explanation blue bibcodes open ADS page with paths to full text
Author name code: jain-rekha
ADS astronomy entries on 2022-09-14
=author:"Jain, Rekha" OR =author:"Jain, R."
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Title: Radial Trapping of Thermal Rossby Waves within the Convection
Zones of Low-mass Stars
Authors: Hindman, Bradley W.; Jain, Rekha
2022ApJ...932...68H Altcode: 2022arXiv220502346H
We explore how thermal Rossby waves propagate within the gravitationally
stratified atmosphere of a low-mass star with an outer convective
envelope. Under the conditions of slow, rotationally constrained
dynamics, we derive a local dispersion relation for atmospheric waves
in a fully compressible stratified fluid. This dispersion relation
describes the zonal and radial propagation of acoustic waves and
gravito-inertial waves. Thermal Rossby waves are just one class of
prograde-propagating gravito-inertial wave that manifests when the
buoyancy frequency is small compared to the rotation rate of the
star. From this dispersion relation, we identify the radii at which
waves naturally reflect and demonstrate how thermal Rossby waves
can be trapped radially in a waveguide that permits free propagation
in the longitudinal direction. We explore this trapping further by
presenting analytic solutions for thermal Rossby waves within an
isentropically stratified atmosphere that models a zone of efficient
convective heat transport. We find that, within such an atmosphere,
waves of short zonal wavelength have a wave cavity that is radially thin
and confined within the outer reaches of the convection zone near the
star's equator. The same behavior is evinced by the thermal Rossby waves
that appear at convective onset in numerical simulations of convection
within rotating spheres. Finally, we suggest that stable thermal Rossby
waves could exist in the lower portion of the Sun's convection zone,
despite that region's unstable stratification. For long wavelengths,
the Sun's rotation rate is sufficiently rapid to stabilize convective
motions, and the resulting overstable convective modes are identical
to thermal Rossby waves.
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Title: Study of Transverse Oscillations in Coronal Loops Excited by
Flares and Eruptions
Authors: Conde C., Sandra M.; Jain, Rekha; Jatenco-Pereira, Vera
2022ApJ...931..151C Altcode: 2022arXiv220512063C
We present measurements of periodicity for transverse loop oscillations
during the periods of activity of two remote and separated (both
temporally and spatially) flares. The oscillations are observed in
the same location more than 100 Mm away from the visible footpoints
of the loops. Evidence for several possible excitation sources
is presented. After close examination, we find that the eruptions
during the flaring activities play an important role in triggering
the oscillations. We investigate periodicities using time-distance,
fast Fourier transform, and wavelet techniques. Despite different
excitation sources in the vicinity of the loops and the changing nature
of amplitudes, the periodicity of multiple oscillations is found to
be 4-6 min.
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Title: <SUP>57</SUP>Zn β-delayed proton emission establishes the
<SUP>56</SUP>Ni rp-process waiting point bypass
Authors: Saxena, M.; -J Ong, W.; Meisel, Z.; Hoff, D. E. M.; Smirnova,
N.; Bender, P. C.; Burcher, S. P.; Carpenter, M. P.; Carroll, J. J.;
Chester, A.; Chiara, C. J.; Conaway, R.; Copp, P. A.; Crider, B. P.;
Derkin, J.; Estradé, A.; Hamad, G.; Harke, J. T.; Jain, R.; Jayatissa,
H.; Liddick, S. N.; Longfellow, B.; Mogannam, M.; Montes, F.; Nepal,
N.; Ogunbeku, T. H.; Richard, A. L.; Schatz, H.; Soltesz, D.; Subedi,
S. K.; Sultana, I.; Tamashiro, A. S.; Tripathi, V.; Xiao, Y.; Zink, R.
2022PhLB..82937059S Altcode: 2022arXiv220401621S
We measured the <SUP>57</SUP>Znβ-delayed proton (βp) and γ emission
at the National Superconducting Cyclotron Laboratory. We find a
<SUP>57</SUP>Zn half-life of 43.6 ± 0.2 ms, βp branching ratio of
(84.7 ± 1.4)%, and identify four transitions corresponding to the
exotic β-γ-p decay mode, the second such identification in the
fp-shell. The p/γ ratio was used to correct for isospin mixing while
determining the <SUP>57</SUP>Zn mass via the isobaric multiplet mass
equation. Previously, it was uncertain as to whether the rp-process
flow could bypass the textbook waiting point <SUP>56</SUP>Ni for
astrophysical conditions relevant to Type-I X-ray bursts. Our results
definitively establish the existence of the <SUP>56</SUP>Ni bypass,
with 14-17% of the rp-process flow taking this route.
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Title: Horizons: Nuclear Astrophysics in the 2020s and Beyond
Authors: Schatz, H.; Becerril Reyes, A. D.; Best, A.; Brown, E. F.;
Chatziioannou, K.; Chipps, K. A.; Deibel, C. M.; Ezzeddine, R.;
Galloway, D. K.; Hansen, C. J.; Herwig, F.; Ji, A. P.; Lugaro, M.;
Meisel, Z.; Norman, D.; Read, J. S.; Roberts, L. F.; Spyrou, A.;
Tews, I.; Timmes, F. X.; Travaglio, C.; Vassh, N.; Abia, C.; Adsley,
P.; Agarwal, S.; Aliotta, M.; Aoki, W.; Arcones, A.; Aryan, A.;
Bandyopadhyay, A.; Banu, A.; Bardayan, D. W.; Barnes, J.; Bauswein,
A.; Beers, T. C.; Bishop, J.; Boztepe, T.; Côté, B.; Caplan, M. E.;
Champagne, A. E.; Clark, J. A.; Couder, M.; Couture, A.; de Mink,
S. E.; Debnath, S.; deBoer, R. J.; den Hartogh, J.; Denissenkov, P.;
Dexheimer, V.; Dillmann, I.; Escher, J. E.; Famiano, M. A.; Farmer,
R.; Fisher, R.; Fröhlich, C.; Frebel, A.; Fryer, C.; Fuller, G.;
Ganguly, A. K.; Ghosh, S.; Gibson, B. K.; Gorda, T.; Gourgouliatos,
K. N.; Graber, V.; Gupta, M.; Haxton, W.; Heger, A.; Hix, W. R.;
Ho, W C. G.; Holmbeck, E. M.; Hood, A. A.; Huth, S.; Imbriani, G.;
Izzard, R. G.; Jain, R.; Jayatissa, H.; Johnston, Z.; Kajino, T.;
Kankainen, A.; Kiss, G. G.; Kwiatkowski, A.; La Cognata, M.; Laird,
A. M.; Lamia, L.; Landry, P.; Laplace, E.; Launey, K. D.; Leahy,
D.; Leckenby, G.; Lennarz, A.; Longfellow, B.; Lovell, A. E.; Lynch,
W. G.; Lyons, S. M.; Maeda, K.; Masha, E.; Matei, C.; Merc, J.; Messer,
B.; Montes, F.; Mukherjee, A.; Mumpower, M.; Neto, D.; Nevins, B.;
Newton, W. G.; Nguyen, L. Q.; Nishikawa, K.; Nishimura, N.; Nunes,
F. M.; O'Connor, E.; O'Shea, B. W.; Ong, W-J.; Pain, S. D.; Pajkos,
M. A.; Pignatari, M.; Pizzone, R. G.; Placco, V. M.; Plewa, T.;
Pritychenko, B.; Psaltis, A.; Puentes, D.; Qian, Y-Z.; Radice, D.;
Rapagnani, D.; Rebeiro, B. M.; Reifarth, R.; Richard, A. L.; Rijal,
N.; Roederer, I. U.; Rojo, J. S.; K, J. S; Saito, Y.; Schwenk, A.;
Sergi, M. L.; Sidhu, R. S.; Simon, A.; Sivarani, T.; Skúladóttir,
Á.; Smith, M. S.; Spiridon, A.; Sprouse, T. M.; Starrfield, S.;
Steiner, A. W.; Strieder, F.; Sultana, I.; Surman, R.; Szücs, T.;
Tawfik, A.; Thielemann, F.; Trache, L.; Trappitsch, R.; Tsang, M. B.;
Tumino, A.; Upadhyayula, S.; Valle Martínez, J. O.; Van der Swaelmen,
M.; Viscasillas Vázquez, C.; Watts, A.; Wehmeyer, B.; Wiescher, M.;
Wrede, C.; Yoon, J.; Zegers, R G. T.; Zermane, M. A.; Zingale, M.
2022arXiv220507996S Altcode:
Nuclear Astrophysics is a field at the intersection of nuclear physics
and astrophysics, which seeks to understand the nuclear engines of
astronomical objects and the origin of the chemical elements. This
white paper summarizes progress and status of the field, the new open
questions that have emerged, and the tremendous scientific opportunities
that have opened up with major advances in capabilities across an
ever growing number of disciplines and subfields that need to be
integrated. We take a holistic view of the field discussing the unique
challenges and opportunities in nuclear astrophysics in regards to
science, diversity, education, and the interdisciplinarity and breadth
of the field. Clearly nuclear astrophysics is a dynamic field with a
bright future that is entering a new era of discovery opportunities.
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Title: The Impact of Neutron Transfer Reactions on the Heating and
Cooling of Accreted Neutron Star Crusts
Authors: Schatz, H.; Meisel, Z.; Brown, E. F.; Gupta, S. S.; Hitt,
G. W.; Hix, W. R.; Jain, R.; Lau, R.; Möller, P.; Ong, W. -J.;
Shternin, P. S.; Xu, Y.; Wiescher, M.
2022ApJ...925..205S Altcode: 2021arXiv211211544S
Nuclear reactions heat and cool the crust of accreting neutron stars
and need to be understood to interpret observations of X-ray bursts
and long-term cooling in transiently accreting systems. It was recently
suggested that previously ignored neutron transfer reactions may play
a significant role in the nuclear processes. We present results from
full nuclear network calculations that now include these reactions and
determine their impact on crust composition, crust impurity, heating,
and cooling. We find that a large number of neutron transfer reactions
indeed occur and impact crust models. In particular, we identify a new
type of reaction cycle that brings a pair of nuclei across the nuclear
chart into equilibrium via alternating neutron capture and neutron
release, interspersed with a neutron transfer. While neutron transfer
reactions lead to changes in crust model predictions and need to be
considered in future studies, previous conclusions concerning heating,
cooling, and compositional evolution are remarkably robust.
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Title: Extragalactic Globular Clusters with Euclid and other wide
surveys
Authors: Lançon, A.; Larsen, S.; Voggel, K.; Cuillandre, J. -C.; Duc,
P. -A.; Chantereau, W.; Jain, R.; Sánchez-Janssen, R.; Cantiello,
M.; Rejkuba, M.; Marleau, F.; Saifollahi, T.; Conselice, C.; Hunt,
L.; N Ferguson, A. M.; Lagadec, E.; Côté, P.
2021sf2a.conf..447L Altcode: 2021arXiv211013783L
Globular clusters play a role in many areas of astrophysics,
ranging from stellar physics to cosmology. New ground-based optical
surveys complemented by observations from space-based telescopes with
unprecedented near-infrared capabilities will help us solve the puzzles
of their formation histories. In this context, the Wide Survey of the
{\em Euclid}\ space mission will provide red and near-infrared data
over about 15\,000 square degrees of the sky. Combined with optical
photometry from the ground, it will allow us to construct a global
picture of the globular cluster populations in both dense and tenuous
environments out to tens of megaparsecs. The homogeneous photometry
of these data sets will rejuvenate stellar population studies that
depend on precise spectral energy distributions. We provide a brief
overview of these perspectives.
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Title: Do Coronal Loops Oscillate in Isolation?
Authors: Hindman, Bradley W.; Jain, Rekha
2021ApJ...921...29H Altcode: 2021arXiv210804362H
Images of the solar corona by extreme-ultraviolet telescopes reveal
elegant arches of glowing plasma that trace the corona's magnetic
field. Typically, these loops are preferentially illuminated segments
of an arcade of vaulted field lines and such loops are often observed
to sway in response to nearby solar flares. A flurry of observational
and theoretical effort has been devoted to the exploitation of these
oscillations with the grand hope that seismic techniques might be
used as probes of the strength and structure of the corona's magnetic
field. The commonly accepted viewpoint is that each visible loop
oscillates as an independent entity and acts as a one-dimensional
wave cavity for magnetohydrodynamic kink waves. We argue that for
many events, this generally accepted model for the wave cavity is
fundamentally flawed. In particular, the 3D magnetic arcade in which
the bright loop resides participates in the oscillation. Thus, the
true wave cavity is larger than the individual loop and inherently
multidimensional. We derive the skin depth of the near-field response
for an oscillating loop and demonstrate that most loops are too close
to other magnetic structures to oscillate in isolation. Further, we
present a simple model of a loop embedded within an arcade and explore
how the eigenmodes of the arcade and the eigenmodes of the loop become
coupled. In particular, we discuss how distinguishing between these
two types of modes can be difficult when the motions within the arcade
are often invisible.
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Title: First direct measurement of <SUP>59</SUP>Cu(p ,α
)<SUP>56</SUP>Ni : A step towards constraining the Ni-Cu cycle in
the cosmos
Authors: Randhawa, J. S.; Kanungo, R.; Refsgaard, J.; Mohr, P.;
Ahn, T.; Alcorta, M.; Andreoiu, C.; Bhattacharjee, S. S.; Davids,
B.; Christian, G.; Chen, A. A.; Coleman, R.; Garrett, P. E.; Grinyer,
G. F.; Gyabeng Fuakye, E.; Hackman, G.; Hollett, J.; Jain, R.; Kapoor,
K.; Krücken, R.; Laffoley, A.; Lennarz, A.; Liang, J.; Meisel,
Z.; Nikhil, B.; Psaltis, A.; Radich, A.; Rocchini, M.; Saei, N.;
Saxena, M.; Singh, M.; Svensson, C.; Subramaniam, P.; Talebitaher,
A.; Upadhyayula, S.; Waterfield, C.; Williams, J.; Williams, M.
2021PhRvC.104d2801R Altcode: 2021arXiv210705606R
Reactions on proton-rich nuclides drive the nucleosynthesis in core
collapse supernovae (CCSNe) and in x-ray bursts (XRBs). CCSNe eject
the nucleosynthesis products to the interstellar medium and hence are a
potential inventory of p nuclei, whereas in XRBs nucleosynthesis powers
the light curves. In both astrophysical sites the Ni-Cu cycle, which
features a competition between <SUP>59</SUP>Cu(p ,α )<SUP>56</SUP>Ni
and <SUP>59</SUP>Cu(p ,γ )<SUP>60</SUP>Zn , could potentially
halt the production of heavier elements. Here, we report the first
direct measurement of <SUP>59</SUP>Cu(p ,α )<SUP>56</SUP>Ni using
a reaccelerated <SUP>59</SUP>Cu beam and a cryogenic solid hydrogen
target. Our results show that the reaction proceeds predominantly to
the ground state of <SUP>56</SUP>Ni, and the experimental rate has
been found to be lower than Hauser-Feshbach based statistical model
predictions. New results hints that the ν p process could operate at
higher temperatures than previously inferred and therefore remains a
viable site for synthesizing the heavier elements.
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Title: Kink Oscillations of Coronal Loops
Authors: Nakariakov, V. M.; Anfinogentov, S. A.; Antolin, P.; Jain, R.;
Kolotkov, D. Y.; Kupriyanova, E. G.; Li, D.; Magyar, N.; Nisticò, G.;
Pascoe, D. J.; Srivastava, A. K.; Terradas, J.; Vasheghani Farahani,
S.; Verth, G.; Yuan, D.; Zimovets, I. V.
2021SSRv..217...73N Altcode: 2021arXiv210911220N
Kink oscillations of coronal loops, i.e., standing kink waves, is
one of the most studied dynamic phenomena in the solar corona. The
oscillations are excited by impulsive energy releases, such as low
coronal eruptions. Typical periods of the oscillations are from a
few to several minutes, and are found to increase linearly with the
increase in the major radius of the oscillating loops. It clearly
demonstrates that kink oscillations are natural modes of the loops,
and can be described as standing fast magnetoacoustic waves with the
wavelength determined by the length of the loop. Kink oscillations are
observed in two different regimes. In the rapidly decaying regime,
the apparent displacement amplitude reaches several minor radii of
the loop. The damping time which is about several oscillation periods
decreases with the increase in the oscillation amplitude, suggesting a
nonlinear nature of the damping. In the decayless regime, the amplitudes
are smaller than a minor radius, and the driver is still debated. The
review summarises major findings obtained during the last decade,
and covers both observational and theoretical results. Observational
results include creation and analysis of comprehensive catalogues of
the oscillation events, and detection of kink oscillations with imaging
and spectral instruments in the EUV and microwave bands. Theoretical
results include various approaches to modelling in terms of the
magnetohydrodynamic wave theory. Properties of kink oscillations are
found to depend on parameters of the oscillating loop, such as the
magnetic twist, stratification, steady flows, temperature variations
and so on, which make kink oscillations a natural probe of these
parameters by the method of magnetohydrodynamic seismology.
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Title: The need for new techniques to identify the high-frequency
MHD waves of an oscillating coronal loop
Authors: Allian, Farhad; Jain, Rekha
2021A&A...650A..91A Altcode: 2021arXiv210508189A
Context. Magnetic arcades in the solar atmosphere, or coronal loops,
are common structures known to host magnetohydrodynamic (MHD) waves
and oscillations. Of particular interest are the observed properties
of transverse loop oscillations, such as their frequency and mode of
oscillation, which have received significant attention in recent years
because of their seismological capability. Previous studies have relied
on standard data analysis techniques, such as a fast Fourier transform
(FFT) and wavelet transform (WT), to correctly extract periodicities
and identify the MHD modes. However, the ways in which these methods
can lead to artefacts requires careful investigation. <BR /> Aims:
We aim to assess whether these two common spectral analysis techniques
in coronal seismology can successfully identify high-frequency waves
from an oscillating coronal loop. <BR /> Methods: We examine extreme
ultraviolet images of a coronal loop observed by the Atmospheric
Imaging Assembly in the 171 Å waveband on board the Solar Dynamics
Observatory. We perform a spectral analysis of the loop waveform and
compare our observation with a basic simulation. <BR /> Results: The
spectral FFT and WT power of the observed loop waveform is found to
reveal a significant signal with frequency ∼2.67 mHz superposed
onto the dominant mode of oscillation of the loop (∼1.33 mHz),
that is, the second harmonic of the loop. The simulated data show
that the second harmonic is completely artificial even though both of
these methods identify this mode as a real signal. This artificial
harmonic, and several higher modes, are shown to arise owing to
the periodic but non-uniform brightness of the loop. We further
illustrate that the reconstruction of the ∼2.67 mHz component,
particularly in the presence of noise, yields a false perception
of oscillatory behaviour that does not otherwise exist. We suggest
that additional techniques, such as a forward model of a 3D coronal
arcade, are necessary to verify such high-frequency waves. <BR />
Conclusions: Our findings have significant implications for coronal
seismology, as we highlight the dangers of attempting to identify
high-frequency MHD wave modes using these standard data analysis
techniques. <P />Movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039763/olm">https://www.aanda.org</A>
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Title: A comparison between X-shooter spectra and PHOENIX models
across the HR-diagram
Authors: Lançon, A.; Gonneau, A.; Verro, K.; Prugniel, P.;
Arentsen, A.; Trager, S. C.; Peletier, R.; Chen, Y. -P.; Coelho,
P.; Falcón-Barroso, J.; Hauschildt, P.; Husser, T. -O.; Jain, R.;
Lyubenova, M.; Martins, L.; Sánchez Blázquez, P.; Vazdekis, A.
2021A&A...649A..97L Altcode: 2020arXiv201209129L
<BR /> Aims: The path towards robust near-infrared extensions of stellar
population models involves the confrontation between empirical and
synthetic stellar spectral libraries across the wavelength ranges of
photospheric emission. Indeed, the theory of stellar emission enters
all population synthesis models, even when this is only implicit in the
association of fundamental stellar parameters with empirical spectral
library stars. With its near-ultraviolet to near-infrared coverage, the
X-shooter Spectral Library (XSL) allows us to examine to what extent
models succeed in reproducing stellar energy distributions (SEDs)
and stellar absorption line spectra simultaneously. <BR /> Methods:
As a first example, this study compares the stellar spectra of XSL with
those of the Göttingen Spectral Library, which are based on the PHOENIX
synthesis code. The comparison was carried out both separately in the
three arms of the X-shooter spectrograph known as UVB, VIS and NIR, and
jointly across the whole spectrum. We did not discard the continuum in
these comparisons; only reddening was allowed to modify the SEDs of the
models. <BR /> Results: When adopting the stellar parameters published
with data release DR2 of XSL, we find that the SEDs of the models are
consistent with those of the data at temperatures above 5000 K. Below
5000 K, there are significant discrepancies in the SEDs. When leaving
the stellar parameters free to adjust, satisfactory representations
of the SEDs are obtained down to about 4000 K. However, in particular
below 5000 K and in the UVB spectral range, strong local residuals
associated with intermediate resolution spectral features are then seen;
the necessity of a compromise between reproducing the line spectra and
reproducing the SEDs leads to dispersion between the parameters favored
by various spectral ranges. We describe the main trends observed and
we point out localized offsets between the parameters preferred in
this global fit to the SEDs and the parameters in DR2. These depend
in a complex way on the position in the Hertzsprung-Russell diagram
(HRD). We estimate the effect of the offsets on bolometric corrections
as a function of position in the HRD and use this for a brief discussion
of their impact on the studies of stellar populations. A review of
the literature shows that comparable discrepancies are mentioned in
studies using other theoretical and empirical libraries.
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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
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Title: VizieR Online Data Catalog: Observation of 31 G-stars at
1.5GHz with GBT (Margot+, 2021)
Authors: Margot, J. -L.; Pinchuk, P.; Geil, R.; Alexander, S.; Arora,
S.; Biswas, S.; Cebreros, J.; Desai, S. P.; Duclos, B.; Dunne, R.;
Lin, Fu K. K.; Goel, S.; Gonzales, J.; Gonzalez, A.; Jain, R.; Lam,
A.; Lewis, B.; Lewis, R.; Li, G.; MacDougall, M.; Makarem, C.; Manan,
I.; Molina, E.; Nagib, C.; Neville, K.; O'Toole, C.; Rockwell, V.;
Rokushima, Y.; Romanek, G.; Schmidgall, C.; Seth, S.; Shah, R.;
Shimane, Y.; Singhal, M.; Tokadjian, A.; Villafana, L.; Wang, Z.;
Yun, In; Zhu, L.; Lynch, R. S.
2021yCat..51610055M Altcode:
We selected 31 Sun-like stars (spectral type G, luminosity class V)
with a median galactic latitude of 0.85°. We observed these stars
with the Green Bank Telescope (GBT) during two 2hr sessions separated
by approximately 1yr. During each observing session, we recorded both
linear polarizations of the L-band receiver with the GUPPI back end in
its baseband recording mode. The center frequency was set to 1.5GHz,
and we sampled 800MHz of bandwidth between 1.1 and 1.9GHz. <P />(2
data files).
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Title: Excitation Sources of Oscillations in Solar Coronal Loops:
A Multi-wavelength Analysis
Authors: Conde C., Sandra M.; Jain, Rekha; Jatenco-Pereira, Vera
2020ApJ...890L..21C Altcode:
An investigation into the excitation sources of oscillations detected in
a coronal loop structure is carried out using the images obtained with
Interface Region Imaging Spectrometer (IRIS) and the Atmospheric Imaging
Assembly (AIA) instrument on board the Solar Dynamics Observatory
(SDO). A loop structure in the active region AR 11967 on 2014 January
28, oscillating in the vicinity of a strong eruption and an M3.6 class
flare site, is clearly noticeable in SDO/AIA 171 Å images. We study
in detail, the oscillations with detected periods between 4 and 13
minutes and their connection in IRIS SJI 1330 Å and SDO/AIA 1700
Å images; both of these wavelengths sample the lower parts of the
solar atmosphere. The simultaneous presence of many oscillations in
the region of interest in all three wavelength passbands suggest that
these oscillations were excited in the lower-chromosphere-photosphere
plasma connected to the loop structure and then propagated at higher
heights. We further investigate the Doppler velocity measurements
from the spectrograph snapshots in IRIS C II 1336 Å, Si IV 1403 Å
and Mg II k 2796 Å. These show signatures of upflows in the vicinity
of the loop structure's endpoints estimated from 171 Å images. We
suggest that some of the oscillations observed in AIA 171 Å have
been triggered by plasma ejections and perturbations seen in the lower
layers of the solar atmosphere. Based on the estimated phase speeds,
the oscillations are likely to be slow magnetoacoustic in nature.
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Title: VizieR Online Data Catalog: Measured atmospheric parameters
of NGC6397 stars (Jain+, 2020)
Authors: Jain, R.; Prugniel, P.; Martins, L.; Lancon, A.
2020yCat..36350161J Altcode:
The table contains the atmospheric parameters determined for stars
of NGC 6397. The spectra of these stars were observed using MUSE
spectrograph by Husser et al. 2016. We use the spectra of these stars
to estimate atmospheric parameters using ELODIE and MILES libraries. <P
/>(1 data file).
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Title: Michael Thompson in Sheffield
Authors: Jain, Rekha
2020ASSP...57....9J Altcode:
Michael Thompson gave huge contributions to the field of Helioseismology
and inspired many young researchers in the discipline with his insight
and new ideas. He spent six years in Sheffield after being appointed
as the Head of Applied Mathematics Department in the University of
Sheffield (UK) where colleagues hold fond memories of him, both as
a committed academic and a very effective leader. His hard work and
sincere approach was infectious to all those who worked around him. This
tribute is an opportunity to share a little part of his work and life
during his time in Sheffield.
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Title: A New Analysis Procedure for Detecting Periodicities within
Complex Solar Coronal Arcades
Authors: Allian, Farhad; Jain, Rekha; Hindman, B. W.
2019ApJ...880....3A Altcode: 2019arXiv190206644A
We study intensity variations, as measured by the Atmospheric
Imaging Assembly on board the Solar Dynamics Observatory, in a solar
coronal arcade using a newly developed analysis procedure that employs
spatio-temporal autocorrelations. We test our new procedure by studying
large-amplitude oscillations excited by nearby flaring activity within
a complex arcade and detect a dominant periodicity of 12.31 minutes. We
compute this period in two ways: from the traditional time-distance
fitting method and using our new autocorrelation procedure. The two
analyses yield consistent results. The autocorrelation procedure is
then implemented on time series for which the traditional method would
fail due to the complexity of overlapping loops and a poor contrast
between the loops and the background. Using this new procedure, we
discover the presence of small-amplitude oscillations within the same
arcade with 9.13 and 9.81 minute periods prior and subsequent to the
large-amplitude oscillations, respectively. Consequently, we identify
these as “decayless” oscillations that have only been previously
observed in nonflaring loop systems.
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Title: A Novel Approach to Resonant Absorption of the Fast
Magnetohydrodynamic Eigenmodes of a Coronal Arcade
Authors: Hindman, Bradley W.; Jain, Rekha
2018ApJ...858....6H Altcode: 2018arXiv180308948H
The arched field lines forming coronal arcades are often observed
to undulate as magnetohydrodynamic waves propagate both across and
along the magnetic field. These waves are most likely a combination of
resonantly coupled fast magnetoacoustic waves and Alfvén waves. The
coupling results in resonant absorption of the fast waves, converting
fast wave energy into Alfvén waves. The fast eigenmodes of the
arcade have proven difficult to compute or derive analytically,
largely because of the mathematical complexity that the coupling
introduces. When a traditional spectral decomposition is employed,
the discrete spectrum associated with the fast eigenmodes is often
subsumed into the continuous Alfvén spectrum. Thus fast eigenmodes
become collective modes or quasi-modes. Here we present a spectral
decomposition that treats the eigenmodes as having real frequencies
but complex wavenumbers. Using this procedure we derive dispersion
relations, spatial damping rates, and eigenfunctions for the resonant,
fast eigenmodes of the arcade. We demonstrate that resonant absorption
introduces a fast mode that would not exist otherwise. This new mode is
heavily damped by resonant absorption, travelling only a few wavelengths
before losing most of its energy.
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Title: Fast magnetohydrodynamic waves in a solar coronal arcade
Authors: Thackray, Hope; Jain, Rekha
2017A&A...608A.108T Altcode:
<BR /> Aims: Our aim is to investigate detailed properties of fast
magnetohydrodynamic (MHD) modes of a three-dimensional waveguide for
a cylindrical magnetic arcade. <BR /> Methods: We derive governing
equations and dispersion relations for different density profiles and
numerically solve them to obtain discrete eigenvalues for fast modes
and the corresponding eigenfunctions. <BR /> Results: We find that
small changes in the density structure in the vicinity of the field
lines can lead to drastic effects on propagating solutions and, under
certain conditions, two evanescent waves arise. <BR /> Conclusions: We
investigate coronal loop oscillations in an arcade as fast MHD modes
of oscillations. We find that coronal loops with slightly different
density structures can exhibit different oscillatory behaviour and
some eigenmodes can be present or absent depending on this density
structure. Though the model has a simple potential field, the role of a
cylindrical waveguide in conjunction with differing density structures
is demonstrated clearly. Multiple-wavelength observations at several
points in the coronal loop arcades is suggested for correct mode
identification; this is crucial for unraveling the plasma properties
of the oscillating loops.
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Title: Predictions of Sunspot Cycle 24: A Comparison with Observations
Authors: Bhatt, N. J.; Jain, R.
2017AGUFMSH11C..05B Altcode:
The space weather is largely affected due to explosions on the Sun
viz. solar flares and CMEs, which, however, in turn depend upon
the magnitude of the solar activity i e. number of sunspots and
their magnetic configuration. Owing to these space weather effects,
predictions of sunspot cycle are important. Precursor techniques,
particularly employing geomagnetic indices, are often used in the
prediction of the maximum amplitude of a sunspot cycle. Based on
the average geomagnetic activity index aa (since 1868 onwards) for
the year of the sunspot minimum and the preceding four years, Bhatt
et al. (2009) made two predictions for sunspot cycle 24 considering
2008 as the year of sunspot minimum: (i) The annual maximum amplitude
would be 92.8±19.6 (1-sigma accuracy) indicating a somewhat weaker
cycle 24 as compared to cycles 21-23, and (ii) smoothed monthly mean
sunspot number maximum would be in October 2012±4 months (1-sigma
accuracy). However, observations reveal that the sunspot minima extended
up to 2009, and the maximum amplitude attained is 79, with a monthly
mean sunspot number maximum of 102.3 in February 2014. In view of the
observations and particularly owing to the extended solar minimum in
2009, we re-examined our prediction model and revised the prediction
results. We find that (i) The annual maximum amplitude of cycle 24 =
71.2 ± 19.6 and (ii) A smoothed monthly mean sunspot number maximum in
January 2014±4 months. We discuss our failure and success aspects and
present improved predictions for the maximum amplitude as well as for
the timing, which are now in good agreement with the observations. Also,
we present the limitations of our forecasting in the view of long term
predictions. We show if year of sunspot minimum activity and magnitude
of geomagnetic activity during sunspot minimum are taken correctly then
our prediction method appears to be a reliable indicator to forecast
the sunspot amplitude of the following solar cycle. References:Bhatt,
N.J., Jain, R. & Aggarwal, M.: 2009, Sol. Phys. 260, 225
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Title: Trapped modes of a cylindrical waveguide in the Sun's corona.
Authors: Thackray, Hope; Jain, Rekha
2016usc..confE...8T Altcode:
By modelling coronal-loop oscillations within three-dimensional magnetic
arcades, it has been shown that MHD fast waves can be trapped within
a 3D waveguide comprised of two shells with sharp discontinuities,
the overlaying one being of denser plasma (Hindman & Jain,
2015). We extend this model to that of a three shell waveguide, with
the outermost shell denser than the innermost, to study the effect of
less sharp discontinuities. Deriving the governing equation for the
MHD waves and finding semi-analytic solutions for the eigenfunctions,
we find that the nature of propagating and evanescent waves as obtained
in the two shell model changes. We will show that the eigenfrequencies
and eigenfunctions depend on the thickness of the middle shell, and its
position in the cylindrical arcade. The investigation has implications
for identification of fast MHD waves in the solar coronal loops.
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Title: Time-dependent Suppression of Oscillatory Power in Evolving
Solar Magnetic Fields
Authors: Krishna Prasad, S.; Jess, D. B.; Jain, R.; Keys, P. H.
2016ApJ...823...45K Altcode: 2016ApJ...823...45P; 2016arXiv160405667K
Oscillation amplitudes are generally smaller within magnetically
active regions like sunspots and plage when compared to their
surroundings. Such magnetic features, when viewed in spatially
resolved power maps, appear as regions of suppressed power due to
reductions in the oscillation amplitudes. Employing high spatial- and
temporal-resolution observations from the Dunn Solar Telescope (DST)
in New Mexico, we study the power suppression in a region of evolving
magnetic fields adjacent to a pore. By utilizing wavelet analysis,
we study for the first time how the oscillatory properties in this
region change as the magnetic field evolves with time. Image sequences
taken in the blue continuum, G-band, Ca II K, and Hα filters were
used in this study. It is observed that the suppression found in the
chromosphere occupies a relatively larger area, confirming previous
findings. Also, the suppression is extended to structures directly
connected to the magnetic region, and is found to get enhanced as the
magnetic field strength increased with time. The dependence of the
suppression on the magnetic field strength is greater at longer periods
and higher formation heights. Furthermore, the dominant periodicity
in the chromosphere was found to be anti-correlated with increases in
the magnetic field strength.
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Title: Periodicities in the X-ray Emission from the Solar Corona:
SphinX and SOXS Observations
Authors: Steślicki, M.; Awasthi, A. K.; Gryciuk, M.; Jain, R.
2016CEAB...40..133S Altcode:
The structure and evolution of the solar magnetic field is driven by
a magnetohydrodynamic dynamo operating in the solar interior, which
induces various solar activities that exhibit periodic variations
on different timescales. Therefore, probing the periodic nature of
emission originating from the solar corona may provide insights of
the convection-zone-photosphere-corona coupling processes. We present
the study of the mid-range periodicities, between rotation period
(∼27 days) and the Schwabe cycle period (∼11 yr), in the solar
soft X-ray emission, based on the data obtained by two instruments:
SphinX and SOXS in various energy bands.
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Title: Eigenmodes of Three-dimensional Magnetic Arcades in the
Sun’s Corona
Authors: Hindman, Bradley W.; Jain, Rekha
2015ApJ...814..105H Altcode: 2015arXiv151109411H
We develop a model of coronal-loop oscillations that treats the
observed bright loops as an integral part of a larger three-dimensional
(3D) magnetic structure comprised of the entire magnetic arcade. We
demonstrate that magnetic arcades within the solar corona can trap
MHD fast waves in a 3D waveguide. This is accomplished through the
construction of a cylindrically symmetric model of a magnetic arcade
with a potential magnetic field. For a magnetically dominated plasma,
we derive a governing equation for MHD fast waves and from this equation
we show that the magnetic arcade forms a 3D waveguide if the Alfvén
speed increases monotonically beyond a fiducial radius. Both magnetic
pressure and tension act as restoring forces, instead of just tension
as is generally assumed in 1D models. Since magnetic pressure plays
an important role, the eigenmodes involve propagation both parallel
and transverse to the magnetic field. Using an analytic solution,
we derive the specific eigenfrequencies and eigenfunctions for an
arcade possessing a discontinuous density profile. The discontinuity
separates a diffuse cylindrical cavity and an overlying shell of
denser plasma that corresponds to the bright loops. We emphasize
that all of the eigenfunctions have a discontinuous axial velocity
at the density interface; hence, the interface can give rise to the
Kelvin-Helmholtz instability. Further, we find that all modes have
elliptical polarization with the degree of polarization changing with
height. However, depending on the line of sight, only one polarization
may be clearly visible.
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Title: Fundamental-mode Oscillations of Two Coronal Loops within a
Solar Magnetic Arcade
Authors: Jain, Rekha; Maurya, Ram A.; Hindman, Bradley W.
2015ApJ...804L..19J Altcode: 2015arXiv150407822J
We analyze intensity variations, as measured by the Atmospheric Imaging
Assembly in the 171 Å passband, in two coronal loops embedded within
a single coronal magnetic arcade. We detect oscillations in the
fundamental mode with periods of roughly 2 minutes and decay times
of 5 minutes. The oscillations were initiated by interaction of the
arcade with a large wavefront issuing from a flare site. Further,
the power spectra of the oscillations evince signatures consistent
with oblique propagation to the field lines and for the existence of
a two-dimensional waveguide instead of a one-dimensional one.
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Title: Five-minute Oscillation Power within Magnetic Elements in
the Solar Atmosphere
Authors: Jain, Rekha; Gascoyne, Andrew; Hindman, Bradley W.; Greer,
Benjamin
2014ApJ...796...72J Altcode: 2014arXiv1405.0695J
It has long been known that magnetic plage and sunspots are regions in
which the power of acoustic waves is reduced within the photospheric
layers. Recent observations now suggest that this suppression of
power extends into the low chromosphere and is also present in small
magnetic elements far from active regions. In this paper we investigate
the observed power suppression in plage and magnetic elements, by
modeling each as a collection of vertically aligned magnetic fibrils
and presuming that the velocity within each fibril is the response
to buffeting by incident p modes in the surrounding field-free
atmosphere. We restrict our attention to modeling observations made
near the solar disk center, where the line-of-sight velocity is
nearly vertical and hence, only the longitudinal component of the
motion within the fibril contributes. Therefore, we only consider the
excitation of axisymmetric sausage waves and ignore kink oscillations
as their motions are primarily horizontal. We compare the vertical
motion within the fibril with the vertical motion of the incident
p mode by constructing the ratio of their powers. In agreement with
observational measurements we find that the total power is suppressed
within strong magnetic elements for frequencies below the acoustic
cut-off frequency. However, further physical effects need to be examined
for understanding the observed power ratios for stronger magnetic field
strengths and higher frequencies. We also find that the magnitude of
the power deficit increases with the height above the photosphere at
which the measurement is made. Furthermore, we argue that the area of
the solar disk over which the power suppression extends increases as
a function of height.
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Title: Importance of Solar Atmospheric Coupling on P-Mode Power
within Magnetic Elements
Authors: Gascoyne, A.; Jain, R.
2014AGUFMSH41B4142G Altcode:
It has long been known that the power of p-mode oscillations is
reducedwithin magnetic plages and sunspots at photospheric level. Recent
observations now suggest that this suppression of power extends into
the low chromosphere and isalso present in small magnetic elements far
from active regions. Weconstruct a model to investigate a possible
mechanism of this powerloss whereby p modes buffet small magnetic
elements and excite MHDsausage tube waves. These magnetic tube
waves propagate along the manymagnetic fibrils which are embedded
in the convection zone and expandinto the chromosphere due to the
fall in density with height of thesurrounding plasma. We treat the
magnetic fibrils as verticallyaligned, thin flux tubes embedded in
a two region polytropic-isothermalatmosphere to study the coupling
of p-mode driven sausage waves,which are excited in the convection
zone and propagate into theoverlying chromosphere. The excited tube
waves carry energy away fromthe p-mode cavity resulting in a deficit
of p-mode energy which wequantify by computing the associated damping
rate and absorptioncoefficient of the driving p modes. We also compare
the verticalmotion within the fibril with the vertical motion of the
incident p modeby constructing the ratio of their powers using HMI
data and theory.In agreement with observational measurements we find
that the totalpower is suppressed within strong magnetic elements for
frequenciesbelow the acoustic cut-off frequency. We also find that
the magnitudeof the power deficit increases with the height above the
photosphereat which the measurement is made. Further, we argue that
the area ofthe solar disk over which the power suppression extends
increases as afunction of height.
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Title: Interpreting Coronal-Loop Oscillations as the Modes of a
2D Waveguide
Authors: Hindman, B.; Jain, R.
2014AGUFMSH13A4072H Altcode:
The bright coronal loops that trace bundles of field lines within
coronal arcades have been observed to oscillate with one or more
preferred frequencies. Recent studies indicate that two distinct
categories of oscillation occur: large-amplitude, transient oscillations
that are initiated by flares and low-amplitude, "decayless" oscillations
that can persist for as long as the loop remains visible. The preferred
frequencies of these oscillations have previously been interpreted as
the resonant frequencies of MHD fast waves that are trapped between the
photospheric footpoints of a bundle of field lines in a 1-D cavity. The
nascent field of coronal-loop seismology attempts to deduce loop
properties, such as the magnetic-field strength, loop length, etc., by
exploiting the information contained in the measured mode periods. We
present an alternative 2D model of the wave cavity whereby the waves
can propagate across field lines and the entire magnetic arcade acts
as a waveguide. Within this framework, the two types of oscillations,
flare-induced waves and decayless oscillations, can both be attributed
to MHD fast waves. The two components of the signal differ only because
of the duration and spatial extent of the source that creates them. The
flare-induced waves are generated by strong, localized sources of
short duration, while the decayless background is excited by a diffuse,
stochastic source. Further, the oscillatory signal induced by a flare
can be interpreted as a pattern of interference fringes produced by
waves that are launched from a compact source and have traveled diverse
routes of various pathlength through the waveguide. The amplitude
of the resulting fringe pattern decays in time without the need for
local dissipation mechanisms. The details of the interference pattern
depend on the shape of the arcade and on the spatial variation of the
Alfvén speed within the arcade. We explore these details with a view
to understanding the excitation mechanism of the oscillations and the
seismological implications of the interference process.
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Title: Homologous flare-CME events and their metric type II radio
burst association
Authors: Yashiro, S.; Gopalswamy, N.; Mäkelä, P.; Akiyama, S.;
Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan,
P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.;
Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P.
2014AdSpR..54.1941Y Altcode:
Active region NOAA 11158 produced many flares during its disk
passage. At least two of these flares can be considered as homologous:
the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on February
14, 2011. Both flares occurred at the same location (eastern edge of
the active region) and have a similar decay of the GOES soft X-ray
light curve. The associated coronal mass ejections (CMEs) were slow
(334 and 337 km/s) and of similar apparent widths (43° and 44°), but
they had different radio signatures. The second event was associated
with a metric type II burst while the first one was not. The COR1
coronagraphs on board the STEREO spacecraft clearly show that the
second CME propagated into the preceding CME that occurred 50 min
before. These observations suggest that CME-CME interaction might be
a key process in exciting the type II radio emission by slow CMEs.
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Title: Energy Loss of Solar p Modes due to the Excitation of Magnetic
Sausage Tube Waves: Importance of Coupling the Upper Atmosphere
Authors: Gascoyne, A.; Jain, R.; Hindman, B. W.
2014ApJ...789..109G Altcode: 2014arXiv1405.0130G
We consider damping and absorption of solar p modes due to their
energy loss to magnetic tube waves that can freely carry energy out of
the acoustic cavity. The coupling of p modes and sausage tube waves
is studied in a model atmosphere composed of a polytropic interior
above which lies an isothermal upper atmosphere. The sausage tube
waves, excited by p modes, propagate along a magnetic fibril which
is assumed to be a vertically aligned, stratified, thin magnetic flux
tube. The deficit of p-mode energy is quantified through the damping
rate, Γ, and absorption coefficient, α. The variation of Γ and
α as a function of frequency and the tube's plasma properties is
studied in detail. Previous similar studies have considered only a
subphotospheric layer, modeled as a polytrope that has been truncated
at the photosphere. Such studies have found that the resulting energy
loss by the p modes is very sensitive to the upper boundary condition,
which, due to the lack of an upper atmosphere, have been imposed
in a somewhat ad hoc manner. The model presented here avoids such
problems by using an isothermal layer to model the overlying atmosphere
(chromosphere, and, consequently, allows us to analyze the propagation
of p-mode-driven sausage waves above the photosphere. In this paper,
we restrict our attention to frequencies below the acoustic cut
off frequency. We demonstrate the importance of coupling all waves
(acoustic, magnetic) in the subsurface solar atmosphere with the
overlying atmosphere in order to accurately model the interaction
of solar f and p modes with sausage tube waves. In calculating the
absorption and damping of p modes, we find that for low frequencies,
below ≈3.5 mHz, the isothermal atmosphere, for the two-region model,
behaves like a stress-free boundary condition applied at the interface
(z = -z <SUB>0</SUB>).
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Title: An Interpretation of Flare-induced and Decayless Coronal-loop
Oscillations as Interference Patterns
Authors: Hindman, Bradley W.; Jain, Rekha
2014ApJ...784..103H Altcode: 2013arXiv1312.1922H
We present an alternative model of coronal-loop oscillations, which
considers that the waves are trapped in a two-dimensional waveguide
formed by the entire arcade of field lines. This differs from the
standard one-dimensional model which treats the waves as the resonant
oscillations of just the visible bundle of field lines. Within the
framework of our two-dimensional model, the two types of oscillations
that have been observationally identified, flare-induced waves and
"decayless" oscillations, can both be attributed to MHD fast waves. The
two components of the signal differ only because of the duration and
spatial extent of the source that creates them. The flare-induced
waves are generated by strong localized sources of short duration,
while the decayless background can be excited by a continuous,
stochastic source. Further, the oscillatory signal arising from a
localized, short-duration source can be interpreted as a pattern of
interference fringes produced by waves that have traveled diverse
routes of various pathlengths through the waveguide. The resulting
amplitude of the fringes slowly decays in time with an inverse square
root dependence. The details of the interference pattern depend on
the shape of the arcade and the spatial variation of the Alfvén
speed. The rapid decay of this wave component, which has previously
been attributed to physical damping mechanisms that remove energy
from resonant oscillations, occurs as a natural consequence of the
interference process without the need for local dissipation.
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Title: Multiwavelength diagnostics of the precursor and main phases
of an M1.8 flare on 2011 April 22
Authors: Awasthi, A. K.; Jain, R.; Gadhiya, P. D.; Aschwanden, M. J.;
Uddin, W.; Srivastava, A. K.; Chandra, R.; Gopalswamy, N.; Nitta,
N. V.; Yashiro, S.; Manoharan, P. K.; Choudhary, D. P.; Joshi, N. C.;
Dwivedi, V. C.; Mahalakshmi, K.
2014MNRAS.437.2249A Altcode: 2013arXiv1310.6029A; 2013MNRAS.tmp.2720A
We study the temporal, spatial and spectral evolution of the M1.8 flare,
which occurred in the active region 11195 (S17E31) on 2011 April 22,
and explore the underlying physical processes during the precursor
phase and their relation to the main phase. The study of the source
morphology using the composite images in 131 Å wavelength observed by
the Solar Dynamics Observatory/Atmospheric Imaging Assembly and 6-14
keV [from the Reuven Ramaty High Energy Solar Spectroscopic Imager
(RHESSI)] revealed a multiloop system that destabilized systematically
during the precursor and main phases. In contrast, hard X-ray emission
(20-50 keV) was absent during the precursor phase, appearing only from
the onset of the impulsive phase in the form of foot-points of emitting
loops. This study also revealed the heated loop-top prior to the loop
emission, although no accompanying foot-point sources were observed
during the precursor phase. We estimate the flare plasma parameters,
namely temperature (T), emission measure (EM), power-law index (γ)
and photon turn-over energy (ɛ<SUB>to</SUB>), and found them to be
varying in the ranges 12.4-23.4 MK, 0.0003-0.6 × 10<SUP>49</SUP>
cm<SUP>-3</SUP>, 5-9 and 14-18 keV, respectively, by forward fitting
RHESSI spectral observations. The energy released in the precursor
phase was thermal and constituted ≈1 per cent of the total energy
released during the flare. The study of morphological evolution of
the filament in conjunction with synthesized T and EM maps was carried
out, which reveals (a) partial filament eruption prior to the onset of
the precursor emission and (b) heated dense plasma over the polarity
inversion line and in the vicinity of the slowly rising filament during
the precursor phase. Based on the implications from multiwavelength
observations, we propose a scheme to unify the energy release during
the precursor and main phase emissions in which the precursor phase
emission was originated via conduction front that resulted due to the
partial filament eruption. Next, the heated leftover S-shaped filament
underwent slow-rise and heating due to magnetic reconnection and finally
erupted to produce emission during the impulsive and gradual phases.
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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.
2013A&A...560C...1J Altcode:
No abstract at ADS
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Title: Solar energetic particle events during the rise phases of
solar cycles 23 and 24
Authors: Chandra, R.; Gopalswamy, N.; Mäkelä, P.; Xie, H.; Yashiro,
S.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Jain,
R.; Awasthi, A. K.; Manoharan, P. K.; Mahalakshmi, K.; Dwivedi, V. C.;
Choudhary, D. P.; Nitta, N. V.
2013AdSpR..52.2102C Altcode:
We present a comparative study of the properties of coronal mass
ejections (CMEs) and flares associated with the solar energetic particle
(SEP) events in the rising phases of solar cycles (SC) 23 (1996-1998)
(22 events) and 24 (2009-2011) (20 events), which are associated
with type II radio bursts. Based on the SEP intensity, we divided the
events into three categories, i.e. weak (intensity < 1 pfu), minor
(1 pfu < intensity < 10 pfu) and major (intensity ⩾ 10 pfu)
events. We used the GOES data for the minor and major SEP events and
SOHO/ERNE data for the weak SEP event. We examine the correlation
of SEP intensity with flare size and CME properties. We find that
most of the major SEP events are associated with halo or partial halo
CMEs originating close to the sun center and western-hemisphere. The
fraction of halo CMEs in SC 24 is larger than the SC 23. For the minor
SEP events one event in SC23 and one event in SC24 have widths <
120° and all other events are associated with halo or partial halo
CMEs as in the case of major SEP events. In case of weak SEP events,
majority (more than 60%) of events are associated with CME width <
120°. For both the SC the average CMEs speeds are similar. For major
SEP events, average CME speeds are higher in comparison to minor and
weak events. The SEP event intensity and GOES X-ray flare size are
poorly correlated. During the rise phase of solar cycle 23 and 24,
we find north-south asymmetry in the SEP event source locations: in
cycle 23 most sources are located in the south, whereas during cycle
24 most sources are located in the north. This result is consistent
with the asymmetry found with sunspot area and intense flares.
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Title: Equilibrium Models of Coronal Loops That Involve Curvature
and Buoyancy
Authors: Hindman, Bradley W.; Jain, Rekha
2013ApJ...778..174H Altcode: 2013arXiv1308.0620H
We construct magnetostatic models of coronal loops in which the
thermodynamics of the loop is fully consistent with the shape and
geometry of the loop. This is achieved by treating the loop as a thin,
compact, magnetic fibril that is a small departure from a force-free
state. The density along the loop is related to the loop's curvature
by requiring that the Lorentz force arising from this deviation
is balanced by buoyancy. This equilibrium, coupled with hydrostatic
balance and the ideal gas law, then connects the temperature of the
loop with the curvature of the loop without resorting to a detailed
treatment of heating and cooling. We present two example solutions:
one with a spatially invariant magnetic Bond number (the dimensionless
ratio of buoyancy to Lorentz forces) and the other with a constant
radius of the curvature of the loop's axis. We find that the density
and temperature profiles are quite sensitive to curvature variations
along the loop, even for loops with similar aspect ratios.
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Title: Flux emergence, flux imbalance, magnetic free energy and
solar flares
Authors: Choudhary, Debi Prasad; Gosain, Sanjay; Gopalswamy, Nat;
Manoharan, P. K.; Chandra, R.; Uddin, W.; Srivastava, A. K.; Yashiro,
S.; Joshi, N. C.; Kayshap, P.; Dwivedi, V. C.; Mahalakshmi, K.;
Elamathi, E.; Norris, Max; Awasthi, A. K.; Jain, R.
2013AdSpR..52.1561C Altcode:
Emergence of complex magnetic flux in the solar active regions lead
to several observational effects such as a change in sunspot area
and flux embalance in photospheric magnetograms. The flux emergence
also results in twisted magnetic field lines that add to free energy
content. The magnetic field configuration of these active regions
relax to near potential-field configuration after energy release
through solar flares and coronal mass ejections. In this paper,
we study the relation of flare productivity of active regions with
their evolution of magnetic flux emergence, flux imbalance and free
energy content. We use the sunspot area and number for flux emergence
study as they contain most of the concentrated magnetic flux in the
active region. The magnetic flux imbalance and the free energy are
estimated using the HMI/SDO magnetograms and Virial theorem method. We
find that the active regions that undergo large changes in sunspot
area are most flare productive. The active regions become flary when
the free energy content exceeds 50% of the total energy. Although,
the flary active regions show magnetic flux imbalance, it is hard to
predict flare activity based on this parameter alone.
---------------------------------------------------------
Title: A multiwavelength study of eruptive events on January 23,
2012 associated with a major solar energetic particle event
Authors: Joshi, N. C.; Uddin, W.; Srivastava, A. K.; Chandra, R.;
Gopalswamy, N.; Manoharan, P. K.; Aschwanden, M. J.; Choudhary, D. P.;
Jain, R.; Nitta, N. V.; Xie, H.; Yashiro, S.; Akiyama, S.; Mäkelä,
P.; Kayshap, P.; Awasthi, A. K.; Dwivedi, V. C.; Mahalakshmi, K.
2013AdSpR..52....1J Altcode: 2013arXiv1303.1251J
We use multiwavelength data from space and ground based instruments
to study the solar flares and coronal mass ejections (CMEs) on January
23, 2012 that were responsible for one of the largest solar energetic
particle (SEP) events of solar cycle 24. The eruptions consisting of two
fast CMEs (≈1400 km s<SUP>-1</SUP> and ≈2000 km s<SUP>-1</SUP>) and
M-class flares that occurred in active region 11402 located at ≈N28
W36. The two CMEs occurred in quick successions, so they interacted
very close to the Sun. The second CME caught up with the first one
at a distance of ≈11-12 R<SUB>sun</SUB>. The CME interaction may be
responsible for the elevated SEP flux and significant changes in the
intensity profile of the SEP event. The compound CME resulted in a
double-dip moderate geomagnetic storm (Dst∼-73nT). The two dips are
due to the southward component of the interplanetary magnetic field in
the shock sheath and the ICME intervals. One possible reason for the
lack of a stronger geomagnetic storm may be that the ICME delivered
a glancing blow to Earth.
---------------------------------------------------------
Title: Height of shock formation in the solar corona inferred from
observations of type II radio bursts and coronal mass ejections
Authors: Gopalswamy, N.; Xie, H.; Mäkelä, P.; Yashiro, S.; Akiyama,
S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan,
P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.;
Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P.
2013AdSpR..51.1981G Altcode: 2013arXiv1301.0893G
Employing coronagraphic and EUV observations close to the solar surface
made by the Solar Terrestrial Relations Observatory (STEREO) mission,
we determined the heliocentric distance of coronal mass ejections
(CMEs) at the starting time of associated metric type II bursts. We
used the wave diameter and leading edge methods and measured the CME
heights for a set of 32 metric type II bursts from solar cycle 24. We
minimized the projection effects by making the measurements from a
view that is roughly orthogonal to the direction of the ejection. We
also chose image frames close to the onset times of the type II bursts,
so no extrapolation was necessary. We found that the CMEs were located
in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs),
with mean and median values of 1.43 and 1.38 Rs, respectively. We
conclusively find that the shock formation can occur at heights
substantially below 1.5 Rs. In a few cases, the CME height at type
II onset was close to 2 Rs. In these cases, the starting frequency
of the type II bursts was very low, in the range 25-40 MHz, which
confirms that the shock can also form at larger heights. The starting
frequencies of metric type II bursts have a weak correlation with the
measured CME/shock heights and are consistent with the rapid decline
of density with height in the inner corona.
---------------------------------------------------------
Title: Geo-effectiveness of Solar Transients and their
interrelationship
Authors: Tripathi, S. C.; Khan, P. A.; Muhammad, A. A.; Gwal, A. K.;
Purohit, P. K.; Jain, R.
2012AGUFMSH21A2197T Altcode:
We probe the geo-effectiveness of Solar Transients observed in the solar
cycle 23 and try to find their interrelationship with each other. In
this investigation we undertake 60 Solar Proton Events of the Solar
Cycle 23 alongwith associated Solar Flares and CMEs. We employ the
X-ray emission in Solar flares observed by Reuven Ramaty Higly Energy
Solar Spectroscopic Imager (RHESSI) and Solar X-Ray Spectrometer (SOXS)
in order to estimate flare plasma parameters. Further, we employ the
observations from Geo-stationary Operational Environmental Satellites
(GOES) and Large Angle and Spectrometric Coronagraph (LASCO), for SEPs
and CMEs parameter estimation respectively. We report a good association
of soft-hard-harder (SHH) spectral behavior in Solar Flares with
occurrence of Solar Proton Events. In addition, we have found a good
correlation (R=0.71) in SEPs spectral hardening and CME velocity. We
conclude that the Protons as well as CMEs gets accelerated at the
Flare site and travel all the way in interplanetary space and then by
re-acceleration in interplanetary space CMEs produce Geomagnetic Storms
in geo-space. This seems to be a statistically significant mechanism
of the SEPs and initial CME acceleration in addition to the standard
scenario of SEP acceleration at the shock front of CMEs.
---------------------------------------------------------
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.
2012A&A...545A..73J Altcode:
<BR /> 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. <BR /> 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, R<SUB>I</SUB>, and compare them with the
sunspot number calculated with the Sunspot Tracking And Recognition
Algorithm (STARA). <BR /> 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: Kink Oscillations of a Curved, Gravitationally Stratified
Coronal Loop
Authors: Hindman, Bradley W.; Jain, Rekha
2012arXiv1209.5734H Altcode:
Loops of magnetic field in the corona are observed to oscillate
and these oscillations have been posited to be the superposition of
resonant kink waves. To date, most analyses of these oscillations
have concentrated on calculating the frequency shifts that result from
spatial variation in the kink wave speed. Further, most have ignored
gravity and treated the loop as a straight tube. Here we ignore spatial
variation in the wave speed, but self-consistently include the effects
of gravity and loop curvature in both the equilibrium loop model and
in the wave equation. We model a coronal loop as an isolated, thin,
magnetic fibril that is anchored at two points in the photosphere. The
equilibrium shape of the loop is determined by a balance between
magnetic buoyancy and magnetic tension, which is characterized by
a Magnetic Bond Number \epsilon, that is typically small |\epsilon|
<< 1. This balance produces a loop that has a variable radius
of curvature. The resonant kink waves of such a loop come in two
polarizations that are decoupled from each other: waves with motion
completely within the plane of the loop (normal oscillations) and waves
with motions that are completely horizontal, perpendicular to the plane
of the loop (binormal oscillations). We solve for the eigensolutions of
both polarizations using perturbation theory for small Magnetic Bond
Number. For modes of the same order, normal oscillations have smaller
eigenfrequencies than binormal oscillations. The additional forces of
buoyancy and magnetic tension from the curvature of the loop increase
and decrease the mode frequencies, respectively. The ratio of the
frequencies of the first overtone to the fundamental mode is modified
by the inclusion of buoyancy and curvature. We find that the normal
polarization possesses a frequency ratio that exceeds the canonical
value of 2, whereas the binormal polarization has a ratio less than 2.
---------------------------------------------------------
Title: What can be learned from the seismology of a coronal loop
using only a handful of frequencies?
Authors: Jain, R.; Hindman, B. W.
2012A&A...545A.138J Altcode:
Context. Transverse oscillating loops in the solar corona have
been observed and the frequencies for a couple of low-order modes
measured. These frequencies have been used as a diagnostic tool to
investigate the internal properties of such oscillating loops. In
particular, the density and magnetic field profiles along the loop
are estimated by comparing the measured frequencies with those of
a reference model. In this paper, we argue that only the kink speed
may be assessed directly and there is no diagnostic capability for
density or magnetic field independent of the wave speed. Further,
with just a handful of measured frequencies available, only broad
spatial averages of the kink speed may be obtained. We demonstrate
using a frequency inversion procedure that with only two frequencies
as inputs, at best one can assess the mean and the contrast of the
kink speed along the loop. One requires access to the frequencies
of many mode orders to perform inversions that offer kink speed
determinations with high spatial resolution. <BR /> Aims: We suggest
a rigorous mathematical formalism that describes the information
content of the measured mode frequencies and we present a method
to infer the kink speed within a coronal loop by inverting those
frequencies. <BR /> Methods: We consider a single magnetic coronal
loop and by using perturbation theory, relate its eigenfrequencies
to the loop's physical properties. <BR /> Results: We derive the
sensitivity kernels that describe how each eigenfrequency contain the
information about the kink speed and density along the loop. <BR />
Conclusions: We conclude that the eigenfrequencies contain information
primarily about the kink speed, and do not strongly depend on the
density. Therefore, all loop models with the same kink speed profile
(but different density and magnetic field profiles) are seismically
indistinguishable. To acheive the spatial resolution neccessary to
uncover the non-uniform nature of the coronal loop, it is necessary
to do inversion of many measured frequencies. Making inferences about
the density stratification and magnetic field varying along the loop
requires supplemental observations that are non-seismic in nature.
---------------------------------------------------------
Title: Spine-fan reconnection. The influence of temporal and spatial
variation in the driver
Authors: Wyper, P. F.; Jain, R.; Pontin, D. I.
2012A&A...545A..78W Altcode:
Context. From observations, the atmosphere of the Sun has been shown to
be highly dynamic with perturbations of the magnetic field often lacking
temporal or spatial symmetry. Despite this, studies of the spine-fan
reconnection mode at 3D nulls have so far focused on the very idealised
case with symmetric driving of a fixed spatial extent. <BR /> Aims:
We investigate the spine-fan reconnection process for less idealised
cases, focusing on asymmetric driving and drivers with different
length scales. We look at the initial current sheet formation and
whether the scalings developed in the idealised models are robust
in more realistic situations. <BR /> Methods: The investigation
was carried out by numerically solving the resistive compressible
3D magnetohydrodynamic equations in a Cartesian box containing a
linear null point. The spine-fan collapse was driven at the null
through tangential boundary driving of the spine foot points. <BR
/> Results: We find significant differences in the initial current
sheet formation with asymmetric driving. Notable is the displacement
of the null point position as a function of driving velocity and
resistivity (η). However, the scaling relations developed in the
idealised case are found to be robust (albeit at reduced amplitudes)
despite this extra complexity. Lastly, the spatial variation is also
shown to play an important role in the initial current sheet formation
through controlling the displacement of the spine foot points. <BR />
Conclusions: We conclude that during the early stages of spine-fan
reconnection both the temporal and spatial nature of the driving play
important roles, with the idealised symmetrically driven case giving
a "best case" for the rate of current development and connectivity
change. As the most interesting eruptive events occur in relatively
short time frames this work clearly shows the need for high temporal
and spatial knowledge of the flows for accurate interpretation of
the reconnection scenario. Lastly, since the scalings developed in
the idealised case remain robust with more complex driving we can be
more confident of their use in interpreting reconnection in complex
magnetic field structures.
---------------------------------------------------------
Title: Axisymmetric Scattering of p Modes by Thin Magnetic Tubes
Authors: Hindman, Bradley W.; Jain, Rekha
2012ApJ...746...66H Altcode: 2011arXiv1106.5078H
We examine the scattering of acoustic p-mode waves from a thin magnetic
fibril embedded in a gravitationally stratified atmosphere. The
scattering is mediated through the excitation of slow sausage waves on
the magnetic tube, and only the scattering of the monopole component of
the wave field is considered. Since such tube waves are not confined
by the acoustic cavity and may freely propagate along the field
lines removing energy from the acoustic wave field, the excitation
of fibril oscillations is a source of acoustic wave absorption as
well as scattering. We compute the mode mixing that is achieved and
the absorption coefficients and phase shifts. We find that for thin
tubes the mode mixing is weak and the absorption coefficient is small
and is a smooth function of frequency over the physically relevant
band of observed frequencies. The prominent absorption resonances
seen in previous studies of unstratified tubes are absent. Despite the
relatively small absorption, the phase shift induced can be surprisingly
large, reaching values as high as 15° for f modes. Further, the phase
shift can be positive or negative depending on the incident mode order
and the frequency.
---------------------------------------------------------
Title: The effect of the environment on the P1/P2 period ratio for
kink oscillations of coronal loops
Authors: Orza, B.; Ballai, I.; Jain, R.; Murawski, K.
2012A&A...537A..41O Altcode: 2011arXiv1111.4859O
<BR /> Aims: The P<SUB>1</SUB>/P<SUB>2</SUB> period ratio of transversal
loop oscillations is currently used for the diagnostics of longitudinal
structuring of coronal loops as its deviation from 2 is intrinsically
connected to the density scale-height along coronal loops and/or the
sub-resolution structure of the magnetic field. The same technique
can be applied not only to coronal structures, but also to other
oscillating magnetic structures. <BR /> Methods: The oscillations
in magnetic structures are described by differential equations whose
coefficients depend on the longitudinal structure of the plasma. Using
a variational principle written for the transversal component of the
velocity vector, developed earlier by McEwan et al. (2008, A&A,
481, 819), we investigate how the different temperature of the
environment compared to the temperature of the magnetic structure will
influence the P<SUB>1</SUB>/P<SUB>2</SUB> ratio for typical coronal
and prominence conditions. The possible changes are translated into
quantities that are used in the process of remote plasma diagnostics
in the solar atmosphere. <BR /> Results: Using a straightforward,
yet comprehensive, procedure we show that under coronal conditions
the effect of the temperature difference between the plasma inside
and outside the magnetic structure can change considerably the
period ratio; in the case of coronal loops the change in the period
ratio can reach even 40%. We also show that once dispersive effects
are taken into account, with oscillation periods shorter than the
cut-off period (determined by the density and temperature difference)
the domain where the model can be applied is reduced. In the case of
prominences embedded in the hot corona, the effect of the environment is
negligeable given the high density and temperature difference between
the chromospheric prominences and corona. Using a numerical approach,
we show that our analytical discussion produces a robust result. We
also discuss what implications our model has on seismological (or
diagnostics) techniques in the solar corona. <BR /> Conclusions:
Our analysis shows that the period ratio P<SUB>1</SUB>/P<SUB>2</SUB>
is sensitive to the temperature difference between the loop and its
environment and this effect should always be taken into account when
estimating the degree of density structuring with period ratio method
of coronal loops. <P />Appendix A is available in electronic form at
<A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Observations of the Interaction of Acoustic Waves and
Small-scale Magnetic Fields in a Quiet Sun
Authors: Chitta, Lakshmi Pradeep; Jain, Rekha; Kariyappa, R.;
Jefferies, Stuart M.
2012ApJ...744...98C Altcode: 2012ApJ...744...98P
The effect of the magnetic field on photospheric intensity and
velocity oscillations at the sites of small-scale magnetic fields
(SMFs) in a quiet Sun near the solar disk center is studied. We use
observations made by the G-band filter in the Solar Optical Telescope
on board Hinode for intensity oscillations; Doppler velocity, magnetic
field, and continuum intensity are derived from an Ni I photospheric
absorption line at 6767.8 Å using the Michelson Doppler Imager on
board the Solar and Heliospheric Observatory. Our analysis shows that
both the high-resolution intensity observed in the G band and velocity
oscillations are influenced by the presence of a magnetic field. While
intensity oscillations are suppressed at all frequencies in strong
magnetic field regions compared to weak magnetic field regions,
velocity oscillations show an enhancement of power in the frequency
band 5.5-7 mHz. We find that there is a drop of 20%-30% in the p-mode
power of velocity oscillations within the SMFs when compared to the
regions surrounding them. Our findings indicate that the nature of the
interaction of acoustic waves with the quiet Sun SMFs is similar to
that of large-scale magnetic fields in active regions. We also report
the first results of the center-to-limb variation of such effects
using the observations of the quiet Sun from the Helioseismic and
Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). The
independent verification of these interactions using SDO/HMI suggests
that the velocity power drop of 20%-30% in p-modes is fairly constant
across the solar disk.
---------------------------------------------------------
Title: Torsional magnetic reconnection: The effects of localizing
the non-ideal (ηJ) term
Authors: Wyper, Peter F.; Jain, Rekha
2011JPlPh..77..843W Altcode:
Magnetic reconnection in three dimensions (3D) is a natural extension
from X-point reconnection in two dimensions. Of central importance in
the 3D process is a localized non-ideal region within which the plasma
and magnetic field decouple allowing for field line connectivity
change. In practice, localized current structures provide this
localization; however, mathematically a similar effect can be achieved
with the localization of plasma resistivity instead. Physically though,
such approaches are unrealistic, as anomalous resistivity requires very
localized currents. Therefore, we wish to know how much information
is lost in localizing η instead of current? In this work we develop
kinematic models for torsional spine and fan reconnection using
both localized η and localized current and compare the non-ideal
flows predicted by each. We find that the flow characteristics are
dictated almost exclusively by the form taken for the current profile
with η acting only to scale the flow. We do, however, note that the
reconnection mechanism is the same in each case. Therefore, from an
understanding point of view, localized η models are still important
first steps into exploring the role of non-ideal effects.
---------------------------------------------------------
Title: Damping rates of p-modes by an ensemble of randomly distributed
thin magnetic flux tubes
Authors: Gascoyne, Andrew; Jain, Rekha
2011IAUS..273..351G Altcode:
The magnetohydrodynamic (MHD) sausage tube waves are excited in the
magnetic flux tubes by p-mode forcing. These tube waves thus carry
energy away from the p-mode cavity which results in the deficit of
incident p-mode energy. We calculate the loss of incident p-mode
energy as a damping rate of f- and p-modes. We calculate the damping
rates of f- and p-modes by a model Sun consisting of an ensemble
of many thin magnetic flux tubes with varying plasma properties and
distributions. Each magnetic flux tube is modelled as axisymmetric,
vertically oriented and untwisted. We find that the magnitude and the
form of the damping rates are sensitive to the plasma-β of the tubes
and the upper boundary condition used.
---------------------------------------------------------
Title: Interaction of p modes with a collection of thin magnetic tubes
Authors: Jain, R.; Gascoyne, A.; Hindman, B. W.
2011MNRAS.415.1276J Altcode: 2011MNRAS.tmp..823J
We investigate the net effect of a multitude of thin magnetic tubes
on the energy of ambient acoustic p modes. A p mode, when incident
on a thin magnetic flux tube, excites magnetohydrodynamic (MHD)
tube waves. These tube waves propagate vertically along the flux
tube carrying away energy from the p-mode cavity resulting in the
absorption of incident p-mode energy. We calculate the absorption
arising from the excitation of sausage MHD waves within a collection
of many non-interacting magnetic flux tubes with differing plasma
properties. We find that the shape and magnitude of the absorption,
when compared with the observationally measured absorption, favours a
model with a maximum-flux boundary condition applied at the photosphere
and a narrow distribution of plasma β in an ensemble with mean β
value between 0.5 and 1.
---------------------------------------------------------
Title: Sensitivity of p-mode absorption on magnetic region properties
and kernel functions
Authors: Gascoyne, A.; Jain, R.; Hindman, B. W.
2011A&A...526A..93G Altcode:
<BR /> Aims: Magnetohydrodynamic (MHD) sausage tube waves are excited
in magnetic flux tubes by p-mode forcing. These tube waves carry energy
away from the p-mode cavity which results in a source of absorption. We
wish to see the effect of an ensemble of randomly distributed thin
magnetic flux tubes on the absorption of p-modes for the model plage
region and also study the effect of the spacial weighting function on
the theoretically calculated absorption coefficients. <BR /> Methods:
We calculate the absorption coefficients of p modes for a model plage,
assumed to consist of an ensemble of many thin magnetic flux tubes
with randomly distributed plasma properties. Each magnetic flux tube in
the ensemble is modelled as axisymmetric, non-interacting, vertically
oriented and untwisted. <BR /> Results: We find that the magnitude and
the form of the absorption coefficient is sensitive to the plasma-β
of the tubes which is consistent with previous work. Both the random
distribution used to model the ensemble of flux tubes and the spatial
weighting function inherent to the measurement of the absorption affect
the absorption. As the width of the weighting function increases,
the absorption increases.
---------------------------------------------------------
Title: Helioseismic Tests With the FLASH Simulation Code
Authors: González-Morales, Pedro A.; Jain, Rekha; Thompson, Michael J.
2011JPhCS.271a2013G Altcode:
We show our first results from local helioseismic simulations using
the numerical code FLASH by testing its suitability for simulating
subphotospheric wave motions in helioseismology. In order to check
the capability of this code for different sources of waves, we have
implemented a non-magnetic plane-parallel atmosphere adding a source
term to the energy equation. We confirm the capabilities of FLASH code
for investigating the propagation of sound waves into a realistically
stratified solar interior.
---------------------------------------------------------
Title: Axisymmetric absorption of p modes by an ensemble of thin,
magnetic-flux tubes
Authors: Jain, R.; Gascoyne, A.; Hindman, B. W.
2011JPhCS.271a2016J Altcode:
The buffeting action of the solar acoustic waves (p modes) on magnetic
fibrils excites magnetohydrodynamic (MHD) tube waves. We model
these fibrils as axisymmetric, untwisted, vertically oriented, thin,
magnetic-flux tubes. The MHD tube waves propagate along the length
of the tube and carry energy away from the p-mode cavity creating a
source of p-mode absorption. We calculate the absorption arising from
the excitation of sausage MHD waves within a model plage composed of
many flux tubes with differing plasma properties. We find that for a
collection of tubes with normally distributed plasma parameters β,
the macroscopic absorption coefficient of the collection effectively
depends on only the mean value of β.
---------------------------------------------------------
Title: Time-Varying Thermal Emission in Solar Flares
Authors: Jain, R.; Rajpurohit, A. S.; Aggarwal, M.; Jamwal, R.;
Awasthi, A.
2010ASSP...19..465J Altcode: 2010mcia.conf..465J
We study thermal emission in solar flares using high-resolution X-ray
spectra obtained with the Si detector of the Solar X-ray Spectrometer
(SOXS) mission onboard the GSAT-2 Indian spacecraft launched in
2003. We model the spectral-temporal evolution of the medium-hard
X-ray flux in terms of an evolving multi-temperature plasma governed by
thermal conduction cooling and find agreement with the observations. By
measuring the DEM power-law index for five M-class flares, we find that
the emission in the 6-20 keV energy range is dominated by temperatures
15-50MK, while the power-law index of the thermal spectrum varies
over 2.2-6.1. The mean value of the thermal conduction cooling time is
1,440 s; the temperature-dependent cooling time varies from 22 to 102 s.
---------------------------------------------------------
Title: Large Amplitude Oscillations in Prominences
Authors: Tripathi, D.; Isobe, H.; Jain, R.
2009SSRv..149..283T Altcode: 2009arXiv0910.4059T
Since the first reports of oscillations in prominences in the 1930s,
there have been major theoretical and observational developments to
understand the nature of these oscillatory phenomena, leading to the
whole new field of the so-called “prominence seismology”. There
are two types of oscillatory phenomena observed in prominences;
“small-amplitude oscillations” (2-3 km s<SUP>-1</SUP>), which
are quite common, and “large-amplitude oscillations” (>20 km
s<SUP>-1</SUP>) for which observations are scarce. Large-amplitude
oscillations have been found as “winking filament” in H α as
well as motion in the plane-of-sky in H α, EUV, micro-wave and
He 10830 observations. Historically, it has been suggested that
the large-amplitude oscillations in prominences were triggered by
disturbances such as fast-mode MHD waves (Moreton wave) produced by
remote flares. Recent observations show, in addition, that near-by
flares or jets can also create such large-amplitude oscillations in
prominences. Large-amplitude oscillations, which are observed both in
transverse as well as longitudinal direction, have a range of periods
varying from tens of minutes to a few hours. Using the observed period
of oscillation and simple theoretical models, the obtained magnetic
field in prominences has shown quite a good agreement with directly
measured one and, therefore, justifies prominence seismology as a
powerful diagnostic tool. On rare occasions, when the large-amplitude
oscillations have been observed before or during the eruption, the
oscillations may be applied to diagnose the stability and the eruption
mechanism. Here we review the recent developments and understanding
in the observational properties of large-amplitude oscillations and
their trigger mechanisms and stability in the context of prominence
seismology.
---------------------------------------------------------
Title: Absorption of p Modes by Magnetic Plage
Authors: Jain, R.; Hindman, B. W.; Braun, D. C.; Birch, A. C.
2009ASPC..416...55J Altcode:
The Sun's magnetic active regions, composed of sunspots and plage,
are topologically complex. The magnetic field is highly structured,
forming a tangle of fibrils within the plage and more compact,
regimented bundles within sunspot umbrae. The fragmented nature
of the field makes helioseismic observations within active regions
rather difficult to interpret. We choose to study the propagation of
acoustic waves through regions of plage, modeling the magnetic field
therein as a collection of thin flux tubes. In this paper, we present
the first results of this research; the computation of the absorption
coefficient from an ensemble of many flux tubes. The incoming acoustic
waves interact with the magnetic flux tube, exciting sausage and kink
tube waves which propagate downward and upward carrying away energy,
thereby producing absorption. We calculate the resulting theoretical
absorption coefficients and compare with the most recent observations.
---------------------------------------------------------
Title: The role of magnetic fields in the scattering of p-modes
Authors: Gascoyne, A.; Jain, R.
2009A&A...501.1131G Altcode:
Aims: We determine the direct and indirect effects of magnetic field on
p-mode scattering. <BR />Methods: We solve a set of magnetohydrodynamic
equations using the Born approximation to determine phase shifts in
p-modes due to a region of inhomogeneity. The region of inhomogeneity
is a magnetic flux tube with the characteristics of flaring field
lines. This enables us to investigate the magnetic field effects on
the phase shifts. <BR />Results: The magnetic configuration of our
flux tube model plays a vital role in the phase shifts of p-modes. The
suppression of sound speed and pressure within the flux tube region is
not the only factor to consider in the scattering of p-modes. There
is a direct effect of the magnetic fields caused by the flaring of
field lines on phase shifts.
---------------------------------------------------------
Title: Absorption of p Modes by Thin Magnetic Flux Tubes
Authors: Jain, Rekha; Hindman, Bradley W.; Braun, Doug C.; Birch,
Aaron C.
2009ApJ...695..325J Altcode:
We study the interaction between p modes and the many magnetic fibrils
that lace the solar convection zone. In particular, we investigate
the resulting absorption of p-mode energy by the fibril magnetic
field. Through mechanical buffeting, the p modes excite tube waves
on the magnetic fibrils—in the form of longitudinal sausage waves
and transverse kink waves. The tube waves propagate up and down the
magnetic fibrils and out of the p-mode cavity, thereby removing energy
from the incident acoustic waves. We compute the absorption coefficient
associated with this damping mechanism and model the absorption that
would be observed for magnetic plage. We compare our results to the
absorption coefficient that is measured using the local-helioseismic
technique of ridge-filtered holography. We find that, depending on the
mode order and the photospheric boundary conditions, we can achieve
absorption coefficients for simulated plage that exceed 50%. The
observed increase of the absorption coefficient as a function of
frequency is reproduced for all model parameters.
---------------------------------------------------------
Title: The Role of Mode Mixing in the Absorption of p-Modes
Authors: Gordovskyy, M.; Jain, Rekha; Hindman, B. W.
2009ApJ...694.1602G Altcode:
Observations show that a p-mode may lose up to 70% of its energy
flux when it interacts with a sunspot. Part of the absorbed energy is
assumed to be converted into other types of waves, while part of it is
re-emitted into modes with different radial orders n. In the present
paper, we investigate absorption of p-modes with the azimuthal order
m = 0 due to their interaction with magnetic flux tubes and attempt to
determine the role of mode mixing in this phenomenon. We consider the
linearized magnetohydrodynamic equations in two-dimensional, cylindrical
geometry, with all the model parameters depending only on radius
r and depth z. It is assumed that the wave field may be decomposed
into incoming and outgoing components that separately satisfy the
governing equations. These components are calculated numerically using
a second-order Runge-Kutta finite difference scheme. The calculations
reveal substantial scattering from higher-to-lower radial orders n,
predominantly into the f-mode (n = 0). Only weak scattering occurs from
lower-to-higher radial orders. At the same time, the amount of energy
transferred from the p-modes to the f-mode can account for 25%-30%
of the energy lost by an incoming p-mode.
---------------------------------------------------------
Title: On Absorption and Scattering of P Modes by Small-Scale
Magnetic Elements
Authors: Jain, Rekha; Gordovskyy, M.
2008SoPh..251..361J Altcode:
The solar surface is characterised everywhere by the presence of
small-scale magnetic structures. Their collective behaviour in the
form of active regions is known to have strong influence on p-mode
power. For example, sunspots and plages are strong absorbers of acoustic
waves. This paper studies the effects of individual small-scale
magnetic elements to understand the details of absorption of p-mode
power. For this, we consider a thin magnetic flux tube and calculate
the phase shifts and the absorption coefficients by numerically
solving the linearised MHD equations. The phase shifts calculated
from the Born Approximation are then compared for the same range of
degrees. The results are discussed with a view to understanding the
physical mechanism.
---------------------------------------------------------
Title: Amplitude Suppression and Absorption of p-Modes by a Magnetic
Flux Tube
Authors: Gordovskyy, Mykola; Jain, Rekha
2008ApJ...681..664G Altcode:
The interaction of p-modes (acoustic waves) with a magnetic flux
tube is investigated. A set of linearized MHD equations is solved
numerically in a two-dimensional domain with cylindrical geometry. The
wave functions for p-modes are calculated in and around magnetic
flux tubes using eigenfunctions from the unperturbed solution as a
boundary condition. The amplitudes of the oscillations are found to be
suppressed in the magnetized region with the suppression decreasing with
depth. It is also found that the absorption of p-modes strongly depends
on the degree l as well as the flux tube radius and the magnetic field
strength. Convergence of magnetic field may be necessary in order to fit
simultaneously the observed phase shifts and absorption coefficients.
---------------------------------------------------------
Title: Prominence Seismology: Wavelet Analysis of Filament
Oscillations
Authors: Pintér, Balázs; Jain, Rekha; Tripathi, Durgesh; Isobe,
Hiroaki
2008ApJ...680.1560P Altcode:
The temporal and spatial behavior of a large-amplitude
filament oscillation is investigated using wavelet analysis. The
extreme-ultraviolet (EUV) images of the phenomenon, which occurred on
2002 October 15, were taken from the EUV Imaging Telescope on board
the Solar and Heliospheric Observatory (SOHO). The wavelet spectra,
extracted from the intensity data, show that the filament oscillates
as a rigid body, with a period of about 2.5-2.6 hr which is almost
constant along the filament. The period slowly decreases with time
until the filament erupts. No clear sign of the eruption is found in
the wavelet spectrum prior to the eruption, that followed the filament
oscillation. The axial component of the magnetic field is estimated
between 1 and 5 G, which is believed to be reasonable for a polar
crown filament of this kind.
---------------------------------------------------------
Title: Iron Abundance of Flare Plasma
Authors: Dennis, B. R.; Dang, L. C.; Jain, R.; Schwartz, R. A.;
Tolbert, A. K.
2008AGUSMSP44A..04D Altcode:
The equivalent width of the iron-line complex at 6.7 keV seen in flare
X-ray spectra suggests that the iron abundance of the hottest plasma
at temperatures >~10MK may sometimes be significantly lower than
the nominal coronal abundance of four times the photospheric value
that is commonly assumed. This conclusion is based on X-ray spectral
observations of several flares seen in common with the Ramaty High
Energy Solar Spectroscopic Imager (RHESSI) and the Solar X-ray
Spectrometer (SOXS) on the second Indian geostationary satellite,
GSAT-2. The implications of this will be discussed as it relates
to the origin of the hot flare plasma - either plasma already in
the corona that is directly heated during the flare energy release
process or chromospheric plasma that is heated by flare-accelerated
particles and driven up into the corona. Other possible explanations
of lower-than-expected equivalent widths of the iron-line complex will
also be discussed.
---------------------------------------------------------
Title: The Generation of Coronal Loop Waves below the Photosphere
by p-Mode Forcing
Authors: Hindman, Bradley W.; Jain, Rekha
2008ApJ...677..769H Altcode: 2008arXiv0805.1942H
Recent observations of coronal-loop waves by TRACE and within the
corona as a whole by CoMP clearly indicate that the dominant oscillation
period is 5 minutes, thus implicating the solar p modes as a possible
source. We investigate the generation of tube waves within the solar
convection zone by the buffeting of p modes. The tube waves—in the
form of longitudinal sausage waves and transverse kink waves—are
generated on the many magnetic fibrils that lace the convection zone
and pierce the solar photosphere. Once generated by p-mode forcing,
the tube waves freely propagate up and down the tubes, since the tubes
act like light fibers and form a waveguide for these magnetosonic
waves. Those waves that propagate upward pass through the photosphere
and enter the upper atmosphere, where they can be measured as loop
oscillations and other forms of propagating coronal waves. We treat the
magnetic fibrils as vertically aligned, thin flux tubes and compute
the energy flux of tube waves that can be generated and driven into
the upper atmosphere. We find that a flux in excess of 10<SUP>5</SUP>
ergs cm<SUP>-2</SUP> s<SUP>-1</SUP> can be produced, easily supplying
enough wave energy to explain the observations. Furthermore, we compute
the associated damping rate of the driving p modes and find that the
damping is significant compared to observed line widths only for the
lowest order p modes.
---------------------------------------------------------
Title: Large-Amplitude Oscillation of an Erupting Filament as Seen
in EUV, Hα, and Microwave Observations
Authors: Isobe, H.; Tripathi, D.; Asai, A.; Jain, R.
2007SoPh..246...89I Altcode: 2007arXiv0711.3952I
We present multiwavelength observations of a large-amplitude oscillation
of a polar-crown filament on 15 October 2002, which has been reported by
Isobe and Tripathi (Astron. Astrophys.449, L17, 2006). The oscillation
occurred during the slow rise (≈1 km s<SUP>−1</SUP>) of the
filament. It completed three cycles before sudden acceleration and
eruption. The oscillation and following eruption were clearly seen in
observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT)
onboard the Solar and Heliospheric Observatory (SOHO). The oscillation
was seen only in a part of the filament, and it appears to be a standing
oscillation rather than a propagating wave. The amplitudes of velocity
and spatial displacement of the oscillation in the plane of the sky were
about 5 km s<SUP>−1</SUP> and 15 000 km, respectively. The period
of oscillation was about two hours and did not change significantly
during the oscillation. The oscillation was also observed in Hα by
the Flare Monitoring Telescope at the Hida Observatory. We determine
the three-dimensional motion of the oscillation from the Hα wing
images. The maximum line-of-sight velocity was estimated to be a few
tens of kilometers per second, although the uncertainty is large owing
to the lack of line-profile information. Furthermore, we also identified
the spatial displacement of the oscillation in 17-GHz microwave images
from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems
to be triggered by magnetic reconnection between a filament barb and
nearby emerging magnetic flux as was evident from the MDI magnetogram
observations. No flare was observed to be associated with the onset
of the oscillation. We also discuss possible implications of the
oscillation as a diagnostic tool for the eruption mechanisms. We
suggest that in the early phase of eruption a part of the filament
lost its equilibrium first, while the remaining part was still in an
equilibrium and oscillated.
---------------------------------------------------------
Title: Amplitude modulation of solar p-modes by surface magnetic
fields
Authors: Jain, R.; Steele, C. D. C.
2007A&A...473..937J Altcode:
Context: It is known from Doppler velocity measurements that the
amplitudes of solar p-modes are modulated by strong photospheric
magnetic field. <BR />Aims: The aim of this paper is to investigate
amplitude modulation by model surface magnetic fields. <BR />Methods:
Linearised magnetohydrodynamics equations, in the absence of gravity,
are used to derive the inhomogeneous wave equation which is then solved
using the Born Approximation. <BR />Results: The amount of modulation
depends on the plasma beta, the distance from the magnetic region and
the wavenumber. It is also found that the direction of observation
could also have an effect on the amount of modulation. Finally, the
applicability of the findings to the observational data suggests that
the modulation depends on the properties of the magnetic field region
and measuring it is an un-contaminating probe for the magnetic field.
---------------------------------------------------------
Title: Scattering of p-Modes by a Thin Magnetic Flux Tube
Authors: Gordovskyy, Mykola; Jain, Rekha
2007ApJ...661..586G Altcode:
There is strong observational evidence for solar p-modes being
scattered by sunspots. Understanding and comparing phase shifts or
travel time delays of scattered waves can present an opportunity to
deduce the subsurface structure of sunspots from the observations of
p-modes. We study the scattering of acoustic waves by magnetic flux
tubes embedded in the stratified atmosphere, taking into account
magnetic field perturbations. For this purpose, we solve a set of
linearized MHD equations using the Born approximation approach. It is
shown that convergence of the magnetic field may substantially affect
the phase shifts of the scattered waves.
---------------------------------------------------------
Title: Scattering of p-modes by a thin fluxtube in a stratified
atmosphere
Authors: Gordovskyy, M.; Jain, R.
2007AN....328..309G Altcode:
In the present paper we investigate scattering of low and intermediate
degree p-modes on a thin magnetic fluxtube embedded into a stratified
polytropic atmosphere. Using the Born approximation approach we find
the solution of linearized MHD equations and calculate resulting
phase shifts of scattered waves for different sets of fluxtube
parameters. Possible application of the results to the analysis of
observational data is discussed.
---------------------------------------------------------
Title: Effects of Horizontal Magnetic Fields on Acoustic Travel Times
Authors: Jain, Rekha
2007ApJ...656..610J Altcode:
Local helioseismology techniques seek to probe the subsurface magnetic
fields and flows by observing waves that emerge at the solar surface
after passing through these inhomogeneities. Active regions on the
surface of the Sun are distinguished by their strong magnetic fields,
and techniques such as time-distance helioseismology can provide
a useful diagnostic for probing these structures. Above the active
regions, the fields fan out to create a horizontal magnetic canopy. We
investigate the effect of a uniform horizontal magnetic field on the
travel time of acoustic waves by considering vertical velocity in a
simple plane-parallel adiabatically stratified polytrope. It is shown
that such fields can lower the upper turning point of p-modes and hence
influence their travel time. It is found that acoustic waves reflected
from magnetically active regions have travel times up to a minute
less than for waves similarly reflected in quiet regions. It is also
found that sound speeds are increased below the active regions. These
findings are consistent with time-distance measurements.
---------------------------------------------------------
Title: MHD Waves Observed in Isolated Bright Points
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2006ASPC..354...13B Altcode:
We examine oscillations in three isolated bright points co-temporal
and co-spatial in the photosphere and chromosphere in the G-band and
Ca IIK line. Wavelet analysis was performed to study waves packets of
traveling magnetohydrodynamic waves. In general, it is thought likely
that the photosphere oscillates in response to granular buffeting, but
it is also influenced strongly by the presence of magnetic fields. The
observed oscillations reveal evidence for kink-mode waves, traveling
up through the chromosphere and coupling with sausage-modes waves. This
provides a means for energy deposition in the upper chromosphere.
---------------------------------------------------------
Title: G-Band Bright Points and Photospheric Magnetic Fields
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2006ASPC..358...61B Altcode:
We present high resolution observations of magnetic flux concentrations
within a decaying active region near disk center. We recorded G-band
images, magnetograms, 2D spectral scan, and continuum images using the
Universal Birefringent Filter at the Dunn Solar Telescope. The main
results can be summarized as follows: The large-scale pattern of G-band
bright points flux in plages are highly correlated, on sub-arcsecond
scales; G-band bright points are cospatial and comorphous, with magnetic
elements in intergranular lanes. Magnetic elements are continually
advected into micropores by the photospheric flow field. We observed
narrow (<0.25 arcsec) channels or sheets of downflowing plasma
around bright points and micropores. This downflowing plasma shows
accelerating nature in deeper layers of solar atmosphere. Upflow and
downflow events are found within bright points while micropores show
upflow. We compare our results with theoretical model predictions.
---------------------------------------------------------
Title: SOXS for IHY 2007 and Beyond
Authors: Jain, R.
2006ihy..workE..40J Altcode:
We present on the utilization of existing mission namely Solar X-ray
Spectrometer (SOXS) for observing the full disk Sun in the X-ray
waveband in 4-56 keV. SOXS has been functioning satisfactorily since
June 2003 though for a limited period of 2-3 hours daily. SOXS mission
has so far observed more than 400 flares of varying intensity and a few
of them are found to be associated with CMEs. We present recent results
from SOXS observations that combined with optical and radio wavebands,
which reveal loop-loop interaction as potential mechanism for those
flares occurred with remote brightening. We also present study of
microflares observed by SOXS mission and found that microflares are
potential candidates for coronal heating. SOXS mission is expected to
continue during ascending phase of solar cycle 24.
---------------------------------------------------------
Title: Effects of horizontal magnetic fields on acoustic travel-times
Authors: Jain, R.
2006ESASP.624E..49J Altcode: 2006soho...18E..49J
No abstract at ADS
---------------------------------------------------------
Title: Effect of sunspot structure from p-modes scattering
Authors: Gordovskyy, M.; Jain, R.; Thompson, M. J.
2006ESASP.624E..14G Altcode: 2006soho...18E..14G
No abstract at ADS
---------------------------------------------------------
Title: The relationship between magnetic field strength and loop
lengths in solar coronal active regions
Authors: Jain, R.; Mandrini, C. H.
2006A&A...450..375J Altcode:
By assuming that coronal active regions are made up of many loops,
we investigate the relationship between the average magnetic field
strength and loop length for a sample of active regions observed by the
Soft X-ray Telescope aboard Yohkoh. We use photospheric magnetic data
from the Michelson Doppler Imager and compute extrapolated field lines
that match the observed soft X-ray emission. We compare our results
with a previous study and find them to be consistent and a logical
extension of such work. Such studies have important implications for
solar coronal heating models.
---------------------------------------------------------
Title: Soft and hard X-ray emission from solar flares observed by
Solar X-ray Spectrometer (SOXS) mission
Authors: Jain, R.; Bharti, L.
2006cosp...36..635J Altcode: 2006cosp.meet..635J
Solar X-ray Spectrometer SOXS mission was launched on 08 May 2003
onboard Indian spacecraft to study the energy release and particle
acceleration in solar flares in the energy range 4-55 keV To achieve
the high spectral resolution Si and CZT detectors were employed We
present the temporal and spectral characteristics of soft and hard X-ray
emission from 18 M-class flares observed by SOXS mission during 2003
and 2005 We present the line emission characteristics of Fe and Fe Ni
features and show the variation of equivalent width and peak energy as
a function of temperature which is interpreted as emission contribution
of different ionic lines vary with temperature The hard X-ray spectra
enabled us to measure the break energy between thermal and non-thermal
components as a function of flare duration that allowing determining the
contribution of accelerated particles in the flares We also analyzed
a few flares associated with CMEs and found that the associated CME
is the cause for the flare and not the consequence of the flare
---------------------------------------------------------
Title: Solar X-ray Spectrometer (SOXS) mission: Observations and
new results
Authors: Jain, R.; Bhatt, N. J.; Bharti, L.
2006ilws.conf...54J Altcode:
We present the observations and recently obtained new results from the
"Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard
GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study
the solar flares. The state-of-the-art solid state detectors viz. Si
PIN and Cadmium-Zinc-Telluride (CZT) were employed that operate at
near room temperature (-20 0C). The dynamic energy range of the Si
PIN and CZT detectors are 4-25 keV and 4-56 keV, respectively. The
Si PIN has sub-keV energy resolution while the CZT has about 1.7 keV
energy resolutions throughout the dynamic range. The high sensitivity
and sub-keV energy resolution of Si PIN detector allows for measuring
the intensity, and equivalent width (w) of the Fe-line and Fe/Ni-line
complexes at approximately 6.7 and 8.0 keV as a function of time. We
present the results related to the Fe-line complex obtained from the
study of 10 M-class flares observed by the SOXS mission. We found that
the equivalent width (w) of the Fe-line feature increases exponentially
with temperature up to 25 MK but later it increases very slowly up
to 35 Mk and then it remains constant up to 45 MK. We compare our
measurements of w of the Fe line feature with calculations made earlier
by various investigators and propose that these measurements may improve
theoretical models. We interpret the variation of w with temperature
as the changes in the ionization and recombination conditions in
the plasma during the flare interval, and, as a consequence, the
contribution from different ionic emission lines also varies.
---------------------------------------------------------
Title: Scientific and Technical aspects of high resolution extreme
ultraviolet imaging spectrometer proposed for future space-borne
Indian mission
Authors: Jain, R.
2006cosp...36..619J Altcode: 2006cosp.meet..619J
We present the scientific and technical aspects of proposed high
resolution extreme ultraviolet imaging spectrometer for future
space-borne Indian spacecraft We briefly describe the science objectives
of the mission and propose that this experiment may improve our current
understanding on coronal heating solar wind acceleration and the cause
of CMEs In order to achieve the science objectives the normal incidence
technique is proposed for high resolution imaging however it needs
specific scientific and technical requirements which are described in
detail We propose the design of the instrument and discuss the same
in preview to scientific and technical perspectives
---------------------------------------------------------
Title: Prediction of the Amplitude in Sunspot Cycle 24
Authors: Jain, R.
2006cosp...36..642J Altcode: 2006cosp.meet..642J
A few prediction methods have been developed using the precursor
techniques and are found to be successful On the basis of geomagnetic
activity aa indices during the descending phase of the preceding cycle
we have established an expression which predicts the maximum annual
mean sunspot number in cycle 24 to be 144 pm 18 This indicates that
cycle 24 would also be a highly active cycle but not equal to last
three solar cycles We also predict the average geomagnetic activity
aa index during the ascending phase of cycle 24 to be 18 pm 3 5
---------------------------------------------------------
Title: Development of soft X-ray imaging spectrometer for proposed
future space-borne Indian mission
Authors: Jain, R.
2006cosp...36..622J Altcode: 2006cosp.meet..622J
We present the scientific and technical aspects of proposed high
resolution soft X-ray imaging spectrometer for future space-borne Indian
spacecraft We briefly describe the science objectives of the mission
and propose that this experiment may improve our current understanding
on quiet and active solar corona and the energy release and particle
acceleration mechanisms in solar flares The proposed energy band is 0
1 to 10 keV for high spatial spectral and temporal imaging Currently
various design are considered in view of scientific and technical
requirements and are being analyzed We discuss both normal incidence and
grazing incidence techniques and the current status of the experiment
---------------------------------------------------------
Title: X-Ray and Radio Emission Characteristics of CME Associated
Flares producing
Authors: Jain, R.; Bhatt, N.
2006cosp...36..613J Altcode: 2006cosp.meet..613J
We present the results of our investigation on the X-ray and Radio
Emission Characteristics of 18 geoeffective flares that were associated
with Coronal Mass Ejection CME and observed by one of the missions among
BATSE YOHKOH and SOXS in X-ray waveband and simultaneous observations
made in radio waveband at Nobeyama Radio Observatory during 1997 to
2005 We identified the geoeffective potential flares based on A p
index 25 We analyzed X-ray and radio temporal and spectral evolution
of these flares and found that their spectra become exceptionally
hard over the growth We also compare the results with the flares of
similar magnitude but did not produce the geomagnetic effects Based
on our analysis and evidence we interpret that in geoeffective flares
extraordinary particle acceleration takes place for a long duration
and the associated coronal mass ejection CME carries most of early
accelerated and energetic particles as well as the magnetized plasma
which in turn during the passage in interplanetary space generate
further shock so as to enhance the particle velocity and density and
thereby to disturb the Earth s magnetic field
---------------------------------------------------------
Title: Probing coronal heating with variability of solar X-ray
emission
Authors: Vekstein, G.; Jain, R.; Katsukawa, Y.; Tsuneta, S.
2006cosp...36...65V Altcode: 2006cosp.meet...65V
If the mechanism responsible for creating hot solar corona is a
magnetic one the resulting coronal heating events are likely to be
highly fragmented in space and in time This makes the nanoflare
heating scenario where both these features are at the heart of
the concept a strong candidate The major problem is to find out
how to test this theory while individual nanoflares remain beyond
observational recognition Here we discuss a possibility of probing
nanoflares with variability of the coronal X-ray emission We present
results of the numerical simulation of X-ray coronal loops that mimics
a sporadic nature of the nanoflare heating The aim is to investigate
how an imposed power-law energy spectrum of heating events nanoflares
translates into fluctuations in the intensity of the X-ray emission
which can be detected observationally as X-ray and EUV brightenings
These theoretical predictions are compared with a recently reported
analysis of observed fluctuations of the solar X-ray emission and
we discuss their implications on the deduced energy and spectrum of
nanoflares A future study envisaged with the upcoming Solar-B mission
is also discussed
---------------------------------------------------------
Title: The Solar Flare and CME Induced as a Collision of Two Opposite
Polarities on 1997 May 12
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2005ASPC..346..327B Altcode:
The multispectral observations of active region NOAA 8038 during 10-13
May 1997 are presented. The observations of MDI/SOHO magnetograms show
that in this active region continual but discrete growth and decay of
magnetic field was taking place indicating either continuous evolution
of magnetic flux or emergence of new flux region. The movie of these
magnetograms reveal two important results that the major opposite
polarities of pre-existing region were approaching towards each other,
and a small north polarity flux i.e. moving magnetic feature (MMF)
was ejecting out from major north polarity at a quasi-periodicity
of about 10 hrs during 10-13 May 1997. It appears that as a result
of flux cancellation by one such ejected north polarity flux with
a newly emerged south polarity flux around 04:30 UT on 12 May 1997,
a moderate but long enduring 1B/C1.3 solar flare. The observation in
Hα is presented in detail.
---------------------------------------------------------
Title: MHD Waves Observed in Isolated Brightpoints
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A.
2005ESASP.600E..79B Altcode: 2005dysu.confE..79B; 2005ESPM...11...79B
No abstract at ADS
---------------------------------------------------------
Title: On the Scaling of Magnetic Field Strength with Loop Length
in Solar Active Regions
Authors: Mandrini, C. H.; Jain, R.
2005ESASP.596E..69M Altcode: 2005ccmf.confE..69M
No abstract at ADS
---------------------------------------------------------
Title: On Solar Coronal Heating by Forced Magnetic Reconnection
Authors: Jain, R.; Browning, P.; Kusano, K.
2005ESASP.596E..23J Altcode: 2005ccmf.confE..23J
No abstract at ADS
---------------------------------------------------------
Title: MHD Waves Propogation and Heating of Solar Atmosphere
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N.
2005AGUSMSH12A..04B Altcode:
We examine oscillations in isolated three bright points co-temporal
and co-spatial in photosphere and chromosphere in G-band and Ca II
K line. Wavelet analysis was used to study wave packets and identify
traveling magnetohydrodynamic waves. In general, it is thought likely
that the photosphere and chromosphere oscillates in response to forcing
by p-modes and granular buffeting, but they are also influenced strongly
by presence of magnetic fields. The observed oscillations reveals
evidence for kink-mode waves, traveling up through the chromosphere
and coupling with sausage-modes waves. This provides a means for energy
depositing in the upper chromosphere.
---------------------------------------------------------
Title: CME and associated phenomena on May 12, 1997
Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N.
2005AGUSMSH51C..05B Altcode:
The multispectral observations of NOAA active region No. 8038 during
10-13 May 1997 are presented. The observations of MDI/SOHO magnetograms
show that in this active region continual but discrete growth and
decay of magnetic field was taking place indicating either continuous
evolution of magnetic flux or emergence of new flux region. The
movie of these magnetograms reveal two important results that the
major opposite polarities of pre-existing region were approaching
towards each other, and a small north polarity flux i.e. moving
magnetic feature (MMF) was ejecting out from major north polarity
at a quasi-periodicity of about 10 hrs during 10-13 May 1997. It
appears that as a result of flux cancellation by one such ejected
north polarity flux with a newly emerged south polarity flux around
04:30 UT on 12 May 1997, a blast wave generated, seen by EIT/SOHO,
producing CME and a moderate but long enduring 1B/C1.3 solar flare. The
observations in Hα, soft X-ray, hard X-ray, ionospheric absorption,
radio and interplanetary scintillations in association to this flare
are presented in detail.. The multiwavelength observations of the
flare showed occurrence of at least two phases of energy release,
first at 04:42 and second at 04:47 UT. We propose a qualitative
model to interpret the observations, which, however, also explains
the generation of CME and associated flare with two stages of energy
release. The occurrence of type II radio burst at 04:54 UT was perhaps
due to shock produced by the plasmoid erupted during second energy
release at higher altitude in the corona. It appears that the plasmoid
traversed through shock in the interplanetary medium so as to enhance
the scintillation index on 14 May as inferred from IPS observations.
---------------------------------------------------------
Title: Solar coronal heating by forced magnetic reconnection:
Multiple reconnection events
Authors: Jain, Rekha; Browning, Philippa; Kusano, K.
2005PhPl...12a2904J Altcode:
Magnetic reconnection is a strong candidate for a coronal heating
mechanism, and heating by forced magnetic reconnection is investigated
here. Two dimensional, nonlinear magnetohydrodynamic simulations are
used to investigate forced magnetic reconnection in a compressible
plasma. The reconnection occurs when a sheared force-free field is
perturbed by a slow disturbance (pulse) at the boundary which is
representative of the solar corona where the reconnection is induced
by the photospheric motions. The case of driving by successive pulses,
which generate a series of heating events which may interact with each
other, is considered. This is in order to model the heating of the
corona by a series of nanoflare events. For small perturbations, the
simulation results are consistent with the previous analytic theory
based on linear approach where a current sheet is formed initially
at the resonant surface followed by reconnection and then release of
magnetic energy. For large amplitude perturbations, or close to the
threshold for tearing instability, the system exhibits strong nonlinear
aspects. Following the second driving pulse, the current sheet expands
along the separatrix before relaxing to a reconnective equilibrium and
releasing even more magnetic energy for the same amplitude perturbation.
---------------------------------------------------------
Title: Coronal Heating by Forced Magnetic Reconnection with
Multi-Pulse Driving
Authors: Browning, P. K.; Jain, R.
2004ESASP.575..474B Altcode: 2004soho...15..474B
No abstract at ADS
---------------------------------------------------------
Title: Nanoflares and Coronal X-Ray Variability
Authors: Jain, R.; Katsukawa, Y.; Tsuneta, S.; Vekstein, G.
2004ASPC..325..271J Altcode:
A possibility of probing nanoflares with variability in the coronal
X-ray emission is discussed. We present results of numerical simulation
of X-ray coronal loops by using a Monte Carlo code, which mimics a
sporadic nature of the nanoflare heating. The aim is to investigate how
the imposed power-law energy spectrum of heating events (nanoflares)
translates into fluctuations in the intensity of the X-ray emission,
which can be detected observationally as X-ray and EUV brightenings. It
was found that probability distribution of these fluctuations is
very sensitive to the power-law index α of the energy spectrum of
nanoflares. If α > 3, intensity fluctuations have a noise-like
nature with a Gaussian distribution originating from interference of
many small nanoflares. For spectral indices 2 < α ≤ 3, histograms
of the intensity deviation from the mean value show positive skewness
indicating significant role of bigger events. Comparison of these
results with the analysis of small fluctuations of coronal X-ray
intensity observed with Yohkoh SXT telescope yields an estimate of
10<SUP>23</SUP> erg for the energy of nanoflares in the active region.
---------------------------------------------------------
Title: Impulsive Solar Flares associated with Coronal Mass Ejections
Authors: Jain, R.; Uddin, W.; Kosugi, T.; Kumar, S.; Chandra, R.;
Sakao, T.; Masuda, S.
2004cosp...35..939J Altcode: 2004cosp.meet..939J
We present the multi-wavelength observations of a few impulsive
solar flares, which are associated with Coronal Mass Ejections (CMEs)
during Solar Cycle 23. The optical and radio waveband observations
of the solar flares considered for this investigation were made in
India and Japan, while SOHO, CGRO, YOHKOH and SOXS missions made the
other wavelength observations. We present the optical, radio and X-ray
emission characteristics of impulsive flares associated with CMEs in
view of their energy release and particle acceleration. We conjecture
a qualitative model to interpret our multi-spectral observations
of these impulsive solar flares. It is proposed that a CME of some
magnitude precede the impulsive solar flares to cause strong particle
acceleration as observed in them. In support of our this concept
we present the magnetograms of the active regions that reveal the
cancellation of magnetic flux in all such impulsive events, which in
turn results in generating a CME as seen in different wavelengths.
---------------------------------------------------------
Title: Multi-wavelength study of the 2003 November 18 Solar Flares
from AR 501
Authors: Chandra, R.; Uddin, W.; Jain, R.; Joshi, A.; Kumar, S.
2004cosp...35.4137C Altcode: 2004cosp.meet.4137C
We present the multi-wavelength observations of three ( SF/C3.8,
2N/M3.2, M3.9) solar flares produced by super active region 0501
(βγα) on 18 November 2003. These flares occurred in south-east
direction of the active region. The M3.2 and M3.9 flares are
two ribbon/LDEs dynamic ares associated with eruption of highly
shear/twisted filament. These two ares are associated with halo
CMEs and strong type II and type IV radio bursts. These ares show
similar morphological evolution in Hα, EUV and SXR wavelengths. At
the are locations the high magnetic field gradient and high shear are
noticed. The analysis of these ares is based upon the State Observatory,
Nainital Hα data and various space born satellite data viz. SOXS, SOHO,
TRACE, RHESSI, GOES. The energy release mechanism of these flares can
be explained by the flux rope model.
---------------------------------------------------------
Title: Results of one year of observations of Solar Flares made by
"Solar X-ray Spectrometer (SOXS)" Mission
Authors: Jain, R.; Dave, H.; Kumar, S.; Deshpande, M. R.
2004cosp...35..744J Altcode: 2004cosp.meet..744J
The first space borne solar astronomy experiment of India namely
“Solar X-ray Spectrometer (SOXS) mission has completed one year of its
successful operation in geostationary orbit. The SOXS mission onboard
GSAT-2 Indian spacecraft was launched successfully by GSLV-D2 rocket
on 08 May 2003 to study the energy release and particle acceleration
in solar flares. We briefly present the scientific objectives and
instrumentation of the SOXS mission. The SOXS is composed of two
independent payloads viz. SOXS Low Energy Detector (SLD) payload, and
SOXS High Energy Detector (SHD) payload. We restrict our presentation
to SLD payload that designed, developed and fabricated by Physical
Research Laboratory (PRL) in collaboration with Space Application
Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore
of Indian Space Research Organization (ISRO). The SLD payload
employs the state-of-the-art solid state detectors viz. Si PIN
and Cadmium-Zinc-Telluride (CZT) devices that operate at near room
temperature (-20 ^0 C). The dynamic energy range of Si PIN and CZT
detectors are 4-25 and 4-56 keV. The Si PIN provides sub-keV energy
resolution while CZT reveals ∼ 2 keV energy resolution throughout
the dynamic range. The instrument has onboard flare triggering logic
software and 5 MB-memory bank. The data is transmitted to Master Control
Facility (MCF), Hasan with 8 kbps telemetry rate. The observations
are made in fixed energy windows (temporal) mode and in spectral mode
with 100ms cadence during the flare. The SLD has observed more than 140
flares of C and M class since its commissioning in the orbit. We present
the preliminary results and the X-ray emission characteristics of
these flares, and a detailed study of a few typical solar flares, which
are impulsive but associated with CMEs, in view of energy release and
particle emission by them. The high sensitivity of the SLD and sub-keV
energy resolution of Si PIN detector allows the intensity and mean
energy of the Fe-line complex at approximately 6.7 keV to be measured
as a function of time in all class of flares. The centroid energy and
width of the iron-line complex at ∼ 6.7 keV, the intensity of the
Fe/Ni line complex at ∼ 8 keV, and the line-to-continuum ratio enabled
to estimate the plasma temperature and other plasma parameters. We also
present how SLD is a potential instrument for the study of microflares.
---------------------------------------------------------
Title: Spectral Hardening and Geoeffectiveness of Solar Flares
Authors: Jain, R.; Kumar, S.; Dave, H.; Deshpande, M. R.
2004cosp...35..761J Altcode: 2004cosp.meet..761J
We present the results of a few typical flares that observed by
the first space borne solar astronomy experiment of India namely
"Solar X-ray Spectrometer (SOXS)" mission, which has completed one
year of its successful operation in geostationary orbit. The SOXS
mission onboard GSAT-2 Indian spacecraft was launched successfully by
GSLV-D2 rocket on 08 May 2003 to study the energy release and particle
acceleration in solar flares. The SOXS is composed of two independent
payloads viz. SOXS Low Energy Detector (SLD) payload, and SOXS High
Energy Detector (SHD) payload. We restrict our presentation to SLD
payload that designed, developed and fabricated by Physical Research
Laboratory (PRL) in collaboration with Space Application Centre
(SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of Indian
Space Research Organization (ISRO). We briefly present the scientific
objectives and instrumentation of the SLD payload. The SLD payload
employs the state-of-art solid state detectors viz. Si PIN and CZT
detectors, which reveal sub-keV spectral and 100ms temporal resolution
characteristics that are necessary to study the spectral response of
the flare components. The dynamic range of Si and CZT detectors is 4-25
and 4-56 keV respectively. The SLD has observed more than 140 flares
of C and M class since its commissioning in the orbit. We present the
X-ray emission characteristics of a few typical flares in view of their
spectral hardening and geo-effectiveness. We extend our study of these
flares to optical and radio waveband observations in order to improve
the relationship of X-ray spectral hardening and geo-effectiveness. The
flares with harder spectra and associated with small or large CME,
and radio emission at frequencies above 10 GHz are found geo-effective.
---------------------------------------------------------
Title: Signatures of a nanoflare heated solar corona
Authors: Vekstein, G. E.; Jain, R.
2003PPCF...45..535V Altcode:
If the mechanism responsible for creating the high-temperature solar
corona is a magnetic one, the resulting coronal heating events are
likely to be highly sporadic and fragmented. Therefore, nanoflare
heating, where both these features are present, by the very meaning of
the concept, is a strong candidate. The major problem is how to test
this theory while individual nanoflares remain beyond observational
recognition. Here, we discuss a possibility of probing the nanoflare
heating scenario by considering statistical characteristics of coronal
active regions, which presumably originate from a large number of random
impulsive heating events. This approach allows one to derive various
parameters of x-ray coronal loops (temperature, emission measure,
filling factor, etc) without specifying particular details of the
heating events. How the energy of individual nanoflares can be estimated
from observed fluctuations in the coronal x-ray emission is also
discussed. Comparison of our results with recently reported analysis
of small fluctuations of coronal x-ray intensity observed with Yohkoh
SXT telescope yields an estimate of (10<SUP>22</SUP>-10<SUP>23</SUP>)
erg for the energy of nanoflares in the active region.
---------------------------------------------------------
Title: Probing coronal heating with X-ray variability of solar and
stellar coronae
Authors: Vekstein, G.; Jain, R.
2003EAEJA.....1455V Altcode:
If mechanism responsible for creating hot solar and stellar coronae is
a magnetic one, the resulting coronal heating events are likely to be
highly fragmented in space and in time. This makes the nanoflare heating
scenario, where both these features are at the heart of the concept,
a strong candidate. The major problem is to find out how to test
this theory while individual nanoflares remain beoynd observational
recognition. Here, we discuss a possibility of probing nanoflares
with variabiiy in the coronal X-ray emission. We present results of
numerical simulation of X-ray coronal loops by using a Monte Carlo
code that mimics a sporadic nature of the nanoflare heating. The aim
is to investigate how the imposed power-law energy spectrum of heating
events (nanoflares) translates into fluctuations in the intensity of
the X-ray emission, which can be detected observationally as X-ray
and EUV brightenings. It was found that probability distribution of
these fluctuations is very sensitive to the power-law index ( of the
energy spectrum of nanoflares. If ( ( 3, intensity fluctuations have
a noise-like nature with a Gaussian distribution that originates from
interference of many small nanoflares. For spectral indices 2 ( ( ( 3,
histograms of the intensity deviation from the mean value show positive
skewness that indicates a significant role of bigger events. These
theoretical predictions are compared with recently reported analysis
of observed fluctuations in solar and stellar coronal X-ray intensity,
and we discuss their implications on the deduced energy and spectrum
of nanoflares.
---------------------------------------------------------
Title: Indications and implications of twisted magnetic flux in
the corona
Authors: Gibson, S. E.; Fan, Y.; Jain, R.; Low, B.
2002AGUFMSH52A0446G Altcode:
The question of whether magnetic flux ropes are fundamental to CMEs and
their precursors will be addressed using a combination of analytic and
numerical models, along with coronal observations. We have developed
computational tools for evaluating observable properties of modeled
magnetic flux ropes suspended in the corona, such as separatrix surfaces
and dipped magnetic fields. We have also developed numerical models to
demonstrate how a flux rope emerging into an overlying coronal magnetic
arcade will relax to a force-free configuration, with associated
formation of current sheets. Using the results of these two parallel
studies, we will directly compare separatrix surfaces determined from
an analytic (non-force-free) equilibrium model to the current sheets
formed during numerical force-free relaxation of the same initial field
configuration. We will then consider these in the context of observed
X-ray sigmoid structures. We have also developed mathematical methods
for determining the magnetic free energy in analytic models of both
magnetic flux ropes, as well as sheared field configurations that
contain no rope. We will compare the free energies thus determined
for both sheared and twisted fields, as functions of spatial size,
magnetic field strength, and degree of shear or twist. We will consider
the implications of these results for the energetics of coronal mass
ejections.
---------------------------------------------------------
Title: Filling factors and magnetic field strengths of
nanoflare-heated coronal active regions: Yohkoh and MDI observations
Authors: Jain, R.; Yashiro, S.
2002A&A...394.1111J Altcode:
The scaling laws describing the relationship between thermal and
magnetic properties of active regions are derived using the concept
that solar coronal active regions are heated by numerous small
flare-like events (nanoflares). Thus, a coronal active region is
viewed as an ensemble of hot elementary filaments created within the
coronal magnetic field by random impulsive heating events. The scaling
laws obtained are governed by the global energy balance of the active
regions and are independent of the details of any heating process (such
as the energy of individual heating event or energy spectral index of
nanoflares). We examined 61 coronal active regions observed with the
soft X-ray telescope aboard Yohkoh and found that such a model yields
filling factors (defined as the ratio of the volume of hot plasma
to the total volume) in the range 0.002 to 0.015 and magnetic field
strengths of 20 G to 40 G. The analysis determining the mean magnetic
field strength and filling factors of a large number of coronal active
regions, observed by Yohkoh, based on nanoflare-heating concept is the
first such analysis. We also examine 24 active regions observed with
the Michelson Doppler Imager aboard Solar and Heliospheric Observatory
and find that the total thermal energy content E_th is related to the
total magnetic flux phi by a power-law index of 1.24 i.e. E_th ~ phi
<SUP>1.24</SUP>. The thermal pressure p_th of the active regions is
related to the magnetic flux density B_p obtained from MDI measurement
as: p_th ~ B_p<SUP>0.5</SUP>.
---------------------------------------------------------
Title: Solar p-modes and surface magnetic fields: Is there an acoustic
emission?. MDI/SOHO observations
Authors: Jain, R.; Haber, D.
2002A&A...387.1092J Altcode:
We study the effect of magnetism on the surface amplitude of p-modes by
creating power maps using Doppler velocity, line-depth and continuum
intensity data taken by the Michelson Doppler Interferometer (MDI)
instrument on board SOHO. This analysis, using proper tracking
procedures, of MDI line-depth data and its comparison with the
simultaneous Doppler velocity data is the first such analysis. All
three datasets show that the p-mode power is suppressed in the magnetic
region with suppression increasing with field strength. However, in
the high-frequency range, the power is enhanced in the Doppler velocity
and line-depth data but not in continuum intensity. This enhancement,
when present, appears to be in intermediate field strength elements
in the immediate vicinity of a magnetically active region.
---------------------------------------------------------
Title: Probing nanoflare heating with X-ray variability of coronal
loops
Authors: Jain, Rekha; Vekstein, Grigory
2002ESASP.477..123J Altcode: 2002scsw.conf..123J
The concept that solar corona is heated by numerous small flare-like
events (nanoflares) is considered. Thus, a hot coronal loop is viewed
as an ensemble of high temperature elementary filaments created within
the coronal magnetic field by random impulsive heating events. The
integral parameters of the loop (thermal energy, emission measure,
filling factor etc.) obey scaling laws (Vekstein and Katsukawa,
2000), which are determined only by its global energy balance. They
are not sensitive to specific details of the heating process such as
the energy of an individual heating event, and the energy spectral
index of nanoflares. To probe the latter, we analyse variability of
the nanoflare heated loops. The aim is to find out how the imposed
power-law spectrum of heating events translates into fluctuations in the
thermal energy and emission measure of the loop, which can be detected
observationally as X-ray and EUV brightenings. It was found that the
numerically simulated spectrum of these fluctuations comprises of two
separate components. For large intensities the spectral index is close
to that imposed for nanoflares, mirroring individual heating events
with high energy. At lower intensities fluctuations have a noise-like
nature generated by interference of several small nanoflares.
---------------------------------------------------------
Title: Processing electronics instrumentation for the low energy
detector of Solar X-ray Spectrometer (SOXS) experiment
Authors: Umapathy, C. N.; Sharma, M. R.; Solanky, Chirag; Kulkarni,
R.; Shah, A. B.; Vadher, N. M.; Jain, R.; Jain, A. K.; Sreekumar, P.
2001BASI...29..475U Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Signatures of the Nanoflare Coronal Heating
Authors: Vekstein, G.; Jain, R.
2001AGUSM..SP51C07V Altcode:
The concept that the solar corona is heated by numerous small
flare-like events (nanoflares) is considered. Thus, the hot coronal
loop is viewed as an ensemble of high-temperature elemental filaments
created within the coronal magnetic field by random impulsive heating
events. As a result, these filaments, each of which is at various
stages of thermal evolution, have a broad distribution in temperature
and density. However, as instantaneous cooling time of the filament
has a maximum when conductive and radiation losses become equal, the
above distribution is strongly peaked at the corresponding transition
temperature. Therefore, the observed temperature of such a loop as a
whole obeys the same Rosner-Tucker-Vaiana scaling as was originally
derived for a simple loop in a steady state thermal equilibrium. It
is shown how this approach allows to predict various signatures of
X-ray coronal loops, in particular, dependence of the filling factor,
emission measure and thermal energy on the size of the loop and strength
of the coronal magnetic field. These integral characteristics of the
loop are determined only by its global energy balance, and are not
sensitive to specific details of the heating process (such as the
energy of individual heating event, spectral index of nanoflates,
etc). To probe the latter, we analysed variability of nanoflare heated
loops. The aim is to find out how the imposed power-law spectrum of
heating events translates into fluctuations in the thermal energy and
emission measure of the loop, which can be detected observationally as
X-ray and EUV transient brightenings. It was found that the numerically
simulated spectrum of these fluctuations typically consists of two
different power-law domains. For large intensities the spectral index
is close to that of nanoflares, mirroring individual heating events
with high energy. However, at lower intensities the spectrum is more
flat, as it is caused by interference of several nanoflares.
---------------------------------------------------------
Title: XTE J1550-564
Authors: Tomsick, J. A.; Smith, E.; Swank, J.; Wijnands, R.; Homan,
J.; Jain, R.; Bailyn, C.; Tomsick, J.
2001IAUC.7575....2T Altcode: 2001IAUC.7575....3J; 2001IAUC.7575B...1T
J. A. Tomsick, University of California at San Diego (UCSD); E. Smith
and J. Swank, Goddard Space Flight Center; R. Wijnands, Massachusetts
Institute of Technology; and J. Homan, University of Amsterdam,
report: "Recent observations of the blackhole x-ray transient XTE
J1550-564 with the Rossi X-ray Timing Explorer (RXTE) indicate that
the source is active again. The last outburst ended in 2000 August,
and a Chandra observation made on 2000 Aug. 16 indicated a flux level
of 1 x 10**-13 erg cm**-2 s**-1 (0.5-8 keV). A 2.5-20-keV source
flux of 9 x 10**-10 erg cm**-2 s**-1 was measured by RXTE on 2001
Jan. 28.7 UT. The spectral and timing properties indicate that the
source is in the low-hard state. The energy spectrum can be described
by a power law with a photon index of 1.52 and a neutral iron line
with an equivalent width of 160 eV. The level of timing noise is about
40-percent rms (0.01-100 Hz; 2-60 keV), with violent flaring activity
having a repetition period of 100-160 s. Currently, it is not clear
if the observed activity will lead to a full outburst. Additional
RXTE observations are scheduled, and coordinated observations at
other wavelengths are encouraged." <P />R. Jain and C. Bailyn, Yale
University; and J. Tomsick, UCSD, report YALO consortium observations of
the optical counterpart of XTE J1550-564 using the Yale 1-m telescope
(+ ANDICAM instrument) at Cerro Tololo Interamerican Observatory:
"XTE J1550-564 has entered a new optical outburst. By Jan. 28.34,
29.34, and 30.34 UT, the object was at V = 18.28 +/- 0.01, 18.27 +/-
0.01, and 18.25 +/- 0.01, respectively. The source is significantly
brighter than the quiescent level of V about 21.6."
---------------------------------------------------------
Title: Long-term Optical Monitoring of X-ray Transients
Authors: Wachter, S.; Hoard, D. W.; Bailyn, C.; Jain, R.; Kaaret,
P.; Corbel, S.; Wijnands, R.
2000HEAD....5.2415W Altcode: 2000BAAS...32.1219W
We present highlights from an optical monitoring program of X-ray
transients designed to assemble long-term optical outburst and decay
lightcurves that can be compared to X-ray lightcurves obtained from the
RXTE All Sky Monitor or from monitoring campaigns with the RXTE pointed
instruments. Since the optical radiation is thought to be largely due to
reprocessing of X-rays in the disk, contemporaneous optical and X-ray
observations offer insight into the outburst mechanism and accretion
dynamics of these objects. Our optical data were obtained during 2000
Feb - Jul under the Synoptic, Service, and Target-of-Opportunity program
on the Cerro Tololo Inter-American Observatory (CTIO) 0.9-m telescope
and on the YALO 1-m telescope, also located at CTIO. We will present
lightcurves for SAX J1808.4-3658 and X1608-522. SAX J1808.4-3658, the
transient 2.5 ms X-ray pulsar, displayed renewed activity in 2000 Jan
- Feb. Our optical data show the same erratic variability as seen in
X-rays. We will also present some of the first data of the quiescent
optical counterpart. X1608-522 is a neutron star X-ray transient that
undergoes large outbursts on a timescale of 700 days. A new outburst
of X1608-522 expected for early 2000 did not materialize; however, the
optical counterpart was visible and we obtained I-band photometry for 68
days before it dropped below the detection limit of our telescopes. The
X-ray data exhibit a series of mini-outbursts. Corresponding brightening
of the counterpart is also seen in the optical. In addition, the optical
lightcurve shows plateaus of emission with a mean level which drops
after each mini-outburst, possibly indicating discrete “emptying”
events in the accretion disk. Cerro Tololo Inter-American Observatory
is operated by AURA, Inc. under cooperative agreement with the NSF.
---------------------------------------------------------
Title: V1333 Aquilae
Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.;
Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D.
2000IAUC.7495....2J Altcode: 2000IAUC.7495R...1J; 2000IAUC.7495B...1J
R. Jain, C. Bailyn, and P. Coppi, Yale University; M. Garcia,
Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts
Institute of Technology; J. Orosz, Utrecht University; P. Lu, Western
Connecticut State University; and J. Espinoza and D. Gonzalez, Cerro
Tololo Interamerican Observatory (CTIO), report on YALO consortium
observations: "Aquila X-1 = V1333 Aql appears to be beginning a new
optical outburst. This x-ray binary outbursts approximately once per
year (e.g., 1999 May 8.3 UT; cf. IAUC 7161), and was due to erupt. We
have been monitoring this source since 2000 Apr. 11 in R using the YALO
1-m telescope at CTIO. Compared to the quiescent average magnitude,
which has a fluctuation < 0.1 mag, the source had brightened in R
by 0.45 +/- 0.02 mag on Sept. 22.15. The R-band brightness continued to
increase, reaching 0.62 +/- 0.02 and 0.71 +/- 0.03 mag above quiescence
on Sept. 23.01 and 24.17, respectively. The amplitude of this outburst
is larger than the peak from recent mini-outbursts (IAUC 7429, 7423,
7017). We will continue monitoring this source at optical, infrared,
and x-ray (using RXTE) wavelengths. Observations at all wavelengths
are encouraged."
---------------------------------------------------------
Title: Mini-outburst of Aql X-1
Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.;
Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D.
2000ATel...59....1J Altcode:
We report YALO consortium observation of a mini-outburst of Aquila
X-1 = V1333 Aql, which occurred between July 04.27 and 07.29 UT. This
X-ray binary outbursts approximately once per year, and most recently
entered a mini-outburst during May 2000 (IAUC 7423,7429). We have been
monitoring this source since April 5 in R using the YALO 1-m telescope
at CTIO. Compared to the quiescent average magnitude, which fluctuates
by less than 0.1 mag, the source had brightened in R by 0.20 +/- 0.02
mag on July 04.27 UT and peaked at 0.31 +/- 0.02 mags on July 05.26 UT.
---------------------------------------------------------
Title: V1333 Aquilae
Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.;
Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D.
2000IAUC.7423....1J Altcode: 2000IAUC.7423A...1J; 2000IAUC.7423Q...1J
R. Jain, C. Bailyn, and P. Coppi, Yale University; M. Garcia,
Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts
Institute of Technology; J. Orosz, Utrecht University; P. Lu, Western
Connecticut State University; and J. Espinoza and D. Gonzalez, Cerro
Tololo Interamerican Observatory (CTIO), report YALO consortium
observations: "V1333 Aql = Aquila X-1 appears to be beginning a new
optical outburst. This x-ray binary outbursts approximately once
per year, and last erupted in May 1999 (IAUC 7161). We have been
monitoring this source since Apr. 5 in R using the YALO 1-m telescope
at CTIO. Compared to the quiescent average magnitude, which fluctuates
by < 0.1 mag, the source had brightened in R by 0.16 +/- 0.02 mag
on May 11.23 UT. During May 12.23-12.40, we obtained four observations
that indicate an increase in brightness of 0.27 to 0.34 +/- 0.02 mag
compared to the quiescent mean. We will continue monitoring this source
at optical, infrared, and x-ray (using RXTE) wavelengths. Observations
at all wavelengths are encouraged."
---------------------------------------------------------
Title: V1333 Aquilae
Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.;
Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D.
2000IAUC.7429....1J Altcode: 2000IAUC.7429Q...1J; 2000IAUC.7429A...1J
R. Jain, C. Bailyn, and P. Coppi, Yale University; M. Garcia,
Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts
Institute of Technology; J. Orosz, Utrecht University; P. Lu, Western
Connecticut State University; and J. Espinoza and D. Gonzalez, Cerro
Tololo Interamerican Observatory (CTIO), report YALO consortium
observations: "The optical outburst of V1333 Aql = Aquila X-1,
which began on May 11.23 UT (IAUC 7423), did not develop into a full
outburst. By May 17.25, the object was back to quiescence. The peak
amplitude of the outburst was 0.34 +/- 0.02 mag brighter than the
quiescent mean in R and occurred on May 12.37. Two observations with
the PCA instrument on RXTE lasting 1500 and 2500 s were taken on
May 14.38 and 16.91, respectively. There is an indication that the
source was detected with the PCA, but the count rates were heavily
background-dominated and low enough that preliminary analysis does not
allow a definitive determination of the flux. We therefore quote an
upper limit of 4 x 10**-11 erg cm**-2 s**-1 (2.5-20 keV). A similar
truncated 'mini-outburst' also occurred in Sept. 1998 (IAUC 7017,
7025)."
---------------------------------------------------------
Title: XTE J1550-564
Authors: Jain , R.; Bailyn, C.
2000IAUC.7400....2J Altcode: 2000IAUC.7400B...1J; 2000IAUC.7400R...1J
R. Jain and C. Bailyn, Yale University, report YALO consortium
observations of the optical counterpart of XTE J1550-564 using the Yale
1-m telescope (+ ANDICAM instrument) at Cerro Tololo Interamerican
Observatory: "XTE J1550-564 has entered a new optical outburst. By
Mar. 24.4 UT, the object was at V = 21.0, significantly brighter than
any of our 12 observations obtained during the period Feb. 28-Mar. 17
(in all of which the source was fainter than V = 21.4). On Mar. 29.3,
we find V = 19.07 +/- 0.03, and on Apr. 6.3, V = 18.24 +/- 0.03. The
rate of brightening has decreased in the past two days to V = 18.09 +/-
0.02 and 18.06 +/- 0.02 on Apr. 9.4 and 10.4, respectively. Further
observations at other wavelengths are encouraged."
---------------------------------------------------------
Title: XTE J1550-564
Authors: McCollough, M. L.; Wilson, C. A.; Sun, X.; Jain, R.;
Bailyn, C.
2000IAUC.7400....1M Altcode: 2000IAUC.7400Q...1M; 2000IAUC.7400A...1M
M. L. McCollough, Universities Space Research Association and Marshall
Space Flight Center (MSFC); C. A. Wilson, NASA/MSFC; and X. Sun,
University of Alabama in Huntsville, report for the Compton Gamma
Ray Observatory (CGRO) BATSE team: "XTE J1550-564 (IAUC 7008, 7010)
was detected in outburst with BATSE in the band 20-300 keV on Apr. 6
at a flux of 0.5 Crab (1.0 x 10**-8 erg cm**-2 s**-1) and had risen to
0.6 Crab (1.2 x 10**-8 erg cm**-2 s**-1) on Apr. 8. XTE J1550-564 is
clearly being detected up to 300 keV. The date that this outburst began
is uncertain because XTE J1550-564 was unobservable with CGRO/BATSE
from Mar. 26 to Apr. 5. The CGRO/BATSE light curve shows evidence for
variability on time scales of less than a day. The energy spectrum
for XTE J1550-564 can be fitted by a bremsstrahlung spectrum with
a temperature of 101 +/- 8 keV or a broken power law with a break
energy of 76 +/- 25 keV, a lower energy photon index of -1.4 +/- 0.4,
and a high energy photon index of -2.4 +/- 0.4."
---------------------------------------------------------
Title: XTE J1550-564
Authors: Jain, R.; Bailyn, C.; Greene, J.; Orosz, J.; McClintock,
J.; Remillard, R.
1999IAUC.7187....2J Altcode: 1999IAUC.7187B...1J; 1999IAUC.7187R...1J
R. Jain, C. Bailyn, and J. Greene, Yale University; J. Orosz,
Pennsylvania State University; J. McClintock, Harvard-Smithsonian
Center for Astrophysics; and R. Remillard, Massachusetts Institute
of Technology, report YALO consortium observations of XTE J1550-564:
"We have obtained data from May 14.40 to June 1.3 UT using the YALO
1-m telescope at Cerro Tololo. The uncalibrated R-band data, with
relative precision of 0.02 mag, show a 1-mag decrease during this
period; hence the optical light curve has not yet reached the true
quiescent level. Between May 14.4 and 23.28, we obtained on average
three 1200-s Johnson R exposures per night; each was separated by
several hours. We detrended the lightcurve by removing a linear decay
of 0.05 mag/day and find clear evidence for a modulation of 0.1 mag
(full amplitude). Using the CLEAN algorithm and performing a fourier
transform, we find a period of 1.5 +/- 0.1 days. Similarly, by using
the phase-dispersion- minimization technique, we find a clear period
at 1.5 days. If this period of about 1.5 days (which was suggested
earlier by Soria and Wu, IAUC 7184) is correct, then the modulation
we see may be due to a 'superhump' or to an illumination effect. On
the other hand, if the light from the secondary dominates the light
from the accretion disk (as suggested by the strong absorption lines
reported by Soria and Wu), then the modulation we observe could be
an ellipsoidal modulation. In this case, the orbital period would
be near 3 days. Further spectroscopic observations will be needed to
definitively determine the orbital period."
---------------------------------------------------------
Title: Optical Outburst of AQL X-1
Authors: Jain, R.; Bailyn, C.; Garcia, M.; Rines, K.; Levine, A.;
Espinoza, J.; Gonzalez, D.
1999ATel...41....1J Altcode:
We report YALO consortium observations using the Yale 1-m telescope at
CTIO and observations with the 48" telescope at the Whipple Observatory:
Aql X-1 = V1333 Aql appears to be beginning a new outburst. This x-ray
binary outbursts approximately once per year, and based on its recent
outbursts was due to erupt.
---------------------------------------------------------
Title: V1333 Aquilae
Authors: Jain, R.; Bailyn, C.; Garcia, M.; Rines, K.; Levine, A.;
Espinoza, J.; Gonzalez, D.
1999IAUC.7161....1J Altcode: 1999IAUC.7161Q...1J; 1999IAUC.7161A...1J
R. Jain and C. Bailyn, Yale University; M. Garcia and K. Rines,
Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts
Institute of Technology; and J. Espinoza and D. Gonzalez, Cerro Tololo
Interamerican Observatory (CTIO), report YALO consortium observations:
"Aquila X-1 = V1333 Aql appears to be beginning a new outburst. This
x-ray binary outbursts approximately once per year, and based on its
recent outbursts was due to erupt. We have monitored the optical
counterpart of the soft x-ray transient Aquila X-1 since early
Mar. in Johnson R, using the YALO 1-m telescope at CTIO. Compared
to the average quiescent level, which has a fluctuation of <
0.1 mag, the source had brightened in R by about 0.2 mag on May 8.3
UT. During May 10.2-10.38, we obtained five data points spanning 9 hr
and found that the brightness increased from 0.4 to 0.55 mag brighter
than the quiescent average. V-band data from the 1.22-m telescope at
the Whipple Observatory show similar increases. We find that by May
9.5 the source had brightened by about 0.4 mag in V, compared to the
average quiescent level. Subsequently we obtained three YALO V images
on May 10.2-10.38 and found an increase in brightness of about 0.45
to 0.6 mag, again compared to the quiescent average. We will continue
monitoring this source both at optical and at x-ray (using RXTE)
wavelengths. Observations at all wavelengths are encouraged."
---------------------------------------------------------
Title: Absorption/Emission of Solar p-Modes: Michelson Doppler
Interferometer/SOHO Observations
Authors: Haber, Deborah; Jain, Rekha; Zweibel, Ellen G.
1999ApJ...515..832H Altcode:
We search for sources and sinks of solar p-mode waves by creating
absorption maps from Dopplergrams taken by the Michelson Doppler
Interferometer instrument on board SOHO. Although the maps are noisy,
we present evidence for sources and sinks, of duration ~0.5-1 hour or
less, based on an autocorrelation analysis of maps made from sequential
intervals of data. Emission and absorption nearly balance each other
in the data. This may imply that emission and absorption are inverse
processes of each other rather than fundamentally different in nature.
---------------------------------------------------------
Title: XTE J1550-564
Authors: Remillard, R.; Morgan, E.; Levine, A.; McClintock, J.;
Sobczak, G.; Bailyn, C.; Jain, R.; Orosz, J.
1999IAUC.7123....2R Altcode: 1999IAUC.7123R...1R; 1999IAUC.7123B...1R
R. Remillard, E. Morgan, and A. Levine, Massachusetts Institute of
Technology; J. McClintock and G. Sobczak, Center for Astrophysics;
C. Bailyn and R. Jain, Yale University; and J. Orosz, Pennsylvania
State University, write: "There is continued evolution of the
high-frequency quasiperiodic oscillations (QPO) in the x-ray nova
and blackhole candidate XTE J1550-564 (see IAUC 7121). An RXTE PCA
observation on Mar. 5.52 UT reveals a QPO at 283 +/- 5 Hz with a FWHM
of 39 +/- 9 Hz, and an rms amplitude of 4.0 +/- 0.7 percent at 6-30
keV, similar to that reported for Mar. 4.80. However, subsequent PCA
observations show changes as follows: 235 +/- 6 Hz (FWHM 30 +/- 11;
amplitude 2.8 +/- 0.8 percent at 6-30 keV) on Mar. 7.50; 182.0 +/-
2.5 Hz (FWHM 12 +/- 4; amplitude 0.91 +/- 0.23 percent at 2-30 keV)
on Mar. 8.37. Thus the frequency has returned to the value at which
the QPO was originally discovered (IAUC 7025). The steep increase
in amplitude with photon energy (IAUC 7121) has lessened on Mar. 8,
as the QPO is weakly visible in the band 2-6 keV, while the profile
fits have poor quality when the energy range is restricted to 6-30 keV."
---------------------------------------------------------
Title: XTE J1550-564
Authors: Jain, R.; Bailyn, C.; McClintock, J.; Sobczak, G.; Remillard,
R.; Orosz, J.
1999IAUC.7114....2J Altcode: 1999IAUC.7114B...1J; 1999IAUC.7114R...1J
R. Jain and C. Bailyn, Yale University; J. McClintock and G. Sobczak,
Harvard-Smithsonian Center for Astrophysics; R. Remillard, Massachusetts
Institute of Technology; and J. Orosz, Pennsylvania State University,
report YALO consortium observations of XTE J1550-564: "We have obtained
B-, V-, and I-band images virtually every night since Jan. 4.3 UT and
most recently covering 3.5 hr of elapsed time per night. We find that,
between Jan. 4.3 and 22.3, the source was steady at V = 16.04, B =
17.48, and I = 14.15. Then on Jan. 22.3, there was a 0.3-mag dip in
the B, V, and I magnitudes. The source then remained steady, with
a slight decline to a new level (V = 16.17, B = 17.62, I = 14.29)
until Feb. 6.3, when another small dip (0.2 mag in I) occurred. This
was followed by another period of steady slow decline. Most recently,
a much larger decrease in optical brightness has occurred: since
Feb. 21, the source has declined by > 0.5 magnitudes in B, V, and
I. RXTE PCA observations show that the 2-20-keV x-ray flux increased
from 6.5 x 10E-8 erg cmE-2 sE-1 on Feb. 21.5 to 7.4 x 10E-8 erg cmE-2
sE-1 on Feb. 23.9. The x-ray spectrum from 2 to 20 keV is dominated
by the disk component, but the change in optical intensity has been
accompanied by a factor of two increase in the power-law component of
the x-ray flux from Feb. 21.5 to 23.9. We will continue to monitor this
object on a daily basis for the foreseeable future, and we strongly
encourage other observations, particularly of optical spectroscopy,
to follow the current change in state of this source."
---------------------------------------------------------
Title: Plasma Heating by Forced Magnetic Reconnection
Authors: Jain, Rekha; Vekstein, Grigory E.
1999Ap&SS.264..113J Altcode: 1998Ap&SS.264..113J
A model of forced magnetic reconnection in a force-free magnetic field
is considered, which allows calculation of the magnetic energy release
during the current sheet reconnection. The dependence of this energy
on characteristics of the magnetic configuration has been studied,
and it was found that the released energy becomes very large when
the field is near the marginal tearing stability. A persistent plasma
heating provided by ongoing external driving and internal reconnection
is also derived. It shows a typical relaxation-type dependence on the
driving frequency, with dissipation becoming most efficient when the
time-scales of the driving and reconnection are comparable. Possible
implications of the obtained results for the problem of solar coronal
heating are discussed.
---------------------------------------------------------
Title: H_α Intensity Oscillations in Solar Flares
Authors: Jain, R.; Tripathy, S.; Bharti, L.; Kumar, B.
1999ASPC..183..531J Altcode: 1999hrsp.conf..531J
No abstract at ADS
---------------------------------------------------------
Title: Helioseismology
Authors: Elsworth, Y.; Jain, R.
1998Obs...118..342E Altcode:
No abstract at ADS
---------------------------------------------------------
Title: XTE J1550-564
Authors: Orosz, J.; Bailyn, C.; Jain, R.
1998IAUC.7009....1O Altcode: 1998IAUC.7009A...1O; 1998IAUC.7009Q...1O
J. Orosz, Pennsylvania State University; and C. Bailyn and R. Jain,
Yale University, report YALO consortium observations using the Yale 1-m
telescope (+ ANDICAM CCD camera) at the Cerro Tololo Interamerican
Observatory: "We have identified a possible optical counterpart
to the recent x-ray transient XTE J1550-564 (IAUC 7008) in V-band
images obtained on Sept. 8.99 UT. The candidate is located at R.A. =
15h50m58s.78, Decl. = -56o28'35".0 (equinox 2000.0), with estimated
errors on each value of about 1"-2". This object is not visible on an
image obtained from the Digitized Sky Survey. We estimate a magnitude of
V = 16, based on comparions with nearby stars selected from the Hubble
Guide Star Catalog. Further observations, especially spectroscopic
confirmation, are urgently needed. A finding chart may be obtained via
the World Wide Web at http://www.astro.psu.edu/users/orosz/xte.html."
---------------------------------------------------------
Title: XTE J1550-564
Authors: Jain, R.; Bailyn, C.; Orosz, J.
1998IAUC.7020....1J Altcode: 1998IAUC.7020Q...1J; 1998IAUC.7020A...1J
R. Jain and C. Bailyn, Yale University; and J. Orosz, Pennsylvania
State University, report YALO consortium observations using the Yale
1-m telescope at the Cerro Tololo Interamerican Observatory: "We have
monitored the optical counterpart to XTE J1550-564 (IAUC 7009) nightly
since Sept. 13 UT. The source has varied by < 0.3 mag in V since
its discovery. We have adjusted our instrumental magnitudes so that V
= 16.7 and V-I = +1.80 near Sept. 16.0, as reported by Castro-Tirado
et al. (IAUC 7013), and we find that 16.6 < V < 16.9 over the
range Sept. 8.99-21.97. Thus there is no dramatic optical response to
the large increase in the x-ray intensity over the last several days
(cf. IAUC 7019). Between Sept. 15.0 and 21.0, there was a trend in the
V-I color where the source became increasingly redder. We find V-I =
1.80 +/- 0.04 near Sept. 15.0 and 1.92 +/- 0.01 near Sept. 21.0. YALO
consortium monitoring observations of XTE J1550-564 will continue;
additional observations are encouraged."
---------------------------------------------------------
Title: The Solar Activity in NOAA Active Region No.8038 During 10-13
May 1997
Authors: Jain, R.; Mehta, Nirav; Vats, Hari Om; Deshpande, M. R.;
Matthew, Shibu K.; Chandra, H.; Bogod, V. Ladimir; Nagai, S.; Sharma,
S.; Sagawa, E.; Tokhchukova, Susan; Iyer, K. N.; Oza, Rupal; Rathore,
Saroj
1997ESASP.415..145J Altcode: 1997cpsh.conf..145J
No abstract at ADS
---------------------------------------------------------
Title: P-Modes, Acoustic Emission and Surface Magnetic Fields
Authors: Jain, Rekha; Haber, Deborah
1997BAAS...29.1120J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Surface Amplitudes and Frequencies of p-Mode Oscillations
in Active Regions
Authors: Hindman, Bradley W.; Jain, Rekha; Zweibel, Ellen G.
1997ApJ...476..392H Altcode:
It is well established that the surface amplitudes of solar p-mode
oscillations are reduced in regions of magnetic activity. In this
paper, we examine the conjecture that this reduction is produced by
direct modification of the surface values of the p-mode eigenfunctions,
rather than changes in the mode energies or alterations in the spectral
line formation process. We calculate the oscillation modes of a solar
model with a horizontal magnetic field, convection, and radiative
diffusion. We find that magnetic fields with strengths characteristic of
solar active regions can produce the observed decrease of surface power.
---------------------------------------------------------
Title: High energy photons detection using scintillation counter
during total solar eclipse of October 24, 1995.
Authors: Jaaffrey, S. N. A.; Jain, R.; Pandya, A.; Bharti, L.
1997KodOB..13..235J Altcode:
The authors report the first observations of absorption and enhancement
in flux of high energy photons during the total solar eclipse of
October 24, 1995. For the purpose of these observations, they employed
a scintillation counter to detect high energy radiation in the energy
range of 10 keV to 5 MeV. The authors interpret the absorption in the
flux below 300 keV due to the passage of the Moon between the Sun and
the Earth, while enhancement above 300 keV could have occurred due to
the production of secondary radiations from high energy photons.
---------------------------------------------------------
Title: The Influence of Magnetism on p-Mode Surface Amplitudes
Authors: Jain, Rekha; Hindman, Bradley W.; Zweibel, Ellen G.
1996ApJ...464..476J Altcode:
We propose a mechanism to explain the observed suppression of p-mode
surface velocities in solar active regions. We show that a horizontal
magnetic field can lower the upper turning point and change the skin
depth for a simple plane-parallel adiabatically stratified polytrope. In
addition to power suppression, the magnetic field alters the phase of
p-modes. Simultaneous measurements of phase as well as amplitude in
the active and quiet regions would provide an additional diagnostic
for probing the structure of active region magnetic fields.
---------------------------------------------------------
Title: Discrete High-Frequency p-Modes
Authors: Jain, Rekha; Roberts, B.
1996ApJ...456..399J Altcode:
Observations report that the p-mode frequencies change with the solar
activity cycle. Over the frequency range 0 to 8.5 mHz, shifts can be
either positive or negative, appearing to exhibit a wavelike behavior
with downturn occurring at ∼4.0 mHz and upturn at ∼5.5 mHz. A
simple polytrope convection zone model overlaid with an isothermal
chromospheric atmosphere threaded by a uniform horizontal magnetic
field demonstrates frequency shifts that are qualitatively similar to
those observed for both high and low frequencies, with shifts being a
consequence of simultaneous increases in chromospheric field strength
and temperature.
---------------------------------------------------------
Title: Hα Intensity Oscillations Observed in Solar Flares
Authors: Jain, R.; Tripathy, S. C.
1995JApAS..16..381J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Frequency Shifts of High-Frequency P-Modes
Authors: Jain, R.
1995ESASP.376b..69J Altcode: 1995help.confP..69J; 1995soho....2...69J
Frequency shifts (the difference between the frequencies from one time
to another during the solar cycle) of high frequency (ν > 4 mHz)
p-modes are calculated for a non-magnetic polytrope convection zone
model over which lies an isothermal chromospheric atmosphere threaded
by a uniform horizontal magnetic field. The relevant observations of
such frequency changes are discussed. Simultaneous changes in field
strength and chromospheric temperature result in frequency shifts
(theoretically calculated) that are similar to those observed.
---------------------------------------------------------
Title: Changes in the Upper Turning Point due to Magnetism
Authors: Jain, R.; Hindman, B. W.; Zweibel, E. G.
1995ESASP.376b..63J Altcode: 1995soho....2...63J; 1995help.confP..63J
It has been observed that p-mode power is substantially suppressed in
magnetic regions. One possible explanation is that the upper turning
point (acoustic cut-off point) of the solar p-modes is lowered in the
presence of a magnetic field (Brown 1994). A related possibility is
that the attenuation length scale in the evanescent region is reduced
in the presence of a magnetic field. Furthermore, it is likely that the
observations sample a different position in the evanescent tails of the
eigenfunctions, in magnetic regions because of different temperature
structure there. The authors use a simple model to quantify the first
of these effects.
---------------------------------------------------------
Title: Solar Cycle Variations in P-Modes and Chromospheric Magnetism
Authors: Jain, Rekha; Roberts, B.
1994SoPh..152..261J Altcode: 1994IAUCo.143..261J; 1994svs..coll..261J
The effect onp-mode frequencies of a horizontal chromospheric canopy
field is studied theoretically and the results compared with Libbrecht
and Woodard's observations of frequency changes. Combined changes in
field strength and chromospheric temperature cause frequency shifts
that are similar in form to those observed. Frequency shifts inp-modes
offer the possibility of signatures of solar activity cycles distinct
from sunspot numbers and butterfly diagrams.
---------------------------------------------------------
Title: Surface effects of a magnetic field on p-modes: two layer
atmosphere
Authors: Jain, R.; Roberts, B.
1994A&A...286..254J Altcode:
The effects of chromospheric canopy fields on p-mode frequencies are
evaluated for a two layer model atmosphere. The convection zone is
field-free, while the chromosphere contains a magnetic field which
is uniform up to a certain height after which it decreases with
height. Frequency shifts due to simultaneous changes in chromospheric
field strengths and temperatures are calculated numerically. The
frequency shifts increase or decrease as a function of frequency,
depending upon the thickness of the middle region.
---------------------------------------------------------
Title: Effects of non-parallel propagation on p- and f-modes
Authors: Jain, R.; Roberts, B.
1994A&A...286..243J Altcode:
The frequencies of p- and f-modes are calculated for a model atmosphere
consisting of an isothermal chromospheric gas, within which is embedded
a non-uniform horizontal magnetic field, resting upon a field-free
medium whose temperature increases linearly with depth. The Alfven speed
within the chromosphere is assumed to be independent of height. The
modes may propagate at an angle θ to the magnetic field. The p-mode
frequencies decrease with an increase in either the magnetic field
strength or the propagation angle θ. The frequency of the f-mode is
increased by the presence of a magnetic field; the frequency decreases
with increasing angle θ.
---------------------------------------------------------
Title: Do p-Mode Frequency Shifts Suggest a Hotter Chromosphere at
Solar Maximum?
Authors: Jain, Rekha; Roberts, B.
1993ApJ...414..898J Altcode:
The frequencies of p-modes are calculated for a model atmosphere
consisting of an isothermal gas, within which is embedded a uniform
horizontal magnetic field, resting upon a field-free medium whose
temperature increases linearly with depth. We compare our results
with Libbrecht & Woodard's recent observations of frequency
changes. It is found that if simultaneously the chromospheric magnetic
field strength and chromospheric temperature are increased, then the
frequencies of the p-modes are shifted in a qualitatively similar
fashion to that found in the observations, i.e., the frequency
shift increases with frequency until about 3.9 mHz, when the shift
decreases dramatically. We suggest that the combined influence of an
increase in magnetic field strength and an increase in chromospheric
temperature plays an important role in determining the observed
downturn in frequency shift. Although the resulting frequency shift
curve resembles the observed shift, with both possessing a gradual rise
phase followed by a turnover, the calculated shift fails to match the
steep downturn. Refinements in our basic model and/or new physics are
thus indicated.
---------------------------------------------------------
Title: Magnetic Field Lines for a Flux Tube
Authors: Steele, C. D. C.; Jain, Rekha
1993SoPh..145..197S Altcode:
Equations for the magnetic field components in a two dimensional
cylindrically symmetric flux tube equilibrium have been derived and, in
a simple case, solved. The resulting magnetic configuration possesses
a strong magnetic field in a thin tube below a reference level (solar
photosphere). Above this reference level the field lines spread out
in all directions.
---------------------------------------------------------
Title: P-Mode Frequency Shifts and Chromospheric Magnetism
Authors: Jain, R.; Roberts, B.
1993ASPC...42...53J Altcode: 1993gong.conf...53J
No abstract at ADS
---------------------------------------------------------
Title: Magnetic surface effects on solar oscillations
Authors: Jain, Rekha
1993PhDT........85J Altcode:
This thesis is concerned with the effects of magnetic atmospheres on
solar oscillations. The behaviour of magnetohydrodynamic surface waves
propagating on a single magnetic interface is discussed ignoring the
effects of gravity. The effects of non-parallel propagation (where
the wave vector is at an angle to the magnetic field direction) are
considered. The effects of chromospheric magnetic fields on solar p-
and f-modes in a stratified atmosphere are examined for three different
models. In the first of these models, the chromosphere is assumed to be
isothermal and permeated by a uniform and horizontal magnetic field. A
dispersion relation for the p-modes trapped below such an atmosphere
is derived. Asymptotic and numerical solutions for the p-modes are
discussed in detail. An increase in chromospheric magnetic field
strength leads to an increase in the frequency of the p-modes, whereas
an increase in the chromospheric temperature leads to a decrease in the
frequencies of these modes. Comparison with observational data suggests
that both these effects may indeed take place. The second model is set
up for magnetic fields which decrease with height in such a way that
the Alfven speed remains constant. In addition to magnetic effects,
the effects of non-parallel propagation on and f-modes are considered
in the presence of such a non-uniform magnetic field. After deriving
a very general dispersion relation, various asymptotic and numerical
solutions have been obtained and the possible effects of magnetic fields
and non-parallel propagation on these modes are examined. The presence
of a horizontal non-uniform chromospheric field produces changes in the
frequencies of the p- and f-modes, reducing the frequencies of p-modes
and increasing the frequency of the f-mode. Besides depending upon
magnetic field strength, frequencies also depend on both the mode's
order n and its degree l. The effects of non-parallel propagation
are found to be most significant for the f-mode and the low order
p-modes. The magnetic structure of the chromosphere has been further
generalised by combining the two models described above. In this three
layer model, a dispersion relation is derived in a general manner and
discussed in detail for the p-modes. The role of mag- netoacoustic
cut-off frequency is studied. Again, the results are qualitatively
similar to those found from observation.
---------------------------------------------------------
Title: Cosmic ray flare of 1989 September 29.
Authors: Jain, R.; Bhatnagar, A.; Sharma, R.
1991BASI...19..208J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetoacoustic surface waves at a single interface
Authors: Jain, Rekha; Roberts, B.
1991SoPh..133..263J Altcode:
The occurrence of magnetoacoustic surface waves at a single magnetic
interface one side of which is field-free is explored for the case
of non-parallel propagation. Phase-speeds and penetration depths of
the waves are investigated for various Alfvén speeds, sound speeds
and angles of propagation to the applied field. Both slow and fast
magnetoacoustic surface waves can exist depending on the values of
sound speeds and propagation angle. The fast waves penetrate more than
the slow waves.
---------------------------------------------------------
Title: Site survey for high spatial resolution solar observations.
Authors: Jain, R.
1991nlt..work..140J Altcode:
The requirements and their measurements for selecting a solar astronomy
site to obtain high spatial resolution solar observations for long
uninterrupted periods are discussed. A new approach for optical testing
and hence to evaluate such a site through the photography of granulation
and determining sunshine hours is also proposed. Possibilities are
explored for location of a suitable site.
---------------------------------------------------------
Title: Properties of Non-Parallel Magnetoacoustic Surface Waves
(With 1 Figure)
Authors: Jain, R.; Roberts, B.
1991mcch.conf..511J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Center to limb variation of solar granulation
Authors: Jain, R.; Muller, R.
1989SoPh..123..185J Altcode:
From high resolution white light photographs it is determined that
the surface density of solar granulation decreases towards limb. A
schematic model is proposed to interpret both decrease of surface
density and size of granules in the upper photosphere.
---------------------------------------------------------
Title: Photopolarimetry of Seyfert Galaxies - NGC 2992, NGC 3081,
NGC 3227, and IC 4329 A
Authors: Joshi, U. C.; Jain, R.; Deshpande, M. R.
1989IAUS..134..321J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Two ribbon flare on April 3, 1980.
Authors: Jain, R.
1988KodOB...9..205J Altcode:
Hα observations of a two-ribbon flare which were associated with
exceptionally high microwave (MW) and hard X-ray emissions are presented
and discussed. The good spatial and temporal resolution of the Hα data
allows to investigate the detailed flare structure and its variation
during each phase of the event. Strong MW emissions were found to
be associated with the smallest flare but located in the inverted
polarity region.
---------------------------------------------------------
Title: Polarimetry of supernova SN 1987A - a dust shell model.
Authors: Joshi, U. C.; Sen, A. K.; Deshpande, M. R.; Jain, R.
1988KodOB..10...43J Altcode:
Time variation of wavelength dependence of linear polarization is
suggestive of a dust shell around SN 1987A. The intrinsic polarization
is due to at least two components: one is due to a dust shell and the
other is perhaps a synchrotron component. The minimum radius of the
dust shell is estimated to be 0.04 pc with an optical thickness at
visual wavelength 0.6. The temperature of the dust shell is expected
to be T<SUB>d</SUB> ≡ 200K.
---------------------------------------------------------
Title: Flare Associated Coronal Loop Systems in Fexiv 5303A Fex 6374
and Hα Morphological Details and Derived Parameters
Authors: Jain, R.; Smartt, R. N.; Zhaug, Z.
1987BASI...15...19J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: H-alpha flare associated microwave emissions
Authors: Jain, R.
1985BASI...13..253J Altcode:
The author has carried out a statistical association of 321 two-ribbon
and 1564 non two-ribbon (normal) H-alpha flares which occurred
during 1976 to 1980 with microwave bursts in the frequency range 3
- 35 GHz. Results obtained are as follows: (1) the two-ribbon (TR)
flares show 1.5 to 3 times higher correlation as compared to normal
(N) flares, indicating that TR flares are strong emitter of microwave
emissions; (2) the TR flares show 2 to 4 times better association as
compared to N flares with impulsive microwave bursts; (3) the higher
correlation of TR flares with impulsive microwave bursts is perhaps
due to their occurrence in complex magnetic configurations; (4) the
strong and weak correlation of TR flares and N flares respectively,
with impulsive microwave bursts at higher frequencies (10 - 35 GHz)
indicates that the source of the TR flares is near the photosphere or
the lower chromosphere (strong magnetic fields) and that of the normal
flare is the upper chromosphere (weak magnetic fields).
---------------------------------------------------------
Title: Detailed Morphology of Flare-Associated Coronal Loops
Authors: Smartt, R. N.; Jain, R.
1985BAAS...17Q.645S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Veil emission associated with the multiribbon flare of 1979
February 18
Authors: Jain, R.; Bhatnagar, A.; Shelke, R. N.
1985PASJ...37..609J Altcode:
An X2 multi-ribbon solar flare of importance class 2B was observed on
1979 February 18, in McMath plage 15830, which distinctly showed a "veil
emission" around the flare. Associated with this flare, soft X-ray and
microwave emission and type II radio bursts were also observed. From
the optical observations it is suggested that the flare core ejected
out a diffuse emission veil during the impulsive or flash phase and
that the emission may be due to low density cloud or electrons emanated
from the flare around the flash phase. The possibility of veil emission
from both the phenomena, i.e., ionization during impulsive phase and
recombination from the ionized hydrogen during decay phase is explained.
---------------------------------------------------------
Title: Eruptive prominences of 1980 April 27 observed during STIP
Interval -X
Authors: Jain, R.; Bhatnagar, A.; Shelke, R. N.
1984JApA....5..323J Altcode:
Observations and analyses of two similar eruptive prominences on the
north-east limb observed on 1980 April 27 at 0231 and 0517 UT, which are
associated with the Boulder active region No. 2416, are presented. Type
II and moving type IV radio bursts are reported in association with
the first H-alpha eruptive prominence at 0231 UT. Both the H-alpha
eruptive prominences showed pulse activity with a quasi-periodicity
of about 2-4 min. A magnetic field in the eruptive prominence of
about 100 G and a build-up rate about 10 to the 26th ergs/s are
estimated. The high build-up rate indicates that the shearing of the
photospheric magnetic field, which fed the energy into the filament,
was rapid. It is proposed that fast-moving H-alpha features must have
initiated the observed coronal transients. From H-alpha, type II,
and coronal-transient observations, a magnetic field of 2.8 G at 1.9
solar radius from the disk center, is estimated, which agrees well
with the earlier results.
---------------------------------------------------------
Title: Recurrent mass ejections associated with flare behind the
limb on 1978 December 20
Authors: Jain, R.; Bhatnagar, A.; Shelke, R. N.
1984BASI...12..162J Altcode:
A solar flare occurred on 1978 December 20 in the McMath active
region No. 15700. In this paper a detailed study of the spray and
surge activities associated with this flare is presented. A possible
explanation for the observed recurring tendency of surges with a
quasi-periodicity of 5 - 30 min is suggested as due to additional
small magnetic flux brought out by buoyancy in or near a satellite
spot which could provide enough collimating energy to squeeze out the
surge material at a quasi-periodic time interval. Another interesting
surge phenomenon was observed which showed up and down motion of a small
surge material between 11.00 - 11.30 UT, with a velocity of about 20 km
s<SUP>-1</SUP>. To explain this event a qualitative model is presented.
---------------------------------------------------------
Title: Growth and separation of flare ribbons.
Authors: Jain, R.; Bhatnagar, A.
1984BASI...12...68J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A statistical study of two ribbon and normal flares during
ascending period of cycle-21.
Authors: Jain, R.; Bhatnagar, A.
1983BASI...11...91J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Joule heating of the equatorial electrojet E-region
Authors: Jain, R.; Nath, N.; Setty, C. S. G. K.
1981JATP...43.1189J Altcode:
Simultaneous data on electron density, electron temperature and current
density obtained from a rocket borne Langmuir probe, a glass-sealed
Langmuir probe and a proton precession magnetometer flown from Thumba
(geomag. lat. 0.99 deg S, geomag. long. 146.79 deg E, magnetic dip of 0
deg 47 min S) have been used to calculate the Joule heating in order to
assess whether it contributes significantly to the thermal imbalance in
the E-region. It is envisaged that the changes in electron temperature
are partially brought about by changes in collision frequency and the
energy loss factor. It is found that the Joule heating alone is not
sufficient to explain the observed differences in electron and neutral
gas temperatures. The inclusion of photoelectron heating and adjustments
of profiles of the collision frequency and the energy loss factor bring
the computed temperature differences closer to the observed differences.
---------------------------------------------------------
Title: The double ribbon flare of December 17, 1976.
Authors: Jain, R.; Ballabh, G. M.; Sreedhar Rao, S.; Bhatnagar, A.
1978BASI....6...44J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On solar flare associated shock wave.
Authors: Bhatnagar, A.; Ballabh, G. M.; Jain, R.; Rao, S.
1976BASI....4...78B Altcode:
No abstract at ADS
