Author name code: jain-kiran
ADS astronomy entries on 2022-09-14
=author:"Jain, Kiran" OR =author:"Jain, K."
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Title: Cycle dependence of a quasi-biennial variability in the
solar interior
Authors: Mehta, T.; Jain, K.; Tripathy, S. C.; Kiefer, R.; Kolotkov,
D.; Broomhall, A. -M.
Bibcode: 2022MNRAS.515.2415M
Altcode: 2022MNRAS.tmp.1980M; 2022arXiv220714560M
We investigated the solar cycle dependence on the presence and
periodicity of the Quasi-Biennial Oscillation (QBO). Using helioseismic
techniques, we used solar oscillation frequencies from the Global
Oscillations Network Group (GONG), Michelson Doppler Imager (MDI),
and Helioseismic and Magnetic Imager (HMI) in the intermediate-degree
range to investigate the frequency shifts over Cycles 23 and 24. We also
examined two solar activity proxies, the F10.7 index and the
Mg II index, for the last four solar cycles to study the associated
QBO. The analyses were performed using Empirical Mode Decomposition
(EMD) and the Fast Fourier Transform (FFT). We found that the EMD
analysis method is susceptible to detecting statistically significant
Intrinsic Mode Functions (IMFs) with periodicities that are overtones of
the length of the data set under examination. Statistically significant
periodicities, which were not due to overtones, were detected in the
QBO range. We see a reduced presence of the QBO in Cycle 24 compared
to Cycle 23. The presence of the QBO was not sensitive to the depth to
which the p-mode travelled, nor the average frequency of the p-mode. The
analysis further suggested that the magnetic field responsible for
producing the QBO in frequency shifts of p-modes is anchored above
approximately 0.95 R⊙.
Title: Improving the Understanding of Subsurface Structure and
Dynamics of Solar Active Regions
Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Pevtsov, A.
Bibcode: 2022heli.conf.4017T
Altcode:
NSO and HAO are promoting the design of a new global ground-based
network. Here we describe additional science goals that could be
addressed by this new network through multi-height observations of
the solar atmosphere.
Title: What Seismic Minimum Reveals about Solar Magnetism below
the Surface
Authors: Jain, Kiran; Jain, Niket; Tripathy, Sushanta C.; Dikpati,
Mausumi
Bibcode: 2022ApJ...924L..20J
Altcode: 2021arXiv211114323J
The Sun's magnetic field varies on multiple timescales. Observations
show that the minimum between cycles 24 and 25 was the second
consecutive minimum that was deeper and wider than several earlier
minima. Since the active regions observed at the Sun's surface are
manifestations of the magnetic field generated in the interior, it is
crucial to investigate/understand the dynamics below the surface. In
this context, we report by probing the solar interior with helioseismic
techniques applied to long-term oscillations data from the Global
Oscillation Network Group, that the seismic minima in deeper layers
have been occurring about a year earlier than that at the surface for
the last two consecutive solar cycles. Our findings also demonstrate
a decrease in strong magnetic fields at the base of the convection
zone, the primary driver of the surface magnetic activity. We conclude
that the magnetic fields located in the core and near-surface shear
layers, in addition to the tachocline fields, play an important role
in modifying the oscillation frequencies. This further strengthens
the existence of a relic magnetic field in the Sun's core.
Title: Horizontal Flows Associated with Anti-Hale Active Regions
Authors: Jain, Kiran; Tripathy, Sushanta; Ravindra, Belur
Bibcode: 2021AGUFMSH55D1865J
Altcode:
Emergence of active regions generally follows two laws; Hale's law
determines the direction of the polarities in strong magnetic field
regions in each hemisphere while Joys law defines the latitudinal
dependence of the tilt of bipolar active regions with respect to the
Equator of the Sun. There were about 60 regions in solar cycle 24 that
violated Hales law, however most of them were relatively small in
sizes. We have carried out a detailed study of the evolution of the
flows in significantly large active regions, NOAA 11429, NOAA 11967
and NOAA 12158, as these regions pass through the disk. The subsurface
flows are calculated using the technique of ring diagrams. We also
compare their flow characteristics with other regions that appeared
on the solar surface at the same time. We further investigate flow
patterns at the surface by employing the Local Correlation Tracking
method. In general, there are significantly large horizontal flows in
active regions, however the direction of the flows in anti-Hale active
regions is equatorward which defies the normal pattern and disrupts
the normal migration of flows towards the pole. The emergence of active
regions generally follows two laws; Hale's law determines the direction
of the polarities in strong magnetic field regions in each hemisphere
while Joys law defines the latitudinal dependence of the tilt of
bipolar active regions with respect to the Equator of the Sun. There
were about 60 regions in solar cycle 24 that violated Hales law,
however most of them were relatively small in sizes. We have carried
out a detailed study of the evolution of the flows in significantly
large active regions, NOAA 11429 (March 2012), NOAA 11967 (February
2014) and NOAA 12158 (September 2014), as these regions pass through
the disk. The subsurface flows are calculated using the technique
of ring diagrams. We also compare their flow characteristics with
other regions that appeared on the solar surface at the same time. We
further investigate flow patterns at the surface by employing the Local
Correlation Tracking method. In general, there are significantly large
horizontal flows in active regions, however the direction of the flows
in anti-Hale active regions is equatorward which defies the normal
pattern and disrupts the normal migration of flows towards the pole.
Title: Subsurface Plasma Flows and the Flare Productivity of Solar
Active Regions
Authors: Biji, Lekshmi; Jain, Kiran; Komm, Rudolf; Nandy, Dibyendu
Bibcode: 2021AGUFMSH54A..07B
Altcode:
Highly energetic solar events such as solar flares and Coronal
Mass Ejections (CMEs) can lead to extreme space weather. Hence, it
is essential to understand their physical drivers and explore what
governs their occurrence and intensity. By using the near-surface
velocities derived by the ring-diagram analysis of active region
patches using Global Oscillation Network Group (GONG) Doppler
velocity measurements, we seek to explore the connection between
subsurface flow properties and solar flares. The temporal evolution
of vorticity and kinetic helicity of flaring and non-flaring active
regions is investigated. The integrated vorticity, kinetic and current
helicities, and magnetic flux one day prior to the flare are observed
to be correlated with the integrated flare intensity. We show that
active regions with strong subsurface vorticity and kinetic helicity
tend to generate high intensity flares. We hypothesize that this is
achieved via energy injection into subsurface magnetic flux systems
by helical plasmas flows.
Title: What Deep and Extended Minima Tell us about Magnetism Below
the Surface?
Authors: Jain, Kiran; Jain, Niket; Tripathy, Sushanta; Dikpati, Mausumi
Bibcode: 2021AGUFMSH55D1883J
Altcode:
Various measures of solar activity show that the minima preceding cycles
24 and 25 were deeper and wider than several earlier minima. These
provide a unique opportunity for studying the Sun's properties that are
otherwise altered in the presence of strong fields. The solar magnetic
field is generated in the interior and the dynamo responsible for
11-year cyclic activity in the Sun is believed to be seated near the
base of the convection zone. Here we use oscillation mode frequencies
computed from the continuous observations from GONG for the last 25
years to investigate the changes occurring below the surface. Since
the oscillation frequencies vary in phase with the solar activity
manifested on the surface and exhibit a strong positive correlation,
we utilize these frequencies to infer important information on the
magnetism of the layers they travel through. We also investigate the
similarities and differences between the last two minima.
Title: The Multiview Observatory for Solar Terrestrial Science (MOST)
Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall,
Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe,
Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung,
Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward;
Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy;
DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen,
P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi,
Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal;
DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran;
Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei;
Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan
Bibcode: 2021AGUFMSH12A..07G
Altcode:
The Multiview Observatory for Solar Terrestrial Science (MOST) is a
comprehensive mission concept targeting the magnetic coupling between
the solar interior and the heliosphere. The wide-ranging imagery and
time series data from MOST will help understand the solar drivers and
the heliospheric responses as a system, discerning and tracking 3D
magnetic field structures, both transient and quiescent in the inner
heliosphere. MOST will have seven remote-sensing and three in-situ
instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate
surface and subsurface magnetism by exploiting the combination of
helioseismic and magnetic-field measurements in the photosphere; (2)
Inner Coronal Imager in EUV (ICIE) to study large-scale structures
such as active regions, coronal holes and eruptive structures by
capturing the magnetic connection between the photosphere and the
corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image
the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to
seamlessly study transient and quiescent large-scale coronal structures
extending from the ICIE field of view (FOV); (5) Faraday Effect
Tracker of Coronal and Heliospheric structures (FETCH), a novel radio
package to determine the magnetic field structure and plasma column
density, and their evolution within 0.5 au; (6) Heliospheric Imager
with Polarization (HIP) to track solar features beyond the WCOR FOV,
study their impact on Earth, and provide important context for FETCH;
(7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams
and shocks propagating into the heliosphere via passive radio emission;
(8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra
of electrons, and ions from H to Fe at multiple spatial locations
and use energetic particles as tracers of magnetic connectivity; (9)
Solar Wind Magnetometer (MAG) to characterize magnetic structures at
1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma
structures at 1 au. MOST will have two large spacecraft with identical
payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4
and behind L5 to carry additional FETCH elements. MOST will build upon
SOHO and STEREO achievements to expand the multiview observational
approach into the first half of the 21st Century.
Title: Subsurface Flow Measurements in the Near Surface Shear Layer
over Two Solar Cycles
Authors: Tripathy, Sushanta; Jain, Kiran; Komm, Rudolf; Kholikov,
Shukirjon
Bibcode: 2021AGUFMSH53C..02T
Altcode:
Helioseismic studies have illustrated that the most significant
changes with the solar cycle occur in the near-surface shear layer
(NSSL) where the density changes by several orders of magnitude. This
layer approximately occupies the outer 5% of the solar interior. It is
also believed that a nonlinear alpha-omega dynamo could be operating
in the NSSL where the velocity shear converts a part of the poloidal
magnetic field into the toroidal field in addition to the global
dynamo operating in the tachocline region. With the advent of local
helioseismic technique of ring diagram, subsurface flows in the outer 2%
have been well studied. Here we extend the measurements of large-scale
flows to deeper layers to provide observational constraints on the
temporal as well as latitudinal variations of the zonal and meridional
flows during the last two solar cycles. The study is based on the GONG
data and uses the technique of ring diagram and 30 degree tiles to
probe deeper layers. We will also compare GONG with HMI results for
solar cycle 24 and beyond.
Title: A Comparative Study of Measurements of the Suns Axisymmetric
Flows: A COFFIES Effort
Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant;
Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger;
Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber,
Shea; Hoeksema, J.
Bibcode: 2021AGUFMSH55D1871U
Altcode:
Consequence Of Fields and Flows in the Interior and Exterior of
the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC),
with the primary objective of developing a data driven model of
solar activity. One of COFFIES five primary science questions is
What drives varying large-scale motions in the Sun? To address this
question, we are developing a comprehensive catalog of the variable
differential rotation and meridional circulation flow patterns. This
catalog includes measurements of these flows as obtained by several
measurement techniques: Doppler imaging, granule tracking, magnetic
pattern tracking, magnetic feature tracking, as well as both time
distance and ring diagram helioseismology. We show a comparison of
these flows across these varied techniques, with a particular focus
on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We
investigate the uncertainties and attempt to reconcile any discrepancies
(e.g., due to flow depth or systematics associated with the different
measurement techniques). This analysis will pave the way toward
accurately determining the global patterns of axisymmetric flows and
their regular and irregular variations during the cycle.
Title: What is Exceptional about Solar Activity in the Early Phase
of Cycle 25?
Authors: Jain, Kiran; Lindsey, Charles; Tripathy, Sushanta C.
Bibcode: 2021RNAAS...5..253J
Altcode:
Solar Cycle 25 began in 2019 December and has been progressing nominally
since. However, a closely associated pair of strong active regions,
NOAA 12786 and 12785, emerged in 2020 November. The greater, northern
component, 12786, attained a maximum sunspot area of 1000 μHemi. The
sudden, uncharacteristic emergence of such a large concentration
of intense magnetic flux in the early phase of the solar cycle has
not been seen in previous cycles. Although the active region pair
survived for two Carrington rotations, it did not produce any X- or
M-class flares. Here we remark on the evolution of NOAA 12786 and
12785, first in the Sun's invisible and subsequently the visible
hemispheres, and compare the irradiance and other characteristic
profiles it manifested in the early ascending phase of cycle 25 with
those of previous solar cycles.
Title: Continuous Solar Observations from the Ground-Assessing Duty
Cycle from GONG Observations
Authors: Jain, Kiran; Tripathy, Sushanta C.; Hill, Frank; Pevtsov,
Alexei A.
Bibcode: 2021PASP..133j5001J
Altcode: 2021arXiv211006319J
Continuous observations play an important role in the studies of solar
variability. While such observations can be achieved from space with
an almost 100% duty cycle, it is difficult to accomplish a very high
duty cycle from the ground. In this context, we assess the duty cycle
that has been achieved from the ground by analyzing the observations of
a six station network of identical instruments, the Global Oscillation
Network Group (GONG). We provide a detailed analysis of the duty cycle
using GONG observations spanning over 18 yr. We also discuss the duty
cycle of individual sites and point out various factors that may impact
individual site or network duty cycles. The mean duty cycle of the
network is 93%, however it reduces by about 5% after all images pass
through the stringent quality-control checks. The standard deviations
in monthly and yearly duty cycle values are found to be 1.9% and 2.2%,
respectively. These results provide a baseline that can be used in
the planning of future ground-based networks.
Title: Solar inertial modes: Observations, identification, and
diagnostic promise
Authors: Gizon, Laurent; Cameron, Robert H.; Bekki, Yuto; Birch,
Aaron C.; Bogart, Richard S.; Brun, Allan Sacha; Damiani, Cilia;
Fournier, Damien; Hyest, Laura; Jain, Kiran; Lekshmi, B.; Liang,
Zhi-Chao; Proxauf, Bastian
Bibcode: 2021A&A...652L...6G
Altcode: 2021arXiv210709499G
The oscillations of a slowly rotating star have long been classified
into spheroidal and toroidal modes. The spheroidal modes include
the well-known 5-min acoustic modes used in helioseismology. Here
we report observations of the Sun's toroidal modes, for which the
restoring force is the Coriolis force and whose periods are on the
order of the solar rotation period. By comparing the observations
with the normal modes of a differentially rotating spherical shell,
we are able to identify many of the observed modes. These are the
high-latitude inertial modes, the critical-latitude inertial modes,
and the equatorial Rossby modes. In the model, the high-latitude
and critical-latitude modes have maximum kinetic energy density at
the base of the convection zone, and the high-latitude modes are
baroclinically unstable due to the latitudinal entropy gradient. As
a first application of inertial-mode helioseismology, we constrain
the superadiabaticity and the turbulent viscosity in the deep
convection zone. Movie associated to Fig. 2 is available at https://www.aanda.org
Title: Deciphering the Deep Origin of Active Regions via Analysis
of Magnetograms
Authors: Dikpati, Mausumi; McIntosh, Scott W.; Chatterjee, Subhamoy;
Norton, Aimee A.; Ambroz, Pavel; Gilman, Peter A.; Jain, Kiran;
Munoz-Jaramillo, Andres
Bibcode: 2021ApJ...910...91D
Altcode:
In this work, we derive magnetic toroids from surface magnetograms
by employing a novel optimization method, based on the trust region
reflective algorithm. The toroids obtained in this way are combinations
of Fourier modes (amplitudes and phases) with low longitudinal
wavenumbers. The optimization also estimates the latitudinal width of
the toroids. We validate the method using synthetic data, generated
as random numbers along a specified toroid. We compute the shapes and
latitudinal widths of the toroids via magnetograms, generally requiring
several m's to minimize residuals. A threshold field strength is
chosen to include all active regions in the magnetograms for toroid
derivation, while avoiding non-contributing weaker fields. Higher
thresholds yield narrower toroids, with an m = 1 dominant pattern. We
determine the spatiotemporal evolution of toroids by optimally weighting
the amplitudes and phases of each Fourier mode for a sequence of five
Carrington Rotations (CRs) to achieve the best amplitude and phases for
the middle CR in the sequence. Taking more than five causes "smearing"
or degradation of the toroid structure. While this method applies no
matter the depth at which the toroids actually reside inside the Sun,
by comparing their global shape and width with analogous patterns
derived from magnetohydrodynamic (MHD) tachocline shallow water model
simulations, we infer that their origin is at/near the convection zone
base. By analyzing the "Halloween" storms as an example, we describe
features of toroids that may have caused the series of space weather
events in 2003 October-November. Calculations of toroids for several
sunspot cycles will enable us to find similarities/differences in
toroids for different major space weather events.
Title: Helioseismic Investigations of the Quasi-Biennial Oscillation
Authors: Mehta, Tishtrya; Broomhall, Anne-Marie; Jain, Kiran; Tripathy,
Sushant; Keifer, René; Kolotkov, Dmitrii Y.
Bibcode: 2021csss.confE..12M
Altcode:
We investigate the behaviour of the Quasi-Biennial Oscillation
(QBO) over solar Cycles 23 and 24, making use of helioseismic
techniques. Using data from GONG and MDI/HMI, we see evidence of the
QBO in frequency shifts of intermediate degree p-modes. By analysing
the frequencies and lower turning points of these modes, we may better
confine where the magnetic field driving the QBO is located. We find
that evidence of the QBO exists over all frequencies and lower turning
points across the full input data range (1600-4000 µHz, 0.2-1 solar
radii) suggesting that the magnetic field generating the QBO must
be anchored in the near surface layer. The periodicity of the QBO is
roughly seen to be between 400-800 days through both Cycles 23 and 24,
although its presence is weaker in Cycle 24. This data was analysed
using AuTomated Empirical Mode Decomposition (ATEMD), a technique
adept at extracting quasi-oscillatory signals.
Title: Investigating Solar Minimum Below and Above the Solar Surface:
Is the Current Solar Minimum Different from the Previous Minimum?
Authors: Farrell, K.; Jain, K.; Tripathy, S. C.
Bibcode: 2020AGUFMSH0180006F
Altcode:
The Solar magnetic field waxes and wanes with time, going through a
cyclic change with a period of about 11 years, commonly known as the
Solar Cycle. Other indicators of solar activity follow a similar trend,
as inferred from direct measurements above the solar surface. However,
there are no direct methods to measure magnetic fields or other forms of
solar activity below the surface. Past studies have demonstrated strong
correlations between the variations in oscillation frequencies of the
waves propagating below the Sun's surface and above-surface magnetic
activity indicators, therefore the frequencies serve as an activity
proxy for the interior. We use oscillation frequencies derived from
the Global Oscillation Network Group's (GONG) observations to study the
conditions in the convection zone while various indicators of the solar
activity are used for above surface conditions. We have identified
the previous minimum, between cycles 23 and 24, was deeper than the
current minimum, while the current minimum is wider. In addition,
similar to the previous minimum, different layers in the convection zone
during the current minimum sensed minima at different times. This
work is carried out through the National Solar Observatory Research
Experiences for Undergraduates (REU) Program, which is funded by the
National Science Foundation (NSF) through Award No. 1659878.
Title: Derivation of Toroid Patterns from Analysis of Magnetograms
And Inferring Their Deep-origin
Authors: Chatterjee, S.; Dikpati, M.; McIntosh, S. W.; Norton, A. A.;
Ambroz, P.; Gilman, P.; Jain, K.; Munoz-Jaramillo, A.
Bibcode: 2020AGUFMSH0020013C
Altcode:
We employ a novel optimization method based on Trust Region Reflective
algorithm to derive magnetic toroids from surface magnetograms. Toroids
obtained are combinations of Fourier modes (amplitudes and phases)
with low longitudinal wavenumbers. After validating the method using
synthetic data generated as random numbers along a specified toroid,
we compute shapes and latitudinal-widths of toroids from magnetograms,
usually requiring several m 's to minimize residuals. By comparing
properties of these toroids with patterns produced in the bottom
toroidal band undergoing MHD evolution in a 3D thin-shell shallow-water
type model, we infer their deep origin at/near convention-zone's base
or tachocline. A threshold field-strength is chosen to include all
active regions in magnetograms for toroid derivation, while avoiding
non-contributing weaker fields. Higher thresholds yield narrower
toroids, with m = 1 dominant, implying that stronger active regions
are erupting from the core of the toroids at bottom. We determine the
spatio-temporal evolution of toroids by optimally weighting amplitudes
and phases of each Fourier mode for a sequence of 5 Carrington Rotations
(CRs) to get the best amplitude and phases for the middle CR in the
sequence. Taking more than 5 causes 'smearing' or degradation of toroid
structure. As an example case, we analyze 'Halloween' storms toroids,
and describe the features that might have caused the series of space
weather events in October-November of 2003. We compare features of
these toroids with analogous patterns derived from model-output. To find
similarities/differences in toroids for different major space weather
events, we will analyze long-term magnetograms for several solar cycles.
Title: Continuous Subsurface Flow Measurements for Solar Cycle 23
from MDI Spherical Harmonic Time Series
Authors: Tripathy, S. C.; Kholikov, S.; Jain, K.
Bibcode: 2020AGUFMSH007..06T
Altcode:
Subsurface flows play an important role in the flux-transport
dynamo models. In particular, the transport of surface poloidal
magnetic field to the bottom of the convection zone is governed by
the meridional circulation, where the poloidal field is converted
into a toroidal field by rotational shear. The past two decades have
witnessed rapid advancements in measuring the subsurface flow patterns
due to the availability of high-resolution observations from space
and ground-based observatories. However, continuous measurement of
meridional flow for the entire solar cycle 23 is not available due
to the limited high-resolution observations from Michelson Doppler
Imager (MDI) instrument on board Solar and Heliospheric Observatory
(SoHO). Here we report on a novel method that combines two methods;
the image reconstruction from spherical harmonic time series, and the
local helioseismic technique of ring diagrams, to produce zonal and
meridional flow measurements from May 1996 to December 2010 up to a
depth of 40 Mm below the surface. In addition to the temporal variation
of the meridional flow, where the flow is faster at solar cycle minimum
and slower at maximum, we find several interesting features notably
that the meridional flows have a strong depth dependence that differs
during the solar minimum and maximum phases. We also find that the
meridional flows in the activity belt differs from the flows at higher
latitude around 20 Mm below the surface. This work is partially
funded by NASA grants NNH18ZDA0001N-HDEE and NNH18ZDA001N-LWS.
Title: Investigating Solar Acoustic Oscillations and Surface Activity
During the Current Minimum
Authors: Farrell, K.; Jain, K.; Tripathy, S.
Bibcode: 2020SPD....5120404F
Altcode:
The Solar Cycle, a cyclic change with a period of about 11 years,
is the waxing and waning of the Solar Magnetic field with time. Other
indicators of solar activity follow a similar trend, as inferred from
direct measurements above the solar surface. However, measuring the
magnetic field beneath the surface cannot be accomplished through direct
methods. Past helioseismic studies have revealed a strong correlation
between the variations in solar acoustic oscillation frequencies of
the waves propagating below the Sun's surface and magnetic activity
indicators above the surface, allowing the frequencies to serve as an
activity proxy for the interior. During the activity minimum between
cycles 23 and 24, several studies identified different minimum periods
in the layers below and above the surface raising questions on the
origin of the solar cycles. In this paper, we evaluate the current
minimum and present results on the identified epochs of minimum. This
allows us to investigate the connection between various layers of solar
interior and the atmosphere. The oscillation frequencies that we use
for this study are derived from the Global Oscillation Network Group
(GONG) observations while several indicators of the solar activity are
used for above surface conditions. This work is carried out through
the National Solar Observatory Research Experiences for Undergraduates
(REU) Program, which is funded by the National Science Foundation
(NSF) through Award No. 1659878.
Title: Study of Acoustic Halos in NOAA Active Region 12683
Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Hill, F.; Cally, P.
Bibcode: 2020ASSP...57..121T
Altcode:
We characterize the spatio-temporal power distribution around the
active region 12683 as a function of height in the solar atmosphere,
wave frequencies, magnetic field strength and inclination of the
magnetic field.
Title: A Comparison of Global Helioseismic-Instrument Performances:
Solar-SONG, GOLF and VIRGO
Authors: Breton, S. N.; García, R. A.; Pallé, P. L.; Mathur, S.;
Hill, F.; Jain, K.; Jiménez, A.; Tripathy, S. C.; Grundahl, F.;
Fredslund-Andersen, M.; Santos, A. R. G.
Bibcode: 2020ASSP...57..327B
Altcode:
The SONG spectrograph has recently demonstrated its ability to perform
solar radial velocity measurement during the first test run of the
Solar-SONG initiative. A preliminary assessment of its performance
is carried out here by comparing the results of Solar-SONG during
the summer 2018 test run, with GOLF and VIRGO/SPM taken as reference
instruments.
Title: Comparing Solar Activity Minima Using Acoustic Oscillation
Frequencies
Authors: Jain, Kiran; Tripathy, Sushanta C.; Hill, Frank
Bibcode: 2020ASSP...57..137J
Altcode:
Using the variability of solar acoustic oscillation mode frequencies,
we investigate the width and timing of last three solar minima at
various depths in the solar interior. We find that the current minimum
is as deep as the previous minimum, however, more data are needed to
reveal the true depth of the current minimum.
Title: Progression of Solar Cycle 24 As Seen in Acoustic Mode
Frequencies of the Sun
Authors: Undzis, B.; Tripathy, S. C.; Jain, K.
Bibcode: 2019AGUFMSH11D3376U
Altcode:
By examining the acoustic waves observed on the surface of the Sun, one
can infer its internal structure and dynamics through the technique
of helioseismology. In this study, we use full-disk high-cadence
Dopplergrams and magnetograms from the Helioseismic and Magnetic Imager
(HMI) on board Solar Dynamics Observatory (SDO) to investigate the
progression of Solar Cycle 24 by analyzing high-degree acoustic
mode frequencies. The frequencies are derived through the local
helioseismic technique of ring diagram and cover a period of about
nine years from June 2010. The temporal variation in frequencies
is explored by examining the physical measures of the solar activity,
e.g., international sunspot number (ISN), 10.7 cm radio flux and
a local magnetic activity index (MAI). Our analysis confirms that
the high-degree frequencies strongly correlate with the changes
during the solar cycle. The analysis of MAI and ISN of individual
hemispheres shows that the northern hemisphere peaked in activity
before the southern hemisphere. The same trend is also observed in the
oscillation frequencies. We further analyze the oscillation frequencies
as a function of latitude and find that the latitudinal bands of higher
magnetic activity correlate best with the frequency shifts computed at
those latitudes. It is expected that the latitudinal variation with
the progression of the solar cycle may provide useful insight into
different solar dynamo models. This research was conducted at
NSO as part of the Boulder Solar Alliance REU program, funded by NSF.
Title: Modeling the Effects of Observational Gaps on p-mode
Oscillation Parameters
Authors: Keith-Hardy, J. Z.; Tripathy, S. C.; Jain, K.
Bibcode: 2019ApJ...877..148K
Altcode:
We investigate the effect of the window function on the parameters of
solar acoustic oscillations, namely frequency, amplitude, and width,
using the data from Global Oscillation Network Group (GONG). This is
carried out by simulating 108 new time series from a base time series
by modifying the window functions. In order to minimize the effect of
solar activity, the base time series was chosen during the activity
minimum period. The new window functions were randomly chosen from a
set of 30 observed window functions to incorporate the reported duty
cycles of the GONG network. The modified time series were processed
through the standard GONG p-mode pipeline to extract the mode parameters
that were fitted to a linear model as a function of the duty cycle
to yield the correction factor. We find significant changes between
the observed and corrected amplitudes and widths while the change in
mode frequencies was found to be insignificant. We also analyze the
variation of the corrected mode parameters over the solar cycles 23
and 24 and compare their correlations with 10.7 cm radio flux, which
represents a proxy of the solar activity.
Title: The HMI Ring-Diagram Pipeline: Recent Developments and Future
Prospects
Authors: Bogart, Richard; Baldner, Charles; Basu, Sarbani; Jain,
Kiran; Webber, Shea Hess
Bibcode: 2018csc..confE..53B
Altcode:
The HMI ring-diagram pipeline produces tracked Doppler data cubes
at three different size and time scales, their power spectra,
two independent types of "mode" (ridge) fits to the spectra, and
inversions of fit parameters measuring the mean near- and sub-surface
flows. Ancillary products include measures of the mean magnetic
activity associated with the tracked cubes, rotation averages of
the power spectra at different Stonyhurst locations, and long-term
averages of the input Dopplergrams. Active efforts are currently
underway to improve many of these products. We review recent changes
to the analysis procedures and products, discuss known problems, and
describe modifications and updates in progress, under development,
and/or contemplated for the near future.
Title: Investigation of Acoustic Halos using Multi-Height SDO
Observations
Authors: Tripathy, S. C.; Jain, Kiran; Kholikov, S.; Burtseva, O.;
Hill, F.; Cally, P.
Bibcode: 2018csc..confE.130T
Altcode:
The interpretation of acoustic waves surrounding active regions has
been a challenging task since the influence of magnetic field on the
incident waves is not fully understood. As a result, structure and
dynamics of active regions beneath the surface show significant
uncertainties. Recent numerical simulations and helioseismic
measurements in active regions have demonstrated that the key to the
understanding of these complex processes requires a synergy between
models and helioseismic inferences from observations. In this context,
using data from Helioseismic Magnetic Imager and Atmospheric Imaging
Assembly instruments on board the Solar Dynamics Observatory, we
characterize the spatio-temporal power distribution around active
regions as a function of the height in the solar atmosphere. We
find power enhancements (acoustic halos) occur above the acoustic
cutoff frequency and extends up to 10 mHz in HMI Doppler and AIA
170 nm observations and are strong functions of magnetic field and
their inclination angle. We also examine the relative phases and
cross-coherence spectra and find different wave characteristics at
different heights.
Title: Impact of observational duty cycle on the measurement of
local helioseismic mode parameters
Authors: Tripathy, Sushanta; Bogart, Richard; Jain, Kiran
Bibcode: 2018csc..confE..56T
Altcode:
The effect of data gaps on the power spectra and the mode parameters
can be explored by imposing a simulated observing window function on
a continuous time series of predefined length as is used in standard
ring diagram analysis. Here, we investigate the effect of these gaps
in HMI data on board SDO through a Monte Carlo analysis. It may be
noted that in case of HMI observations, the data gaps occur primarily
due to the eclipses and calibrations and thus the distribution can be
characterized by a two-element quasi-periodic population. From the
Monte Carlo simulations, we examine (i) the presence or absence of
the individual modes in the different fitting methods, (ii) systematic
effects in frequencies and flow parameters, (iii) systematic effects
in the inversions, and (iv) the extent to which these effects depend
on the length of the analysis interval. As a base line, we use the
absolutely continuous HMI data (no gaps) that are available for periods
of up to a week but no more due to the weekly calibration of HMI and/or
AIA data. The study uses data both from quiet and active periods.
Title: Variation in Sun's Seismic Radius and its implication on the
TSI variability
Authors: Jain, Kiran; Tripathy, Sushanta; Hill, Frank
Bibcode: 2018csc..confE.131J
Altcode:
Space-borne instruments on-board SoHO and SDO have been collecting
uninterrupted helioseismic data since 1996 and are providing a unique
opportunity to study changes occurring below the surface over two
solar cycles, 23 and 24. Here we study the variation in solar seismic
radius with the changing level of the surface magnetic activity. The
seismic radius is calculated from the fundamental modes of solar
oscillations utilizing the observations from SoHO/MDI and SDO/HMI. Our
study suggests that the sub-surface layers shrinks with increasing
magnetic activity. We interpret these changes in seismic radius to be
caused by the variation of sound speed, temperature or the changes
in the super-adiabatic superficial layers. Our estimated maximum
change in seismic radius during a solar cycle is about 5 kilometers,
and is consistent in both solar cycles 23 and 24. We also explore the
relationship between seismic solar radius and the total solar irradiance
(TSI) and find that the radius variation plays a secondary role in TSI
variability. We further observe that the solar irradiance increases
with decreasing seismic radius, however the anti-correlation between
them is moderately weak.
Title: The Sun's Seismic Radius as Measured from the Fundamental
Modes of Oscillations and Its Implications for the TSI Variations
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2018ApJ...859L...9J
Altcode: 2018arXiv180505307J
In this Letter we explore the relationship between the solar seismic
radius and total solar irradiance (TSI) during the last two solar
cycles using the uninterrupted data from space-borne instruments on
board the Solar and Heliospheric Observatory (SoHO) and the Solar
Dynamics Observatory (SDO). The seismic radius is calculated from the
fundamental (f) modes of solar oscillations utilizing the observations
from SoHO/Michelson Doppler Imager (MDI) and SDO/Helioseismic and
Magnetic Imager (HMI), and the TSI measurements are obtained from
SoHO/VIRGO. Our study suggests that the major contribution to the TSI
variation arises from the changes in magnetic field, while the radius
variation plays a secondary role. We find that the solar irradiance
increases with decreasing seismic radius; however, the anti-correlation
between them is moderately weak. The estimated maximum change in seismic
radius during a solar cycle is about 5 km, and is consistent in both
solar cycles 23 and 24. Previous studies ;suggest a radius change at
the surface of the order of 0.06 arcsec to explain the 0.1% variation
in the TSI values during the solar cycle; however, our inferred seismic
radius change is significantly smaller, hence the TSI variations cannot
be fully explained by the temporal changes in seismic radius.
Title: Un-interrupted Sun-as-a-star Helioseismic Observations over
Multiple Solar Cycles
Authors: Jain, Kiran; Tripathy, Sushanta; Hill, Frank; Salabert,
David; García, Rafael A.; Broomhall, Anne-Marie
Bibcode: 2018IAUS..340...27J
Altcode: 2018arXiv180505298J
We analyze Sun-as-a-star observations spanning over solar cycles
22 - 24 from the ground-based network BiSON and solar cycles 23 -
24 collected by the space-based VIRGO and GOLF instruments on board
the SoHO satellite. Using simultaneous observations from all three
instruments, our analysis suggests that the structural and magnetic
changes responsible for modifying the frequencies remained comparable
between cycle 23 and cycle 24 but differ from cycle 22. Thus we
infer that the magnetic layer of the Sun has become thinner since the
beginning of cycle 23 and continues during the current cycle.
Title: 22 Year Solar Magnetic Cycle and its relation to Convection
Zone Dynamics
Authors: Jain, Kiran; Tripathy, Sushanta; Komm, Rudolf; Hill, Frank;
Simoniello, Rosaria
Bibcode: 2018IAUS..340....9J
Altcode: 2018arXiv180505371J
Using continuous observations for 22 years from ground-based network
GONG and space-borne instruments MDI onboard SoHO and HMI onboard SDO,
we report both global and local properties of the convection zone and
their variations with time.
Title: A study of acoustic halos in active region NOAA 11330 using
multi-height SDO observations
Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Hill, F.; Rajaguru,
S. P.; Cally, P. S.
Bibcode: 2018AdSpR..61..691T
Altcode: 2017arXiv171101259T
We analyze data from the Helioseismic Magnetic Imager (HMI) and the
Atmospheric Imaging Assembly (AIA) instruments on board the Solar
Dynamics Observatory (SDO) to characterize the spatio-temporal acoustic
power distribution in active regions as a function of the height in
the solar atmosphere. For this, we use Doppler velocity and continuum
intensity observed using the magnetically sensitive line at 6173 Å
as well as intensity at 1600 Å and 1700 Å. We focus on the power
enhancements seen around AR 11330 as a function of wave frequency,
magnetic field strength, field inclination and observation height. We
find that acoustic halos occur above the acoustic cutoff frequency and
extends up to 10 mHz in HMI Doppler and AIA 1700 Å observations. Halos
are also found to be strong functions of magnetic field and their
inclination angle. We further calculate and examine the spatially
averaged relative phases and cross-coherence spectra and find different
wave characteristics at different heights.
Title: Arecibo - HF experiments in the E_region
Authors: Nossa, E.; Jain, K.; Sulzer, M. P.; Perillat, P.
Bibcode: 2017AGUFMSM23B2611N
Altcode:
The new Arecibo Observatory - HF facility started operations in
2015. The HF facility is fully operational, acquiring consecutive days
of data without unwanted interruptions. It has a maximum transmitted
power of 600kW, with center frequencies at 5.125 MHz and 8.175 MHz. The
8.175 (5.125) MHz band frequency has a gain of 25.5 (22) dB and HPBW of
8.5 (13) degrees. The effects of the HF experiments in the ionosphere
are being observed with the Arecibo incoherent scatter radar (ISR). The
ISR has two beams that simultaneously could sense the modified region
and the region outside of the affected volume. The ISR has height
resolution of 300 m. and allows to observe from altitudes 95 km to the
topside ionosphere. Observation of the E-region - HF experiments are
sparse but possible at Arecibo. High ionization at a height 100 km are
needed to modify the region artificially. This paper presents examples
of E-region enhanced plasma lines (See Figure). Diagnostic of the layers
is made using the ISR to estimate electron density, temperatures, ion
drifts, among others. The data shows exceptional modifications of the
ionosphere that range from creating artificial cavities and layers,
induced irregularities, substantial variations in temperature profiles
to enhanced ion and plasma densities.Previously, the HF experiments
were performed to study specific effects in a narrow region. However,
the extent of the data collected with the ISR during 2017 is revealing
new features and different kind of forces that artificially modify
extended regions of the ionosphere. This paper exhibits examples
where the interaction between the E and F-region when HF experiments
are evident. A theory of a correlation between the two layers due to
different conductivities is explored to illustrate how the enhancement
of irregularities is produced and maintained over time. Examples of
strong artificially induced irregularities formed at F-region heights
when Sporadic E-layer is present are shown to support the theory.The
Figure shows an enhanced plasma line for the diurnal E-region. For this
HF experiment, the plasma density increased from 3.6 MHz to 5.1MHz
(which corresponds to the HF frequency). The vertical lines observed
in the Figure are artifacts from the data, as well as the fake enhanced
plasma lines at frequencies different than the HF frequency.
Title: Mesospheric Na Variability and Dependence on Geomagnetic and
Solar Activity over Arecibo
Authors: Jain, K.; Raizada, S.; Brum, C. G. M.
Bibcode: 2017AGUFMSA11A2247J
Altcode:
The Sodium (Na) resonance lidars located at the Arecibo Observatory
offer an excellent opportunity to study the mesosphere/lower
thermosphere(MLT) region. Different metals like Fe, Mg, Na, K, Ca and
their ions are deposited in the 80 - 120 km altitude range due to the
ablation of meteors caused by frictional heating during their entry
into the Earth's atmosphere. We present an investigation of the neutral
mesospheric Na atom layers over Arecibo. Data on the Na concentrations
was collected using a resonance lidar tuned to the of Na wavelength
at 589 nm. This wavelength is achieved with a dye-laser pumped by the
second harmonic (532 nm) generated from a state-of-the-art commercial
Nd:YAG laser. The backscattered signal is received on a 0.8 m (diameter)
Cassegrain telescope. The study is based on this data acquired from
1998-2017 and its relation to variations in geomagnetic and solar
conditions. We also investigate seasonal and long term trends in the
data. The nightly-averaged altitude profiles were modeled as Gaussian
curves. From this modeled data we obtain parameters such as the peak,
abundance, centroid and width of the main Na layer. Preliminary
results show that the Na abundance is more sensitive to changes in
geomagnetic and solar variations as compared to the width and centroid
height. The seasonal variation exhibits higher peak densities during
the local summer and has a secondary maximum during the winter [as
shown in the attached figure]. Our analysis demonstrates a decrease
in the peak and the abundance of Na atoms with the increase of solar
and geomagnetic activity.
Title: Probing Subsurface Flows in NOAA Active Region 12192:
Comparison with NOAA 10486
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2017ApJ...849...94J
Altcode: 2017arXiv171002137J
NOAA Active Region (AR) 12192 is the biggest AR observed in solar cycle
24 so far. This was a long-lived AR that survived for four Carrington
rotations (CRs) and exhibited several unusual phenomena. We measure
the horizontal subsurface flows in this AR in multiple rotations using
the ring-diagram technique of local helioseismology and the Global
Oscillation Network Group (GONG+) Dopplergrams, and we investigate how
different was the plasma flow in AR 12192 from that in AR 10486. Both
regions produced several high M- and X-class flares, but they had
different coronal mass ejection (CME) productivity. Our analysis
suggests that these ARs had unusually large horizontal flow amplitude
with distinctly different directions. While meridional flow in AR
12192 was poleward that supports the flux transport to poles, it was
equatorward in AR 10486. Furthermore, there was a sudden increase in the
magnitude of estimated zonal flow in shallow layers in AR 12192 during
the X3.1 flare; however, it reversed direction in AR 10486 with the
X17.2 flare. These flow patterns produced strong twists in horizontal
velocity with depth in AR 10486 that persisted throughout the disk
passage, as opposed to AR 12192, which produced a twist only after
the eruption of the X3.1 flare that disappeared soon after. Our study
indicates that the sunspot rotation combined with the reorganization
of magnetic field in AR 10486 was not sufficient to decrease the flow
energy even after several large flares that might have triggered
CMEs. Furthermore, in the absence of sunspot rotation in AR 12192,
this reorganization of magnetic field contributed significantly to
the substantial release of flow energy after the X3.1 flare.
Title: Cross-Spectral Fitting of HMI Velocity and Intensity Data
Authors: Tripathy, Sushanta C.; Barban, Caroline; Jain, Kiran;
Kholikov, Shukur; Hill, Frank
Bibcode: 2016usc..confE..84T
Altcode:
The simultaneous HMI velocity and intensity observations are used
to obtain better estimates of solar acoustic mode parameters. This
is achieved by fitting four spectra simultaneously viz. velocity,
intensity, the phase difference and the coherence between the
intensity and velocity spectra. We further compare the oscillation mode
parameters obtained from the single-observable fitting and those from
the cross-spectral fitting method. We find that the mode frequencies
derived from the cross-spectral procedure are lower than those derived
from the velocity spectrum fitted with an asymmetrical profile. We
further note a clear solar cycle dependence in the mode frequencies
while other mode parameters e.g. amplitudes and line widths do not show
significant variation with solar activity. This corroborates earlier
findings that the interpretation of model fit parameters based on
measurements of a single spectra should be examined critically.
Title: Magnetoseismology of Active Regions using Multi-wavelength
Observations from SDO
Authors: Tripathy Sushanta C.; Jain, Kiran; Kholikov, Shukur; Hill,
Frank; Cally, Paul S.
Bibcode: 2016usc..confE..85T
Altcode:
The structure and dynamics of active regions beneath the surface show
significant uncertainties due to our limited understanding of the
wave interaction with magnetic field. Recent numerical simulations
further demonstrate that the atmosphere above the photospheric
levels also modifies the seismic observables at the surface. Thus
the key to improve helioseismic interpretation beneath the active
regions requires a synergy between models and helioseismic inferences
from observations. In this context, using data from Helioseismic
Magnetic Imager and Atmospheric Imaging Assembly onboard Solar
Dynamics Observatory, we characterize the spatio-temporal power
distribution in and around active regions. Specifically, we focus on
the power enhancements seen around active regions as a function of wave
frequencies, strength, inclination of magnetic field and observation
height as well as the relative phases of the observables and their
cross-coherence functions. It is expected that these effects will help
us to comprehend the interaction of acoustic waves with fast and slow
MHD waves in the solar photosphere.
Title: A New Challenge to Solar Dynamo Models from Helioseismic
Observations: The Latitudinal Dependence of the Progression of the
Solar Cycle
Authors: Simoniello, R.; Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2016ApJ...828...41S
Altcode: 2016arXiv160603037S
The onset of the solar cycle at mid-latitudes, the slowdown in the
drift of sunspots toward the equator, the tail-like attachment, and
the overlap of successive cycles at the time of minimum activity are
delicate issues in models of the αΩ dynamo wave and the flux transport
dynamo. Very different parameter values produce similar results, making
it difficult to understand the origin of the properties of these solar
cycles. We use helioseismic data from the Global Oscillation Network
Group to investigate the progression of the solar cycle as observed
in intermediate-degree global p-mode frequency shifts at different
latitudes and subsurface layers, from the beginning of solar cycle
23 up to the maximum of the current solar cycle. We also analyze
those for high-degree modes in each hemisphere obtained through
the ring-diagram technique of local helioseismology. The analysis
highlights differences in the progression of the cycle below 15°
compared to higher latitudes. While the cycle starts at mid-latitudes
and then migrates equatorward/poleward, the sunspot eruptions of the old
cycle are still ongoing below 15° latitude. This prolonged activity
causes a delay in the onset of the cycle and an overlap of successive
cycles, whose extent differs in the two hemispheres. Then the activity
level rises faster, reaching a maximum characterized by a single-peak
structure as opposed to the double peak at higher latitudes. Afterwards
the descending phase shows up with a slower decay rate. The latitudinal
properties of the progression of the solar cycle highlighted in this
study provide useful constraints for discerning among the multitude
of solar dynamo models.
Title: Solar origins of space weather
Authors: Jain, Kiran; Komm, Rudolf W.
Bibcode: 2016AsJPh..25..363J
Altcode:
Space weather refers to the varying conditions in the space environment
near Earth that are driven by the Sun and its changing magnetic
field. The magnetic field originates in the interior of the Sun and
extends throughout the solar atmosphere. We discuss the solar sources
of space weather and focus on coronal mass ejections (CMEs), flares,
and solar energetic particles (SEP) and on the on-going efforts to
predict these eruptive events and their effect on space weather.
Title: Magnetoseismology of Active Regions using Multi-wavelength
Observations from GONG and SDO
Authors: Tripathy, Sushanta; Jain, Kiran; Kholikov, Shukur; Hill,
Frank; Cally, Paul
Bibcode: 2016SPD....47.0721T
Altcode:
The structure and dynamics of active regions beneath the surface show
significant uncertainties due to our limited understanding of the wave
interaction with magnetic field. Recent numerical simulations further
demonstrate that the atmosphere above the photospheric levels also
modifies the seismic observables at the surface. Thus the key to improve
helioseismic interpretation beneath the active regions requires a
synergy between models and helioseismic inferences from observations. In
this context, using data from Global Oscillation Network Group and from
Helioseismic Magnetic Imager and Atmospheric Imaging Assembly onboard
Solar Dynamics Observatory, we characterize the spatio-temporal power
distribution in and around active regions. Specifically, we focus on
the power enhancements seen around active regions as a function of wave
frequencies, strength, inclination of magnetic field and observation
height as well as the relative phases of the observables and their
cross-coherence functions. It is expected that these effects will help
us to comprehend the interaction of acoustic waves with magnetic field
in the solar photosphere.
Title: Solar Activity in Cycle 24 - What do Acoustic Oscillations
tell us?
Authors: Jain, Kiran; Tripathy, Sushant; Simoniello, Rosaria; Hill,
Frank
Bibcode: 2016SPD....47.0716J
Altcode:
Solar Cycle 24 is the weakest cycle in modern era of space- and
ground-based observations. The number of sunspots visible on solar disk
and other measures of magnetic activity have significantly decreased
from the last cycle. It was also preceeded by an extended phase of low
activity, a period that raised questions on our understanding of the
solar activity cycle and its origin. This unusual behavior was not only
limited to the visible features in Sun's atmosphere, the helioseismic
observations also revealed peculiar behavior in the interior. It
was suggested that the changes in magnetic activity were confined
to shallower layers only, as a result low-degree mode frequencies
were found to be anti-correlated with solar activity. Here we present
results on the progression of Cycle 24 by analyzing the uninterrupted
helioseismic data from GONG and SDO/HMI, and discuss differences and
similarity between cycles 23 and 24 in relation to the solar activity.
Title: GONG ClassicMerge: Pipeline and Product
Authors: Hughes, Anna L. H.; Jain, Kiran; Kholikov, Shukur; the NISP
Solar Interior Group
Bibcode: 2016arXiv160300836H
Altcode:
A recent processing effort has been undertaken in order to extend the
range-of-coverage of the GONG merged dopplergrams. The GONG-Classic-era
observations have now been merged to provide, albeit at lower
resolution, mrvzi data as far back as May of 1995. The contents
of this document provide an overview of what these data look like,
the processing steps used to generate them from the original site
observations, and the outcomes of a few initial quality-assurance tests
designed to validate the final merged images. Based on these tests,
the GONG project is releasing this data product to the user community
(http://nisp.nso.edu/data).
Title: Horizontal Flows in Active Regions from Ring-diagram and
Local Correlation Tracking Methods
Authors: Jain, Kiran; Tripathy, S. C.; Ravindra, B.; Komm, R.; Hill, F.
Bibcode: 2016ApJ...816....5J
Altcode: 2015arXiv151103208J
Continuous high-cadence and high spatial resolution Dopplergrams allow
us to study subsurface dynamics that may be further extended to explore
precursors of visible solar activity on the surface. Since the p-mode
power is absorbed in the regions of high magnetic field, the inferences
in these regions are often presumed to have large uncertainties. In
this paper, using the Dopplergrams from space-borne Helioseismic
Magnetic Imager, we compare horizontal flows in a shear layer below the
surface and the photospheric layer in and around active regions. The
photospheric flows are calculated using the local correlation tracking
(LCT) method, while the ring-diagram technique of helioseismology
is used to infer flows in the subphotospheric shear layer. We find
a strong positive correlation between flows from both methods near
the surface. This implies that despite the absorption of acoustic
power in the regions of strong magnetic field, the flows inferred
from the helioseismology are comparable to those from the surface
measurements. However, the magnitudes are significantly different;
the flows from the LCT method are smaller by a factor of 2 than the
helioseismic measurements. Also, the median difference between the
direction of corresponding vectors is 49°.
Title: Response of Solar Oscillations to Magnetic Activity in Cycle 24
Authors: Jain, K.; Tripathy, S. C.; Hill, F.
Bibcode: 2015AGUFMSH23A2422J
Altcode:
Acoustic mode parameters are generally used to study the variability
of the solar interior in response to changing magnetic activity. While
oscillation frequencies do vary in phase with the solar activity,
the mode amplitudes are anti-correlated. Now, continuous measurements
from ground and space allow us study the origin of such variability
in detail. Here we use intermediate-dgree mode frequencies computed
from a ground-based 6-site network ( GONG), covering almost two solar
cycles from the minimum of cycle 23 to the declining phase of cycle
24, to investigate the effect of remarkably low solar activity on
the solar oscillations in current cycle and the preceding minimum;
is the response of acoustic oscillations to magnetic activity in cycle
24 similar to cycle 23 or there are differences between cycles 23 and
24? In this paper, we analyze results for both solar cycles, and try
to understand the origin of similarities/differences between them. We
will also compare our findings with the contemporaneous observations
from space (SOHO/MDI and SDO/HMI).
Title: Variations in High Degree Acoustic Mode Frequencies of the
Sun during Solar Cycles 23 and 24
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2015ApJ...812...20T
Altcode: 2015arXiv150905474T
We examine continuous measurements of the high-degree acoustic mode
frequencies of the Sun covering the period from 2001 July to 2014
June. These are obtained through the ring-diagram technique applied
to the full-disk Doppler observations made by the Global Oscillation
Network Group. The frequency shifts in the degree range of 180
≤slant {\ell } ≤slant 1200 are correlated with different proxies
of solar activity, e.g., 10.7 cm radio flux, the International Sunspot
Number, and the strength of the local magnetic field. In general,
a good agreement is found between the shifts and activity indices,
and the correlation coefficients are found to be comparable with
intermediate-degree mode frequencies. Analyzing the frequency shifts
separately for the two cycles, we find that cycle 24 is weaker than
cycle 23. Since the magnetic activity is known to be different in the
two hemispheres, for the first time, we compute the frequency shifts
over the two hemispheres separately and find that the shifts also
display hemispheric asymmetry; the amplitude of shifts in the northern
hemisphere peaked during late 2011, more than two years earlier than
in the south. We further correlate the hemispheric frequency shifts
with the hemispheric sunspot number and mean magnetic activity index
(MAI). Since the frequency shifts and the hemispheric activity indices
are found to be significantly correlated, we suggest that the shifts
be used as an indicator of hemispheric activity since not many indices
are measured over the two hemispheres separately. We also investigate
the variation at different latitudinal bands and conclude that the
shifts in active latitudes correlate well with the local MAI.
Title: Divergent Horizontal Sub-surface Flows within Active Region
11158
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2015ApJ...808...60J
Altcode: 2015arXiv150800519J
We measure the horizontal subsurface flow in a fast emerging
active region (AR; NOAA 11158) using the ring-diagram technique
and the Helioseismic and Magnetic Imager high spatial resolution
Dopplergrams. This AR had a complex magnetic structure and displayed
significant changes in morphology during its disk passage. Over a
period of six days from 2011 February 11 to 16, the temporal variation
in the magnitude of the total velocity is found to follow the trend
of magnetic field strength. We further analyze regions of individual
magnetic polarity within AR 11158 and find that the horizontal velocity
components in these sub-regions have significant variation with time and
depth. The leading and trailing polarity regions move faster than the
mixed-polarity region. Furthermore, both zonal and meridional components
have opposite signs for trailing and leading polarity regions at all
depths showing divergent flows within the AR. We also find a sharp
decrease in the magnitude of total horizontal velocity in deeper
layers around major flares. It is suggested that the re-organization
of magnetic fields during flares, combined with the sunspot rotation,
decreases the magnitude of horizontal flows or that the flow kinetic
energy has been converted into the energy released by flares. After
the decline in flare activity and sunspot rotation, the flows tend
to follow the pattern of magnetic activity. We also observe less
variation in the velocity components near the surface but these tend
to increase with depth, further demonstrating that the deeper layers
are more affected by the topology of ARs.
Title: Helioseismic Mode Parameters from 20 Years of Global
Oscillation Network Group (GONG) Observations
Authors: Jain, Kiran; Tripathy, Sushant C.; Hill, Frank; Simoniello,
Rosaria
Bibcode: 2015TESS....110305J
Altcode:
The intermediate-degree mode parameters are used to study the
variability of solar oscillations and their dependence on the
magnetic-activity. We use uninterrupted observations from the 6-site
network, Global Oscillation Network Group (GONG), for about 20 years
that covers a period from the minimum of cycle 23 to the declining
phase of cycle 24. Using the observations for cycle 23, it was
demonstrated that the frequencies do vary in phase with the solar
activity indices. However, the degree of correlation differs from phase
to phase of the cycle; the mode frequency shifts are strongly correlated
with the activity proxies during the rising and declining phases whereas
this correlation is significantly lower during the high-activity
period. Here we present and compare results for two solar cycles,
and try to understand the origin of the differences between both cycles.
Title: Tracking Active Region NOAA 12192 in Multiple Carrington
Rotations
Authors: Jain, Kiran; Tripathy, Sushant C.; Hill, Frank
Bibcode: 2015TESS....110306J
Altcode:
Active region NOAA 12192 appeared on the visible solar disk on
October 18, 2014 and grew rapidly into the largest such region since
1990. During its entire transit across the Earth facing side of the
Sun, it produced a significant number of X- and M-class flares. The
combination of front-side and helioseismic far-side images clearly
indicated that it lived through several Carrington rotations. In this
paper, using Dopplergrams from GONG and HMI, we present a study on mode
parameters, viz. oscillation frequencies, amplitude, and sub-surface
flows and investigate how these vary with the evolution of active
region in multiple rotations. We also present a detailed comparison
between NOAA 10486 (the biggest active region in cycle 23) and NOAA
12192, and discuss the similarities/differences between them.
Title: Fitting of Intensity-Velocity Cross Spectrum using GONG and
HMI Oscillation Data
Authors: Tripathy, S. C.; Barban, C.; Jain, K.; Kholikov, S.; Hill, F.
Bibcode: 2014AGUFMSH13B4096T
Altcode:
The fitting of solar intensity-velocity cross spectrum together with
coherence and intensity-velocity phase difference provides us with
better estimates of the oscillation mode parameters. This also serves
as a diagnostic tool to improve our understanding of the excitation of
the p-modes by convection by estimating the contribution of the solar
backgrounds which may or may not be correlated with the acoustic
modes. Using both GONG and HMI data, we will present our results
of fitting four spectra simultaneously viz. velocity, intensity,
the phase difference and the coherence between the intensity and
velocity spectra. We will compare the mode parameters obtained from
a single-observable and those from cross-spectral fitting method and
comment on the solar cycle variation of mode parameters. We will also
characterize and compare the contribution from different background
components.
Title: Photospheric and sub-photospheric Flows in Active Regions
Authors: Jain, Kiran; Komm, Rudolf W; Tripathy, Sushanta; Ravindra,
B.; Hill, Frank
Bibcode: 2014AAS...22421821J
Altcode:
The availability of continuous high-cadence and high-spatial resolution
Dopplergrams allows us to study sub-surface dynamics that may be further
extended to explore precursors of the solar activity. Since p-mode power
is absorbed in high magnetic field regions, the helioseismic inferences
in these regions are associated with large errors. In order to validate
results, we use Dopplergrams from both space-borne (Helioseismic
Magnetic Imager-HMI) and ground-based (Global Oscillation Network
Group-GONG) observations to infer horizontal flows in photospheric
and sub-photospheric layers in and around several active regions with
different characteristics. The photospheric flows are calculated using
local correlation tracking (LCT) method while ring-diagram analysis
technique is used to infer flows in the sub-photospheric regions. A
detailed comparison between flows in shear layer and photospheric
layer will be made in order to study similarities and discrepancies
in these results.
Title: A Full-Sun Magnetic Index from Helioseismology Inferences
Authors: González Hernández, I.; Díaz Alfaro, M.; Jain, K.; Tobiska,
W. K.; Braun, D. C.; Hill, F.; Pérez Hernández, F.
Bibcode: 2014SoPh..289..503G
Altcode:
Solar magnetic indices are used to model the solar irradiance and
ultimately to forecast it. However, the observation of such indices is
generally limited to the Earth-facing hemisphere of the Sun. Seismic
maps of the far side of the Sun have proven their capability to locate
and track medium-large active regions at the non-visible hemisphere. We
present here the possibility of using the average signal from these
seismic far-side maps, combined with similarly calculated near-side
maps, as a proxy to the full-Sun magnetic activity.
Title: Assessing Ring-Diagram Fitting Methods
Authors: Jain, K.; Tripathy, S. C.; Basu, S.; Baldner, C. S.; Bogart,
R. S.; Hill, F.; Howe, R.
Bibcode: 2013ASPC..478..193J
Altcode:
The ring-diagram technique is widely used to study oscillation mode
parameters and dynamics of the sub-surface layers of the Sun. In
this technique, the three-dimensional power spectrum is fitted to a
model to calculate mode parameters. The fitted velocities are then
inverted to infer the depth dependence of sub-surface flows. Here,
we examine the influence of various models on inferred quantities and
also compare results obtained with contemporaneous Dopplergrams from
SDO/HMI and GONG.
Title: Subsurface Flows in Active Region 11158
Authors: Jain, K.; Tripathy, S. C.; Komm, R.; González Hernández,
I.; Hill, F.
Bibcode: 2013ASPC..478..225J
Altcode:
We apply the ring-diagram technique to study the temporal evolution of
horizontal velocity in sub-photospheric layers beneath active regions
as they move across the solar disk. Here we present results for the
AR 11158 for six days and investigate how flows get organized within
the active region by the morphology of individual sunspots or vice
versa. We find abrupt changes in depth profiles for smaller regions
in going from one day to another, however the average flows for the
active region do not show significant temporal variation.
Title: Ring-Diagram Determinations of Solar Subsurface Flows
Authors: Bogart, R. S.; Baldner, C. S.; Burtseva, O.; Howe, R.; Jain,
K.; Rabello-Soares, M. C.; Tripathy, S. C.
Bibcode: 2013ASPC..478..211B
Altcode:
In an effort to assess and if possible to improve the quality and
reliability of large-scale near-surface flows inferred from ring-diagram
analysis, we compare results determined from uniform analysis techniques
applied to three different sets of helioseismic data sets obtained at
the same time. We discuss several observational and analysis effects
known or suspected to affect the flow inferences.
Title: Are We Entering a Period of Reduced Activity or a Grand
Minima State?
Authors: Simoniello, R.; Jain, K.; Tripathy, S. C.; Baldner, C. S.;
Turck-Chièze, S.; Hill, F.
Bibcode: 2013ASPC..478..167S
Altcode:
Solar cycle 23 has been characterized by an unpredicted deepest
minimum in nearly a century, and solar cycle 24 has turned out to be
20% less strong than the previous cycle, against expectations. Are
the current solar dynamics indicative that we might enter a period
of reduced activity or even a Grand Minima state? To answer this
question, we investigated the properties of the cyclic behavior
of solar magnetic activity, characterized by the 11- and 2-year
periodicity, the latter also known as the quasi-biennial periodicity
(QBP). Recently it has been shown that the QBP signal might be the
cycle period related to the quadrupolar component of the magnetic
dynamo configuration. Observationally and theoretically, it has been
shown that this component might play a key role over period of reduced
activity by inducing a strong North-South asymmetry. We, therefore,
wonder if the QBP signatures might be used as a precursor of solar
magnetic activity. To this aim we used 17 years of Global Oscillation
Network Group (GONG) observations to investigate the signatures and
properties of the QBP in the dipolar and quadrupolar component of
p-mode frequency shifts and in the even-order splitting coefficients
of spherical degree ℓ = 0 - 120, as the latter are related to the
magnetic field strength and oblateness. The observational findings
seem to indicate that the QBP signal strength has been particularly
strong over the ascending phase of solar cycle 23, but suddenly in
2003 became weaker and has remained weak over the ascending phase of
solar cycle 24. We argue that the QBP, since 2003, suggested a week
solar cycle 24 compared to cycle 23.
Title: Solar Cycle Variation of High-Degree Acoustic Mode Frequencies
Authors: Tripathy, S. C.; Jain, K.; Komm, R. W.; Hill, F.
Bibcode: 2013ASPC..478..221T
Altcode:
We investigate the temporal variations of the high-degree mode
frequencies measured over localized regions of the Sun though
the technique of ring-diagrams. We observe that the high-degree
mode frequencies have a solar cycle variation similar to those of
intermediate-degree modes but ten times greater. We also find that
the averaged frequency shifts are linearly correlated with routinely
measured solar activity indices e.g. 10.7 cm radio flux. We do not,
however, find any evidence of a quadratic relation between the
frequencies of individual multiplets and solar activity indices as
reported earlier from the study of global high-degree modes.
Title: Variation of solar oscillation frequencies in solar cycle 23
and their relation to sunspot area and number (Corrigendum)
Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.;
Jain, K.; Hill, F.
Bibcode: 2013A&A...560C...1J
Altcode:
No abstract at ADS
Title: Analysis of Active Region 11339 using Multi-Spectral Data
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R. S.; Basu,
S.; Hill, F.
Bibcode: 2013ASPC..478..237T
Altcode:
We apply the local helioseismic technique of ring-diagrams to Doppler
and intensity images from Helioseismic Magnetic Imager and Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory and investigate
the variation in high-degree mode frequencies and sub-surface flows of
a complex active region 11339. After subtracting the frequencies of the
quiet region from the active region, we find a reasonable agreement
between the frequencies measured from different observables. We also
observe that the depth profiles of zonal and meridional components
of the horizontal subsurface flow agree with each other within three
sigma if the contribution of quiet regions is removed.
Title: Fifty Years of Seismology of the Sun and Stars
Authors: Jain, K.; Tripathy, S. C.; Hill, F.; Leibacher, J. W.;
Pevtsov, A. A.
Bibcode: 2013ASPC..478.....J
Altcode:
No abstract at ADS
Title: Latest Results Found with Ring-Diagram Analysis
Authors: Baldner, C. S.; Basu, S.; Bogart, R. S.; Burtseva, O.;
González Hernández, I.; Haber, D.; Hill, F.; Howe, R.; Jain, K.;
Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S.
Bibcode: 2013SoPh..287...57B
Altcode: 2012SoPh..tmp..294B
Ring-diagram analysis is a helioseismic tool useful for studying
the near-surface layers of the Sun. It has been employed to study
near-surface shear, meridional circulation, flows around sunspots,
and thermal structure beneath active regions. We review recent results
obtained using ring-diagram analysis, state some of the more important
outstanding difficulties in the technique, and point out several
extensions to the technique that are just now beginning to bear fruit.
Title: Solar cycle and quasi-biennial variations in helioseismic
frequencies
Authors: Tripathy, Sushanta C.; Jain, Kiran; Simoniello, Rosaria;
Hill, Frank; Turck-Chièze, Sylvaine
Bibcode: 2013IAUS..294...73T
Altcode:
The prolonged period of solar minimum between cycles 23 and 24 has
invoked a great deal of interest to understand the origin of the
unusually low solar activity. Even though the origin of solar activity
is believed to lie in the shear layer at the base of the convection
zone, the analysis of helioseismic data seem to orientate us toward
the near surface. In this context, we analyze the signature of the
quasi-biennial periodicity seen in the oscillation frequencies which
may provide additional constraints on the solar dynamo models.
Title: Validating the Ring-diagram Flows through Numerical Simulations
Authors: Tripathy, Sushanta; Jain, K.; Basu, S.; Bogart, R. S.; Howe,
R.; Hill, F.
Bibcode: 2013SPD....44...90T
Altcode:
Among many techniques of local helioseismology, the ring-diagram
method has been quite popular because of its ability to quickly analyze
vast amounts of high-resolution data. In ring analysis, the speed and
direction of horizontal flows beneath the solar surface are assessed
by inverting fitted surface velocities for a given set of modes. Here
we discuss the validationof the inversion technique through the use
of supergranulation scale hydrodynamic numerical simulations.
Title: Solar oscillations in cycle 24 ascending
Authors: Jain, Kiran; Tripathy, Sushanta; Hill, Frank; Larson, Timothy
Bibcode: 2013JPhCS.440a2023J
Altcode:
Solar oscillation frequencies are known to follow the trend of
solar cycle and show a strong correlation with various activity
indices. However, the extended minimum between cycles 23 and 24 has
raised several questions on the correlation between frequencies and
solar activity where frequencies with different mode sets sensed
different minima. In this paper, we analyze intermediate-degree mode
frequencies as the Sun emerges from the unusually long period of minimal
magnetic activity to study their behaviour with activity indices and
compare results with the corresponding phase of cycle 23. We show that
a model based on the rising phase of cycle 23 is a good predictor for
behaviour in the rising phase of cycle 24.
Title: Temporal Variations of High-Degree Solar p-Modes using
Ring-Diagram Analysis
Authors: Burtseva, Olga; Tripathy, Sushant; Bogart, Richard; Jain,
Kiran; Howe, Rachel; Hill, Frank; Rabello-Soares, Maria Cristina
Bibcode: 2013JPhCS.440a2027B
Altcode: 2013arXiv1303.6722B
We study temporal variations in the amplitudes and widths of high-degree
acoustic modes by applying the ring-diagram technique to the GONG+,
MDI and HMI Dopplergrams during the declining phase of cycle 23 and
rising phase of cycle 24. The mode parameters from all three instruments
respond similarly to the varying magnetic activity. The mode amplitudes
and widths show consistently lower variation due to smaller magnetic
activity in cycle 24 as compared to the previous solar cycle.
Title: Low-degree multi-spectral p-mode fitting
Authors: Howe, R.; Broomhall, A. -M.; Chaplin, W. J.; Elsworth, Y.;
Jain, K.
Bibcode: 2013JPhCS.440a2011H
Altcode:
We combine unresolved-Sun velocity and intensity observations at
multiple wavelengths from the Helioseismic and Magnetic Imager and
Atmospheric Imaging Array onboard the Solar Dynamics Observatory to
investigate the possibility of multi-spectral mode-frequency estimation
at low spherical harmonic degree. We test a simple multi-spectral
algorithm using a common line width and frequency for each mode and a
separate amplitude, background and asymmetry parameter, and compare the
results with those from fits to the individual spectra. The preliminary
results suggest that this approach may provide a more stable fit than
using the observables separately.
Title: Multi-spectral study of acoustic mode parameters and
sub-surface flows
Authors: Jain, Kiran; Tripathy, S.; Basu, S.; Bogart, R.; González
Hernández, I.; Hill, F.; Howe, R.
Bibcode: 2013JPhCS.440a2012J
Altcode:
Simultaneous measurements at different wavelengths offer the prospect
of studying the sensitivity of helioseismic inferences to the choice of
observing height both in quiet-Sun and magnetically active regions. In
this context, we use observations from space-borne measurements from
the Solar Dynamics Observatory and ground-based Global Oscillation
Network Group to analyze high-degree acoustic mode parameters and
sub-surface flows obtained with different observables. We also quantify
differences and interpret results in the framework of the formation
height in solar atmosphere.
Title: Multi-wavelength analysis of active regions using ring-diagram
technique
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R.; Basu, S.;
Rabello-Soares, M. C.; Hill, F.
Bibcode: 2013JPhCS.440a2026T
Altcode:
With the availability of high-cadence and high-resolution Doppler and
intensity images from the Solar Dynamics Observatory's Helioseismic
Magnetic Imager (HMI) and Atmospheric Imager Assembly (AIA), we analyze
the characteristics of high-degree solar acoustic modes in active
regions. We apply the ring-diagram technique to Doppler, continuum
intensity measurements from HMI, and intensity images from AIA 1600
Å and 1700 Å passband to examine the high-degree mode parameters
and sub-surface horizontal flows.
Title: The Quasi-biennial Periodicity as a Window on the Solar
Magnetic Dynamo Configuration
Authors: Simoniello, R.; Jain, K.; Tripathy, S. C.; Turck-Chièze,
S.; Baldner, C.; Finsterle, W.; Hill, F.; Roth, M.
Bibcode: 2013ApJ...765..100S
Altcode: 2012arXiv1210.6796S
Manifestations of the solar magnetic activity through periodicities
of about 11 and 2 years are now clearly seen in all solar activity
indices. In this paper, we add information about the mechanism driving
the 2-year period by studying the time and latitudinal properties of
acoustic modes that are sensitive probes of the subsurface layers. We
use almost 17 years of high-quality resolved data provided by the Global
Oscillation Network Group to investigate the solar cycle changes in
p-mode frequencies for spherical degrees l from 0 to 120 and 1600 μHz
<=ν <= 3500 μHz. For both periodic components of solar activity,
we locate the origin of the frequency shift in the subsurface layers
and find evidence that a sudden enhancement in amplitude occurs in just
the last few hundred kilometers. We also show that, in both cases, the
size of the shift increases toward equatorial latitudes and from minimum
to maximum solar activity, but, in agreement with previous findings,
the quasi-biennial periodicity (QBP) causes a weaker shift in mode
frequencies and a slower enhancement than that caused by the 11-year
cycle. We compare our observational findings with the features predicted
by different models, that try to explain the origin of this QBP and
conclude that the observed properties could result from the beating
between a dipole and quadrupole magnetic configuration of the dynamo.
Title: Ring-Diagram Analysis of Active Regions using HMI and AIA data
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R.; Basu, S.;
Hill, F.
Bibcode: 2013enss.confE..42T
Altcode:
With the launch of the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory, high-resolution observations of the Sun are
available in Doppler velocity and continuum intensity. In addition,
data is also available from the Atmospheric Imaging Assembly in 160
and 170 nm bands, which are useful for helioseismic studies. Here
we use the ring-diagram technique and analyze six active regions,
simple and complex, observed simultaneously in different wavelengths,
and focus on the characteristics of high-degree modes e.g. frequencies
and asymmetry parameters. We further investigate the dependence of
sub-surface flows on the choice of the observables to comprehend
the effect of the observing heights, which may be important in
multi-wavelength local helioseismic studies.
Title: Acoustic Mode Frequencies of the Sun During the Minimum Phase
Between Solar Cycles 23 and 24
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2013SoPh..282....1T
Altcode: 2012SoPh..tmp..239T; 2012arXiv1210.0060T
We investigate the spatial and temporal variations of the high-degree
mode frequencies calculated over localized regions of the Sun during the
extended minimum phase between solar cycles 23 and 24. The frequency
shifts measured relative to the spatial average over the solar disk
indicate that the correlation between the frequency shift and magnetic
field strength during the low-activity phase is weak. The disk-averaged
frequency shifts computed relative to a minimal activity period also
reveal a moderate correlation with different activity indices, with
a maximum linear correlation of about 72 %. From the investigation of
the frequency shifts at different latitudinal bands, we do not find a
consensus period for the onset of solar cycle 24. The frequency shifts
corresponding to most of the latitudes in the northern hemisphere and
30° south of the equator indicate the minimum epoch to be February
2008, which is earlier than inferred from solar activity indices.
Title: Helioseismic analysis of active regions using HMI and AIA data
Authors: Tripathy, S. C.; Jain, K.; Howe, R.; Bogart, R. S.; Hill, F.
Bibcode: 2012AN....333.1013T
Altcode:
We apply the ring-diagram technique to analyze three active regions
located near the central meridian. Using Doppler, continuum intensity,
and line depth images from the Helioseismic Magnetic Imager (HMI),
we investigate the variation in the high-degree mode asymmetry,
frequencies, and horizontal flows. We find that the sub-surface zonal
and meridional flows do not change significantly with the choice of
different observables representing different heights in the solar
photosphere, while the mode frequencies differ. We also examine the
2-d acoustic power distribution using data from HMI and the Atmospheric
Imaging Assembly (AIA) 1600 and 1700 Å, bands.
Title: Two-Dimensional Helioseismic Power, Phase, and Coherence
Spectra of Solar Dynamics Observatory Photospheric and Chromospheric
Observables
Authors: Howe, Rachel; Jain, Kiran; Bogart, Richard S.; Haber,
Deborah A.; Baldner, Charles S.
Bibcode: 2012SoPh..281..533H
Altcode: 2012arXiv1208.1644H; 2012SoPh..tmp..200H
While the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamics Observatory (SDO) provides Doppler-velocity [V],
continuum-intensity [IC], and line-depth [Ld] observations,
each of which is sensitive to the five-minute acoustic spectrum,
the Atmospheric Imaging Array (AIA) also observes at wavelengths -
specifically the 1600 and 1700 Å bands - that are partly formed in
the upper photosphere and have good sensitivity to acoustic modes. In
this article we consider the characteristics of the spatio-temporal
Fourier spectra in AIA and HMI observables for a 15-degree region
around NOAA Active Region 11072. We map the spatio-temporal-power
distribution for the different observables and the HMI Line Core
[IL], or Continuum minus Line Depth, and the phase and
coherence functions for selected observable pairs, as a function
of position and frequency. Five-minute oscillation power in all
observables is suppressed in the sunspot and also in plage areas. Above
the acoustic cut-off frequency, the behaviour is more complicated:
power in HMI IC is still suppressed in the presence of
surface magnetic fields, while power in HMI IL and the
AIA bands is suppressed in areas of surface field but enhanced in an
extended area around the active region, and power in HMI V is enhanced
in a narrow zone around strong-field concentrations and suppressed
in a wider surrounding area. The relative phases of the observables
and their cross-coherence functions are also altered around the active
region. These effects may help us to understand the interaction of waves
and magnetic fields in the different layers of the photosphere and will
need to be taken into account in multi-wavelength local-helioseismic
analysis of active regions.
Title: Seismic comparison of the 11- and 2-year cycle signatures in
the Sun
Authors: Simoniello, R.; Jain, K.; Tripathy, S. C.; Turck-Chiéze,
S.; Finsterle, W.; Roth, M.
Bibcode: 2012AN....333.1018S
Altcode: 2012arXiv1210.6182S
The solar magnetic activity consists of two periodic components: the
main cycle with a period of 11 yr and a shorter cycle with a period
of ≈2 yr. The origin of this second periodicity is still not well
understood. We use almost 15 years of long high-quality resolved data
provided by the Global Oscillation Network Group (GONG) to investigate
the solar cycle changes in p-mode oscillations with spherical degree
ℓ= 0-120 and in the range of 1600 \muHz \le\nu\le 3500 \muHz. For both
periodic components of solar magnetic activity our findings locate the
origin of the frequency shift in the subsurface layers with a sudden
enhancement in the amplitude of the shift in the last few hundred
kilometers. We also show that the size of the shift increases towards
equatorial latitudes and from minimum to maximum of solar activity. On
the other hand, the signatures of the 2-yr cycle differ from the one
of the 11-yr cycle in the magnitude of the shift, as the 2-yr cycle
causes a weaker shift in mode frequencies and a slower enhancement in
the last few hundred kilometers. Based on these findings we speculate
that a possible physical mechanism behind the quasi biennial periodicity
(QBP) could be the beating between different dynamo modes (dipole and
quadrupole mode).
Title: Variation of solar oscillation frequencies in solar cycle 23
and their relation to sunspot area and number
Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.;
Jain, K.; Hill, F.
Bibcode: 2012A&A...545A..73J
Altcode:
Aims: Studying the long term evolution of the solar acoustic
oscillations is necessary for understanding how the large-scale solar
dynamo operates. In particular, an understanding of the solar cycle
variation in the frequencies of solar oscillations can provide a
powerful diagnostic tool for constraining various dynamo models. In
this work, we report the temporal evolution of solar oscillations
for the solar cycle 23, and correlate with solar magnetic activity
indices.
Methods: We use solar oscillation frequencies obtained
from the Michelson Doppler Imager on board the Solar and Heliospheric
Observatory, correlate them with the sunspot number provided by the
international sunspot number, RI, and compare them with the
sunspot number calculated with the Sunspot Tracking And Recognition
Algorithm (STARA).
Results: We find that the mean frequency
shifts correlate very well with the sunspot numbers obtained from
two different datasets. We also find a hysteresis-type behaviour
for the STARA sunspot area and mean magnetic field strength for the
different phases of the solar cycle. The increase in solar oscillation
frequencies precedes slightly the increase in total sunspot area and
the mean magnetic field strength for the solar cycle 23. We briefly
discuss the cyclic behaviour in the context of p-mode frequencies.
Title: Subsurface Flows in and Around Active Regions with Rotating
and Non-rotating Sunspots
Authors: Jain, K.; Komm, R. W.; González Hernández, I.; Tripathy,
S. C.; Hill, F.
Bibcode: 2012SoPh..279..349J
Altcode: 2012arXiv1205.2356J
The temporal variation of the horizontal velocity in sub-surface layers
beneath three different types of active region is studied using the
technique of ring diagrams. In this study, we select active regions
(ARs) 10923, 10930, 10935 from three consecutive Carrington rotations:
AR 10930 contains a fast-rotating sunspot in a strong emerging active
region while other two have non-rotating sunspots with emerging flux
in AR 10923 and decaying flux in AR 10935. The depth range covered is
from the surface to about 12 Mm. In order to minimize the influence
of systematic effects, the selection of active and quiet regions is
made so that these were observed at the same heliographic locations
on the solar disk. We find a significant variation in both components
of the horizontal velocity in active regions as compared to quiet
regions. The magnitude is higher in emerging-flux regions than in the
decaying-flux region, in agreement with earlier findings. Further,
we clearly see a significant temporal variation in depth profiles
of both zonal and meridional flow components in AR 10930, with the
variation in the zonal component being more pronounced. We also notice
a significant influence of the plasma motion in areas closest to the
rotating sunspot in AR 10930, while areas surrounding the non-rotating
sunspots in all three cases are least affected by the presence of the
active region in their neighborhood.
Title: Temporal Variation of Subsurface Flows in Active Regions
Authors: Komm, Rudolf W.; Jain, K.; Tripathy, S. C.; Gonzalez
Hernandez, I.; Hill, F.
Bibcode: 2012shin.confE.121K
Altcode:
We apply the ring-diagram technique to study the temporal variation of
horizontal velocity in sub-photospheric layers beneath active regions
as they move across the solar disk. We categorize these active regions
on the basis of their dynamical characteristics and investigate
how velocity components beneath rotating sunspots differ from that
in non-rotating sunspots. Our study clearly shows that there is a
singnificant temporal variation in depth profiles of both zonal and
meridional components in active regions with rotating sunspots while
these variations remain small for non-rotating sunspots.
Title: Multi-Wavelength Helioseismology: Power and Phase Maps in an
Active Region
Authors: Hill, Frank; Howe, R.; Jain, K.; Tripathy, S.; Bogart, R.;
Baldner, C.; Haber, D.
Bibcode: 2012AAS...22020504H
Altcode:
The phase and amplitude of acoustic waves in the solar atmosphere is
modified in the presence of magnetic regions. Waves at frequencies
above the acoustic cutoff show a complex pattern of changes depending
on both temporal frequency and the height of formation of the quantity
observed, with phase shifts as well as enhancement and suppression of
power surrounding the active region. We show some examples of these
effects in Doppler and intensity observations from the Helioseismic
and Magnetic Imager and in the 1600 and 1700 Angstrom bands of the
Atmospheric Imaging Array aboard the Solar Dynamics Observatory,
probing the photosphere and lower chromosphere.
Title: The Evolution of Large-Scale Subsurface Flow Patterns in
the Sun
Authors: Bogart, Richard S.; Baldner, C. S.; Basu, S.; Burtseva, O.;
Gonzalez-Hernandez, I.; Haber, D. A.; Hill, F.; Howe, R.; Jain, K.;
Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S.
Bibcode: 2012AAS...22020509B
Altcode:
Ring-diagram analysis permits us to infer large-scale flow fields at the
photosphere and down to depths of about 0.95 R. We present comparisons
of the mean zonal and meridional velocity profiles determined from
uniform analysis techniques applied to three observational data sets,
those from the SDO/HMI and SOHO/MDI missions and the GONG project,
over the last 18 years. We pay special attention to measurements
obtained during the summer of 2010, when observations from all three
observatories were available. We discuss systematic effects affecting
the individual datasets in order to analyse evolution of global flows
over the time scale of the solar cycle.
Title: Data From The HMI Ring-Diagram Pipelines
Authors: Bogart, Richard S.; Baldner, C. S.; Basu, S.;
Gonzalez-Hernandez, I.; Haber, D. A.; Hill, F.; Howe, R.; Jain, K.;
Komm, R. W.; Rabello-Soares, M. C.; Tripathy, S.
Bibcode: 2012AAS...22020512B
Altcode:
The HMI data pipeline for measurement of sub-surface flows with
ring-diagram analysis has been running for nearly two years, and
virtually all HMI Doppler data have been analyzed. Nearly 5 million
local-area power spectra have been produced and fitted for regions of
various sizes, and inversions for the depth structure of flows have
been performed for over 150,000 of the larger regions. The pipeline
for determination of the sub-surface thermal structure is still under
active development, with test results for a number of strong active
regions currently available for analysis. We describe the ring-diagram
pipelines, report on their performance, describe the data products
available, and discuss outstanding problems and issues for further
development.
Title: Multi-spectral Analysis of Heliseismic Acoustic Mode Parameters
Authors: Jain, Kiran; Tripathy, S.; Basu, S.; Bogart, R.; Gonzalez
Hernandez, I.; Hill, F.; Howe, R.; Kholikov, S.; Komm, R.
Bibcode: 2011sdmi.confE..33J
Altcode:
Simultaneous measurements at different wavelengths from SDO offer
the prospect of studying the sensitivity of helioseismic inferences
to the choice of observing height both in quiet-Sun and magnetically
active regions. In this poster, we present comparison of mode parameters
obtained with different observables, quantify differences, and interpret
results in the context of the formation height and the anticipated phase
relationships between the oscillations at those heights. This work is
expected to enhance our understanding of the excitation and damping
of the oscillations and the uncertainties in helioseismic inferences.
Title: Multi-wavelength acoustic power maps and 3-d power spectra
from SDO
Authors: Howe, R.; Baldner, C.; Bogart, R. S.; Haber, D. A.; Jain, K.
Bibcode: 2011sdmi.confE..60H
Altcode:
The 1600 and 1700 Angstrom bands of AIA are sensitive to the five-minute
oscillations used in helioseismology. We investigate the acoustic
response of these bands and the HMI velocity and continuum intensity
to various kinds of local magnetic activity, including a current active
region, a decayed active region, and quiet Sun. We will present maps of
the acoustic power at various frequencies as a function of position and
of spatial wavelength, for the AIA bands and for the HMI velocity and
continuum intensity, and also maps of the relative phase and coherence
of these observables. We will also consider the results of small-area
local helioseismology for the HMI velocity in corresponding regions,
and show that even weak fields can have distinct effects on the behavior
of acoustic waves near the surface.
Title: Subsurface kinetic helicity of flows near active regions
Authors: Komm, R.; Jain, K.; Petrie, G.; Pevtsov, A.; González
Hernández I.; Hill, F.
Bibcode: 2011sdmi.confE..68K
Altcode:
We study the temporal variation of subsurface flows associated with
emerging and decaying active regions on the Sun. We measure the
subsurface flows analyzing GONG high-resolution Doppler data with
ring-diagram analysis. We can detect the emergence of magnetic flux
in these flows when averaging over a sufficiently large sample. In a
previous study, we have found that emerging flux has a faster rotation
than the ambient fluid and pushes it up, as indicated by enhanced
vertical velocity and faster-than-average zonal flow. Here, we show
that the kinetic helicity density of subsurface flows increases when
new flux emerges and decreases when flux decays.
Title: Latest Results Found With Ring-Diagram Analysis
Authors: Haber, D. A.; Baldner, C.; Basu, S.; Bogart, R. S.;
González-Hernández, I.; Hill, F.; Howe, R.; Jain, K.; Komm, R. W.;
. Rabello-Soares, C.; Pinkerton, S.; Tripathy, S.
Bibcode: 2011sdmi.confE..51H
Altcode:
This talk will mainly be a preview of the posters generated by
the HMI Rings Team on large-scale (meridional and zonal) flows;
characterizations of active regions at various stages of evolution using
data from AIA as well as from HMI; systematic changes in frequencies,
flows, and other fitted parameters as a function of disk placement,
underlying magnetism, B angle, etc.; and the status of the Rings
pipeline. It will also include any new ring-diagram results from GONG
and MDI.
Title: The HMI Ring-Diagram Pipelines: A Status Report
Authors: Bogart, R. S.; Baldner, C. S.; Basu, S.; Haber, D. A.; Howe,
R.; Gonzalez Hernandez, I.; Hill, F.; Jain, K.; Rabello-Soares, M. C.;
Tripathy, S.
Bibcode: 2011sdmi.confE..55B
Altcode:
The HMI analysis pipeline for determination of sub-surface flows
has been running for nearly one year, and virtually all HMI Doppler
data from the beginning of the mission have been analyzed. Over 3.5
million local-area power spectra of regions of various sizes have
been produced and fitted, and inversions for the depth structure of
flows have been produced for over 130,000 of the larger regions. The
pipeline for determination of the sub-surface thermal structure is still
under active development, with test results available for analysis
for a number of strong active regions. We describe the ring-diagram
pipelines, report on their performance as part of the overall HMI data
analysis pipeline, describe the data products available, and discuss
outstanding problems and issues for further development.
Title: How Peculiar Was the Recent Extended Minimum: A Hint toward
Double Minima
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2011ApJ...739....6J
Altcode: 2011arXiv1107.0049J
In this paper, we address the controversy regarding the recent extended
solar minimum as seen in helioseismic low- and intermediate-degree
mode frequencies: studies from different instruments identify different
epochs of seismic minima. Here we use mode frequencies from a network
of six identical instruments, the Global Oscillation Network Group,
continuously collecting data for more than 15 years, to investigate the
epoch of minimum in solar oscillation frequencies prior to the beginning
of solar cycle 24. We include both low- and intermediate-degree
modes in the l range of 0-120 and frequency range of 2.0-3.5 mHz. In
this analysis, we demonstrate that there were indeed two minima in
oscillation frequencies, depending upon the degree of modes, or more
precisely the lower turning point radius of the propagating wave. We
also analyze frequencies as a function of latitude to identify the
beginning of solar cycle 24. We observe two minima at high latitudes
and a single minimum at mid/low latitudes. This scenario is in contrast
to cycle 23 where the epoch of seismic minimum did not change with
latitude or depth. Our results also hint at a possible role of the
relic magnetic field in modifying the oscillation frequencies of modes
sampling deeper layers.
Title: Subsurface flows associated with rotating sunspots
Authors: Jain, Kiran; Komm, Rudolf; Hernández, Irene González;
Tripathy, Sushant C.; Hill, Frank
Bibcode: 2011IAUS..273..356J
Altcode: 2011arXiv1107.5032J
In this paper, we compare components of the horizontal flow below
the solar surface in and around regions consisting of rotating and
non-rotating sunspots. Our analysis suggests that there is a significant
variation in both components of the horizontal flow at the beginning
of sunspot rotation as compared to the non-rotating sunspot. The flows
in surrounding areas are in most cases relatively small. However,
there is a significant influence of the motion on flows in an area
closest to the sunspot rotation.
Title: Solar subsurface flows of active regions: flux emergence and
flare activity
Authors: Komm, Rudolf; Howe, Rachel; Hill, Frank; Jain, Kiran
Bibcode: 2011IAUS..273..148K
Altcode:
We study the temporal variation of subsurface flows associated
with active regions within 16 Mm of the solar surface. We have
analyzed the subsurface flows of nearly 1000 active and quiet regions
applying ring-diagram analysis to Global Oscillation Network Group
(GONG) Dopplergram data. We find that newly emerging active regions
are characterized by enhanced upflows and fast zonal flows in the
near-surface layers, as expected for a flux tube rising from deeper
layers of the convection zone. The subsurface flows associated with
strong active regions are highly twisted, as indicated by their large
vorticity and helicity values. The dipolar pattern exhibited by the
zonal and meridional vorticity component leads to the interpretation
that these subsurface flows resemble vortex rings, when measured on
the spatial scales of the standard ring-diagram analysis.
Title: Subsurface kinetic helicity of flows near active regions
Authors: Komm, Rudolf; Jain, K.; Petrie, G.; Pevtsov, A.; González
Hernández, I.; Hill, F.
Bibcode: 2011shin.confE.142K
Altcode:
We study the flows in the upper solar convection zone determined from
GONG data using the standard dense-pack ring-diagram analysis and derive
daily and synoptic maps of the velocity components. We also calculate
the vorticity and the kinetic helicity density of the flows. Previous
studies have shown that the vorticity is enhanced near locations
of active regions and that the kinetic helicity density associated
with active regions correlates well with the X-ray flare intensity of
active regions. These fluid dynamics descriptors are thus promising
indicators for investigating the relation between active regions and
associated subsurface flows. Here, we focus on the temporal evolution of
subsurface kinetic helicity density during flux emergence and decay. We
will present the latest results.
Title: Helioseismic Studies With Multi-wavelength Data From HMI And
AIA Onboard SDO
Authors: Hill, Frank; Jain, K.; Tripathy, S.; Kholikov, S.; Gonzalez
Hernandez, I.; Leibacher, J.; Howe, R.; Baudin, F.; Carlsson, M.;
Chaplin, W.; Tarbell, T.
Bibcode: 2011SPD....42.2111H
Altcode: 2011BAAS..43S.2111H
The successful launch of the Solar Dynamics Observatory (SDO) in
February 2010 opens important, new possibilities for helioseismic
exploration of the solar interior and atmosphere using multi-wavelength
observations from multiple instruments. In order to better understand
the solar interior and atmosphere, as well as the physics of the
helioseismic modes and waves themselves, we exploit the potential of
the Atmospheric Imaging Assembly (AIA) 1600 and 1700 Angstrom continuum
measurements and the contemporaneous Helioseismic and Magnetic Imager
(HMI) Fe I 6173.3 Angstrom velocity and intensity observations. Standard
techniques of helioseismology e.g Sun-as-a-star, spherical harmonic
analysis, ring diagrams, and time- distance analysis are applied to
obtain acoustic mode parameters and other characteristics. Here we
present our preliminary results, and interpret these in the context
of the differences in the heights of formation of the lines.
Title: The far-side solar magnetic index
Authors: González Hernández, Irene; Jain, Kiran; Tobiska, W. Kent;
Hill, Frank
Bibcode: 2011JPhCS.271a2028G
Altcode:
Several magnetic indices are used to model the solar irradiance and
ultimately to forecast it. However, the observation of such indices are
generally limited to the Earth-facing hemisphere of the Sun. Seismic
maps of the far side of the Sun have proven their capability to locate
and track medium-large active regions at the non-visible hemisphere. We
present here the possibility of using the average signal from these
seismic far-side maps as a proxy to the non-visible solar activity
which can complement the current front-side solar activity indices.
Title: Solar flares and temporal changes in subsurface vorticity
measurements
Authors: Komm, R.; Jain, K.; Reinard, A.; Howe, R.; Hill, F.
Bibcode: 2011JPhCS.271a2019K
Altcode:
We derive the kinetic helicity density of subsurface flows applying
ring-diagram analysis to Global Oscillation Network Group (GONG)
data. Here, we focus on flows derived from times series of 8 hours
and compare them to daily values for a high- and a low-activity
sample. Compared with daily values, the horizontal flows derived from
8-hour time series are reasonable near disk center and less reliable
near the limb. Also, the errors are larger for shorter time series. A
dipolar helicity pattern is present in the flows derived from 8-hour
and 24-hour time series of flare-productive active region 10808. For
the quiet-Sun sample, the subsurface kinetic helicity is considerably
smaller without any pattern.
Title: Comparison of HMI Dopplergrams with GONG and MDI data
Authors: Howe, R.; Jain, K.; Hill, F.; Komm, R.; González Hernández,
I.; Bogart, R.
Bibcode: 2011JPhCS.271a2060H
Altcode:
We compare sample Dopplergrams from the Helioseismic and Magnetic
Imager, the Michelson Doppler Imager and the Global Oscillation Network
Group. Each instrument has a distinct static velocity patterm across
the disk; once this has been subtracted and the images interpolated
to a common grid, the agreement is satisfactory.
Title: Variation of high-degree mode frequencies during the declining
phase of solar cycle 23
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2011JPhCS.271a2024T
Altcode:
We investigate the spatial and temporal variation of the high-degree
mode frequencies during the declining phase of the solar cycle
23 and the extended minimum between the cycle 23 and 24. We find
that the frequency shifts of high-degree modes obtained through the
ring-diagram analysis in different phases of the solar cycle are not
equally correlated with the local magnetic activity index.
Title: Towards near real time high-resolution Dopplergrams from GONG
Authors: Jain, Kiran; McManus, S.; González Hernández, I.; Tripathy,
S. C.; Bolding, J.; Hill, F.; Wentzel, T. M.
Bibcode: 2011JPhCS.271a2018J
Altcode:
The GONG network, consisting of six sites around the globe, provides
continuous observations of the Sun. The processing and merging of
Dopplergrams from various sites usually takes several months before
these are made available to the community for analysis. In this paper,
we discuss our recent attempts to reduce the delay between observations
and the availability of merged Dopplergrams. Our analysis indicates that
the modified approach does not influence mode parameters and inferred
helioseismic flows. However, the duty cycle plays a significant role in
inferring the sub-surface flows and a low duty cycle, if less stations
contribute, may lead to qualitatively different results.
Title: Effect of Solar Flares on Acoustic Oscillations Within the Sun
Authors: Kellogg, Kendra; Tripathy, S.; Jain, K.
Bibcode: 2011AAS...21715504K
Altcode: 2011BAAS...4315504K
We investigate the effects that energetic flares have on the
acoustic oscillations observed on the surface of the sun. We use the
ring-diagram technique, one of the local helio-seismology method, in
order to comprehend the role of the flare in exciting the oscillation
modes. We analyze these oscillations before, during and after the
onset of the flare. The ratio of the mode parameters at different
phases of the flare with respect to the pre-flare phase provides us
with insight as to how the modes of oscillation are changing with the
evolution of the flare. We find that in 32% of the cases studied,
the power is absorbed almost completely in the active region. Out
of the remaining 68%, a clear enhancement of the power is seen in
23% while a partial enhancement is seen in the other 45%. This
work is carried out through the National Solar Observatory Research
Experiences for Undergraduate (REU) site program, which is co-funded
by the Department of Defense in partnership with the National Science
Foundation REU Program. The National Solar Observatory is operated by
the Association of Universities for Research in Astronomy, Inc. (AURA)
under cooperative agreement with the National Science Foundation.
Title: Angular-degree dependence of p-mode frequencies during solar
cycle 23
Authors: Tripathy, S. C.; Jain, K.; Salabert, D.; Garcia, R. A.;
Hill, F.; Leibacher, J. W.
Bibcode: 2011JPhCS.271a2055T
Altcode:
We analyze simultaneous helioseismic observations collected by the
ground- and space-based instruments during solar cycle 23 by computing
oscillation frequencies for low- and intermediate-degree p-modes on a
time scale of 36 days. We find that the frequency shifts corresponding
to different angular degree, ell, indicate different epochs for the
onset of the solar cycle 24. The analysis also indicates the presence
of double minima between cycles 23 and 24 for some range of ell values.
Title: Temporal Variations of High-Degree Solar p-Modes from GONG
and MDI
Authors: Burtseva, Olga; Tripathy, Sushant; Howe, Rachel; Jain, Kiran;
Hill, Frank; Bogart, Richard; Rabello-Soares, Maria Cristina
Bibcode: 2011JPhCS.271a2012B
Altcode: 2010arXiv1012.5128B
We study temporal variations in the amplitudes and widths of high-degree
acoustic modes in the quiet and active Sun by applying ring-diagram
technique to the GONG+ and MDI Dopplergrams during the declining phase
of cycle 23. The increase in amplitudes and decrease in line-widths in
the declining phase of the solar activity is in agreement with previous
studies. A similar solar cycle trend in the mode parameters is also
seen in the quiet-Sun regions but with a reduced magnitude. Moreover,
the amplitudes obtained from GONG+ data show long-term variations on
top of the solar cycle trend.
Title: Testing the GONG ring-diagram pipeline with HMI Dopplergrams
Authors: Jain, Kiran; Tripathy, S. C.; González Hernández, I.;
Kholikov, S.; Hill, F.; Komm, R.; Bogart, R.; Haber, D.
Bibcode: 2011JPhCS.271a2017J
Altcode:
The GONG ring-diagram pipeline was developed to analyze GONG+
Dopplergrams in order to extract information about solar subsurface
flows and has been extensively tested for this purpose. Here we present
preliminary results obtained by analyzing the HMI Dopplergrams with
the GONG pipeline and compare them with those obtained from the HMI
ring-diagram pipeline.
Title: Helioseismic Studies of a Sunspot using HMI Data
Authors: Tripathy, S. C.; Jain, K.; Gonzalez Hernandez, I.; Komm,
R.; Hill, F.; McManus, S.; Bogart, R.; Rabello-Soares, M. C.; Basu,
S.; Baldner, C.; Haber, D. A.
Bibcode: 2010AGUFMSH11A1603T
Altcode:
We study the mode parameters and sub-surface properties of the sunspot
in NOAA active region 10093 during its disk passage between August
6-14, 2010. This is one of the major active regions recorded so far
during the cycle 24 and continuous observations are available from the
Helioseismic and Magnetic Imager (HMI). We will present the results
using the HMI data processed through the HMI ring-diagram pipeline and
compare those obtained with the GONG pipeline. We will also present
results by analyzing the GONG observations through GONG pipeline.
Title: Global and Local Helioseismology from HMI and AIA
Authors: Howe, R.; Komm, R.; Gonzalez Hernandez, I.; Jain, K.; Hill,
F.; Haber, D. A.; Bogart, R.
Bibcode: 2010AGUFMSH11A1601H
Altcode:
Data from the HMI [Helioseismic and Magnetic Imager] and AIA
[Atmospheric Imaging Assembly] instruments aboard the Solar Dynamics
observatory have been available for some months. We present some
preliminary results from these data, including subsurface flow maps
and activity-related local mode parameter shifts from helioseismic
ring-diagram analysis of HMI data, HMI helioseismic sensing of the far
side of the Sun, and low-degree p-mode spectra from the high-photosphere
bands on AIA as well as from HMI velocity and continuum intensity. The
results will be compared with those from the Michelson Doppler Imager
and the Global Oscillation Network Group.
Title: What Solar Oscillation Tell Us About the Solar Minimum
Authors: Jain, K.; Tripathy, S. C.; Burtseva, O.; H´Ndez, I. G.;
Hill, F.; Howe, R.; Kholikov, S.; Komm, R.; Leibacher, J.
Bibcode: 2010ASPC..428...57J
Altcode: 2010arXiv1002.2411J
The availability of continuous helioseismic data for two consecutive
solar minima has provided a unique opportunity to study the changes
in the solar interior that might have led to this unusual minimum. We
present preliminary analysis of intermediate-degree mode frequencies in
the 3 mHz band during the current period of minimal solar activity and
show that the mode frequencies are significantly lower than those during
the previous activity minimum. Our analysis does not show any signature
of the beginning of cycle 24 until the end of 2008. In addition, the
zonal and meridional flow patterns inferred from inverting frequencies
also hint at a delayed onset of a new cycle. The estimates of travel
time are higher than the previous minimum confirming a relatively weak
solar activity during the current minimum.
Title: Acoustic Oscillations During the Extended Solar Minimum
Authors: Tripathy, Sushanta; Jain, K.; Hill, F.
Bibcode: 2010AAS...21631901T
Altcode: 2010BAAS...41..909T
The acoustic oscillation frequencies of the Sun vary with the
progress of the solar cycle and in general, the frequencies increase
as solar magnetic activity increases. Our recent study on frequencies
of intermediate degree modes of the Sun during the extended minimum
phase between cycles 23 and 24 shows a surprising anti-correlation
between the frequencies and the measures of solar activity. In this
paper, we present results of our analysis on the temporal evolution
of frequency shifts measured locally over the solar disk during the
period of 2007-2009 and show that the extended minimum period between
cycles 23 and 24 is rather unusual.
Title: Unusual Trends in Solar P-Mode Frequencies During the Current
Extended Minimum
Authors: Tripathy, S. C.; Jain, K.; Hill, F.; Leibacher, J. W.
Bibcode: 2010ApJ...711L..84T
Altcode: 2010arXiv1002.1690T
We investigate the behavior of the intermediate-degree mode frequencies
of the Sun during the current extended minimum phase to explore the
time-varying conditions in the solar interior. Using contemporaneous
helioseismic data from the Global Oscillation Network Group (GONG) and
the Michelson Doppler Imager (MDI), we find that the changes in resonant
mode frequencies during the activity minimum period are significantly
greater than the changes in solar activity as measured by different
proxies. We detect a seismic minimum in MDI p-mode frequency shifts
during 2008 July-August but no such signature is seen in mean shifts
computed from GONG frequencies. We also analyze the frequencies of
individual oscillation modes from GONG data as a function of latitude
and observe a signature of the onset of the solar cycle 24 in early
2009. Thus, the intermediate-degree modes do not confirm the onset
of the cycle 24 during late 2007 as reported from the analysis of the
low-degree Global Oscillations at Low Frequency frequencies. Further,
both the GONG and MDI frequencies show a surprising anti-correlation
between frequencies and activity proxies during the current minimum,
in contrast to the behavior during the minimum between cycles 22 and 23.
Title: Inhomogeneous Power Distribution in Magnetic Oscillations
Authors: Jain, Kiran; Tripathy, S. C.; Kholikov, S.; Hill, F.
Bibcode: 2010arXiv1003.5013J
Altcode:
We apply ring-diagram analysis and spherical harmonic decomposition
methods to compute 3-dimensional power spectra of magnetograms obtained
by the Global Oscillation Network Group (GONG) during quiet periods of
solar activity. This allows us to investigate the power distribution
in acoustic waves propagating in localized directions on the solar
disk. We find evidence of the presence of five-minute oscillations
in magnetic signals that suggests a non-homogeneous distribution of
acoustic power. In this paper, we present our results on the asymmetry
in oscillatory power and its behaviour as a function of frequency,
time and magnetic field strength. These characteristics are compared
with simultaneous velocity measurements.
Title: Do Active Regions Modify Oscillation Frequencies?
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2010ASSP...19..374T
Altcode: 2009arXiv0903.2077T; 2010mcia.conf..374T
We investigate the variation of high-degree mode frequencies as a local
response to the active regions in two different phases of the solar
activity cycle. We find that the correlation between frequency shifts
and the surface magnetic activity measured locally are significantly
different during the two activity periods.
Title: Variation of Oscillation Mode Parameters over Solar Cycle 23:
An Analysis on Different Time Scales
Authors: Tripathy, S. C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2009ASPC..416..285T
Altcode: 2009arXiv0903.2074T
We investigate the variation in the mode parameters obtained from time
series of length nine, 36, 72 and 108 days to understand the changes
occurring on different time-scales. The regression analysis between
frequency shifts and activity proxies indicates that the correlation
and slopes are correlated and both increase in going from time series
of nine to 108 days. We also observe that the energy of the mode is
anti-correlated with solar activity while the rate at which the energy
is supplied remains constant over the solar cycle.
Title: Correlation Analysis of Mode Frequencies with Activity Proxies
at Different Phases of the Solar Cycle
Authors: Jain, K.; Tripathy, S. C.; Hill, F.
Bibcode: 2009ASPC..416..189J
Altcode: 2009arXiv0902.1555J
We analyze intermediate degree p- and f-mode eigenfrequencies measured
by GONG and SoHO/MDI for a complete solar cycle to study their
correlation with solar activity. We demonstrate that the frequencies
do vary linearly with the activity, however the degree of correlation
differs from phase to phase of the cycle. During the rising and the
declining phases, the mode frequencies are strongly correlated with the
activity proxies whereas during the low- and high-activity periods,
the frequencies have significantly lower correlation with all the
activity proxies considered here.
Title: Does the Selection of a Quiet Region Influence the Local
Helioseismic Inferences?
Authors: Tripathy, S. C.; Antia, H. M.; Jain, K.; Hill, F.
Bibcode: 2009ASPC..416..139T
Altcode: 2009arXiv0901.4939T
We apply the ring-diagram technique to high resolution Dopplergrams in
order to estimate the variation in oscillation mode parameters between
active and quiet regions. We demonstrate that the difference in mode
parameters between two quiet regions can be as large as those between
a pair of active and quiet region. This leads us to conclude that the
results derived on the basis of a single quiet region could be biased.
Title: Solar Minimum and Helioseismic Inferences
Authors: Komm, Rudolph; Howe, R.; Jain, K.; Tripathy, S.; Burtseva,
O.; Hill, F.
Bibcode: 2009SPD....40.0718K
Altcode:
We have analyzed Global Oscillation Network Group (GONG) data of
cycle 23 to the end of the year 2008 covering the last/current solar
minimum. We study the rotation rate in the solar convection zone with a
global helioseismic analysis during this minimum and compare it to the
previous one. We also study the subsurface flows in the near-surface
layers of the convection zone with a ring-diagram analysis focusing on
the meridional flow and the divergence and vorticity of subsurface
flows during this epoch. In addition, we study frequency shifts
(from global and local analyses) and their correlation with magnetic
activity during solar minimum. Latitudinal variations of the p-mode
parameters from ring-diagram analysis during solar minimum will be
investigated. We will present the latest results.
Title: A Helioseismic Comparison of the Solar Minima Preceding Cycles
23 and 24
Authors: Hill, Frank; Howe, R.; Komm, R.; Gonzallez Hernandez, I.;
Tripathy, S.; Jain, K.
Bibcode: 2009SPD....40.2401H
Altcode:
The current solar minimum is clearly unusual in a variety of
ways, including length, solar wind pressure, cosmic ray flux, and
marked absence of sunspots. This talk will compare the current
minimum with the previous one in terms of its helioseismic and
subsurface flow characteristics. The helioseismic characteristics are
primarily activity-related changes in the frequencies, amplitudes
and lifetimes. The relevant flows are the torsional oscillation,
meridional flow, subsurface vorticity, and the subsurface rotation rate.
Title: Temporal Variations of High-Degree Solar Acoustic Modes in
the Quiet Sun
Authors: Burtseva, Olga; Tripathy, S. C.; Hill, F.; Jain, K.
Bibcode: 2009SPD....40.0719B
Altcode:
Temporal variations in the quiet Sun can be associated with changes
in the convective properties and magnetic fields connected to the
convective motions. Here we characterize the high-degree acoustic
modes in quiet regions of the Sun during different phases of the solar
cycle. We apply ring-diagram technique to the Global Oscillation
Network Group Dopplergrams and focus on high latitudes above the
activity belts. We also analyze the solar cycle variations of the
magnetic field in the quiet Sun using Michelson Doppler Imager full-disk
magnetograms. The results of this study will be presented.
Title: Oscillatory Power Distribution in Full-disk Magnetograms
Authors: Hill, Frank; Jain, K.; Tripathy, S. C.; Kholikov, S.
Bibcode: 2009SPD....40.0928H
Altcode:
It has been shown that the interaction of p-modes with the magnetic
field modifies the mode's characteristics. The power around the
5-minute band is absorbed while there is an enhancement at higher
frequencies. Here we present recent results showing an inhomogeneous
power distribution in magnetic oscillations which may be useful in
characterizing the energy transport mechanisms in the upper solar
atmosphere. We use data from the high-cadence GONG magnetograms during
the low-activity phase of the solar cycle and compare our results with
simultaneous velocity oscillations.
Title: Solar Activity Phases and Intermediate-Degree Mode Frequencies
Authors: Jain, Kiran; Tripathy, S. C.; Hill, F.
Bibcode: 2009ApJ...695.1567J
Altcode: 2009arXiv0902.1557J
We analyze intermediate-degree p-mode eigenfrequencies measured by
Global Oscillation Network Group and Michelson Doppler Imager/Solar and
Heliospheric Observatory over a solar cycle to study the source of their
variability. We carry out a correlation analysis between the change in
frequencies and several measures of the Sun's magnetic activity that are
sensitive to changes at different levels in the solar atmosphere. The
observations span a period of about 12 years starting from mid-1996
(the minimum of cycle 23) to early-2008 (near minimum of cycle 24),
corresponding to a nearly complete solar activity cycle. We demonstrate
that the frequencies do vary in phase with the solar activity indices,
however, the degree of correlation differs from phase to phase of the
cycle. During the rising and declining phases, the mode frequency shifts
are strongly correlated with the activity proxies whereas during the
high-activity period, the shifts have significantly lower correlation
with all activity proxies, except for the 10.7 cm radio flux. In
particular, the proxies that are only influenced by the variation of
the strong component of the magnetic field in the photosphere have
a much lower correlation at the high-activity period. On the other
hand, the shifts are better correlated with the proxies sensitive to
changes in the weak component of the magnetic field. Our correlation
analysis suggests that more than 90% of the variation in the oscillation
frequencies in all activity phases can be explained by changes in both
components of the magnetic field. Further, the slopes obtained from
the linear regression analysis also differ from phase to phase and
show a strong correlation with the correlation coefficients between
frequency shifts and solar activity.
Title: Comparison of High-Degree Solar Acoustic Frequencies and
Asymmetry Between Velocity and Intensity Data
Authors: Tripathy, S. C.; Antia, H. M.; Jain, K.; Hill, F.
Bibcode: 2009ApJ...691..365T
Altcode: 2008arXiv0809.4486T
Using the local helioseismic technique of ring diagram we analyze the
frequencies of high-degree f- and p-modes derived from both velocity and
continuum intensity data observed by Michelson Doppler Imager. Fitting
the spectra with asymmetric peak profiles, we find that the asymmetry
associated with velocity line profiles is negative for all frequency
ranges, agreeing with previous observations, while the asymmetry
of the intensity profiles shows a complex and frequency-dependent
behavior. We also observe systematic frequency differences between
intensity and velocity spectra at the high end of the frequency range,
mostly above 4 mHz. We infer that this difference arises from the
fitting of the intensity rather than the velocity spectra. We also
show that the frequency differences between intensity and velocity
do not vary significantly from the disk center to the limb when the
spectra are fitted with the asymmetric profile and conclude that only
a part of the background is correlated with the intensity oscillations.
Title: Selection of Quiet Regions in Local Helioseismic Analysis
Authors: Tripathy, S. C.; Jain, K.; Hill, F.
Bibcode: 2008AGUSMSP41A..01T
Altcode:
In local helioseismic studies, the mode characteristics of an active
region are compared with those of a quiet region to estimate the
influence of the magnetic field or differences in structure. Hence the
selection of a proper quiet region is important in order to estimate
the true variations. There are at least three possible ways in which
a quiet region can be selected: (i) a common quiet region for all the
events analyzed (ii) a quiet region at the same heliographic longitude
and latitude within the same Carrington rotation, and (iii) an ensemble
average of quiet regions. The first choice minimizes the differences
that may arise from different quiet regions, but neglects the effect
of temporal variations. On the other hand, the second choice introduces
inherent variations present between quiet regions. It is believed that
the differences in mode parameters between two quiet regions are small
compared to a pair of active and quiet regions. However our analysis
indicates that the differences in mode parameters between two quiet
regions can be significantly large. In this paper we will illustrate the
variations between quiet regions and their effect on the mode properties
of the active region by selecting quiet regions in all three categories.
Title: Helioseismic ring analysis of CME source regions
Authors: Tripathy, S. C.; Wet, S.; Jain, K.; Clark, R.; Hill, F.
Bibcode: 2008JApA...29..207T
Altcode: 2007arXiv0712.1995T
We apply the ring diagram technique to source regions of halo coronal
mass ejections (CMEs) to study changes in acoustic mode parameters
before, during, and after the onset of CMEs. We find that CME regions
associated with a low value of magnetic flux have line widths smaller
than the quiet regions implying a longer life-time for the oscillation
modes. We suggest that this criterion may be used to forecast the
active regions which may trigger CMEs.
Title: Multi-Spectral Analysis of Acoustic Mode Characteristics in
Active Regions
Authors: Jain, K.; Hill, F.; Tripathy, S. C.; González-Hernández,
I.; Armstrong, J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P.
Bibcode: 2008ASPC..383..389J
Altcode:
We study the relative differences in acoustic mode parameters
in regions of high magnetic fields at different heights in the
solar atmosphere. The data sets include simultaneous Dopplergrams
obtained with the Ni I 676.8~nm from Global Oscillation Network Group
(GONG+) and K I 769.9 nm from Magneto-Optical Filters at Two Heights
(MOTH). The technique used here is the ring-diagram analysis, which has
been proven to be a powerful tool to study the localized regions on the
solar surface. We find that there is a difference in power suppression
and relative changes in frequencies in active regions with increasing
height. This is explained in terms of the expanding magnetic flux tubes.
Title: Solar Oscillation Frequency Changes on Time Scales of Nine Days
Authors: Tripathy, S. C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2007SoPh..243..105T
Altcode: 2006astro.ph..8348T
We establish that global solar p-mode frequencies can be measured with
sufficient precision on time scales as short as nine days to detect
activity-related shifts. Using ten years of GONG data, we report
that mode-mass and error-weighted frequency shifts derived from nine
days are significantly correlated with the strength of solar activity
and are consistent with long-duration measurements from GONG and the
SOHO/MDI instrument. The analysis of the year-wise distribution of the
frequency shifts with change in activity indices shows that both the
linear-regression slopes and the magnitude of the correlation varies
from year to year and they are well correlated with each other. The
study also indicates that the magnetic indices behave differently in the
rising and falling phases of the activity cycle. For the short-duration
nine-day observations, we report a higher sensitivity to activity.
Title: Suppression Of Acoustic Power In Solar Active Regions: An
Analysis At Different Heights
Authors: Tripathy, Sushanta; Jain, K.; Hill, F.; Gonzalez-Hernandez,
I.; Armstrong, J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P. J.
Bibcode: 2007AAS...210.2411T
Altcode: 2007BAAS...39..130T
The presence of enhanced magnetic fields in active regions is known to
suppress acoustic power and modify oscillation frequencies. Applying
the ring diagram technique to data from three different spectral lines
at different heights in the solar atmosphere, we analyze the variation
of the acoustic power with height. The data sets include simultaneous
Dopplergrams obtained with the Ni I 676.8 nm from Global Oscillation
Network Group (GONG), K I 769.9 nm from Magneto-Optical Filters at Two
Heights (MOTH) and Na I 589.0 nm from MOTH and Mount Wilson Observatory
(MWO). It should be noted that the Ni and K lines are formed in the
photosphere while Na line is formed in lower chromosphere. Preliminary
results suggest a difference in power suppression with increasing
height, which can be explained in terms of the expanding magnetic
flux tubes.
Title: Helioseismic Analysis Of Mode Parameters In The Source Regions
Of CMEs
Authors: DeWet, Stephanie; Tripathy, S. C.; Jain, K.; Clark, R.;
Hill, F.
Bibcode: 2007AAS...210.2909D
Altcode: 2007BAAS...39..138D
We apply ring-diagram technique to high-resolution Global Oscillation
Network Group (GONG) Dopplergrams in order to examine the source regions
of halo coronal mass ejections (CMEs). We study the changes in acoustic
mode parameters such as frequency, line width, and amplitude before,
during, and after CMEs. The CMEs were chosen to have a wide variety
of source regions, including active regions, filament regions, and
transequatorial filament regions. We find that regions associated
with low magnetic flux that produce CMEs have shorter line widths
than corresponding quiet regions. This implies a longer lifetime
or slow damping process for the oscillation modes. We suggest that
this characteristic could be useful in modeling CMEs or forecasting
regions in which CMEs may occur. This work is carried out through
the National Solar Observatory Research Experiences for Undergraduate
(REU) site program, which is co-funded by the Department of Defense
in partnership with the National Science Foundation REU Program.
Title: A comparison of acoustic mode parameters using multi-spectral
data
Authors: Jain, K.; Hill, F.; Tripathy, S. C.; Antia, H. M.; Armstrong,
J. D.; Jefferies, S. M.; Rhodes, E. J., Jr.; Rose, P. J.
Bibcode: 2006ESASP.624E.103J
Altcode: 2006soho...18E.103J
No abstract at ADS
Title: Comparison of local frequency shifts between MDI velocity
and intensity data
Authors: Tripathy, S. C.; Antia, H. M.; Hill, F.; Jain, K.; González
Hernández, I.
Bibcode: 2006ESASP.624E.104T
Altcode: 2006soho...18E.104T
No abstract at ADS
Title: Does the inference of solar subsurface flow change with choice
of the spectral line?
Authors: Jain, K.; Hill, F.; González Hernández, I.; Toner, C. G.;
Tripathy, S. C.; Armstrong, J. D.; Jefferies, S. M.
Bibcode: 2006ESASP.624E.127J
Altcode: 2006soho...18E.127J
No abstract at ADS
Title: Changes to global mode parameters over a solar cycle
Authors: Tripathy, S. C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2006ESASP.624E..93T
Altcode: 2006soho...18E..93T
No abstract at ADS
Title: MDI and GONG Inferences of the Changing Sun
Authors: Burtseva, O.; González Hernández, I.; Hill, F.; Howe, R.;
Jain, K.; Kholikov, S.; Komm, R.; Leibacher, J.; Toner, C.; Tripathy,
S.; Haber, D.; Hindman, B.; Ladenkov, O.; Chou, D. -Y.
Bibcode: 2006ESASP.617E..41B
Altcode: 2006soho...17E..41B
No abstract at ADS
Title: Frequency Shifts on Time Scales of Nine Days
Authors: Tripathy, Sushanta C.; Hill, F.; Jain, K.; Leibacher, J. W.
Bibcode: 2006SPD....37.0501T
Altcode: 2006BAAS...38R.223T
Since the p-mode frequency changes are thought to be associated
with individual active regions that come and go continuously, one
would anticipate that the frequencies alsochange continuously on
any time scale. However, due to the finite life time of the mode,
the correlation between the frequency and activity may depend on the
length of the observing run. To test this hypothesis, we calculate and
analyze frequency variations on time scales as short as nine-days. Using
10 years of GONG data, we establish that the global p-mode frequencies
can be measured with sufficient precision on this timescale to exhibit
temporal variations. We also find that these modes are significantly
correlated with the strength of solar activity but the correlation
coefficients are smaller as compared to long-term measurements from
the GONG and SOHO/MDI.
Title: How Sensitive are Helioseismic Mode Parameters and Subsurface
Flows to Choice of the Spectral Line?
Authors: Hill, Frank; Jain, K.; Gonzalez-Hernandez, I.; Toner, C. G.;
Tripathy, S. C.; Armstrong, J. D.; Jefferies, S.; Rhodes, E. J., Jr.;
Rose, P. J.
Bibcode: 2006SPD....37.0511H
Altcode: 2006BAAS...38Q.225H
We analyze simultaneous multi-spectral line observations to investigate
how the results of helioseismology are affected by the spectral
line used to observe the solar oscillations. The data sets include
observations obtained with the Ni I 676.8 nm (from Global Oscillation
Network Group - GONG), K I 769.9 nm (from Magneto Optical Filters
at Two Heights - MOTH experiment) and Na I D2 589.0 nm
(from MOTH experiment and Mount Wilson Observatory) lines during the
Austral summer of 2002-03. The depth formation of these lines occurs
about 200 km, 420 km and 780 km above the base of the photosphere,
respectively. The simultaneous observations in several atmospheric
layers allow us to determine the propagation behavior of acoustic
waves between these layers. We carry out ring-diagram analysis,
a local helioseismology technique, to study the relative changes in
local mode parameters and subsurface velocity fields inferred from
the different data sets. Preliminary analysis of the mode parameters
obtained from the Ni I 676.8 nm and K I 769.9 nm spectral lines clearly
show a significant increase in mode amplitude with increasing observing
height but with no apparent change in the mode width.
Title: Characteristic Patterns of the Mode Frequencies With Solar
Activity Indices
Authors: Tripathy, S. C.; Jain, K.; Bachmann, K. T.
Bibcode: 2005AGUSMSP11B..13T
Altcode:
The variability of solar p-mode oscillation frequencies during the
course of a solar cycle is the result of perturbations due to changing
average magnetic flux near the solar surface and is an important clue
toward understanding the mechanisms of solar activity. We analyze
temporal relationships among p-mode frequencies measured by GONG and
MDI having ℓ ≤ 200 and 1.5 mHz ≤ ν ≤ 3.5 mHz to establish
the presence of characteristic loop patterns with the 10.7-cm flux
(F10), the Kitt Peak Magnetic Index (KPMI), International Sunspot
Number (RZ), and the radiative indices: He I equivalent width and Mg
II core-to-wing ratio. The data cover the ascending and descending
phases of the current solar activity cycle 23. Our preliminary results
indicate that p-mode frequencies vary closely with F10z and KPMI but
lead the radiative indices and lag RZ by approximately one month. This
implies that the more generalized magnetic flux responsible for F10
and KPMI, which is known to follow the emergence of the powerful
localized flux of sunspots, is more closely linked to the variation
of intermediate-degree p-mode frequencies.
Title: Modulation in the solar irradiance due to surface magnetism
during cycles 21, 22 and 23
Authors: Jain, K.; Hasan, S. S.
Bibcode: 2004A&A...425..301J
Altcode:
Magnetic field indices derived from synoptic magnetograms of the
Mt. Wilson Observatory, i.e. Magnetic Plage Strength Index (MPSI)
and Mt. Wilson Sunspot Index (MWSI), are used to study the effects of
surface magnetism on total solar irradiance variability during solar
cycles 21, 22 and 23. We find that most of the solar cycle variation in
the total solar irradiance can be accounted for by the absolute magnetic
field strength on the solar disk, if fields associated with dark and
bright regions are considered separately. However, there is a large
scatter in the calculated and observed values of TSI during solar cycle
21. On the other hand, the multiple correlation coefficients obtained
for solar cycles 22 and 23 are 0.88 and 0.91 respectively. Furthermore,
separate regression analyses for solar cycles 22 and 23 do not show
any significant differences in the total solar irradiance during these
cycles. Our study further strengthens the view that surface magnetism
indeed plays a dominant role in modulating solar irradiance.
Title: Reconstruction of the past total solar irradiance on short
timescales
Authors: Jain, Kiran; Hasan, S. S.
Bibcode: 2004JGRA..109.3105J
Altcode:
The aim of this investigation is to present a new analysis of short-term
variations in total solar irradiance by developing regression models
and to extend these to epochs when irradiance measurements were not
available. In our models the sunspot area is used to quantify sunspot
darkening while facular brightening is calculated using facular area,
10.7 cm radio flux and Mg II core-to-wing ratio. Models developed
with various proxies are compared with a view to identify the role of
key parameters in solar variability. We also study the relationship
between different facular proxies and show that the facular area and
10.7 cm radio flux do not vary linearly with the Mg II core-to-wing
ratio. We emphasize that the facular term in current empirical models
(using facular area or radio flux proxies) on short time scale needs to
have a nonlinear component in order to obtain a better correlation with
observed irradiance. Our analysis demonstrates that the correlation for
daily variations in solar irradiance improves by 10% using a quadratic
term in the model based on radio flux as a facular proxy, which is
a significant improvement on earlier models. On the other hand, the
correlation remains unchanged in the model using Mg II core-to-wing
ratio. Thus we point out that various proxies for facular brightenings
contribute differently to solar irradiance. We estimate the solar
irradiance variations at epochs before irradiance observation began,
in particular to the start of the radio flux measurements, and find that
there is no drastic increase in radiative output during the most active
solar cycle 19 while for cycle 20 we observe a much lower irradiance
during maximum.
Title: Variations in Oscillation Frequencies From Minimum to Maximum
of Solar Activity
Authors: Jain, Kiran; Bhatnagar, A.
Bibcode: 2003SoPh..213..257J
Altcode:
The temporal variation in intermediate-degree-mode frequencies is
analysed using helioseismic data which cover the minimum to the maximum
phase of the current solar cycle. To study the variation in detail,
the measured frequency shifts of f and p modes are decomposed into
two components, viz., oscillatory and non-oscillatory. The f-mode
frequencies exhibit prominent oscillatory behavior in contrast to p
modes where the oscillatory nature of the frequencies is not clearly
seen. Also, the oscillatory part contributes significantly to the
f-mode frequencies while p-mode frequencies have maximum contribution
from the non-oscillatory part. The amplitude of both oscillatory and
non-oscillatory parts is found to be a function of frequency. The
non-oscillatory part is observed to have a strong correlation with
solar activity.
Title: On the p-mode Asymmetry between Velocity and Intensity from
the GONG+ Data
Authors: Tripathy, S. C.; Jain, Kiran; Hill, Frank; Toner, C. G.
Bibcode: 2003BASI...31..321T
Altcode: 2003astro.ph..6027T
We have analyzed the local acoustic spectra of small regions over the
solar surface at different locations from disk center to limb via the
technique of ring diagrams. The analysis suggest that the frequency
shifts between velocity and intensity is a function of location on
the disk and is higher near the disk center than those near the limb.
Title: Reconstruction of Total Solar Irradiance on Multiple Time
Scales
Authors: Jain, Kiran; Hasan, S. S.
Bibcode: 2003BASI...31..315J
Altcode:
We have developed regression models of total solar irradiance on
different time scales by parameterizing the combined influence of
sunspots and faculae. These models are useful in identifying the key
parameters responsible for temporal variations.
Title: Variation of solar irradiance and mode frequencies during
Maunder minimum
Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C.
Bibcode: 2002Ap&SS.281..761B
Altcode: 2002astro.ph..1025B
Using the sunspot numbers reported during the Maunder minimum and the
empirical relations between the mode frequencies and solar activity
indices, the variations in the total solar irradiance and 10.7 cm radio
flux for the period 1645 to 1715 is estimated. We find that the total
solar irradiance and radio flux during the Maunder minimum decreased
by 0.19% and 52% respectively, as compared to the values for solar
cycle 22.
Title: How Good are the Predictions for Oscillation Frequencies?
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
Bibcode: 2002SoPh..206..213J
Altcode: 2002astro.ph..1024J
We have used available intermediate degree p-mode frequencies for
solar cycle 23 to check the validity of previously derived empirical
relations for frequency shifts (Jain et al., 2000). We find that the
calculated and observed frequency shifts during the rising phase of
cycle 23 are in good agreement. The observed frequency shift from
minimum to maximum of this cycle as calculated from MDI frequency data
sets is 251±7 nHz and from GONG data is 238±11 nHz. These values are
in close agreement with the empirically predicted value of 271±22 nHz.
Title: Solar rotation rate from minimum to maximum of activity cycle
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.; Kumar, Brajesh
Bibcode: 2001BASI...29..239J
Altcode:
Using helioseismic data from SOI/MDI and GONG for the current solar
cycle 23, from solar minimum to near maximum phase, we report here on
the temporal variation of the rotation rate.
Title: Analysis of hysteresis effect in p-mode frequency shifts and
solar activity indices
Authors: Tripathy, S. C.; Kumar, Brajesh; Jain, Kiran; Bhatnagar,
Arvind
Bibcode: 2001SoPh..200....3T
Altcode: 2001astro.ph..3129T
Using intermediate degree p-mode frequency datasets for solar cycle
22, we find that the frequency shifts and magnetic indices show a
`hysteresis' phenomenon. It is observed that the magnetic indices
follow different paths for the ascending and descending phases of the
solar cycle, as the descending path always seems to follow a higher
track than the ascending one. However, for the radiative indices,
the paths cross each other indicating phase reversal.
Title: Comparison of GONG+ Velocity and Intensity Local Acoustic
Spectra via Ring Diagrams
Authors: Jain, K.; Toner, C. G.; Hill, F.
Bibcode: 2001AGUSM..SP31A13J
Altcode:
The local acoustic spectra of small regions over the solar surface
have been studied by using the ring diagram technique. The data
used here consist of velocity and intensity images obtained by GONG+
instrument at Tucson for the period from 2000 June 10-15. By studying
the local regions on the solar surface, we construct a three-dimensional
power spectrum (ω , kx, ky) of high degree
solar acoustic modes. A suitable normalization is applied to both
the spectra in order to investigate any observable difference in the
size and power of the rings. This will be compared to the differences
observed in global acoustic spectra obtained in velocity and intensity
to provide information about the driving and damping of local acoustic
oscillations.
Title: Temporal evolution of f-mode frequencies and radius
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
Bibcode: 2001ESASP.464...95J
Altcode: 2001astro.ph..3163J; 2001soho...10...95J
We have analysed temporal evolution in centroid frequencies and
splitting coefficients of solar f-modes obtained from MDI/SOHO. The
data were divided into 20 sets covering a period from May 1, 1996 to
August 31, 2000. The variation in frequencies is estimated to be 68 nHz
over the period of four years which includes the rapidly rising phase
of the solar cycle 23. This change is much smaller than that observed
for p-mode frequencies. It is also noticed that the f-mode frequencies
appear to be weakly correlated with solar activity indices as compared
to the p-mode frequencies. We have also inferred the relative change in
the solar radii and notice a 1 year periodicity which may be associated
with the solar cycle variation.
Title: On the solar rotation rate in the upper convection zone
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
Bibcode: 2001ESASP.464..641J
Altcode: 2001soho...10..641J; 2001astro.ph..3164J
We present results on variation in rotation rate in the upper convection
zone using data from GONG and MDI/SOHO covering a period of more than
four years. We find that the first few odd-order splitting coefficients
vary systematically with the solar cycle. The rotation rate near the
solar surface calculated from analytical methods agrees well with that
of inversion techniques. The residual rotation rate in the outer layers
seem to be correlated with the solar activity.
Title: Solar Cycle-induced Variations in GONG P-Mode Frequencies
and Splittings
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
Bibcode: 2000ApJ...542..521J
Altcode: 2000astro.ph..6015J
We have analyzed the recently available Global Oscillation Network Group
(GONG) p-mode frequencies and splitting coefficients for a period of
three and a half years including the rapidly rising phase of solar
cycle 23. The analysis of mean frequency shift with different activity
indices shows that the shift is equally correlated with both magnetic
and radiative indices. During the onset of the new cycle 23, we notice
that the change in the b4 splitting coefficient is more
prominent than the change in b2. We have estimated the solar
rotation rate with varying depth and latitude. In the equatorial region,
the rotation first increases with depth and then decreases, while an
opposite behavior is seen in the polar region. We also find a small but
significant temporal variation in the rotation rate at high latitudes.
Title: Observation of Hysteresis Between Solar Activity Indicators
and p-mode Frequency Shifts for Solar Cycle 22
Authors: Tripathy, S. C.; Kumar, B.; Jain, K.; Bhatnagar, A.
Bibcode: 2000JApA...21..357T
Altcode:
No abstract at ADS
Title: Heliseismic Solar Cycle Changes and Splitting Coefficients
Authors: Tripathy, S. C.; Jain, Kiran; Bhatnagar, A.
Bibcode: 2000JApA...21..349T
Altcode:
No abstract at ADS
Title: Empirical estimate of p-mode frequency shift for solar cycle 23
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.; Kumar, Brajesh
Bibcode: 2000SoPh..192..487J
Altcode: 1999astro.ph.12518J
We have obtained empirical relations between the p-mode frequency shift
and the change in solar activity indices. The empirical relations are
determined on the basis of frequencies obtained from BBSO and GONG
stations during solar cycle 22. These relations are applied to estimate
the change in mean frequency for the cycle 21 and 23. A remarkable
agreement between the calculated and observed frequency shifts for
the ascending phase of cycle 23, indicates that the derived relations
are independent of epoch and do not change significantly from cycle to
cycle. We propose that these relations could be used to estimate the
shift in p-mode frequencies for past, present and future solar activity
cycles, if the solar activity index is known. The maximum frequency
shift for cycle 23 is estimated to be 265±90 nHz, corresponding to
a predicted maximum smoothed sunspot number 118.1±35.
Title: A relation between frequency shift and the changes in activity
indices
Authors: Jain, Kiran; Tripathy, S. C.; Kumar, Brajesh; Bhatnagar,
Arvind
Bibcode: 2000BASI...28...89J
Altcode:
We present a linear relation between the shift in p-mode frequencies
and variation in two solar activity indices, namely the sunspot number
and 10.7 cm radio flux. From this relation, an empirical model is
constructed to estimate the mean frequency shifts with respect to
activity index. We also compare the observed and estimated shifts
for solar cycle 22 and comment on the systematic errors in different
helioseismic data sets.
Title: GONG p-mode frequency changes with solar activity
Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C.
Bibcode: 2000BASI...28...91B
Altcode:
In this paper, we present a correlation study of nine solar activity
indices with p-mode frequency shifts obtained from the GONG data. It
is found that the two are closely correlated and a linear relationship
exits. Further, the GONG p-mode frequencies for the period 1995 August
to 1997 August show that the mean frequency decreases by 0.06 μHz
during the descending phase of the solar cycle 22 and increases by
0.04 μHz in the ascending phase of the new solar cycle 23.
Title: GONG p-Mode Frequency Changes with Solar Activity
Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C.
Bibcode: 1999ApJ...521..885B
Altcode: 1999astro.ph..3493B
We present a correlation analysis of GONG p-mode frequencies with
nine solar activity indices for the period from 1995 August to
1997 August. This study includes spherical harmonic degrees in the
range 2-150 and the frequency range of 1500-3500 μHz. Using three
statistical tests, the measured mean frequency shifts show strong
to good correlation with activity indices. A decrease of 0.06 μHz
in frequency during the descending phase of solar cycle 22 and an
increase of 0.04 μHz in the ascending phase of solar cycle 23 are
observed. These results provide the first evidence for change in p-mode
frequencies around the declining phase of cycle 22 and the beginning
of new cycle 23. This analysis further confirms that the temporal
behavior of the solar frequency shifts closely follow the phase of
the solar activity cycle.
Title: Rotational Bands in Derformed Odd-A Nuclei in the Actinide
Region
Authors: Jain, K.; Jain, A. K.
Bibcode: 1992ADNDT..50..269J
Altcode:
Tables of experimentally known energy levels of odd- A rotational
bands in the actinide region ( A ≥ 221) are presented along with
the configuration assignments. This includes the newly defined
quadrupole-octupole deformation region ( A ≤ 229). The moment of
inertia and the decoupling parameters have been calculated for each band
if sufficient data are available. Useful theoretical and experimental
information for each band/nucleus is also given. The cutoff date for
the present compilation is December 1990.