explanation blue bibcodes open ADS page with paths to full text
Author name code: joshi-anand
ADS astronomy entries on 2022-09-14
=author: "Joshi, Anand D."
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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.
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
10<SUP>7</SUP> K at the loop top during the flare. The measured Doppler
velocity (redshifts of 100-500 km s<SUP>-1</SUP>) and the nonthermal
velocity (≥100 km s<SUP>-1</SUP>) from Fe XXIV also increase with
loop height. The electron density increases from 0.3 × 10<SUP>9</SUP>
cm<SUP>-3</SUP> early in the flare rise to 1.3 × 10<SUP>9</SUP>
cm<SUP>-3</SUP> 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.
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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
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<SUP>-1</SUP> in Doppler velocity and strong enhancement
of the non-thermal velocity (line width enhancement) larger than 100
km s<SUP>-1</SUP>. 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.
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Title: Statistical Study of Eruptive Filaments using Automated
Detection and Tracking Technique
Authors: Joshi, Anand D.; Hanaoka, Yoichiro
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.
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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
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.
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Title: Pre-Eruption Oscillations in Quiescent Filament Observed in
AIA 171 Å
Authors: Joshi, Anand D.; Yurchyshyn, Vasyl; Cho, Kyung-Suk
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.
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Title: A Trio of Confined Flares in AR 11087
Authors: Joshi, Anand D.; Forbes, Terry G.; Park, Sung-Hong; Cho,
Kyung-Suk
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.
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Title: A Statistical Study on Characteristics of Disappearing
Prominences
Authors: Joshi, Anand D.; Bong, Su-Chan; Srivastava, Nandita
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.
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Title: On the onset of recurrent eruptions of a filament observed
during August 2012
Authors: Srivastava, Nandita; Joshi, Anand D.; Mathew, Shibu K.
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.
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Title: Rapid Formation and Disappearance of a Filament Barb
Authors: Joshi, Anand D.; Srivastava, Nandita; Mathew, Shibu K.;
Martin, Sara F.
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.
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Title: Acceleration of Coronal Mass Ejections from Three-dimensional
Reconstruction of STEREO Images
Authors: Joshi, Anand D.; Srivastava, Nandita
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 <SUB>sun</SUB>. 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 <SUB>sun</SUB>,
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<SUP>-2</SUP>. 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.
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Title: Rolling motion in erupting prominences observed by STEREO
Authors: Panasenco, Olga; Martin, Sara; Joshi, Anand D.; Srivastava,
Nandita
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.
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Title: Kinematics of Two Eruptive Prominences Observed by EUVI/STEREO
Authors: Joshi, Anand D.; Srivastava, Nandita
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.
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Title: 3D reconstruction and kinematics of eruptive prominences
using STEREO observations
Authors: Srivastava, Nandita; Joshi, Anand D.
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.
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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.
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.
