Author name code: jain-rekha ADS astronomy entries on 2022-09-14 =author:"Jain, Rekha" OR =author:"Jain, R." ------------------------------------------------------------------------ Title: Radial Trapping of Thermal Rossby Waves within the Convection Zones of Low-mass Stars Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2022ApJ...932...68H Altcode: 2022arXiv220502346H We explore how thermal Rossby waves propagate within the gravitationally stratified atmosphere of a low-mass star with an outer convective envelope. Under the conditions of slow, rotationally constrained dynamics, we derive a local dispersion relation for atmospheric waves in a fully compressible stratified fluid. This dispersion relation describes the zonal and radial propagation of acoustic waves and gravito-inertial waves. Thermal Rossby waves are just one class of prograde-propagating gravito-inertial wave that manifests when the buoyancy frequency is small compared to the rotation rate of the star. From this dispersion relation, we identify the radii at which waves naturally reflect and demonstrate how thermal Rossby waves can be trapped radially in a waveguide that permits free propagation in the longitudinal direction. We explore this trapping further by presenting analytic solutions for thermal Rossby waves within an isentropically stratified atmosphere that models a zone of efficient convective heat transport. We find that, within such an atmosphere, waves of short zonal wavelength have a wave cavity that is radially thin and confined within the outer reaches of the convection zone near the star's equator. The same behavior is evinced by the thermal Rossby waves that appear at convective onset in numerical simulations of convection within rotating spheres. Finally, we suggest that stable thermal Rossby waves could exist in the lower portion of the Sun's convection zone, despite that region's unstable stratification. For long wavelengths, the Sun's rotation rate is sufficiently rapid to stabilize convective motions, and the resulting overstable convective modes are identical to thermal Rossby waves. Title: Study of Transverse Oscillations in Coronal Loops Excited by Flares and Eruptions Authors: Conde C., Sandra M.; Jain, Rekha; Jatenco-Pereira, Vera Bibcode: 2022ApJ...931..151C Altcode: 2022arXiv220512063C We present measurements of periodicity for transverse loop oscillations during the periods of activity of two remote and separated (both temporally and spatially) flares. The oscillations are observed in the same location more than 100 Mm away from the visible footpoints of the loops. Evidence for several possible excitation sources is presented. After close examination, we find that the eruptions during the flaring activities play an important role in triggering the oscillations. We investigate periodicities using time-distance, fast Fourier transform, and wavelet techniques. Despite different excitation sources in the vicinity of the loops and the changing nature of amplitudes, the periodicity of multiple oscillations is found to be 4-6 min. Title: 57Zn β-delayed proton emission establishes the 56Ni rp-process waiting point bypass Authors: Saxena, M.; -J Ong, W.; Meisel, Z.; Hoff, D. E. M.; Smirnova, N.; Bender, P. C.; Burcher, S. P.; Carpenter, M. P.; Carroll, J. J.; Chester, A.; Chiara, C. J.; Conaway, R.; Copp, P. A.; Crider, B. P.; Derkin, J.; Estradé, A.; Hamad, G.; Harke, J. T.; Jain, R.; Jayatissa, H.; Liddick, S. N.; Longfellow, B.; Mogannam, M.; Montes, F.; Nepal, N.; Ogunbeku, T. H.; Richard, A. L.; Schatz, H.; Soltesz, D.; Subedi, S. K.; Sultana, I.; Tamashiro, A. S.; Tripathi, V.; Xiao, Y.; Zink, R. Bibcode: 2022PhLB..82937059S Altcode: 2022arXiv220401621S We measured the 57Znβ-delayed proton (βp) and γ emission at the National Superconducting Cyclotron Laboratory. We find a 57Zn half-life of 43.6 ± 0.2 ms, βp branching ratio of (84.7 ± 1.4)%, and identify four transitions corresponding to the exotic β-γ-p decay mode, the second such identification in the fp-shell. The p/γ ratio was used to correct for isospin mixing while determining the 57Zn mass via the isobaric multiplet mass equation. Previously, it was uncertain as to whether the rp-process flow could bypass the textbook waiting point 56Ni for astrophysical conditions relevant to Type-I X-ray bursts. Our results definitively establish the existence of the 56Ni bypass, with 14-17% of the rp-process flow taking this route. Title: Horizons: Nuclear Astrophysics in the 2020s and Beyond Authors: Schatz, H.; Becerril Reyes, A. D.; Best, A.; Brown, E. F.; Chatziioannou, K.; Chipps, K. A.; Deibel, C. M.; Ezzeddine, R.; Galloway, D. K.; Hansen, C. J.; Herwig, F.; Ji, A. P.; Lugaro, M.; Meisel, Z.; Norman, D.; Read, J. S.; Roberts, L. F.; Spyrou, A.; Tews, I.; Timmes, F. X.; Travaglio, C.; Vassh, N.; Abia, C.; Adsley, P.; Agarwal, S.; Aliotta, M.; Aoki, W.; Arcones, A.; Aryan, A.; Bandyopadhyay, A.; Banu, A.; Bardayan, D. W.; Barnes, J.; Bauswein, A.; Beers, T. C.; Bishop, J.; Boztepe, T.; Côté, B.; Caplan, M. E.; Champagne, A. E.; Clark, J. A.; Couder, M.; Couture, A.; de Mink, S. E.; Debnath, S.; deBoer, R. J.; den Hartogh, J.; Denissenkov, P.; Dexheimer, V.; Dillmann, I.; Escher, J. E.; Famiano, M. A.; Farmer, R.; Fisher, R.; Fröhlich, C.; Frebel, A.; Fryer, C.; Fuller, G.; Ganguly, A. K.; Ghosh, S.; Gibson, B. K.; Gorda, T.; Gourgouliatos, K. N.; Graber, V.; Gupta, M.; Haxton, W.; Heger, A.; Hix, W. R.; Ho, W C. G.; Holmbeck, E. M.; Hood, A. A.; Huth, S.; Imbriani, G.; Izzard, R. G.; Jain, R.; Jayatissa, H.; Johnston, Z.; Kajino, T.; Kankainen, A.; Kiss, G. G.; Kwiatkowski, A.; La Cognata, M.; Laird, A. M.; Lamia, L.; Landry, P.; Laplace, E.; Launey, K. D.; Leahy, D.; Leckenby, G.; Lennarz, A.; Longfellow, B.; Lovell, A. E.; Lynch, W. G.; Lyons, S. M.; Maeda, K.; Masha, E.; Matei, C.; Merc, J.; Messer, B.; Montes, F.; Mukherjee, A.; Mumpower, M.; Neto, D.; Nevins, B.; Newton, W. G.; Nguyen, L. Q.; Nishikawa, K.; Nishimura, N.; Nunes, F. M.; O'Connor, E.; O'Shea, B. W.; Ong, W-J.; Pain, S. D.; Pajkos, M. A.; Pignatari, M.; Pizzone, R. G.; Placco, V. M.; Plewa, T.; Pritychenko, B.; Psaltis, A.; Puentes, D.; Qian, Y-Z.; Radice, D.; Rapagnani, D.; Rebeiro, B. M.; Reifarth, R.; Richard, A. L.; Rijal, N.; Roederer, I. U.; Rojo, J. S.; K, J. S; Saito, Y.; Schwenk, A.; Sergi, M. L.; Sidhu, R. S.; Simon, A.; Sivarani, T.; Skúladóttir, Á.; Smith, M. S.; Spiridon, A.; Sprouse, T. M.; Starrfield, S.; Steiner, A. W.; Strieder, F.; Sultana, I.; Surman, R.; Szücs, T.; Tawfik, A.; Thielemann, F.; Trache, L.; Trappitsch, R.; Tsang, M. B.; Tumino, A.; Upadhyayula, S.; Valle Martínez, J. O.; Van der Swaelmen, M.; Viscasillas Vázquez, C.; Watts, A.; Wehmeyer, B.; Wiescher, M.; Wrede, C.; Yoon, J.; Zegers, R G. T.; Zermane, M. A.; Zingale, M. Bibcode: 2022arXiv220507996S Altcode: Nuclear Astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated. We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities. Title: The Impact of Neutron Transfer Reactions on the Heating and Cooling of Accreted Neutron Star Crusts Authors: Schatz, H.; Meisel, Z.; Brown, E. F.; Gupta, S. S.; Hitt, G. W.; Hix, W. R.; Jain, R.; Lau, R.; Möller, P.; Ong, W. -J.; Shternin, P. S.; Xu, Y.; Wiescher, M. Bibcode: 2022ApJ...925..205S Altcode: 2021arXiv211211544S Nuclear reactions heat and cool the crust of accreting neutron stars and need to be understood to interpret observations of X-ray bursts and long-term cooling in transiently accreting systems. It was recently suggested that previously ignored neutron transfer reactions may play a significant role in the nuclear processes. We present results from full nuclear network calculations that now include these reactions and determine their impact on crust composition, crust impurity, heating, and cooling. We find that a large number of neutron transfer reactions indeed occur and impact crust models. In particular, we identify a new type of reaction cycle that brings a pair of nuclei across the nuclear chart into equilibrium via alternating neutron capture and neutron release, interspersed with a neutron transfer. While neutron transfer reactions lead to changes in crust model predictions and need to be considered in future studies, previous conclusions concerning heating, cooling, and compositional evolution are remarkably robust. Title: Extragalactic Globular Clusters with Euclid and other wide surveys Authors: Lançon, A.; Larsen, S.; Voggel, K.; Cuillandre, J. -C.; Duc, P. -A.; Chantereau, W.; Jain, R.; Sánchez-Janssen, R.; Cantiello, M.; Rejkuba, M.; Marleau, F.; Saifollahi, T.; Conselice, C.; Hunt, L.; N Ferguson, A. M.; Lagadec, E.; Côté, P. Bibcode: 2021sf2a.conf..447L Altcode: 2021arXiv211013783L Globular clusters play a role in many areas of astrophysics, ranging from stellar physics to cosmology. New ground-based optical surveys complemented by observations from space-based telescopes with unprecedented near-infrared capabilities will help us solve the puzzles of their formation histories. In this context, the Wide Survey of the {\em Euclid}\ space mission will provide red and near-infrared data over about 15\,000 square degrees of the sky. Combined with optical photometry from the ground, it will allow us to construct a global picture of the globular cluster populations in both dense and tenuous environments out to tens of megaparsecs. The homogeneous photometry of these data sets will rejuvenate stellar population studies that depend on precise spectral energy distributions. We provide a brief overview of these perspectives. Title: Do Coronal Loops Oscillate in Isolation? Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2021ApJ...921...29H Altcode: 2021arXiv210804362H Images of the solar corona by extreme-ultraviolet telescopes reveal elegant arches of glowing plasma that trace the corona's magnetic field. Typically, these loops are preferentially illuminated segments of an arcade of vaulted field lines and such loops are often observed to sway in response to nearby solar flares. A flurry of observational and theoretical effort has been devoted to the exploitation of these oscillations with the grand hope that seismic techniques might be used as probes of the strength and structure of the corona's magnetic field. The commonly accepted viewpoint is that each visible loop oscillates as an independent entity and acts as a one-dimensional wave cavity for magnetohydrodynamic kink waves. We argue that for many events, this generally accepted model for the wave cavity is fundamentally flawed. In particular, the 3D magnetic arcade in which the bright loop resides participates in the oscillation. Thus, the true wave cavity is larger than the individual loop and inherently multidimensional. We derive the skin depth of the near-field response for an oscillating loop and demonstrate that most loops are too close to other magnetic structures to oscillate in isolation. Further, we present a simple model of a loop embedded within an arcade and explore how the eigenmodes of the arcade and the eigenmodes of the loop become coupled. In particular, we discuss how distinguishing between these two types of modes can be difficult when the motions within the arcade are often invisible. Title: First direct measurement of 59Cu(p ,α )56Ni : A step towards constraining the Ni-Cu cycle in the cosmos Authors: Randhawa, J. S.; Kanungo, R.; Refsgaard, J.; Mohr, P.; Ahn, T.; Alcorta, M.; Andreoiu, C.; Bhattacharjee, S. S.; Davids, B.; Christian, G.; Chen, A. A.; Coleman, R.; Garrett, P. E.; Grinyer, G. F.; Gyabeng Fuakye, E.; Hackman, G.; Hollett, J.; Jain, R.; Kapoor, K.; Krücken, R.; Laffoley, A.; Lennarz, A.; Liang, J.; Meisel, Z.; Nikhil, B.; Psaltis, A.; Radich, A.; Rocchini, M.; Saei, N.; Saxena, M.; Singh, M.; Svensson, C.; Subramaniam, P.; Talebitaher, A.; Upadhyayula, S.; Waterfield, C.; Williams, J.; Williams, M. Bibcode: 2021PhRvC.104d2801R Altcode: 2021arXiv210705606R Reactions on proton-rich nuclides drive the nucleosynthesis in core collapse supernovae (CCSNe) and in x-ray bursts (XRBs). CCSNe eject the nucleosynthesis products to the interstellar medium and hence are a potential inventory of p nuclei, whereas in XRBs nucleosynthesis powers the light curves. In both astrophysical sites the Ni-Cu cycle, which features a competition between 59Cu(p ,α )56Ni and 59Cu(p ,γ )60Zn , could potentially halt the production of heavier elements. Here, we report the first direct measurement of 59Cu(p ,α )56Ni using a reaccelerated 59Cu beam and a cryogenic solid hydrogen target. Our results show that the reaction proceeds predominantly to the ground state of 56Ni, and the experimental rate has been found to be lower than Hauser-Feshbach based statistical model predictions. New results hints that the ν p process could operate at higher temperatures than previously inferred and therefore remains a viable site for synthesizing the heavier elements. Title: Kink Oscillations of Coronal Loops Authors: Nakariakov, V. M.; Anfinogentov, S. A.; Antolin, P.; Jain, R.; Kolotkov, D. Y.; Kupriyanova, E. G.; Li, D.; Magyar, N.; Nisticò, G.; Pascoe, D. J.; Srivastava, A. K.; Terradas, J.; Vasheghani Farahani, S.; Verth, G.; Yuan, D.; Zimovets, I. V. Bibcode: 2021SSRv..217...73N Altcode: 2021arXiv210911220N Kink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillations are observed in two different regimes. In the rapidly decaying regime, the apparent displacement amplitude reaches several minor radii of the loop. The damping time which is about several oscillation periods decreases with the increase in the oscillation amplitude, suggesting a nonlinear nature of the damping. In the decayless regime, the amplitudes are smaller than a minor radius, and the driver is still debated. The review summarises major findings obtained during the last decade, and covers both observational and theoretical results. Observational results include creation and analysis of comprehensive catalogues of the oscillation events, and detection of kink oscillations with imaging and spectral instruments in the EUV and microwave bands. Theoretical results include various approaches to modelling in terms of the magnetohydrodynamic wave theory. Properties of kink oscillations are found to depend on parameters of the oscillating loop, such as the magnetic twist, stratification, steady flows, temperature variations and so on, which make kink oscillations a natural probe of these parameters by the method of magnetohydrodynamic seismology. Title: The need for new techniques to identify the high-frequency MHD waves of an oscillating coronal loop Authors: Allian, Farhad; Jain, Rekha Bibcode: 2021A&A...650A..91A Altcode: 2021arXiv210508189A Context. Magnetic arcades in the solar atmosphere, or coronal loops, are common structures known to host magnetohydrodynamic (MHD) waves and oscillations. Of particular interest are the observed properties of transverse loop oscillations, such as their frequency and mode of oscillation, which have received significant attention in recent years because of their seismological capability. Previous studies have relied on standard data analysis techniques, such as a fast Fourier transform (FFT) and wavelet transform (WT), to correctly extract periodicities and identify the MHD modes. However, the ways in which these methods can lead to artefacts requires careful investigation.
Aims: We aim to assess whether these two common spectral analysis techniques in coronal seismology can successfully identify high-frequency waves from an oscillating coronal loop.
Methods: We examine extreme ultraviolet images of a coronal loop observed by the Atmospheric Imaging Assembly in the 171 Å waveband on board the Solar Dynamics Observatory. We perform a spectral analysis of the loop waveform and compare our observation with a basic simulation.
Results: The spectral FFT and WT power of the observed loop waveform is found to reveal a significant signal with frequency ∼2.67 mHz superposed onto the dominant mode of oscillation of the loop (∼1.33 mHz), that is, the second harmonic of the loop. The simulated data show that the second harmonic is completely artificial even though both of these methods identify this mode as a real signal. This artificial harmonic, and several higher modes, are shown to arise owing to the periodic but non-uniform brightness of the loop. We further illustrate that the reconstruction of the ∼2.67 mHz component, particularly in the presence of noise, yields a false perception of oscillatory behaviour that does not otherwise exist. We suggest that additional techniques, such as a forward model of a 3D coronal arcade, are necessary to verify such high-frequency waves.
Conclusions: Our findings have significant implications for coronal seismology, as we highlight the dangers of attempting to identify high-frequency MHD wave modes using these standard data analysis techniques.

Movie associated to Fig. 1 is available at https://www.aanda.org Title: A comparison between X-shooter spectra and PHOENIX models across the HR-diagram Authors: Lançon, A.; Gonneau, A.; Verro, K.; Prugniel, P.; Arentsen, A.; Trager, S. C.; Peletier, R.; Chen, Y. -P.; Coelho, P.; Falcón-Barroso, J.; Hauschildt, P.; Husser, T. -O.; Jain, R.; Lyubenova, M.; Martins, L.; Sánchez Blázquez, P.; Vazdekis, A. Bibcode: 2021A&A...649A..97L Altcode: 2020arXiv201209129L
Aims: The path towards robust near-infrared extensions of stellar population models involves the confrontation between empirical and synthetic stellar spectral libraries across the wavelength ranges of photospheric emission. Indeed, the theory of stellar emission enters all population synthesis models, even when this is only implicit in the association of fundamental stellar parameters with empirical spectral library stars. With its near-ultraviolet to near-infrared coverage, the X-shooter Spectral Library (XSL) allows us to examine to what extent models succeed in reproducing stellar energy distributions (SEDs) and stellar absorption line spectra simultaneously.
Methods: As a first example, this study compares the stellar spectra of XSL with those of the Göttingen Spectral Library, which are based on the PHOENIX synthesis code. The comparison was carried out both separately in the three arms of the X-shooter spectrograph known as UVB, VIS and NIR, and jointly across the whole spectrum. We did not discard the continuum in these comparisons; only reddening was allowed to modify the SEDs of the models.
Results: When adopting the stellar parameters published with data release DR2 of XSL, we find that the SEDs of the models are consistent with those of the data at temperatures above 5000 K. Below 5000 K, there are significant discrepancies in the SEDs. When leaving the stellar parameters free to adjust, satisfactory representations of the SEDs are obtained down to about 4000 K. However, in particular below 5000 K and in the UVB spectral range, strong local residuals associated with intermediate resolution spectral features are then seen; the necessity of a compromise between reproducing the line spectra and reproducing the SEDs leads to dispersion between the parameters favored by various spectral ranges. We describe the main trends observed and we point out localized offsets between the parameters preferred in this global fit to the SEDs and the parameters in DR2. These depend in a complex way on the position in the Hertzsprung-Russell diagram (HRD). We estimate the effect of the offsets on bolometric corrections as a function of position in the HRD and use this for a brief discussion of their impact on the studies of stellar populations. A review of the literature shows that comparable discrepancies are mentioned in studies using other theoretical and empirical libraries. Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: VizieR Online Data Catalog: Observation of 31 G-stars at 1.5GHz with GBT (Margot+, 2021) Authors: Margot, J. -L.; Pinchuk, P.; Geil, R.; Alexander, S.; Arora, S.; Biswas, S.; Cebreros, J.; Desai, S. P.; Duclos, B.; Dunne, R.; Lin, Fu K. K.; Goel, S.; Gonzales, J.; Gonzalez, A.; Jain, R.; Lam, A.; Lewis, B.; Lewis, R.; Li, G.; MacDougall, M.; Makarem, C.; Manan, I.; Molina, E.; Nagib, C.; Neville, K.; O'Toole, C.; Rockwell, V.; Rokushima, Y.; Romanek, G.; Schmidgall, C.; Seth, S.; Shah, R.; Shimane, Y.; Singhal, M.; Tokadjian, A.; Villafana, L.; Wang, Z.; Yun, In; Zhu, L.; Lynch, R. S. Bibcode: 2021yCat..51610055M Altcode: We selected 31 Sun-like stars (spectral type G, luminosity class V) with a median galactic latitude of 0.85°. We observed these stars with the Green Bank Telescope (GBT) during two 2hr sessions separated by approximately 1yr. During each observing session, we recorded both linear polarizations of the L-band receiver with the GUPPI back end in its baseband recording mode. The center frequency was set to 1.5GHz, and we sampled 800MHz of bandwidth between 1.1 and 1.9GHz.

(2 data files). Title: Excitation Sources of Oscillations in Solar Coronal Loops: A Multi-wavelength Analysis Authors: Conde C., Sandra M.; Jain, Rekha; Jatenco-Pereira, Vera Bibcode: 2020ApJ...890L..21C Altcode: An investigation into the excitation sources of oscillations detected in a coronal loop structure is carried out using the images obtained with Interface Region Imaging Spectrometer (IRIS) and the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory (SDO). A loop structure in the active region AR 11967 on 2014 January 28, oscillating in the vicinity of a strong eruption and an M3.6 class flare site, is clearly noticeable in SDO/AIA 171 Å images. We study in detail, the oscillations with detected periods between 4 and 13 minutes and their connection in IRIS SJI 1330 Å and SDO/AIA 1700 Å images; both of these wavelengths sample the lower parts of the solar atmosphere. The simultaneous presence of many oscillations in the region of interest in all three wavelength passbands suggest that these oscillations were excited in the lower-chromosphere-photosphere plasma connected to the loop structure and then propagated at higher heights. We further investigate the Doppler velocity measurements from the spectrograph snapshots in IRIS C II 1336 Å, Si IV 1403 Å and Mg II k 2796 Å. These show signatures of upflows in the vicinity of the loop structure's endpoints estimated from 171 Å images. We suggest that some of the oscillations observed in AIA 171 Å have been triggered by plasma ejections and perturbations seen in the lower layers of the solar atmosphere. Based on the estimated phase speeds, the oscillations are likely to be slow magnetoacoustic in nature. Title: VizieR Online Data Catalog: Measured atmospheric parameters of NGC6397 stars (Jain+, 2020) Authors: Jain, R.; Prugniel, P.; Martins, L.; Lancon, A. Bibcode: 2020yCat..36350161J Altcode: The table contains the atmospheric parameters determined for stars of NGC 6397. The spectra of these stars were observed using MUSE spectrograph by Husser et al. 2016. We use the spectra of these stars to estimate atmospheric parameters using ELODIE and MILES libraries.

(1 data file). Title: Michael Thompson in Sheffield Authors: Jain, Rekha Bibcode: 2020ASSP...57....9J Altcode: Michael Thompson gave huge contributions to the field of Helioseismology and inspired many young researchers in the discipline with his insight and new ideas. He spent six years in Sheffield after being appointed as the Head of Applied Mathematics Department in the University of Sheffield (UK) where colleagues hold fond memories of him, both as a committed academic and a very effective leader. His hard work and sincere approach was infectious to all those who worked around him. This tribute is an opportunity to share a little part of his work and life during his time in Sheffield. Title: A New Analysis Procedure for Detecting Periodicities within Complex Solar Coronal Arcades Authors: Allian, Farhad; Jain, Rekha; Hindman, B. W. Bibcode: 2019ApJ...880....3A Altcode: 2019arXiv190206644A We study intensity variations, as measured by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, in a solar coronal arcade using a newly developed analysis procedure that employs spatio-temporal autocorrelations. We test our new procedure by studying large-amplitude oscillations excited by nearby flaring activity within a complex arcade and detect a dominant periodicity of 12.31 minutes. We compute this period in two ways: from the traditional time-distance fitting method and using our new autocorrelation procedure. The two analyses yield consistent results. The autocorrelation procedure is then implemented on time series for which the traditional method would fail due to the complexity of overlapping loops and a poor contrast between the loops and the background. Using this new procedure, we discover the presence of small-amplitude oscillations within the same arcade with 9.13 and 9.81 minute periods prior and subsequent to the large-amplitude oscillations, respectively. Consequently, we identify these as “decayless” oscillations that have only been previously observed in nonflaring loop systems. Title: A Novel Approach to Resonant Absorption of the Fast Magnetohydrodynamic Eigenmodes of a Coronal Arcade Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2018ApJ...858....6H Altcode: 2018arXiv180308948H The arched field lines forming coronal arcades are often observed to undulate as magnetohydrodynamic waves propagate both across and along the magnetic field. These waves are most likely a combination of resonantly coupled fast magnetoacoustic waves and Alfvén waves. The coupling results in resonant absorption of the fast waves, converting fast wave energy into Alfvén waves. The fast eigenmodes of the arcade have proven difficult to compute or derive analytically, largely because of the mathematical complexity that the coupling introduces. When a traditional spectral decomposition is employed, the discrete spectrum associated with the fast eigenmodes is often subsumed into the continuous Alfvén spectrum. Thus fast eigenmodes become collective modes or quasi-modes. Here we present a spectral decomposition that treats the eigenmodes as having real frequencies but complex wavenumbers. Using this procedure we derive dispersion relations, spatial damping rates, and eigenfunctions for the resonant, fast eigenmodes of the arcade. We demonstrate that resonant absorption introduces a fast mode that would not exist otherwise. This new mode is heavily damped by resonant absorption, travelling only a few wavelengths before losing most of its energy. Title: Fast magnetohydrodynamic waves in a solar coronal arcade Authors: Thackray, Hope; Jain, Rekha Bibcode: 2017A&A...608A.108T Altcode:
Aims: Our aim is to investigate detailed properties of fast magnetohydrodynamic (MHD) modes of a three-dimensional waveguide for a cylindrical magnetic arcade.
Methods: We derive governing equations and dispersion relations for different density profiles and numerically solve them to obtain discrete eigenvalues for fast modes and the corresponding eigenfunctions.
Results: We find that small changes in the density structure in the vicinity of the field lines can lead to drastic effects on propagating solutions and, under certain conditions, two evanescent waves arise.
Conclusions: We investigate coronal loop oscillations in an arcade as fast MHD modes of oscillations. We find that coronal loops with slightly different density structures can exhibit different oscillatory behaviour and some eigenmodes can be present or absent depending on this density structure. Though the model has a simple potential field, the role of a cylindrical waveguide in conjunction with differing density structures is demonstrated clearly. Multiple-wavelength observations at several points in the coronal loop arcades is suggested for correct mode identification; this is crucial for unraveling the plasma properties of the oscillating loops. Title: Predictions of Sunspot Cycle 24: A Comparison with Observations Authors: Bhatt, N. J.; Jain, R. Bibcode: 2017AGUFMSH11C..05B Altcode: The space weather is largely affected due to explosions on the Sun viz. solar flares and CMEs, which, however, in turn depend upon the magnitude of the solar activity i e. number of sunspots and their magnetic configuration. Owing to these space weather effects, predictions of sunspot cycle are important. Precursor techniques, particularly employing geomagnetic indices, are often used in the prediction of the maximum amplitude of a sunspot cycle. Based on the average geomagnetic activity index aa (since 1868 onwards) for the year of the sunspot minimum and the preceding four years, Bhatt et al. (2009) made two predictions for sunspot cycle 24 considering 2008 as the year of sunspot minimum: (i) The annual maximum amplitude would be 92.8±19.6 (1-sigma accuracy) indicating a somewhat weaker cycle 24 as compared to cycles 21-23, and (ii) smoothed monthly mean sunspot number maximum would be in October 2012±4 months (1-sigma accuracy). However, observations reveal that the sunspot minima extended up to 2009, and the maximum amplitude attained is 79, with a monthly mean sunspot number maximum of 102.3 in February 2014. In view of the observations and particularly owing to the extended solar minimum in 2009, we re-examined our prediction model and revised the prediction results. We find that (i) The annual maximum amplitude of cycle 24 = 71.2 ± 19.6 and (ii) A smoothed monthly mean sunspot number maximum in January 2014±4 months. We discuss our failure and success aspects and present improved predictions for the maximum amplitude as well as for the timing, which are now in good agreement with the observations. Also, we present the limitations of our forecasting in the view of long term predictions. We show if year of sunspot minimum activity and magnitude of geomagnetic activity during sunspot minimum are taken correctly then our prediction method appears to be a reliable indicator to forecast the sunspot amplitude of the following solar cycle. References:Bhatt, N.J., Jain, R. & Aggarwal, M.: 2009, Sol. Phys. 260, 225 Title: Trapped modes of a cylindrical waveguide in the Sun's corona. Authors: Thackray, Hope; Jain, Rekha Bibcode: 2016usc..confE...8T Altcode: By modelling coronal-loop oscillations within three-dimensional magnetic arcades, it has been shown that MHD fast waves can be trapped within a 3D waveguide comprised of two shells with sharp discontinuities, the overlaying one being of denser plasma (Hindman & Jain, 2015). We extend this model to that of a three shell waveguide, with the outermost shell denser than the innermost, to study the effect of less sharp discontinuities. Deriving the governing equation for the MHD waves and finding semi-analytic solutions for the eigenfunctions, we find that the nature of propagating and evanescent waves as obtained in the two shell model changes. We will show that the eigenfrequencies and eigenfunctions depend on the thickness of the middle shell, and its position in the cylindrical arcade. The investigation has implications for identification of fast MHD waves in the solar coronal loops. Title: Time-dependent Suppression of Oscillatory Power in Evolving Solar Magnetic Fields Authors: Krishna Prasad, S.; Jess, D. B.; Jain, R.; Keys, P. H. Bibcode: 2016ApJ...823...45K Altcode: 2016ApJ...823...45P; 2016arXiv160405667K Oscillation amplitudes are generally smaller within magnetically active regions like sunspots and plage when compared to their surroundings. Such magnetic features, when viewed in spatially resolved power maps, appear as regions of suppressed power due to reductions in the oscillation amplitudes. Employing high spatial- and temporal-resolution observations from the Dunn Solar Telescope (DST) in New Mexico, we study the power suppression in a region of evolving magnetic fields adjacent to a pore. By utilizing wavelet analysis, we study for the first time how the oscillatory properties in this region change as the magnetic field evolves with time. Image sequences taken in the blue continuum, G-band, Ca II K, and Hα filters were used in this study. It is observed that the suppression found in the chromosphere occupies a relatively larger area, confirming previous findings. Also, the suppression is extended to structures directly connected to the magnetic region, and is found to get enhanced as the magnetic field strength increased with time. The dependence of the suppression on the magnetic field strength is greater at longer periods and higher formation heights. Furthermore, the dominant periodicity in the chromosphere was found to be anti-correlated with increases in the magnetic field strength. Title: Periodicities in the X-ray Emission from the Solar Corona: SphinX and SOXS Observations Authors: Steślicki, M.; Awasthi, A. K.; Gryciuk, M.; Jain, R. Bibcode: 2016CEAB...40..133S Altcode: The structure and evolution of the solar magnetic field is driven by a magnetohydrodynamic dynamo operating in the solar interior, which induces various solar activities that exhibit periodic variations on different timescales. Therefore, probing the periodic nature of emission originating from the solar corona may provide insights of the convection-zone-photosphere-corona coupling processes. We present the study of the mid-range periodicities, between rotation period (∼27 days) and the Schwabe cycle period (∼11 yr), in the solar soft X-ray emission, based on the data obtained by two instruments: SphinX and SOXS in various energy bands. Title: Eigenmodes of Three-dimensional Magnetic Arcades in the Sun’s Corona Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2015ApJ...814..105H Altcode: 2015arXiv151109411H We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger three-dimensional (3D) magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3D waveguide if the Alfvén speed increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade possessing a discontinuous density profile. The discontinuity separates a diffuse cylindrical cavity and an overlying shell of denser plasma that corresponds to the bright loops. We emphasize that all of the eigenfunctions have a discontinuous axial velocity at the density interface; hence, the interface can give rise to the Kelvin-Helmholtz instability. Further, we find that all modes have elliptical polarization with the degree of polarization changing with height. However, depending on the line of sight, only one polarization may be clearly visible. Title: Fundamental-mode Oscillations of Two Coronal Loops within a Solar Magnetic Arcade Authors: Jain, Rekha; Maurya, Ram A.; Hindman, Bradley W. Bibcode: 2015ApJ...804L..19J Altcode: 2015arXiv150407822J We analyze intensity variations, as measured by the Atmospheric Imaging Assembly in the 171 Å passband, in two coronal loops embedded within a single coronal magnetic arcade. We detect oscillations in the fundamental mode with periods of roughly 2 minutes and decay times of 5 minutes. The oscillations were initiated by interaction of the arcade with a large wavefront issuing from a flare site. Further, the power spectra of the oscillations evince signatures consistent with oblique propagation to the field lines and for the existence of a two-dimensional waveguide instead of a one-dimensional one. Title: Five-minute Oscillation Power within Magnetic Elements in the Solar Atmosphere Authors: Jain, Rekha; Gascoyne, Andrew; Hindman, Bradley W.; Greer, Benjamin Bibcode: 2014ApJ...796...72J Altcode: 2014arXiv1405.0695J It has long been known that magnetic plage and sunspots are regions in which the power of acoustic waves is reduced within the photospheric layers. Recent observations now suggest that this suppression of power extends into the low chromosphere and is also present in small magnetic elements far from active regions. In this paper we investigate the observed power suppression in plage and magnetic elements, by modeling each as a collection of vertically aligned magnetic fibrils and presuming that the velocity within each fibril is the response to buffeting by incident p modes in the surrounding field-free atmosphere. We restrict our attention to modeling observations made near the solar disk center, where the line-of-sight velocity is nearly vertical and hence, only the longitudinal component of the motion within the fibril contributes. Therefore, we only consider the excitation of axisymmetric sausage waves and ignore kink oscillations as their motions are primarily horizontal. We compare the vertical motion within the fibril with the vertical motion of the incident p mode by constructing the ratio of their powers. In agreement with observational measurements we find that the total power is suppressed within strong magnetic elements for frequencies below the acoustic cut-off frequency. However, further physical effects need to be examined for understanding the observed power ratios for stronger magnetic field strengths and higher frequencies. We also find that the magnitude of the power deficit increases with the height above the photosphere at which the measurement is made. Furthermore, we argue that the area of the solar disk over which the power suppression extends increases as a function of height. Title: Importance of Solar Atmospheric Coupling on P-Mode Power within Magnetic Elements Authors: Gascoyne, A.; Jain, R. Bibcode: 2014AGUFMSH41B4142G Altcode: It has long been known that the power of p-mode oscillations is reducedwithin magnetic plages and sunspots at photospheric level. Recent observations now suggest that this suppression of power extends into the low chromosphere and isalso present in small magnetic elements far from active regions. Weconstruct a model to investigate a possible mechanism of this powerloss whereby p modes buffet small magnetic elements and excite MHDsausage tube waves. These magnetic tube waves propagate along the manymagnetic fibrils which are embedded in the convection zone and expandinto the chromosphere due to the fall in density with height of thesurrounding plasma. We treat the magnetic fibrils as verticallyaligned, thin flux tubes embedded in a two region polytropic-isothermalatmosphere to study the coupling of p-mode driven sausage waves,which are excited in the convection zone and propagate into theoverlying chromosphere. The excited tube waves carry energy away fromthe p-mode cavity resulting in a deficit of p-mode energy which wequantify by computing the associated damping rate and absorptioncoefficient of the driving p modes. We also compare the verticalmotion within the fibril with the vertical motion of the incident p modeby constructing the ratio of their powers using HMI data and theory.In agreement with observational measurements we find that the totalpower is suppressed within strong magnetic elements for frequenciesbelow the acoustic cut-off frequency. We also find that the magnitudeof the power deficit increases with the height above the photosphereat which the measurement is made. Further, we argue that the area ofthe solar disk over which the power suppression extends increases as afunction of height. Title: Interpreting Coronal-Loop Oscillations as the Modes of a 2D Waveguide Authors: Hindman, B.; Jain, R. Bibcode: 2014AGUFMSH13A4072H Altcode: The bright coronal loops that trace bundles of field lines within coronal arcades have been observed to oscillate with one or more preferred frequencies. Recent studies indicate that two distinct categories of oscillation occur: large-amplitude, transient oscillations that are initiated by flares and low-amplitude, "decayless" oscillations that can persist for as long as the loop remains visible. The preferred frequencies of these oscillations have previously been interpreted as the resonant frequencies of MHD fast waves that are trapped between the photospheric footpoints of a bundle of field lines in a 1-D cavity. The nascent field of coronal-loop seismology attempts to deduce loop properties, such as the magnetic-field strength, loop length, etc., by exploiting the information contained in the measured mode periods. We present an alternative 2D model of the wave cavity whereby the waves can propagate across field lines and the entire magnetic arcade acts as a waveguide. Within this framework, the two types of oscillations, flare-induced waves and decayless oscillations, can both be attributed to MHD fast waves. The two components of the signal differ only because of the duration and spatial extent of the source that creates them. The flare-induced waves are generated by strong, localized sources of short duration, while the decayless background is excited by a diffuse, stochastic source. Further, the oscillatory signal induced by a flare can be interpreted as a pattern of interference fringes produced by waves that are launched from a compact source and have traveled diverse routes of various pathlength through the waveguide. The amplitude of the resulting fringe pattern decays in time without the need for local dissipation mechanisms. The details of the interference pattern depend on the shape of the arcade and on the spatial variation of the Alfvén speed within the arcade. We explore these details with a view to understanding the excitation mechanism of the oscillations and the seismological implications of the interference process. Title: Homologous flare-CME events and their metric type II radio burst association Authors: Yashiro, S.; Gopalswamy, N.; Mäkelä, P.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan, P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.; Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P. Bibcode: 2014AdSpR..54.1941Y Altcode: Active region NOAA 11158 produced many flares during its disk passage. At least two of these flares can be considered as homologous: the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on February 14, 2011. Both flares occurred at the same location (eastern edge of the active region) and have a similar decay of the GOES soft X-ray light curve. The associated coronal mass ejections (CMEs) were slow (334 and 337 km/s) and of similar apparent widths (43° and 44°), but they had different radio signatures. The second event was associated with a metric type II burst while the first one was not. The COR1 coronagraphs on board the STEREO spacecraft clearly show that the second CME propagated into the preceding CME that occurred 50 min before. These observations suggest that CME-CME interaction might be a key process in exciting the type II radio emission by slow CMEs. Title: Energy Loss of Solar p Modes due to the Excitation of Magnetic Sausage Tube Waves: Importance of Coupling the Upper Atmosphere Authors: Gascoyne, A.; Jain, R.; Hindman, B. W. Bibcode: 2014ApJ...789..109G Altcode: 2014arXiv1405.0130G We consider damping and absorption of solar p modes due to their energy loss to magnetic tube waves that can freely carry energy out of the acoustic cavity. The coupling of p modes and sausage tube waves is studied in a model atmosphere composed of a polytropic interior above which lies an isothermal upper atmosphere. The sausage tube waves, excited by p modes, propagate along a magnetic fibril which is assumed to be a vertically aligned, stratified, thin magnetic flux tube. The deficit of p-mode energy is quantified through the damping rate, Γ, and absorption coefficient, α. The variation of Γ and α as a function of frequency and the tube's plasma properties is studied in detail. Previous similar studies have considered only a subphotospheric layer, modeled as a polytrope that has been truncated at the photosphere. Such studies have found that the resulting energy loss by the p modes is very sensitive to the upper boundary condition, which, due to the lack of an upper atmosphere, have been imposed in a somewhat ad hoc manner. The model presented here avoids such problems by using an isothermal layer to model the overlying atmosphere (chromosphere, and, consequently, allows us to analyze the propagation of p-mode-driven sausage waves above the photosphere. In this paper, we restrict our attention to frequencies below the acoustic cut off frequency. We demonstrate the importance of coupling all waves (acoustic, magnetic) in the subsurface solar atmosphere with the overlying atmosphere in order to accurately model the interaction of solar f and p modes with sausage tube waves. In calculating the absorption and damping of p modes, we find that for low frequencies, below ≈3.5 mHz, the isothermal atmosphere, for the two-region model, behaves like a stress-free boundary condition applied at the interface (z = -z 0). Title: An Interpretation of Flare-induced and Decayless Coronal-loop Oscillations as Interference Patterns Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2014ApJ...784..103H Altcode: 2013arXiv1312.1922H We present an alternative model of coronal-loop oscillations, which considers that the waves are trapped in a two-dimensional waveguide formed by the entire arcade of field lines. This differs from the standard one-dimensional model which treats the waves as the resonant oscillations of just the visible bundle of field lines. Within the framework of our two-dimensional model, the two types of oscillations that have been observationally identified, flare-induced waves and "decayless" oscillations, can both be attributed to MHD fast waves. The two components of the signal differ only because of the duration and spatial extent of the source that creates them. The flare-induced waves are generated by strong localized sources of short duration, while the decayless background can be excited by a continuous, stochastic source. Further, the oscillatory signal arising from a localized, short-duration source can be interpreted as a pattern of interference fringes produced by waves that have traveled diverse routes of various pathlengths through the waveguide. The resulting amplitude of the fringes slowly decays in time with an inverse square root dependence. The details of the interference pattern depend on the shape of the arcade and the spatial variation of the Alfvén speed. The rapid decay of this wave component, which has previously been attributed to physical damping mechanisms that remove energy from resonant oscillations, occurs as a natural consequence of the interference process without the need for local dissipation. Title: Multiwavelength diagnostics of the precursor and main phases of an M1.8 flare on 2011 April 22 Authors: Awasthi, A. K.; Jain, R.; Gadhiya, P. D.; Aschwanden, M. J.; Uddin, W.; Srivastava, A. K.; Chandra, R.; Gopalswamy, N.; Nitta, N. V.; Yashiro, S.; Manoharan, P. K.; Choudhary, D. P.; Joshi, N. C.; Dwivedi, V. C.; Mahalakshmi, K. Bibcode: 2014MNRAS.437.2249A Altcode: 2013arXiv1310.6029A; 2013MNRAS.tmp.2720A We study the temporal, spatial and spectral evolution of the M1.8 flare, which occurred in the active region 11195 (S17E31) on 2011 April 22, and explore the underlying physical processes during the precursor phase and their relation to the main phase. The study of the source morphology using the composite images in 131 Å wavelength observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly and 6-14 keV [from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)] revealed a multiloop system that destabilized systematically during the precursor and main phases. In contrast, hard X-ray emission (20-50 keV) was absent during the precursor phase, appearing only from the onset of the impulsive phase in the form of foot-points of emitting loops. This study also revealed the heated loop-top prior to the loop emission, although no accompanying foot-point sources were observed during the precursor phase. We estimate the flare plasma parameters, namely temperature (T), emission measure (EM), power-law index (γ) and photon turn-over energy (ɛto), and found them to be varying in the ranges 12.4-23.4 MK, 0.0003-0.6 × 1049 cm-3, 5-9 and 14-18 keV, respectively, by forward fitting RHESSI spectral observations. The energy released in the precursor phase was thermal and constituted ≈1 per cent of the total energy released during the flare. The study of morphological evolution of the filament in conjunction with synthesized T and EM maps was carried out, which reveals (a) partial filament eruption prior to the onset of the precursor emission and (b) heated dense plasma over the polarity inversion line and in the vicinity of the slowly rising filament during the precursor phase. Based on the implications from multiwavelength observations, we propose a scheme to unify the energy release during the precursor and main phase emissions in which the precursor phase emission was originated via conduction front that resulted due to the partial filament eruption. Next, the heated leftover S-shaped filament underwent slow-rise and heating due to magnetic reconnection and finally erupted to produce emission during the impulsive and gradual phases. Title: Variation of solar oscillation frequencies in solar cycle 23 and their relation to sunspot area and number (Corrigendum) Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.; Jain, K.; Hill, F. Bibcode: 2013A&A...560C...1J Altcode: No abstract at ADS Title: Solar energetic particle events during the rise phases of solar cycles 23 and 24 Authors: Chandra, R.; Gopalswamy, N.; Mäkelä, P.; Xie, H.; Yashiro, S.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Jain, R.; Awasthi, A. K.; Manoharan, P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Choudhary, D. P.; Nitta, N. V. Bibcode: 2013AdSpR..52.2102C Altcode: We present a comparative study of the properties of coronal mass ejections (CMEs) and flares associated with the solar energetic particle (SEP) events in the rising phases of solar cycles (SC) 23 (1996-1998) (22 events) and 24 (2009-2011) (20 events), which are associated with type II radio bursts. Based on the SEP intensity, we divided the events into three categories, i.e. weak (intensity < 1 pfu), minor (1 pfu < intensity < 10 pfu) and major (intensity ⩾ 10 pfu) events. We used the GOES data for the minor and major SEP events and SOHO/ERNE data for the weak SEP event. We examine the correlation of SEP intensity with flare size and CME properties. We find that most of the major SEP events are associated with halo or partial halo CMEs originating close to the sun center and western-hemisphere. The fraction of halo CMEs in SC 24 is larger than the SC 23. For the minor SEP events one event in SC23 and one event in SC24 have widths < 120° and all other events are associated with halo or partial halo CMEs as in the case of major SEP events. In case of weak SEP events, majority (more than 60%) of events are associated with CME width < 120°. For both the SC the average CMEs speeds are similar. For major SEP events, average CME speeds are higher in comparison to minor and weak events. The SEP event intensity and GOES X-ray flare size are poorly correlated. During the rise phase of solar cycle 23 and 24, we find north-south asymmetry in the SEP event source locations: in cycle 23 most sources are located in the south, whereas during cycle 24 most sources are located in the north. This result is consistent with the asymmetry found with sunspot area and intense flares. Title: Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2013ApJ...778..174H Altcode: 2013arXiv1308.0620H We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios. Title: Flux emergence, flux imbalance, magnetic free energy and solar flares Authors: Choudhary, Debi Prasad; Gosain, Sanjay; Gopalswamy, Nat; Manoharan, P. K.; Chandra, R.; Uddin, W.; Srivastava, A. K.; Yashiro, S.; Joshi, N. C.; Kayshap, P.; Dwivedi, V. C.; Mahalakshmi, K.; Elamathi, E.; Norris, Max; Awasthi, A. K.; Jain, R. Bibcode: 2013AdSpR..52.1561C Altcode: Emergence of complex magnetic flux in the solar active regions lead to several observational effects such as a change in sunspot area and flux embalance in photospheric magnetograms. The flux emergence also results in twisted magnetic field lines that add to free energy content. The magnetic field configuration of these active regions relax to near potential-field configuration after energy release through solar flares and coronal mass ejections. In this paper, we study the relation of flare productivity of active regions with their evolution of magnetic flux emergence, flux imbalance and free energy content. We use the sunspot area and number for flux emergence study as they contain most of the concentrated magnetic flux in the active region. The magnetic flux imbalance and the free energy are estimated using the HMI/SDO magnetograms and Virial theorem method. We find that the active regions that undergo large changes in sunspot area are most flare productive. The active regions become flary when the free energy content exceeds 50% of the total energy. Although, the flary active regions show magnetic flux imbalance, it is hard to predict flare activity based on this parameter alone. Title: A multiwavelength study of eruptive events on January 23, 2012 associated with a major solar energetic particle event Authors: Joshi, N. C.; Uddin, W.; Srivastava, A. K.; Chandra, R.; Gopalswamy, N.; Manoharan, P. K.; Aschwanden, M. J.; Choudhary, D. P.; Jain, R.; Nitta, N. V.; Xie, H.; Yashiro, S.; Akiyama, S.; Mäkelä, P.; Kayshap, P.; Awasthi, A. K.; Dwivedi, V. C.; Mahalakshmi, K. Bibcode: 2013AdSpR..52....1J Altcode: 2013arXiv1303.1251J We use multiwavelength data from space and ground based instruments to study the solar flares and coronal mass ejections (CMEs) on January 23, 2012 that were responsible for one of the largest solar energetic particle (SEP) events of solar cycle 24. The eruptions consisting of two fast CMEs (≈1400 km s-1 and ≈2000 km s-1) and M-class flares that occurred in active region 11402 located at ≈N28 W36. The two CMEs occurred in quick successions, so they interacted very close to the Sun. The second CME caught up with the first one at a distance of ≈11-12 Rsun. The CME interaction may be responsible for the elevated SEP flux and significant changes in the intensity profile of the SEP event. The compound CME resulted in a double-dip moderate geomagnetic storm (Dst∼-73nT). The two dips are due to the southward component of the interplanetary magnetic field in the shock sheath and the ICME intervals. One possible reason for the lack of a stronger geomagnetic storm may be that the ICME delivered a glancing blow to Earth. Title: Height of shock formation in the solar corona inferred from observations of type II radio bursts and coronal mass ejections Authors: Gopalswamy, N.; Xie, H.; Mäkelä, P.; Yashiro, S.; Akiyama, S.; Uddin, W.; Srivastava, A. K.; Joshi, N. C.; Chandra, R.; Manoharan, P. K.; Mahalakshmi, K.; Dwivedi, V. C.; Jain, R.; Awasthi, A. K.; Nitta, N. V.; Aschwanden, M. J.; Choudhary, D. P. Bibcode: 2013AdSpR..51.1981G Altcode: 2013arXiv1301.0893G Employing coronagraphic and EUV observations close to the solar surface made by the Solar Terrestrial Relations Observatory (STEREO) mission, we determined the heliocentric distance of coronal mass ejections (CMEs) at the starting time of associated metric type II bursts. We used the wave diameter and leading edge methods and measured the CME heights for a set of 32 metric type II bursts from solar cycle 24. We minimized the projection effects by making the measurements from a view that is roughly orthogonal to the direction of the ejection. We also chose image frames close to the onset times of the type II bursts, so no extrapolation was necessary. We found that the CMEs were located in the heliocentric distance range from 1.20 to 1.93 solar radii (Rs), with mean and median values of 1.43 and 1.38 Rs, respectively. We conclusively find that the shock formation can occur at heights substantially below 1.5 Rs. In a few cases, the CME height at type II onset was close to 2 Rs. In these cases, the starting frequency of the type II bursts was very low, in the range 25-40 MHz, which confirms that the shock can also form at larger heights. The starting frequencies of metric type II bursts have a weak correlation with the measured CME/shock heights and are consistent with the rapid decline of density with height in the inner corona. Title: Geo-effectiveness of Solar Transients and their interrelationship Authors: Tripathi, S. C.; Khan, P. A.; Muhammad, A. A.; Gwal, A. K.; Purohit, P. K.; Jain, R. Bibcode: 2012AGUFMSH21A2197T Altcode: We probe the geo-effectiveness of Solar Transients observed in the solar cycle 23 and try to find their interrelationship with each other. In this investigation we undertake 60 Solar Proton Events of the Solar Cycle 23 alongwith associated Solar Flares and CMEs. We employ the X-ray emission in Solar flares observed by Reuven Ramaty Higly Energy Solar Spectroscopic Imager (RHESSI) and Solar X-Ray Spectrometer (SOXS) in order to estimate flare plasma parameters. Further, we employ the observations from Geo-stationary Operational Environmental Satellites (GOES) and Large Angle and Spectrometric Coronagraph (LASCO), for SEPs and CMEs parameter estimation respectively. We report a good association of soft-hard-harder (SHH) spectral behavior in Solar Flares with occurrence of Solar Proton Events. In addition, we have found a good correlation (R=0.71) in SEPs spectral hardening and CME velocity. We conclude that the Protons as well as CMEs gets accelerated at the Flare site and travel all the way in interplanetary space and then by re-acceleration in interplanetary space CMEs produce Geomagnetic Storms in geo-space. This seems to be a statistically significant mechanism of the SEPs and initial CME acceleration in addition to the standard scenario of SEP acceleration at the shock front of CMEs. Title: Variation of solar oscillation frequencies in solar cycle 23 and their relation to sunspot area and number Authors: Jain, R.; Tripathy, S. C.; Watson, F. T.; Fletcher, L.; Jain, K.; Hill, F. Bibcode: 2012A&A...545A..73J Altcode:
Aims: Studying the long term evolution of the solar acoustic oscillations is necessary for understanding how the large-scale solar dynamo operates. In particular, an understanding of the solar cycle variation in the frequencies of solar oscillations can provide a powerful diagnostic tool for constraining various dynamo models. In this work, we report the temporal evolution of solar oscillations for the solar cycle 23, and correlate with solar magnetic activity indices.
Methods: We use solar oscillation frequencies obtained from the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, correlate them with the sunspot number provided by the international sunspot number, RI, and compare them with the sunspot number calculated with the Sunspot Tracking And Recognition Algorithm (STARA).
Results: We find that the mean frequency shifts correlate very well with the sunspot numbers obtained from two different datasets. We also find a hysteresis-type behaviour for the STARA sunspot area and mean magnetic field strength for the different phases of the solar cycle. The increase in solar oscillation frequencies precedes slightly the increase in total sunspot area and the mean magnetic field strength for the solar cycle 23. We briefly discuss the cyclic behaviour in the context of p-mode frequencies. Title: Kink Oscillations of a Curved, Gravitationally Stratified Coronal Loop Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2012arXiv1209.5734H Altcode: Loops of magnetic field in the corona are observed to oscillate and these oscillations have been posited to be the superposition of resonant kink waves. To date, most analyses of these oscillations have concentrated on calculating the frequency shifts that result from spatial variation in the kink wave speed. Further, most have ignored gravity and treated the loop as a straight tube. Here we ignore spatial variation in the wave speed, but self-consistently include the effects of gravity and loop curvature in both the equilibrium loop model and in the wave equation. We model a coronal loop as an isolated, thin, magnetic fibril that is anchored at two points in the photosphere. The equilibrium shape of the loop is determined by a balance between magnetic buoyancy and magnetic tension, which is characterized by a Magnetic Bond Number \epsilon, that is typically small |\epsilon| << 1. This balance produces a loop that has a variable radius of curvature. The resonant kink waves of such a loop come in two polarizations that are decoupled from each other: waves with motion completely within the plane of the loop (normal oscillations) and waves with motions that are completely horizontal, perpendicular to the plane of the loop (binormal oscillations). We solve for the eigensolutions of both polarizations using perturbation theory for small Magnetic Bond Number. For modes of the same order, normal oscillations have smaller eigenfrequencies than binormal oscillations. The additional forces of buoyancy and magnetic tension from the curvature of the loop increase and decrease the mode frequencies, respectively. The ratio of the frequencies of the first overtone to the fundamental mode is modified by the inclusion of buoyancy and curvature. We find that the normal polarization possesses a frequency ratio that exceeds the canonical value of 2, whereas the binormal polarization has a ratio less than 2. Title: What can be learned from the seismology of a coronal loop using only a handful of frequencies? Authors: Jain, R.; Hindman, B. W. Bibcode: 2012A&A...545A.138J Altcode: Context. Transverse oscillating loops in the solar corona have been observed and the frequencies for a couple of low-order modes measured. These frequencies have been used as a diagnostic tool to investigate the internal properties of such oscillating loops. In particular, the density and magnetic field profiles along the loop are estimated by comparing the measured frequencies with those of a reference model. In this paper, we argue that only the kink speed may be assessed directly and there is no diagnostic capability for density or magnetic field independent of the wave speed. Further, with just a handful of measured frequencies available, only broad spatial averages of the kink speed may be obtained. We demonstrate using a frequency inversion procedure that with only two frequencies as inputs, at best one can assess the mean and the contrast of the kink speed along the loop. One requires access to the frequencies of many mode orders to perform inversions that offer kink speed determinations with high spatial resolution.
Aims: We suggest a rigorous mathematical formalism that describes the information content of the measured mode frequencies and we present a method to infer the kink speed within a coronal loop by inverting those frequencies.
Methods: We consider a single magnetic coronal loop and by using perturbation theory, relate its eigenfrequencies to the loop's physical properties.
Results: We derive the sensitivity kernels that describe how each eigenfrequency contain the information about the kink speed and density along the loop.
Conclusions: We conclude that the eigenfrequencies contain information primarily about the kink speed, and do not strongly depend on the density. Therefore, all loop models with the same kink speed profile (but different density and magnetic field profiles) are seismically indistinguishable. To acheive the spatial resolution neccessary to uncover the non-uniform nature of the coronal loop, it is necessary to do inversion of many measured frequencies. Making inferences about the density stratification and magnetic field varying along the loop requires supplemental observations that are non-seismic in nature. Title: Spine-fan reconnection. The influence of temporal and spatial variation in the driver Authors: Wyper, P. F.; Jain, R.; Pontin, D. I. Bibcode: 2012A&A...545A..78W Altcode: Context. From observations, the atmosphere of the Sun has been shown to be highly dynamic with perturbations of the magnetic field often lacking temporal or spatial symmetry. Despite this, studies of the spine-fan reconnection mode at 3D nulls have so far focused on the very idealised case with symmetric driving of a fixed spatial extent.
Aims: We investigate the spine-fan reconnection process for less idealised cases, focusing on asymmetric driving and drivers with different length scales. We look at the initial current sheet formation and whether the scalings developed in the idealised models are robust in more realistic situations.
Methods: The investigation was carried out by numerically solving the resistive compressible 3D magnetohydrodynamic equations in a Cartesian box containing a linear null point. The spine-fan collapse was driven at the null through tangential boundary driving of the spine foot points.
Results: We find significant differences in the initial current sheet formation with asymmetric driving. Notable is the displacement of the null point position as a function of driving velocity and resistivity (η). However, the scaling relations developed in the idealised case are found to be robust (albeit at reduced amplitudes) despite this extra complexity. Lastly, the spatial variation is also shown to play an important role in the initial current sheet formation through controlling the displacement of the spine foot points.
Conclusions: We conclude that during the early stages of spine-fan reconnection both the temporal and spatial nature of the driving play important roles, with the idealised symmetrically driven case giving a "best case" for the rate of current development and connectivity change. As the most interesting eruptive events occur in relatively short time frames this work clearly shows the need for high temporal and spatial knowledge of the flows for accurate interpretation of the reconnection scenario. Lastly, since the scalings developed in the idealised case remain robust with more complex driving we can be more confident of their use in interpreting reconnection in complex magnetic field structures. Title: Axisymmetric Scattering of p Modes by Thin Magnetic Tubes Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2012ApJ...746...66H Altcode: 2011arXiv1106.5078H We examine the scattering of acoustic p-mode waves from a thin magnetic fibril embedded in a gravitationally stratified atmosphere. The scattering is mediated through the excitation of slow sausage waves on the magnetic tube, and only the scattering of the monopole component of the wave field is considered. Since such tube waves are not confined by the acoustic cavity and may freely propagate along the field lines removing energy from the acoustic wave field, the excitation of fibril oscillations is a source of acoustic wave absorption as well as scattering. We compute the mode mixing that is achieved and the absorption coefficients and phase shifts. We find that for thin tubes the mode mixing is weak and the absorption coefficient is small and is a smooth function of frequency over the physically relevant band of observed frequencies. The prominent absorption resonances seen in previous studies of unstratified tubes are absent. Despite the relatively small absorption, the phase shift induced can be surprisingly large, reaching values as high as 15° for f modes. Further, the phase shift can be positive or negative depending on the incident mode order and the frequency. Title: The effect of the environment on the P1/P2 period ratio for kink oscillations of coronal loops Authors: Orza, B.; Ballai, I.; Jain, R.; Murawski, K. Bibcode: 2012A&A...537A..41O Altcode: 2011arXiv1111.4859O
Aims: The P1/P2 period ratio of transversal loop oscillations is currently used for the diagnostics of longitudinal structuring of coronal loops as its deviation from 2 is intrinsically connected to the density scale-height along coronal loops and/or the sub-resolution structure of the magnetic field. The same technique can be applied not only to coronal structures, but also to other oscillating magnetic structures.
Methods: The oscillations in magnetic structures are described by differential equations whose coefficients depend on the longitudinal structure of the plasma. Using a variational principle written for the transversal component of the velocity vector, developed earlier by McEwan et al. (2008, A&A, 481, 819), we investigate how the different temperature of the environment compared to the temperature of the magnetic structure will influence the P1/P2 ratio for typical coronal and prominence conditions. The possible changes are translated into quantities that are used in the process of remote plasma diagnostics in the solar atmosphere.
Results: Using a straightforward, yet comprehensive, procedure we show that under coronal conditions the effect of the temperature difference between the plasma inside and outside the magnetic structure can change considerably the period ratio; in the case of coronal loops the change in the period ratio can reach even 40%. We also show that once dispersive effects are taken into account, with oscillation periods shorter than the cut-off period (determined by the density and temperature difference) the domain where the model can be applied is reduced. In the case of prominences embedded in the hot corona, the effect of the environment is negligeable given the high density and temperature difference between the chromospheric prominences and corona. Using a numerical approach, we show that our analytical discussion produces a robust result. We also discuss what implications our model has on seismological (or diagnostics) techniques in the solar corona.
Conclusions: Our analysis shows that the period ratio P1/P2 is sensitive to the temperature difference between the loop and its environment and this effect should always be taken into account when estimating the degree of density structuring with period ratio method of coronal loops.

Appendix A is available in electronic form at http://www.aanda.org Title: Observations of the Interaction of Acoustic Waves and Small-scale Magnetic Fields in a Quiet Sun Authors: Chitta, Lakshmi Pradeep; Jain, Rekha; Kariyappa, R.; Jefferies, Stuart M. Bibcode: 2012ApJ...744...98C Altcode: 2012ApJ...744...98P The effect of the magnetic field on photospheric intensity and velocity oscillations at the sites of small-scale magnetic fields (SMFs) in a quiet Sun near the solar disk center is studied. We use observations made by the G-band filter in the Solar Optical Telescope on board Hinode for intensity oscillations; Doppler velocity, magnetic field, and continuum intensity are derived from an Ni I photospheric absorption line at 6767.8 Å using the Michelson Doppler Imager on board the Solar and Heliospheric Observatory. Our analysis shows that both the high-resolution intensity observed in the G band and velocity oscillations are influenced by the presence of a magnetic field. While intensity oscillations are suppressed at all frequencies in strong magnetic field regions compared to weak magnetic field regions, velocity oscillations show an enhancement of power in the frequency band 5.5-7 mHz. We find that there is a drop of 20%-30% in the p-mode power of velocity oscillations within the SMFs when compared to the regions surrounding them. Our findings indicate that the nature of the interaction of acoustic waves with the quiet Sun SMFs is similar to that of large-scale magnetic fields in active regions. We also report the first results of the center-to-limb variation of such effects using the observations of the quiet Sun from the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). The independent verification of these interactions using SDO/HMI suggests that the velocity power drop of 20%-30% in p-modes is fairly constant across the solar disk. Title: Torsional magnetic reconnection: The effects of localizing the non-ideal (ηJ) term Authors: Wyper, Peter F.; Jain, Rekha Bibcode: 2011JPlPh..77..843W Altcode: Magnetic reconnection in three dimensions (3D) is a natural extension from X-point reconnection in two dimensions. Of central importance in the 3D process is a localized non-ideal region within which the plasma and magnetic field decouple allowing for field line connectivity change. In practice, localized current structures provide this localization; however, mathematically a similar effect can be achieved with the localization of plasma resistivity instead. Physically though, such approaches are unrealistic, as anomalous resistivity requires very localized currents. Therefore, we wish to know how much information is lost in localizing η instead of current? In this work we develop kinematic models for torsional spine and fan reconnection using both localized η and localized current and compare the non-ideal flows predicted by each. We find that the flow characteristics are dictated almost exclusively by the form taken for the current profile with η acting only to scale the flow. We do, however, note that the reconnection mechanism is the same in each case. Therefore, from an understanding point of view, localized η models are still important first steps into exploring the role of non-ideal effects. Title: Damping rates of p-modes by an ensemble of randomly distributed thin magnetic flux tubes Authors: Gascoyne, Andrew; Jain, Rekha Bibcode: 2011IAUS..273..351G Altcode: The magnetohydrodynamic (MHD) sausage tube waves are excited in the magnetic flux tubes by p-mode forcing. These tube waves thus carry energy away from the p-mode cavity which results in the deficit of incident p-mode energy. We calculate the loss of incident p-mode energy as a damping rate of f- and p-modes. We calculate the damping rates of f- and p-modes by a model Sun consisting of an ensemble of many thin magnetic flux tubes with varying plasma properties and distributions. Each magnetic flux tube is modelled as axisymmetric, vertically oriented and untwisted. We find that the magnitude and the form of the damping rates are sensitive to the plasma-β of the tubes and the upper boundary condition used. Title: Interaction of p modes with a collection of thin magnetic tubes Authors: Jain, R.; Gascoyne, A.; Hindman, B. W. Bibcode: 2011MNRAS.415.1276J Altcode: 2011MNRAS.tmp..823J We investigate the net effect of a multitude of thin magnetic tubes on the energy of ambient acoustic p modes. A p mode, when incident on a thin magnetic flux tube, excites magnetohydrodynamic (MHD) tube waves. These tube waves propagate vertically along the flux tube carrying away energy from the p-mode cavity resulting in the absorption of incident p-mode energy. We calculate the absorption arising from the excitation of sausage MHD waves within a collection of many non-interacting magnetic flux tubes with differing plasma properties. We find that the shape and magnitude of the absorption, when compared with the observationally measured absorption, favours a model with a maximum-flux boundary condition applied at the photosphere and a narrow distribution of plasma β in an ensemble with mean β value between 0.5 and 1. Title: Sensitivity of p-mode absorption on magnetic region properties and kernel functions Authors: Gascoyne, A.; Jain, R.; Hindman, B. W. Bibcode: 2011A&A...526A..93G Altcode:
Aims: Magnetohydrodynamic (MHD) sausage tube waves are excited in magnetic flux tubes by p-mode forcing. These tube waves carry energy away from the p-mode cavity which results in a source of absorption. We wish to see the effect of an ensemble of randomly distributed thin magnetic flux tubes on the absorption of p-modes for the model plage region and also study the effect of the spacial weighting function on the theoretically calculated absorption coefficients.
Methods: We calculate the absorption coefficients of p modes for a model plage, assumed to consist of an ensemble of many thin magnetic flux tubes with randomly distributed plasma properties. Each magnetic flux tube in the ensemble is modelled as axisymmetric, non-interacting, vertically oriented and untwisted.
Results: We find that the magnitude and the form of the absorption coefficient is sensitive to the plasma-β of the tubes which is consistent with previous work. Both the random distribution used to model the ensemble of flux tubes and the spatial weighting function inherent to the measurement of the absorption affect the absorption. As the width of the weighting function increases, the absorption increases. Title: Helioseismic Tests With the FLASH Simulation Code Authors: González-Morales, Pedro A.; Jain, Rekha; Thompson, Michael J. Bibcode: 2011JPhCS.271a2013G Altcode: We show our first results from local helioseismic simulations using the numerical code FLASH by testing its suitability for simulating subphotospheric wave motions in helioseismology. In order to check the capability of this code for different sources of waves, we have implemented a non-magnetic plane-parallel atmosphere adding a source term to the energy equation. We confirm the capabilities of FLASH code for investigating the propagation of sound waves into a realistically stratified solar interior. Title: Axisymmetric absorption of p modes by an ensemble of thin, magnetic-flux tubes Authors: Jain, R.; Gascoyne, A.; Hindman, B. W. Bibcode: 2011JPhCS.271a2016J Altcode: The buffeting action of the solar acoustic waves (p modes) on magnetic fibrils excites magnetohydrodynamic (MHD) tube waves. We model these fibrils as axisymmetric, untwisted, vertically oriented, thin, magnetic-flux tubes. The MHD tube waves propagate along the length of the tube and carry energy away from the p-mode cavity creating a source of p-mode absorption. We calculate the absorption arising from the excitation of sausage MHD waves within a model plage composed of many flux tubes with differing plasma properties. We find that for a collection of tubes with normally distributed plasma parameters β, the macroscopic absorption coefficient of the collection effectively depends on only the mean value of β. Title: Time-Varying Thermal Emission in Solar Flares Authors: Jain, R.; Rajpurohit, A. S.; Aggarwal, M.; Jamwal, R.; Awasthi, A. Bibcode: 2010ASSP...19..465J Altcode: 2010mcia.conf..465J We study thermal emission in solar flares using high-resolution X-ray spectra obtained with the Si detector of the Solar X-ray Spectrometer (SOXS) mission onboard the GSAT-2 Indian spacecraft launched in 2003. We model the spectral-temporal evolution of the medium-hard X-ray flux in terms of an evolving multi-temperature plasma governed by thermal conduction cooling and find agreement with the observations. By measuring the DEM power-law index for five M-class flares, we find that the emission in the 6-20 keV energy range is dominated by temperatures 15-50MK, while the power-law index of the thermal spectrum varies over 2.2-6.1. The mean value of the thermal conduction cooling time is 1,440 s; the temperature-dependent cooling time varies from 22 to 102 s. Title: Large Amplitude Oscillations in Prominences Authors: Tripathi, D.; Isobe, H.; Jain, R. Bibcode: 2009SSRv..149..283T Altcode: 2009arXiv0910.4059T Since the first reports of oscillations in prominences in the 1930s, there have been major theoretical and observational developments to understand the nature of these oscillatory phenomena, leading to the whole new field of the so-called “prominence seismology”. There are two types of oscillatory phenomena observed in prominences; “small-amplitude oscillations” (2-3 km s-1), which are quite common, and “large-amplitude oscillations” (>20 km s-1) for which observations are scarce. Large-amplitude oscillations have been found as “winking filament” in H α as well as motion in the plane-of-sky in H α, EUV, micro-wave and He 10830 observations. Historically, it has been suggested that the large-amplitude oscillations in prominences were triggered by disturbances such as fast-mode MHD waves (Moreton wave) produced by remote flares. Recent observations show, in addition, that near-by flares or jets can also create such large-amplitude oscillations in prominences. Large-amplitude oscillations, which are observed both in transverse as well as longitudinal direction, have a range of periods varying from tens of minutes to a few hours. Using the observed period of oscillation and simple theoretical models, the obtained magnetic field in prominences has shown quite a good agreement with directly measured one and, therefore, justifies prominence seismology as a powerful diagnostic tool. On rare occasions, when the large-amplitude oscillations have been observed before or during the eruption, the oscillations may be applied to diagnose the stability and the eruption mechanism. Here we review the recent developments and understanding in the observational properties of large-amplitude oscillations and their trigger mechanisms and stability in the context of prominence seismology. Title: Absorption of p Modes by Magnetic Plage Authors: Jain, R.; Hindman, B. W.; Braun, D. C.; Birch, A. C. Bibcode: 2009ASPC..416...55J Altcode: The Sun's magnetic active regions, composed of sunspots and plage, are topologically complex. The magnetic field is highly structured, forming a tangle of fibrils within the plage and more compact, regimented bundles within sunspot umbrae. The fragmented nature of the field makes helioseismic observations within active regions rather difficult to interpret. We choose to study the propagation of acoustic waves through regions of plage, modeling the magnetic field therein as a collection of thin flux tubes. In this paper, we present the first results of this research; the computation of the absorption coefficient from an ensemble of many flux tubes. The incoming acoustic waves interact with the magnetic flux tube, exciting sausage and kink tube waves which propagate downward and upward carrying away energy, thereby producing absorption. We calculate the resulting theoretical absorption coefficients and compare with the most recent observations. Title: The role of magnetic fields in the scattering of p-modes Authors: Gascoyne, A.; Jain, R. Bibcode: 2009A&A...501.1131G Altcode: Aims: We determine the direct and indirect effects of magnetic field on p-mode scattering.
Methods: We solve a set of magnetohydrodynamic equations using the Born approximation to determine phase shifts in p-modes due to a region of inhomogeneity. The region of inhomogeneity is a magnetic flux tube with the characteristics of flaring field lines. This enables us to investigate the magnetic field effects on the phase shifts.
Results: The magnetic configuration of our flux tube model plays a vital role in the phase shifts of p-modes. The suppression of sound speed and pressure within the flux tube region is not the only factor to consider in the scattering of p-modes. There is a direct effect of the magnetic fields caused by the flaring of field lines on phase shifts. Title: Absorption of p Modes by Thin Magnetic Flux Tubes Authors: Jain, Rekha; Hindman, Bradley W.; Braun, Doug C.; Birch, Aaron C. Bibcode: 2009ApJ...695..325J Altcode: We study the interaction between p modes and the many magnetic fibrils that lace the solar convection zone. In particular, we investigate the resulting absorption of p-mode energy by the fibril magnetic field. Through mechanical buffeting, the p modes excite tube waves on the magnetic fibrils—in the form of longitudinal sausage waves and transverse kink waves. The tube waves propagate up and down the magnetic fibrils and out of the p-mode cavity, thereby removing energy from the incident acoustic waves. We compute the absorption coefficient associated with this damping mechanism and model the absorption that would be observed for magnetic plage. We compare our results to the absorption coefficient that is measured using the local-helioseismic technique of ridge-filtered holography. We find that, depending on the mode order and the photospheric boundary conditions, we can achieve absorption coefficients for simulated plage that exceed 50%. The observed increase of the absorption coefficient as a function of frequency is reproduced for all model parameters. Title: The Role of Mode Mixing in the Absorption of p-Modes Authors: Gordovskyy, M.; Jain, Rekha; Hindman, B. W. Bibcode: 2009ApJ...694.1602G Altcode: Observations show that a p-mode may lose up to 70% of its energy flux when it interacts with a sunspot. Part of the absorbed energy is assumed to be converted into other types of waves, while part of it is re-emitted into modes with different radial orders n. In the present paper, we investigate absorption of p-modes with the azimuthal order m = 0 due to their interaction with magnetic flux tubes and attempt to determine the role of mode mixing in this phenomenon. We consider the linearized magnetohydrodynamic equations in two-dimensional, cylindrical geometry, with all the model parameters depending only on radius r and depth z. It is assumed that the wave field may be decomposed into incoming and outgoing components that separately satisfy the governing equations. These components are calculated numerically using a second-order Runge-Kutta finite difference scheme. The calculations reveal substantial scattering from higher-to-lower radial orders n, predominantly into the f-mode (n = 0). Only weak scattering occurs from lower-to-higher radial orders. At the same time, the amount of energy transferred from the p-modes to the f-mode can account for 25%-30% of the energy lost by an incoming p-mode. Title: On Absorption and Scattering of P Modes by Small-Scale Magnetic Elements Authors: Jain, Rekha; Gordovskyy, M. Bibcode: 2008SoPh..251..361J Altcode: The solar surface is characterised everywhere by the presence of small-scale magnetic structures. Their collective behaviour in the form of active regions is known to have strong influence on p-mode power. For example, sunspots and plages are strong absorbers of acoustic waves. This paper studies the effects of individual small-scale magnetic elements to understand the details of absorption of p-mode power. For this, we consider a thin magnetic flux tube and calculate the phase shifts and the absorption coefficients by numerically solving the linearised MHD equations. The phase shifts calculated from the Born Approximation are then compared for the same range of degrees. The results are discussed with a view to understanding the physical mechanism. Title: Amplitude Suppression and Absorption of p-Modes by a Magnetic Flux Tube Authors: Gordovskyy, Mykola; Jain, Rekha Bibcode: 2008ApJ...681..664G Altcode: The interaction of p-modes (acoustic waves) with a magnetic flux tube is investigated. A set of linearized MHD equations is solved numerically in a two-dimensional domain with cylindrical geometry. The wave functions for p-modes are calculated in and around magnetic flux tubes using eigenfunctions from the unperturbed solution as a boundary condition. The amplitudes of the oscillations are found to be suppressed in the magnetized region with the suppression decreasing with depth. It is also found that the absorption of p-modes strongly depends on the degree l as well as the flux tube radius and the magnetic field strength. Convergence of magnetic field may be necessary in order to fit simultaneously the observed phase shifts and absorption coefficients. Title: Prominence Seismology: Wavelet Analysis of Filament Oscillations Authors: Pintér, Balázs; Jain, Rekha; Tripathi, Durgesh; Isobe, Hiroaki Bibcode: 2008ApJ...680.1560P Altcode: The temporal and spatial behavior of a large-amplitude filament oscillation is investigated using wavelet analysis. The extreme-ultraviolet (EUV) images of the phenomenon, which occurred on 2002 October 15, were taken from the EUV Imaging Telescope on board the Solar and Heliospheric Observatory (SOHO). The wavelet spectra, extracted from the intensity data, show that the filament oscillates as a rigid body, with a period of about 2.5-2.6 hr which is almost constant along the filament. The period slowly decreases with time until the filament erupts. No clear sign of the eruption is found in the wavelet spectrum prior to the eruption, that followed the filament oscillation. The axial component of the magnetic field is estimated between 1 and 5 G, which is believed to be reasonable for a polar crown filament of this kind. Title: Iron Abundance of Flare Plasma Authors: Dennis, B. R.; Dang, L. C.; Jain, R.; Schwartz, R. A.; Tolbert, A. K. Bibcode: 2008AGUSMSP44A..04D Altcode: The equivalent width of the iron-line complex at 6.7 keV seen in flare X-ray spectra suggests that the iron abundance of the hottest plasma at temperatures >~10MK may sometimes be significantly lower than the nominal coronal abundance of four times the photospheric value that is commonly assumed. This conclusion is based on X-ray spectral observations of several flares seen in common with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Solar X-ray Spectrometer (SOXS) on the second Indian geostationary satellite, GSAT-2. The implications of this will be discussed as it relates to the origin of the hot flare plasma - either plasma already in the corona that is directly heated during the flare energy release process or chromospheric plasma that is heated by flare-accelerated particles and driven up into the corona. Other possible explanations of lower-than-expected equivalent widths of the iron-line complex will also be discussed. Title: The Generation of Coronal Loop Waves below the Photosphere by p-Mode Forcing Authors: Hindman, Bradley W.; Jain, Rekha Bibcode: 2008ApJ...677..769H Altcode: 2008arXiv0805.1942H Recent observations of coronal-loop waves by TRACE and within the corona as a whole by CoMP clearly indicate that the dominant oscillation period is 5 minutes, thus implicating the solar p modes as a possible source. We investigate the generation of tube waves within the solar convection zone by the buffeting of p modes. The tube waves—in the form of longitudinal sausage waves and transverse kink waves—are generated on the many magnetic fibrils that lace the convection zone and pierce the solar photosphere. Once generated by p-mode forcing, the tube waves freely propagate up and down the tubes, since the tubes act like light fibers and form a waveguide for these magnetosonic waves. Those waves that propagate upward pass through the photosphere and enter the upper atmosphere, where they can be measured as loop oscillations and other forms of propagating coronal waves. We treat the magnetic fibrils as vertically aligned, thin flux tubes and compute the energy flux of tube waves that can be generated and driven into the upper atmosphere. We find that a flux in excess of 105 ergs cm-2 s-1 can be produced, easily supplying enough wave energy to explain the observations. Furthermore, we compute the associated damping rate of the driving p modes and find that the damping is significant compared to observed line widths only for the lowest order p modes. Title: Large-Amplitude Oscillation of an Erupting Filament as Seen in EUV, Hα, and Microwave Observations Authors: Isobe, H.; Tripathi, D.; Asai, A.; Jain, R. Bibcode: 2007SoPh..246...89I Altcode: 2007arXiv0711.3952I We present multiwavelength observations of a large-amplitude oscillation of a polar-crown filament on 15 October 2002, which has been reported by Isobe and Tripathi (Astron. Astrophys.449, L17, 2006). The oscillation occurred during the slow rise (≈1 km s−1) of the filament. It completed three cycles before sudden acceleration and eruption. The oscillation and following eruption were clearly seen in observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT) onboard the Solar and Heliospheric Observatory (SOHO). The oscillation was seen only in a part of the filament, and it appears to be a standing oscillation rather than a propagating wave. The amplitudes of velocity and spatial displacement of the oscillation in the plane of the sky were about 5 km s−1 and 15 000 km, respectively. The period of oscillation was about two hours and did not change significantly during the oscillation. The oscillation was also observed in Hα by the Flare Monitoring Telescope at the Hida Observatory. We determine the three-dimensional motion of the oscillation from the Hα wing images. The maximum line-of-sight velocity was estimated to be a few tens of kilometers per second, although the uncertainty is large owing to the lack of line-profile information. Furthermore, we also identified the spatial displacement of the oscillation in 17-GHz microwave images from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems to be triggered by magnetic reconnection between a filament barb and nearby emerging magnetic flux as was evident from the MDI magnetogram observations. No flare was observed to be associated with the onset of the oscillation. We also discuss possible implications of the oscillation as a diagnostic tool for the eruption mechanisms. We suggest that in the early phase of eruption a part of the filament lost its equilibrium first, while the remaining part was still in an equilibrium and oscillated. Title: Amplitude modulation of solar p-modes by surface magnetic fields Authors: Jain, R.; Steele, C. D. C. Bibcode: 2007A&A...473..937J Altcode: Context: It is known from Doppler velocity measurements that the amplitudes of solar p-modes are modulated by strong photospheric magnetic field.
Aims: The aim of this paper is to investigate amplitude modulation by model surface magnetic fields.
Methods: Linearised magnetohydrodynamics equations, in the absence of gravity, are used to derive the inhomogeneous wave equation which is then solved using the Born Approximation.
Results: The amount of modulation depends on the plasma beta, the distance from the magnetic region and the wavenumber. It is also found that the direction of observation could also have an effect on the amount of modulation. Finally, the applicability of the findings to the observational data suggests that the modulation depends on the properties of the magnetic field region and measuring it is an un-contaminating probe for the magnetic field. Title: Scattering of p-Modes by a Thin Magnetic Flux Tube Authors: Gordovskyy, Mykola; Jain, Rekha Bibcode: 2007ApJ...661..586G Altcode: There is strong observational evidence for solar p-modes being scattered by sunspots. Understanding and comparing phase shifts or travel time delays of scattered waves can present an opportunity to deduce the subsurface structure of sunspots from the observations of p-modes. We study the scattering of acoustic waves by magnetic flux tubes embedded in the stratified atmosphere, taking into account magnetic field perturbations. For this purpose, we solve a set of linearized MHD equations using the Born approximation approach. It is shown that convergence of the magnetic field may substantially affect the phase shifts of the scattered waves. Title: Scattering of p-modes by a thin fluxtube in a stratified atmosphere Authors: Gordovskyy, M.; Jain, R. Bibcode: 2007AN....328..309G Altcode: In the present paper we investigate scattering of low and intermediate degree p-modes on a thin magnetic fluxtube embedded into a stratified polytropic atmosphere. Using the Born approximation approach we find the solution of linearized MHD equations and calculate resulting phase shifts of scattered waves for different sets of fluxtube parameters. Possible application of the results to the analysis of observational data is discussed. Title: Effects of Horizontal Magnetic Fields on Acoustic Travel Times Authors: Jain, Rekha Bibcode: 2007ApJ...656..610J Altcode: Local helioseismology techniques seek to probe the subsurface magnetic fields and flows by observing waves that emerge at the solar surface after passing through these inhomogeneities. Active regions on the surface of the Sun are distinguished by their strong magnetic fields, and techniques such as time-distance helioseismology can provide a useful diagnostic for probing these structures. Above the active regions, the fields fan out to create a horizontal magnetic canopy. We investigate the effect of a uniform horizontal magnetic field on the travel time of acoustic waves by considering vertical velocity in a simple plane-parallel adiabatically stratified polytrope. It is shown that such fields can lower the upper turning point of p-modes and hence influence their travel time. It is found that acoustic waves reflected from magnetically active regions have travel times up to a minute less than for waves similarly reflected in quiet regions. It is also found that sound speeds are increased below the active regions. These findings are consistent with time-distance measurements. Title: MHD Waves Observed in Isolated Bright Points Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A. Bibcode: 2006ASPC..354...13B Altcode: We examine oscillations in three isolated bright points co-temporal and co-spatial in the photosphere and chromosphere in the G-band and Ca IIK line. Wavelet analysis was performed to study waves packets of traveling magnetohydrodynamic waves. In general, it is thought likely that the photosphere oscillates in response to granular buffeting, but it is also influenced strongly by the presence of magnetic fields. The observed oscillations reveal evidence for kink-mode waves, traveling up through the chromosphere and coupling with sausage-modes waves. This provides a means for energy deposition in the upper chromosphere. Title: G-Band Bright Points and Photospheric Magnetic Fields Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A. Bibcode: 2006ASPC..358...61B Altcode: We present high resolution observations of magnetic flux concentrations within a decaying active region near disk center. We recorded G-band images, magnetograms, 2D spectral scan, and continuum images using the Universal Birefringent Filter at the Dunn Solar Telescope. The main results can be summarized as follows: The large-scale pattern of G-band bright points flux in plages are highly correlated, on sub-arcsecond scales; G-band bright points are cospatial and comorphous, with magnetic elements in intergranular lanes. Magnetic elements are continually advected into micropores by the photospheric flow field. We observed narrow (<0.25 arcsec) channels or sheets of downflowing plasma around bright points and micropores. This downflowing plasma shows accelerating nature in deeper layers of solar atmosphere. Upflow and downflow events are found within bright points while micropores show upflow. We compare our results with theoretical model predictions. Title: SOXS for IHY 2007 and Beyond Authors: Jain, R. Bibcode: 2006ihy..workE..40J Altcode: We present on the utilization of existing mission namely Solar X-ray Spectrometer (SOXS) for observing the full disk Sun in the X-ray waveband in 4-56 keV. SOXS has been functioning satisfactorily since June 2003 though for a limited period of 2-3 hours daily. SOXS mission has so far observed more than 400 flares of varying intensity and a few of them are found to be associated with CMEs. We present recent results from SOXS observations that combined with optical and radio wavebands, which reveal loop-loop interaction as potential mechanism for those flares occurred with remote brightening. We also present study of microflares observed by SOXS mission and found that microflares are potential candidates for coronal heating. SOXS mission is expected to continue during ascending phase of solar cycle 24. Title: Effects of horizontal magnetic fields on acoustic travel-times Authors: Jain, R. Bibcode: 2006ESASP.624E..49J Altcode: 2006soho...18E..49J No abstract at ADS Title: Effect of sunspot structure from p-modes scattering Authors: Gordovskyy, M.; Jain, R.; Thompson, M. J. Bibcode: 2006ESASP.624E..14G Altcode: 2006soho...18E..14G No abstract at ADS Title: The relationship between magnetic field strength and loop lengths in solar coronal active regions Authors: Jain, R.; Mandrini, C. H. Bibcode: 2006A&A...450..375J Altcode: By assuming that coronal active regions are made up of many loops, we investigate the relationship between the average magnetic field strength and loop length for a sample of active regions observed by the Soft X-ray Telescope aboard Yohkoh. We use photospheric magnetic data from the Michelson Doppler Imager and compute extrapolated field lines that match the observed soft X-ray emission. We compare our results with a previous study and find them to be consistent and a logical extension of such work. Such studies have important implications for solar coronal heating models. Title: Soft and hard X-ray emission from solar flares observed by Solar X-ray Spectrometer (SOXS) mission Authors: Jain, R.; Bharti, L. Bibcode: 2006cosp...36..635J Altcode: 2006cosp.meet..635J Solar X-ray Spectrometer SOXS mission was launched on 08 May 2003 onboard Indian spacecraft to study the energy release and particle acceleration in solar flares in the energy range 4-55 keV To achieve the high spectral resolution Si and CZT detectors were employed We present the temporal and spectral characteristics of soft and hard X-ray emission from 18 M-class flares observed by SOXS mission during 2003 and 2005 We present the line emission characteristics of Fe and Fe Ni features and show the variation of equivalent width and peak energy as a function of temperature which is interpreted as emission contribution of different ionic lines vary with temperature The hard X-ray spectra enabled us to measure the break energy between thermal and non-thermal components as a function of flare duration that allowing determining the contribution of accelerated particles in the flares We also analyzed a few flares associated with CMEs and found that the associated CME is the cause for the flare and not the consequence of the flare Title: Solar X-ray Spectrometer (SOXS) mission: Observations and new results Authors: Jain, R.; Bhatt, N. J.; Bharti, L. Bibcode: 2006ilws.conf...54J Altcode: We present the observations and recently obtained new results from the "Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard GSAT-2 Indian spacecraft on 08 May 2003 by GSLV-D2 rocket to study the solar flares. The state-of-the-art solid state detectors viz. Si PIN and Cadmium-Zinc-Telluride (CZT) were employed that operate at near room temperature (-20 0C). The dynamic energy range of the Si PIN and CZT detectors are 4-25 keV and 4-56 keV, respectively. The Si PIN has sub-keV energy resolution while the CZT has about 1.7 keV energy resolutions throughout the dynamic range. The high sensitivity and sub-keV energy resolution of Si PIN detector allows for measuring the intensity, and equivalent width (w) of the Fe-line and Fe/Ni-line complexes at approximately 6.7 and 8.0 keV as a function of time. We present the results related to the Fe-line complex obtained from the study of 10 M-class flares observed by the SOXS mission. We found that the equivalent width (w) of the Fe-line feature increases exponentially with temperature up to 25 MK but later it increases very slowly up to 35 Mk and then it remains constant up to 45 MK. We compare our measurements of w of the Fe line feature with calculations made earlier by various investigators and propose that these measurements may improve theoretical models. We interpret the variation of w with temperature as the changes in the ionization and recombination conditions in the plasma during the flare interval, and, as a consequence, the contribution from different ionic emission lines also varies. Title: Scientific and Technical aspects of high resolution extreme ultraviolet imaging spectrometer proposed for future space-borne Indian mission Authors: Jain, R. Bibcode: 2006cosp...36..619J Altcode: 2006cosp.meet..619J We present the scientific and technical aspects of proposed high resolution extreme ultraviolet imaging spectrometer for future space-borne Indian spacecraft We briefly describe the science objectives of the mission and propose that this experiment may improve our current understanding on coronal heating solar wind acceleration and the cause of CMEs In order to achieve the science objectives the normal incidence technique is proposed for high resolution imaging however it needs specific scientific and technical requirements which are described in detail We propose the design of the instrument and discuss the same in preview to scientific and technical perspectives Title: Prediction of the Amplitude in Sunspot Cycle 24 Authors: Jain, R. Bibcode: 2006cosp...36..642J Altcode: 2006cosp.meet..642J A few prediction methods have been developed using the precursor techniques and are found to be successful On the basis of geomagnetic activity aa indices during the descending phase of the preceding cycle we have established an expression which predicts the maximum annual mean sunspot number in cycle 24 to be 144 pm 18 This indicates that cycle 24 would also be a highly active cycle but not equal to last three solar cycles We also predict the average geomagnetic activity aa index during the ascending phase of cycle 24 to be 18 pm 3 5 Title: Development of soft X-ray imaging spectrometer for proposed future space-borne Indian mission Authors: Jain, R. Bibcode: 2006cosp...36..622J Altcode: 2006cosp.meet..622J We present the scientific and technical aspects of proposed high resolution soft X-ray imaging spectrometer for future space-borne Indian spacecraft We briefly describe the science objectives of the mission and propose that this experiment may improve our current understanding on quiet and active solar corona and the energy release and particle acceleration mechanisms in solar flares The proposed energy band is 0 1 to 10 keV for high spatial spectral and temporal imaging Currently various design are considered in view of scientific and technical requirements and are being analyzed We discuss both normal incidence and grazing incidence techniques and the current status of the experiment Title: X-Ray and Radio Emission Characteristics of CME Associated Flares producing Authors: Jain, R.; Bhatt, N. Bibcode: 2006cosp...36..613J Altcode: 2006cosp.meet..613J We present the results of our investigation on the X-ray and Radio Emission Characteristics of 18 geoeffective flares that were associated with Coronal Mass Ejection CME and observed by one of the missions among BATSE YOHKOH and SOXS in X-ray waveband and simultaneous observations made in radio waveband at Nobeyama Radio Observatory during 1997 to 2005 We identified the geoeffective potential flares based on A p index 25 We analyzed X-ray and radio temporal and spectral evolution of these flares and found that their spectra become exceptionally hard over the growth We also compare the results with the flares of similar magnitude but did not produce the geomagnetic effects Based on our analysis and evidence we interpret that in geoeffective flares extraordinary particle acceleration takes place for a long duration and the associated coronal mass ejection CME carries most of early accelerated and energetic particles as well as the magnetized plasma which in turn during the passage in interplanetary space generate further shock so as to enhance the particle velocity and density and thereby to disturb the Earth s magnetic field Title: Probing coronal heating with variability of solar X-ray emission Authors: Vekstein, G.; Jain, R.; Katsukawa, Y.; Tsuneta, S. Bibcode: 2006cosp...36...65V Altcode: 2006cosp.meet...65V If the mechanism responsible for creating hot solar corona is a magnetic one the resulting coronal heating events are likely to be highly fragmented in space and in time This makes the nanoflare heating scenario where both these features are at the heart of the concept a strong candidate The major problem is to find out how to test this theory while individual nanoflares remain beyond observational recognition Here we discuss a possibility of probing nanoflares with variability of the coronal X-ray emission We present results of the numerical simulation of X-ray coronal loops that mimics a sporadic nature of the nanoflare heating The aim is to investigate how an imposed power-law energy spectrum of heating events nanoflares translates into fluctuations in the intensity of the X-ray emission which can be detected observationally as X-ray and EUV brightenings These theoretical predictions are compared with a recently reported analysis of observed fluctuations of the solar X-ray emission and we discuss their implications on the deduced energy and spectrum of nanoflares A future study envisaged with the upcoming Solar-B mission is also discussed Title: The Solar Flare and CME Induced as a Collision of Two Opposite Polarities on 1997 May 12 Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A. Bibcode: 2005ASPC..346..327B Altcode: The multispectral observations of active region NOAA 8038 during 10-13 May 1997 are presented. The observations of MDI/SOHO magnetograms show that in this active region continual but discrete growth and decay of magnetic field was taking place indicating either continuous evolution of magnetic flux or emergence of new flux region. The movie of these magnetograms reveal two important results that the major opposite polarities of pre-existing region were approaching towards each other, and a small north polarity flux i.e. moving magnetic feature (MMF) was ejecting out from major north polarity at a quasi-periodicity of about 10 hrs during 10-13 May 1997. It appears that as a result of flux cancellation by one such ejected north polarity flux with a newly emerged south polarity flux around 04:30 UT on 12 May 1997, a moderate but long enduring 1B/C1.3 solar flare. The observation in Hα is presented in detail. Title: MHD Waves Observed in Isolated Brightpoints Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. A. Bibcode: 2005ESASP.600E..79B Altcode: 2005dysu.confE..79B; 2005ESPM...11...79B No abstract at ADS Title: On the Scaling of Magnetic Field Strength with Loop Length in Solar Active Regions Authors: Mandrini, C. H.; Jain, R. Bibcode: 2005ESASP.596E..69M Altcode: 2005ccmf.confE..69M No abstract at ADS Title: On Solar Coronal Heating by Forced Magnetic Reconnection Authors: Jain, R.; Browning, P.; Kusano, K. Bibcode: 2005ESASP.596E..23J Altcode: 2005ccmf.confE..23J No abstract at ADS Title: MHD Waves Propogation and Heating of Solar Atmosphere Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. Bibcode: 2005AGUSMSH12A..04B Altcode: We examine oscillations in isolated three bright points co-temporal and co-spatial in photosphere and chromosphere in G-band and Ca II K line. Wavelet analysis was used to study wave packets and identify traveling magnetohydrodynamic waves. In general, it is thought likely that the photosphere and chromosphere oscillates in response to forcing by p-modes and granular buffeting, but they are also influenced strongly by presence of magnetic fields. The observed oscillations reveals evidence for kink-mode waves, traveling up through the chromosphere and coupling with sausage-modes waves. This provides a means for energy depositing in the upper chromosphere. Title: CME and associated phenomena on May 12, 1997 Authors: Bharti, L.; Jain, R.; Joshi, C.; Jaaffrey, S. N. Bibcode: 2005AGUSMSH51C..05B Altcode: The multispectral observations of NOAA active region No. 8038 during 10-13 May 1997 are presented. The observations of MDI/SOHO magnetograms show that in this active region continual but discrete growth and decay of magnetic field was taking place indicating either continuous evolution of magnetic flux or emergence of new flux region. The movie of these magnetograms reveal two important results that the major opposite polarities of pre-existing region were approaching towards each other, and a small north polarity flux i.e. moving magnetic feature (MMF) was ejecting out from major north polarity at a quasi-periodicity of about 10 hrs during 10-13 May 1997. It appears that as a result of flux cancellation by one such ejected north polarity flux with a newly emerged south polarity flux around 04:30 UT on 12 May 1997, a blast wave generated, seen by EIT/SOHO, producing CME and a moderate but long enduring 1B/C1.3 solar flare. The observations in Hα, soft X-ray, hard X-ray, ionospheric absorption, radio and interplanetary scintillations in association to this flare are presented in detail.. The multiwavelength observations of the flare showed occurrence of at least two phases of energy release, first at 04:42 and second at 04:47 UT. We propose a qualitative model to interpret the observations, which, however, also explains the generation of CME and associated flare with two stages of energy release. The occurrence of type II radio burst at 04:54 UT was perhaps due to shock produced by the plasmoid erupted during second energy release at higher altitude in the corona. It appears that the plasmoid traversed through shock in the interplanetary medium so as to enhance the scintillation index on 14 May as inferred from IPS observations. Title: Solar coronal heating by forced magnetic reconnection: Multiple reconnection events Authors: Jain, Rekha; Browning, Philippa; Kusano, K. Bibcode: 2005PhPl...12a2904J Altcode: Magnetic reconnection is a strong candidate for a coronal heating mechanism, and heating by forced magnetic reconnection is investigated here. Two dimensional, nonlinear magnetohydrodynamic simulations are used to investigate forced magnetic reconnection in a compressible plasma. The reconnection occurs when a sheared force-free field is perturbed by a slow disturbance (pulse) at the boundary which is representative of the solar corona where the reconnection is induced by the photospheric motions. The case of driving by successive pulses, which generate a series of heating events which may interact with each other, is considered. This is in order to model the heating of the corona by a series of nanoflare events. For small perturbations, the simulation results are consistent with the previous analytic theory based on linear approach where a current sheet is formed initially at the resonant surface followed by reconnection and then release of magnetic energy. For large amplitude perturbations, or close to the threshold for tearing instability, the system exhibits strong nonlinear aspects. Following the second driving pulse, the current sheet expands along the separatrix before relaxing to a reconnective equilibrium and releasing even more magnetic energy for the same amplitude perturbation. Title: Coronal Heating by Forced Magnetic Reconnection with Multi-Pulse Driving Authors: Browning, P. K.; Jain, R. Bibcode: 2004ESASP.575..474B Altcode: 2004soho...15..474B No abstract at ADS Title: Nanoflares and Coronal X-Ray Variability Authors: Jain, R.; Katsukawa, Y.; Tsuneta, S.; Vekstein, G. Bibcode: 2004ASPC..325..271J Altcode: A possibility of probing nanoflares with variability in the coronal X-ray emission is discussed. We present results of numerical simulation of X-ray coronal loops by using a Monte Carlo code, which mimics a sporadic nature of the nanoflare heating. The aim is to investigate how the imposed power-law energy spectrum of heating events (nanoflares) translates into fluctuations in the intensity of the X-ray emission, which can be detected observationally as X-ray and EUV brightenings. It was found that probability distribution of these fluctuations is very sensitive to the power-law index α of the energy spectrum of nanoflares. If α > 3, intensity fluctuations have a noise-like nature with a Gaussian distribution originating from interference of many small nanoflares. For spectral indices 2 < α ≤ 3, histograms of the intensity deviation from the mean value show positive skewness indicating significant role of bigger events. Comparison of these results with the analysis of small fluctuations of coronal X-ray intensity observed with Yohkoh SXT telescope yields an estimate of 1023 erg for the energy of nanoflares in the active region. Title: Impulsive Solar Flares associated with Coronal Mass Ejections Authors: Jain, R.; Uddin, W.; Kosugi, T.; Kumar, S.; Chandra, R.; Sakao, T.; Masuda, S. Bibcode: 2004cosp...35..939J Altcode: 2004cosp.meet..939J We present the multi-wavelength observations of a few impulsive solar flares, which are associated with Coronal Mass Ejections (CMEs) during Solar Cycle 23. The optical and radio waveband observations of the solar flares considered for this investigation were made in India and Japan, while SOHO, CGRO, YOHKOH and SOXS missions made the other wavelength observations. We present the optical, radio and X-ray emission characteristics of impulsive flares associated with CMEs in view of their energy release and particle acceleration. We conjecture a qualitative model to interpret our multi-spectral observations of these impulsive solar flares. It is proposed that a CME of some magnitude precede the impulsive solar flares to cause strong particle acceleration as observed in them. In support of our this concept we present the magnetograms of the active regions that reveal the cancellation of magnetic flux in all such impulsive events, which in turn results in generating a CME as seen in different wavelengths. Title: Multi-wavelength study of the 2003 November 18 Solar Flares from AR 501 Authors: Chandra, R.; Uddin, W.; Jain, R.; Joshi, A.; Kumar, S. Bibcode: 2004cosp...35.4137C Altcode: 2004cosp.meet.4137C We present the multi-wavelength observations of three ( SF/C3.8, 2N/M3.2, M3.9) solar flares produced by super active region 0501 (βγα) on 18 November 2003. These flares occurred in south-east direction of the active region. The M3.2 and M3.9 flares are two ribbon/LDEs dynamic ares associated with eruption of highly shear/twisted filament. These two ares are associated with halo CMEs and strong type II and type IV radio bursts. These ares show similar morphological evolution in Hα, EUV and SXR wavelengths. At the are locations the high magnetic field gradient and high shear are noticed. The analysis of these ares is based upon the State Observatory, Nainital Hα data and various space born satellite data viz. SOXS, SOHO, TRACE, RHESSI, GOES. The energy release mechanism of these flares can be explained by the flux rope model. Title: Results of one year of observations of Solar Flares made by "Solar X-ray Spectrometer (SOXS)" Mission Authors: Jain, R.; Dave, H.; Kumar, S.; Deshpande, M. R. Bibcode: 2004cosp...35..744J Altcode: 2004cosp.meet..744J The first space borne solar astronomy experiment of India namely ``Solar X-ray Spectrometer (SOXS) mission has completed one year of its successful operation in geostationary orbit. The SOXS mission onboard GSAT-2 Indian spacecraft was launched successfully by GSLV-D2 rocket on 08 May 2003 to study the energy release and particle acceleration in solar flares. We briefly present the scientific objectives and instrumentation of the SOXS mission. The SOXS is composed of two independent payloads viz. SOXS Low Energy Detector (SLD) payload, and SOXS High Energy Detector (SHD) payload. We restrict our presentation to SLD payload that designed, developed and fabricated by Physical Research Laboratory (PRL) in collaboration with Space Application Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of Indian Space Research Organization (ISRO). The SLD payload employs the state-of-the-art solid state detectors viz. Si PIN and Cadmium-Zinc-Telluride (CZT) devices that operate at near room temperature (-20 ^0 C). The dynamic energy range of Si PIN and CZT detectors are 4-25 and 4-56 keV. The Si PIN provides sub-keV energy resolution while CZT reveals ∼ 2 keV energy resolution throughout the dynamic range. The instrument has onboard flare triggering logic software and 5 MB-memory bank. The data is transmitted to Master Control Facility (MCF), Hasan with 8 kbps telemetry rate. The observations are made in fixed energy windows (temporal) mode and in spectral mode with 100ms cadence during the flare. The SLD has observed more than 140 flares of C and M class since its commissioning in the orbit. We present the preliminary results and the X-ray emission characteristics of these flares, and a detailed study of a few typical solar flares, which are impulsive but associated with CMEs, in view of energy release and particle emission by them. The high sensitivity of the SLD and sub-keV energy resolution of Si PIN detector allows the intensity and mean energy of the Fe-line complex at approximately 6.7 keV to be measured as a function of time in all class of flares. The centroid energy and width of the iron-line complex at ∼ 6.7 keV, the intensity of the Fe/Ni line complex at ∼ 8 keV, and the line-to-continuum ratio enabled to estimate the plasma temperature and other plasma parameters. We also present how SLD is a potential instrument for the study of microflares. Title: Spectral Hardening and Geoeffectiveness of Solar Flares Authors: Jain, R.; Kumar, S.; Dave, H.; Deshpande, M. R. Bibcode: 2004cosp...35..761J Altcode: 2004cosp.meet..761J We present the results of a few typical flares that observed by the first space borne solar astronomy experiment of India namely "Solar X-ray Spectrometer (SOXS)" mission, which has completed one year of its successful operation in geostationary orbit. The SOXS mission onboard GSAT-2 Indian spacecraft was launched successfully by GSLV-D2 rocket on 08 May 2003 to study the energy release and particle acceleration in solar flares. The SOXS is composed of two independent payloads viz. SOXS Low Energy Detector (SLD) payload, and SOXS High Energy Detector (SHD) payload. We restrict our presentation to SLD payload that designed, developed and fabricated by Physical Research Laboratory (PRL) in collaboration with Space Application Centre (SAC), Ahmedabad and ISRO Satellite Centre (ISAC), Bangalore of Indian Space Research Organization (ISRO). We briefly present the scientific objectives and instrumentation of the SLD payload. The SLD payload employs the state-of-art solid state detectors viz. Si PIN and CZT detectors, which reveal sub-keV spectral and 100ms temporal resolution characteristics that are necessary to study the spectral response of the flare components. The dynamic range of Si and CZT detectors is 4-25 and 4-56 keV respectively. The SLD has observed more than 140 flares of C and M class since its commissioning in the orbit. We present the X-ray emission characteristics of a few typical flares in view of their spectral hardening and geo-effectiveness. We extend our study of these flares to optical and radio waveband observations in order to improve the relationship of X-ray spectral hardening and geo-effectiveness. The flares with harder spectra and associated with small or large CME, and radio emission at frequencies above 10 GHz are found geo-effective. Title: Signatures of a nanoflare heated solar corona Authors: Vekstein, G. E.; Jain, R. Bibcode: 2003PPCF...45..535V Altcode: If the mechanism responsible for creating the high-temperature solar corona is a magnetic one, the resulting coronal heating events are likely to be highly sporadic and fragmented. Therefore, nanoflare heating, where both these features are present, by the very meaning of the concept, is a strong candidate. The major problem is how to test this theory while individual nanoflares remain beyond observational recognition. Here, we discuss a possibility of probing the nanoflare heating scenario by considering statistical characteristics of coronal active regions, which presumably originate from a large number of random impulsive heating events. This approach allows one to derive various parameters of x-ray coronal loops (temperature, emission measure, filling factor, etc) without specifying particular details of the heating events. How the energy of individual nanoflares can be estimated from observed fluctuations in the coronal x-ray emission is also discussed. Comparison of our results with recently reported analysis of small fluctuations of coronal x-ray intensity observed with Yohkoh SXT telescope yields an estimate of (1022-1023) erg for the energy of nanoflares in the active region. Title: Probing coronal heating with X-ray variability of solar and stellar coronae Authors: Vekstein, G.; Jain, R. Bibcode: 2003EAEJA.....1455V Altcode: If mechanism responsible for creating hot solar and stellar coronae is a magnetic one, the resulting coronal heating events are likely to be highly fragmented in space and in time. This makes the nanoflare heating scenario, where both these features are at the heart of the concept, a strong candidate. The major problem is to find out how to test this theory while individual nanoflares remain beoynd observational recognition. Here, we discuss a possibility of probing nanoflares with variabiiy in the coronal X-ray emission. We present results of numerical simulation of X-ray coronal loops by using a Monte Carlo code that mimics a sporadic nature of the nanoflare heating. The aim is to investigate how the imposed power-law energy spectrum of heating events (nanoflares) translates into fluctuations in the intensity of the X-ray emission, which can be detected observationally as X-ray and EUV brightenings. It was found that probability distribution of these fluctuations is very sensitive to the power-law index ( of the energy spectrum of nanoflares. If ( ( 3, intensity fluctuations have a noise-like nature with a Gaussian distribution that originates from interference of many small nanoflares. For spectral indices 2 ( ( ( 3, histograms of the intensity deviation from the mean value show positive skewness that indicates a significant role of bigger events. These theoretical predictions are compared with recently reported analysis of observed fluctuations in solar and stellar coronal X-ray intensity, and we discuss their implications on the deduced energy and spectrum of nanoflares. Title: Indications and implications of twisted magnetic flux in the corona Authors: Gibson, S. E.; Fan, Y.; Jain, R.; Low, B. Bibcode: 2002AGUFMSH52A0446G Altcode: The question of whether magnetic flux ropes are fundamental to CMEs and their precursors will be addressed using a combination of analytic and numerical models, along with coronal observations. We have developed computational tools for evaluating observable properties of modeled magnetic flux ropes suspended in the corona, such as separatrix surfaces and dipped magnetic fields. We have also developed numerical models to demonstrate how a flux rope emerging into an overlying coronal magnetic arcade will relax to a force-free configuration, with associated formation of current sheets. Using the results of these two parallel studies, we will directly compare separatrix surfaces determined from an analytic (non-force-free) equilibrium model to the current sheets formed during numerical force-free relaxation of the same initial field configuration. We will then consider these in the context of observed X-ray sigmoid structures. We have also developed mathematical methods for determining the magnetic free energy in analytic models of both magnetic flux ropes, as well as sheared field configurations that contain no rope. We will compare the free energies thus determined for both sheared and twisted fields, as functions of spatial size, magnetic field strength, and degree of shear or twist. We will consider the implications of these results for the energetics of coronal mass ejections. Title: Filling factors and magnetic field strengths of nanoflare-heated coronal active regions: Yohkoh and MDI observations Authors: Jain, R.; Yashiro, S. Bibcode: 2002A&A...394.1111J Altcode: The scaling laws describing the relationship between thermal and magnetic properties of active regions are derived using the concept that solar coronal active regions are heated by numerous small flare-like events (nanoflares). Thus, a coronal active region is viewed as an ensemble of hot elementary filaments created within the coronal magnetic field by random impulsive heating events. The scaling laws obtained are governed by the global energy balance of the active regions and are independent of the details of any heating process (such as the energy of individual heating event or energy spectral index of nanoflares). We examined 61 coronal active regions observed with the soft X-ray telescope aboard Yohkoh and found that such a model yields filling factors (defined as the ratio of the volume of hot plasma to the total volume) in the range 0.002 to 0.015 and magnetic field strengths of 20 G to 40 G. The analysis determining the mean magnetic field strength and filling factors of a large number of coronal active regions, observed by Yohkoh, based on nanoflare-heating concept is the first such analysis. We also examine 24 active regions observed with the Michelson Doppler Imager aboard Solar and Heliospheric Observatory and find that the total thermal energy content E_th is related to the total magnetic flux phi by a power-law index of 1.24 i.e. E_th ~ phi 1.24. The thermal pressure p_th of the active regions is related to the magnetic flux density B_p obtained from MDI measurement as: p_th ~ B_p0.5. Title: Solar p-modes and surface magnetic fields: Is there an acoustic emission?. MDI/SOHO observations Authors: Jain, R.; Haber, D. Bibcode: 2002A&A...387.1092J Altcode: We study the effect of magnetism on the surface amplitude of p-modes by creating power maps using Doppler velocity, line-depth and continuum intensity data taken by the Michelson Doppler Interferometer (MDI) instrument on board SOHO. This analysis, using proper tracking procedures, of MDI line-depth data and its comparison with the simultaneous Doppler velocity data is the first such analysis. All three datasets show that the p-mode power is suppressed in the magnetic region with suppression increasing with field strength. However, in the high-frequency range, the power is enhanced in the Doppler velocity and line-depth data but not in continuum intensity. This enhancement, when present, appears to be in intermediate field strength elements in the immediate vicinity of a magnetically active region. Title: Probing nanoflare heating with X-ray variability of coronal loops Authors: Jain, Rekha; Vekstein, Grigory Bibcode: 2002ESASP.477..123J Altcode: 2002scsw.conf..123J The concept that solar corona is heated by numerous small flare-like events (nanoflares) is considered. Thus, a hot coronal loop is viewed as an ensemble of high temperature elementary filaments created within the coronal magnetic field by random impulsive heating events. The integral parameters of the loop (thermal energy, emission measure, filling factor etc.) obey scaling laws (Vekstein and Katsukawa, 2000), which are determined only by its global energy balance. They are not sensitive to specific details of the heating process such as the energy of an individual heating event, and the energy spectral index of nanoflares. To probe the latter, we analyse variability of the nanoflare heated loops. The aim is to find out how the imposed power-law spectrum of heating events translates into fluctuations in the thermal energy and emission measure of the loop, which can be detected observationally as X-ray and EUV brightenings. It was found that the numerically simulated spectrum of these fluctuations comprises of two separate components. For large intensities the spectral index is close to that imposed for nanoflares, mirroring individual heating events with high energy. At lower intensities fluctuations have a noise-like nature generated by interference of several small nanoflares. Title: Processing electronics instrumentation for the low energy detector of Solar X-ray Spectrometer (SOXS) experiment Authors: Umapathy, C. N.; Sharma, M. R.; Solanky, Chirag; Kulkarni, R.; Shah, A. B.; Vadher, N. M.; Jain, R.; Jain, A. K.; Sreekumar, P. Bibcode: 2001BASI...29..475U Altcode: No abstract at ADS Title: Signatures of the Nanoflare Coronal Heating Authors: Vekstein, G.; Jain, R. Bibcode: 2001AGUSM..SP51C07V Altcode: The concept that the solar corona is heated by numerous small flare-like events (nanoflares) is considered. Thus, the hot coronal loop is viewed as an ensemble of high-temperature elemental filaments created within the coronal magnetic field by random impulsive heating events. As a result, these filaments, each of which is at various stages of thermal evolution, have a broad distribution in temperature and density. However, as instantaneous cooling time of the filament has a maximum when conductive and radiation losses become equal, the above distribution is strongly peaked at the corresponding transition temperature. Therefore, the observed temperature of such a loop as a whole obeys the same Rosner-Tucker-Vaiana scaling as was originally derived for a simple loop in a steady state thermal equilibrium. It is shown how this approach allows to predict various signatures of X-ray coronal loops, in particular, dependence of the filling factor, emission measure and thermal energy on the size of the loop and strength of the coronal magnetic field. These integral characteristics of the loop are determined only by its global energy balance, and are not sensitive to specific details of the heating process (such as the energy of individual heating event, spectral index of nanoflates, etc). To probe the latter, we analysed variability of nanoflare heated loops. The aim is to find out how the imposed power-law spectrum of heating events translates into fluctuations in the thermal energy and emission measure of the loop, which can be detected observationally as X-ray and EUV transient brightenings. It was found that the numerically simulated spectrum of these fluctuations typically consists of two different power-law domains. For large intensities the spectral index is close to that of nanoflares, mirroring individual heating events with high energy. However, at lower intensities the spectrum is more flat, as it is caused by interference of several nanoflares. Title: XTE J1550-564 Authors: Tomsick, J. A.; Smith, E.; Swank, J.; Wijnands, R.; Homan, J.; Jain, R.; Bailyn, C.; Tomsick, J. Bibcode: 2001IAUC.7575....2T Altcode: 2001IAUC.7575....3J; 2001IAUC.7575B...1T J. A. Tomsick, University of California at San Diego (UCSD); E. Smith and J. Swank, Goddard Space Flight Center; R. Wijnands, Massachusetts Institute of Technology; and J. Homan, University of Amsterdam, report: "Recent observations of the blackhole x-ray transient XTE J1550-564 with the Rossi X-ray Timing Explorer (RXTE) indicate that the source is active again. The last outburst ended in 2000 August, and a Chandra observation made on 2000 Aug. 16 indicated a flux level of 1 x 10**-13 erg cm**-2 s**-1 (0.5-8 keV). A 2.5-20-keV source flux of 9 x 10**-10 erg cm**-2 s**-1 was measured by RXTE on 2001 Jan. 28.7 UT. The spectral and timing properties indicate that the source is in the low-hard state. The energy spectrum can be described by a power law with a photon index of 1.52 and a neutral iron line with an equivalent width of 160 eV. The level of timing noise is about 40-percent rms (0.01-100 Hz; 2-60 keV), with violent flaring activity having a repetition period of 100-160 s. Currently, it is not clear if the observed activity will lead to a full outburst. Additional RXTE observations are scheduled, and coordinated observations at other wavelengths are encouraged."

R. Jain and C. Bailyn, Yale University; and J. Tomsick, UCSD, report YALO consortium observations of the optical counterpart of XTE J1550-564 using the Yale 1-m telescope (+ ANDICAM instrument) at Cerro Tololo Interamerican Observatory: "XTE J1550-564 has entered a new optical outburst. By Jan. 28.34, 29.34, and 30.34 UT, the object was at V = 18.28 +/- 0.01, 18.27 +/- 0.01, and 18.25 +/- 0.01, respectively. The source is significantly brighter than the quiescent level of V about 21.6." Title: Long-term Optical Monitoring of X-ray Transients Authors: Wachter, S.; Hoard, D. W.; Bailyn, C.; Jain, R.; Kaaret, P.; Corbel, S.; Wijnands, R. Bibcode: 2000HEAD....5.2415W Altcode: 2000BAAS...32.1219W We present highlights from an optical monitoring program of X-ray transients designed to assemble long-term optical outburst and decay lightcurves that can be compared to X-ray lightcurves obtained from the RXTE All Sky Monitor or from monitoring campaigns with the RXTE pointed instruments. Since the optical radiation is thought to be largely due to reprocessing of X-rays in the disk, contemporaneous optical and X-ray observations offer insight into the outburst mechanism and accretion dynamics of these objects. Our optical data were obtained during 2000 Feb - Jul under the Synoptic, Service, and Target-of-Opportunity program on the Cerro Tololo Inter-American Observatory (CTIO) 0.9-m telescope and on the YALO 1-m telescope, also located at CTIO. We will present lightcurves for SAX J1808.4-3658 and X1608-522. SAX J1808.4-3658, the transient 2.5 ms X-ray pulsar, displayed renewed activity in 2000 Jan - Feb. Our optical data show the same erratic variability as seen in X-rays. We will also present some of the first data of the quiescent optical counterpart. X1608-522 is a neutron star X-ray transient that undergoes large outbursts on a timescale of 700 days. A new outburst of X1608-522 expected for early 2000 did not materialize; however, the optical counterpart was visible and we obtained I-band photometry for 68 days before it dropped below the detection limit of our telescopes. The X-ray data exhibit a series of mini-outbursts. Corresponding brightening of the counterpart is also seen in the optical. In addition, the optical lightcurve shows plateaus of emission with a mean level which drops after each mini-outburst, possibly indicating discrete ``emptying'' events in the accretion disk. Cerro Tololo Inter-American Observatory is operated by AURA, Inc. under cooperative agreement with the NSF. Title: V1333 Aquilae Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.; Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D. Bibcode: 2000IAUC.7495....2J Altcode: 2000IAUC.7495R...1J; 2000IAUC.7495B...1J R. Jain, C. Bailyn, and P. Coppi, Yale University; M. Garcia, Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts Institute of Technology; J. Orosz, Utrecht University; P. Lu, Western Connecticut State University; and J. Espinoza and D. Gonzalez, Cerro Tololo Interamerican Observatory (CTIO), report on YALO consortium observations: "Aquila X-1 = V1333 Aql appears to be beginning a new optical outburst. This x-ray binary outbursts approximately once per year (e.g., 1999 May 8.3 UT; cf. IAUC 7161), and was due to erupt. We have been monitoring this source since 2000 Apr. 11 in R using the YALO 1-m telescope at CTIO. Compared to the quiescent average magnitude, which has a fluctuation < 0.1 mag, the source had brightened in R by 0.45 +/- 0.02 mag on Sept. 22.15. The R-band brightness continued to increase, reaching 0.62 +/- 0.02 and 0.71 +/- 0.03 mag above quiescence on Sept. 23.01 and 24.17, respectively. The amplitude of this outburst is larger than the peak from recent mini-outbursts (IAUC 7429, 7423, 7017). We will continue monitoring this source at optical, infrared, and x-ray (using RXTE) wavelengths. Observations at all wavelengths are encouraged." Title: Mini-outburst of Aql X-1 Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.; Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D. Bibcode: 2000ATel...59....1J Altcode: We report YALO consortium observation of a mini-outburst of Aquila X-1 = V1333 Aql, which occurred between July 04.27 and 07.29 UT. This X-ray binary outbursts approximately once per year, and most recently entered a mini-outburst during May 2000 (IAUC 7423,7429). We have been monitoring this source since April 5 in R using the YALO 1-m telescope at CTIO. Compared to the quiescent average magnitude, which fluctuates by less than 0.1 mag, the source had brightened in R by 0.20 +/- 0.02 mag on July 04.27 UT and peaked at 0.31 +/- 0.02 mags on July 05.26 UT. Title: V1333 Aquilae Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.; Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D. Bibcode: 2000IAUC.7423....1J Altcode: 2000IAUC.7423A...1J; 2000IAUC.7423Q...1J R. Jain, C. Bailyn, and P. Coppi, Yale University; M. Garcia, Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts Institute of Technology; J. Orosz, Utrecht University; P. Lu, Western Connecticut State University; and J. Espinoza and D. Gonzalez, Cerro Tololo Interamerican Observatory (CTIO), report YALO consortium observations: "V1333 Aql = Aquila X-1 appears to be beginning a new optical outburst. This x-ray binary outbursts approximately once per year, and last erupted in May 1999 (IAUC 7161). We have been monitoring this source since Apr. 5 in R using the YALO 1-m telescope at CTIO. Compared to the quiescent average magnitude, which fluctuates by < 0.1 mag, the source had brightened in R by 0.16 +/- 0.02 mag on May 11.23 UT. During May 12.23-12.40, we obtained four observations that indicate an increase in brightness of 0.27 to 0.34 +/- 0.02 mag compared to the quiescent mean. We will continue monitoring this source at optical, infrared, and x-ray (using RXTE) wavelengths. Observations at all wavelengths are encouraged." Title: V1333 Aquilae Authors: Jain, R.; Bailyn, C.; Coppi, P.; Garcia, M.; Levine, A.; Orosz, J.; Lu, P.; Espinoza, J.; Gonzalez, D. Bibcode: 2000IAUC.7429....1J Altcode: 2000IAUC.7429Q...1J; 2000IAUC.7429A...1J R. Jain, C. Bailyn, and P. Coppi, Yale University; M. Garcia, Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts Institute of Technology; J. Orosz, Utrecht University; P. Lu, Western Connecticut State University; and J. Espinoza and D. Gonzalez, Cerro Tololo Interamerican Observatory (CTIO), report YALO consortium observations: "The optical outburst of V1333 Aql = Aquila X-1, which began on May 11.23 UT (IAUC 7423), did not develop into a full outburst. By May 17.25, the object was back to quiescence. The peak amplitude of the outburst was 0.34 +/- 0.02 mag brighter than the quiescent mean in R and occurred on May 12.37. Two observations with the PCA instrument on RXTE lasting 1500 and 2500 s were taken on May 14.38 and 16.91, respectively. There is an indication that the source was detected with the PCA, but the count rates were heavily background-dominated and low enough that preliminary analysis does not allow a definitive determination of the flux. We therefore quote an upper limit of 4 x 10**-11 erg cm**-2 s**-1 (2.5-20 keV). A similar truncated 'mini-outburst' also occurred in Sept. 1998 (IAUC 7017, 7025)." Title: XTE J1550-564 Authors: Jain , R.; Bailyn, C. Bibcode: 2000IAUC.7400....2J Altcode: 2000IAUC.7400B...1J; 2000IAUC.7400R...1J R. Jain and C. Bailyn, Yale University, report YALO consortium observations of the optical counterpart of XTE J1550-564 using the Yale 1-m telescope (+ ANDICAM instrument) at Cerro Tololo Interamerican Observatory: "XTE J1550-564 has entered a new optical outburst. By Mar. 24.4 UT, the object was at V = 21.0, significantly brighter than any of our 12 observations obtained during the period Feb. 28-Mar. 17 (in all of which the source was fainter than V = 21.4). On Mar. 29.3, we find V = 19.07 +/- 0.03, and on Apr. 6.3, V = 18.24 +/- 0.03. The rate of brightening has decreased in the past two days to V = 18.09 +/- 0.02 and 18.06 +/- 0.02 on Apr. 9.4 and 10.4, respectively. Further observations at other wavelengths are encouraged." Title: XTE J1550-564 Authors: McCollough, M. L.; Wilson, C. A.; Sun, X.; Jain, R.; Bailyn, C. Bibcode: 2000IAUC.7400....1M Altcode: 2000IAUC.7400Q...1M; 2000IAUC.7400A...1M M. L. McCollough, Universities Space Research Association and Marshall Space Flight Center (MSFC); C. A. Wilson, NASA/MSFC; and X. Sun, University of Alabama in Huntsville, report for the Compton Gamma Ray Observatory (CGRO) BATSE team: "XTE J1550-564 (IAUC 7008, 7010) was detected in outburst with BATSE in the band 20-300 keV on Apr. 6 at a flux of 0.5 Crab (1.0 x 10**-8 erg cm**-2 s**-1) and had risen to 0.6 Crab (1.2 x 10**-8 erg cm**-2 s**-1) on Apr. 8. XTE J1550-564 is clearly being detected up to 300 keV. The date that this outburst began is uncertain because XTE J1550-564 was unobservable with CGRO/BATSE from Mar. 26 to Apr. 5. The CGRO/BATSE light curve shows evidence for variability on time scales of less than a day. The energy spectrum for XTE J1550-564 can be fitted by a bremsstrahlung spectrum with a temperature of 101 +/- 8 keV or a broken power law with a break energy of 76 +/- 25 keV, a lower energy photon index of -1.4 +/- 0.4, and a high energy photon index of -2.4 +/- 0.4." Title: XTE J1550-564 Authors: Jain, R.; Bailyn, C.; Greene, J.; Orosz, J.; McClintock, J.; Remillard, R. Bibcode: 1999IAUC.7187....2J Altcode: 1999IAUC.7187B...1J; 1999IAUC.7187R...1J R. Jain, C. Bailyn, and J. Greene, Yale University; J. Orosz, Pennsylvania State University; J. McClintock, Harvard-Smithsonian Center for Astrophysics; and R. Remillard, Massachusetts Institute of Technology, report YALO consortium observations of XTE J1550-564: "We have obtained data from May 14.40 to June 1.3 UT using the YALO 1-m telescope at Cerro Tololo. The uncalibrated R-band data, with relative precision of 0.02 mag, show a 1-mag decrease during this period; hence the optical light curve has not yet reached the true quiescent level. Between May 14.4 and 23.28, we obtained on average three 1200-s Johnson R exposures per night; each was separated by several hours. We detrended the lightcurve by removing a linear decay of 0.05 mag/day and find clear evidence for a modulation of 0.1 mag (full amplitude). Using the CLEAN algorithm and performing a fourier transform, we find a period of 1.5 +/- 0.1 days. Similarly, by using the phase-dispersion- minimization technique, we find a clear period at 1.5 days. If this period of about 1.5 days (which was suggested earlier by Soria and Wu, IAUC 7184) is correct, then the modulation we see may be due to a 'superhump' or to an illumination effect. On the other hand, if the light from the secondary dominates the light from the accretion disk (as suggested by the strong absorption lines reported by Soria and Wu), then the modulation we observe could be an ellipsoidal modulation. In this case, the orbital period would be near 3 days. Further spectroscopic observations will be needed to definitively determine the orbital period." Title: Optical Outburst of AQL X-1 Authors: Jain, R.; Bailyn, C.; Garcia, M.; Rines, K.; Levine, A.; Espinoza, J.; Gonzalez, D. Bibcode: 1999ATel...41....1J Altcode: We report YALO consortium observations using the Yale 1-m telescope at CTIO and observations with the 48" telescope at the Whipple Observatory: Aql X-1 = V1333 Aql appears to be beginning a new outburst. This x-ray binary outbursts approximately once per year, and based on its recent outbursts was due to erupt. Title: V1333 Aquilae Authors: Jain, R.; Bailyn, C.; Garcia, M.; Rines, K.; Levine, A.; Espinoza, J.; Gonzalez, D. Bibcode: 1999IAUC.7161....1J Altcode: 1999IAUC.7161Q...1J; 1999IAUC.7161A...1J R. Jain and C. Bailyn, Yale University; M. Garcia and K. Rines, Harvard-Smithsonian Center for Astrophysics; A. Levine, Massachusetts Institute of Technology; and J. Espinoza and D. Gonzalez, Cerro Tololo Interamerican Observatory (CTIO), report YALO consortium observations: "Aquila X-1 = V1333 Aql appears to be beginning a new outburst. This x-ray binary outbursts approximately once per year, and based on its recent outbursts was due to erupt. We have monitored the optical counterpart of the soft x-ray transient Aquila X-1 since early Mar. in Johnson R, using the YALO 1-m telescope at CTIO. Compared to the average quiescent level, which has a fluctuation of < 0.1 mag, the source had brightened in R by about 0.2 mag on May 8.3 UT. During May 10.2-10.38, we obtained five data points spanning 9 hr and found that the brightness increased from 0.4 to 0.55 mag brighter than the quiescent average. V-band data from the 1.22-m telescope at the Whipple Observatory show similar increases. We find that by May 9.5 the source had brightened by about 0.4 mag in V, compared to the average quiescent level. Subsequently we obtained three YALO V images on May 10.2-10.38 and found an increase in brightness of about 0.45 to 0.6 mag, again compared to the quiescent average. We will continue monitoring this source both at optical and at x-ray (using RXTE) wavelengths. Observations at all wavelengths are encouraged." Title: Absorption/Emission of Solar p-Modes: Michelson Doppler Interferometer/SOHO Observations Authors: Haber, Deborah; Jain, Rekha; Zweibel, Ellen G. Bibcode: 1999ApJ...515..832H Altcode: We search for sources and sinks of solar p-mode waves by creating absorption maps from Dopplergrams taken by the Michelson Doppler Interferometer instrument on board SOHO. Although the maps are noisy, we present evidence for sources and sinks, of duration ~0.5-1 hour or less, based on an autocorrelation analysis of maps made from sequential intervals of data. Emission and absorption nearly balance each other in the data. This may imply that emission and absorption are inverse processes of each other rather than fundamentally different in nature. Title: XTE J1550-564 Authors: Remillard, R.; Morgan, E.; Levine, A.; McClintock, J.; Sobczak, G.; Bailyn, C.; Jain, R.; Orosz, J. Bibcode: 1999IAUC.7123....2R Altcode: 1999IAUC.7123R...1R; 1999IAUC.7123B...1R R. Remillard, E. Morgan, and A. Levine, Massachusetts Institute of Technology; J. McClintock and G. Sobczak, Center for Astrophysics; C. Bailyn and R. Jain, Yale University; and J. Orosz, Pennsylvania State University, write: "There is continued evolution of the high-frequency quasiperiodic oscillations (QPO) in the x-ray nova and blackhole candidate XTE J1550-564 (see IAUC 7121). An RXTE PCA observation on Mar. 5.52 UT reveals a QPO at 283 +/- 5 Hz with a FWHM of 39 +/- 9 Hz, and an rms amplitude of 4.0 +/- 0.7 percent at 6-30 keV, similar to that reported for Mar. 4.80. However, subsequent PCA observations show changes as follows: 235 +/- 6 Hz (FWHM 30 +/- 11; amplitude 2.8 +/- 0.8 percent at 6-30 keV) on Mar. 7.50; 182.0 +/- 2.5 Hz (FWHM 12 +/- 4; amplitude 0.91 +/- 0.23 percent at 2-30 keV) on Mar. 8.37. Thus the frequency has returned to the value at which the QPO was originally discovered (IAUC 7025). The steep increase in amplitude with photon energy (IAUC 7121) has lessened on Mar. 8, as the QPO is weakly visible in the band 2-6 keV, while the profile fits have poor quality when the energy range is restricted to 6-30 keV." Title: XTE J1550-564 Authors: Jain, R.; Bailyn, C.; McClintock, J.; Sobczak, G.; Remillard, R.; Orosz, J. Bibcode: 1999IAUC.7114....2J Altcode: 1999IAUC.7114B...1J; 1999IAUC.7114R...1J R. Jain and C. Bailyn, Yale University; J. McClintock and G. Sobczak, Harvard-Smithsonian Center for Astrophysics; R. Remillard, Massachusetts Institute of Technology; and J. Orosz, Pennsylvania State University, report YALO consortium observations of XTE J1550-564: "We have obtained B-, V-, and I-band images virtually every night since Jan. 4.3 UT and most recently covering 3.5 hr of elapsed time per night. We find that, between Jan. 4.3 and 22.3, the source was steady at V = 16.04, B = 17.48, and I = 14.15. Then on Jan. 22.3, there was a 0.3-mag dip in the B, V, and I magnitudes. The source then remained steady, with a slight decline to a new level (V = 16.17, B = 17.62, I = 14.29) until Feb. 6.3, when another small dip (0.2 mag in I) occurred. This was followed by another period of steady slow decline. Most recently, a much larger decrease in optical brightness has occurred: since Feb. 21, the source has declined by > 0.5 magnitudes in B, V, and I. RXTE PCA observations show that the 2-20-keV x-ray flux increased from 6.5 x 10E-8 erg cmE-2 sE-1 on Feb. 21.5 to 7.4 x 10E-8 erg cmE-2 sE-1 on Feb. 23.9. The x-ray spectrum from 2 to 20 keV is dominated by the disk component, but the change in optical intensity has been accompanied by a factor of two increase in the power-law component of the x-ray flux from Feb. 21.5 to 23.9. We will continue to monitor this object on a daily basis for the foreseeable future, and we strongly encourage other observations, particularly of optical spectroscopy, to follow the current change in state of this source." Title: Plasma Heating by Forced Magnetic Reconnection Authors: Jain, Rekha; Vekstein, Grigory E. Bibcode: 1999Ap&SS.264..113J Altcode: 1998Ap&SS.264..113J A model of forced magnetic reconnection in a force-free magnetic field is considered, which allows calculation of the magnetic energy release during the current sheet reconnection. The dependence of this energy on characteristics of the magnetic configuration has been studied, and it was found that the released energy becomes very large when the field is near the marginal tearing stability. A persistent plasma heating provided by ongoing external driving and internal reconnection is also derived. It shows a typical relaxation-type dependence on the driving frequency, with dissipation becoming most efficient when the time-scales of the driving and reconnection are comparable. Possible implications of the obtained results for the problem of solar coronal heating are discussed. Title: H_α Intensity Oscillations in Solar Flares Authors: Jain, R.; Tripathy, S.; Bharti, L.; Kumar, B. Bibcode: 1999ASPC..183..531J Altcode: 1999hrsp.conf..531J No abstract at ADS Title: Helioseismology Authors: Elsworth, Y.; Jain, R. Bibcode: 1998Obs...118..342E Altcode: No abstract at ADS Title: XTE J1550-564 Authors: Orosz, J.; Bailyn, C.; Jain, R. Bibcode: 1998IAUC.7009....1O Altcode: 1998IAUC.7009A...1O; 1998IAUC.7009Q...1O J. Orosz, Pennsylvania State University; and C. Bailyn and R. Jain, Yale University, report YALO consortium observations using the Yale 1-m telescope (+ ANDICAM CCD camera) at the Cerro Tololo Interamerican Observatory: "We have identified a possible optical counterpart to the recent x-ray transient XTE J1550-564 (IAUC 7008) in V-band images obtained on Sept. 8.99 UT. The candidate is located at R.A. = 15h50m58s.78, Decl. = -56o28'35".0 (equinox 2000.0), with estimated errors on each value of about 1"-2". This object is not visible on an image obtained from the Digitized Sky Survey. We estimate a magnitude of V = 16, based on comparions with nearby stars selected from the Hubble Guide Star Catalog. Further observations, especially spectroscopic confirmation, are urgently needed. A finding chart may be obtained via the World Wide Web at http://www.astro.psu.edu/users/orosz/xte.html." Title: XTE J1550-564 Authors: Jain, R.; Bailyn, C.; Orosz, J. Bibcode: 1998IAUC.7020....1J Altcode: 1998IAUC.7020Q...1J; 1998IAUC.7020A...1J R. Jain and C. Bailyn, Yale University; and J. Orosz, Pennsylvania State University, report YALO consortium observations using the Yale 1-m telescope at the Cerro Tololo Interamerican Observatory: "We have monitored the optical counterpart to XTE J1550-564 (IAUC 7009) nightly since Sept. 13 UT. The source has varied by < 0.3 mag in V since its discovery. We have adjusted our instrumental magnitudes so that V = 16.7 and V-I = +1.80 near Sept. 16.0, as reported by Castro-Tirado et al. (IAUC 7013), and we find that 16.6 < V < 16.9 over the range Sept. 8.99-21.97. Thus there is no dramatic optical response to the large increase in the x-ray intensity over the last several days (cf. IAUC 7019). Between Sept. 15.0 and 21.0, there was a trend in the V-I color where the source became increasingly redder. We find V-I = 1.80 +/- 0.04 near Sept. 15.0 and 1.92 +/- 0.01 near Sept. 21.0. YALO consortium monitoring observations of XTE J1550-564 will continue; additional observations are encouraged." Title: The Solar Activity in NOAA Active Region No.8038 During 10-13 May 1997 Authors: Jain, R.; Mehta, Nirav; Vats, Hari Om; Deshpande, M. R.; Matthew, Shibu K.; Chandra, H.; Bogod, V. Ladimir; Nagai, S.; Sharma, S.; Sagawa, E.; Tokhchukova, Susan; Iyer, K. N.; Oza, Rupal; Rathore, Saroj Bibcode: 1997ESASP.415..145J Altcode: 1997cpsh.conf..145J No abstract at ADS Title: P-Modes, Acoustic Emission and Surface Magnetic Fields Authors: Jain, Rekha; Haber, Deborah Bibcode: 1997BAAS...29.1120J Altcode: No abstract at ADS Title: The Surface Amplitudes and Frequencies of p-Mode Oscillations in Active Regions Authors: Hindman, Bradley W.; Jain, Rekha; Zweibel, Ellen G. Bibcode: 1997ApJ...476..392H Altcode: It is well established that the surface amplitudes of solar p-mode oscillations are reduced in regions of magnetic activity. In this paper, we examine the conjecture that this reduction is produced by direct modification of the surface values of the p-mode eigenfunctions, rather than changes in the mode energies or alterations in the spectral line formation process. We calculate the oscillation modes of a solar model with a horizontal magnetic field, convection, and radiative diffusion. We find that magnetic fields with strengths characteristic of solar active regions can produce the observed decrease of surface power. Title: High energy photons detection using scintillation counter during total solar eclipse of October 24, 1995. Authors: Jaaffrey, S. N. A.; Jain, R.; Pandya, A.; Bharti, L. Bibcode: 1997KodOB..13..235J Altcode: The authors report the first observations of absorption and enhancement in flux of high energy photons during the total solar eclipse of October 24, 1995. For the purpose of these observations, they employed a scintillation counter to detect high energy radiation in the energy range of 10 keV to 5 MeV. The authors interpret the absorption in the flux below 300 keV due to the passage of the Moon between the Sun and the Earth, while enhancement above 300 keV could have occurred due to the production of secondary radiations from high energy photons. Title: The Influence of Magnetism on p-Mode Surface Amplitudes Authors: Jain, Rekha; Hindman, Bradley W.; Zweibel, Ellen G. Bibcode: 1996ApJ...464..476J Altcode: We propose a mechanism to explain the observed suppression of p-mode surface velocities in solar active regions. We show that a horizontal magnetic field can lower the upper turning point and change the skin depth for a simple plane-parallel adiabatically stratified polytrope. In addition to power suppression, the magnetic field alters the phase of p-modes. Simultaneous measurements of phase as well as amplitude in the active and quiet regions would provide an additional diagnostic for probing the structure of active region magnetic fields. Title: Discrete High-Frequency p-Modes Authors: Jain, Rekha; Roberts, B. Bibcode: 1996ApJ...456..399J Altcode: Observations report that the p-mode frequencies change with the solar activity cycle. Over the frequency range 0 to 8.5 mHz, shifts can be either positive or negative, appearing to exhibit a wavelike behavior with downturn occurring at ∼4.0 mHz and upturn at ∼5.5 mHz. A simple polytrope convection zone model overlaid with an isothermal chromospheric atmosphere threaded by a uniform horizontal magnetic field demonstrates frequency shifts that are qualitatively similar to those observed for both high and low frequencies, with shifts being a consequence of simultaneous increases in chromospheric field strength and temperature. Title: Hα Intensity Oscillations Observed in Solar Flares Authors: Jain, R.; Tripathy, S. C. Bibcode: 1995JApAS..16..381J Altcode: No abstract at ADS Title: Frequency Shifts of High-Frequency P-Modes Authors: Jain, R. Bibcode: 1995ESASP.376b..69J Altcode: 1995help.confP..69J; 1995soho....2...69J Frequency shifts (the difference between the frequencies from one time to another during the solar cycle) of high frequency (ν > 4 mHz) p-modes are calculated for a non-magnetic polytrope convection zone model over which lies an isothermal chromospheric atmosphere threaded by a uniform horizontal magnetic field. The relevant observations of such frequency changes are discussed. Simultaneous changes in field strength and chromospheric temperature result in frequency shifts (theoretically calculated) that are similar to those observed. Title: Changes in the Upper Turning Point due to Magnetism Authors: Jain, R.; Hindman, B. W.; Zweibel, E. G. Bibcode: 1995ESASP.376b..63J Altcode: 1995soho....2...63J; 1995help.confP..63J It has been observed that p-mode power is substantially suppressed in magnetic regions. One possible explanation is that the upper turning point (acoustic cut-off point) of the solar p-modes is lowered in the presence of a magnetic field (Brown 1994). A related possibility is that the attenuation length scale in the evanescent region is reduced in the presence of a magnetic field. Furthermore, it is likely that the observations sample a different position in the evanescent tails of the eigenfunctions, in magnetic regions because of different temperature structure there. The authors use a simple model to quantify the first of these effects. Title: Solar Cycle Variations in P-Modes and Chromospheric Magnetism Authors: Jain, Rekha; Roberts, B. Bibcode: 1994SoPh..152..261J Altcode: 1994IAUCo.143..261J; 1994svs..coll..261J The effect onp-mode frequencies of a horizontal chromospheric canopy field is studied theoretically and the results compared with Libbrecht and Woodard's observations of frequency changes. Combined changes in field strength and chromospheric temperature cause frequency shifts that are similar in form to those observed. Frequency shifts inp-modes offer the possibility of signatures of solar activity cycles distinct from sunspot numbers and butterfly diagrams. Title: Surface effects of a magnetic field on p-modes: two layer atmosphere Authors: Jain, R.; Roberts, B. Bibcode: 1994A&A...286..254J Altcode: The effects of chromospheric canopy fields on p-mode frequencies are evaluated for a two layer model atmosphere. The convection zone is field-free, while the chromosphere contains a magnetic field which is uniform up to a certain height after which it decreases with height. Frequency shifts due to simultaneous changes in chromospheric field strengths and temperatures are calculated numerically. The frequency shifts increase or decrease as a function of frequency, depending upon the thickness of the middle region. Title: Effects of non-parallel propagation on p- and f-modes Authors: Jain, R.; Roberts, B. Bibcode: 1994A&A...286..243J Altcode: The frequencies of p- and f-modes are calculated for a model atmosphere consisting of an isothermal chromospheric gas, within which is embedded a non-uniform horizontal magnetic field, resting upon a field-free medium whose temperature increases linearly with depth. The Alfven speed within the chromosphere is assumed to be independent of height. The modes may propagate at an angle θ to the magnetic field. The p-mode frequencies decrease with an increase in either the magnetic field strength or the propagation angle θ. The frequency of the f-mode is increased by the presence of a magnetic field; the frequency decreases with increasing angle θ. Title: Do p-Mode Frequency Shifts Suggest a Hotter Chromosphere at Solar Maximum? Authors: Jain, Rekha; Roberts, B. Bibcode: 1993ApJ...414..898J Altcode: The frequencies of p-modes are calculated for a model atmosphere consisting of an isothermal gas, within which is embedded a uniform horizontal magnetic field, resting upon a field-free medium whose temperature increases linearly with depth. We compare our results with Libbrecht & Woodard's recent observations of frequency changes. It is found that if simultaneously the chromospheric magnetic field strength and chromospheric temperature are increased, then the frequencies of the p-modes are shifted in a qualitatively similar fashion to that found in the observations, i.e., the frequency shift increases with frequency until about 3.9 mHz, when the shift decreases dramatically. We suggest that the combined influence of an increase in magnetic field strength and an increase in chromospheric temperature plays an important role in determining the observed downturn in frequency shift. Although the resulting frequency shift curve resembles the observed shift, with both possessing a gradual rise phase followed by a turnover, the calculated shift fails to match the steep downturn. Refinements in our basic model and/or new physics are thus indicated. Title: Magnetic Field Lines for a Flux Tube Authors: Steele, C. D. C.; Jain, Rekha Bibcode: 1993SoPh..145..197S Altcode: Equations for the magnetic field components in a two dimensional cylindrically symmetric flux tube equilibrium have been derived and, in a simple case, solved. The resulting magnetic configuration possesses a strong magnetic field in a thin tube below a reference level (solar photosphere). Above this reference level the field lines spread out in all directions. Title: P-Mode Frequency Shifts and Chromospheric Magnetism Authors: Jain, R.; Roberts, B. Bibcode: 1993ASPC...42...53J Altcode: 1993gong.conf...53J No abstract at ADS Title: Magnetic surface effects on solar oscillations Authors: Jain, Rekha Bibcode: 1993PhDT........85J Altcode: This thesis is concerned with the effects of magnetic atmospheres on solar oscillations. The behaviour of magnetohydrodynamic surface waves propagating on a single magnetic interface is discussed ignoring the effects of gravity. The effects of non-parallel propagation (where the wave vector is at an angle to the magnetic field direction) are considered. The effects of chromospheric magnetic fields on solar p- and f-modes in a stratified atmosphere are examined for three different models. In the first of these models, the chromosphere is assumed to be isothermal and permeated by a uniform and horizontal magnetic field. A dispersion relation for the p-modes trapped below such an atmosphere is derived. Asymptotic and numerical solutions for the p-modes are discussed in detail. An increase in chromospheric magnetic field strength leads to an increase in the frequency of the p-modes, whereas an increase in the chromospheric temperature leads to a decrease in the frequencies of these modes. Comparison with observational data suggests that both these effects may indeed take place. The second model is set up for magnetic fields which decrease with height in such a way that the Alfven speed remains constant. In addition to magnetic effects, the effects of non-parallel propagation on and f-modes are considered in the presence of such a non-uniform magnetic field. After deriving a very general dispersion relation, various asymptotic and numerical solutions have been obtained and the possible effects of magnetic fields and non-parallel propagation on these modes are examined. The presence of a horizontal non-uniform chromospheric field produces changes in the frequencies of the p- and f-modes, reducing the frequencies of p-modes and increasing the frequency of the f-mode. Besides depending upon magnetic field strength, frequencies also depend on both the mode's order n and its degree l. The effects of non-parallel propagation are found to be most significant for the f-mode and the low order p-modes. The magnetic structure of the chromosphere has been further generalised by combining the two models described above. In this three layer model, a dispersion relation is derived in a general manner and discussed in detail for the p-modes. The role of mag- netoacoustic cut-off frequency is studied. Again, the results are qualitatively similar to those found from observation. Title: Cosmic ray flare of 1989 September 29. Authors: Jain, R.; Bhatnagar, A.; Sharma, R. Bibcode: 1991BASI...19..208J Altcode: No abstract at ADS Title: Magnetoacoustic surface waves at a single interface Authors: Jain, Rekha; Roberts, B. Bibcode: 1991SoPh..133..263J Altcode: The occurrence of magnetoacoustic surface waves at a single magnetic interface one side of which is field-free is explored for the case of non-parallel propagation. Phase-speeds and penetration depths of the waves are investigated for various Alfvén speeds, sound speeds and angles of propagation to the applied field. Both slow and fast magnetoacoustic surface waves can exist depending on the values of sound speeds and propagation angle. The fast waves penetrate more than the slow waves. Title: Site survey for high spatial resolution solar observations. Authors: Jain, R. Bibcode: 1991nlt..work..140J Altcode: The requirements and their measurements for selecting a solar astronomy site to obtain high spatial resolution solar observations for long uninterrupted periods are discussed. A new approach for optical testing and hence to evaluate such a site through the photography of granulation and determining sunshine hours is also proposed. Possibilities are explored for location of a suitable site. Title: Properties of Non-Parallel Magnetoacoustic Surface Waves (With 1 Figure) Authors: Jain, R.; Roberts, B. Bibcode: 1991mcch.conf..511J Altcode: No abstract at ADS Title: Center to limb variation of solar granulation Authors: Jain, R.; Muller, R. Bibcode: 1989SoPh..123..185J Altcode: From high resolution white light photographs it is determined that the surface density of solar granulation decreases towards limb. A schematic model is proposed to interpret both decrease of surface density and size of granules in the upper photosphere. Title: Photopolarimetry of Seyfert Galaxies - NGC 2992, NGC 3081, NGC 3227, and IC 4329 A Authors: Joshi, U. C.; Jain, R.; Deshpande, M. R. Bibcode: 1989IAUS..134..321J Altcode: No abstract at ADS Title: Two ribbon flare on April 3, 1980. Authors: Jain, R. Bibcode: 1988KodOB...9..205J Altcode: Hα observations of a two-ribbon flare which were associated with exceptionally high microwave (MW) and hard X-ray emissions are presented and discussed. The good spatial and temporal resolution of the Hα data allows to investigate the detailed flare structure and its variation during each phase of the event. Strong MW emissions were found to be associated with the smallest flare but located in the inverted polarity region. Title: Polarimetry of supernova SN 1987A - a dust shell model. Authors: Joshi, U. C.; Sen, A. K.; Deshpande, M. R.; Jain, R. Bibcode: 1988KodOB..10...43J Altcode: Time variation of wavelength dependence of linear polarization is suggestive of a dust shell around SN 1987A. The intrinsic polarization is due to at least two components: one is due to a dust shell and the other is perhaps a synchrotron component. The minimum radius of the dust shell is estimated to be 0.04 pc with an optical thickness at visual wavelength 0.6. The temperature of the dust shell is expected to be Td ≡ 200K. Title: Flare Associated Coronal Loop Systems in Fexiv 5303A Fex 6374 and Hα Morphological Details and Derived Parameters Authors: Jain, R.; Smartt, R. N.; Zhaug, Z. Bibcode: 1987BASI...15...19J Altcode: No abstract at ADS Title: H-alpha flare associated microwave emissions Authors: Jain, R. Bibcode: 1985BASI...13..253J Altcode: The author has carried out a statistical association of 321 two-ribbon and 1564 non two-ribbon (normal) H-alpha flares which occurred during 1976 to 1980 with microwave bursts in the frequency range 3 - 35 GHz. Results obtained are as follows: (1) the two-ribbon (TR) flares show 1.5 to 3 times higher correlation as compared to normal (N) flares, indicating that TR flares are strong emitter of microwave emissions; (2) the TR flares show 2 to 4 times better association as compared to N flares with impulsive microwave bursts; (3) the higher correlation of TR flares with impulsive microwave bursts is perhaps due to their occurrence in complex magnetic configurations; (4) the strong and weak correlation of TR flares and N flares respectively, with impulsive microwave bursts at higher frequencies (10 - 35 GHz) indicates that the source of the TR flares is near the photosphere or the lower chromosphere (strong magnetic fields) and that of the normal flare is the upper chromosphere (weak magnetic fields). Title: Detailed Morphology of Flare-Associated Coronal Loops Authors: Smartt, R. N.; Jain, R. Bibcode: 1985BAAS...17Q.645S Altcode: No abstract at ADS Title: Veil emission associated with the multiribbon flare of 1979 February 18 Authors: Jain, R.; Bhatnagar, A.; Shelke, R. N. 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: 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: On Joule heating of the equatorial electrojet E-region Authors: Jain, R.; Nath, N.; Setty, C. S. G. K. Bibcode: 1981JATP...43.1189J Altcode: Simultaneous data on electron density, electron temperature and current density obtained from a rocket borne Langmuir probe, a glass-sealed Langmuir probe and a proton precession magnetometer flown from Thumba (geomag. lat. 0.99 deg S, geomag. long. 146.79 deg E, magnetic dip of 0 deg 47 min S) have been used to calculate the Joule heating in order to assess whether it contributes significantly to the thermal imbalance in the E-region. It is envisaged that the changes in electron temperature are partially brought about by changes in collision frequency and the energy loss factor. It is found that the Joule heating alone is not sufficient to explain the observed differences in electron and neutral gas temperatures. The inclusion of photoelectron heating and adjustments of profiles of the collision frequency and the energy loss factor bring the computed temperature differences closer to the observed differences. Title: The double ribbon flare of December 17, 1976. Authors: Jain, R.; Ballabh, G. M.; Sreedhar Rao, S.; Bhatnagar, A. Bibcode: 1978BASI....6...44J Altcode: No abstract at ADS Title: On solar flare associated shock wave. Authors: Bhatnagar, A.; Ballabh, G. M.; Jain, R.; Rao, S. Bibcode: 1976BASI....4...78B Altcode: No abstract at ADS