explanation      blue bibcodes open ADS page with paths to full text
Author name code: banerjee
ADS astronomy entries on 2022-09-14
=author:"Banerjee, Dipankar" 

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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
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.

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Title: X-ray and ultraviolet observations of flares on AT Microscopii
    with AstroSat
Authors: Kuznetsov, Alexey; Banerjee, Dipankar; Karakotov, Ruslan;
   Chandrashekhar, Kalugodu
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.

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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.
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).

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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.
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).

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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
2022SSRv..218...13N    Altcode:
  No abstract at ADS

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Title: A Simple Radial Gradient Filter for Batch-Processing of
    Coronagraph Images
Authors: Patel, Ritesh; Majumdar, Satabdwa; Pant, Vaibhav; Banerjee,
   Dipankar
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.

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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
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.

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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
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<SUP>∘</SUP>
  latitude in the evolution, and possible production, of solar magnetism.

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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
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.

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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
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 (&lt;3 R<SUB>⊙</SUB>)
  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.

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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.
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).

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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
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.

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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
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.

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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.
2021SoPh..296...31P    Altcode: 2020arXiv201014786P
  Solar eruptions such as coronal mass ejections (CMEs) observed in
  the inner solar corona (up to 4 R<SUB>⊙</SUB>) 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<SUP>∘</SUP> 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.

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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
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 &gt; 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.

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Title: A statistical study of plasmoids associated with a post-CME
    current sheet
Authors: Patel, Ritesh; Pant, Vaibhav; Chandrashekhar, Kalugodu;
   Banerjee, Dipankar
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. <BR />
  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. <BR /> 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. <BR /> 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<SUP>-1</SUP> and ∼191 km s<SUP>-1</SUP>, respectively
  in the EUV channels of observation. The average speed of plasmoids
  increases to ∼671 km s<SUP>-1</SUP> and ∼1080 km s<SUP>-1</SUP>
  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<SUP>-1</SUP> to over 8 km s<SUP>-1</SUP>. We also find that the
  null point of the current sheet is located at ≈1.15 R<SUB>⊙</SUB>,
  where bidirectional plasmoid motion is observed. <BR /> 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 = 115.69W<SUP>0.37</SUP>. The presence of accelerating
  plasmoids near the neutral point indicates a longer diffusion
  region as predicted by MHD models. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202039000/olm">https://www.aanda.org</A>

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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.
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.

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Title: Connecting 3D Evolution of Coronal Mass Ejections to Their
    Source Regions
Authors: Majumdar, Satabdwa; Pant, Vaibhav; Patel, Ritesh; Banerjee,
   Dipankar
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 (&lt;3 R<SUB>⊙</SUB>)
  and outer (&gt;3 R<SUB>⊙</SUB>) 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<SUB>⊙</SUB>. We find a broad range in the distribution
  of peak 3D speeds and accelerations, ranging from 396 to 2465 km
  s<SUP>-1</SUP> and 176 to 10,922 m s<SUP>-2</SUP> 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
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. <BR /> 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. <BR /> 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. <BR /> 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. <P />Generated
  composites are available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78</A>
  and at <A
  href="http://www2.mps.mpg.de/projects/sun-climate/data.html">http://www2.mps.mpg.de/projects/sun-climate/data.html</A>

---------------------------------------------------------
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.
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. <BR /> 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. <BR /> 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. <BR /> 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. <BR /> 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. <P />The whole series described in
  the paper are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88</A>

---------------------------------------------------------
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.
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 H<SUB>α</SUB> 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
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 (B<SUB>max</SUB>) 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 (γ<SUB>0</SUB>) initially increases slowly with the increase of
  B<SUB>max</SUB>. However, when B<SUB>max</SUB> ≳ 2 kG, γ<SUB>0</SUB>
  decreases. Scatter of the BMR tilt around Joy's law systematically
  decreases with the increase of B<SUB>max</SUB>. The decrease of observed
  γ<SUB>0</SUB> with B<SUB>max</SUB> 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
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. <BR /> Aims: We analyse oscillations in the threads
  of a filament and utilize seismology techniques to estimate magnetic
  field strength and length of filament threads. <BR /> 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. <BR />
  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. <BR />
  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. <P />Movies associated to Figs. 2 and 3 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936453/olm">https://www.aanda.org</A>

---------------------------------------------------------
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.
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
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
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
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 &lt;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
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
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. <BR /> 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
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
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
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
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 &amp;
  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
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
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
  10<SUP>12</SUP> cm<SUP>2</SUP> s<SUP>-1</SUP>. 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
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−<SUP>1</SUP>) images of the corona from 1.05
  R⊙-3<SUB><SUB>R⊙</SUB> 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. <P /></SUB>

---------------------------------------------------------
Title: Century-long, multi-wavelength Solar Database From Kodaikanal
    Solar Observatory
Authors: Banerjee, Dipankar
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
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.
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<SUP>-1</SUP>) and
  temporal (1 s) resolution images of corona from 1.05 R<SUB>⊙</SUB>
  to 3 R<SUB>⊙</SUB>, 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
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
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
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
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.
2017ApJ...849...44C    Altcode: 2017arXiv170705658C
  The century long (1914-2007) {{{H}}}<SUB>α </SUB> (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}}}<SUB>α </SUB>. 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.
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
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
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
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.
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. <BR /> 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. <BR />
  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. <BR />
  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. <P />Sunspot area time series
  (1921-2011) are available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A106">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/601/A106</A>

---------------------------------------------------------
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
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 arcmin<SUP>2</SUP> 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
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
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
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
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
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.
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}}<SUP>2</SUP> 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.
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
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 &gt; 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
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
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
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
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
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−<SUP>1</SUP>,
  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
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 <SUB> d </SUB>)
  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 <SUB> d </SUB>
  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
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
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
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
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
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<SUP>-1</SUP>. 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
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
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
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
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
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.
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
  (&gt; 1.35 and area &gt; 1-arc-min2) , enhanced-network (&gt;1.35,
  area &lt; 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
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
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
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
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
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.
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
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
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
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
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
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 &gt;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
2011CSci..100..167S    Altcode:
  The outer atmosphere of the sun - called the corona - has been observed
  during total solar eclipse for short periods (typically &lt;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
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.
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
2010cosp...38.2937G    Altcode: 2010cosp.meet.2937G
  We present EIS/Hinode &amp; 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
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.
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(&lt; 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
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
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
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
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
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.
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
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.

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Title: The influence of magnetic fields on radiative damping of
    magnetoatmospheric oscillations
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
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 &amp;
  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.

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Title: Effect of Newtonian Cooling on Waves in a Magnetized Isothermal
    Atmosphere
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
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.

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Title: Wave leakage in a magnetized isothermal atmosphere
Authors: Banerjee, Dipankar; Hasan, S. S.; Christensen-Dalsgaard, J.
1996BASI...24..325B    Altcode:
  No abstract at ADS

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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.
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 &amp; 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.

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Title: Energy Transport to the Solar Corona by Magnetic Kink Waves
Authors: Choudhuri, Arnab R.; Dikpati, Mausumi; Banerjee, Dipankar
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.