Author name code: bhatnagar ADS astronomy entries on 2022-09-14 author:("Bhatnagar, Arvind" OR "Bhatnagar, Aditi") ------------------------------------------------------------------------ Title: Sunspot Cycle 25 is Brewing: Early Signs Herald its Onset Authors: Nandy, Dibyendu; Bhatnagar, Aditi; Pal, Sanchita Bibcode: 2020RNAAS...4...30N Altcode: No abstract at ADS Title: Why Study the Sun? Authors: Bhatnagar, Arvind Bibcode: 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. Title: Fundamentals of Solar Astronomy Authors: Bhatnagar, Arvind; Livingston, William; Holman, Gordon D. Bibcode: 2006PhT....59j..66B Altcode: No abstract at ADS Title: Fundamentals of Solar Astronomy Authors: Bhatnagar, Arvind; Livingston, William Bibcode: 2005fsa..book.....B Altcode: No abstract at ADS Title: Fundamentals Of Solar Astronomy Authors: Bhatnagar, Arvind; Livingston, William Bibcode: 2005WSSAA...6.....B Altcode: No abstract at ADS Title: Variations in Oscillation Frequencies From Minimum to Maximum of Solar Activity Authors: Jain, Kiran; Bhatnagar, A. Bibcode: 2003SoPh..213..257J Altcode: The temporal variation in intermediate-degree-mode frequencies is analysed using helioseismic data which cover the minimum to the maximum phase of the current solar cycle. To study the variation in detail, the measured frequency shifts of f and p modes are decomposed into two components, viz., oscillatory and non-oscillatory. The f-mode frequencies exhibit prominent oscillatory behavior in contrast to p modes where the oscillatory nature of the frequencies is not clearly seen. Also, the oscillatory part contributes significantly to the f-mode frequencies while p-mode frequencies have maximum contribution from the non-oscillatory part. The amplitude of both oscillatory and non-oscillatory parts is found to be a function of frequency. The non-oscillatory part is observed to have a strong correlation with solar activity. Title: Instrumentation and Observational Techniques in Solar Astronomy Authors: Bhatnagar, A. Bibcode: 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. Title: Lectures on Solar Physics Authors: Antia, H. M.; Bhatnagar, A.; Ulmschneider, P. Bibcode: 2003LNP...619.....A Altcode: 2003lsp..conf.....A No abstract at ADS Title: Variation of solar irradiance and mode frequencies during Maunder minimum Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C. Bibcode: 2002Ap&SS.281..761B Altcode: 2002astro.ph..1025B Using the sunspot numbers reported during the Maunder minimum and the empirical relations between the mode frequencies and solar activity indices, the variations in the total solar irradiance and 10.7 cm radio flux for the period 1645 to 1715 is estimated. We find that the total solar irradiance and radio flux during the Maunder minimum decreased by 0.19% and 52% respectively, as compared to the values for solar cycle 22. Title: How Good are the Predictions for Oscillation Frequencies? Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A. Bibcode: 2002SoPh..206..213J Altcode: 2002astro.ph..1024J We have used available intermediate degree p-mode frequencies for solar cycle 23 to check the validity of previously derived empirical relations for frequency shifts (Jain et al., 2000). We find that the calculated and observed frequency shifts during the rising phase of cycle 23 are in good agreement. The observed frequency shift from minimum to maximum of this cycle as calculated from MDI frequency data sets is 251±7 nHz and from GONG data is 238±11 nHz. These values are in close agreement with the empirically predicted value of 271±22 nHz. Title: Solar rotation rate from minimum to maximum of activity cycle Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.; Kumar, Brajesh Bibcode: 2001BASI...29..239J Altcode: Using helioseismic data from SOI/MDI and GONG for the current solar cycle 23, from solar minimum to near maximum phase, we report here on the temporal variation of the rotation rate. Title: Analysis of hysteresis effect in p-mode frequency shifts and solar activity indices Authors: Tripathy, S. C.; Kumar, Brajesh; Jain, Kiran; Bhatnagar, Arvind Bibcode: 2001SoPh..200....3T Altcode: 2001astro.ph..3129T Using intermediate degree p-mode frequency datasets for solar cycle 22, we find that the frequency shifts and magnetic indices show a `hysteresis' phenomenon. It is observed that the magnetic indices follow different paths for the ascending and descending phases of the solar cycle, as the descending path always seems to follow a higher track than the ascending one. However, for the radiative indices, the paths cross each other indicating phase reversal. Title: Temporal evolution of f-mode frequencies and radius Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A. Bibcode: 2001ESASP.464...95J Altcode: 2001astro.ph..3163J; 2001soho...10...95J We have analysed temporal evolution in centroid frequencies and splitting coefficients of solar f-modes obtained from MDI/SOHO. The data were divided into 20 sets covering a period from May 1, 1996 to August 31, 2000. The variation in frequencies is estimated to be 68 nHz over the period of four years which includes the rapidly rising phase of the solar cycle 23. This change is much smaller than that observed for p-mode frequencies. It is also noticed that the f-mode frequencies appear to be weakly correlated with solar activity indices as compared to the p-mode frequencies. We have also inferred the relative change in the solar radii and notice a 1 year periodicity which may be associated with the solar cycle variation. Title: On the solar rotation rate in the upper convection zone Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A. Bibcode: 2001ESASP.464..641J Altcode: 2001soho...10..641J; 2001astro.ph..3164J We present results on variation in rotation rate in the upper convection zone using data from GONG and MDI/SOHO covering a period of more than four years. We find that the first few odd-order splitting coefficients vary systematically with the solar cycle. The rotation rate near the solar surface calculated from analytical methods agrees well with that of inversion techniques. The residual rotation rate in the outer layers seem to be correlated with the solar activity. Title: Solar Cycle-induced Variations in GONG P-Mode Frequencies and Splittings Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A. Bibcode: 2000ApJ...542..521J Altcode: 2000astro.ph..6015J We have analyzed the recently available Global Oscillation Network Group (GONG) p-mode frequencies and splitting coefficients for a period of three and a half years including the rapidly rising phase of solar cycle 23. The analysis of mean frequency shift with different activity indices shows that the shift is equally correlated with both magnetic and radiative indices. During the onset of the new cycle 23, we notice that the change in the b4 splitting coefficient is more prominent than the change in b2. We have estimated the solar rotation rate with varying depth and latitude. In the equatorial region, the rotation first increases with depth and then decreases, while an opposite behavior is seen in the polar region. We also find a small but significant temporal variation in the rotation rate at high latitudes. Title: Observation of Hysteresis Between Solar Activity Indicators and p-mode Frequency Shifts for Solar Cycle 22 Authors: Tripathy, S. C.; Kumar, B.; Jain, K.; Bhatnagar, A. Bibcode: 2000JApA...21..357T Altcode: No abstract at ADS Title: Heliseismic Solar Cycle Changes and Splitting Coefficients Authors: Tripathy, S. C.; Jain, Kiran; Bhatnagar, A. Bibcode: 2000JApA...21..349T Altcode: No abstract at ADS Title: Empirical estimate of p-mode frequency shift for solar cycle 23 Authors: Jain, Kiran; Tripathy, S. C.; Bhatnagar, A.; Kumar, Brajesh Bibcode: 2000SoPh..192..487J Altcode: 1999astro.ph.12518J We have obtained empirical relations between the p-mode frequency shift and the change in solar activity indices. The empirical relations are determined on the basis of frequencies obtained from BBSO and GONG stations during solar cycle 22. These relations are applied to estimate the change in mean frequency for the cycle 21 and 23. A remarkable agreement between the calculated and observed frequency shifts for the ascending phase of cycle 23, indicates that the derived relations are independent of epoch and do not change significantly from cycle to cycle. We propose that these relations could be used to estimate the shift in p-mode frequencies for past, present and future solar activity cycles, if the solar activity index is known. The maximum frequency shift for cycle 23 is estimated to be 265±90 nHz, corresponding to a predicted maximum smoothed sunspot number 118.1±35. Title: A relation between frequency shift and the changes in activity indices Authors: Jain, Kiran; Tripathy, S. C.; Kumar, Brajesh; Bhatnagar, Arvind Bibcode: 2000BASI...28...89J Altcode: We present a linear relation between the shift in p-mode frequencies and variation in two solar activity indices, namely the sunspot number and 10.7 cm radio flux. From this relation, an empirical model is constructed to estimate the mean frequency shifts with respect to activity index. We also compare the observed and estimated shifts for solar cycle 22 and comment on the systematic errors in different helioseismic data sets. Title: GONG p-mode frequency changes with solar activity Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C. Bibcode: 2000BASI...28...91B Altcode: In this paper, we present a correlation study of nine solar activity indices with p-mode frequency shifts obtained from the GONG data. It is found that the two are closely correlated and a linear relationship exits. Further, the GONG p-mode frequencies for the period 1995 August to 1997 August show that the mean frequency decreases by 0.06 μHz during the descending phase of the solar cycle 22 and increases by 0.04 μHz in the ascending phase of the new solar cycle 23. Title: GONG p-Mode Frequency Changes with Solar Activity Authors: Bhatnagar, A.; Jain, Kiran; Tripathy, S. C. Bibcode: 1999ApJ...521..885B Altcode: 1999astro.ph..3493B We present a correlation analysis of GONG p-mode frequencies with nine solar activity indices for the period from 1995 August to 1997 August. This study includes spherical harmonic degrees in the range 2-150 and the frequency range of 1500-3500 μHz. Using three statistical tests, the measured mean frequency shifts show strong to good correlation with activity indices. A decrease of 0.06 μHz in frequency during the descending phase of solar cycle 22 and an increase of 0.04 μHz in the ascending phase of solar cycle 23 are observed. These results provide the first evidence for change in p-mode frequencies around the declining phase of cycle 22 and the beginning of new cycle 23. This analysis further confirms that the temporal behavior of the solar frequency shifts closely follow the phase of the solar activity cycle. Title: Circular polarization measurement using a tunable lithium niobate Fabry-Perot filter Authors: Mathew, S. K.; Bhatnagar, A.; Debi Prasad, C.; Ambastha, A. Bibcode: 1999ASSL..243..321M Altcode: 1999sopo.conf..321M No abstract at ADS 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. Bibcode: 1999ASPC..183..256M Altcode: 1999hrsp.conf..256M No abstract at ADS Title: Fabry-Perot filter based solar video magnetograph Authors: Mathew, S. K.; Bhatnagar, A.; Prasad, C. D.; Ambastha, A. Bibcode: 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. Title: A viewpoint on moderate size solar telescope Authors: Bhatnagar, Arvind Bibcode: 1998BASI...26..407B Altcode: No abstract at ADS Title: Solar Photospheric and Chromospheric Observations using a Lithium Niobate Fabry-Perot ETALON Authors: Debi Prasad, C.; Mathew, Shibu K.; Bhatnagar, Arvind; Ambastha, Ashok Bibcode: 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. Title: International collaboration - Global Oscillation Network Group (GONG) Authors: Bhatnagar, Arvind Bibcode: 1998BASI...26..157B Altcode: No abstract at ADS Title: Solar Mass Ejection and Coronal Holes Authors: Bhatnagar, Arvind Bibcode: 1998asct.conf..267B Altcode: No abstract at ADS 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. Bibcode: 1997KodOB..13..101B Altcode: No abstract at ADS Title: Determination of times of second and third contact from flash spectrum sequence. Authors: Bhatnagar, A. K. Bibcode: 1997KodOB..13..119B Altcode: No abstract at ADS 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. Bibcode: 1997KodOB..13...99B Altcode: No abstract at ADS 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. Bibcode: 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. 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. Bibcode: 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. 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 Bibcode: 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. Title: Solar mass ejections and coronal holes Authors: Bhatnagar, Arvind Bibcode: 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’. 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. Bibcode: 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. Title: Solar Observations Using Lithium Niobate Fabry-Perot ETALON Authors: Bhatnagar, A.; Prasad, C. D.; Mathew, S. K. Bibcode: 1995JApAS..16..384B Altcode: No abstract at ADS Title: Two-Dimensional Velocity Field Measurement of Eruptive Prominence Observed 1993JAN14 Authors: Bhatnagar, A.; Tripathy, S. C. Bibcode: 1995JApAS..16..382B Altcode: No abstract at ADS Title: Imaging Polarimetry of Comet Austin Authors: Joshi, U. C.; Chauhan, J. S.; Deshpande, M. R.; Sen, A. K.; Bhatnagar, A. K. Bibcode: 1995JApAS..16..395J Altcode: No abstract at ADS Title: Soft X-ray Blow-outs and Coronal Holes Authors: Bhatnagar, A. Bibcode: 1995SPD....26..617B Altcode: 1995BAAS...27..965B No abstract at ADS Title: A Graphical User Interface for a Development Environment (GUIDE) Authors: Bhatnagar, A. Bibcode: 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. 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 Bibcode: 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. Title: Imaging polarimetry of comet Austin. Authors: Joshi, U. C.; Chauhan, J. S.; Deshpande, M. R.; Sen, A. K.; Bhatnagar, A. K. Bibcode: 1993BASI...21..651J Altcode: Comet Austin (1989c1) 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. Title: Magnetic Field Configuration in H alpha Flare Loops and Flaring Arches Authors: Bhatnagar, A.; Srivastava, N. Bibcode: 1993ASPC...46..351B Altcode: 1993IAUCo.141..351B; 1993mvfs.conf..351B No abstract at ADS Title: Book reviews Authors: Bhatnagar, Arvind; Achterberg, A.; de Jager, Cornelis; Kaufmann, P.; van Gent, R. H.; Rodríguez, L. F. Bibcode: 1992SSRv...59..407B Altcode: No abstract at ADS Title: Book-Review - Advances in Geosciences Authors: Schroeder, W.; Bhatnagar, A. Bibcode: 1992SSRv...59..409S Altcode: No abstract at ADS Title: Filament Eruptions Flaring Arches and Eruptive Flares Authors: Bhatnagar, A.; Ambastha, A.; Srivastava, N. Bibcode: 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. Title: Helically twisted prominence eruption event of 1979 March 11. Authors: Srivastava, N.; Ambastha, A.; Bhatnagar, A. Bibcode: 1991BASI...19..208S Altcode: No abstract at ADS 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. Bibcode: 1991BASI...19..211A Altcode: No abstract at ADS Title: Cosmic ray flare of 1989 September 29. Authors: Jain, R.; Bhatnagar, A.; Sharma, R. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 1011 A which decreased with time. Correspondingly, it is estimated that the rate of energy release was ≈ 1028 erg s−1 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. Bibcode: 1990IAUS..141..186B Altcode: No abstract at ADS Title: The Footpoints of Giant Arches Authors: Martin, Sara F.; Svestka, Zdenek F.; Bhatnagar, Arvind Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 1988BASI...16...52B Altcode: No abstract at ADS Title: Optical observations of the Sun. Authors: Bhatnagar, A. Bibcode: 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. Bibcode: 1987BASI...15...19A Altcode: No abstract at ADS Title: System of Astronomical Constants in Hindu Astronomy Authors: Bandyopadhyay, A.; Bhatnagar, A. K. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1985Natur.313..124S Altcode: During a solar eclipse the Moon's shadow moves at supersonic speed through the Earth's atmosphere. Chimonas and Hines1,2 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 detected3. Ground-level pressure changes during solar eclipses occur near the region of totality4, but the measured wave velocity and period do not agree with that of the predicted disturbance5,6. 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-1. Title: Veil emission associated with the multiribbon flare of 1979 February 18 Authors: Jain, R.; Bhatnagar, A.; Shelke, R. N. Bibcode: 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. Bibcode: 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. Bibcode: 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-1. To explain this event a qualitative model is presented. Title: Growth and separation of flare ribbons. Authors: Jain, R.; Bhatnagar, A. Bibcode: 1984BASI...12...68J Altcode: No abstract at ADS Title: Optical Observations of Solar Flares Authors: Bhatnagar, A. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1978BASI....6...44J Altcode: No abstract at ADS Title: The orbit of the Dhajala meteorite Authors: Ballabh, G. M.; Bhatnagar, A.; Bhandari, N. Bibcode: 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∞ < 25 km/sec (which causes nearly complete evaporation of the meteoroid). Taking V∞ = 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. Bibcode: 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. Bibcode: 1976BASI....4...78B Altcode: No abstract at ADS Title: Vedshala, Ahmedabad. Annual report for the year 1975. Authors: Bhatnagar, A. Bibcode: 1976BASI....4...61B Altcode: No abstract at ADS Title: The Dhajala Meteorite Shower Authors: Bhandari, N.; Lal, D.; Trivedi, J. R.; Bhatnagar, A. Bibcode: 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. Bibcode: 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. Bibcode: 1975BASI....3...27B Altcode: No abstract at ADS Title: Video-magnetograph observations of moving magnetic features around sunspots. Authors: Michalitsanos, A. G.; Bhatnagar, A. Bibcode: 1975BASI....3...27M Altcode: No abstract at ADS Title: Observations of Large-Scale Moving Magnetic Features Near Sunspots Authors: Michalitsanos, A. G.; Bhatnagar, A. Bibcode: 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. Bibcode: 1974imra.conf...25B Altcode: No abstract at ADS Title: Investigation of Two Delta Scuti Suspects Authors: Bhatnagar, A. K.; Gupta, S. K. Bibcode: 1973IBVS..778....1B Altcode: No abstract at ADS Title: Light Variations of 59 Piscium Authors: Gupta, S. K.; Bhatnagar, A. K. Bibcode: 1972IBVS..751....1G Altcode: No abstract at ADS Title: Observations of Sunspot Umbral Velocity Oscillations Authors: Bhatnagar, Arvind; Livingston, W. C.; Harvey, J. W. Bibcode: 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−1. Title: Observations of Sunspot Umbral Velocity Oscillations Authors: Bhatnagar, A.; Livingston, W. C.; Harvey, J. W. Bibcode: 1972BAAS....4R.378B Altcode: No abstract at ADS Title: Intensity Oscillation in Hα-Fine Structure Authors: Bhatnagar, Arvind; Tanaka, Katsuo Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1971SoPh...18...40B Altcode: No abstract at ADS Title: On the oscillatory velocity field in sunspot atmosphere. Authors: Bhatnagar, A. Bibcode: 1971BAAS....3R.259B Altcode: No abstract at ADS Title: Fine-Scan Velocity and Magnetic- field Measurements in Solar Active Regions Authors: Bhatnagar, A. Bibcode: 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. Bibcode: 1970KodOB.204..189B Altcode: No abstract at ADS Title: On the Spectrum of Granular and Intergranular Regions Authors: Howard, R.; Bhatnagar, A. Bibcode: 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. Bibcode: 1969BAAS....1T.279H Altcode: No abstract at ADS Title: A New Technique to Obtain Solar-Velocity Maps Directly in One Spectroheliogram Authors: Bhatnagar, A.; Stenflo, J. O. Bibcode: 1969BAAS....1S.273B Altcode: No abstract at ADS Title: A Method to obtain a Solar Velocity Map Directly in One Spectroheliogram Authors: Bhatnagar, A.; Stenflo, J. O. Bibcode: 1969SoPh....7..329B Altcode: No abstract at ADS Title: The solar corona of July 20, 1963. Authors: Bappu, M. K. V.; Bhatnagar, A. Bibcode: 1969KodOB.190.....B Altcode: No abstract at ADS Title: Monochromatic polarization measures of comet Ikeya-Seki (1965f) Authors: Bappu, M. K. V.; Sivaraman, K. R.; Bhatnagar, A.; Natarajan, V. Bibcode: 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. - Title: Variation in Continuum Brightness and Equivalent Widths of Lines in Sunspot Penumbrae Authors: Bhatnagar, A. Bibcode: 1966ZA.....64..460B Altcode: No abstract at ADS Title: The Evershed effect in sunspots Authors: Bhatnagar, Arvind Bibcode: 1964PhDT.......105B Altcode: No abstract at ADS Title: The influence of superflares in the H alpha striation pattern Authors: Bappu, M. K. V.; Bhatnagar, A.; Punetha, L. M. Bibcode: 1962Obs....82..192B Altcode: No abstract at ADS