shear. We make use of the hmi.sharp to determine shear in the active region. We suggest that the oscillations are a result of natural perturbation, and the flares acted as a destabilising factor which resulted in the eruption. Title: A Trio of Confined Flares in AR 11087 Authors: Joshi, Anand D.; Forbes, Terry G.; Park, Sung-Hong; Cho, Kyung-Suk Bibcode: 2015ApJ...798...97J Altcode: We investigate three flares that occurred in active region, AR 11087, observed by the Dutch Open Telescope (DOT) on 2010 July 13, in a span of three hours. The first two flares have soft X-ray class B3, whereas the third flare has class C3. The third flare not only was the largest in terms of area and brightness but also showed a very faint coronal mass ejection (CME) associated with it, while the earlier two flares had no associated CME. The active region, located at 27° N, 26° E, has a small U-shaped active region filament to the south of the sunspot, and a quiescent filament is located to its west. Hα observations from DOT, as well as extreme-ultraviolet images and magnetograms from the STEREO spacecraft and Solar Dynamics Observatory, are used to study the dynamics of the active region during the three flares. Our observations imply that the first two flares are confined and that some filament material drains to the surface during these flares. At the onset of the third flare downflows are again observed within the active region, but a strong upflow is also observed at the northern end of the adjacent quiescent filament to the west. It is at the latter location that the CME originates. The temporal evolution of the flare ribbons and the dynamics of the filaments are both consistent with the idea that reconnection in a pre-existing current sheet leads to a loss of equilibrium. Title: A Statistical Study on Characteristics of Disappearing Prominences Authors: Joshi, Anand D.; Bong, Su-Chan; Srivastava, Nandita Bibcode: 2014IAUS..300..422J Altcode: Real-time monitoring of filaments is essential for the prediction of their eruption and the ensuing coronal mass ejection (CME). We apply an automated algorithm for the detection and tracking of filaments in full-disc Hα images to obtain their physical attributes. This provides an accurate onset time of the eruption, and also allows us to study the physical characteristics of the erupting filaments in an objective manner. Title: On the onset of recurrent eruptions of a filament observed during August 2012 Authors: Srivastava, Nandita; Joshi, Anand D.; Mathew, Shibu K. Bibcode: 2014IAUS..300..495S Altcode: We report observations of a long filament that underwent recurrent partial eruptions on August 4, 6, and 8, 2012. The filament reappeared in the subsequent rotation of the Sun, and disappeared completely on August 31, 2012. We implemented an automated filament detection algorithm developed by us for estimating different attributes of these filaments few hours prior to its disappearance in Hα and studied their evolution. Based on these attributes, we determine the onset time of the disappearance of Hα filaments. We then compared these onset times with that of the associated CMEs observed by LASCO/SOHO coronagraphs. This is also useful to understand temporal relationship of EUV and X-ray flux variation associated with filament disappearances in Hα. Our results show the importance of such studies in understanding the mechanism of CME initiation, particularly the role of eruptive filaments, in this process. Title: Rapid Formation and Disappearance of a Filament Barb Authors: Joshi, Anand D.; Srivastava, Nandita; Mathew, Shibu K.; Martin, Sara F. Bibcode: 2013SoPh..288..191J Altcode: We present observations of an activated quiescent filament obtained in Hα from the high-resolution Dutch Open Telescope (DOT) on 20 August 2010. The filament developed a barb in 10 min, which disappeared within the next 35 min. A data set from the DOT spanning 2 h was used to analyse this event. Line-of-sight velocity maps were constructed from the Doppler images, which reveal flows in filament spine during this period. Photospheric magnetograms were used from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to determine the changes in magnetic flux in the region surrounding the barb location. The analysis shows flows in the filament spine towards the barb location preceding its formation, and flows in the barb towards the spine during its disappearance. Magnetograms reveal patches of minority polarity flux close to the end of the barb at its greatest elongation. The flows in the spine and barbs are along numerous threads that compose these typical filament structures. The flows are consistent with field-aligned threads and demonstrate that the replacement time of the mass in barbs, and by inference, in the spine is very rapid. Title: Acceleration of Coronal Mass Ejections from Three-dimensional Reconstruction of STEREO Images Authors: Joshi, Anand D.; Srivastava, Nandita Bibcode: 2011ApJ...739....8J Altcode: 2011arXiv1107.1769J We employ a three-dimensional (3D) reconstruction technique for the first time to study the kinematics of six coronal mass ejections (CMEs), using images obtained from the COR1 and COR2 coronagraphs on board the twin STEREO spacecraft, and also the eruptive prominences (EPs) associated with three of them using images from the Extreme UltraViolet Imager. A feature in the EPs and leading edges (LEs) of all the CMEs was identified and tracked in images from the two spacecraft, and a stereoscopic reconstruction technique was used to determine the 3D coordinates of these features. True velocity and acceleration were determined from the temporal evolution of the true height of the CME features. Our study of the kinematics of the CMEs in 3D reveals that the CME LE undergoes maximum acceleration typically below 2 R sun. The acceleration profiles of CMEs associated with flares and prominences exhibit different behaviors. While the CMEs not associated with prominences show a bimodal acceleration profile, those associated with prominences do not. Two of the three associated prominences in the study show a high and increasing value of acceleration up to a distance of almost 4 R sun, but acceleration of the corresponding CME LE does not show the same behavior, suggesting that the two may not be always driven by the same mechanism. One of the CMEs, although associated with a C-class flare, showed unusually high acceleration of over 1500 m s-2. Our results therefore suggest that only the flare-associated CMEs undergo residual acceleration, which indicates that the flux injection theoretical model holds well for the flare-associated CMEs, but a different mechanism should be considered for EP-associated CMEs. Title: Rolling motion in erupting prominences observed by STEREO Authors: Panasenco, Olga; Martin, Sara; Joshi, Anand D.; Srivastava, Nandita Bibcode: 2011JASTP..73.1129P Altcode: We analyze the large-scale dynamical forms of three erupting prominences (filaments) observed by at least one of the two STEREO spacecraft and which reveal evidence of sideways rolling motion beginning at the crest of the erupting filament. We find that all three events were also highly non-radial and occurred adjacent to large coronal holes. For each event, the rolling motion and the average non-radial outward motion of the erupting filament and associated CME were away from a neighboring coronal hole. The location of each coronal hole was adjacent to the outer boundary of the arcade of loops overlying the filaments. The erupting filaments were all more non-radial than the CMEs but in the same general direction. From these associations, we make the hypothesis that the degree of the roll effect depends on the level of force imbalances inside the filament arcade related to the coronal hole and the relative amount of magnetic flux on each side of the filament, while the non-radial motion of the CME is related to global magnetic configuration force imbalances. Our analyses of the prominence eruption best observed from both STEREO-A and STEREO-B shows that its spine retained the thin ribbon-like topology that it had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption. Title: Kinematics of Two Eruptive Prominences Observed by EUVI/STEREO Authors: Joshi, Anand D.; Srivastava, Nandita Bibcode: 2011ApJ...730..104J Altcode: 2011arXiv1101.4543J Two large northern polar crown prominences that erupted on 2010 April 13 and 2010 August 1 were analyzed using images obtained from the Extreme UltraViolet Imager on the twin Solar Terrestrial Relations Observatory spacecraft. Several features along the prominence legs were reconstructed using a stereoscopic reconstruction technique developed by us. The three-dimensional changes exhibited by the prominences can be explained as an interplay between two different motions, namely helical twist in the prominence spine, and overall non-radial equatorward motion of the entire prominence structure. The sense of twist in both the prominences is determined from the changes in latitudes and longitudes of the reconstructed features. The prominences are observed starting from a few hours before the eruption. Increase in height before and during the eruption allowed us to study the kinematics of the prominences in the two phases of eruption, the slow-rise and the fast-eruptive phase. A constant value of acceleration was found for each reconstructed feature in each phase, but it showed a significant change from one leg to the other in both the prominences. The magnitude of acceleration during the eruptive phase is found to be commensurate with the net effect of the two motions stated above. Title: 3D reconstruction and kinematics of eruptive prominences using STEREO observations Authors: Srivastava, Nandita; Joshi, Anand D. Bibcode: 2011ASInC...3R.100S Altcode: We present observations of two large northern polar crown prominences that erupted on 2010 April 13 and 2010 August 1 on the Sun. For 3D studies of these events, we developed a stereoscopic reconstruction technique for the images obtained from the SECCHI suite of instruments on board the twin Solar TErrestrial RElations Observatory (STEREO) spacecraft. This technique was applied to images obtained from the Extreme UltraViolet Imager to reconstruct several features along the prominences. The three-dimensional changes exhibited by the prominences can be explained as an interplay of two different motions, namely, the twist in the prominence spine, and the overall non-radial motion of the entire prominence structure. The sense of twist in both the prominences is determined from the changes in latitudes and longitudes of the reconstructed features. The study of kinematics of these features reveals crucial information of the early phase of eruptive prominences and initiation of the associated CMEs. Our results from 3D reconstruction of observations from two view points (STEREO) provide a better understanding of the physical mechanism in the lower corona as compared to previous results obtained using observation from a single vantage point, for e.g. SOHO. Title: A Dual Beam H-alpha Doppler System to Acquire, Analyse and Anticipate Solar Eruptive Events Directed towards Earth Authors: Joshi, Anand D.; Mathew, Shibu K.; Srivastava, Nandita; Martin, Sara F.; Gupta, Sudhir K. Bibcode: 2009arXiv0905.3037J Altcode: A new instrument with a dual-beam H-alpha Doppler system is being developed at the Udaipur Solar Observatory (USO) in order to improve the quality and quantity of data on quiet, activated and erupting filaments and prominences on the Sun, especially those associated with geo-effective coronal mass ejections. These data can be potentially used to construct three-dimensional topology of erupting filaments as they leave the surface of the Sun and can be compared with multi-wavelength data obtained from space missions such as STEREO, SOHO, and Hinode. The characterization of various optical components for the instrument is being carried out, and some preliminary results are described in the paper.