explanation blue bibcodes open ADS page with paths to full text
Author name code: bhatnagar
ADS astronomy entries on 2022-09-14
author:("Bhatnagar, Arvind" OR "Bhatnagar, Aditi")
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Title: Sunspot Cycle 25 is Brewing: Early Signs Herald its Onset
Authors: Nandy, Dibyendu; Bhatnagar, Aditi; Pal, Sanchita
2020RNAAS...4...30N Altcode:
No abstract at ADS
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Title: Why Study the Sun?
Authors: Bhatnagar, Arvind
2006JApA...27...59B Altcode:
In this presentation we briefly describe the Sun through large number
of illustrations and pictures of the Sun taken from early times to
the present day space missions. The importance of the study of the Sun
is emphasized as it is the nearest star which presents unparallelled
views of surface details and numerous phenomena. Our Sun offers a
unique celestial laboratory where a large variety of phenomena take
place, ranging in temporal domain from a few milliseconds to several
decades, in spatial domain from a few hundred kilometers to thousands of
kilometers, and in the temperature domain from a few thousand degrees
to several million degrees. Its mass motion ranges from thousandths
to thousands of kilometers per second. Such an object provides us with
a unique laboratory to study the state of matter in the Universe. The
existing solar ground-based and space missions have already revealed
several mysteries of the outer environment of our Sun and much more
is going to come in the near future from planned newsophisticated
ground-based solar telescopes and Space missions. The new technique
of helioseismology has unravelled many secrets of the solar interior
and has put the Standard Solar Model (SSM) on firm footing. The
long-standing problem of solar neutrinos has been recently sorted out,
and even the `back side' view of the Sun can be seen using the technique
of holographic helioseismology.
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Title: Fundamentals of Solar Astronomy
Authors: Bhatnagar, Arvind; Livingston, William; Holman, Gordon D.
2006PhT....59j..66B Altcode:
No abstract at ADS
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Title: Fundamentals of Solar Astronomy
Authors: Bhatnagar, Arvind; Livingston, William
2005fsa..book.....B Altcode:
No abstract at ADS
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Title: Fundamentals Of Solar Astronomy
Authors: Bhatnagar, Arvind; Livingston, William
2005WSSAA...6.....B Altcode:
No abstract at ADS
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Title: Variations in Oscillation Frequencies From Minimum to Maximum
of Solar Activity
Authors: Jain, Kiran; Bhatnagar, A.
2003SoPh..213..257J Altcode:
The temporal variation in intermediate-degree-mode frequencies is
analysed using helioseismic data which cover the minimum to the maximum
phase of the current solar cycle. To study the variation in detail,
the measured frequency shifts of f and p modes are decomposed into
two components, viz., oscillatory and non-oscillatory. The f-mode
frequencies exhibit prominent oscillatory behavior in contrast to p
modes where the oscillatory nature of the frequencies is not clearly
seen. Also, the oscillatory part contributes significantly to the
f-mode frequencies while p-mode frequencies have maximum contribution
from the non-oscillatory part. The amplitude of both oscillatory and
non-oscillatory parts is found to be a function of frequency. The
non-oscillatory part is observed to have a strong correlation with
solar activity.
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Title: Instrumentation and Observational Techniques in Solar Astronomy
Authors: Bhatnagar, A.
2003LNP...619...27B Altcode: 2003lsp..conf...27B
Basic concepts in solar physics are described with an attempt to
bring out the importance of the Sun as a "Rosetta Stone" to understand
other stars. Our Sun being the nearest star, shows intricate surface
details and a wide variety of dynamic phenomena. These range in size
from a few kilometres to millions of kilometres and in the temporal
domain from a fraction of a second to decades. In addition, the Sun
displays a great variety of magnetic and velocity fields, as well
as radiative energy spectra. The close connection between the solar
activity and the Earth's ionosphere, atmosphere and geomagnetic field
makes the Solar-Terrestrial relations a very interesting and valuable
field of study for a whole variety of disciplines. The principles
and details of various kinds of solar instruments are described,
especially solar telescopes from the simplest to the advanced types,
along with several kinds of back-end instruments, such as monochromatic
filters, spectrographs, spectroheliographs, magnetographs, etc., used
for photospheric, chromospheric and coronal observations. Standard
techniques for making solar observations, e.g., measurements of
sunspot areas, coordinates and position of solar features, etc., are
described. Solar observations made even with simple equipments are
of great importance for short and long term synoptic studies and can
even be taken up as a hobby by amateur solar astronomers along with
professional solar physicists.
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Title: Lectures on Solar Physics
Authors: Antia, H. M.; Bhatnagar, A.; Ulmschneider, P.
2003LNP...619.....A Altcode: 2003lsp..conf.....A
No abstract at ADS
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Title: Variation of solar irradiance and mode frequencies during
Maunder minimum
Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C.
2002Ap&SS.281..761B Altcode: 2002astro.ph..1025B
Using the sunspot numbers reported during the Maunder minimum and the
empirical relations between the mode frequencies and solar activity
indices, the variations in the total solar irradiance and 10.7 cm radio
flux for the period 1645 to 1715 is estimated. We find that the total
solar irradiance and radio flux during the Maunder minimum decreased
by 0.19% and 52% respectively, as compared to the values for solar
cycle 22.
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Title: How Good are the Predictions for Oscillation Frequencies?
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
2002SoPh..206..213J Altcode: 2002astro.ph..1024J
We have used available intermediate degree p-mode frequencies for
solar cycle 23 to check the validity of previously derived empirical
relations for frequency shifts (Jain et al., 2000). We find that the
calculated and observed frequency shifts during the rising phase of
cycle 23 are in good agreement. The observed frequency shift from
minimum to maximum of this cycle as calculated from MDI frequency data
sets is 251±7 nHz and from GONG data is 238±11 nHz. These values are
in close agreement with the empirically predicted value of 271±22 nHz.
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Title: Solar rotation rate from minimum to maximum of activity cycle
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.; Kumar, Brajesh
2001BASI...29..239J Altcode:
Using helioseismic data from SOI/MDI and GONG for the current solar
cycle 23, from solar minimum to near maximum phase, we report here on
the temporal variation of the rotation rate.
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Title: Analysis of hysteresis effect in p-mode frequency shifts and
solar activity indices
Authors: Tripathy, S. C.; Kumar, Brajesh; Jain, Kiran; Bhatnagar,
Arvind
2001SoPh..200....3T Altcode: 2001astro.ph..3129T
Using intermediate degree p-mode frequency datasets for solar cycle
22, we find that the frequency shifts and magnetic indices show a
`hysteresis' phenomenon. It is observed that the magnetic indices
follow different paths for the ascending and descending phases of the
solar cycle, as the descending path always seems to follow a higher
track than the ascending one. However, for the radiative indices,
the paths cross each other indicating phase reversal.
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Title: Temporal evolution of f-mode frequencies and radius
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
2001ESASP.464...95J Altcode: 2001astro.ph..3163J; 2001soho...10...95J
We have analysed temporal evolution in centroid frequencies and
splitting coefficients of solar f-modes obtained from MDI/SOHO. The
data were divided into 20 sets covering a period from May 1, 1996 to
August 31, 2000. The variation in frequencies is estimated to be 68 nHz
over the period of four years which includes the rapidly rising phase
of the solar cycle 23. This change is much smaller than that observed
for p-mode frequencies. It is also noticed that the f-mode frequencies
appear to be weakly correlated with solar activity indices as compared
to the p-mode frequencies. We have also inferred the relative change in
the solar radii and notice a 1 year periodicity which may be associated
with the solar cycle variation.
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Title: On the solar rotation rate in the upper convection zone
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
2001ESASP.464..641J Altcode: 2001soho...10..641J; 2001astro.ph..3164J
We present results on variation in rotation rate in the upper convection
zone using data from GONG and MDI/SOHO covering a period of more than
four years. We find that the first few odd-order splitting coefficients
vary systematically with the solar cycle. The rotation rate near the
solar surface calculated from analytical methods agrees well with that
of inversion techniques. The residual rotation rate in the outer layers
seem to be correlated with the solar activity.
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Title: Solar Cycle-induced Variations in GONG P-Mode Frequencies
and Splittings
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.
2000ApJ...542..521J Altcode: 2000astro.ph..6015J
We have analyzed the recently available Global Oscillation Network Group
(GONG) p-mode frequencies and splitting coefficients for a period of
three and a half years including the rapidly rising phase of solar
cycle 23. The analysis of mean frequency shift with different activity
indices shows that the shift is equally correlated with both magnetic
and radiative indices. During the onset of the new cycle 23, we notice
that the change in the b<SUB>4</SUB> splitting coefficient is more
prominent than the change in b<SUB>2</SUB>. We have estimated the solar
rotation rate with varying depth and latitude. In the equatorial region,
the rotation first increases with depth and then decreases, while an
opposite behavior is seen in the polar region. We also find a small but
significant temporal variation in the rotation rate at high latitudes.
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Title: Observation of Hysteresis Between Solar Activity Indicators
and p-mode Frequency Shifts for Solar Cycle 22
Authors: Tripathy, S. C.; Kumar, B.; Jain, K.; Bhatnagar, A.
2000JApA...21..357T Altcode:
No abstract at ADS
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Title: Heliseismic Solar Cycle Changes and Splitting Coefficients
Authors: Tripathy, S. C.; Jain, Kiran; Bhatnagar, A.
2000JApA...21..349T Altcode:
No abstract at ADS
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Title: Empirical estimate of p-mode frequency shift for solar cycle 23
Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.; Kumar, Brajesh
2000SoPh..192..487J Altcode: 1999astro.ph.12518J
We have obtained empirical relations between the p-mode frequency shift
and the change in solar activity indices. The empirical relations are
determined on the basis of frequencies obtained from BBSO and GONG
stations during solar cycle 22. These relations are applied to estimate
the change in mean frequency for the cycle 21 and 23. A remarkable
agreement between the calculated and observed frequency shifts for
the ascending phase of cycle 23, indicates that the derived relations
are independent of epoch and do not change significantly from cycle to
cycle. We propose that these relations could be used to estimate the
shift in p-mode frequencies for past, present and future solar activity
cycles, if the solar activity index is known. The maximum frequency
shift for cycle 23 is estimated to be 265±90 nHz, corresponding to
a predicted maximum smoothed sunspot number 118.1±35.
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Title: A relation between frequency shift and the changes in activity
indices
Authors: Jain, Kiran; Tripathy, S. C.; Kumar, Brajesh; Bhatnagar,
Arvind
2000BASI...28...89J Altcode:
We present a linear relation between the shift in p-mode frequencies
and variation in two solar activity indices, namely the sunspot number
and 10.7 cm radio flux. From this relation, an empirical model is
constructed to estimate the mean frequency shifts with respect to
activity index. We also compare the observed and estimated shifts
for solar cycle 22 and comment on the systematic errors in different
helioseismic data sets.
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Title: GONG p-mode frequency changes with solar activity
Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C.
2000BASI...28...91B Altcode:
In this paper, we present a correlation study of nine solar activity
indices with p-mode frequency shifts obtained from the GONG data. It
is found that the two are closely correlated and a linear relationship
exits. Further, the GONG p-mode frequencies for the period 1995 August
to 1997 August show that the mean frequency decreases by 0.06 μHz
during the descending phase of the solar cycle 22 and increases by
0.04 μHz in the ascending phase of the new solar cycle 23.
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Title: GONG p-Mode Frequency Changes with Solar Activity
Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C.
1999ApJ...521..885B Altcode: 1999astro.ph..3493B
We present a correlation analysis of GONG p-mode frequencies with
nine solar activity indices for the period from 1995 August to
1997 August. This study includes spherical harmonic degrees in the
range 2-150 and the frequency range of 1500-3500 μHz. Using three
statistical tests, the measured mean frequency shifts show strong
to good correlation with activity indices. A decrease of 0.06 μHz
in frequency during the descending phase of solar cycle 22 and an
increase of 0.04 μHz in the ascending phase of solar cycle 23 are
observed. These results provide the first evidence for change in p-mode
frequencies around the declining phase of cycle 22 and the beginning
of new cycle 23. This analysis further confirms that the temporal
behavior of the solar frequency shifts closely follow the phase of
the solar activity cycle.
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Title: Circular polarization measurement using a tunable lithium
niobate Fabry-Perot filter
Authors: Mathew, S. K.; Bhatnagar, A.; Debi Prasad, C.; Ambastha, A.
1999ASSL..243..321M Altcode: 1999sopo.conf..321M
No abstract at ADS
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Title: High Resolution Longitudinal Magnetic Field Measurements
Using a Fabry-Perot Lithium Niobate Filter Based Video Magnetograph
Authors: Mathew, S.; Bhatnagar, A.; Debi Prasad, C.; Ambastha, A.
1999ASPC..183..256M Altcode: 1999hrsp.conf..256M
No abstract at ADS
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Title: Fabry-Perot filter based solar video magnetograph
Authors: Mathew, S. K.; Bhatnagar, A.; Prasad, C. D.; Ambastha, A.
1998A&AS..133..285M Altcode:
A tunable Lithium Niobate (LiNbO_3) Fabry-Perot filter (FP) (passband
165 m Angstroms/ at 6122 Angstroms) based video magnetograph has
been designed and fabricated. This instrument is capable of providing
near simultaneous observations of photospheric longitudinal magnetic
field, chromospheric Hα , and photospheric CaI pictures using the same
telescope and back-end set-up. The magnetic field measurements are made
by using the polarization properties of the Zeeman components of the
photospheric CaI line at 6122 Angstroms/ (Landé g factor of 1.75). The
CaI line has been chosen due to its low temperature sensitivity and no
blend with other solar or atmospheric lines. A variable electro-optic
quarter wave retarder, KD(*) P (Potassium di-Deuterium Phosphate)
along with a linear polarizer is used for analyzing the circular
polarization of the Zeeman components. The filter tuned at 140 m
Angstroms/ away from the line center in the blue wing is found to give
the best linear response for the field strength up to 1500 Gauss. A
field of view (FOV) of ~ 4 x 3 arcmin on the solar disk is imaged
using a 699 x 288 pixel Cohu CCD camera in synchronous with the KD(*)
P modulation. The <~mbda/4 modulation is achieved by applying +/-2100
volts to the KD(*) P to obtain alternate frames of oppositely circular
polarized images. These images are stored in separate frame buffers of
an image acquisition system. To achieve high signal to noise ratio,
a large number of images (maximum 256) are added in the respective
frame buffers and then the difference between the left and the right
circularly polarized images is obtained. This difference is related to
the magnetic field strength. On comparing the video magnetograms (VMG)
obtained at Udaipur Solar Observatory (USO) on 09 April 1997 at 09:32
UT with those taken by SOHO/MDI at 09:41 UT, it was found that all
the magnetic features matched very well in both the magnetograms. In
this paper we present the details of the instrument and examples
of observations.
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Title: A viewpoint on moderate size solar telescope
Authors: Bhatnagar, Arvind
1998BASI...26..407B Altcode:
No abstract at ADS
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Title: Solar Photospheric and Chromospheric Observations using a
Lithium Niobate Fabry-Perot ETALON
Authors: Debi Prasad, C.; Mathew, Shibu K.; Bhatnagar, Arvind;
Ambastha, Ashok
1998ExA.....8..125D Altcode:
We have made a narrow band tunable filter for solar observations using
a Lithium Niobate Fabry-Perot etalon. The 60 mm aperture etalon with
a free spectral range of 4.22 Å and finesse of 26 at lambda = 6122
Å has been procured from CSIRO, Australia. The wavelength tuning is
achieved by applying high voltage to the etalon substrate at the rate
of 0.45 Å per 1000 Volts. The filter is being used for imaging the
sun in Hα line and obtaining Doppler- and Magnetogram in CaI 6122 Å
line. In this paper, we present some initial observations carried out
with this filter at Udaipur Solar Observatory.
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Title: International collaboration - Global Oscillation Network Group
(GONG)
Authors: Bhatnagar, Arvind
1998BASI...26..157B Altcode:
No abstract at ADS
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Title: Solar Mass Ejection and Coronal Holes
Authors: Bhatnagar, Arvind
1998asct.conf..267B Altcode:
No abstract at ADS
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Title: Total solar eclipse observations MiG-25 at 80,000 ft.
Authors: Bhatnagar, A.; Mukerji, S.; Babu, Y. S.; Sehgal, N. K.;
Kamble, V. B.; Pandya, R. P.; Pandya, N. P.; Bhavsar, K. M.; Prajapati,
R. P.
1997KodOB..13..101B Altcode:
No abstract at ADS
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Title: Determination of times of second and third contact from flash
spectrum sequence.
Authors: Bhatnagar, A. K.
1997KodOB..13..119B Altcode:
No abstract at ADS
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Title: Observations of October 24, 1995 total solar eclipse from
ground and from Canberra Aircraft at 40,000 ft. altitude.
Authors: Bhatnagar, A.; Nijhavan, A. K.; Sehgal, N. K.; Kamble, V. B.;
Pandya, R. P.; Pandya, N. P.; Bhavsar, K. M.; Prajapati, R. P.
1997KodOB..13...99B Altcode:
No abstract at ADS
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Title: Travelling Interplanetary Disturbances Detected Using
Interplanetary Scintillation at 327 MHz
Authors: Janardhan, P.; Balasubramanian, V.; Ananthakrishnan, S.;
Dryer, M.; Bhatnagar, A.; McIntosh, P. S.
1996SoPh..166..379J Altcode:
Based on the advance predictions of two flare-generated shock fronts,
obtained from the Space Environment Centre (SEC, NOAA, Boulder),
observations of interplanetary scintillation (IPS) were carried out
with the Ooty Radio Telescope (ORT) on a grid of appropriately located
sources during the period 31 October to 5 November, 1992. Solar wind
velocities were derived by fitting model spectra to the observed spectra
and two travelling interplanetary disturbances were detected. Both
disturbances were traced back to an active region on the Sun which
was located close to a large coronal hole. The roles of flares and
coronal holes in producing such disturbances are examined and it is
shown that in the present case both the coronal hole and the active
region probably played key roles in generating the two IPS disturbances.
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Title: The Global Oscillation Network Group (GONG) Project
Authors: Harvey, J. W.; Hill, F.; Hubbard, R. P.; Kennedy, J. R.;
Leibacher, J. W.; Pintar, J. A.; Gilman, P. A.; Noyes, R. W.; Title,
A. M.; Toomre, J.; Ulrich, R. K.; Bhatnagar, A.; Kennewell, J. A.;
Marquette, W.; Patron, J.; Saa, O.; Yasukawa, E.
1996Sci...272.1284H Altcode:
Helioseismology requires nearly continuous observations of the
oscillations of the solar surface for long periods of time in
order to obtain precise measurements of the sun's normal modes of
oscillation. The GONG project acquires velocity images from a network
of six identical instruments distributed around the world. The GONG
network began full operation in October 1995. It has achieved a duty
cycle of 89 percent and reduced the magnitude of spectral artifacts by
a factor of 280 in power, compared with single-site observations. The
instrumental noise is less than the observed solar background.
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Title: The Global Oscillation Network Group Project
Authors: Leibacher, J. W.; Harvey, J. W.; Hill, F.; Hubbard, R.;
Kennedy, J. R.; Pintar, J. A.; Bhatnagar, A.; Kennewell, J. A.;
Marquette, W.; Patron, J.; Saa, O.; Yasukawa, E.; GONG Project Team
1996AAS...188.5301L Altcode: 1996BAAS...28..903L
The NSF-sponsored Global Oscillation Network Group (GONG) project
has developed and is operating a network of six velocity imaging
instruments around the world, and a data analysis system that can keep
up with the massive data flow, in support of a vigorous community that
shares in all aspects of this program to explore the structure and
dynamics of the solar interior. Data from the first three stations
were obtained starting in March 1995, and the full six-station
network became operational in early October 1995. The system noise
is below the solar background of incoherent surface motions, and the
overall data processing pipeline is maintaining cadence with the data
flood. The scientific objectives, design and performance of the network,
instrumentation, and data processing, and plans for the future will be
presented. The National Optical Astronomy Observatories are operated
by the Association of Universities for Research in Astronomy, Inc.,
under cooperative agreement with the National Science Foundation.
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Title: Solar mass ejections and coronal holes
Authors: Bhatnagar, Arvind
1996Ap&SS.243..105B Altcode: 1996IAUCo.154..105B
In this paper we present observations of two types of solar
mass ejections, which seem to be associated with the location of
coronal, holes. In the first type, a filament eruption was observed
near a coronal hole, which gave rise to a strong interplanetary
scintillations. as detected by IPS observations. In the second type,
several large scale soft X-ray ‘blow-outs’ were observed in the
YOHKOH SXT X-ray movies, in all the cases they erupted from or near
the boundary of coronal holes and over the magnetic neutral line. It
is proposed that the open magnetic field configuration of the coronal
hole provides, the necessary field structure for reconnection to
take place, which in turn is responsible for filament eruption, from
relatively lower heights. While, in the case of X-ray ‘blow-outs’,
the reconnection takes place at a greater height, resulting in high
temperature soft X-ray emission visible as X-ray ‘blow-outs’.
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Title: Transient Phenomena in the Energetic Behind-the-Limb Solar
Flare of September 29, 1989
Authors: Bhatnagar, A.; Jain, R. M.; Burkepile, J. T.; Chertok, I. M.;
Magun, A.; Urbarz, H.; Zlobec, P.
1996Ap&SS.243..209B Altcode: 1996IAUCo.154..209B
The powerful cosmic ray flare of Sept. 29, 1989 occurred behind
the limb and was observed over a wide spectral range. The analysis
of optical, radio, and other relevant data suggest two phases of
energy release. After an impulsive phase a prolonged post eruption
energy release occurred in an extended region of the corona following
the eruption of a large coronal mass ejection (CME). This phase is
responsible for numerous coronal and interplanetary phenomena including
the ground-level increase of cosmic rays.
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Title: Solar Observations Using Lithium Niobate Fabry-Perot ETALON
Authors: Bhatnagar, A.; Prasad, C. D.; Mathew, S. K.
1995JApAS..16..384B Altcode:
No abstract at ADS
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Title: Two-Dimensional Velocity Field Measurement of Eruptive
Prominence Observed 1993JAN14
Authors: Bhatnagar, A.; Tripathy, S. C.
1995JApAS..16..382B Altcode:
No abstract at ADS
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Title: Imaging Polarimetry of Comet Austin
Authors: Joshi, U. C.; Chauhan, J. S.; Deshpande, M. R.; Sen, A. K.;
Bhatnagar, A. K.
1995JApAS..16..395J Altcode:
No abstract at ADS
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Title: Soft X-ray Blow-outs and Coronal Holes
Authors: Bhatnagar, A.
1995SPD....26..617B Altcode: 1995BAAS...27..965B
No abstract at ADS
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Title: A Graphical User Interface for a Development Environment
(GUIDE)
Authors: Bhatnagar, A.
1995ASPC...77..109B Altcode: 1995adass...4..109B
“GUIDE” (Graphical User Interface for a Data Environment) is an
interactive IDL widget-based package that enables users to retrieve
selected sets of satellite instrument data and perform various types of
graphical analyses on them, without writing a specialized program. GUIDE
simplifies the task of laying out multiple plots on a page by (1) using
a page-editor to define and laying out multiple “panels” which contain
the “plot objects”, and (2) integrating data retrieval functions.
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Title: The Global Oscillation Network Group Site Survey - Part Two
Authors: Hill, Frank; Fischer, George; Forgach, Suzanne; Grier,
Jennifer; Leibacher, John W.; Jones, Harrison P.; Jones, Patricia
B.; Kupke, Renate; Stebbins, Robin T.; Clay, Donald W.; Ingram,
Robert E. L.; Libbrecht, Kenneth G.; Zirin, Harold; Ulrichi, Roger
K.; Websteri, Lawrence; Hieda, Lester S.; Labonte, Barry J.; Lu,
Wayne M. T.; Sousa, Edwin M.; Garcia, Charles J.; Yasukawa, Eric
A.; Kennewell, John A.; Cole, David G.; Zhen, Huang; Su-Min, Xiao;
Bhatnagar, Arvind; Ambastha, Aashok; Al-Khashlan, Abdulrahman Sa'ad;
Abdul-Samad, Muhammad-Saleh; Benkhaldoun, Zouhair; Kadiri, Samir;
Sánchez, Francisco; Pallé, Pere L.; Duhalde, Oscar; Solis, Hernan;
Saá, Oscar; González, Ricardo
1994SoPh..152..351H Altcode:
The Global Oscillation Network Group (GONG) Project will place a
network of instruments around the world to observe solar oscillations as
continuously as possible for three years. The Project has now chosen the
six network sites based on analysis of survey data from fifteen sites
around the world. The chosen sites are: Big Bear Solar Observatory,
California; Mauna Loa Solar Observatory, Hawaii; Learmonth Solar
Observatory, Australia; Udaipur Solar Observatory, India; Observatorio
del Teide, Tenerife; and Cerro Tololo Interamerican Observatory, Chile.
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Title: Imaging polarimetry of comet Austin.
Authors: Joshi, U. C.; Chauhan, J. S.; Deshpande, M. R.; Sen, A. K.;
Bhatnagar, A. K.
1993BASI...21..651J Altcode:
Comet Austin (1989c<SUB>1</SUB>) was observed during Apr and May 1990
when its phase was between 106° and 110°. No unusual activity in
the form of jet is seen in the polarization map. Polarization is low
near the nucleus and high (≡16%) in the outer region, suggesting
segregation of grains.
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Title: Magnetic Field Configuration in H alpha Flare Loops and
Flaring Arches
Authors: Bhatnagar, A.; Srivastava, N.
1993ASPC...46..351B Altcode: 1993IAUCo.141..351B; 1993mvfs.conf..351B
No abstract at ADS
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Title: Book reviews
Authors: Bhatnagar, Arvind; Achterberg, A.; de Jager, Cornelis;
Kaufmann, P.; van Gent, R. H.; Rodríguez, L. F.
1992SSRv...59..407B Altcode:
No abstract at ADS
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Title: Book-Review - Advances in Geosciences
Authors: Schroeder, W.; Bhatnagar, A.
1992SSRv...59..409S Altcode:
No abstract at ADS
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Title: Filament Eruptions Flaring Arches and Eruptive Flares
Authors: Bhatnagar, A.; Ambastha, A.; Srivastava, N.
1992LNP...399...59B Altcode: 1992esf..coll...59B; 1992IAUCo.133...59B
Several cases of erupting filaments showing distinctly their feet
have been studied. Role of the feet and their anchorage with the
photosphere in maintaining filament stability is established; apart
from the footpoint separation and height criteria. Further, a homologous
series of more energetic events, namely, the flaring arches and eruptive
flares of March 5-7, 1991, suggest a repetitive restoration of magnetic
field conditions and energy build-up within a day. High resolution
H-alpha observations of these events indicate that large amount of
ejected material was siphoned out from the chromosphere through,
the top. of a low-lying compact emission loop within the active region.
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Title: Helically twisted prominence eruption event of 1979 March 11.
Authors: Srivastava, N.; Ambastha, A.; Bhatnagar, A.
1991BASI...19..208S Altcode:
No abstract at ADS
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Title: Results of GONG site survey program at the Udaipur Solar
Observatory.
Authors: Ambastha, A.; Bhatnagar, A.; Srivastava, N.; Jain, R. M.;
Gupta, S. K.; Sharma, R.; Agrawal, G.
1991BASI...19..211A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Cosmic ray flare of 1989 September 29.
Authors: Jain, R.; Bhatnagar, A.; Sharma, R.
1991BASI...19..208J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: GONG site evaluation program at Udaipur Solar Observatory
Authors: Ambastha, Ashok; Bhatnagar, Arvind; Jain, Rajmal; Srivastava,
Nandita; Gupta, Sudhir; Sharma, Richa; Agrawal, Gopal; Kumawat,
Vishnu; Hill, Frank; Fischer, George
1991BASI...19..215A Altcode:
The Global Oscillations Network Group (GONG) project to study the
internal structure and dynamic of the sun is discussed. The GONG project
will measure waves that penetrate throughout the sun's core. Power
spectra of the monthly average transparency for each calendar month were
obtained and analyzed. The resulting clear and dark time distributions
and monthly average extinction coefficients and transparency power
spectra are shown and discussed. The various possible networks from
the candidate sites participating in the GONG project are compared.
---------------------------------------------------------
Title: Expedition to Mauritius for observing supernova 1987A
Authors: Babu, G. S. D.; Bhatnagar, A. K.; Narayanan, R. S.
1991BASI...19..251B Altcode:
A two-member expedition to the island country of Mauritius was
organized in February/March 1988 to observe the supernova 1987A
photometrically. The only occasion when one complete set of observations
of SN 1987A could be obtained was on 1988 March 4.89 (UT). In that
one observation, the brightest part of the supernova was found to be
in the H-alpha region followed by forbidden O I and the R band. The
transformation coefficients obtained for this setup are presented.
---------------------------------------------------------
Title: Evolution of helically twisted prominence structures of March
11, 1979
Authors: Srivastava, N.; Ambastha, A.; Bhatnagar, A.
1991SoPh..133..339S Altcode:
Helical structures are generally associated with many eruptive solar
prominences. Thus, study of their evolution in the solar atmosphere
assumes importance. We present a study of a flare-associated
erupting prominence of March 11, 1979, with conspicuous helically
twisted structure, observed in Hα line center. We have attempted to
understand the role played by twisted force-free magnetic fields in this
event. In the analysis, we have assumed that the helical structures
visible in Hα outline the field lines in which prominence tubes are
embedded. Untwisting of observed prominence tubes and later, formation
of open prominence structures provide evidence of restructuring of the
magnetic field configuration over the active region during the course
of prominence eruption. Temporal evolution of the force-free parameter
α is obtained for two main prominence tubes observed to be intertwined
in a rope-like structure. Axial electric currents associated with the
prominence tubes are estimated to be of the order of 10<SUP>11</SUP>
A which decreased with time. Correspondingly, it is estimated that the
rate of energy release was ≈ 10<SUP>28</SUP> erg s<SUP>−1</SUP>
during the prominence eruption.
---------------------------------------------------------
Title: Effect of the New Equinox Definition on the Zero-Point of
Longitude of the Indian Calendar
Authors: Bhatnagar, A. K.
1990IAUS..141..186B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Footpoints of Giant Arches
Authors: Martin, Sara F.; Svestka, Zdenek F.; Bhatnagar, Arvind
1989SoPh..124..339M Altcode:
We have detected chromospheric footpoints of the giant post-flare
coronal arches discovered by HXIS a few years ago. Hα photographs
obtained at Big Bear and Udaipur Solar Observatories show chromospheric
signatures associated with 5 sequential giant arch events observed
in the interval from 6 to 10 November, 1980. The set of footpoints at
one end of the arches consists of enhancements within a plage at the
northeast periphery of the active region and the set of footpoints at
the other end of the arch consists of brightenings of the chromosphere
south of the active region. Both sets of footpoints show very slow
brightness variations correlated in time with the brightness variations
of the X-ray arches. Current-free modelling of the coronal magnetic
field by Kopp and Poletto (1989), based on a Kitt Peak magnetogram,
confirms the identification of the two sets of footpoints by showing
magnetic field lines connecting them.
---------------------------------------------------------
Title: On impulsive and gradual optical solar flares.
Authors: Bhatnagar, A.; Ambastha, A.; Jain, R. M.; Srivastava, N.
1989sasf.confP.207B Altcode: 1988sasf.conf..207B; 1989IAUCo.104P.207B
A comparative study of H-alpha intensity and area development of several
flares is presented in an attempt to investigate characteristic features
of various types of optical solar flares.
---------------------------------------------------------
Title: Proceedings of the Indo-US Workshop on Interplanetary
Scintillations and Solar Activity
Authors: Bhonsle, R. V.; Bhatnagar, A.; Dryer, M.; Alurkar, S. K.;
Ambastha, A.; Vats, H. O.
1988issa.conf.....B Altcode:
Under the Indo-US sub-commission on science and technology, the
Department of Science and technology had approved two projects for
the study of solar activity and interplanetary medium in 1987. The
objectives of these projects include the study of solar activity using
optical technique and solar wind using IPS technique. These proceedings
are an attempt to capture some of the highlights of the deliberations of
the workshop organised in Udaipur and Ahmedabad during January-February
1988 to have mutual discussions by Indian and American sides on these
inter-related projects.
---------------------------------------------------------
Title: Sunspot proper motions in active region NOAA 2372 and its
flare activity during SMY period of 1980 April 4-13
Authors: Ambastha, Ashok; Bhatnagar, Arvind
1988JApA....9..137A Altcode:
Solar active region NOAA 2372 was observed extensively by the Solar
Maximum Mission (SMM) satellite and several ground-based observatories
during 1980 April 4 - 13 in the Solar Maximum Year. The authors have
studied photospheric and chromospheric observations of this active
region together with Marshall Space Flight Center magnetograms and
X-ray data from HXIS aboard the SMM satellite. In particular, they
discuss the relationship of the flare-productivity with sunspot proper
motions and emergence of new regions of magnetic flux in the active
region from its birth to its disappearance at the W-limb.
---------------------------------------------------------
Title: Book-Review - Solar and Lunar Eclipses during 1986-2010AD
Authors: Ballabh, G. M.; Bhatnagar, A. K.
1988BASI...16...52B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Optical observations of the Sun.
Authors: Bhatnagar, A.
1988KodOB...9..225B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Motion in NOAA:2372 and Associated Flare Activity
during Solar Maximum Year Period 1980APR4-13
Authors: Ambastha, A.; Bhatnagar, A.
1987BASI...15...19A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: System of Astronomical Constants in Hindu Astronomy
Authors: Bandyopadhyay, A.; Bhatnagar, A. K.
1987hooa.coll...85B Altcode: 1987IAUCo..91...85B
Astronomical constants such as the length of the solar year, sidereal
and synodic periods of revolutions of the Moon and five brighter
planets have been computed using the system of astronomy in ancient
and mediaeval India and a comparison made with their modern values.
---------------------------------------------------------
Title: Optical aspects of solar activity.
Authors: Bhatnagar, A.
1986KodOB...6....1B Altcode:
A review of optical observations of some solar phenomena is
presented. From the photospheric observations of the birth, growth and
decay of pores, spots and sunspot groups and associated velocity and
magnetic field structure have been discussed. Some dynamic phenomena
associated with sunspots are also discussed. High resolution H-alpha
chromospheric observations offer remarkable advantage to understand
the evolution of solar activity and the associated magnetic field
development and decay.
---------------------------------------------------------
Title: Photographic atlas of the solar chromosphere
Authors: Ambastha, Ashok; Bhatnagar, A.
1985pasc.book.....A Altcode: 1985QB528.A45......
In this atlas, we present sequences of chromospheric photographs
of some typical solar phenomena observed during 1976-84, through a
15-cm aperture refractor in conjunction with a Halle narrow passband
H-alpha filter mounted on a 4.5 m solar spar at the Udaipur Solar
Observatory, Udaipur, India. The solar photographs are grouped to
present characteristics of solar flares, mass ejections, filament
activations, etc. The purpose of this photographic atlas is to
apprise new entrants, students, and researchers in solar physics,
both observational and theoretical, with the variety of intricate
active phenomena that occur on the Sun's chromosphere.
---------------------------------------------------------
Title: Evidence of atmospheric gravity waves produced during the 11
June 1983 total solar eclipse
Authors: Seykora, E. J.; Bhatnagar, A.; Jain, R. M.; Streete, J. L.
1985Natur.313..124S Altcode:
During a solar eclipse the Moon's shadow moves at supersonic speed
through the Earth's atmosphere. Chimonas and Hines<SUP>1,2</SUP>
suggested that the resultant cooling of the atmosphere would generate
a bow wave of atmospheric gravity waves, which may be detectable as a
travelling ionospheric disturbance or as a ground-level atmospheric
pressure variation. Although the evidence for gravity waves in the
ionosphere from a solar eclipse is still weak, they may have been
detected<SUP>3</SUP>. Ground-level pressure changes during solar
eclipses occur near the region of totality<SUP>4</SUP>, but the
measured wave velocity and period do not agree with that of the
predicted disturbance<SUP>5,6</SUP>. We now report the detection of
a ground-level pressure wave detected at three stations in India and
one station in Java, Indonesia. These data may provide the first
direct observation of eclipse generated gravity waves over a very
long range. The most distant station in India was 6,600 km from the
eclipse centre line. The microbarometer recordings indicate that a
wave disturbance was recorded at each station with a quasi-period of
~4 h and a wave velocity of ~320 m s<SUP>-1</SUP>.
---------------------------------------------------------
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: Optical Observations of Solar Flares
Authors: Bhatnagar, A.
1984stp..conf...73B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: U-shaped type II solar radio bursts associated with the 1980
March 28 flare
Authors: Markeev, A. K.; Formichev, V. V.; Chertok, I. M.; Bhatnagar,
A.; Jain, R. M.; Shelke, R. N.; Bhonsle, R. V.
1983BASI...11..318M Altcode:
Observations of the 1980 March 28, 2B flare in optical, radio microwave
and metric and X-ray wavelengths are presented. In the dynamic radio
spectrum, unusual and rare U-shaped type II radio bursts associated
with this flare have been observed. The normal type II bursts display
negative frequency drift, due to the flare-triggered shock wave
travelling outwards in the solar corona. But in this case the type
II emission first showed the usual negative frequency drift, and then
after reaching a plateau level, showed a positive drift, thus giving
the shape of an inverted "U". The authors propose a model for this
type II emission.
---------------------------------------------------------
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: Mass ejections associated with flare behind the solar limb
on 1978 December 20.
Authors: Bhatnagar, A.; Jain, R. M.; Shelke, R. N.
1982BASI...10Q..36B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photoelectric Observations of Shadow Bands during 16 February
1980 Total Solar Eclipse from Japal-Rangapur Observatory
Authors: Bhatnagar, A.; Jadhav, D. B.; Jain, R. M.; Shelke, R. N.;
Purohit, S. P.; Bhonsle, R. V.; Pratap, R.
1982tsef.conf..260B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Study of optical, radio and X-ray emissions associates with
the solar flare of 1980 March 28.
Authors: Bhatnagar, A.; Jain, R. M.; Shelke, R. N.
1982BASI...10R..36B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photoelectric observations of shadow bands during 16 February
1980 total solar eclipse from Japal-Rangapur Observatory.
Authors: Bhatnagar, A.; Jadhav, D. B.; Jain, R. M.; Shelke, R. N.;
Purohit, S. P.; Bhonsle, R. V.; Pratap, R.
1982PINSA..48..260B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations for Coronal Velocity Field and Colour Movie of
Flash Spectrum during Total Solar Eclipse of 16 February 1980
Authors: Bhatnagar, A.; Jadhav, D. B.; Jain, R. M.; Shelke, R. N.;
Purohit, S. P.
1982tsef.conf...29B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations for coronal velocity field and colour movie of
flash spectrum during total solar eclipse of 16 February 1980.
Authors: Bhatnagar, A.; Jadhav, D. B.; Jain, R. M.; Shelke, R. N.;
Purohit, S. P.
1982PINSA..48...29B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of timings of the four contacts.
Authors: Bandyopadhyay, A.; Bhatnagar, A.; Sridharan, S.; Dasgupta, B.
1981otse.conf...48B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Coronal Velocity Field Flash Spectrum and
Shadow Bands during Solar Eclipse 1980
Authors: Bhatnagar, A.; Jadhav, D. B.; Jain, R. M.; Shelke, R. N.;
Purohit, S. P.
1980BASI....8..129B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar Flares in Boulder Active Region No. 2372 during April
7-13 1980
Authors: Bhatnagar, A.; Jadhav, D. B.; Jain, R. M.; Shelke, R. N.;
Purohit, S. P.
1980BAAS...12..899B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flare associated eruptive prominence activity of February
1, 1979
Authors: Bhatnagar, A.; Jain, R. M.; Jadhav, D. B.; Shelke, R. N.;
Bhonsle, R. V.
1980IAUS...91..235B Altcode:
The ascending fountain-type prominence of February 1, 1979 associated
with solar flare activity is discussed. The fountain prominence rose
to 180,000 km above the solar surface and gave rise to a number of
ascending loops and helical structures. The observations show that
the plasma rising from the flare active region starts as bright and
dense areas of plasma permeated with a complex magnetic field. Due
to the flare shock wave, the dense plasma ascends rapidly, carrying
with it the magnetic field. As the spray plasma ascends and expands,
the observed helical loop structures open up to manifest the magnetic
field configuration.
---------------------------------------------------------
Title: The Veil Emission and Associated Radio Events
Authors: Bhatnagar, A.; Jadhav, D. B.; Shelke, R. N.; Jain, R. M.
1979BASI....7R.120B Altcode:
No abstract at ADS
---------------------------------------------------------
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: The orbit of the Dhajala meteorite
Authors: Ballabh, G. M.; Bhatnagar, A.; Bhandari, N.
1978Icar...33..361B Altcode:
Observations of the trail caused by the meteorite which fell around
Dhajala, Gujarat (India), on 28 January 1976 have been used to compute
the probable orbit of the meteoroid in space. The cosmic ray effects in
the meteorite fragments indicate high mass ablation (≳90%), suggesting
a high velocity (≳20 km/sec) of entry into the Earth's atmosphere. The
atmospheric trajectory is reasonably well documented and its deviation
from the projected ground fallout can be understood in terms of the
ambient wind pattern. The apparent radiant of the trail was at a point
in the sky with right ascension 165°, declination +60°. Considering
the errors in estimating the radiant, we get a range of orbits with a =
2.3 ± 0.8 AU, e = 0.6 ± 0.1, and i = 28 ± 4° with the constraints
of a ⩾ 1.5 AU and V<SUB>∞</SUB> < 25 km/sec (which causes nearly
complete evaporation of the meteoroid). Taking V<SUB>∞</SUB> = 21.5
lm/sec as indicated by the measured mass ablation of the meteorite,
the orbital elements are deduced to be a = 1.8 AU, e = 0.59, i =
27°.6, ω = 109°.1, Ω = 307°.8, and q = 0.74 .
---------------------------------------------------------
Title: Determination of some astronomical constants by ancient
Indian astronomers.
Authors: Bandyopadhyay, A.; Bhatnagar, A. K.
1978BASI....6Q..51B 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
---------------------------------------------------------
Title: Vedshala, Ahmedabad. Annual report for the year 1975.
Authors: Bhatnagar, A.
1976BASI....4...61B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Dhajala Meteorite Shower
Authors: Bhandari, N.; Lal, D.; Trivedi, J. R.; Bhatnagar, A.
1976Metic..11..137B Altcode:
Observations of the trail of the Dhajala meteorite, which fell on
Jan. 28, 1976, are reported together with results of a preliminary
examination of the fragments. The trail was observed over a wide-spread
area and had an apparent magnitude of -20. The fallout area was highly
elliptical. The size of the 300 fragments, found over an area of about
50 sq km, increased systematically with the distance from the first
impact point. Chemical and mineralogical studies indicate that the
chondrite belongs to the H group, possibly type 3 or 4. The cosmic ray
exposure age is about 7 million years. Cosmic ray density measurements
and the activity levels of cosmic ray produced radionuclides suggest
that the pre-atmospheric size of the meteoroid was about a meter.
---------------------------------------------------------
Title: The orbit of the Dhajala meteorite.
Authors: Ballabh, G. M.; Bhatnagar, A.; Bhandari, N.
1976BASI....4R..79B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Report on the new solar observatory and H-alpha observations
of the sun.
Authors: Bhatnagar, A.; Ballabh, G. M.
1975BASI....3...27B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Video-magnetograph observations of moving magnetic features
around sunspots.
Authors: Michalitsanos, A. G.; Bhatnagar, A.
1975BASI....3...27M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Large-Scale Moving Magnetic Features Near
Sunspots
Authors: Michalitsanos, A. G.; Bhatnagar, A.
1975ApL....16...43M Altcode:
High time and spatial resolution magnetograms taken with a longitudinal
video magnetograph show the systematic motion of large crescents and
ridges of magnetic field at the outer penumbral boundary of a large
complex sunspot group. Both ridges and crescents are resolved into
knots of flux which are typically 2 arc sec to 3 arc sec in extent,
and which move in unison with velocities in the range of 0.2 to 0.3
km/sec. Over a four-hour period, these ridges of magnetic field,
which are predominantly of opposite polarity to the parent sunspot,
are observed to move over distances of from 4 arc sec to 6 arc sec,
and merge with existing outlying magnetic fields. It is suggested that
large-scale crescents or ridges of magnetic field emerge periodically at
penumbral boundaries. Preliminary models for the transport of magnetic
fields around sunspots are proposed.
---------------------------------------------------------
Title: Site survey for an infrared observatory.
Authors: Bhatnagar, A.
1974imra.conf...25B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Investigation of Two Delta Scuti Suspects
Authors: Bhatnagar, A. K.; Gupta, S. K.
1973IBVS..778....1B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Light Variations of 59 Piscium
Authors: Gupta, S. K.; Bhatnagar, A. K.
1972IBVS..751....1G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Sunspot Umbral Velocity Oscillations
Authors: Bhatnagar, Arvind; Livingston, W. C.; Harvey, J. W.
1972SoPh...27...80B Altcode:
Sunspot umbral molecular lines have been used to look for the
oscillatory velocities in the umbra. Power spectrum analysis showed
conspicuous power for periods in the range between 448 and 310 s. The
maximum peak-to-peak amplitude of the umbral oscillatory velocity
component is observed to be in the order of 0.5 km s<SUP>−1</SUP>.
---------------------------------------------------------
Title: Observations of Sunspot Umbral Velocity Oscillations
Authors: Bhatnagar, A.; Livingston, W. C.; Harvey, J. W.
1972BAAS....4R.378B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Intensity Oscillation in Hα-Fine Structure
Authors: Bhatnagar, Arvind; Tanaka, Katsuo
1972SoPh...24...87B Altcode:
Using a new technique of directly measuring the intensity variation
from the 16 mm time-lapse filtergram movies taken in the blue wing and
in the line center of Hα, we found periodic intensity oscillations in
the center of Hα-supergranulation network, in rosette centers and in
plage granules. The oscillatory period of intensity in the network is of
the order of 170 ± 44 seconds while in regions of stronger magnetic
field, such as in plages and in rosettes, the period was found to
be longer, on the order of 300 ± 50 seconds. It is suggested that
observed intensity oscillation in the rosette center is related to
the shooting out of dark mottles from rosettes. Oscillatory intensity
fluctuations have been also observed in the sunspot umbra.
---------------------------------------------------------
Title: Two-Dimensional Observations of the Velocity Fields in and
around Sunspots
Authors: Sheeley, N. R., Jr.; Bhatnagar, A.
1971SoPh...19..338S Altcode:
Doppler spectroheliograms of sunspots and their surroundings have
been obtained with a spatial resolution approaching one second
of arc and a time resolution of 20 s per frame. Observations of 5
sunspots, located 18°, 45°, 56°, 60° and 72° from the disk center
respectively, showed considerable long-lived fine structure and, in
particular, indicated the following: The Evershed outflow terminated
in spoke-like structures that constitute the ragged outer boundary of
the penumbra. Some of these spokes extended more than 8000 km beyond
the average outer boundary.
---------------------------------------------------------
Title: Measurements of the Oscillatory and Slowly-Varying Components
of the Solar Velocity Field
Authors: Sheeley, N. R., Jr.; Bhatnagar, A.
1971SoPh...18..379S Altcode:
Spectroheliograms with high spatial resolution are presented to
illustrate the decomposition of the solar velocity field into its
oscillatory and slowly-varying components. An analysis of data obtained
in the lines FEIλ 5434 and FeIIλ 4924 yield essentially the same
principal results: Spectroheliograms of the oscillatory component
have a mottled appearance of rising and falling elements ranging from
2000 km to 3000 km in size. These elements oscillate vertically with
a period in the range 275-300 s and an amplitude of 0.5 km/s. Although
most oscillations last two cycles some have been observed for as many
as four cycles.
---------------------------------------------------------
Title: The Reduction of the Solar Velocity Field into Its Oscillatory
and Slowly-Varying Components
Authors: Sheeley, N. R., Jr.; Bhatnagar, A.
1971SoPh...18..195S Altcode:
Spectroheliogram movies of the solar velocity field have been made in
the λ4924 line of FeII with a time resolution of 20 sec/frame and a
spatial resolution in the range 1-2 sec of arc. A conventional doppler
movie has been used to generate two additional movies which show
the slowly-varying and oscillatory components of the velocity field
separately. A basic result is the simplicity of the field patterns
into which the relatively complex velocity field can be decomposed.
---------------------------------------------------------
Title: On the Oscillatory Velocity Field in Sunspot Atmosphere
Authors: Bhatnagar, A.
1971SoPh...18...40B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the oscillatory velocity field in sunspot atmosphere.
Authors: Bhatnagar, A.
1971BAAS....3R.259B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fine-Scan Velocity and Magnetic- field Measurements in Solar
Active Regions
Authors: Bhatnagar, A.
1971SoPh...16...40B Altcode:
Fine scan (5″ × 5″ aperture) simultaneous Doppler and magnetograms
have been obtained over solar active regions near the central meridian
passage. Besides the mainly horizontal Evershed motion in sunspots,
there appears a conspicuous descending motion over all active regions. A
comparison of Hα-filtergrams with the fine scan magnetograms shows that
dark filaments generally lie along the neutral longitudinal magnetic
zone, while the Hα-fibrils lie along the field lines, joining regions
of opposite polarity.
---------------------------------------------------------
Title: On the polar coronal rays of the sun.
Authors: Bhatnagar, A.; Raheem, K. C. A.
1970KodOB.204..189B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Spectrum of Granular and Intergranular Regions
Authors: Howard, R.; Bhatnagar, A.
1969SoPh...10..245H Altcode:
A very high quality wiggly-line spectrogram was analyzed by making
high-resolution spectral scans of numerous small solar features. An
attempt from the line profiles to detect a magnetic field difference
between the granular and intergranular regions, resulted in a field
increase of 20 ± 15 G in the darker regions of the granular field. Line
width increases apparently due to small-scale turbulent velocities are
seen in the darker regions. It is postulated that in general darker
regions show increased turbulent velocities. Conspicuous asymmetries in
line profiles are seen in dark intergranular regions. It is suggested
that these are the result of velocity gradients in the downward flow
of material. An ionized Cr line showed a conspicuous increase in
equivalent width in the darker regions of the granular field, thus
indicating a decrease in electron pressure in these areas.
---------------------------------------------------------
Title: The Difference between the Spectra of Granular and
Intergranular Regions
Authors: Howard, R.; Bhatnagar, A.
1969BAAS....1T.279H Altcode:
No abstract at ADS
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Title: A New Technique to Obtain Solar-Velocity Maps Directly in
One Spectroheliogram
Authors: Bhatnagar, A.; Stenflo, J. O.
1969BAAS....1S.273B Altcode:
No abstract at ADS
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Title: A Method to obtain a Solar Velocity Map Directly in One
Spectroheliogram
Authors: Bhatnagar, A.; Stenflo, J. O.
1969SoPh....7..329B Altcode:
No abstract at ADS
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Title: The solar corona of July 20, 1963.
Authors: Bappu, M. K. V.; Bhatnagar, A.
1969KodOB.190.....B Altcode:
No abstract at ADS
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Title: Monochromatic polarization measures of comet Ikeya-Seki (1965f)
Authors: Bappu, M. K. V.; Sivaraman, K. R.; Bhatnagar, A.; Natarajan,
V.
1967MNRAS.136...19B Altcode:
Monochromatic measures of polarization of Comet Ikeya-Seki (I 965f)
at 3 890 A, 4 300 A, 4 740 A and 5 875 A are described. The relative
contributions of emission and continuum to radiation transmitted by
the fflters at 3 890 A and 4740 A are evaluated. The polarization
at phase angle 900 of the CN (o,o) band is 6'9% while that of the C2
(1,0) band is %, in close agreement with the theoretical values for
resonance fluorescence. The polarization value of the continuum is
% at phase angle 900, while for the same phase angle, a measure of
the polarization in the tail, 3' away from the head, is 13' 6%. The
agencies responsible for the continuum in both head and tail are likely
to have a difference in the major constituent. The role of ices and
iron particles as scattering agencies is discussed. -
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Title: Variation in Continuum Brightness and Equivalent Widths of
Lines in Sunspot Penumbrae
Authors: Bhatnagar, A.
1966ZA.....64..460B Altcode:
No abstract at ADS
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Title: The Evershed effect in sunspots
Authors: Bhatnagar, Arvind
1964PhDT.......105B Altcode:
No abstract at ADS
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Title: The influence of superflares in the H alpha striation pattern
Authors: Bappu, M. K. V.; Bhatnagar, A.; Punetha, L. M.
1962Obs....82..192B Altcode:
No abstract at ADS
