maurya

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Author name code: maurya
ADS astronomy entries on 2022-09-14
author:"Maurya, Ram Ajor"

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Title: Magnetic and Velocity Field Topology in Active Regions of
Descending Phase of Solar Cycle 23
Authors: Maurya, R. A.; Ambastha, A.
2020SoPh..295..106M Altcode: 2020arXiv200613602M
We analyze the topology of photospheric magnetic fields and
sub-photospheric flows of several active regions (ARs) that are
observed during the peak to descending phase of Solar Cycle 23. Our
analysis shows clear evidence of hemispheric preferences in all the
topological parameters such as the magnetic, current and kinetic
helicities, and the `curl-divergence'. We found that 68%(67%) ARs in
the northern (southern) hemisphere with negative (positive) magnetic
helicity. Same hemispheric preference sign is found for the current
helicity in 68%(68%) ARs. The hemispheric preferences are found to exist
statistically for all the time except in a few ARs observed during the
peak and the end phases of the solar cycle. This means that magnetic
fields are dominantly left(right)-helical in scales smaller than
individual ARs of northern(southern) hemisphere. We found that magnetic
and current helicity parameters show equatorward propagation similar
to the sunspot cycle. The kinetic helicity showed similar hemispheric
trend to that of magnetic and current helicity parameters. There are
65%(56%) ARs with negative (positive) kinetic helicity as well as
divergence-curl, at the depth of 2.4 Mm, in the northern (southern)
hemisphere. The hemispheric preference of the kinetic helicity
becomes more evident at larger depths, e.g., 69%(67%) at the depth
of 12.6 Mm. A similar hemispheric trend of kinetic helicity to that
of the current helicity supports the mean-field dynamo model. We also
found that the hemispheric preference of all the parameters increases
with the field strength of ARs. The topology of photospheric magnetic
fields and near-surface sub-photospheric flow fields did not show good
association but the correlation between them enhances with depths,
which could be indicating more aligned flows at deeper layers of ARs.

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Title: Multi-wavelength view of an M2.2 solar flare on 26 november
2000
Authors: Chandra, R.; Verma, V. K.; Rani, S.; Maurya, R. A.
2017NewA...51..105C Altcode: 2016arXiv160805796C
In this paper, we present a study of an M2.2 class solar flare of
26 November 2000 from NOAA AR 9236. The flare was well observed
by various ground based observatories (ARIES, Learmonths Solar
Observatory) and space borne instruments (SOHO, HXRS, GOES) in
time interval between 02:30 UT to 04:00 UT. The flare started with
long arc-shape outer flare ribbon. Afterwards the main flare starts
with two main ribbons. Initially the outer ribbons start to expand
with an average speed (∼20 km s-1) and later it shows
contraction. The flare was associated with partial halo coronal mass
ejection (CMEs) which has average speed of 495 km s-1. The
SOHO/MDI observations show that the active region was in quadrupolar
magnetic configuration. The flux cancellation was observed before the
flare onset close to flare site. Our analysis indicate the flare was
initiated by the magnetic breakout mechanism.

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Title: Strong Blue Asymmetry in Hα Line as a Preflare Activity
Authors: Cho, Kyuhyoun; Lee, Jeongwoo; Chae, Jongchul; Wang, Haimin;
Ahn, Kwangsu; Yang, Heesu; Lim, Eun-kyung; Maurya, Ram Ajor
2016SoPh..291.2391C Altcode: 2016SoPh..tmp..131C; 2020arXiv200506404C
Chromospheric activities before solar flares provide important clues
to the mechanisms that initiate solar flares, but are as yet poorly
understood. We report a significant and rapid Hα line broadening
before the solar flare SOL2011-09-29T18:08 that was detected using
the unprecedented high-resolution Hα imaging spectroscopy with the
Fast Imaging Solar Spectrograph (FISS) installed on the 1.6 m New
Solar Telescope (NST) at Big Bear Solar Observatory. The strong Hα
broadening extends as a blue excursion up to −4.5 Å and as a red
excursion up to 2.0 Å, which implies a mixture of velocities in the
range of −130 kms−1 to 38 km s−1 derived
by applying the cloud model, comparable to the highest chromospheric
motions reported before. The Hα blueshifted broadening lasts for
about six minutes and is temporally and spatially correlated with the
start of a rising filament, which is later associated with the main
phase of the flare as detected by the Atmosphere Imaging Assembly (AIA)
onboard the Solar Dynamics Observatory (SDO). The potential importance
of this Hα blueshifted broadening as a preflare chromospheric activity
is briefly discussed within the context of the two-step eruption model.

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Title: Fundamental-mode Oscillations of Two Coronal Loops within a
Solar Magnetic Arcade
Authors: Jain, Rekha; Maurya, Ram A.; Hindman, Bradley W.
2015ApJ...804L..19J Altcode: 2015arXiv150407822J
We analyze intensity variations, as measured by the Atmospheric Imaging
Assembly in the 171 Å passband, in two coronal loops embedded within
a single coronal magnetic arcade. We detect oscillations in the
fundamental mode with periods of roughly 2 minutes and decay times
of 5 minutes. The oscillations were initiated by interaction of the
arcade with a large wavefront issuing from a flare site. Further,
the power spectra of the oscillations evince signatures consistent
with oblique propagation to the field lines and for the existence of
a two-dimensional waveguide instead of a one-dimensional one.

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Title: On the Association of Topologies of the Photospheric Magnetic
Fields and Sub-photospheric Flows of Active Regions
Authors: Maurya, Ram Ajor
2014cosp...40E2042M Altcode:
Solar magnetic fields are believed to be generated near the solar
tachocline jointly by differential rotation and turbulent motion,
which are further transported toward the photosphere by convective
flows. Therefore, we expect linear correlation between the topologies
of the photospheric magnetic fields and the sub-photospheric flows. If
observed magnetic fields conserve their helicity when they rise
through the convection zone, the variation of kinetic helicity in the
convection zone may be used as an observational tool for study the solar
interior. Another important aspect of studying these parameters is due
to their role in the energetic transients, e.g., flares and CMES. In
order to examine the correlation between the two kinds of topologies,
we analysed the photospheric and sub-photospheric properties of
several active regions of the solar cycle 23 and 24. We computed the
near sub-photospheric flows and topology parameters (e.g., vorticity,
kinetic helicity) using local heliosiesmic techniques employed to the
Doppler velocity observations. The photospheric magnetic field topology
parameters, e.g., magnetic and current helicities, were determined from
the magnetic field observations. We found opposite hemispheric trend
in the topologies of the sub-photospheric flows and the photospheric
magnetic fields. Details of the analysis will be presented in the paper.

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Title: Activity-related variations of high-degree p-mode amplitude,
width, and energy in solar active regions
Authors: Maurya, R. A.; Ambastha, A.; Chae, J.
2014A&A...561A.123M Altcode: 2013arXiv1310.6458M
Context. Solar energetic transients such as flares and coronal mass
ejections occur mostly within active regions (ARs) and release large
amounts of energy, which is expected to excite acoustic waves by
transferring the mechanical impulse of the thermal expansion of the
flare on the photosphere. On the other hand, strong magnetic fields of
AR sunspots absorb the power of the photospheric oscillation modes. Aims: We study the properties of high-degree p-mode oscillations in
flaring and dormant ARs and compare them with those in corresponding
quiet regions (QRs) to find the association of the mode parameters with
magnetic- and flare-related activities. Methods: We computed the
mode parameters using the ring-diagram technique. The magnetic-activity
indices (MAIs) of ARs and QRs were determined from the line-of-sight
magnetograms. The flare indices (FIs) of ARs were obtained from the GOES
X-ray fluxes. Mode parameters were corrected for foreshortening, duty
cycle, and MAI using multiple non-linear regression. Results:
Our analysis of several flaring and dormant ARs observed during the
Carrington rotations 1980-2109 showed a strong association of the mode
amplitude, width, and energy with magnetic and flare activities,
although their changes are combined effects of foreshortening,
duty cycle, magnetic-activity, flare-activity, and measurement
uncertainties. We find that the largest reduction in mode amplitude
and background power of an AR are caused by the angular distance of
the AR from the solar disc centre. After correcting the mode parameters
for foreshortening and duty cycle, we find that the mode amplitudes of
flaring and dormant ARs are lower than in corresponding QRs reducing
with increasing MAI, suggesting a stronger mode power suppression in
ARs with larger magnetic fields. The mode widths in ARs are larger
than in corresponding QRs and increase with MAI, indicating shorter
lifetimes of modes in ARs than in QRs. The variations in mode amplitude
and width with MAI are not same in different frequency bands. The
largest amplification (reduction) in mode amplitude (mode width) of
dormant ARs is found in the five-minute frequency band. The average
mode energy of both the flaring and dormant ARs is smaller than in
their corresponding QRs, reducing with increasing MAI. But the average
mode energy reduction rate in flaring ARs is smaller than in dormant
ARs. Moreover, the increase in mode width rate in dormant (flaring)
ARs is followed by a decrease (increase) in the amplitude variation
rate. Furthermore, including the mode corrections for MAI shows that
mode amplitude and mode energy of flaring ARs escalate with FI, while
the mode width shows an opposite trend, suggesting excitations of modes
and growth in their lifetimes by flares. The increase (decrease) in mode
amplitude (width) is larger in the five-minute and higher-frequency
bands. The enhancement in width variation rate is followed by a rapid
decline in the amplitude variation rate.

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Title: Chromospheric Doppler Velocity Oscillations in a Sunspot
Authors: Maurya, R. A.
2013ASPC..478..339M Altcode: 2013arXiv1310.6462M
We analyse the chromospheric Doppler velocity oscillations in a sunspot
using the high resolution spectral observations obtained from the Fast
Imaging Solar Spectrograph (FISS) of the New Solar Telescope at the
Big Bear Solar Observatory. The Doppler velocity maps are constructed
from the bisectors of the spectral observations. We find that the peak
power frequency decreases gradually from the umbra to outward.

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Title: Seismology of Flaring and Dormant Active Regions
Authors: Maurya, R. A.
2013ASPC..478..231M Altcode: 2013arXiv1310.6464M
We study photospheric and sub-photospheric properties of active and
quiet regions observed during 11 - 17 February 2011 including the
first X-class flare X2.2 of the solar cycle 24 which occurred in the
active region NOAA 11158 on 15 February 2011. The p-mode parameters
and sub-photospheric flows are computed from the ring-diagrams and
inversions. We found larger frequency shifts in active regions than
quiet regions. The active region NOAA 11158 shows stronger twisted
sub-photospheric flows than dormant active regions. The kinetic helicity
density of sub-photospheric flows of the active region NOAA 11158 shows
different structure on the flare day than the pre- and post-flare days.

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Title: Temperature of Solar Prominences Obtained with the Fast Imaging
Solar Spectrograph on the 1.6 m New Solar Telescope at the Big Bear
Solar Observatory
Authors: Park, Hyungmin; Chae, Jongchul; Song, Donguk; Maurya, Ram
Ajor; Yang, Heesu; Park, Young-Deuk; Jang, Bi-Ho; Nah, Jakyoung; Cho,
Kyung-Suk; Kim, Yeon-Han; Ahn, Kwangsu; Cao, Wenda; Goode, Philip R.
2013SoPh..288..105P Altcode:
We observed solar prominences with the Fast Imaging Solar Spectrograph
(FISS) at the Big Bear Solar Observatory on 30 June 2010 and 15 August
2011. To determine the temperature of the prominence material, we
applied a nonlinear least-squares fitting of the radiative transfer
model. From the Doppler broadening of the Hα and Ca II lines, we
determined the temperature and nonthermal velocity separately. The
ranges of temperature and nonthermal velocity were 4000 - 20 000 K and
4 - 11 km s−1. We also found that the temperature varied
much from point to point within one prominence.

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Title: Velocities and Temperatures of an Ellerman Bomb and Its
Associated Features
Authors: Yang, Heesu; Chae, Jongchul; Lim, Eun-Kyung; Park, Hyungmin;
Cho, Kyuhyoun; Maurya, Ram Ajor; Song, Donguk; Kim, Yeon-Han; Goode,
Philip R.
2013SoPh..288...39Y Altcode:
We investigated the velocity and temperature characteristics of an
Ellerman bomb (EB) and its associated features based on observations
made with the Fast Imaging Solar Spectrograph (FISS) and a broadband
TiO filter of the 1.6 meter New Solar Telescope at Big Bear Solar
Observatory. In the TiO images of the photospheric level, we found a
granular cell expanding in two opposite directions near the site of the
EB. When one end of this granule reached the EB site, the transverse
speed of the tip of the expanding granule rapidly decreased and the EB
brightened. The wings of the Hα profile of the EB indicated that the
EB was blueshifted up to 7 km s−1. About 260 s after the EB
brightening, a surge was seen in absorption and varied from a blueshift
of 20 km s−1 to a redshift of 40 km s−1 seen
in the Hα and Ca II 8542 Å lines. From the Doppler absorption width
of the two lines determined by applying the cloud model, we estimated
the mean temperature of the surge material to be about 29000 K and the
mean speed of nonthermal motion to be about 11 km s−1. We
discuss the physical implications of our results in terms of magnetic
reconnection and processes related to it.

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Title: Chromospheric Sunspot Oscillations in Hα and Ca II 8542 Å
Authors: Maurya, Ram Ajor; Chae, Jongchul; Park, Hyungmin; Yang,
Heesu; Song, Donguk; Cho, Kyuhyoun
2013SoPh..288...73M Altcode:
We study chromospheric oscillations including umbral flashes and running
penumbral waves in a sunspot of active region NOAA 11242 using scanning
spectroscopy in Hα and Ca II 8542 Å with the Fast Imaging Solar
Spectrograph (FISS) at the 1.6 meter New Solar Telescope at the Big Bear
Solar Observatory. A bisector method is applied to spectral observations
to construct chromospheric Doppler-velocity maps. Temporal-sequence
analysis of these shows enhanced high-frequency oscillations inside
the sunspot umbra in both lines. Their peak frequency gradually
decreases outward from the umbra. The oscillation power is found to be
associated with magnetic-field strength and inclination, with different
relationships in different frequency bands.

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Title: Helicity injection by flux motions and its role in flare
and CMEs
Authors: Panditi, Vemareddy; Ambastha, A.; Maurya, R.; Chae, J.;
Ambstha, A.; Maurya, R. A.; Chae, J.
2013SPD....4430003P Altcode:
An investigation of helicity injection by photospheric shear motions
is carried out for two active regions (ARs), NOAA 11158 and 11166,
using line-of-sight magnetic field observations obtained from
the Helioseismic and Magnetic Imager on board the Solar Dynamics
Observatory. We derived the horizontal velocities in the ARs from the
differential affine velocity estimator (DAVE) technique. Persistent
strong shear motions at maximum velocities in the range of 0.6-0.9
km s-1 along the magnetic polarity inversion line and outward flows
from the peripheral regions of the sunspots were observed in the two
ARs. The helicities injected in NOAA 11158 and 11166 during their
six-day evolution period were estimated as 14.16x10$^42$ Mx$^2$
and 9.5x10$^42$ Mx$^2$, respectively. The estimated injection rates
decreased up to 13% by increasing the time interval between the
magnetograms from 12 minutes to 36 minutes, and increased up to 9%
by decreasing the DAVE window size from 21x18 to 9x6 pixel$^2$,
resulting in 10% variation in the accumulated helicity. In both
ARs, the flare-prone regions (R2) had inhomogeneous helicity flux
distribution with mixed helicities of both signs and coronal mass
ejection (CME) prone regions had almost homogeneous distribution of
helicity flux dominated by a single sign. The temporal profiles of
helicity injection showed impulsive variations during some flares/CMEs
due to negative helicity injection into the dominant region of positive
helicity flux. A quantitative analysis reveals a marginally significant
association of helicity flux with CMEs but not flares in AR 11158,
while for the AR 11166, we find a marginally significant association
of helicity flux with flares but not CMEs, providing evidence of the
role of helicity injection at localized sites of the events. These
short-term variations of helicity flux are further discussed in
view of possible flare-related effects. This study suggests that flux
motions and spatial distribution of helicity injection are important to
understanding the complex nature of the magnetic flux system of the AR,
and how it can lead to conditions favorable for eruptive events.

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Title: On the Role of Rotating Sunspots in the Activity of Solar
Active Region NOAA 11158
Authors: Panditi, Vemareddy; Ambastha, A.; Maurya, R.
2013SPD....44..120P Altcode:
We study the role of rotating sunspots in relation to the evolution
of various physical parameters characterizing the non-potentiality
of the active region (AR) NOAA 11158 and its eruptive events using
the magnetic field data from the Helioseismic and Magnetic Imager
(HMI) and multi-wavelength observations from the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory. From the
evolutionary study of HMI intensity and AIA channels, it is observed
that the AR consists of two major rotating sunspots, one connected
to a flare-prone region and another with coronal mass ejection
(CME). The constructed space-time intensity maps reveal that the
sunspots exhibited peak rotation rates coinciding with the occurrence of
major eruptive events. Further, temporal profiles of twist parameters,
namely, average shear angle, αav, αbest, derived from HMI vector
magnetograms, and the rate of helicity injection, obtained from the
horizontal flux motions of HMI line-of-sight magnetograms, correspond
well with the rotational profile of the sunspot in the CME-prone
region, giving predominant evidence of rotational motion causig
magnetic non-potentiality. Moreover, the mean value of free energy
from the virial theorem calculated at the photospheric level shows
a clear step-down decrease at the onset time of the flares revealing
unambiguous evidence of energy release intermittently that is stored
by flux emergence and/or motions in pre-flare phases. Additionally,
distribution of helicity injection is homogeneous in the CME-prone
region while in the flare-prone region it is not and often changes
sign. This study provides a clear picture that both proper and
rotational motions of the observed fluxes played significant roles
in enhancing the magnetic non-potentiality of the AR by injecting
helicity, twisting the magnetic fields and thereby increasing the free
energy, leading to favorable conditions for the observed transient
activity.Abstract (2,250 Maximum Characters): We study the role of
rotating sunspots in relation to the evolution of various physical
parameters characterizing the non-potentiality of the active region
(AR) NOAA 11158 and its eruptive events using the magnetic field data
from the Helioseismic and Magnetic Imager (HMI) and multi-wavelength
observations from the Atmospheric Imaging Assembly (AIA) on board
the Solar Dynamics Observatory. From the evolutionary study of HMI
intensity and AIA channels, it is observed that the AR consists of
two major rotating sunspots, one connected to a flare-prone region and
another with coronal mass ejection (CME). The constructed space-time
intensity maps reveal that the sunspots exhibited peak rotation rates
coinciding with the occurrence of major eruptive events. Further,
temporal profiles of twist parameters, namely, average shear angle,
αav, αbest, derived from HMI vector magnetograms, and the rate of
helicity injection, obtained from the horizontal flux motions of HMI
line-of-sight magnetograms, correspond well with the rotational profile
of the sunspot in the CME-prone region, giving predominant evidence
of rotational motion causig magnetic non-potentiality. Moreover,
the mean value of free energy from the virial theorem calculated at
the photospheric level shows a clear step-down decrease at the onset
time of the flares revealing unambiguous evidence of energy release
intermittently that is stored by flux emergence and/or motions in
pre-flare phases. Additionally, distribution of helicity injection is
homogeneous in the CME-prone region while in the flare-prone region
it is not and often changes sign. This study provides a clear picture
that both proper and rotational motions of the observed fluxes played
significant roles in enhancing the magnetic non-potentiality of the
AR by injecting helicity, twisting the magnetic fields and thereby
increasing the free energy, leading to favorable conditions for the
observed transient activity.

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Title: Rotating sunspots and their role in the activity of solar
active region NOAA 11158
Authors: Vemareddy, P.; Ambastha, A.; Maurya, R. A.
2013enss.confE...6V Altcode:
We study the role of rotating sunspots in relation to the evolution
of various physical parameters characterizing the non-potentiality of
the active region (AR) NOAA 11158 and its eruptive events using the
magnetic field data from the Helioseismic and Magnetic Imager (HMI)
and multi-wavelength observations from the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamics Observatory. From the evolutionary
study of HMI intensity and AIA channels, it is observed that the AR
consists of two major rotating sunspots, one connected to a flare-prone
region and another with coronal mass ejection (CME). The constructed
space-time intensity maps reveal that the sunspots exhibited peak
rotation rates coinciding with the occurrence of major eruptive
events. Further, temporal profiles of twist parameters, namely,
average shear angle, α_{av}, α_{best}, derived from HMI vector
magnetograms, and the rate of helicity injection, obtained from the
horizontal flux motions of HMI line-of-sight magnetograms, correspond
well with the rotational profile of the sunspot in the CME-prone
region, giving predominant evidence of rotational motion causing
magnetic non-potentiality. Moreover, the mean value of free energy
from the virial theorem calculated at the photospheric level shows
a clear step-down decrease at the onset time of the flares revealing
unambiguous evidence of energy release intermittently that is stored
by flux emergence and/or motions in pre-flare phases. Additionally,
distribution of helicity injection is homogeneous in the CME-prone
region while in the flare-prone region it is not and often changes
sign. This study provides a clear picture that both proper and
rotational motions of the observed fluxes played significant roles in
enhancing the magnetic non-potentiality of the AR by injecting helicity,
twisting the magnetic fields and thereby increasing the free energy,
leading to favorable conditions for the observed transient activity.

---------------------------------------------------------
Title: Helicity Injection by the Shearing Motion of Fluxes in Relation
to Flares and Coronal Mass Ejections
Authors: Vemareddy, P.; Ambastha, A.; Maurya, R. A.; Chae, J.
2013enss.confE...8V Altcode:
An investigation of helicity injection by photospheric shear motions is
carried out for two active regions (ARs), NOAA 11158 and 11166, using
line-of-sight magnetic field observations obtained from the Helioseismic
and Magnetic Imager on board the Solar Dynamics Observatory. We derived
the horizontal velocities in the ARs from the differential affine
velocity estimator (DAVE) technique. Persistent strong shear motions at
maximum velocities in the range of 0.6-0.9 km s^{-1} along the magnetic
polarity inversion line and outward flows from the peripheral regions
of the sunspots were observed in the two ARs. The helicities injected
in NOAA 11158 and 11166 during their six-day evolution period were
estimated as 14.16x10^{42} Mx^2 and 9.5×10^{42} Mx^2, respectively. The
estimated injection rates decreased up to 13% by increasing the time
interval between the magnetograms from 12 minutes to 36 minutes, and
increased up to 9% by decreasing the DAVE window size from 21×18 to
9×6 pixel2, resulting in 10% variation in the accumulated helicity. In
both ARs, the flare-prone regions (R2) had inhomogeneous helicity
flux distribution with mixed helicities of both signs and coronal
mass ejection (CME) prone regions had almost homogeneous distribution
of helicity flux dominated by a single sign. The temporal profiles of
helicity injection showed impulsive variations during some flares/CMEs
due to negative helicity injection into the dominant region of positive
helicity flux. A quantitative analysis reveals a marginally significant
association of helicity flux with CMEs but not flares in AR 11158,
while for the AR 11166, we find a marginally significant association
of helicity flux with flares but not CMEs, providing evidence of the
role of helicity injection at localized sites of the events. These
short-term variations of helicity flux are further discussed in
view of possible flare-related effects. This study suggests that flux
motions and spatial distribution of helicity injection are important to
understanding the complex nature of the magnetic flux system of the AR,
and how it can lead to conditions favorable for eruptive events.

---------------------------------------------------------
Title: Chromospheric Waves and Oscillations in Sunspots
Authors: Maurya, R. A.; Chae, J.
2013enss.confE..45M Altcode:
We studied the chromospheric oscillations in and around a sunspot
of the active region NOAA 11242 using high spectral and spatial
resolution observations in the spectral lines Hα and Ca II 8542Å
obtained from the Fast Imaging Solar Spectrograph (FISS) of 1.6 meter
New Solar Telescope (NST) at Big Bear Solar Observatory. A suitable
bisector method is applied to the spectral observations, to construct
the chromospheric Doppler Velocity maps. Time series analysis of
Doppler maps, in both the spectral bands, revealed enhanced high
frequency oscillations inside the umbra of the sunspot. The frequency
of oscillations gradually decreases from the umbra to outward. We have
found clear evidence of two boundaries for the peak power frequency
transformation, one of which occurs close to the umbral and penumbral
boundary, and the other near the penumbral and super-penumbral boundary
of the sunspot. The oscillation power is found to be associated with
magnetic field strength and inclination, although they showed different
relationships in different frequency bands.

---------------------------------------------------------
Title: On the Role of Rotating Sunspots in the Activity of Solar
Active Region NOAA 11158
Authors: Vemareddy, P.; Ambastha, A.; Maurya, R. A.
2012ApJ...761...60V Altcode: 2012arXiv1210.3912V
We study the role of rotating sunspots in relation to the evolution
of various physical parameters characterizing the non-potentiality
of the active region (AR) NOAA 11158 and its eruptive events using
the magnetic field data from the Helioseismic and Magnetic Imager
(HMI) and multi-wavelength observations from the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory. From the
evolutionary study of HMI intensity and AIA channels, it is observed
that the AR consists of two major rotating sunspots, one connected to
a flare-prone region and another with coronal mass ejection (CME). The
constructed space-time intensity maps reveal that the sunspots exhibited
peak rotation rates coinciding with the occurrence of major eruptive
events. Further, temporal profiles of twist parameters, namely, average
shear angle, αav, αbest, derived from HMI vector
magnetograms, and the rate of helicity injection, obtained from the
horizontal flux motions of HMI line-of-sight magnetograms, correspond
well with the rotational profile of the sunspot in the CME-prone
region, giving predominant evidence of rotational motion causing
magnetic non-potentiality. Moreover, the mean value of free energy
from the virial theorem calculated at the photospheric level shows
a clear step-down decrease at the onset time of the flares revealing
unambiguous evidence of energy release intermittently that is stored
by flux emergence and/or motions in pre-flare phases. Additionally,
distribution of helicity injection is homogeneous in the CME-prone
region while in the flare-prone region it is not and often changes
sign. This study provides a clear picture that both proper and
rotational motions of the observed fluxes played significant roles in
enhancing the magnetic non-potentiality of the AR by injecting helicity,
twisting the magnetic fields and thereby increasing the free energy,
leading to favorable conditions for the observed transient activity.

---------------------------------------------------------
Title: On the Injection of Helicity by the Shearing Motion of Fluxes
in Relation to Flares and Coronal Mass Ejections
Authors: Vemareddy, P.; Ambastha, A.; Maurya, R. A.; Chae, J.
2012ApJ...761...86V Altcode: 2012arXiv1202.5195V
An investigation of helicity injection by photospheric shear motions is
carried out for two active regions (ARs), NOAA 11158 and 11166, using
line-of-sight magnetic field observations obtained from the Helioseismic
and Magnetic Imager on board the Solar Dynamics Observatory. We derived
the horizontal velocities in the ARs from the differential affine
velocity estimator (DAVE) technique. Persistent strong shear motions at
maximum velocities in the range of 0.6-0.9 km s-1 along the
magnetic polarity inversion line and outward flows from the peripheral
regions of the sunspots were observed in the two ARs. The helicities
injected in NOAA 11158 and 11166 during their six-day evolution
period were estimated as 14.16 × 1042 Mx2 and
9.5 × 1042 Mx2, respectively. The estimated
injection rates decreased up to 13% by increasing the time interval
between the magnetograms from 12 minutes to 36 minutes, and increased
up to 9% by decreasing the DAVE window size from 21 × 18 to 9 ×
6 pixel2, resulting in 10% variation in the accumulated
helicity. In both ARs, the flare-prone regions (R2) had inhomogeneous
helicity flux distribution with mixed helicities of both signs and
coronal mass ejection (CME) prone regions had almost homogeneous
distribution of helicity flux dominated by a single sign. The temporal
profiles of helicity injection showed impulsive variations during
some flares/CMEs due to negative helicity injection into the dominant
region of positive helicity flux. A quantitative analysis reveals
a marginally significant association of helicity flux with CMEs but
not flares in AR 11158, while for the AR 11166, we find a marginally
significant association of helicity flux with flares but not CMEs,
providing evidence of the role of helicity injection at localized
sites of the events. These short-term variations of helicity flux
are further discussed in view of possible flare-related effects. This
study suggests that flux motions and spatial distribution of helicity
injection are important to understanding the complex nature of the
magnetic flux system of the AR, and how it can lead to conditions
favorable for eruptive events.

---------------------------------------------------------
Title: On the Injection of Helicity by Shearing Motion of Fluxes in
Relation to Flares and CMEs
Authors: Panditi, Vemareddy; Ambastha, Ashok; Maurya, Ram Ajor
2012cosp...39.1440P Altcode: 2012cosp.meet.1440P
An investigation of helicity injection by photospheric shear motions
is presented for two active regions (ARs) NOAA 11158 and 11166,
using line-of-sight magnetic field observations obtained from
the Helioseismic and magnetic Imager (HMI) on-board Solar Dynamics
Observatory (SDO). We derived the horizontal flux velocities in the ARs
from Differential Affine Velocity Estimator (DAVE) technique. During
the six day evolution period of the ARs, we found persistent strong
shear motions at a maximum velocity in the range of 0.5-0.7 km-s-1
along the magnetic polarity inversion line (PIL) and outward flows
from the peripheral regions of the sunspots. The helicities injected
in AR 11158 and AR 11166 during the six days' period were estimated as
13.30×10^42 Mx2 and 9.5×10^42 Mx2, respectively. Temporal profiles
of helicity injection showed impulsive variations at the onset times
of flares/CMEs due to the negative helicity injection in the dominant
region of positive helicity density. The spatial examination of helicity
density maps showed that these variations resulted mainly due to the
negative helicity injection in the regions of opposite helicity that
were co-spatial with flaring sites. These co-spatial and co-temporal
variations of helicity injection with flares are interpreted to be due
to the relaxation from the state of high shear by the observed motions
to a lower or shear-free state releasing energy in the form of eruptive
events. This agrees with the simulations by Kusano et al. (2004)
for the triggering mechanism of flares. However, for the flares of
smaller magnitude no clear evidence of such changes was available. We
expect that this difficulty could be addressed by careful calculations
for the emergence term of helicity injection using the vector magnetic
field data. Our study suggests that the existence of opposite helicity
fluxes can trigger eruptive events, viz., flares and CMEs, and promises
to be useful in forecasting the transient activity of ARs.

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Title: Photospheric Transients and Spectral Line Changes Associated
with a Large X2.2 Flare
Authors: Ambastha, Ashok; Maurya, Ram Ajor; Panditi, Vemareddy
2012cosp...39...42A Altcode: 2012cosp.meet...42A
Solar energetic transients occurring in solar atmosphere are associated
with catastrophic release of energy in the solar corona. These
transients inject a part of their energy by various physical processes
to the deeper, denser photospheric layer at which velocity and magnetic
fields are measured using suitable spectral lines. Some signatures of
these processes have been observed during the first X-class flare of
the current solar cycle 24 in Active Region NOAA 11158 of 2011 February
15 using the data obtained from the Helioseismic and Magnetic Imager
(HMI) on board Solar Dynamics Observatory (SDO). In particular, we
detected short-lived magnetic and Doppler velocity transients together
with abnormal polarity reversals during the impulsive phase of this
large energetic flare. The observed photospheric changes associated
with energetic transients have been an issue of serious debates as
the magnetic (and Doppler) measurements are expected to be affected by
flare-induced line profile changes. We explain the observed transient
phenomena during the flare's impulsive phase using the SDO-HMI spectral
data obtained before, during and after the flare. The corresponding
physical processes are discussed in the light of recent flare models.

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Title: Filament Eruption in NOAA 11093 Leading to a Two-Ribbon M1.0
Class Flare and CME
Authors: Vemareddy, P.; Maurya, R. A.; Ambastha, A.
2012SoPh..277..337V Altcode: 2011SoPh..tmp..413V; 2011arXiv1103.3168V; 2011SoPh..tmp..416V;
2011arXiv1103.3168R
We present a multi-wavelength analysis of an eruption event that
occurred in active region NOAA 11093 on 7 August 2010, using
data obtained from SDO, STEREO, RHESSI, and the GONG Hα network
telescope. From these observations, we inferred that an upward
slow rising motion of an inverse S-shaped filament lying along the
polarity inversion line resulted in a CME subsequent to a two-ribbon
flare. Interaction of overlying field lines across the filament with
the side-lobe field lines, associated EUV brightening, and flux
emergence/cancelation around the filament were the observational
signatures of the processes leading to its destabilization and the
onset of eruption. Moreover, the time profile of the rising motion of
the filament/flux rope corresponded well with flare characteristics,
viz., the reconnection rate and hard X-ray emission profiles. The flux
rope was accelerated to the maximum velocity as a CME at the peak phase
of the flare, followed by deceleration to an average velocity of 590 km
s−1. We suggest that the observed emergence/cancelation
of magnetic fluxes near the filament caused it to rise, resulting
in the tethers to cut and reconnection to take place beneath the
filament; in agreement with the tether-cutting model. The corresponding
increase/decrease in positive/negative photospheric fluxes found in
the post-peak phase of the eruption provides unambiguous evidence of
reconnection as a consequence of tether cutting.

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Title: Velocity and Magnetic Transients Driven by the X2.2 White-light
Flare of 2011 February 15 in NOAA 11158
Authors: Maurya, R. A.; Vemareddy, P.; Ambastha, A.
2012ApJ...747..134M Altcode: 2011arXiv1106.4166M
The first X-class flare of the current solar cycle 24 occurred in
Active Region NOAA 11158 during its central meridian passage on 2011
February 15. This two-ribbon white-light flare was observed by the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory. During the peak phase of the flare, we detected magnetic
and Doppler velocity (DV) transients appearing near the umbral boundary
of the main sunspot. These transients persisted for a few minutes and
showed spatial and temporal correspondence with the flare kernels. The
observed magnetic polarity at the transients' locations underwent a sign
reversal, together with a large enhancement in DVs. We explain this
observational phenomenon using the HMI spectral data obtained before,
during, and after the flare. These changes were reflected in the maps
of the active region in all the Stokes parameters. Association of the
transient features with various signatures of the flare and the cause
and effects of their appearance are also presented on the basis of
present theoretical models.

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Title: Spectral line profile changes associated with energetic
solar transients
Authors: Ambastha, Ashok; Maurya, Ram A.
2012ASInC...6..197A Altcode: 2012arXiv1203.3326A
Solar energetic transients occurring in solar atmosphere are associated
with catastrophic release of energy in the solar corona. These
transients inject a part of their energy by various physical processes
to the deeper, denser photospheric layer at which velocity and
magnetic fields are measured using suitable spectral lines. Serious
questions have been raised about the nature of the observed magnetic
(and velocity) field changes associated with energetic transients as
their measurements are expected to be affected by flare-induced line
profile changes. In this paper, we shall discuss some recent progress on
our understanding of the physical processes associated with such events.

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Title: Long term evolution of super active regions
Authors: Maurya, Ram Ajor
2011ASInC...3..102M Altcode:
In the solar cycle 23, there were some active regions (ARs) which
produced energetic events, e.g. flares, CMEs, of unprecedented
magnitudes during their disc passes, termed as super active regions
(SARs). For example, NOAA 10486 stood unrivaled as it produced
flares of unprecedented magnitude, such as X17/4B, X10/2B and
X28 in quick succession. Occurrence of flares of such magnitude
at this rate evidently requires extremely rapid energy buildup
mechanism. Therefore, from their energetic considerations, these SARs
are expected to possess distinctly different sup-photospheric flows
as compared to less productive ARs. Study of such SARs is expected to
provide important insights in our understanding of flare productivity,
characterization of ARs, and in space-weather predictions. We derived
sup-photospheric flows beneath these SARs using ring diagram technique,
one of the local helioseismic techniques. We found strong and largely
twisted sub-photospheric flows in the interior of SARs as compared to
ARs. We present maps of sub-photospheric flows beneath some SARs and
their evolution from one to next Carrington rotation.

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Title: Kinetic and magnetic helicities in solar active regions
Authors: Maurya, Ram Ajor; Ambastha, Ashok; Reddy, Vema
2011JPhCS.271a2003M Altcode:
We have studied the kinetic and magnetic helicities in sub-photospheric
flows and photospheric magnetic fields, respectively, of a sample of
91 ARs of solar cycle 23. Hemispheric trend is investigated in the
kinetic helicity of sub-photospheric flows averaged in the depth range
of 2.5-12 Mms. Magnetic helicity parameters for the ARs are derived
using photospheric vector magnetograms to examine their correlation
with the corresponding kinetic helicities. We found no significant
association between the two helicity parameters.

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Title: Variations in p-mode parameters and sub-surface flows of
active regions with flare activity
Authors: Maurya, R. A.; Ambastha, A.
2011ASInC...2..189M Altcode: 2011arXiv1106.4180M
We examine the characteristic properties of photospheric p-modes and
sub-photospheric flows of active regions (ARs) observed during the
period of 26-31 October 2003. Using ring diagram analysis of Doppler
velocity data obtained from the Global Oscillations Network Group
(GONG), we have found that p-mode parameters evolve with ARs and show a
strong association with flare activity. Sub-photospheric flows, derived
using inversions of p-modes, show strong twist at the locations of ARs,
and large variation with flare activity.

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Title: A Study of Oscillations in Solar Active Regions
Authors: Maurya, Ram Ajor
2010PhDT.........2M Altcode:
Solar active regions (ARs) are three-dimensional magnetic structures
extending from deep sub-photosphere to coronal heights. These ARs
are responsible for producing most of the energetic transients,
such as flares and Coronal Mass Ejections (CMEs). The energetic
charged particles released during these transients may also affect
the measurements of magnetic and Doppler velocity fields. In addition,
the energetic transients are expected to excite p-mode oscillations in
ARs by imparting a mechanical impulse associated with their thermal
expansion on the photosphere. While studying the magnetic and
velocity fields in AR NOAA 10486, we detected some puzzling moving
transient features during the X17/4B and the X10/2B flares of 28 and
29 October 2003, respectively. We have examined the origin of these
features and their relationship with various other aspects of the
flares, viz., hard X-ray emission sources and flare kernels observed
at different layers of solar atmosphere. We have determined the
characteristic properties of local oscillation modes by applying the
ring diagram technique to 3-D power spectra of NOAA 10486. Strong
evidence of substantial increase in mode amplitude and systematic
variations in sub-surface flows are found from comparison of the pre-
to the post-are phases of energetic flares. Furthermore, we have found
statistically significant association between the mode energy and
flare energy from the study of several ARs of Solar Cycle 23. Our
study has revealed strongly twisted, sheared flows in the interior
of flaring ARs having complex magnetic fields. Using the Doppler
data obtained for a sample of 74 ARs, we discovered steep gradients
in meridional velocity at depths ranging from 1.5 to 5 Mm in flare
productive ARs. The gradients showed an interesting hemispheric trend
of negative (positive) sign in the northern (southern) hemispheres. An
important inference derived from our analysis is that the location of
the deepest zero vertical vorticity is correlated with the remaining
lifetime of ARs. These new findings may be employed as important
tool for predicting the life expectancy of an AR and space weather
predictions. Finally, we have found using the data for 91 ARs of solar
cycle 23 that kinetic helicity in sub-photospheric flows and magnetic
helicity in photospheric magnetic fields show very weak correlation.

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Title: Sub-surface Meridional Flow, Vorticity, and the Lifetime of
Solar Active Regions
Authors: Maurya, R. A.; Ambastha, A.
2010ApJ...714L.196M Altcode: 2010arXiv1003.5273M
Solar sub-surface fluid topology provides an indirect approach to
examine the internal characteristics of active regions (ARs). Earlier
studies have revealed the prevalence of strong flows in the interior
of ARs having complex magnetic fields. Using the Doppler data obtained
by the Global Oscillation Network Group project for a sample of 74
ARs, we have discovered the presence of steep gradients in meridional
velocity at depths ranging from 1.5 to 5 Mm in flare productive ARs. The
sample of these ARs is taken from the Carrington rotations 1980-2052
covering the period 2001 August-2007 January. The gradients showed
an interesting hemispheric trend of negative (positive) signs in the
northern (southern) hemisphere, i.e., directed toward the equator. We
have discovered three sheared layers in the depth range of 0-10 Mm,
providing evidence of complex flow structures in several ARs. An
important inference derived from our analysis is that the location of
the deepest zero vertical vorticity is correlated with the remaining
lifetime of ARs. This new finding may be employed as a tool for
predicting the life expectancy of an AR.

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Title: A Technique for Automated Determination of Flare Ribbon
Separation and Energy Release
Authors: Maurya, R. A.; Ambastha, A.
2010SoPh..262..337M Altcode: 2009arXiv0910.4245M; 2010SoPh..tmp...21M
We present a technique for automatic determination of flare ribbon
separation and the energy released during the course of two-ribbon
flares. We have used chromospheric Hα filtergrams and photospheric
line-of-sight magnetograms to analyse flare ribbon separation and
magnetic field structures, respectively. Flare ribbons were first
enhanced and then extracted by the technique of "region growing", i.e.,
a morphological operator to help resolve the flare ribbons. Separation
of flare ribbons was then estimated from the magnetic-polarity reversal
line using an automatic technique implemented into an Interactive Data
Language (IDLTM) platform. Finally, the rate of flare-energy
release was calculated using photospheric magnetic field data and the
corresponding separation of the chromospheric Hα flare ribbons. This
method could be applied to measure the motion of any feature of interest
(e.g., intensity, magnetic, Doppler) from a given point of reference.

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Title: Magnetic and Velocity Field Changes Related to the Solar
Flares of 28 and 29 October 2003
Authors: Maurya, R. A.; Ambastha, A.
2010ASSP...19..517M Altcode: 2010mcia.conf..517M; 2009arXiv0906.3965M
Magnetic and velocity field measurements of solar active regions
suffer from ambiguities caused by the change in spectral line profiles
that occur during the impulsive phase of a major flare. This leads
to difficulties in correct interpretation of any flare-related
changes. Using magnetic and Doppler movies taken with GONG and MDI,
we have detected transient, "moving" features around the peak phases
of the X17.2/4B flare observed on 28 October 2003 and the X10/2B flare
observed on 29 October 2003 in super-active region NOAA 10486. These
features were located near the compact acoustic sources reported earlier
by Donea and Lindsey (2005) and the seismic sources reported by Zharkova
and Zharkov (2007).We find a moving feature, spatially and temporally
associated with the flare ribbons, that separates away at speeds
ranging from 30 to 50 km s-1 as observed in photospheric
white light and in temperature-minimum (1600 Å), chromospheric (Hα),
and transition-region (284Å ) intensities.We suggest that such moving
features arise from the line-profile changes attributed to downward
electron jets associated with the flare, and do not reflect real changes
in the photospheric magnetic and velocity fields. However, abrupt and
persistent changes in the pre- and post-flare phases were also found,
which do not seem to be affected by line-profile changes. The detailed
results have been appeared in Maurya and Ambastha (2009).

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Title: Flows in Flaring and Dormant Active Regions
Authors: Maurya, R. A.; Ambastha, A.
2010ASSP...19..516M Altcode: 2010mcia.conf..516M
During cycle 23, some active regions (ARs) produced extremely energetic
flares and coronal mass ejections. These ARs are expected to be distinct
from dormant ARs and quiet regions (QRs). It is of interest to identify
whether the internal structure and dynamics of ARs is related to their
outburst activity. For this investigation, we have obtained subsurface
velocity flows in several ARs and QRs using ring diagram analysis, and
derived the corresponding vorticities and kinetic helicity densities.

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Title: The Association of Energetic Events with p-Mode Energy
Authors: Maurya, Ram Ajor; Ambastha, Ashok
2010cosp...38.3025M Altcode: 2010cosp...38.3025A; 2010cosp.meet.3025M
The energetic events, e.g., flares, CMEs, etc. release large amount
of energy, which may be able to excite acoustic waves (p-mode) by
exerting mechanical impulse of the thermal expansion of the flare on
the photosphere. This implied that during an energetic flare, energy
of p-modes must be weighted by the energy of excited modes. To get
the inferences of flare related enhances of p-mode energy, we have
derived the magnetic energy released during a flare from magnetic
field observations and associated p-mode energy from ring-diagram
analysis. For the statistical studied of their association, we took
samples of several high energy flares from Carrington rota-tions
1980-2052 covering the period August 2001-January 2007. We find
significant relationship between them. A detailed description of our
findings will be presented in the paper.

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Title: Variations in p-Mode Parameters with Changing Onset Time of
a Large Flare
Authors: Maurya, R. A.; Ambastha, A.; Tripathy, S. C.
2009ApJ...706L.235M Altcode: 2009arXiv0910.4247M
It is expected that energetic solar flares releasing a large amount
of energy at the photosphere may be able to excite the acoustic
(p-) modes of oscillations. We have determined the characteristic
properties of mode parameters by applying the ring diagram technique
to three-dimensional power spectra obtained for solar active region
NOAA 10486 during the long-duration energetic X17.2/4B flare of 2003
October 28. Strong evidence of substantial increase in mode amplitude
and systematic variations in sub-surface flows, i.e., meridional
and zonal components of velocity, kinetic helicity, and vorticity,
is found from comparison of the pre- to the post-flare phases.

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Title: Transient Magnetic and Doppler Features Related to the
White-Light Flares in NOAA 10486
Authors: Maurya, R. A.; Ambastha, A.
2009SoPh..258...31M Altcode: 2009arXiv0903.2138M
Rapidly moving transient features have been detected in magnetic
and Doppler images of super-active region NOAA 10486 during the
X17/4B flare of 28 October 2003 and the X10/2B flare of 29 October
2003. Both these flares were extremely energetic white-light events. The
transient features appeared during impulsive phases of the flares and
moved with speeds ranging from 30 to 50 km s−1. These
features were located near the previously reported compact acoustic
(Donea and Lindsey, Astrophys. J.630, 1168, 2005) and seismic sources
(Zharkova and Zharkov, Astrophys. J.664, 573, 2007). We examine the
origin of these features and their relationship with various aspects
of the flares, viz., hard X-ray emission sources and flare kernels
observed at different layers: i) photosphere (white-light continuum),
ii) chromosphere (Hα 6563 Å), iii) temperature minimum region (UV
1600 Å), and iv) transition region (UV 284 Å).

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Title: Magnetic and velocity field variations in the active regions
NOAA 10486 and NOAA 10488
Authors: Maurya, Ram Ajor; Ambastha, Ashok
2008JApA...29..103M Altcode:
We study the magnetic and velocity field evolution in the two
magnetically complex active regions NOAA 10486 and NOAA 10488 observed
during October-November 2003. We have used the available data to
examine net flux and Doppler velocity time profiles to identify changes
associated with evolutionary and transient phenomena. In particular,
we report detection of rapid moving features observed in NOAA 10486
during the maximum phase of the X17.2/4B superflare of October 28,
2003. The velocity of this moving feature is estimated around 40 km/s,
i.e., much greater than the usual Hα flare-ribbons' separation speed
of 3-10 km/s, but similar to the velocity of seismic waves, i.e.,
∼45 km/s reported earlier by Kosovichev &amp; Zharkova (1998).

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Title: Hα intensity oscillations in large flares
Authors: Maurya, Ram Ajor; Ambastha, Ashok
2008JApA...29..249M Altcode:
We reinvestigate the problem of HÎ± intensity oscillations in large
flares, particularly those classified as X-class flares. We have used
high spatial and temporal resolution digital observations obtained
from Udaipur Solar Observatory during the period 1998-2006 and selected
several events. Normalized Lomb-Scargle periodogram method for spectral
analysis was used to study the oscillatory power in quiet and active
chromospheric locations, including the flare ribbons.