Author name code: banerjee ADS astronomy entries on 2022-09-14 =author:"Banerjee, Dipankar" ------------------------------------------------------------------------ Title: Defining the Middle Corona Authors: West, Matthew J.; Seaton, Daniel B.; Wexler, David B.; Raymond, John C.; Del Zanna, Giulio; Rivera, Yeimy J.; Kobelski, Adam R.; DeForest, Craig; Golub, Leon; Caspi, Amir; Gilly, Chris R.; Kooi, Jason E.; Alterman, Benjamin L.; Alzate, Nathalia; Banerjee, Dipankar; Berghmans, David; Chen, Bin; Chitta, Lakshmi Pradeep; Downs, Cooper; Giordano, Silvio; Higginson, Aleida; Howard, Russel A.; Mason, Emily; Mason, James P.; Meyer, Karen A.; Nykyri, Katariina; Rachmeler, Laurel; Reardon, Kevin P.; Reeves, Katharine K.; Savage, Sabrina; Thompson, Barbara J.; Van Kooten, Samuel J.; Viall, Nicholeen M.; Vourlidas, Angelos Bibcode: 2022arXiv220804485W Altcode: The middle corona, the region roughly spanning heliocentric altitudes from $1.5$ to $6\,R_\odot$, encompasses almost all of the influential physical transitions and processes that govern the behavior of coronal outflow into the heliosphere. Eruptions that could disrupt the near-Earth environment propagate through it. Importantly, it modulates inflow from above that can drive dynamic changes at lower heights in the inner corona. Consequently, this region is essential for comprehensively connecting the corona to the heliosphere and for developing corresponding global models. Nonetheless, because it is challenging to observe, the middle corona has been poorly studied by major solar remote sensing missions and instruments, extending back to the Solar and Heliospheric Observatory (SoHO) era. Thanks to recent advances in instrumentation, observational processing techniques, and a realization of the importance of the region, interest in the middle corona has increased. Although the region cannot be intrinsically separated from other regions of the solar atmosphere, there has emerged a need to define the region in terms of its location and extension in the solar atmosphere, its composition, the physical transitions it covers, and the underlying physics believed to be encapsulated by the region. This paper aims to define the middle corona and give an overview of the processes that occur there. Title: X-ray and ultraviolet observations of flares on AT Microscopii with AstroSat Authors: Kuznetsov, Alexey; Banerjee, Dipankar; Karakotov, Ruslan; Chandrashekhar, Kalugodu Bibcode: 2022cosp...44.2214K Altcode: We present observations of the active M-dwarf binary AT Mic (dM4.5e+dM4.5e) obtained with the orbital observatory AstroSat. During 20 ks of observations, in the far ultraviolet ($130-180$ nm) and soft X-ray ($0.2-8$ keV) spectral ranges, we detected both quiescent emission and at least five flares on different components of the binary. The X-ray flares were typically longer than and delayed (by $5-6$ min) with respect to their ultraviolet counterparts, in agreement with the Neupert effect. Using X-ray spectral fits, we have estimated the parameters of the emitting plasma. The results indicate the presence of a hot multi-thermal corona with the temperatures in the range of $\sim 5-30$ MK and the emission measure of $\sim (3-5)\times 10^{52}$ $\textrm{cm}^{-3}$; both the temperature and the emission measure increased during the flares. The estimated abundance of heavy elements in the corona of AT Mic is considerably lower than at the Sun, indicating an inverse FIP effect; the coronal abundance increased during the flares due to chromospheric evaporation. The detected flares had the energies of $\sim 10^{31}-10^{32}$ erg; the energy-duration relations indicate the presence of magnetic fields stronger than in typical solar flares. Title: uGMRT observations of recurrent nova - U Sco Authors: Nayana, A. J.; Anupama, G. C.; Banerjee, Dipankar; Roy, Nirupam; Singh, K. P.; Sonith, L. S.; Kamath, U. S. Bibcode: 2022ATel15449....1N Altcode: The latest outburst of recurrent nova U Sco has been reported by Masayuki Moriyama on 2022 June 6.72 UT (VSNET Alert N0:26798). We carried out upgraded Giant Metrewave Radio Telescope (uGMRT) observations of U Sco in band-5 (1000-1460 MHz) on 2022 June 13.85 UT (t ~ 7.13 days post-discovery). Title: uGMRT detection of Galactic Nova - V1405 Cas Authors: Nayana, A. J.; Anupama, G. C.; Banerjee, Dipankar; Roy, Nirupam; Singh, K. P.; Sonith, S.; Kamath, U. S. Bibcode: 2022ATel15383....1N Altcode: 2022ATel15383....1J We observed the classical nova V1405 Cas (a.k.a Nova Cassiopeiae 2021 = PNV J23244760+6111140) discovered by Yuji Nakamura on 2021 March 18.42 UTC (CBET #4945) with the upgraded Giant Metrewave Radio Telescope (uGMRT). Title: Editorial to the Topical Collection: Oscillatory Processes in Solar and Stellar Coronae Authors: Nakariakov, Valery M.; Banerjee, Dipankar; Li, Bo; Wang, Tongjiang; Zimovets, Ivan V.; Falanga, Maurizio Bibcode: 2022SSRv..218...13N Altcode: No abstract at ADS Title: A Simple Radial Gradient Filter for Batch-Processing of Coronagraph Images Authors: Patel, Ritesh; Majumdar, Satabdwa; Pant, Vaibhav; Banerjee, Dipankar Bibcode: 2022SoPh..297...27P Altcode: 2022arXiv220113043P Images of the extended solar corona, as observed by different white-light coronagraphs, include the K- and F-corona and suffer from a radial variation in intensity. These images require separation of the two coronal components with some additional image-processing to reduce the intensity gradient and analyse the structures and processes occurring at different heights in the solar corona within the full field of view. Over the past few decades, coronagraphs have been producing enormous amounts of data, which will be continued with the launch of new telescopes. To process these bulk coronagraph images with steep radial-intensity gradients, we have developed the algorithm Simple Radial Gradient Filter (SiRGraF). This algorithm is based on subtracting a minimum background (F-corona) created using long-duration images and then dividing the resultant by a uniform-intensity-gradient image to enhance the K-corona. We demonstrate the utility of this algorithm to bring out the short-time-scale transient structures of the corona. SiRGraF can be used to reveal and analyse such structures. It is not suitable for quantitative estimations based on intensity. We have successfully tested the algorithm on images of the Large Angle Spectroscopic COronagraph (LASCO)-C2 onboard the Solar and Heliospheric Observatory (SOHO) and COR-2A onboard the Solar TErrestrial RElations Observatory (STEREO) with good signal-to-noise ratio (SNR) along with low-SNR images of STEREO/COR-1A and the KCoronagraph (KCor). We also compared the performance of SiRGraF with the existing widely used algorithm Normalizing Radial Gradient Filter (NRGF). We found that when hundreds of images have to be processed, SiRGraF works faster than NRGF, providing similar brightness and contrast in the images and separating the transient features. Moreover, SiRGraF works better on low-SNR images of COR-1A than on NRGF, providing better identification of dynamic coronal structures throughout the field of view. We discuss the advantages and limitations of the algorithm. The application of SiRGraF to COR-1 images can be extended for an automated coronal mass ejection (CME) detection algorithm in the future, which will help in our study of the characteristics of CMEs in the inner corona. Title: Evolution of the Sun's activity and the poleward transport of remnant magnetic flux in Cycles 21-24 Authors: Mordvinov, Alexander V.; Karak, Bidya Binay; Banerjee, Dipankar; Golubeva, Elena M.; Khlystova, Anna I.; Zhukova, Anastasiya V.; Kumar, Pawan Bibcode: 2022MNRAS.510.1331M Altcode: 2021arXiv211115585M; 2021MNRAS.tmp.3199M Detailed study of the solar magnetic field is crucial to understand its generation, transport, and reversals. The timing of the reversals may have implications on space weather and thus identification of the temporal behaviour of the critical surges that lead to the polar field reversals is important. We analyse the evolution of solar activity and magnetic flux transport in Cycles 21-24. We identify critical surges of remnant flux that reach the Sun's poles and lead to the polar field reversals. We reexamine the polar field build-up and reversals in their causal relation to the Sun's low-latitude activity. We further identify the major remnant flux surges and their sources in the time-latitude aspect. We find that special characteristics of individual 11-yr cycles are generally determined by the spatiotemporal organization of emergent magnetic flux and its unusual properties. We find a complicated restructuring of high-latitude magnetic fields in Cycle 21. The global rearrangements of solar magnetic fields were caused by surges of trailing and leading polarities that occurred near the activity maximum. The decay of non-Joy and anti-Hale active regions resulted in the remnant flux surges that disturbed the usual order in magnetic flux transport. We finally show that the leading-polarity surges during cycle minima sometimes link the following cycle and a collective effect of these surges may lead to secular changes in the solar activity. The magnetic field from a Babcock-Leighton dynamo model generally agrees with these observations. Title: Deciphering Solar Magnetic Activity: 140 Years of the `Extended Solar Cycle' - Mapping the Hale Cycle Authors: McIntosh, Scott W.; Leamon, Robert J.; Egeland, Ricky; Dikpati, Mausumi; Altrock, Richard C.; Banerjee, Dipankar; Chatterjee, Subhamoy; Srivastava, Abhishek K.; Velli, Marco Bibcode: 2021SoPh..296..189M Altcode: 2020arXiv201006048M We investigate the occurrence of the "extended solar cycle" (ESC) as it occurs in a host of observational data spanning 140 years. Investigating coronal, chromospheric, photospheric, and interior diagnostics, we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) and previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recurrent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder's butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of 55∘ latitude in the evolution, and possible production, of solar magnetism. Title: Solar Cycle Evolution of Filaments over a Century: Investigations with the Meudon and McIntosh Hand-drawn Archives Authors: Mazumder, Rakesh; Chatterjee, Subhamoy; Nandy, Dibyendu; Banerjee, Dipankar Bibcode: 2021ApJ...919..125M Altcode: 2021arXiv210604320M Hand-drawn synoptic maps from the Meudon Observatory (1919 onwards) and the McIntosh archive (1967 onwards) are two important sources of long-term, manually recorded filament observations. In this study, we calibrate the Meudon maps and subsequently identify filaments through an automated method. We extract physical parameters from this filament database and perform a comparative study of their long-term evolution focusing on the cotemporal period of the McIntosh and Meudon observations. The spatiotemporal evolution of filaments manifests in the form of a filament butterfly diagram, further indicating that they are intimately related to the large-scale solar cycle. Physical descriptors such as the number and length of filaments, which are tracers of the solar surface magnetic field, have cycles which are phase locked with the ~11 yr sunspot cycle. The tilt-angle distribution of filaments-both near to or distant from active region locations-indicates that their origin is due to either large-scale surface magnetic field or inter-active-region field evolution. This study paves the way for constructing a composite series of hand-drawn filament data with minimal gaps stretching over the time span of solar filament observations up to a century. On the one hand, this would serve as a useful constraint for models of magnetic field emergence and evolution on the Sun's surface over multiple solar cycles, and on the other hand, this filament database may be used to guide the reconstruction of filament/prominence associated eruptive events before the space age. Title: An Insight into the Coupling of CME Kinematics in Inner and Outer Corona and the Imprint of Source Regions Authors: Majumdar, Satabdwa; Patel, Ritesh; Pant, Vaibhav; Banerjee, Dipankar Bibcode: 2021ApJ...919..115M Altcode: 2021arXiv210708198M Despite studying coronal mass ejections (CMEs) for several years, we do not yet have a complete understanding of their kinematics. To this end, it is essential to understand the change in kinematics of the CMEs as they travel from the inner corona (<3 R⊙) up to the higher heights of the outer corona. We conduct a follow-up statistical study of several 3D kinematic parameters of 59 CMEs previously studied by Majumdar et al. (2020). The source regions of these CMEs are identified and classified as active regions (ARs), active prominences (APs), or prominence eruptions (PEs). We study several statistical correlations between different kinematic parameters of the CMEs. We show that the CMEs' average kinematic parameters change as they propagate from the inner to the outer corona, indicating the importance of a region where the common practice is to perform averaging. We also find that the CME parameters in the outer corona are highly influenced by those in the inner corona, indicating the importance of the inner corona in the understanding of the kinematics. Furthermore, we find that the source regions of the CMEs tend to have a distinct imprint on the statistical correlations between different kinematic parameters, and that an overall correlation tends to wash away this crucial information. The results of this work supports the possibility of different dynamical classes for the CMEs from ARs and prominences, which gets manifested in their kinematics. Title: uGMRT observations of the 2021 outburst of RS Ophiuchi Authors: Nayana, A. J.; Anupama, G. C.; Banerjee, Dipankar; Roy, Nirupam; Singh, K. P.; Sonith, L. S. Bibcode: 2021ATel14899....1N Altcode: 2021ATel14899....1J We report observations of the recurrent nova RS Ophiuchi (AAVSO Alert Notice 752) with the upgraded Giant Metrewave Radio Telescope (uGMRT). The observations were done in the 550-850 MHz band (band-4) on 2021 August 31.67 UT (t ~ 23 days post outburst discovery) and in the 1000-1460 MHz band (band-5) on 2021 Sep 02.53 UT (t ~ 25 days post outburst discovery). Title: Characterizing Spectral Channels of Visible Emission Line Coronagraph of Aditya-L1 Authors: Patel, Ritesh; Megha, A.; Shrivastav, Arpit Kumar; Pant, Vaibhav; Vishnu, M.; Sankarasubramanian, K.; Banerjee, Dipankar Bibcode: 2021FrASS...8...88P Altcode: 2021arXiv210505880P Aditya-L1 is India's first solar mission with Visible Emission Line Coronagraph (VELC) consisting of three spectral channels taking high-resolution spectroscopic observations of the inner corona up to 1.5 R$_\odot$ at 5303 \AA, 7892 \AA, and 10747 \AA. In this work, we present the strategy for the slit-width optimization for the VELC using synthetic line profiles by taking into account the instrument characteristics and coronal conditions for log(T) varying from 6 to 6.5. The synthetic profiles are convolved with simulated instrumental scattered light and noise to estimate the signal-to-noise ratio (SNR), which will be crucial to design the future observation plans. We find that the optimum slit width for VELC turns out to be 50 $\mu$m providing sufficient SNR for observations in different solar conditions. We also analyzed the effect of plasma temperature on the SNR at different heights in the VELC field-of-view for the optimized slit-width. We also studied the expected effect of the presence of a CME on the spectral channel observations. This analysis will help to plan the science observations of VELC in different solar conditions. Title: Migration of Solar Polar Crown Filaments in the Past 100 Years Authors: Xu, Yan; Banerjee, Dipankar; Chatterjee, Subhamoy; Pötzi, Werner; Wang, Ziran; Ruan, Xindi; Jing, Ju; Wang, Haimin Bibcode: 2021ApJ...909...86X Altcode: Polar crown filaments (PCFs) are formed above the polarity inversion line, which separates unipolar polar fields and the nearest dispersed fields. They are important features in studying solar polar fields and their cyclical variations. Due to the relatively weak field strength and projection effects, measuring polar magnetic fields is more difficult than obtaining the field strengths concentrated in active regions at lower latitudes. "Rush-to-the-pole" of PCFs represent the progress of unipolar polar fields from the previous solar cycle being canceled by the dispersed fields generated in the current cycle. Such progress is a good indicator of the polarity reversal in the polar areas and a precursor for the solar maximum. In this study, PCFs are identified from a 100 yr archive, covering cycles 16-24. This archive consists of full-disk Hα images obtained from the Kodaikanal Solar Observatory of the Indian Institute of Astrophysics, Kanzelhöhe Solar Observatory, and Big Bear Solar Observatory. The poleward migration speeds are measured and show an obvious asymmetry in the northern and southern hemispheres. In addition, our results show that the PCFs usually reach their highest latitudes first in the northern hemisphere, except cycle 17. Similarly, previous studies show that the magnetic field reversed first at the north pole in six out of nine cycles. We also compare the temporal variations of PCF migration and the latitude gradient factor of the differential rotation, which shows a trend in the southern hemisphere. Moreover, the migration speed of PCFs does not seem to be well correlated with the maximum sunspot numbers. Title: Automated Detection of Accelerating Solar Eruptions Using Parabolic Hough Transform Authors: Patel, Ritesh; Pant, Vaibhav; Iyer, Priyanka; Banerjee, Dipankar; Mierla, Marilena; West, Matthew J. Bibcode: 2021SoPh..296...31P Altcode: 2020arXiv201014786P Solar eruptions such as coronal mass ejections (CMEs) observed in the inner solar corona (up to 4 R⊙) show acceleration profiles that appear as parabolic ridges in height-time plots. Inspired by the white-light automated detection algorithms Computer Aided CME Tracking System (CACTus) and Solar Eruptive Events Detection System (SEEDS), we employ the parabolic Hough transform for the first time to automatically detect off-disk solar eruptions from height-time plots. Due to the limited availability of white-light observations in the inner corona, we use extreme ultraviolet (EUV) images of the Sun. In this article we present a new algorithm, CME Identification in Inner Solar Corona (CIISCO), that is based on Fourier motion filtering and the parabolic Hough transform, and we demonstrate its implementation using EUV observations taken by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), Extreme Ultra Violet Imager (EUVI) onboard the STEREO-A and -B spacecraft, and Sun Watcher using Active Pixel System detector and Image Processing (SWAP) onboard the PRoject for On-Board Autonomy-2 (PROBA2) spacecraft. We show that CIISCO is able to identify off-disk, outward-moving features in EUV images. The use of automated detection algorithms, such as CIISCO, can potentially be used to provide early warnings of CMEs if an EUV telescope is located at ±90∘ from the Sun-Earth line, providing CME characteristics and kinematics close to the Sun. This article also presents the limitations of this algorithm and the prospects for future improvement. Title: Measurements of Solar Differential Rotation Using the Century Long Kodaikanal Sunspot Data Authors: Jha, Bibhuti Kumar; Priyadarshi, Aditya; Mandal, Sudip; Chatterjee, Subhamoy; Banerjee, Dipankar Bibcode: 2021SoPh..296...25J Altcode: 2021arXiv210101941J The rotational profile of the Sun is considered to be one of the key inputs in a solar dynamo model. Hence, precise and long-term measurements of this quantity is important for our understanding of solar magnetism and its variability. In this study, we use the newly digitised, white-light sunspot data (1923 - 2011) from Kodaikanal Solar Observatory (KoSO) to derive the solar rotation profile. An automated correlation-based sunspot tracking algorithm is implemented to measure the rotation parameters, A , the equatorial rotation rate, and B , the latitudinal gradient. Our measurements of A =14.381 ±0.004 deg/day and B =−2.72 ±0.04 deg/day compare well with previous studies. In our analysis, we find that the bigger sunspots (with area > 400 μHem) rotate slower than the smaller ones. At the same time, we do not find any variation in the rotation rates between activity extremes, i.e. solar maxima and minima. Lastly, we employ our tracking algorithm on the Michelson Doppler Imager (MDI) data and compare the MDI results with our KoSO values. Title: A statistical study of plasmoids associated with a post-CME current sheet Authors: Patel, Ritesh; Pant, Vaibhav; Chandrashekhar, Kalugodu; Banerjee, Dipankar Bibcode: 2020A&A...644A.158P Altcode: 2020arXiv201003326P Context. Coronal mass ejections (CMEs) are often observed to be accompanied by flare, current sheets, and plasmoids/plasma blobs. 2D and 3D numerical simulations and observations reported plasmoids moving upward as well as downward along the current sheet.
Aims: We aim to investigate the properties of plasmoids observed in the current sheet formed after an X-8.3 flare and followed by a fast CME eruption on September 10, 2017 using extreme-ultraviolet (EUV) and white-light coronagraph images. The main goal is to understand the evolution of plasmoids in different spatio-temporal scales using existing ground- and space-based instruments.
Methods: We identified the plasmoids manually and tracked them along the current sheet in the successive images of Atmospheric Imaging Assembly (AIA) taken at the 131 Å pass band and in running difference images of the white-light coronagraphs, K-Cor and LASCO/C2. The location and size of the plasmoids in each image were recorded and analyzed, covering the current sheet from the inner to outer corona.
Results: We find that the observed current sheet has an Alfvén Mach number of 0.018-0.35. The fast reconnection is also accompanied by plasmoids moving upward and downward. We identified 20 downward-moving and 16 upward-moving plasmoids using AIA 131 Å images. In white-light coronagraph images, only upward-moving plasmoids are observed. Our analysis shows that the downward-moving plasmoids have an average width of 5.92 Mm, whereas upward-moving blobs have an average size of 5.65 Mm in the AIA field of view (FOV). The upward-moving plasmoids, when observed in the white-light images, have an average width of 64 Mm in the K-Cor, which evolves to a mean width of 510 Mm in the LASCO/C2 FOV. Upon tracking the plasmoids in successive images, we find that downward- and upward-moving plasmoids have average speeds of ∼272 km s-1 and ∼191 km s-1, respectively in the EUV channels of observation. The average speed of plasmoids increases to ∼671 km s-1 and ∼1080 km s-1 in the K-Cor and LASCO/C2 FOVs, respectively, implying that the plasmoids become super-Alfvénic when they propagate outward. The downward-moving plasmoids show an acceleration in the range of -11 km s-1 to over 8 km s-1. We also find that the null point of the current sheet is located at ≈1.15 R⊙, where bidirectional plasmoid motion is observed.
Conclusions: The width distribution of plasmoids formed during the reconnection process is governed by a power law with an index of -1.12. Unlike previous studies, there is no difference in trend for small- and large-scale plasmoids. The evolution of width W of the plasmoids moving at an average speed V along the current sheet is governed by an empirical relation: V = 115.69W0.37. The presence of accelerating plasmoids near the neutral point indicates a longer diffusion region as predicted by MHD models.

Movies are available at https://www.aanda.org Title: Long-term Evolution of the Sun's Magnetic Field during Cycles 15-19 Based on Their Proxies from Kodaikanal Solar Observatory Authors: Mordvinov, Alexander V.; Karak, Bidya Binay; Banerjee, Dipankar; Chatterjee, Subhamoy; Golubeva, Elena M.; Khlystova, Anna I. Bibcode: 2020ApJ...902L..15M Altcode: 2020arXiv200911174M The regular observation of the solar magnetic field is available only for about the last five cycles. Thus, to understand the origin of the variation of the solar magnetic field, it is essential to reconstruct the magnetic field for the past cycles, utilizing other data sets. Long-term uniform observations for the past 100 yr as recorded at the Kodaikanal Solar Observatory (KoSO) provide such an opportunity. We develop a method for the reconstruction of the solar magnetic field using the synoptic observations of the Sun's emission in the Ca II K and Hα lines from KoSO for the first time. The reconstruction method is based on the fact that the Ca II K intensity correlates well with the unsigned magnetic flux, while the sign of the flux is derived from the corresponding Hα map that provides the information of the dominant polarities. Based on this reconstructed magnetic map, we study the evolution of the magnetic field in Cycles 15-19. We also study bipolar magnetic regions (BMRs) and their remnant flux surges in their causal relation. Time-latitude analysis of the reconstructed magnetic flux provides an overall view of magnetic field evolution: emergent magnetic flux, its further transformations with the formation of unipolar magnetic regions (UMRs), and remnant flux surges. We identify the reversals of the polar field and critical surges of following and leading polarities. We found that the poleward transport of opposite polarities led to multiple changes of the dominant magnetic polarities in poles. Furthermore, the remnant flux surges that occur between adjacent 11 yr cycles reveal physical connections between them. Title: Connecting 3D Evolution of Coronal Mass Ejections to Their Source Regions Authors: Majumdar, Satabdwa; Pant, Vaibhav; Patel, Ritesh; Banerjee, Dipankar Bibcode: 2020ApJ...899....6M Altcode: 2020arXiv200700923M Since coronal mass ejections (CMEs) are the major drivers of space weather, it is crucial to study their evolution starting from the inner corona. In this work we use graduated cylindrical shell model to study the 3D evolution of 59 CMEs in the inner (<3 R⊙) and outer (>3 R⊙) corona using observations from COR-1 and COR-2 on board the Solar TErrestrial RElations Observatory (STEREO) spacecraft. We identify the source regions of these CMEs and classify them as CMEs associated with active regions (ARs), active prominences (APs), and prominence eruptions. We find 27% of CMEs show true expansion and 31% show true deflections as they propagate outwards. Using 3D kinematic profiles of CMEs, we connect the evolution of true acceleration with the evolution of true width in the inner and outer corona, thereby providing observational evidence for the influence of the Lorentz force on the kinematics to lie in the height range 2.5-3 R⊙. We find a broad range in the distribution of peak 3D speeds and accelerations, ranging from 396 to 2465 km s-1 and 176 to 10,922 m s-2 respectively, with a long tail toward high values coming mainly from CMEs originating from ARs or APs. Further, we find that the magnitude of true acceleration is inversely correlated with its duration with a power-law index of -1.19. We believe that these results will provide important inputs for the planning of upcoming space missions that will observe the inner corona and for models that study CME initiation and propagation. Title: Sunspot area catalog revisited: Daily cross-calibrated areas since 1874 Authors: Mandal, Sudip; Krivova, Natalie A.; Solanki, Sami K.; Sinha, Nimesh; Banerjee, Dipankar Bibcode: 2020A&A...640A..78M Altcode: 2020arXiv200414618M Context. Long and consistent sunspot area records are important for understanding long-term solar activity and variability. Multiple observatories around the globe have regularly recorded sunspot areas, but such individual records only cover restricted periods of time. Furthermore, there are systematic differences between these records and require cross-calibration before they can reliably be used for further studies.
Aims: We produce a cross-calibrated and homogeneous record of total daily sunspot areas, both projected and corrected, covering the period between 1874 and 2019. In addition, we generated a catalog of calibrated individual group areas for the same period.
Methods: We compared the data from nine archives: Royal Greenwich Observatory (RGO), Kislovodsk, Pulkovo, Debrecen, Kodaikanal, Solar Optical Observing Network (SOON), Rome, Catania, and Yunnan Observatories, covering the period between 1874 and 2019. Cross-comparisons of the individual records were done to produce homogeneous and inter-calibrated records of daily projected and corrected areas. As in earlier studies, the basis of the composite is formed by the data from RGO. After 1976, the only datasets used are those from Kislovodsk, Pulkovo, and Debrecen observatories. This choice was made based on the temporal coverage and the quality of the data. While there are still 776 days missing in the final composite, these remaining gaps could not be filled with data from the other archives as the missing days lie either before 1922 or after 2016 and none of the additional archives cover these periods.
Results: In contrast to the SOON data used in previous area composites for the post-RGO period, the properties of the data from Kislovodsk and Pulkovo are very similar to those from the RGO series. They also directly overlap the RGO data in time, which makes their cross-calibration with RGO much more reliable. Indeed, comparing our area catalog with previous such composites, we find improvements both in data quality and coverage. We also computed the daily Photometric Sunspot Index, which is widely used, for example, in empirical reconstructions of solar irradiance.

Generated composites are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78 and at http://www2.mps.mpg.de/projects/sun-climate/data.html Title: Analysis of full-disc Ca II K spectroheliograms. III. Plage area composite series covering 1892-2019 Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova, Natalie A.; Solanki, Sami K.; Banerjee, Dipankar; Barata, Teresa; Belik, Marcel; Gafeira, Ricardo; Garcia, Adriana; Hanaoka, Yoichiro; Hegde, Manjunath; Klimeš, Jan; Korokhin, Viktor V.; Lourenço, Ana; Malherbe, Jean-Marie; Marchenko, Gennady P.; Peixinho, Nuno; Sakurai, Takashi; Tlatov, Andrey G. Bibcode: 2020A&A...639A..88C Altcode: 2020arXiv200501435C Context. Studies of long-term solar activity and variability require knowledge of the past evolution of the solar surface magnetism. The archives of full-disc Ca II K observations that have been performed more or less regularly at various sites since 1892 can serve as an important source of such information.
Aims: We derive the plage area evolution over the last 12 solar cycles by employing data from all Ca II K archives that are publicly available in digital form, including several as-yet-unexplored Ca II K archives.
Methods: We analysed more than 290 000 full-disc Ca II K observations from 43 datasets spanning the period between 1892-2019. All images were consistently processed with an automatic procedure that performs the photometric calibration (if needed) and the limb-darkening compensation. The processing also accounts for artefacts affecting many of the images, including some very specific artefacts, such as bright arcs found in Kyoto and Yerkes data. Our employed methods have previously been tested and evaluated on synthetic data and found to be more accurate than other methods used in the literature to treat a subset of the data analysed here.
Results: We produced a plage area time-series from each analysed dataset. We found that the differences between the plage areas derived from individual archives are mainly due to the differences in the central wavelength and the bandpass used to acquire the data at the various sites. We empirically cross-calibrated and combined the results obtained from each dataset to produce a composite series of plage areas. The 'backbone' approach was used to bridge the series together. We have also shown that the selection of the backbone series has little effect on the final composite of the plage area. We quantified the uncertainty of determining the plage areas with our processing due to shifts in the central wavelength and found it to be less than 0.01 in fraction of the solar disc for the average conditions found on historical data. We also found the variable seeing conditions during the observations to slightly increase the plage areas during the activity maxima.
Conclusions: We provide the most complete so far time series of plage areas based on corrected and calibrated historical and modern Ca II K images. Consistent plage areas are now available on 88% of all days from 1892 onwards and on 98% from 1907 onwards.

The whole series described in the paper are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88 Title: Time-Latitude Distribution of Prominences for 10 Solar Cycles: A Study Using Kodaikanal, Meudon, and Kanzelhohe Data Authors: Chatterjee, Subhamoy; Hegde, Manjunath; Banerjee, Dipankar; Ravindra, B.; McIntosh, Scott W. Bibcode: 2020E&SS....700666C Altcode: 2018arXiv180207556C Solar prominences are structures of importance because of their role in polar field reversal. We study the long-term variation of the time latitude distribution of solar prominences in this article. To accomplish this, we primarily used the digitized disc-blocked Ca II K spectroheliograms as recorded from Kodaikanal Solar Observatory for the period of 1906-2002. For improving the data statistics we included full disc Hα images from Meudon and Kanzelhohe Observatory, which are available after 1980. We developed an automated technique to identify the latitudinal locations of prominences in daily images from all three data sets. Derived time-latitude distribution clearly depicted poleward migration of prominence structures for 10 cycles (15-24). Unlike previous studies, we separated the rate of poleward migration during onset and near pole, using piece-wise linear fits. In most cases, we found acceleration in poleward migration with the change occurring near ±70° latitudes. The derived migration rates for such large number of solar cycles can provide important inputs toward understanding polar field buildup process. Title: Magnetic Field Dependence of Bipolar Magnetic Region Tilts on the Sun: Indication of Tilt Quenching Authors: Jha, Bibhuti Kumar; Karak, Bidya Binay; Mandal, Sudip; Banerjee, Dipankar Bibcode: 2020ApJ...889L..19J Altcode: 2019arXiv191213223J The tilt of the bipolar magnetic region (BMR) is crucial in the Babcock-Leighton process for the generation of the poloidal magnetic field in the Sun. Based on the thin flux-tube model of the BMR formation, the tilt is believed to be caused by the Coriolis force acting on the rising flux tube of the strong toroidal magnetic field from the base of the convection zone. We analyze the magnetic field dependence of BMR tilts using the magnetograms of the Michelson Doppler Imager (1996-2011) and Helioseismic and Magnetic Imager (2010-2018). We observe that the distribution of the maximum magnetic field (Bmax) of BMRs is bimodal. Its first peak at the low field corresponds to BMRs that do not have sunspots as counterparts in the white-light images, whereas the second peak corresponds to sunspots as recorded in both type of images. We find that the slope of Joy's law (γ0) initially increases slowly with the increase of Bmax. However, when Bmax ≳ 2 kG, γ0 decreases. Scatter of the BMR tilt around Joy's law systematically decreases with the increase of Bmax. The decrease of observed γ0 with Bmax provides a hint to a nonlinear tilt quenching in the Babcock-Leighton process. We finally discuss how our results may be used to make a connection with the thin flux-tube model. Title: Simultaneous longitudinal and transverse oscillations in filament threads after a failed eruption Authors: Mazumder, Rakesh; Pant, Vaibhav; Luna, Manuel; Banerjee, Dipankar Bibcode: 2020A&A...633A..12M Altcode: 2019arXiv191011260M Context. Longitudinal and transverse oscillations are frequently observed in the solar prominences and/or filaments. These oscillations are excited by a large-scale shock wave, impulsive flares at one leg of the filament threads, or due to any low coronal eruptions. We report simultaneous longitudinal and transverse oscillations in the filament threads of a quiescent region filament. We observe a large filament in the northwest of the solar disk on July 6, 2017. On July 7, 2017, it starts rising around 13:00 UT. We then observe a failed eruption and subsequently the filament threads start to oscillate around 16:00 UT.
Aims: We analyse oscillations in the threads of a filament and utilize seismology techniques to estimate magnetic field strength and length of filament threads.
Methods: We placed horizontal and vertical artificial slits on the filament threads to capture the longitudinal and transverse oscillations of the threads. Data from Atmospheric Imaging Assembly onboard Solar Dynamics Observatory were used to detect the oscillations.
Results: We find signatures of large-amplitude longitudinal oscillations (LALOs). We also detect damping in LALOs. In one thread of the filament, we observe large-amplitude transverse oscillations (LATOs). Using the pendulum model, we estimate the lower limit of magnetic field strength and radius of curvature from the observed parameter of LALOs.
Conclusions: We show the co-existence of two different wave modes in the same filament threads. We estimate magnetic field from LALOs and suggest a possible range of the length of the filament threads using LATOs.

Movies associated to Figs. 2 and 3 are available at https://www.aanda.org Title: On the Observations of Rapid Forced Reconnection in the Solar Corona Authors: Srivastava, A. K.; Mishra, S. K.; Jelínek, P.; Samanta, Tanmoy; Tian, Hui; Pant, Vaibhav; Kayshap, P.; Banerjee, Dipankar; Doyle, J. G.; Dwivedi, B. N. Bibcode: 2019ApJ...887..137S Altcode: 2019arXiv190107971S Using multiwavelength imaging observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory on 2012 May 3, we present a novel physical scenario for the formation of a temporary X-point in the solar corona, where plasma dynamics are forced externally by a moving prominence. Natural diffusion was not predominant; however, a prominence driven inflow occurred first, forming a thin current sheet, thereafter enabling a forced magnetic reconnection at a considerably high rate. Observations in relation to the numerical model reveal that forced reconnection may rapidly and efficiently occur at higher rates in the solar corona. This physical process may also heat the corona locally even without establishing a significant and self-consistent diffusion region. Using a parametric numerical study, we demonstrate that the implementation of the external driver increases the rate of the reconnection even when the resistivity required for creating normal diffusion region decreases at the X-point. We conjecture that the appropriate external forcing can bring the oppositely directed field lines into the temporarily created diffusion region first via the plasma inflows as seen in the observations. The reconnection and related plasma outflows may occur thereafter at considerably larger rates. Title: Generation of solar spicules and subsequent atmospheric heating Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu; Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie Bibcode: 2019Sci...366..890S Altcode: 2020arXiv200602571S Spicules are rapidly evolving fine-scale jets of magnetized plasma in the solar chromosphere. It remains unclear how these prevalent jets originate from the solar surface and what role they play in heating the solar atmosphere. Using the Goode Solar Telescope at the Big Bear Solar Observatory, we observed spicules emerging within minutes of the appearance of opposite-polarity magnetic flux around dominant-polarity magnetic field concentrations. Data from the Solar Dynamics Observatory showed subsequent heating of the adjacent corona. The dynamic interaction of magnetic fields (likely due to magnetic reconnection) in the partially ionized lower solar atmosphere appears to generate these spicules and heat the upper solar atmosphere. Title: Delving into the Historical Ca II K Archive from the Kodaikanal Observatory: The Potential of the Most Recent Digitized Series Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.; Krivova, Natalie A.; Banerjee, Dipankar; Jha, Bibhuti K.; Chatterjee, Subhamoy Bibcode: 2019SoPh..294..145C Altcode: 2019arXiv190805493C Full-disc Ca II K photographic observations of the Sun carry direct information as regards the evolution of solar-plage regions for more than a century and are therefore a unique dataset for solar-activity studies. For a long time Ca II K observations were barely explored, but recent digitizations of multiple archives have allowed their extensive analysis. However, various studies have reported diverse results partly due to the insufficient quality of the digitized data. Furthermore, inhomogeneities have been identified within the individual archives, which, at least partly, could be due to the digitization. As a result, some of the archives, e.g. that from the Kodaikanal observatory, were re-digitized. The results obtained by different authors who analyzed the data from the new digitization of the Kodaikanal archive differ from each other and from those derived from the old digitization. Since the data were processed and analyzed using different techniques, it is not clear, however, whether the differences are due to the digitization or the processing of the data. To understand the reasons for such discrepancies, we analyze here the data from the two most recent digitizations of this archive. We use the same techniques to consistently process the images from both archives and to derive the plage areas from them. Some issues have been identified in both digitizations, implying that they are intrinsic characteristics of the data. Moreover, errors in timing of the observations plague both digitizations. Overall, the most recent 16-bit digitization offers an improvement over the earlier 8-bit one. It also includes considerably more data and should be preferred. Title: Study of Sunspot Penumbra to Umbra Area Ratio Using Kodaikanal White-light Digitised Data Authors: Jha, Bibhuti Kumar; Mandal, Sudip; Banerjee, Dipankar Bibcode: 2019SoPh..294...72J Altcode: 2019arXiv190506888J We study the long-term behaviour of the sunspot penumbra to umbra area ratio by analysing recently digitised Kodaikanal white-light data (1923 - 2011). We implement an automatic umbra extraction method and compute the ratio over eight solar cycles (Cycles 16 - 23). Although the average ratio does not show any variation with spot latitudes, cycle phases and strengths, it increases from 5.5 to 6 as the sunspot size increases from 100 μhem to 2000 μhem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area <100 μhem) does not have any long-term systematic trend as was earlier reported from the photographic results of the Royal Observatory, Greenwich (RGO). To verify the same, we apply our automated extraction technique to Solar and Heliospheric Observatory (SOHO)/Michelson Doppler Imager (MDI) continuum images (1996 - 2010). Results from this data not only confirm our previous findings, but they also show the robustness of our analysis method. Title: High-frequency dynamics of an active region moss as observed by IRIS Authors: Narang, Nancy; Pant, Vaibhav; Banerjee, Dipankar; Van Doorsselaere, Tom Bibcode: 2019FrASS...6...36N Altcode: 2019arXiv190500722N The high temporal, spatial and spectral resolution of Interface Region Imaging Spectrograph (IRIS) has provided new insights into the understanding of different small-scale processes occurring at the chromospheric and transition region (TR) heights. We study the dynamics of high-frequency oscillations of an active region (AR 2376) moss as recorded by simultaneous imaging and spectral data of IRIS. Wavelet transformation, power maps generated from slit-jaw images in Si IV 1400 Å passband, and sit-and-stare spectroscopic observations of Si IV 1403 Å spectral line reveal the presence of high-frequency oscillations with ∼1-2 minutes periods in the bright moss regions. The presence of such low periodicities is further confirmed by intrinsic mode functions (IMFs) as obtained by empirical mode decomposition (EMD) technique. We find the evidence of the presence of slow waves and reconnection-like events, and together they cause the high-frequency oscillations in the bright moss regions. Title: Can the long-term hemispheric asymmetry of solar activity result from fluctuations in dynamo parameters? Authors: Nepomnyashchikh, Alexander; Mandal, Sudip; Banerjee, Dipankar; Kitchatinov, Leonid Bibcode: 2019A&A...625A..37N Altcode: 2019arXiv190310707N Context. The hemispheric asymmetry of sunspot activity observed possesses a regular component varying on a timescale of several solar cycles whose origin and properties are currently debated. Aims This paper addresses the question of whether the long-term hemispheric asymmetry can result from random variations of solar dynamo parameters in time and latitude.
Methods: Scatter in the observed tilt angles of sunspot groups was estimated to infer constraints on fluctuations in the dynamo mechanism for poloidal field regeneration. A dynamo model with fluctuations in the Babcock-Leighton type α-effect was designed in accordance with these constraints and then used to compute a large number of magnetic cycles for statistical analyses of their hemispheric asymmetry. Results Hemispheric asymmetry in the simulated dynamo results from the presence of an equator-symmetric part in the oscillating magnetic field. The sub-dominant quadrupolar oscillations are stochastically forced by dominant dipolar oscillations via the equator-symmetric part of the fluctuating α-effect. The amplitude and sense of the asymmetry of individual cycles varies on a timescale of the order of four dynamo-cycle periods. The variations are irregular and not periodic. The model suggests that asymmetry in the polar magnetic fields in the solar minima can be used as a precursor for asymmetry of sunspot activity in the following solar cycle. Title: Association of Calcium Network Bright Points with Underneath Photospheric Magnetic Patches Authors: Narang, Nancy; Banerjee, Dipankar; Chandrashekhar, Kalugodu; Pant, Vaibhav Bibcode: 2019SoPh..294...40N Altcode: 2019arXiv190203764N Recent dedicated Hinode polar region campaigns revealed the presence of concentrated kilogauss patches of the magnetic field in the polar regions of the Sun, which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. The small-scale bright elements visible in the bright network lanes of the solar network structure as seen in the Ca II H images are termed network bright points. We use special Hinode campaigns devoted to the observation of polar regions of the Sun to study the polar network bright points during the phase of the last extended solar minimum. We use Ca II H images of chromosphere observed by the Solar Optical Telescope. For magnetic field information, level-2 data of the spectro-polarimeter is used. We observe a considerable association between the polar network bright points and magnetic field concentrations. The intensity of such bright points is found to be correlated well with the photospheric magnetic field strength underneath with a linear relation existing between them. Title: Signature of Extended Solar Cycles as Detected from Ca II K Synoptic Maps of Kodaikanal and Mount Wilson Observatory Authors: Chatterjee, Subhamoy; Banerjee, Dipankar; McIntosh, Scott W.; Leamon, Robert J.; Dikpati, Mausumi; Srivastava, Abhishek K.; Bertello, Luca Bibcode: 2019ApJ...874L...4C Altcode: 2019arXiv190303598C In recent years there has been a resurgence of the study of extended solar cycles (ESCs) through observational proxies mainly in extreme ultraviolet. But most of them are limited only to the space-based era covering only about two solar cycles. Long-term historical data sets are worth examining for the consistency of ESCs. The Kodaikanal Solar Observatory (KSO) and the Mount Wilson Observatory (MWO) are two major sources of long-term Ca II K digitized spectroheliograms covering the temporal spans of 1907-2007 and 1915-1985 respectively. In this study, we detected supergranule boundaries, commonly known as networks, using the Carrington maps from both KSO and MWO data sets. Subsequently we excluded the plage areas to consider only the quiet Sun (QS) and detected small-scale bright features through intensity thresholding over the QS network. Latitudinal density of those features, which we named “Network Bright Elements,” could clearly depict the existence of overlapping cycles with equatorward branches starting at latitude ≈55° and taking about 15 ± 1 yr to reach the equator. We performed a superposed epoch analysis to depict the similarity of those extended cycles. Knowledge of such equatorward band interaction, for several cycles, may provide critical constraints on solar dynamo models. Title: Triggering The Birth of New Cycle's Sunspots by Solar Tsunami Authors: Dikpati, Mausumi; McIntosh, Scott W.; Chatterjee, Subhamoy; Banerjee, Dipankar; Yellin-Bergovoy, Ron; Srivastava, Abhishek Bibcode: 2019NatSR...9.2035D Altcode: When will a new cycle's sunspots appear? We demonstrate a novel physical mechanism, namely, that a "solar tsunami" occurring in the Sun's interior shear-fluid layer can trigger new cycle's magnetic flux emergence at high latitudes, a few weeks after the cessation of old cycle's flux emergence near the equator. This tsunami is excited at the equator when magnetic dams, created by the oppositely-directed old cycle's toroidal field in North and South hemispheres, break due to mutual annihilation of toroidal flux there. The fluid supported by these dams rushes to the equator; the surplus of fluid cannot be contained there, so it reflects back towards high latitudes, causing a tsunami. This tsunami propagates poleward at a speed of 300 m/s until it encounters the new cycle's spot-producing toroidal fields in mid-latitudes, where it perturbs the fields, triggering their surface-eruption in the form of new cycle spots. A new sunspot cycle is preceded for several years by other forms of high-latitude magnetic activity, such as coronal bright points and ephemeral regions, until the tsunami causes the birth of new cycle's spots. The next tsunami is due by 2020, portending the start of intense `space weather' that can adversely impact the Earth. Title: NEAR-INFRARED SPECTROSCOPY OF SN 2017EAW: CARBON MONOXIDE AND DUST FORMATION IN A TYPE II-P SUPERNOVA Authors: Rho, Jeonghee; Geball, Thomas; Banerjee, Dipankar; Dessart, Luc; Evans, Nye; Joshi, Vjoshi Bibcode: 2019AAS...23333502R Altcode: The origin of dust in the early universe has been the subject of considerable debate. Core-collapse supernovae (ccSNe), which occur several million years after their massive progenitors are born, could be a major source of that dust, as in the local universe, several ccSNe have been observed to be copious dust producers. Here we report nine near-infrared (0.8-2.5 micron) spectra, obtained with GNIRS on Gemini North, of the Type II-P supernova (SN) 2017eaw in NGC 6946, spanning the time interval 22-205 days after discovery. The spectra show the onset of CO formation and continuum emission at wavelengths greater than 2.1 micron from newly formed hot dust, in addition to numerous lines of hydrogen and metals, which reveal the change in ionization as the density of much of the ejecta decreases. The observed CO masses estimated from local thermodynamic equilibrium (LTE) model are typically 10-4Msun during days 124-205, but could be an order of magnitude larger if non-LTE conditions are present in the emitting region. The timing of the appearance of CO is remarkably consistent with the chemically controlled dust models of Sarangi & Cherchneff. We will also present additional observations taken in 2018 and discuss the implication of CO and dust formation in the SN ejecta and compare with the measurements of SN1987A. Title: The Extended Solar Cycle: Muddying the Waters of Solar/Stellar Dynamo Modeling Or Providing Crucial Observational Constraints? Authors: Srivastava, Abhishek K.; McIntosh, Scott W.; Arge, N.; Banerjee, Dipankar; Dikpati, Mausumi; Dwivedi, Bhola N.; Guhathakurta, Madhulika; Karak, B. B.; Leamon, Robert J.; Matthew, Shibu K.; Munoz-Jaramillo, Andres; Nandy, D.; Norton, Aimee; Upton, L.; Chatterjee, S.; Mazumder, Rakesh; Rao, Yamini K.; Yadav, Rahul Bibcode: 2018FrASS...5...38S Altcode: 2018arXiv180707601S In 1844 Schwabe discovered that the number of sunspots increased and decreased over a period of about 11 years, that variation became known as the sunspot cycle. Almost eighty years later, Hale described the nature of the Sun's magnetic field, identifying that it takes about 22 years for the Sun's magnetic polarity to cycle. It was also identified that the latitudinal distribution of sunspots resembles the wings of a butterfly showing migration of sunspots in each hemisphere that abruptly start at mid-latitudes (about ±35(o) ) towards the Sun's equator over the next 11 years. These sunspot patterns were shown to be asymmetric across the equator. In intervening years, it was deduced that the Sun (and sun-like stars) possess magnetic activity cycles that are assumed to be the physical manifestation of a dynamo process that results from complex circulatory transport processes in the star's interior. Understanding the Sun's magnetism, its origin and its variation, has become a fundamental scientific objective the distribution of magnetism, and its interaction with convective processes, drives various plasma processes in the outer atmosphere that generate particulate, radiative, eruptive phenomena and shape the heliosphere. In the past few decades, a range of diagnostic techniques have been employed to systematically study finer scale magnetized objects, and associated phenomena. The patterns discerned became known as the ``Extended Solar Cycle'' (ESC). The patterns of the ESC appeared to extend the wings of the activity butterfly back in time, nearly a decade before the formation of the sunspot pattern, and to much higher solar latitudes. In this short review, we describe their observational patterns of the ESC and discuss possible connections to the solar dynamo as we depart on a multi-national collaboration to investigate the origins of solar magnetism through a blend of archived and contemporary data analysis with the goal of improving solar dynamo understanding and modeling. Title: Double Peaks of the Solar Cycle: An Explanation from a Dynamo Model Authors: Karak, Bidya Binay; Mandal, Sudip; Banerjee, Dipankar Bibcode: 2018ApJ...866...17K Altcode: 2018arXiv180803922K One peculiar feature of the solar cycle that is yet to be understood properly is the frequent occurrence of double peaks (also known as the Gnevyshev peaks). The double peaks, and also multiple peaks and spikes, are often observed in any phase of the cycle. We propose that these peaks and spikes are generated due to fluctuations in the Babcock-Leighton process (the poloidal field generation from tilted bipolar magnetic regions). When the polar field develops, large negative fluctuations in the Babcock-Leighton process can reduce the net polar field abruptly. As these fluctuations in the polar field are propagated to the new toroidal field, these can promote double peaks in the next solar cycle. When fluctuations in the polar field occur outside the solar maximum, we observe their effects as spikes or dips in the following sunspot cycle. Using an axisymmetric Babcock-Leighton dynamo model, we first demonstrate this idea. Later, we perform a long simulation by including random scatter in the poloidal field generation process and successfully reproduce the double-peaked solar cycles. These results are robust under reasonable changes in the model parameters, as long as the diffusivity is not too much larger than 1012 cm2 s-1. Finally, we analyze the observed polar field data to show a close connection between the short-term fluctuations in the polar field and the double peaks/spikes in the next cycle. Thereby, this supports our theoretical idea that the fluctuations in the Babcock-Leighton process can be responsible for the double peaks/spikes in the observed solar cycle. Title: Onboard Automated CME Detection Algorithm for the Visible Emission Line Coronagraph on ADITYA-L1 Authors: Patel, Ritesh; Amareswari, K.; Pant, Vaibhav; Banerjee, Dipankar; Sankarasubramanian, K.; Kumar, Amit Bibcode: 2018SoPh..293..103P Altcode: 2018arXiv180607932P ADITYA-L1 is India's first space mission to study the Sun from the Lagrange 1 position. The Visible Emission Line Coronagraph (VELC) is one of seven payloads on the ADITYA-L1 mission, which is scheduled to be launched around 2020. One of the primary objectives of the VELC is to study the dynamics of coronal mass ejections (CMEs) in the inner corona. This will be accomplished by taking high-resolution (≈2.51 arcsecpixel−1) images of the corona from 1.05 R⊙-3R⊙ at a high cadence of 1 s in the 10 Å passband centered at 5000 Å. Because telemetry at the Lagrangian 1 position is limited, we plan to implement an onboard automated CME detection algorithm. The detection algorithm is based on intensity thresholding followed by area thresholding in successive difference images that are spatially rebinned to improve the signal-to-noise ratio. We present the results of the application of this algorithm on the data from existing coronagraphs such as STEREO/SECCHI COR-1, which is a space-based coronagraph, and K-Cor, a ground-based coronagraph, because they have a field of view (FOV) that is most similar to that of VELC. Since no existing space-based coronagraph has a FOV similar to VELC, we have created synthetic coronal images for the VELC FOV after including photon noise and injected CMEs of different types. The performance of the CME detection algorithm was tested on these images. We found that for VELC images, the telemetry can be reduced by a factor of 85% or more while maintaining a CME detection rate of 70% or higher at the same time. Finally, we discuss the advantages and disadvantages of this algorithm. The application of such an onboard algorithm in future will enable us to take higher resolution images with an improved cadence from space and simultaneously reduce the load on limited telemetry. This will help understanding CMEs better by studying their characteristics with improved spatial and temporal resolution.

Title: Century-long, multi-wavelength Solar Database From Kodaikanal Solar Observatory Authors: Banerjee, Dipankar Bibcode: 2018cosp...42E.191B Altcode: The Kodaikanal observatory has been obtaining solar images since 1904 in broad band white light, narrow band Ca-K 393.37 nm and H_ 656.3 nm wavelengths. Many of these observations are still continuing. The historical data which were on photographic plates has been digitized. The calibration of the Ca-K, white light and H_ images have been completed. The digitized data are available through an online portal. Cross calibration between different data sources as collected from observatory across the globe is underway. Some new results from this multi-wavelength database will be presented. Title: A Statistical Study on the Frequency-dependent Damping of the Slow-mode Waves in Polar Plumes and Interplumes Authors: Mandal, Sudip; Krishna Prasad, S.; Banerjee, Dipankar Bibcode: 2018ApJ...853..134M Altcode: 2017arXiv171203673M We perform a statistical study on the frequency-dependent damping of slow waves propagating along polar plumes and interplumes in the solar corona. Analysis of a large sample of extreme ultraviolet imaging data with high spatial and temporal resolutions obtained from Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observatory suggests an inverse power-law dependence of the damping length on the periodicity of slow waves (i.e., the shorter-period oscillations exhibit longer damping lengths), in agreement with the previous case studies. Similar behavior is observed in both plume and interplume regions studied in AIA 171 Å and AIA 193 Å passbands. It is found that the short-period (2-6 minutes) waves are relatively more abundant than their long-period (7-30 minutes) counterparts, in contrast to the general belief that the polar regions are dominated by the longer-period slow waves. We also derived the slope of the power spectra (α, the power-law index) statistically to better understand the characteristics of turbulence present in the region. It is found that the α values and their distributions are similar in both plume and interplume structures across the two AIA passbands. At the same time, the spread of these distributions also indicates the complexity of the underlying turbulence mechanism. Title: Automated detection of Coronal Mass Ejections in Visible Emission Line Coronagraph (VELC) on-board ADITYA-L1 Authors: Patel, Ritesh; Amareswari, K.; Pant, Vaibhav; Banerjee, Dipankar; Sankarasubramanian, K. Bibcode: 2018IAUS..340..171P Altcode: 2018arXiv180505802P An onboard automated coronal mass ejections (CMEs) detection algorithm has been developed for Visible Emission Line Coronagraph (VELC) onboard ADITYA-L1. The aim of this algorithm is to reduce the load on telemetry by sending the high spatial (~ 2.51 arcsec pixel-1) and temporal (1 s) resolution images of corona from 1.05 R⊙ to 3 R⊙, containing CMEs and rejecting others. It is based on intensity thresholding followed by an area thresholding in successive running difference images which are re-binned to lower resolution to improve signal to noise. Here we present the results of application of the algorithm on synthetic corona images generated for the VELC field of view (FOV). Title: An Overview of Science Results Obtained From Kodaikanal Digitized White-Light Data Archive: 1921-2011 Authors: Mandal, Sudip; Banerjee, Dipankar Bibcode: 2018IAUS..340..196M Altcode: 2018arXiv180504816M In this proceeding, we present a summary of the recent scientific results that have been derived using the newly digitized whit-light (WL) data obtained from the Kodaikanal Solar Observatory. Title: Long-term variation of sunspot penumbra to umbra area ratio Authors: Jha, Bibhuti Kumar; Mandal, Sudip; Banerjee, Dipankar Bibcode: 2018IAUS..340..185J Altcode: 2018arXiv180506307J A typical sunspot, as seen in white-light intensity images, has a two part structure: a dark umbra and a lighter penumbra. Such distinction primarily arises due to the different orientations of magnetic fields in these two regions. In this study, we use the Kodaikanal white-light digitized data archive to analyze the long-term evolution of umbral and penumbal area. We used an `automated algorithm' to uniquely identify the sunspot umbra (including the calculation of penumbra to umbra ratio) from these digitized intensity images. Our analysis reveals that the ratio increases slightly with the increase of sunspot area upto 100 μHem but eventually settles down to a constant value after that. This study, not only allows us to better understand the evolution of an individual spot and its corresponding magnetic field but this is also beneficial for solar dynamo studies which aim to reproduce such structures using a MHD theory. Title: Association of calcium network brightness with polar magnetic fields Authors: Narang, Nancy; Chandrashekhar, Kalugodu; Pant, Vaibhav; Banerjee, Dipankar Bibcode: 2018IAUS..340..198N Altcode: Recent dedicated HINODE polar region campaign revealed the presence of concentrated kilogauss patches of magnetic field in the polar regions of Sun which are also shown to be correlated with facular bright points at the photospheric level. In this work, we demonstrate that this spatial intermittency of the magnetic field persists even up to the chromospheric heights. Polar network bright points are the ones which are present in the polar regions of the Sun (above 70° latitudes). We use special HINODE campaigns devoted to observe polar regions of the Sun to study the polar network bright points during the phase of last extended solar minimum. We are able to find a considerable association between the polar network bright points and magnetic field concentrations which led us to conclude that these bright points can serve as a good proxy for polar magnetic fields where the direct and regular measurements of polar magnetic fields are not available (before 1970). Title: Latitude Distribution of Sunspots: Analysis Using Sunspot Data and a Dynamo Model Authors: Mandal, Sudip; Karak, Bidya Binay; Banerjee, Dipankar Bibcode: 2017ApJ...851...70M Altcode: 2017arXiv171100222M In this paper, we explore the evolution of sunspot latitude distribution and explore its relations with the cycle strength. With the progress of the solar cycle, the distributions in two hemispheres from mid-latitudes propagate toward the equator and then (before the usual solar minimum) these two distributions touch each other. By visualizing the evolution of the distributions in two hemispheres, we separate the solar cycles by excluding this hemispheric overlap. From these isolated solar cycles in two hemispheres, we generate latitude distributions for each cycle, starting from cycle 8 to cycle 23. We find that the parameters of these distributions, namely the central latitude (C), width (δ), and height (H), evolve with the cycle number, and they show some hemispheric asymmetries. Although the asymmetries in these parameters persist for a few successive cycles, they get corrected within a few cycles, and the new asymmetries appear again. In agreement with the previous study, we find that distribution parameters are correlated with the strengths of the cycles, although these correlations are significantly different in two hemispheres. The general trend features, i.e., (i) stronger cycles that begin sunspot eruptions at relatively higher latitudes, and (ii) stronger cycles that have wider bands of sunspot emergence latitudes, are confirmed when combining the data from two hemispheres. We explore these features using a flux transport dynamo model with stochastic fluctuations. We find that these features are correctly reproduced in this model. The solar cycle evolution of the distribution center is also in good agreement with observations. Possible explanations of the observed features based on this dynamo model are presented. Title: Long-term Study of the Solar Filaments from the Synoptic Maps as Derived from {{\rm{H}}}_{\alpha } Spectroheliograms of the Kodaikanal Observatory Authors: Chatterjee, Subhamoy; Hegde, Manjunath; Banerjee, Dipankar; Ravindra, B. Bibcode: 2017ApJ...849...44C Altcode: 2017arXiv170705658C The century long (1914-2007) {{{H}}}α (656.28 nm) spectroheliograms from the Kodaikanal Solar Observatory (KSO) have been recently digitized. Using these newly calibrated, processed images we study the evolution of dark elongated on-disk structures called filaments, which are potential representatives of magnetic activities on the Sun. To our knowledge, this is the oldest uniform digitized data set with daily images available today in {{{H}}}α . We generate Carrington maps for the entire time duration and try to find the correlations with maps of the same Carrington rotation from the Ca II K KSO data. Filaments are segmented from the Carrington maps using a semi-automated technique and are studied individually to extract their centroids and tilts. We plot the time-latitude distribution of the filament centroids, producing a butterfly diagram which clearly shows the presence of poleward migration. We separate polar filaments for each cycle and try to estimate the delay between the polar filament number cycle and the sunspot number cycle peaks. We correlate this delay with the delay between polar reversal and sunspot number maxima. This provides new insight on the role of polar filaments on polar reversal. Title: The Solar Ultraviolet Imaging Telescope on-board Aditya-L1 Authors: Tripathi, Durgesh; Ramaprakash, A. N.; Khan, Aafaque; Ghosh, Avyarthana; Chatterjee, Subhamoy; Banerjee, Dipankar; Chordia, Pravin; Gandorfer, Achim; Krivova, Natalie; Nandy, Dibyendu; Rajarshi, Chaitanya; Solanki, Sami K. Bibcode: 2017CSci..113..616T Altcode: 2022arXiv220407732T The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 mission of ISRO that will measure and monitor the solar radiation emitted in the near-ultraviolet wavelength range (200-400 nm). SUIT will simultaneously map the photosphere and the chromosphere of the Sun using 11 filters sensitive to different wavelengths and covering different heights in the solar atmosphere and help us understand the processes involved in the transfer of mass and energy from one layer to the other. SUIT will also allow us to measure and monitor spatially resolved solar spectral irradiance that governs the chemistry of oxygen and ozone in the stratosphere of Earth's atmosphere. This is central to our understanding of the Sun climate relationship. Title: Visible Emission Line Coronagraph on Aditya-L1 Authors: Raghavendra Prasad, B.; Banerjee, Dipankar; Singh, Jagdev; Nagabhushana, S.; Kumar, Amit; Kamath, P. U.; Kathiravan, S.; Venkata, Suresh; Rajkumar, N.; Natarajan, V.; Juneja, Madhur; Somu, Pawan; Pant, Vaibhav; Shaji, Nigar; Sankarsubramanian, K.; Patra, Asit; Venkateswaran, R.; Adoni, Abhijit Avinash; Narendra, S.; Haridas, T. R.; Mathew, Shibu K.; Mohan Krishna, R.; Amareswari, K.; Jaiswal, Bhavesh Bibcode: 2017CSci..113..613R Altcode: No abstract at ADS Title: Association of Supergranule Mean Scales with Solar Cycle Strengths and Total Solar Irradiance Authors: Mandal, Sudip; Chatterjee, Subhamoy; Banerjee, Dipankar Bibcode: 2017ApJ...844...24M Altcode: 2017arXiv170511171M We analyze the long-term behavior of the supergranule scale parameter, in active regions (ARs) and quiet regions (QRs), using the Kodaikanal digitized data archive. This database provides century-long daily full disk observations of the Sun in Ca II K wavelengths. In this paper, we study the distributions of the supergranular scales, over the whole data duration, which show identical shape in these two regimes. We found that the AR mean scale values are always higher than that of the QR for every solar cycle. The mean scale values are highly correlated with the sunspot number cycle amplitude and also with total solar irradiance (TSI) variations. Such a correlation establishes the cycle-wise mean scale as a potential calibrator for the historical data reconstructions. We also see an upward trend in the mean scales, as has already been reported in TSI. This may provide new input for climate forcing models. These results also give us insight into the different evolutionary scenarios of the supergranules in the presence of strong (AR) and weak (QR) magnetic fields. Title: Variation of Supergranule Parameters with Solar Cycles: Results from Century-long Kodaikanal Digitized Ca II K Data Authors: Chatterjee, Subhamoy; Mandal, Sudip; Banerjee, Dipankar Bibcode: 2017ApJ...841...70C Altcode: 2017arXiv170500175C The Ca II K spectroheliograms spanning over a century (1907-2007) from Kodaikanal Solar Observatory, India, have recently been digitized and calibrated. Applying a fully automated algorithm (which includes contrast enhancement and the “Watershed method”) to these data, we have identified the supergranules and calculated the associated parameters, such as scale, circularity, and fractal dimension. We have segregated the quiet and active regions and obtained the supergranule parameters separately for these two domains. In this way, we have isolated the effect of large-scale and small-scale magnetic fields on these structures and find a significantly different behavior of the supergranule parameters over solar cycles. These differences indicate intrinsic changes in the physical mechanism behind the generation and evolution of supergranules in the presence of small-scale and large-scale magnetic fields. This also highlights the need for further studies using solar dynamo theory along with magneto-convection models. Title: Kodaikanal digitized white-light data archive (1921-2011): Analysis of various solar cycle features Authors: Mandal, Sudip; Hegde, Manjunath; Samanta, Tanmoy; Hazra, Gopal; Banerjee, Dipankar; Ravindra, B. Bibcode: 2017A&A...601A.106M Altcode: 2016A&A...601A.106M; 2016arXiv160804665M Context. Long-term sunspot observations are key to understanding and predicting the solar activities and its effects on space weather. Consistent observations, which are crucial for long-term variations studies, are generally not available due to upgradation/modification of observatories over the course of time. We present data for a period of 90 yr acquired from persistent observation at the Kodaikanal observatory in India.
Aims: We aim to build a uniform sunspot area time series along with their positions for a 90-yr period between 1921 and 2011, as obtained from the newly digitized and calibrated white-light images from the Kodaikanal observatory. Our aim is to compare this new time series with known sources and confirm some of the earlier reported results with additional new aspects.
Methods: We use an advanced semi-automated algorithm to detect the sunspots form each calibrated white-light image. Area, longitude and latitude of each of the detected sunspots are derived. Implementation of a semi-automated method is extremely necessary in such studies as it minimizes the human bias in the detection procedure.
Results: Daily, monthly, and yearly sunspot area variations, obtained from the Kodaikanal, compared well with the Greenwich sunspot area data. We find an exponentially decaying distribution for the individual sunspot area for each of the solar cycles. Analyzing the histograms of the latitudinal distribution of the detected sunspots, we find Gaussian distributions, in both the hemispheres, with centers at 15° latitude. The height of the Gaussian distributions are different for the two hemispheres for a particular cycle. Using our data, we show clear presence of Waldmeier effect, which correlates the rise time with the cycle amplitude. Using the wavelet analysis, we explored different periodicities on different time scales present in the sunspot area times series.

Sunspot area time series (1921-2011) are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A106 Title: Association of Plages with Sunspots: A Multi-Wavelength Study Using Kodaikanal Ca II K and Greenwich Sunspot Area Data Authors: Mandal, Sudip; Chatterjee, Subhamoy; Banerjee, Dipankar Bibcode: 2017ApJ...835..158M Altcode: 2016arXiv161205711M Plages are the magnetically active chromospheric structures prominently visible in the Ca II K line (3933.67 Å). A plage may or may not be associated with a sunspot, which is a magnetic structure visible in the solar photosphere. In this study we explore this aspect of association of plages with sunspots using the newly digitized Kodaikanal Ca II K plage data and the Greenwich sunspot area data. Instead of using the plage index or fractional plage area and its comparison with the sunspot number, we use, to our knowledge for the first time, the individual plage areas and compare them with the sunspot area time series. Our analysis shows that these two structures, formed in two different layers, are highly correlated with each other on a timescale comparable to the solar cycle. The area and the latitudinal distributions of plages are also similar to those of sunspots. Different area thresholdings on the “butterfly diagram” reveal that plages of area ≥4 arcmin2 are mostly associated with a sunspot in the photosphere. Apart from this, we found that the cyclic properties change when plages of different sizes are considered separately. These results may help us to better understand the generation and evolution of the magnetic structures in different layers of the solar atmosphere. Title: Dynamics of Subarcsecond Bright Dots in the Transition Region above Sunspots and Their Relation to Penumbral Micro-jets Authors: Samanta, Tanmoy; Tian, Hui; Banerjee, Dipankar; Schanche, Nicole Bibcode: 2017ApJ...835L..19S Altcode: 2017arXiv170102531S Recent high-resolution observations have revealed that subarcsecond bright dots (BDs) with sub-minute lifetimes appear ubiquitously in the transition region (TR) above sunspot penumbra. The presence of penumbral micro-jets (PMJs) in the chromosphere was previously reported. It was proposed that both the PMJs and BDs are formed due to a magnetic reconnection process and may play an important role in heating of the penumbra. Using simultaneous observations of the chromosphere from the Solar Optical Telescope (SOT) on board Hinode and observations of the TR from the Interface Region Imaging Spectrograph, we study the dynamics of BDs and their relation to PMJs. We find two types of BDs, one that is related to PMJs, and another that does not show any visible dynamics in the SOT Ca II H images. From a statistical analysis we show that these two types have different properties. The BDs that are related to PMJs always appear at the top of the PMJs, the vast majority of which show inward motion and originate before the generation of the PMJs. These results may indicate that the reconnection occurs at the lower coronal/TR height and initiates PMJs at the chromosphere. This formation mechanism is in contrast with the formation of PMJs by reconnection in the (upper) photosphere between differently inclined fields. Title: Solar Active Longitudes from Kodaikanal White-light Digitized Data Authors: Mandal, Sudip; Chatterjee, Subhamoy; Banerjee, Dipankar Bibcode: 2017ApJ...835...62M Altcode: 2016arXiv161107637M The study of solar active longitudes has generated great interest in recent years. In this work we have used a unique, continuous sunspot data series obtained from the Kodaikanal observatory and revisited the problem. An analysis of the data shows a persistent presence of active longitudes during the whole 90 years of data. We compared two well-studied analysis methods and presented their results. The separation between the two most active longitudes is found be roughly 180° for the majority of time. Additionally, we also find a comparatively weaker presence of separations at 90° and 270°. The migration pattern of these active longitudes as revealed by our data is found to be consistent with the solar differential rotation curve. We also study the periodicities in the active longitudes and found two dominant periods of ≈1.3 and ≈2.2 years. These periods, also found in other solar proxies, indicate their relation with the global solar dynamo mechanism. Title: Simultaneous Longitudinal and Transverse Oscillations in an Active-Region Filament Authors: Pant, Vaibhav; Mazumder, Rakesh; Yuan, Ding; Banerjee, Dipankar; Srivastava, Abhishek K.; Shen, Yuandeng Bibcode: 2016SoPh..291.3303P Altcode: 2016arXiv161103984P; 2016SoPh..tmp..185P We report on the co-existence of longitudinal and transverse oscillations in an active-region filament. On March 15, 2013, an M1.1 class flare was observed in Active Region AR 11692. A coronal mass ejection (CME) was found to be associated with the flare. The CME generated a shock wave that triggered the oscillations in a nearby filament, situated south-west of the active region as observed from National Solar Observatory (NSO) Global Oscillation Network Group (GONG) Hα images. In this work we report the longitudinal oscillations in the two ends of the filament, which co-existed with the transverse oscillations. We propose a scenario in which an incoming shock wave hits the filament obliquely and triggers both longitudinal and transverse oscillations. Using the observed parameters, we estimate the lower limit of the magnetic field strength. We use a simple pendulum model with gravity as the restoring force to estimate the radius of curvature. We also calculate the mass accretion rate that causes the filament motions to damp quite fast. Title: Sunspot Sizes and the Solar Cycle: Analysis Using Kodaikanal White-light Digitized Data Authors: Mandal, Sudip; Banerjee, Dipankar Bibcode: 2016ApJ...830L..33M Altcode: 2016arXiv161002531M Sizes of the sunspots vary widely during the progression of a solar cycle. Long-term variation studies of different sunspot sizes are key to better understand the underlying process of sunspot formation and their connection to the solar dynamo. The Kodaikanal white-light digitized archive provides daily sunspot observations for a period of 90 years (1921-2011). Using different size criteria on the detected individual sunspots, we have generated yearly averaged sunspot area time series for the full Sun as well as for the individual hemispheres. In this Letter, we have used the sunspot area values instead of sunspot numbers used in earlier studies. Analysis of these different time series show that different properties of the sunspot cycles depend on the sunspot sizes. The “odd-even rule” double peaks during the cycle maxima and the long-term periodicities in the area data are found to be present for specific sunspot sizes and are absent or not so prominent in other size ranges. Apart from that, we also find a range of periodicities in the asymmetry index that have a dependency on the sunspot sizes. These statistical differences in the different size ranges may indicate that a complex dynamo action is responsible for the generation and dynamics of sunspots with different sizes. Title: Reflection of Propagating Slow Magneto-acoustic Waves in Hot Coronal Loops: Multi-instrument Observations and Numerical Modeling Authors: Mandal, Sudip; Yuan, Ding; Fang, Xia; Banerjee, Dipankar; Pant, Vaibhav; Van Doorsselaere, Tom Bibcode: 2016ApJ...828...72M Altcode: 2016arXiv160408133M Slow MHD waves are important tools for understanding coronal structures and dynamics. In this paper, we report a number of observations from the X-Ray Telescope (XRT) on board HINODE and Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA) of reflecting longitudinal waves in hot coronal loops. To our knowledge, this is the first report of this kind as seen from the XRT and simultaneously with the AIA. The wave appears after a micro-flare occurs at one of the footpoints. We estimate the density and temperature of the loop plasma by performing differential emission measure (DEM) analysis on the AIA image sequence. The estimated speed of propagation is comparable to or lower than the local sound speed, suggesting it to be a propagating slow wave. The intensity perturbation amplitude, in every case, falls very rapidly as the perturbation moves along the loop and eventually vanishes after one or more reflections. To check the consistency of such reflection signatures with the obtained loop parameters, we perform a 2.5D MHD simulation, which uses the parameters obtained from our observation as inputs, and perform forward modeling to synthesize AIA 94 Å images. Analyzing the synthesized images, we obtain the same properties of the observables as for the real observation. From the analysis we conclude that a footpoint heating can generate a slow wave which then reflects back and forth in the coronal loop before fading. Our analysis of the simulated data shows that the main agent for this damping is anisotropic thermal conduction. Title: A Butterfly Diagram and Carrington Maps for Century-long CA II K Spectroheliograms from The Kodaikanal Observatory Authors: Chatterjee, Subhamoy; Banerjee, Dipankar; Ravindra, B. Bibcode: 2016ApJ...827...87C Altcode: 2016arXiv160508219C The century-long (1907-2007) Ca II K spectroheliograms from the Kodaikanal Solar Observatory (KSO) are calibrated, processed, and analyzed to follow the evolution of the bright on-disc structures called plages, possible representatives of magnetic activity on the Sun. This is the longest data set studied in Ca II K to date, covering about 9.5 cycles of 11 yr periods. Plages are segmented with area ≥slant 1 {{arcmin}}2 using global thresholds for individual full disc images and subsequent application of a morphological closing operation. The plage index is calculated and is seen to have a close positive correlation with the fractional disc area covered by plages. The newly generated plage area cycle (from KSO) was compared with the same from the Mount Wilson Observatory (correlation 95.6%) for the overlapping years, I.e., 1915-2000. This study illustrates the time-latitude distribution of plage centroids by rendering a butterfly diagram (as observed for sunspots). The 3D visualization of the diagram shows one-to-one mapping between plage location, time, and area. This work further delineates the positional correlation between magnetic patches and plage regions through the comparison of synoptic maps derived from both KSO Ca II K images and space-based full disc line-of-sight magnetograms. Regular synoptic magnetograms from ground-based observatories are available only after 1970s. Thus the long term Ca II K data from KSO can be used as a proxy for estimating magnetic activity locations and their strengths at earlier times. Title: The Solar Ultraviolet Imaging Telescope onboard Aditya-L1 Authors: Ghosh, Avyarthana; Chatterjee, Subhamoy; Khan, Aafaque R.; Tripathi, Durgesh; Ramaprakash, A. N.; Banerjee, Dipankar; Chordia, Pravin; Gandorfer, Achim M.; Krivova, Natalie; Nandy, Dibyendu; Rajarshi, Chaitanya; Solanki, Sami K.; Sriram, S. Bibcode: 2016SPIE.9905E..03G Altcode: The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard the Aditya-L1 spacecraft, the first dedicated solar mission of the Indian Space Research Organization (ISRO), which will be put in a halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis Ritchey-Chrétien configuration with a combination of 11 narrow and broad bandpass filters which will be used for full-disk solar imaging in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide near simultaneous observations of lower and middle layers of the solar atmosphere, namely the Photosphere and Chromosphere. These observations will help to improve our understanding of coupling and dynamics of various layers of the solar atmosphere, mechanisms responsible for stability, dynamics and eruption of solar prominences and Coronal Mass ejections, and possible causes of solar irradiance variability in the Near and Middle UV regions, which is of central interest for assessing the Sun's influence on climate. Title: Long term variation study of the Sun from kodaikanal Digitised data Authors: Banerjee, Dipankar; Ravindra, B.; Chatterjee, Subhamoy Bibcode: 2016cosp...41E.142B Altcode: The century long (1907-2007) CaK spectroheliograms from Kodaikanal Solar Observatory (KSO) were calibrated, processed and analysed to study the the evolution plages, a possible representative of magnetic activity on the Sun. This has been the longest dataset studied in CaK till date covering about 9.5 cycles of 11 year periods. Plages were segmented with area > 1 arcmin2 using global thresholds for individual full disc images and subsequent application of morphological closing. Plage index was calculated and seen to have close positive correlation with fractional plage area. Obtained plage area cycle was compared with the same from Mount Wilson observatory (Correlation 94:7%) for the overlapping period 1915-2000. Study illustrated time-latitude distribution of plage centroids rendering Butterfly diagram (as observed for sunspots) and its 3D visualization combining the individual plage areas. This study further delineated positional correlation between magnetic patches and plage regions through comparison of synoptic maps derived from both Kodaikanal CaK images and space based full disc LOS (line of sight) magnetograms. Magnetograms from ground based observatories being available after 1950, this long term CaK data from KSO can be used as a proxy for estimating magnetic activity locations and their strengths at earlier times. Title: Tornados and Transverse Oscillations during Prominence Eruption Authors: Banerjee, Dipankar; Chandrashekhar, K.; Morton, Richard; Pant, Vaibhav; Datta, Ajanta Bibcode: 2016cosp...41E.141B Altcode: We report and analyse different phases of a prominence eruption. The winding-unwinding of two footpoints and a tornado like swirling motion is studied. The prominence eruption is observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). This prominence eruption is associated with a CME at a central principal angle of 340 degree, according to the SOHO/LASCO CME catalogue. We can observe the prominence threads and the time distance maps reveal that the loop threads are entangled. We also study the transverse oscillations in the threads. Swirling motions after the eruptions are also quantified and its possible link with the CME kinematics is also studied Title: Kinematics of slow and fast CMEs in soar cycle 23 and 24 Authors: Banerjee, Dipankar; Gopalswamy, Nat; Pant, Vaibhav Bibcode: 2016cosp...41E.140B Altcode: CMEs are episodic expulsion of plasma and magnetic fields from Sun into heliosphere. CMEs can be classified, based on their speeds, as slow CMEs and fast CMEs. We find that slow CMEs and fast CMEs behave differently in two cycles. While fast CMEs seem to follow the sunspot variations, slow CMEs have much flatter distribution. Thus the distribution of total CMEs is affected by slow CME populations. We find double peak behaviour in fast CMEs, since they follow the sunspot distribution, in both the cycles without any significant delay from sunspot variation. It suggests that most of the fast CMEs originates from active regions associated with sunspots. We also find double peak behaviour in slow CMEs in cycle 24 but not in cycle 23. In addition to this the number of slow CMEs are far more than in cycle 23. These findings point towards the fact that in cycle 24 slow CMEs to some extent are associated with sunspots and due to weak heliospheric field they could somehow escape easily thus giving double peak behaviour and larger distribution in cycle 24. Apart from this we also find that slow and fast CMEs follow different power laws. This may shed light on their origin as well. Title: Source of Quasi-Periodic Brightenings of Solar Coronal Bright Points: Waves or Repeated Reconnections Authors: Samanta, Tanmoy; Tian, Hui; Banerjee, Dipankar Bibcode: 2016cosp...41E1696S Altcode: Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening. Title: Coronal Mass Ejections propagating towards Mars and the consequent Forbush decreases Authors: Guo, Jingnan; Banerjee, Dipankar; Wimmer-Schweingruber, Robert; Pant, Vaibhav Bibcode: 2016cosp...41E.768G Altcode: In order to study the impact of interplanetary coronal mass ejections (ICMEs) on planet Mars, we explore the CME lists observed by coronagraphic images at Earth location heading towards Mars, i.e., the separation of the two planets are about 90 degrees. This is realized by the application of CACTus which detects CMEs in image sequences from LASCO/SOHO at Earth's L1 location. The properties of these ICMEs and their propagation towards Mars are modeled and compared with in-situ observations of Forbush decreases at the surface of Mars by the Radiation Assessment Detector (RAD) onboard of Mars Science Laboratory (MSL). This helps us to understand the contributions of ICMEs towards the onset of Forbush decreases at Mars as well as the evolution and propagation ICMEs in the inter-planetary space. Title: Statistical Study of Network Jets Observed in the Solar Transition Region: a Comparison Between Coronal Holes and Quiet-Sun Regions Authors: Narang, Nancy; Arbacher, Rebecca T.; Tian, Hui; Banerjee, Dipankar; Cranmer, Steven R.; DeLuca, Ed E.; McKillop, Sean Bibcode: 2016SoPh..291.1129N Altcode: 2016arXiv160406295N; 2016SoPh..tmp...56N Recent IRIS observations have revealed a prevalence of intermittent small-scale jets with apparent speeds of 80 -250 kms−1, emanating from small-scale bright regions inside network boundaries of coronal holes. We find that these network jets appear not only in coronal holes but also in quiet-sun regions. Using IRIS 1330 Å (C II) slit-jaw images, we extracted several parameters of these network jets, e.g. apparent speed, length, lifetime, and increase in foot-point brightness. Using several observations, we find that some properties of the jets are very similar, but others are obviously different between the quiet Sun and coronal holes. For example, our study shows that the coronal-hole jets appear to be faster and longer than those in the quiet Sun. This can be directly attributed to a difference in the magnetic configuration of the two regions, with open magnetic field lines rooted in coronal holes and magnetic loops often present in the quiet Sun. We also detected compact bright loops that are most likely transition region loops and are mostly located in quiet-Sun regions. These small loop-like regions are generally devoid of network jets. In spite of different magnetic structures in the coronal hole and quiet Sun in the transition region, there appears to be no substantial difference for the increase in footpoint brightness of the jets, which suggests that the generation mechanism of these network jets is very likely the same in both regions. Title: Forward Modeling of Propagating Slow Waves in Coronal Loops and Their Frequency-dependent Damping Authors: Mandal, Sudip; Magyar, Norbert; Yuan, Ding; Van Doorsselaere, Tom; Banerjee, Dipankar Bibcode: 2016ApJ...820...13M Altcode: 2016arXiv160200787M Propagating slow waves in coronal loops exhibit a damping that depends upon the frequency of the waves. In this study we aim to investigate the relationship of the damping length (L d ) with the frequency of the propagating wave. We present a 3D coronal loop model with uniform density and temperature and investigate the frequency-dependent damping mechanism for the four chosen wave periods. We include the thermal conduction to damp the waves as they propagate through the loop. The numerical model output has been forward modeled to generate synthetic images of SDO/AIA 171 and 193 Å channels. The use of forward modeling, which incorporates the atomic emission properties into the intensity images, allows us to directly compare our results with the real observations. The results show that the damping lengths vary linearly with the periods. We also measure the contributions of the emission properties on the damping lengths by using density values from the simulation. In addition to that we have also calculated the theoretical dependence of L d with wave periods and showed that it is consistent with the results we obtained from the numerical modeling and earlier observations. Title: Solar coronal magnetic fields derived using seismology techniques applied to omnipresent sunspot waves Authors: Jess, David B.; Reznikova, Veronika E.; Ryans, Robert S. I.; Christian, Damian J.; Keys, Peter H.; Mathioudakis, Mihalis; Mackay, Duncan H.; Krishna Prasad, S.; Banerjee, Dipankar; Grant, Samuel D. T.; Yau, Sean; Diamond, Conor Bibcode: 2016NatPh..12..179J Altcode: 2016arXiv160506112J Sunspots on the surface of the Sun are the observational signatures of intense manifestations of tightly packed magnetic field lines, with near-vertical field strengths exceeding 6,000 G in extreme cases. It is well accepted that both the plasma density and the magnitude of the magnetic field strength decrease rapidly away from the solar surface, making high-cadence coronal measurements through traditional Zeeman and Hanle effects difficult as the observational signatures are fraught with low-amplitude signals that can become swamped with instrumental noise. Magneto-hydrodynamic (MHD) techniques have previously been applied to coronal structures, with single and spatially isolated magnetic field strengths estimated as 9-55 G (refs ,,,). A drawback with previous MHD approaches is that they rely on particular wave modes alongside the detectability of harmonic overtones. Here we show, for the first time, how omnipresent magneto-acoustic waves, originating from within the underlying sunspot and propagating radially outwards, allow the spatial variation of the local coronal magnetic field to be mapped with high precision. We find coronal magnetic field strengths of 32 +/- 5 G above the sunspot, which decrease rapidly to values of approximately 1 G over a lateral distance of 7,000 km, consistent with previous isolated and unresolved estimations. Our results demonstrate a new, powerful technique that harnesses the omnipresent nature of sunspot oscillations to provide magnetic field mapping capabilities close to a magnetic source in the solar corona. Title: Propagating Disturbances in the Solar Corona and Spicular Connection Authors: Samanta, Tanmoy; Pant, Vaibhav; Banerjee, Dipankar Bibcode: 2015ApJ...815L..16S Altcode: 2015arXiv151107354S Spicules are small, hairy-like structures seen at the solar limb, mainly at chromospheric and transition region lines. They generally live for 3-10 minutes. We study these spicules in a south polar region of the Sun with coordinated observations using the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) instruments on board the Solar Dynamics Observatory. Propagating disturbances (PDs) are observed everywhere in the polar off-limb regions of the Sun at coronal heights. From these simultaneous observations, we show that the spicules and the PDs may have originated through a common process. From spacetime maps, we find that the start of the trajectory of PDs is almost cotemporal with the time of the rise of the spicular envelope as seen by IRIS slit-jaw images at 2796 and 1400 Å. During the return of spicular material, brightenings are seen in AIA 171 and 193 Å images. The quasi-periodic nature of the spicular activity, as revealed by the IRIS spectral image sequences, and its relation to coronal PDs, as recorded by the coronal AIA channels, suggest that they share a common origin. We propose that reconnection-like processes generate the spicules and waves simultaneously. The waves escape while the cool spicular material falls back. Title: Propagating disturbances along fan-like coronal loops in an active region Authors: Mandal, Sudip; Samanta, Tanmoy; Banerjee, Dipankar; Krishna Prasad, S.; Teriaca, Luca Bibcode: 2015RAA....15.1832M Altcode: 2015arXiv150504710M Propagating disturbances are often observed in active region fan-like coronal loops. They were thought to be due to slow mode magnetohydrodynamic waves based on some of the observed properties. However, recent studies involving spectroscopy indicate that they could be due to high speed quasi-periodic upflows which are difficult to distinguish from upward propagating slow waves. In this context, we have studied a fan loop structure in the active region AR 11465 using simultaneous spectroscopic and imaging observations from the Extreme Ultraviolet Imaging Spectrometer onboard Hinode and Atmospheric Imaging Assembly onboard Solar Dynamics Observatory. Analysis of the data shows significant oscillations at different locations. We explore the variations in different line parameters to determine whether the waves or flows could cause these oscillations to improve the current understanding of the nature of these disturbances. Title: MHD Seismology of a loop-like filament tube by observed kink waves Authors: Pant, Vaibhav; Srivastava, Abhishek K.; Banerjee, Dipankar; Goossens, Marcel; Chen, Peng-Fei; Joshi, Navin Chandra; Zhou, Yu-Hao Bibcode: 2015RAA....15.1713P Altcode: 2015arXiv150302281P We report and analyze observational evidence of global kink oscillations in a solar filament as observed in Hα by instruments administered by National Solar Observatory (NSO)/Global Oscillation Network Group (GONG). An M1.1-class flare in active region (AR) 11692 occurred on 2013 March 15 and induced a global kink mode in the filament lying towards the southwest of AR 11692. We find periods of about 61-67 minutes and damping times of 92-117 minutes at positions of three vertical slices chosen in and around the filament apex. We find that the waves are damped. From the observed period of the global kink mode and damping timescale using the theory of resonant absorption, we perform prominence seismology. We estimate a lower cut-off value for the inhomogeneity length scale to be around 0.34-0.44 times the radius of the filament cross-section. Title: Propagating disturbances along a coronal loop from simultaneous EUV imaging and spectroscopic observations Authors: Datta, Ajanta; Krishna Prasad, S.; Banerjee, Dipankar Bibcode: 2015RAA....15.1027D Altcode: Propagating disturbances (PDs) were studied along an active region loop using simultaneous imaging and spectroscopy. An image sequence recorded in the Fe IX/Fe X 171Å channel, from TRACE and spectral data in the Si XII 520.6 Å line obtained from CDS/SOHO, are analyzed. A space-time map constructed from the TRACE image sequence shows the presence of PDs close to the loop foot point propagating with an apparent speed of 39 km s-1. The periodicity was found to be 5.4 min. The corresponding spectroscopic data from CDS, at a location away from the foot point, show oscillations in all three line parameters roughly at the same period. At locations farther from the foot point, the line width oscillation seems to disappear while the Doppler velocity oscillation becomes prominent. We attribute this to the signature of propagating slow waves that get affected by flows/other events close to the foot point. Spectral line profiles do not show much asymmetry, however, it is difficult to infer anything due to the broadened Gaussian shape of the CDS line profiles. Title: Dynamics of On-disk Plumes as Observed with the Interface Region Imaging Spectrograph, the Atmospheric Imaging Assembly, and the Helioseismic and Magnetic Imager Authors: Pant, Vaibhav; Dolla, Laurent; Mazumder, Rakesh; Banerjee, Dipankar; Krishna Prasad, S.; Panditi, Vemareddy Bibcode: 2015ApJ...807...71P Altcode: 2015arXiv150504473P We examine the role of small-scale transients in the formation and evolution of solar coronal plumes. We study the dynamics of plume footpoints seen in the vicinity of a coronal hole using the Atmospheric Imaging Assembly (AIA) images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory and spectroscopic data from the Interface Region Imaging Spectrograph (IRIS). Quasi-periodic brightenings are observed in the base of the plumes and are associated with magnetic flux changes. With the high spectral and spatial resolution of IRIS, we identify the sources of these oscillations and try to understand what role the transients at the footpoints can play in sustaining the coronal plumes. IRIS “sit-and-stare” observations provide a unique opportunity to study the evolution of footpoints of the plumes. We notice enhanced line width and intensity, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of flows at the footpoints of plumes. We propose that outflows (jet-like features) as a result of small-scale reconnections affect the line profiles. These jet-like features may also be responsible for the generation of propagating disturbances (PDs) within the plumes, which are observed to be propagating to larger distances as recorded from multiple AIA channels. These PDs can be explained in terms of slow magnetoacoustic waves. Title: Quasi-periodic Oscillation of a Coronal Bright Point Authors: Samanta, Tanmoy; Banerjee, Dipankar; Tian, Hui Bibcode: 2015ApJ...806..172S Altcode: 2015arXiv150500587S Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening. Title: Correlation Between Decay Rate and Amplitude of Solar Cycles as Revealed from Observations and Dynamo Theory Authors: Hazra, Gopal; Karak, Bidya Binay; Banerjee, Dipankar; Choudhuri, Arnab Rai Bibcode: 2015SoPh..290.1851H Altcode: 2015SoPh..tmp...80H; 2014arXiv1410.8641H Using different proxies of solar activity, we have studied the following features of the solar cycle: i) The linear correlation between the amplitude of cycle and its decay rate, ii) the linear correlation between the amplitude of cycle n and the decay rate of cycle (n −1 ), and iii) the anti-correlation between the amplitude of cycle n and the period of cycle (n −1 ). Features ii) and iii) are very useful because they provide precursors for future cycles. We have reproduced these features using a flux-transport dynamo model with stochastic fluctuations in the Babcock-Leighton α effect and in the meridional circulation. Only when we introduce fluctuations in meridional circulation, are we able to reproduce different observed features of the solar cycle. We discuss the possible reasons for these correlations. Title: Polar Network Index as a Magnetic Proxy for the Solar Cycle Studies Authors: Priyal, Muthu; Banerjee, Dipankar; Karak, Bidya Binay; Muñoz-Jaramillo, Andrés; Ravindra, B.; Choudhuri, Arnab Rai; Singh, Jagdev Bibcode: 2014ApJ...793L...4P Altcode: 2014arXiv1407.4944P The Sun has a polar magnetic field which oscillates with the 11 yr sunspot cycle. This polar magnetic field is an important component of the dynamo process which operates in the solar convection zone and produces the sunspot cycle. We have direct systematic measurements of the Sun's polar magnetic field only from about the mid-1970s. There are, however, indirect proxies which give us information about this field at earlier times. The Ca-K spectroheliograms taken at the Kodaikanal Solar Observatory during 1904-2007 have now been digitized with 4k × 4k CCD and have higher resolution (~0.86 arcsec) than the other available historical data sets. From these Ca-K spectroheliograms, we have developed a completely new proxy (polar network index, hereafter PNI) for the Sun's polar magnetic field. We calculate PNI from the digitized images using an automated algorithm and calibrate our measured PNI against the polar field as measured by the Wilcox Solar Observatory for the period 1976-1990. This calibration allows us to estimate the polar fields for the earlier period up to 1904. The dynamo calculations performed with this proxy as input data reproduce reasonably well the Sun's magnetic behavior for the past century. Title: Damping of Slow waves and coronal heating Authors: Banerjee, Dipankar; Prasad Samayamanthula, Krishna; Van Doorsselaere, Tom Bibcode: 2014cosp...40E.203B Altcode: Propagating slow magneto-acoustic waves are often observed in polar plumes and active region fan loops. The observed periodicities of these waves range from a few minutes to few tens of minutes and their amplitudes were found to decay rapidly as they travel along the supporting structure. Thermal conduction, compressive viscosity, radiation, density stratication, and area divergence, were identified to be some of the causes for change in the slow wave amplitude. Recent studies indicate that the observed damping in these waves is frequency dependent. We used imaging data from SDO/AIA, to study this dependence in detail and for the first time from observations we attempted to deduce a quantitative relation between damping length and frequency of these oscillations. We developed a new analysis method to obtain this relation. It was found that the waves observed in the polar regions show a different dependence from those observed in the on-disk loop structures despite the similarity in their properties. The implications to coronal heating will be also addressed. Title: Digitized archive of Kodaikanal Ca-K Spectroheliograms and solar activity cycle Authors: Priyal, Muthu; Banerjee, Dipankar; Singh, Jagdev; Ravindra, B. Bibcode: 2014cosp...40E2628P Altcode: Abstract: The spectroheliograms in Ca-II K line obtained at Kodaikanal since 1907 have been digitized using 4k x 4k CCD camera. After CCD and intensity calibration we identified different chromospheric features. Using different thresholds of the intensity contrast and size criterion different features are classified as the plage (> 1.35 and area > 1-arc-min2) , enhanced-network (>1.35, area < 1-arcmin2) , active-network (1.25 -1.35), and quiet-Sun (1.15-1.25). For 100 years Ca-K spectroheliograms (1907 - 2007), the variation of Plage index, enhanced-work, active-network and quiet network index are studied with the solar cycle phase. The centroid of each individual plages corresponding to different latitudes are also identified using auto detection methods as developed using IDL, and the chromospheric differential rotation rates are calculated. Furthermore, we study the variation of the contribution of CaII K plage flux to the total solar irradiance. In this presentation we will present the Kodaikanal data archive and some important and interesting result obtained from our KKL Ca-K Spectroheliograms as outlined above. Title: Transverse Oscillations observed in a Jet and coronal seismology Authors: Banerjee, Dipankar; Chandrashekhar, K.; Morton, Richard Bibcode: 2014cosp...40E.204B Altcode: Extreme Ultra Violet (EUV) jets situated in coronal holes are thought to play an important role in supplying heated material to the corona and solar wind. The multi-wavelength capabilities and high signal-to-noise ratio of detectors on-board Solar Dynamic Observatory (SDO) allows for detailed study of these jet’s evolution. We aim to exploit SDO’s capabilities to reveal information on the jet dynamics and to obtain estimates for plasma properties associated with the jet. We studied the dynamics an EUV jet with SDO at a coronal hole boundary. The details of the jet evolution are discussed and measurements of the jet’s parameters, e.g. length, width, life time, and outward speed, are obtained. Furthermore, automated emission measure analysis is exploited to determine estimates for the temperature and density of the jet. A propagating transverse wave supported by the jet spire is also observed. Measurement of the wave properties are exploited for magneto-seismology and are used in conjunction with the emission measure results to estimate the magnetic field strength of the jet. We present a detailed description of the jet’s evolution, with new evidence of plasma flows, prior to the jet’s initiation, along the loops at the base of the jet and also find further evidence that flows along the jet spire consist of multiple, quasi-periodic small scale plasma ejection events. In addition, spectroscopic analysis reveal that the jet has temperatures of log 5.89 ±0.08 K and electron densities of log 8.75 ± 0.05 cm(-3) . Measured properties of the transverse wave provide evidence that a strong damping of the wave occurs as it propagates along the jet spire with speeds of 110 km/s. The magneto-seismological inversion of the wave parameters provides values of B = 1.21 ±0.2 G along the jet spire, which is in line with previous estimates for open fields in coronal holes. Title: Multi wavelength Study of Polar X-ray Jets using Hinode and SDO Authors: Chandrashekhar, K.; Gupta, Girjesh R.; Banerjee, Dipankar; Teriaca, Luca Bibcode: 2012cosp...39..310C Altcode: 2012cosp.meet..310C High spatial and temporal resolution images of the solar transition region in quiet and coronal hole regions show a dynamical environment where mass flows and jets are commonly observed. We study a polar jet with a combination of imaging from EIS and XRT on board Hinode. We measure jet parameters, e.g. length, width, life time, outward speed. The bright point associated with the jet is part of a sigmoidal structure. The time of appearance of the sigmoid and ejection of plasma from the bright point suggests that the sigmoid is a progenitor of the jet. Before and after the main jet event, we observe small collimated plasma flows from the bright point to the footpoint of the jet. These observations suggest that repetitive reconnection between emerging flux and the ambient open field in the coronal hole causes the polar jets. Average outward speed of the jet is 160 km/s, well below the escape speed. The enhancement in the light curves of low temperature EIS lines after the occurrence of the jet suggests that the jet material is falling back. To supplement these results we studied two polar coronal jets observed by AIA and HMI on board SDO. These jets have speeds around 200 to 300 km/s. The temperature response and the associated magnetic flux changes are studied using the multiple channels of AIA and HMI. The light curves as recorded with different AIA channels are compared with magnetic flux evolution as recorded by HMI. We will show that in spite of the better time and spatial resolution of AIA, the overlapping temperature response of AIA channels causes difficulty in proper diagnosis. Title: Propagating disturbances in open structures and coronal heating Authors: Banerjee, Dipankar Bibcode: 2012cosp...39...95B Altcode: 2012cosp.meet...95B Coronal holes are the coolest and darkest regions of the solar atmosphere, as observed both on the solar disk and above the solar limb. These are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. Using a combination of spectroscopy and imaging instruments presence of waves and or flows have been established in these open structures. Waves, observed via remote sensing and detected in-situ in the wind streams, are most likely responsible for the wind and several theoretical models describe the role of MHD waves in the acceleration of the fast solar wind. Though, recently the role of flows have also been claimed to be important. In this talk I will review the observational status of these propagating disturbances in open structures with an emphasis on their origin and the chromosphere - corona connection. Title: Spectroscopic Observations of Propagating Disturbances in Polar Coronal Hole Authors: Gupta, Girjesh R.; Marsch, Eckart; Solanki, Sami K.; Banerjee, Dipankar; Teriaca, Luca Bibcode: 2012cosp...39..689G Altcode: 2012cosp.meet..689G We focus on long duration spectroscopic observations of the south polar coronal hole taken on 1997 February 25 by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer aboard SOHO. We analyze the data in the on-disk part of the coronal hole to find any signature of propagating waves or high speed up-flows. We find the clear presence of propagating disturbances in intensity and Doppler velocity with a projected propagation speed of about 60~km~s^{-1} and a periodicity of ≈14.5~min. During the propagation, the intensity enhancement is associated with a blue-shifted Doppler velocity. These disturbances are clearly seen in intensity at higher latitudes (i.e. closer to the limb), whereas disturbances in Doppler velocity becomes faint there. We study average spectral line profiles at the roots of these disturbances and along the propagating ridge. Based on our analysis, we interpret these disturbances in terms of propagating slow magneto-acoustic waves. Title: Diagnosing Chromosphere- Corona connection by waves in open structures Authors: Banerjee, Dipankar Bibcode: 2012cosp...39...96B Altcode: 2012cosp.meet...96B Polar coronal holes are associated with rapidly expanding open magnetic fields and the acceleration of the high-speed solar wind. Using a combination of spectroscopy and imaging instruments presence of waves and or flows have been established in these open structures. Waves, observed via remote sensing and detected in-situ in the wind streams, are most likely responsible for the wind and several theoretical models describe the role of MHD waves in the acceleration of the fast solar wind. Though, recently the role of flows have also been claimed to be important. First I will review the observational status of these propagating disturbances in open structures with an emphasis on their origin and the chromosphere - corona connection. The role of small scale transient events on the generation of these disturbances will be one of the themes of this talk. Title: Digitization of the Kodaikanal Solar Photographic White Light Image Archive Authors: Ravindra, B.; Banerjee, Dipankar; Singh, Jagdev; Priyal, Muthu; Priya, T. G.; Amareswari, K.; Khyrun, Fathima; Afreen Ahmed, Nazia; Banu, Aysha; Kamesh, S. Bibcode: 2012cosp...39.1591R Altcode: 2012cosp.meet.1591R Solar telescope at Kodaikanal Obsrvatory has produced synoptic observations since 1904 while taking white light images of the sun and it has been still continuing today. The white light photographic archive has more than 44000 plates that has been acquired over 100 years. The digitization of the white light photographic plates have been carried out and completed at Kodaikanal. Here, we summarize the white light photographic data, its digitization and calibration. A few preliminary results comparing the solar cycle variations as recorded by similar archival data will be presented. Title: On the nature of propagating disturbances through open structures Authors: Prasad Samayamanthula, Krishna; Banerjee, Dipankar; Singh, Jagdev Bibcode: 2012cosp...39.1664P Altcode: 2012cosp.meet.1664P Propagating disturbances are observed along open and closed magnetic structures of the sun. For characterizing the nature of the propagating disturbances a combination of spectroscopy and imaging is essential. In this presentation I will show examples of such observations using EIS/Hinode with imaging sequences from AIA/SDO. While studying the variations of line parameters with time it allows us to characterize the nature of these propagating disturbances. Often the longer period variations show significant power in intensity and Doppler shift but not in line width and line profiles at these locations do not show any visible blue-shifted component and can be fitted well with a single Gaussian. The combination of the presence of flows and waves makes it even difficult to ascertain which one is more important for heating and acceleration of the winds. While looking at the frequency dependence of these propagating disturbances and the nature of power distribution we will argue that the waves are more important for the energy budget as far as heating and acceleration of the wind is concerned. Title: Indian Solar mission to study inner solar corona: Aditya 1 Authors: Singh, Jagdev; Banerjee, Dipankar; Venkatakrishnan, Parameswaran; Kasiviswanathan, Sankarasubramanian; Prasad B, Raghavendra Bibcode: 2012cosp...39.1824S Altcode: 2012cosp.meet.1824S Aditya-I is India's first dedicated scientific mission to study the sun. This is a low-earth orbit (LEO) mission at an altitude of 800 km. A visible emission line space solar coronagraph (VELC) has been selected as a payload under the small-satellite program of ISRO. It will provide high time cadence sharp images of the solar corona in the Green and Red Emission lines. These images will be used to study the highly dynamic nature of the solar corona including the small-scale coronal loops and large-scale Coronal Mass Ejections (CMEs). The uniqueness of this payload compared to previously flown space instruments are: (a) Observations in the visible wavelength closer to the disk (down to 1.05 solar radii), (b) high time cadence capability (better than 2-images per second), and (c) Simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations. I will update the current status of the project and will point out the complimentary role Aditya can play in conjunction with other solar big missions like SDO. Title: Complex variation of spectral line widths observed in polar corona Authors: Prasad Samayamanthula, Krishna; Banerjee, Dipankar; Singh, Jagdev Bibcode: 2012cosp...39.1665P Altcode: 2012cosp.meet.1665P Spectroscopic observations of the solar corona, using high spatial and spectral resolution 25cm coronagraph, at Norikura observatory, were made on large number of days during 2004 at the mid latitude and polar coronal regions. We have analyzed several raster scans that cover mid and high latitude regions on the off-limb corona in four bright emission lines of iron, namely, [Fe X] 6374 Å, [Fe XI]~7892~Å, [Fe XIII] 10747~Å, and [Fe XIV]~5303~Å. We find that the FWHM of red line increases with height and that of green line decreases with height as observed earlier, at equatorial regions. The comparison of line widths and their gradients with the results from equatorial regions indicate that these are higher for polar regions for the observed emission lines except for the green line. FWHM values show an increase towards poles in all the lines except for the green line which shows little or no change. Higher values of FWHM at polar regions may imply higher non-thermal velocities which could be linked to the solar wind, but the behavior of green emission line with almost same values of FWHM at equatorial and polar regions is surprising. This may also give some indications on the existence of preferential heating. Title: Oscillations in open loop structures Authors: Banerjee, Dipankar; Prasad Samayamanthula, Krishna; Singh, Jagdev Bibcode: 2012cosp...39...97B Altcode: 2012cosp.meet...97B Waves and oscillations in the solar atmosphere are often searched for and studied to investigate their role in coronal heating and fast solar wind acceleration. Another important application of them is coronal seismology, a tool to indirectly determine the physical properties of the corona which are difficult otherwise, using the properties of the waves. Different MHD modes, slow, fast and Alfven modes exist in the corona and it is important first to identify the wave mode using the observed properties, before exploiting it further. Compressive slow modes were extensively observed using the imaging data from various instruments such as EIT and TRACE. These modes were identified by the alternate brightenings in the time-distance maps. But the recent observations indicate that they could also be caused by the quasi-periodic high speed upflows and it is difficult to distinguish them using imaging data alone. To explore this, we studied several open loop structures both on-disk and off-limb which show propagating disturbances, using imaging data from AIA/SDO in different channels. We discuss some of the observed properties which may help to distinguish the waves from flows. Title: T Pyx: a long-overdue recurrent nova Authors: Evans, Aneurin; Woodward, Charles; Gehrz, Robert; Helton, Andrew; Starrfield, Sumner; Ness, Jan-Uwe; Bode, Michael; Eyres, Stewart; Banerjee, Dipankar; Ashok, N. M.; Krautter, Joachim; Kuulkers, Erik Bibcode: 2011sptz.prop70206E Altcode: We request DDT observations of the recurrent nova T Pyx, whose 2011 eruption was long overdue. Spitzer/IRAC observations at 3.6 and 4.5 microns will complement the 1-2.5 micron data we are getting from the ground, and the >50 micron data we are getting from Herschel (DDT approved). For the first time we will get infra-red data on an erupting nova from 1-100 microns, throwing new and unique insight into the evolution of a recurrent nova. Title: Proposed visible emission line space solar coronagraph Authors: Singh, Jagdev; Prasad, B. Raghavendra; Venkatakrishnan, P.; Sankarasubramanian, K.; Banerjee, Dipankar; Bayanna, Raja; Mathew, Shibu; Murthy, Jayant; Subramanian, Prasad; Ramesh, R.; Kathiravan, S.; Nagabhushana, S.; Mahesh, P. K.; Manoharan, P. K.; Uddin, Wahab; Sriram, S.; Kumar, Amir; Srivastava, N.; Rao, Koteswara; Nagendra, C. L.; Chakraborthy, P.; Sriram, K. V.; Venkateswaran, R.; Krishnamurthy, T.; Sreekumar, P.; Sarma, K. S.; Murthy, Raghava; Navalgund, K. HJ.; Samudraiah, D. R. M.; Babu, P. Narayan; Patra, Asit Bibcode: 2011CSci..100..167S Altcode: The outer atmosphere of the sun - called the corona - has been observed during total solar eclipse for short periods (typically <6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be fully understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wave-driven coronal heating; (ii) the dynamics and formation of coronal loops and temperature structure of the coronal features; (iii) the origin, cause and acceleration of coronal mass ejections (CMEs) and other solar active features, and (iv) coronal magnetic field topology and three-dimensional structures of CMEs using polarization information. The uniqueness of this payload compared to previously flown space instruments is as follows: (a) observations in the visible wavelength closer to the disk (down to 1.05 solar radii); (b) high time cadence capability (better than two-images per second), and (c) simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations. Title: On the nature of propagating MHD waves in polar coronal hole Authors: Gupta, Girjesh R.; Banerjee, Dipankar Bibcode: 2011ASInC...3..102G Altcode: Waves play an important role in the heating of the solar corona and in the acceleration of the fast solar wind from polar Coronal Holes (pCHs). Recently using EIS/Hinode and SUMER/SOHO, we have reported the presence of accelerating waves in polar region (Gupta et al. 2010, ApJ, 718, 11). These waves appeared to be originating from a bright location on-disk, presumably the footprint of the coronal funnels. These waves were interpreted in terms of either propagating Alfven waves or fast magneto-acoustic waves. The new sets of observations are obtained from the EIS/Hinode 2'' slit and imaging data from AIA/SDO in various filters over plume and inter-plume regions as HOP175 programme. The combination of spectroscopic and imaging data will provide further details on mode identification and properties of these waves and will help in the energy calculations. In this presentation, preliminary results obtained from these observations in terms of different nature of propagating waves in plume and inter-plume regions and energy carried by these waves will be presented. Title: Detection of high frequency oscillations from space experiments and eclipses Authors: Banerjee, Dipankar; Singh, Jagdev; Hasan, Siraj; Gupta, Girjesh R.; Nagaraju, K. Bibcode: 2010cosp...38.2851B Altcode: 2010cosp.meet.2851B We performed high resolution spectroscopy of the solar corona during the total solar eclipse of July 22, 2009 in two emission lines, namely the red line at 530.3 nm due to [Fe xiv] and the green line at 637.4 nm due to [Fex] simultaneously from Anji, China. Two mirror coelostat with 100 cm focal length lens made 9.2 mm image of the sun. The spectrograph using 140 cm focal length lens in Littrow mode and a grating with 600 lines per mm blazed at 2 micron provided a dispersion of 30 mA and 42 mA per pixel in the 4th order around green line and 3rd order red emission line, respectively. Two Peltier cooled 1K x 1K CCD cameras with pixel size of 13 micron square and 14-bit read out at 10 MHz operated in frame transfer mode, were used to obtain the time sequence spectra in each emission lines simultaneously. We detected presence of high frequency oscillations in intensity, velocity and line widths. We also studied the variation of line widths with height. The results will be discussed in terms of different MHD waves. Possibility of detecting these oscillations from space based experiments will be addressed. India is going to launch a emission line coronagraph on a small satellite platform called Aditya. The scientific goals of Aditya in pursuit to wave detection will be presented. Title: Accelerating disturbances in polar plume and inter-plume Authors: Gupta, Girjesh R.; Banerjee, Dipankar; Teriaca, Luca; Imada, Shinsuke; Solanki, Sami Bibcode: 2010cosp...38.2937G Altcode: 2010cosp.meet.2937G We present EIS/Hinode & SUMER/SoHO joint observations allowing the first spectroscopic detection of accelerating disturbances as recorded with coronal lines in inter-plume and plume regions of a polar coronal hole. From time-distance radiance maps, we detect the presence of propagating disturbances in a polar inter-plume region with a period of 15 to 20 min and a propagation speed increasing from 130±14 km/s just above the limb, to 330±140 km/s around 160" above the limb. These disturbances can also be traced to originate from a bright region of the on-disk part of the coronal hole where the propagation speed was found to be in the range of 25±1.3 to 38±4.5 km/s, with the same periodicity. These on-disk bright regions can be vi-sualized as the base of the coronal funnels. The adjacent plume region also shows the presence of propagating disturbance with the same range of period but with propagation speeds in the range of 135±18 to 165±43 km/s only. A comparison between the time-distance radiance map of both regions, indicate that the disturbances within the plumes are not observable (may be getting dissipated) far off-limb whereas this is not the case in the inter-plume region. Conclu-sions drawn from these observations in terms of accelerating waves or high speed jets/upflows will be discussed. Title: A study of quiet Sun oscillations using the Hinode, SoHO and Trace spacecrafts Authors: Gupta, Girjesh R.; Subramanian, Srividya; Banerjee, Dipankar; Doyle, Gerry Bibcode: 2010cosp...38.2829G Altcode: 2010cosp.meet.2829G A sequence of simultaneous quiet Sun images obtained by SOT/HINODE in the G-band and Ca II filters and by TRACE in the 1550A UV passband at disk center are studied using Fourier power and phase analysis. The results are then combined with the photospheric magnetic field information as obtained by the MDI/SoHO to study wave behavior in both magnetic and non-magnetic regions. Using simultaneous spectroscopic observations from SUMER/SoHO, the nature of oscillations in different layers of the transition region are also explored. The high resolution images of SOT allows us to identify the small scale chromospheric dynamics which could be also related to the emergence of small scale magnetic bipoles. The results indicate the presence of different oscillatory power and phases in magnetic and non-magnetic regions. The implication of these results in the context of coronal heating and wave propagation will be addressed. Title: Propagating slow magneto-acoustic waves in coronal loops as seen from trace and cds Authors: Prasad Samayamanthula, Krishna; Banerjee, Dipankar; Gupta, Girjesh R. Bibcode: 2010cosp...38.2835P Altcode: 2010cosp.meet.2835P Propagating intensity disturbances along various Active region loop structures with projected speeds less than and close to acoustic speeds, now commonly called magneto-acoustic waves, are proposed to be photospheric p-modes leaking into solar atmosphere. Though there is a wide range of periodicities observed, the 3 min. and 5 min. periodicities, which are character-istic of sunspot umbral and penumbral regions lifted their importance of study. Simultaneous observations of these waves at different heights from photosphere, through transition region to corona will give us direct evidence for their involvement and contribution to coronal heating. AR 10457 had been extensively studied for the presence of such propagating oscillations, when it is on-disk, on 11th September 2003, using the CDS/SoHO, TRACE, and MDI data of JOP 165 campaign. Different periodicities are found and the resonance feature in the periodicity is observed in few locations, but the speeds are found to be quite low(< 20 km/s). Comparison will be made between sunspot and non-sunspot linked open structures. There is also a signature of decelerating propagation in a structure. Significance of the results in the context of coronal heating and future observations with SDO will be discussed. Title: Dust formation in V838 Mon and V4332 Sgr Authors: Misselt, Karl; Ashok, Nagarhalli; Banerjee, Dipankar; Marengo, Massimo; Su, Kate Bibcode: 2008sptz.prop50106M Altcode: We propose follow-up observations of the unusual eruptive variables V838 Monocerotis (V838 Mon) and V4332 Sagitarrii (V4332 Sgr) to study the early formation and evolution of dust condensates in their ejecta. Both underwent powerful eruptions (2002 and 1994, respectively) characterized by multiple peaks and cool super-giant like spectra. Shortly after eruption, an optical light echo was discovered around V838 Mon. Spitzer observations carried out by us revealed the presence of an extremely rare infrared light echo and suggest an interstellar origin for the material. While no extended emission has been noted around V4332 Sgr, it spectrum (both in the optical and the Spitzer infrared) is characterized by the presence of rare AlO radicals. More recently, our Spitzer data have shown the presence of alumina and titanium oxides in the ejecta around V4332 Sgr, the older of the two eruptions. Spectra of V838 Mon have also shown strong evidence for the presence of the these early dust condensate species. In addition to their infrared evolution, both objects have been seen to undergo significant evolution in their optical spectra. The ongoing formation and evolution of dust condensates in the ejecta of both objects provides a unique opportunity to study and test theories of dust condensation in oxygen rich environments. Title: NGC 6834 - 80 Myr old cluster with 4 emission line stars Authors: Subramaniam, Annapurni; Mathew, Blesson; Varricatt, Watson; Bhatt, B. C.; Ashok, N. M.; Banerjee, Dipankar Bibcode: 2008BASIP..25R..48S Altcode: 2008BASI...25R..48S NGC 6834 is a poorly studied cluster and known to be 80 Myr old. We detect 4 early type stars with Halpha in emission, which is a surprising result as these type of stars are not expected in a cluster of this age. We present a complete analysis of the cluster NG 6834 based on UBV CCD data, spectra of 4 stars with Halpha in emission (both obtained using the HCT), NIR spectrum of two stars using the UKIRT and 2MASS JHK. Title: The Infrared Light Echo of V838 Monoceritis Authors: Su, Kate; Ashok, Nagarhalli; Banerjee, Dipankar; Misselt, Karl; Retter, Alon Bibcode: 2006sptz.prop30472S Altcode: We propose follow-up observations of the extremely interesting object V838 Monocerotis (V838 Mon). V838 Mon underwent a powerful nova-like eruption in 2002 and has been the object of intensive study ever since. A spectacular light echo was observed following the outburst and subsequent observations revealed a rapid evolution of V838 Mon with time. Our previous Spitzer observations have revealed an infrared light echo well correlated with the optical echo. In addition, we have discovered an unresolved hot dust component, perhaps representing material newly formed in the recent outburst. We propose to continue and expand our observations of V838 Mon to follow the time evolution of the infrared light echo, the unresolved hot dust, and constrain the environment and nature (models) of the V838 Mon phenomena. Title: Transition Region Dynamics Authors: Banerjee, Dipankar Bibcode: 2005BASI...33..339B Altcode: No abstract at ADS Title: Infrared studies of V838 Mon and V4332 Sgr - a new class of nova-like variables. Authors: Ashok, Nagarhalli; Banerjee, Dipankar; Misselt, Karl; Su, Kate Bibcode: 2005sptz.prop20581A Altcode: Based on encouraging results that we have obtained with Spitzer Cycle 1 observations, we propose to extend our studies of the extremely interesting objects V838 Mon and V4332 Sgr. These objects, which had powerful nova-like outbursts in the recent past, are being recognized as a new class of eruptive variables. Our recent work on them in the optical and near-infrared have yielded several exciting results on them. These have given valuable insights into the nature of their circumstellar environment. However, while much has been learned about them, the cause of their mysterious outbursts is not a completely resolved issue. Our Spitzer observations detects the presence of extended nebulosity around V838 Mon. We show that while a part of this nebulosity could be the IR equivalent of the optical light echo, a significant part of it could be due to intrinsic emission from extended cold dust that surrounds the object. We propose observations that have the potential to (i) establish the origin and location of the dust causing the nebulosity (ii) study whether VMon-type objects have more than one outburst (iii) attempt to establish whether V838 Mon has a hot B type companion as suggested by the optical data and (iv) make the first study of the evolution of the light echo in the mid/far infrared in case the extended nebulosity around V838 Mon is basically a light-echo. Our proposed studies of V4332 Sgr will monitor the evolution of an object which is shown to display significant short-term photometric and spectroscopic changes. Title: Infrared studies of the Helium nova V445 Puppis. Authors: Banerjee, Dipankar; Su, Kate; Ashok, N. M.; Gehrz, R. D.; Henden, A.; Lynch, D. K.; Misselt, K.; Polomski, E. F.; Rudy, R. J.; Starrfield, S.; Su, K. Y. L.; Varricatt, W. P.; Wagner, R. M.; Woodward, C. E. Bibcode: 2005sptz.prop20100B Altcode: V445 Puppis, which erupted in a nova-like outburst in Dec. 2000, could well be the first, observed example of a "Helium nova". A classical nova eruption occurs on the surface of white-dwarf (WD) due to a thermo-nuclear runaway in the matter accreted by the WD from its companion main sequence star. Since this material is H rich, the outburst spectrum is expected to be rich in H lines in the optical and near-IR regions. Such H lines are invariably observed in novae spectra. However, V445 Puppis showed no sign of any H lines in the optical or near-IR spectra obtained after outburst and also in spectra obtained very recently. Instead it shows an unusual enrichment of Helium and Carbon spectral features. The object defies classification in known categories of eruptive variables and appears to be a potential Helium nova candidate. A "Helium nova" outburst had been predicted to occur when the accreted matter on the WD was Helium rich and appropriate physical conditions prevailed. But such a theoretical prediction had no observable counterpart till the outburst of V445 Puppis. Now, several theoretical studies, which have modelled the low outburst-amplitude observed in V445 Pup and also its slowly-declining light curve, indicate that it has strong potential as a genuine He nova candidate. Our proposed Spitzer observations will (i) study the properties of the thick dust shell that enshrouds V445 Pup. A significant part of the object's emission is in the infrared (ii) explore its spectra in the mid-IR and compare it with spectra of classical novae to see the differences between them. Such spectra, given the nature of V445 Pup, will have the potential to yield new/unanticipated results (iii) estimate physical properties like temperature, electron density etc. of the object's environment based on its spectra and (iv) try to detect the expanding nova shell from the 2000 outburst whose detection in the optical has been reported recently. Title: Study of a New Class of Nova-Like Variables Authors: Ashok, Nagarhalli; Banerjee, Dipankar; Misselt, Karl; Su, Kate Bibcode: 2004sptz.prop.3242A Altcode: There have recently been instances of nova-like explosions on two stars viz. V4332 Sgr and V838 Mon which have evoked keen and sustained interest in a large segment of the astronomical community. This interest has been heightened by the spectacular and rare light echo seen around V838 Mon. Both these objects - for which we have proposed the name quasi-novae - have displayed outburst properties which are significantly different from other known classes of eruptive variables like classical novae, symbiotic novae or born-gain AGB stars. Though the cause for their outburst is poorly understood at present, it is being recognized that the mechanism involved could be fundamentally different from conventional scenarios for classical novae eruptions. Thus there is an imperative need to study these objects in greater detail. Available data on them, as elaborated in the science case, shows a richness in their optical and near-IR spectra that is truly exceptional. We wish to study these objects further in the mid and far-IR regime. Such a study will help to get better insights into the cool circumstellar environment of this new class of objects and understand the nature of their outburst better. The proposed objects have already yielded very interesting optical and near-IR results so far. We anticipate - with a fair deal of conviction - that mid/far-IR studies will yield equally striking results. The Spitzer Space Telescope provides a unique opportunity - that does not come often - for carrying out such studies. Title: The influence of magnetic fields on radiative damping of magnetoatmospheric oscillations Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J. Bibcode: 1998IAUS..185..423B Altcode: We examine the non adiabatic effects on the modes of an isothermal stratified magnetic atmosphere. The present investigation is a continuation of earlier work by Banerjee, Hasan & Christensen-Dalsgaard (1995, 1996, 1997), where the interaction of various elementary modes in a stratified magnetised atmosphere was studied in the purely adiabatic limit. The inclusion of radiative dissipation in magnetoatmospheric wave problem - even in the over simplified Newtonian Cooling approximation - is of great importance. Including Newtonian Cooling, in the weak field limit, an analytic expression for the dispersion relation is derived which allows the effect of weak magnetic field on the modes to be studied. We examine the nature of the eigen frequency curves in the diagnostic diagram and find that, similar to the previous analysis, the modes undergo avoided crossings. We study the full frequency spectrum and the interaction amongst various modes. Strong mode coupling in the avoided crossing regions permits energy leakage. Our results, find application in the analysis of waves in flux-tubes on the Sun. We study the influence of magnetoatmospheric waves on spectral line profiles. Title: Effect of Newtonian Cooling on Waves in a Magnetized Isothermal Atmosphere Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J. Bibcode: 1997SoPh..172...53B Altcode: 1997ESPM....8...53B We examine the influence of nonadiabatic effects on the modes of an isothermal stratified magnetic atmosphere. The present investigation is a continuation of earlier work by Hasan and Christensen-Dalsgaard (1992) and Banerjee, Hasan, and Christensen-Dalsgaard (1995, 1996), where the interaction of various elementary modes in a stratified magnetized atmosphere was studied in the purely adiabatic limit. The inclusion of radiative dissipation based on Newton's law of cooling demonstrates the importance of this effect in the study of magnetoatmospheric waves. We analyze the physical nature of magnetoacoustic gravity (or MAG) oscillations in the presence of Newtonian cooling and find that the eigenfrequency curves in the diagnostic diagram, as in the previous analysis, undergo avoided crossings. However, the qualitative nature of the mode interaction is strongly influenced by radiative dissipation, which leads to strong mode damping in the avoided-crossing regions. We demonstrate this effect for the interaction between the Lamb mode and a magnetic mode. Our results could be important in the analysis of waves in flux tubes on the Sun. Title: Wave leakage in a magnetized isothermal atmosphere Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J. Bibcode: 1996BASI...24..325B Altcode: No abstract at ADS Title: The Influence of a Vertical Magnetic Field on Oscillations in an Isothermal Stratified Atmosphere. II. Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J. Bibcode: 1995ApJ...451..825B Altcode: We examine the effect of a uniform vertical magnetic field on the modes of an isothermal stratified atmosphere. The present investigation is a continuation of earlier work by Hasan & Christensen-Dalsgaard in which this problem was studied for rigid boundary conditions. In this paper, the earlier results are extended to different sets of boundary conditions. We demonstrate explicitly how these boundary conditions affect the various elementary wave modes present in the atmosphere. In the weak-field limit, an analytic expression for the dispersion relation is derived, which allows the effect of a weak magnetic field on the modes to be studied. We show that, to lowest order in our perturbation expansion, the oscillation spectrum can be analyzed in terms of (a) p- and g-like modes; (b) a magnetic Lamb mode; (c) magnetic or slow modes; and (d) a gravity- Lamb mode. The first three of these were present in the previous analysis for rigid boundaries, whereas the last is a consequence of the vertical gradients of the displacements at the boundaries. We focus our attention on the properties of this mode and show that it is present even in the moderate to strong field case as a magnetogravity-Lamb mode. The recognition and physical interpretation of this mode is a new feature of the present analysis. We also examine the nature of the eigenfrequency curves in the diagnostic (or K-Ω) diagram and find that, similar to the previous analysis, the modes undergo avoided crossings. However, the nature of the solutions in the present case is more complicated, especially when triple-mode interactions occur. Furthermore, the connectivity of the curves in the K-Ω diagram can be strongly influenced by the choice of boundary conditions. Our results, though somewhat idealized, find application in the analysis of waves in sunspots. It is conjectured that conditions for the existence of the magnetogravity-Lamb mode may also be satisfied in the subphotospheric layers of the Sun. Title: Energy Transport to the Solar Corona by Magnetic Kink Waves Authors: Choudhuri, Arnab R.; Dikpati, Mausumi; Banerjee, Dipankar Bibcode: 1993ApJ...413..811C Altcode: We show that the magnetic kink waves generated by the motions of photospheric footpoints of the coronal flux tubes can supply adequate energy for heating the quiet corona, provided there are occasional rapid motions of these footpoints as found in recent observations. Choudhuri et al. (1992) modeled the solar corona as isothermal atmosphere and showed that these rapid motions are much more efficient for transporting energy compared to the slow footpoint motions taking place most of the time. We extend these calculations for a two-layer atmosphere, with the lower layer having chromospheric thickness and temperature, and the upper layer having coronal temperature. Even in the presence of such a temperature jump we find that the rapid footpoint motions are still much more efficient for transporting energy to the corona and the estimated energy flux is sufficient for quiet coronal heating. We discuss the general problem of the propagation of kink pulses in a two-layer atmosphere for different possible values of the basic parameters. We find a fairly complicated behavior which could not be anticipated from the analysis of a pure Fourier mode.