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Author name code: bharti
ADS astronomy entries on 2022-09-14
author:"Bharti, Lokesh"
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Title: Variation in cosmic ray flux during Solar Eclipse on 21 June,
2020 at Jaipur, India
Authors: Pandya, Aalok; Gupta, S. K.; Meena, Dalpat; Bharti, Lokesh
2022APh...13602659P Altcode:
Variation in gamma ray flux was recorded during the Annular Solar
Eclipse on 21 June, 2020 at Jaipur, India where 88.3% of the solar
disk was eclipsed. Two Sodium Iodide NaI (Tl) scintillation detectors
were employed for the experiment and flux was recorded in the energy
range 300 keV to 2 MeV. The first detector employed to record data
for the duration of 3 h and 30 min records a sizeable enhancement at
the characteristic energy 1460 keV and the corresponding single escape
peak at 949 keV. No substantial variation in the radiations was noticed
by the detector employed for recording data for 20 critical minutes
during the peak of the eclipse.
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Title: Chromospheric plasma ejection above a pore
Authors: Bharti, L.; Sobha, B.; Quintero Noda, C.; Joshi, C.;
Pandya, U.
2020MNRAS.493.3036B Altcode: 2020arXiv200204503B
We present high spatial resolution observations of short-lived
transients, ribbons and jet-like events above a pore in Ca II H images
where fine structure, like umbral dots, light bridges and penumbral
microfilaments, is present in the underlying photosphere. We found
that current layers are formed at the edges of the convective fine
structure, due to the shear between their horizontal field and the
ambient vertical field. High vertical electric current density patches
are observed in the photosphere around these events, which indicates
the formation of a current sheet at the reconnection site. In the
framework of past studies, low altitude reconnection could be the
mechanism that produces such events. The reconnection is caused by
an opposite polarity field produced by the bending of field lines by
convective downflows at the edge of pore fine structure.
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Title: Opposite Polarity Magnetic Fields and Convective Downflows
in a Simulated Sunspot Penumbra
Authors: Bharti, Lokesh; Rempel, Matthias
2019ApJ...884...94B Altcode: 2019arXiv190806439B
Recent numerical simulations and observations of sunspots show a
significant amount of opposite polarity magnetic fields within the
sunspot penumbra. Most of the opposite polarity fields are associated
with convective downflows. We present an analysis of 3D MHD simulations
through forward modeling of synthetic Stokes profiles of the Fe I
6301.5 Å and Fe I 6302.5 Å lines. The synthetic Stokes profiles
are spatially and spectrally degraded considering typical instrument
properties. Line bisector shifts of the Fe I 6301.5 Å line are
used to determine line-of-sight velocities. Far wing magnetograms are
constructed from the Stokes V profiles of the Fe I 6302.5 Å line. While
we find an overall good agreement between observations and simulations,
the fraction of opposite polarity magnetic fields, the downflow filling
factor, and the opposite polarity-downflow association are strongly
affected by spatial smearing and presence of strong gradients in the
line-of-sight magnetic fields and velocity. A significant fraction
of opposite polarity magnetic fields and downflows is hidden in the
observations due to typical instrumental noise. Comparing simulations
that differ by more than a factor of two in grid spacing, we find that
these quantities are robust within the simulations.
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Title: Small-Scale Activity Above the Penumbra of a Fast-Rotating
Sunspot
Authors: Bharti, L.; Quintero Noda, C.; Rakesh, S.; Sobha, B.; Pandya,
A.; Joshi, C.
2018SoPh..293...46B Altcode:
High-resolution observations of small-scale activity above the
filamentary structure of a fast-rotating sunspot of NOAA Active Region
10930 are presented. The penumbral filament that intrudes into the
umbra shows a central dark core and substructures. It almost approached
another end of the umbra, like a light bridge. The chromospheric Ca II
H images show many jet-like structures with a bright leading edge above
it. These bright jets move across the filament tips and show coordinated
up and down motions. Transition region images also show brightening at
the same location above the intrusion. Coronal 195 Å images suggest
that one end of the bright coronal loop footpoints resides in this
structure. The intrusion has opposite polarity with respect to the
umbra. Strong downflows are observed at the edges along the length
of the intrusion where the opposite-polarity field is enhanced. We
also observe a counter-Evershed flow in the filamentary structure
that also displays brightening and energy dissipation in the upper
atmosphere. This scenario suggests that the jets and brightenings are
caused by low-altitude reconnection driven by opposite-polarity fields
and convective downflows above such structures.
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Title: Lambda-shaped jets from a penumbral intrusion into a sunspot
umbra: a possibility for magnetic reconnection
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
2017A&A...597A.127B Altcode:
We present the results of high resolution co-temporal and co-spatial
photospheric and chromospheric observations of sunspot penumbral
intrusions. The data were taken with the Swedish Solar Telescope
(SST) on the Canary Islands. Time series of Ca II H images show
a series of transient jets extending roughly 3000 km above a
penumbral intrusion into the umbra. For most of the time series,
jets were seen along the whole length of the intruding bright
filament. Some of these jets develop a clear λ-shaped structure,
with a small loop appearing at their footpoint and lasting for around
a minute. In the framework of earlier studies, the observed transient
λ shape of these jets suggests that they could be caused by magnetic
reconnection between a curved arcade-like or flux rope-like field in
the lower part of the penumbral intrusion and the more vertical umbral
magnetic field forming a cusp-shaped structure above the penumbral
intrusion. <P />Movies associated to Figs. 1 and 2 are available at
<A href="http://www.aanda.org">http://www.aanda.org</A>
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Title: Fine structures at pore boundary
Authors: Bharti, L.; Quintero Noda, C.; Joshi, C.; Rakesh, S.;
Pandya, A.
2016MNRAS.462L..93B Altcode:
We present high resolution observations of fine structures at
pore boundaries. The inner part of granules towards umbra show dark
striations which evolve into a filamentary structure with dark core and
`Y' shape at the head of the filaments. These filaments migrate into
the umbra similar to penumbral filaments. These filaments show higher
temperature, lower magnetic field strength and more inclined field
compared to the background umbra. The optical depth stratification
of physical quantities suggests their similarity with penumbral
filaments. However, line-of-sight velocity pattern is different from
penumbral filaments where they show downflows in the deeper layers of
the atmosphere while the higher layers show upflows. These observations
show filamentation in a simple magnetic configuration.
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Title: Magnetic reconnection as a source of jets from a penumbral
intrusion into a sunspot umbra
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
2015arXiv150902123B Altcode:
We present the results of high resolution co-temporal and co-spatial
photospheric and chromospheric observations of sunspot penumbral
intrusions. The data was taken with the Swedish Solar Telescope (SST)
on the Canary Islands. Time series of Ca\,II H images show a series of
transient jets extending roughly 3000 km above a penumbral intrusion
into the umbra. For most of the time series jets were seen along
the whole length of the intruding bright filament. Some of these jets
develop a clear $\lambda$-shaped structure, with a small loop appearing
at their footpoint and lasting for around a minute. In the framework
of earlier studies, the observed transient $\lambda$ shape of these
jets strongly suggests that they are caused by magnetic reconnection
between a curved arcade-like or flux-rope like field in the lower part
of the penumbral intrusion and the more vertical umbral magnetic field
forming a cusp-shaped structure above the penumbral intrusion.
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Title: Fine structure above a light bridge in the transition region
and corona
Authors: Bharti, L.
2015MNRAS.452L..16B Altcode: 2015arXiv150502412B
We present the results of multiwavelength, co-spatial and near
co-temporal observations of jets above a sunspot light bridge (LB). The
data were obtained with the Solar Optical Telescope on board Hinode,
the Interface Region Spectrograph (IRIS) and the Atmospheric Imaging
Assembly (AIA) on the Solar Dynamic Observatory. Most of the jets in the
Ca II H images show decreasing brightness with height while in the IRIS
slit-jaw images at 1330 Å jets show a bright leading edge. These jets
show rising and falling motion as evident from the parabolic profile
obtained from the time-distance diagram. The rising and falling speeds
of the jets are similar. These jets show a coordinated behaviour between
neighbouring jets moving jointly up and down. Some of the jets show
a plasma ejection from the leading edge which is also hotter at the
transition region (TR) and coronal temperatures. A similar behaviour
is seen in the AIA wavebands that suggests that jets above the LB
reach up to the lower corona and the leading edges are heated up to
coronal temperatures. Such jets are important means of transfer mass
and energy to the TR and corona above sunspots.
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Title: Fine structures in the atmosphere above a sunspot umbra
Authors: Bharti, L.; Hirzberger, J.; Solanki, S. K.
2013A&A...552L...1B Altcode: 2013arXiv1302.2772B
We present simultaneous photospheric and chromospheric observations
of the trailing sunspot in NOAA 10904, obtained with the Swedish
Solar Telescope (SST) La Palma, Canary Islands. Time series of high
resolution Ca ii H images show transient jet-like structures in sunspot
umbrae are elongated, which we call umbral microjets. These jets are
directed roughly parallel to nearby penumbral microjets, suggesting
that they are aligned with the background magnetic field. In general,
first a bright dot-like structure appears, from which a jet later
emerges, although some jets appear without an associated chromospheric
dot. Bright photospheric umbral dots are associated with umbral
microjets arising in the outer umbra. Nevertheless, a one-to-one
correspondence between jet-like events and underlying umbral dots
is not seen. They are typically less than 1” long and less than 0.3
arcsec wide. The typical lifetime of umbral microjets is around one
minute. The brightness of these structures increases from the center of
the umbra toward the umbra-penumbra boundary along with the brightness
of the local background.
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Title: Observational study of an eruptive event in vicinity of umbral
bright features
Authors: Joshi, Chandan; Jaaffrey, S. N. A.; Bharti, Lokesh
2012cosp...39..846J Altcode: 2012cosp.meet..846J
The solar chromosphere is very dynamic. The magnetic field and waves
play the important role in eruptive events in chromosphere on different
spatial and temporal scales. With the increase in the observational
capabilities with Hinode the diagnostic of chromosphere can be
improved. We present here the observations of eruptive event in the
vicinity of umbral bright features with the help of SOT on board Hinode.
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Title: Waves as the Source of Apparent Twisting Motions in Sunspot
Penumbrae
Authors: Bharti, L.; Cameron, R. H.; Rempel, M.; Hirzberger, J.;
Solanki, S. K.
2012ApJ...752..128B Altcode: 2012arXiv1204.2221B
The motion of dark striations across bright filaments in a sunspot
penumbra has become an important new diagnostic of convective gas
flows in penumbral filaments. The nature of these striations has,
however, remained unclear. Here, we present an analysis of small-scale
motions in penumbral filaments in both simulations and observations. The
simulations, when viewed from above, show fine structure with dark lanes
running outward from the dark core of the penumbral filaments. The
dark lanes either occur preferentially on one side or alternate
between both sides of the filament. We identify this fine structure
with transverse (kink) oscillations of the filament, corresponding to
a sideways swaying of the filament. These oscillations have periods in
the range of 5-7 minutes and propagate outward and downward along the
filament. Similar features are found in observed G-band intensity time
series of penumbral filaments in a sunspot located near disk center
obtained by the Broadband Filter Imager on board the Hinode. We also
find that some filaments show dark striations moving to both sides
of the filaments. Based on the agreement between simulations and
observations we conclude that the motions of these striations are
caused by transverse oscillations of the underlying bright filaments.
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Title: Can Overturning Motions in Penumbral Filaments BE Detected?
Authors: Bharti, Lokesh; Schuessler, Manfred; Rempel, Matthias
2011sdmi.confE..79B Altcode:
Numerical simulations indicate that the filamentation of sunspot
penumbrae and the associated systematic outflow (the Evershed effect)
are due to convectively driven fluid motions constrained by the inclined
magnetic field. We investigate whether these motions, in particular the
upflows in the bright filaments and the downflows at their edges, can be
reliably observed with existing instrumentation. We use a snapshot from
a sunspot simulation to calculate two-dimensional maps of synthetic
line profiles for the spectral lines Fe I 7090.4 Å and C I 5380.34
Å. The maps are spatially and spectrally degraded according to typical
instrument properties. Line-of-sight velocities are determined from
line bisector shifts. We find that the detectability of the convective
flows is strongly affected by spatial smearing, particularly so for
the downflows. Furthermore, the line-of-sight velocities are dominated
by the Evershed flow unless the observation is made very near the disk
center. These problems may have compromised recent attempts to detect
overturning penumbral convection. Lines with a low formation height
are best suited for detecting the convective flows.
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Title: Can Overturning Motions in Penumbral Filaments Be Detected?
Authors: Bharti, Lokesh; Schüssler, Manfred; Rempel, Matthias
2011ApJ...739...35B Altcode: 2011arXiv1107.0398B
Numerical simulations indicate that the filamentation of sunspot
penumbrae and the associated systematic outflow (the Evershed effect)
are due to convectively driven fluid motions constrained by the inclined
magnetic field. We investigate whether these motions, in particular the
upflows in the bright filaments and the downflows at their edges, can be
reliably observed with existing instrumentation. We use a snapshot from
a sunspot simulation to calculate two-dimensional maps of synthetic
line profiles for the spectral lines Fe I 7090.4 Å and C I 5380.34
Å. The maps are spatially and spectrally degraded according to typical
instrument properties. Line-of-sight velocities are determined from
line bisector shifts. We find that the detectability of the convective
flows is strongly affected by spatial smearing, particularly so for
the downflows. Furthermore, the line-of-sight velocities are dominated
by the Evershed flow unless the observation is made very near the disk
center. These problems may have compromised recent attempts to detect
overturning penumbral convection. Lines with a low formation height
are best suited for detecting the convective flows.
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Title: Probing the Role of Magnetic-Field Variations in NOAA AR 8038
in Producing a Solar Flare and CME on 12 May 1997
Authors: Jain, Rajmal; Awasthi, Arun K.; Chandel, Babita; Bharti,
Lokesh; Hanaoka, Y.; Kiplinger, A. L.
2011SoPh..271...57J Altcode: 2011SoPh..tmp..127J; 2011SoPh..tmp..182J; 2011SoPh..tmp..251J;
2011arXiv1106.2702J
We carried out a multi-wavelength study of a Coronal Mass Ejection
(CME) and an associated flare, occurring on 12 May 1997. We present
a detailed investigation of magnetic-field variations in NOAA Active
Region 8038 which was observed on the Sun during 7 - 16 May 1997. This
region was quiet and decaying and produced only a very small flare
activity during its disk passage. However, on 12 May 1997 it produced a
CME and associated medium-size 1B/C1.3 flare. Detailed analyses of Hα
filtergrams and SOHO/MDI magnetograms revealed continual but discrete
surge activity, and emergence and cancellation of flux in this active
region. The movie of these magnetograms revealed the two important
results that the major opposite polarities of pre-existing region as
well as in the emerging-flux region were approaching towards each other
and moving magnetic features (MMF) were ejected from the major north
polarity at a quasi-periodicity of about ten hours during 10 - 13 May
1997. These activities were probably caused by magnetic reconnection
in the lower atmosphere driven by photospheric convergence motions,
which were evident in magnetograms. The quantitative measurements of
magnetic-field variations such as magnetic flux, gradient, and sunspot
rotation revealed that in this active region, free energy was slowly
being stored in the corona. Slow low-layer magnetic reconnection may be
responsible for the storage of magnetic free energy in the corona and
the formation of a sigmoidal core field or a flux rope leading to the
eventual eruption. The occurrence of EUV brightenings in the sigmoidal
core field prior to the rise of a flux rope suggests that the eruption
was triggered by the inner tether-cutting reconnection, but not the
external breakout reconnection. An impulsive acceleration, revealed
from fast separation of the Hα ribbons of the first 150 seconds,
suggests that the CME accelerated in the inner corona, which is also
consistent with the temporal profile of the reconnection electric
field. Based on observations and analysis we propose a qualitative
model, and we conclude that the mass ejections, filament eruption,
CME, and subsequent flare were connected with one another and should
be regarded within the framework of a solar eruption.
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Title: Evidence for Convection in Sunspot Penumbrae
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
2010ApJ...722L.194B Altcode: 2010arXiv1009.2919B
We present an analysis of twisting motions in penumbral filaments in
sunspots located at heliocentric angles from 30° to 48° using three
time series of blue continuum images obtained by the Broadband Filter
Imager (BFI) on board Hinode. The relations of the twisting motions to
the filament brightness and the position within the filament and within
the penumbra, respectively, are investigated. Only certain portions
of the filaments show twisting motions. In a statistical sense, the
part of the twisting portion of a filament located closest to the
umbra is brightest and possesses the fastest twisting motion, with a
mean twisting velocity of 2.1 km s<SUP>-1</SUP>. The middle and outer
sections of the twisting portion of the filament (lying increasingly
further from the umbra), which are less bright, have mean velocities
of 1.7 km s<SUP>-1</SUP> and 1.35 km s<SUP>-1</SUP>, respectively. The
observed reduction of brightness and twisting velocity toward the
outer section of the filaments may be due to reducing upflow along the
filament's long axis. No significant variation of twisting velocity as
a function of viewing angles was found. The obtained correlation of
brightness and velocity suggests that overturning convection causes
the twisting motions observed in penumbral filament and may be the
source of the energy needed to maintain the brightness of the filaments.
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Title: Properties of simulated sunspot umbral dots
Authors: Bharti, L.; Beeck, B.; Schüssler, M.
2010A&A...510A..12B Altcode: 2009arXiv0911.5068B
Realistic 3D radiative MHD simulations reveal the magneto-convective
processes underlying the formation of the photospheric fine structure
of sunspots, including penumbral filaments and umbral dots. Here we
provide results from a statistical analysis of simulated umbral dots
and compare them with reports from high-resolution observations. A
multi-level segmentation and tracking algorithm has been used to isolate
the bright structures in synthetic bolometric and continuum brightness
images. Areas, brightness, and lifetimes of the resulting set of umbral
dots are found to be correlated: larger umbral dots tend to be brighter
and live longer. The magnetic field strength and velocity structure of
umbral dots on surfaces of constant optical depth in the continuum at
630 nm indicate that the strong field reduction and high velocities in
the upper parts of the upflow plumes underlying umbral dots are largely
hidden from spectro-polarimetric observations. The properties of the
simulated umbral dots are generally consistent with the results of
recent high-resolution observations. However, the observed population
of small, short-lived umbral dots is not reproduced by the simulations,
possibly owing to insufficient spatial resolution.
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Title: Fine Structure of Chromospheric Brightenings above a Light
Bridge and Penumbral Filaments
Authors: Bharti, Lokesh
2010cosp...38.2848B Altcode: 2010cosp.meet.2848B
We present simultaneous photospheric and chromospheric observations of
the trailing sunspot in NOAA 10904. At the limit of the instrumental
spatial resolution Ca II H images show jet-like brightenings above a
lightbridge and a penumbral filament that intrudes into the umbra. The
observations were carried out with the Swedish Solar Telescope (SST)
on 13 August 2006. The Solar Optical Universal Polarimeter (SOUP)
filter was used to scan the Fe I 6302.5 ˚ line at A 6 wavelength
positions. Full Stokes polarimetry was performed and the magnetic
field vector was obtained by means of a Milne-Eddington inversion
of the radiative transfer equation. The data reveal a more inclined
field in the light bridge and penumbral filament than in the umbra
with a vertical current density higher than 200 mA m-2 . Also
opposite polarity patches were found in the light bridge. Such a
magnetic configuration indicates low altitude reconnection. A similar
mechanism causes penumbral microjets which were also observed along
other penumbral filaments.
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Title: Spectropolarimetery of umbral fine structures from Hinode:
evidence for magnetoconvection
Authors: Bharti, Lokesh; Joshi, Chandan; Jaaffrey, S. N. A.; Jain,
Rajmal
2009MNRAS.393...65B Altcode: 2008arXiv0811.1722B
We present spectropolarimetric analysis of umbral dots and a light
bridge fragment that show dark lanes in G-band images. Umbral dots
show upflow as well as associated positive Stokes V area asymmetry
in their central parts. Larger umbral dots show downflow patches in
their surrounding parts that are associated with negative Stokes V
area asymmetry. Umbral dots show weaker magnetic field in central part
and higher magnetic field in peripheral area. Umbral fine structures
are much better visible in total circularly polarized light than in
continuum intensity. Umbral dots show a temperature deficit above dark
lanes. The magnetic field inclination shows a cusp structure above
umbral dots and a light bridge fragment. We compare our observational
findings with 3D magnetohydrodynamic simulations.
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Title: A High Resolution Study of Umbral Flashes and Running Penumbral
Waves using Hinode Observations
Authors: Joshi, C.; Bharti, L.; Jaaffrey, S. N. A.
2008ESPM...12.2.27J Altcode:
We present a study of intensity oscillations in sunspots using high
resolution ( temporal and spatial) CaII H data and Gband data from
Hinode. The intensity variations show increased power at 5.5mHz in umbra
and frequency decreases as we move towards penumbra and outwards. An
attempt was also made to find any relationship between the dark umbra
and oscillation power and umbral fine structure and oscillation power
but no obious relation could be established.
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Title: Spectropolarimetery of Umbral Fine Structures from Hinode:
Evidence for Magnetoconvection
Authors: Bharti, L.; Joshi, C.; Jaaffrey, S. N. A.
2008ESPM...12..2.7B Altcode:
We present spectropolarimetric analysis of umbral dots and light bridge
fragment that show dark lanes in G-band images. Umbral dots show upflow
as well as associated positive stokes V area asymmetry in central
part. Bigger umbral dots show down flow patches in surrounding part
that associated with negative stokes V area asymmetry. <P />Umbral dots
show weaker magnetic field in central part and higher magnetic field
in peripheral area. Umbral fine structures are much clear in total
circular polarization as compared to continuum intensity. Umbral dots
show temperature deficit above dark lanes. Magnetic field inclination
show cusp above umbral dots and light bridge fragment. We compare our
observational findings with 3D magnetohydrodynamic simulations.
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Title: Enhanced Joule Heating in Umbral Dots
Authors: Joshi, Chandan; Bharti, Lokesh; Jaaffrey, S. N. A.
2008cosp...37.1411J Altcode: 2008cosp.meet.1411J
We present a study of magnetic fields in umbral dots (UDs) and its
consequences on the Joule heating of the UDs. Hamedivafa (2003)
studied the Joule heating using the vertical component of the
magnetic field. In this paper the magnetic field profile in the UDs
is investigated including a new azimuthal component of the magnetic
field which might explain a relatively large enhancement of Joule
heating causing higher brightness near the circumference of the UDs.
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Title: A High resolution study of Umbral Flashes and Running
penumbral waves
Authors: Joshi, Chandan; Bharti, Lokesh; Jaaffrey, S. N. A.
2008cosp...37.1410J Altcode: 2008cosp.meet.1410J
We present a study of intensity oscillations in sunspots using high
resolution ( temporal and spatial) CaII H data and Gband data from
Hinode. The intensity variations show increased power at 5.5mHz in umbra
and at 3.3mHz in penumbra. We also found that umbra does not oscillate
as a single element at above mentioned freqencies but there are several
elements in different phases, penumbra seems to oscillate as a whole in
same phase. An attempt was also made to find any relationship between
Gband mean intensity and oscillation power.
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Title: Observations of Dark Lanes in Umbral Fine Structure from the
Hinode Solar Optical Telescope: Evidence for Magnetoconvection
Authors: Bharti, Lokesh; Joshi, Chandan; Jaaffrey, S. N. A.
2007ApJ...669L..57B Altcode:
An analysis of high-resolution G-band images of active region NOAA
10930 is presented. The observations were recorded with the Broadband
Filter Imager (BFI) attached to the Solar Optical Telescope (SOT)
on board the Hinode mission. We observed dark lanes in umbral dots
up to six folds in larger ones. Formation of umbral dots from dark
core penumbral filament shows dark lanes. The evolution of the light
bridge from the dark core penumbral filament is observed, which further
disintegrates into umbral dots. These observations are compatible with
the simulations of three-dimensional radiative magnetoconvection with
gray radiative transfer in sunspot umbra by Schüssler & Vögler,
which support the notion that these structures appear as a result
of magnetoconvection.
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Title: Enhanced Joule Heating in Umbral Dots
Authors: Joshi, Chandan; Bharti, Lokesh; Jaaffrey, S. N. A.
2007SoPh..245..239J Altcode: 2007arXiv0705.1141J
We present a study of magnetic fields in umbral dots (UDs)
and its consequences on the Joule heating of the UDs. Hamedivafa
(Astron. Astrophys.407, 761, 2003) studied the Joule heating using the
vertical component of the magnetic field. In this paper the magnetic
field profile in the UDs is investigated by including a new azimuthal
component of the magnetic field that might explain a relatively
large enhancement of Joule heating causing higher brightness near the
circumference of the UDs.
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Title: Evidence for Magnetoconvection in Sunspot Umbral Dots
Authors: Bharti, Lokesh; Jain, Rajmal; Jaaffrey, S. N. A.
2007ApJ...665L..79B Altcode:
An analysis of high-resolution Dopplergrams and continuum images of NOAA
AR 8350 is presented. The observations were recorded with the universal
birefringent filter attached to the Dunn Solar Telescope at the National
Solar Observatory, Sunspot, New Mexico. We find upward velocity of
the order of 400 m s<SUP>-1</SUP> within umbral dots, surrounded
by downward velocity of the order of 300 m s<SUP>-1</SUP>. This
observation is compatible with the simulations of three-dimensional
radiative magnetoconvection with gray radiative transfer in sunspot
umbra by Schüssler & Vögler, which support the idea that umbral
dots appear as a result of magnetoconvection.
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Title: Detection of opposite polarities in a sunspot light bridge:
evidence of low-altitude magnetic reconnection
Authors: Bharti, Lokesh; Rimmele, Thomas; Jain, Rajmal; Jaaffrey,
S. N. A.; Smartt, R. N.
2007MNRAS.376.1291B Altcode: 2007astro.ph..1674B; 2007MNRAS.tmp..160B
A multiwavelength photometric analysis was performed in order to study
the sub-structure of a sunspot light bridge in the photosphere and
the chromosphere. Active region NOAA 8350 was observed on 1998 October
8. The data consist of a 100 min time series of 2D spectral scans of
the lines FeI 5576 Å, Hα 6563 Å, FeI 6302.5 Å, and continuum images
at 5571 Å. We recorded line-of-sight magnetograms in 6302.5 Å. The
observations were taken at the Dunn Solar Telescope at US National Solar
Observatory, Sacramento Peak. We find evidence for plasma ejection
from a light bridge followed by Ellerman bombs. Magnetograms of the
same region reveal opposite polarity in light bridge with respect to
the umbra. These facts support the notion that low-altitude magnetic
reconnection can result in the magnetic cancellation as observed in
the photosphere.
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Title: MHD Waves Observed in Isolated Bright Points
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2006ASPC..354...13B Altcode:
We examine oscillations in three isolated bright points co-temporal
and co-spatial in the photosphere and chromosphere in the G-band and
Ca IIK line. Wavelet analysis was performed to study waves packets of
traveling magnetohydrodynamic waves. In general, it is thought likely
that the photosphere oscillates in response to granular buffeting, but
it is also influenced strongly by the presence of magnetic fields. The
observed oscillations reveal evidence for kink-mode waves, traveling
up through the chromosphere and coupling with sausage-modes waves. This
provides a means for energy deposition in the upper chromosphere.
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Title: G-Band Bright Points and Photospheric Magnetic Fields
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2006ASPC..358...61B Altcode:
We present high resolution observations of magnetic flux concentrations
within a decaying active region near disk center. We recorded G-band
images, magnetograms, 2D spectral scan, and continuum images using the
Universal Birefringent Filter at the Dunn Solar Telescope. The main
results can be summarized as follows: The large-scale pattern of G-band
bright points flux in plages are highly correlated, on sub-arcsecond
scales; G-band bright points are cospatial and comorphous, with magnetic
elements in intergranular lanes. Magnetic elements are continually
advected into micropores by the photospheric flow field. We observed
narrow (<0.25 arcsec) channels or sheets of downflowing plasma
around bright points and micropores. This downflowing plasma shows
accelerating nature in deeper layers of solar atmosphere. Upflow and
downflow events are found within bright points while micropores show
upflow. We compare our results with theoretical model predictions.
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Title: Intensity and Velocity Oscillations in Magnetic Flux
Concentrations (P9)
Authors: Bharti, L.; Rimmele, Thomas
2006ihy..workE.101B Altcode:
We analyzed intensity and velocity oscillations in magnetic network
using high-resolution 2D spectral scan images from Interferometric
Bi- dimensional Spectrometer (IBIS). In photosphere, oscillations in
intensity and velocity in 2-5.2 mHz band shows reduced amplitude while
at higher frequencies 5.2-7.0 mHz and 7.3-25.8 mHz band oscillations
amplitude enhance in line core intensity and shows reduced amplitude
in line core velocity however in chromosphere the oscillations
have different character, we found higher power in 2-5.2 mHz,
5.2-7.0 mHz and 7.3-25.8 mHz band in core velocity compared to core
intensity. Amplitude variation with height is also inferred from our
analysis. These findings are manifestation of high frequencies halos
around strong flux concentrations (pores) in intermediate field strength
network and mode conversion of solar p-modes in magnetic fields.
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Title: Plasma Flow In And Around Magnetic Flux Concentrations
Authors: Bharti, Lokesh; Jain, Rajmal; Joshi, Chanda; Jaaffrey,
S. N. A.
2006IAUJD...3E..37B Altcode:
Introduction: The interaction of magnetic fields and plsma flows is one
of the fundamental physical processes that leads to many of the dynamic
effects observed on the Sun. The present work aims at the correlation
of physical quantities such as line of sight magnetic field strength
and the bisector velocity at small spatial scales. Methods: We have
observed a solar region NOAA 8350 on 1998 October 8 with Universal
Birefringent Filter (UBF) in 5576 Å, 6563 Å, 5571 Å continuum
and line of sight magnetogram in 6302 Åsimultaneously with G-band
images. Bisector velocities were measured for 5576 Å line. Results:
Our data analysis reveals that bright points and flux sheets associated
to upward and downward motions while micropores and pores associated to
upward motions. These flux concentrations shows accelerated motions in
deeper layers. Discussion: Upward and downward motions within magnetic
flux concentrations is probably due to there dynamic behaviour.
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Title: Soft and hard X-ray emission from solar flares observed by
Solar X-ray Spectrometer (SOXS) mission
Authors: Jain, R.; Bharti, L.
2006cosp...36..635J Altcode: 2006cosp.meet..635J
Solar X-ray Spectrometer SOXS mission was launched on 08 May 2003
onboard Indian spacecraft to study the energy release and particle
acceleration in solar flares in the energy range 4-55 keV To achieve
the high spectral resolution Si and CZT detectors were employed We
present the temporal and spectral characteristics of soft and hard X-ray
emission from 18 M-class flares observed by SOXS mission during 2003
and 2005 We present the line emission characteristics of Fe and Fe Ni
features and show the variation of equivalent width and peak energy as
a function of temperature which is interpreted as emission contribution
of different ionic lines vary with temperature The hard X-ray spectra
enabled us to measure the break energy between thermal and non-thermal
components as a function of flare duration that allowing determining the
contribution of accelerated particles in the flares We also analyzed
a few flares associated with CMEs and found that the associated CME
is the cause for the flare and not the consequence of the flare
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Title: Solar X-ray Spectrometer (SOXS) mission: Observations and
new results
Authors: Jain, R.; Bhatt, N. J.; Bharti, L.
2006ilws.conf...54J Altcode:
We present the observations and recently obtained new results from the
"Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard
GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study
the solar flares. The state-of-the-art solid state detectors viz. Si
PIN and Cadmium-Zinc-Telluride (CZT) were employed that operate at
near room temperature (-20 0C). The dynamic energy range of the Si
PIN and CZT detectors are 4-25 keV and 4-56 keV, respectively. The
Si PIN has sub-keV energy resolution while the CZT has about 1.7 keV
energy resolutions throughout the dynamic range. The high sensitivity
and sub-keV energy resolution of Si PIN detector allows for measuring
the intensity, and equivalent width (w) of the Fe-line and Fe/Ni-line
complexes at approximately 6.7 and 8.0 keV as a function of time. We
present the results related to the Fe-line complex obtained from the
study of 10 M-class flares observed by the SOXS mission. We found that
the equivalent width (w) of the Fe-line feature increases exponentially
with temperature up to 25 MK but later it increases very slowly up
to 35 Mk and then it remains constant up to 45 MK. We compare our
measurements of w of the Fe line feature with calculations made earlier
by various investigators and propose that these measurements may improve
theoretical models. We interpret the variation of w with temperature
as the changes in the ionization and recombination conditions in
the plasma during the flare interval, and, as a consequence, the
contribution from different ionic emission lines also varies.
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Title: The Solar Flare and CME Induced as a Collision of Two Opposite
Polarities on 1997 May 12
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2005ASPC..346..327B Altcode:
The multispectral observations of active region NOAA 8038 during 10-13
May 1997 are presented. The observations of MDI/SOHO magnetograms show
that in this active region continual but discrete growth and decay of
magnetic field was taking place indicating either continuous evolution
of magnetic flux or emergence of new flux region. The movie of these
magnetograms reveal two important results that the major opposite
polarities of pre-existing region were approaching towards each other,
and a small north polarity flux i.e. moving magnetic feature (MMF)
was ejecting out from major north polarity at a quasi-periodicity
of about 10 hrs during 10-13 May 1997. It appears that as a result
of flux cancellation by one such ejected north polarity flux with
a newly emerged south polarity flux around 04:30 UT on 12 May 1997,
a moderate but long enduring 1B/C1.3 solar flare. The observation in
Hα is presented in detail.
---------------------------------------------------------
Title: MHD Waves Observed in Isolated Brightpoints
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2005ESASP.600E..79B Altcode: 2005dysu.confE..79B; 2005ESPM...11...79B
No abstract at ADS
---------------------------------------------------------
Title: MHD Waves Propogation and Heating of Solar Atmosphere
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N.
2005AGUSMSH12A..04B Altcode:
We examine oscillations in isolated three bright points co-temporal
and co-spatial in photosphere and chromosphere in G-band and Ca II
K line. Wavelet analysis was used to study wave packets and identify
traveling magnetohydrodynamic waves. In general, it is thought likely
that the photosphere and chromosphere oscillates in response to forcing
by p-modes and granular buffeting, but they are also influenced strongly
by presence of magnetic fields. The observed oscillations reveals
evidence for kink-mode waves, traveling up through the chromosphere
and coupling with sausage-modes waves. This provides a means for energy
depositing in the upper chromosphere.
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Title: CME and associated phenomena on May 12, 1997
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N.
2005AGUSMSH51C..05B Altcode:
The multispectral observations of NOAA active region No. 8038 during
10-13 May 1997 are presented. The observations of MDI/SOHO magnetograms
show that in this active region continual but discrete growth and
decay of magnetic field was taking place indicating either continuous
evolution of magnetic flux or emergence of new flux region. The
movie of these magnetograms reveal two important results that the
major opposite polarities of pre-existing region were approaching
towards each other, and a small north polarity flux i.e. moving
magnetic feature (MMF) was ejecting out from major north polarity
at a quasi-periodicity of about 10 hrs during 10-13 May 1997. It
appears that as a result of flux cancellation by one such ejected
north polarity flux with a newly emerged south polarity flux around
04:30 UT on 12 May 1997, a blast wave generated, seen by EIT/SOHO,
producing CME and a moderate but long enduring 1B/C1.3 solar flare. The
observations in Hα, soft X-ray, hard X-ray, ionospheric absorption,
radio and interplanetary scintillations in association to this flare
are presented in detail.. The multiwavelength observations of the
flare showed occurrence of at least two phases of energy release,
first at 04:42 and second at 04:47 UT. We propose a qualitative
model to interpret the observations, which, however, also explains
the generation of CME and associated flare with two stages of energy
release. The occurrence of type II radio burst at 04:54 UT was perhaps
due to shock produced by the plasmoid erupted during second energy
release at higher altitude in the corona. It appears that the plasmoid
traversed through shock in the interplanetary medium so as to enhance
the scintillation index on 14 May as inferred from IPS observations.
---------------------------------------------------------
Title: H_α Intensity Oscillations in Solar Flares
Authors: Jain, R.; Tripathy, S.; Bharti, L.; Kumar, B.
1999ASPC..183..531J Altcode: 1999hrsp.conf..531J
No abstract at ADS
---------------------------------------------------------
Title: High energy photons detection using scintillation counter
during total solar eclipse of October 24, 1995.
Authors: Jaaffrey, S. N. A.; Jain, R.; Pandya, A.; Bharti, L.
1997KodOB..13..235J Altcode:
The authors report the first observations of absorption and enhancement
in flux of high energy photons during the total solar eclipse of
October 24, 1995. For the purpose of these observations, they employed
a scintillation counter to detect high energy radiation in the energy
range of 10 keV to 5 MeV. The authors interpret the absorption in the
flux below 300 keV due to the passage of the Moon between the Sun and
the Earth, while enhancement above 300 keV could have occurred due to
the production of secondary radiations from high energy photons.
