Author name code: chatterjee
ADS astronomy entries on 2022-09-14
author:"Chatterjee, Piyali" 
------------------------------------------------------------------------  

Title: The Solar Activity Monitor Network - SAMNet
Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang,
   Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.;
   Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša,
   Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez,
   Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.;
   Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu,
   Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer,
   James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen,
   Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz,
   Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili,
   Teimuraz; Zuccarello, Francesca
Bibcode: 2022JSWSC..12....2E
Altcode:
  The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a
  future UK-led international network of ground-based solar telescope
  stations. SAMNet, at its full capacity, will continuously monitor
  the Sun's intensity, magnetic, and Doppler velocity fields at
  multiple heights in the solar atmosphere (from photosphere to upper
  chromosphere). Each SAMM sentinel will be equipped with a cluster of
  identical telescopes each with a different magneto-optical filter (MOFs)
  to take observations in K I, Na D, and Ca I spectral bands. A subset
  of SAMM stations will have white-light coronagraphs and emission line
  coronal spectropolarimeters. The objectives of SAMNet are to provide
  observational data for space weather research and forecast. The goal
  is to achieve an operationally sufficient lead time of e.g., flare
  warning of 2-8 h and provide many sought-after continuous synoptic
  maps (e.g., LoS magnetic and velocity fields, intensity) of the lower
  solar atmosphere with a spatial resolution limited only by seeing or
  diffraction limit, and with a cadence of 10 min. The individual SAMM
  sentinels will be connected to their master HQ hub where data received
  from all the slave stations will be automatically processed and flare
  warning issued up to 26 h in advance.

Title: Polymeric jets throw light on the origin and nature of the
    forest of solar spicules
Authors: Dey, Sahel; Chatterjee, Piyali; Murthy, O. V. S. N.; Korsós,
   Marianna B.; Liu, Jiajia; Nelson, Christopher J.; Erdélyi, Robertus
Bibcode: 2022NatPh..18..595D
Altcode:
  Spicules are plasma jets that are observed in the dynamic interface
  region between the visible solar surface and the hot corona. At any
  given time, it is estimated that about 3 million spicules are present
  on the Sun. We find an intriguing parallel between the simulated
  spicular forest in a solar-like atmosphere and the numerous jets of
  polymeric fluids when both are subjected to harmonic forcing. In a
  radiative magnetohydrodynamic numerical simulation with sub-surface
  convection, solar global surface oscillations are excited similarly to
  those harmonic vibrations. The jets thus produced match remarkably well
  with the forests of spicules detected in observations of the Sun. Taken
  together, the numerical simulations of the Sun and the laboratory fluid
  dynamics experiments provide insights into the mechanism underlying
  the ubiquity of jets. The non-linear focusing of quasi-periodic waves
  in anisotropic media of magnetized plasma as well as polymeric fluids
  under gravity is sufficient to generate a forest of jets.

Title: Configuration files for simulations of the solar spicule forest
Authors: Chatterjee, Piyali; Dey, Sahel
Bibcode: 2022zndo...5807020C
Altcode:
  The open source radiative MHD code, the
  pencil code and the manual, can be downloaded from
  https://github.com/pencil-code/pencil-code. Recommended pencil code
  version to check-out: 51b321b888ebb5adb60eaff205cee8e64d5cf689
  (dated 5-Jan-2022) Executing >> git describe
  51b321b888ebb5adb60eaff205cee8e64d5cf689 stable-4234-g51b321b
  Important note/Additional instruction: For the stratification.dat
  file, kindly replicated the first 3 rows at first and
  last 3 rows at last so that # of rows is 3078 (and not
  3072). The beginning and end of this file should looks like
  --------------------------------------------------------------
  -5.0351391 7.3070121 10.421405 -5.0351391 7.3070121 10.421405
  -5.0351391 7.3070121 10.421405 -5.0351391 7.3070121 10.421405
  ......rows in between ......rows in between 44.044453 -25.910588
  13.815511 44.060440 -25.910931 13.815511 44.060440 -25.910931
  13.815511 44.060440 -25.910931 13.815511 44.060440 -25.910931 13.815511
  --------------------------------------------------------------- Tar
  file setup_fig2b contains the run directory used to produce Fig 2 b
  and c in Dey et al (2022, Nature Physics).

Title: The Pencil Code, a modular MPI code for partial differential
equations and particles: multipurpose and multiuser-maintained
Authors: Pencil Code Collaboration; Brandenburg, Axel; Johansen,
   Anders; Bourdin, Philippe; Dobler, Wolfgang; Lyra, Wladimir;
   Rheinhardt, Matthias; Bingert, Sven; Haugen, Nils; Mee, Antony; Gent,
   Frederick; Babkovskaia, Natalia; Yang, Chao-Chin; Heinemann, Tobias;
   Dintrans, Boris; Mitra, Dhrubaditya; Candelaresi, Simon; Warnecke,
   Jörn; Käpylä, Petri; Schreiber, Andreas; Chatterjee, Piyali;
   Käpylä, Maarit; Li, Xiang-Yu; Krüger, Jonas; Aarnes, Jørgen;
   Sarson, Graeme; Oishi, Jeffrey; Schober, Jennifer; Plasson, Raphaël;
   Sandin, Christer; Karchniwy, Ewa; Rodrigues, Luiz; Hubbard, Alexander;
   Guerrero, Gustavo; Snodin, Andrew; Losada, Illa; Pekkilä, Johannes;
   Qian, Chengeng
Bibcode: 2021JOSS....6.2807P
Altcode: 2021JOSS....6.2807C; 2020arXiv200908231B
  The Pencil Code is a highly modular physics-oriented simulation code
  that can be adapted to a wide range of applications. It is primarily
  designed to solve partial differential equations (PDEs) of compressible
  hydrodynamics and has lots of add-ons ranging from astrophysical
  magnetohydrodynamics (MHD) to meteorological cloud microphysics and
  engineering applications in combustion. Nevertheless, the framework
  is general and can also be applied to situations not related to
  hydrodynamics or even PDEs, for example when just the message passing
  interface or input/output strategies of the code are to be used. The
  code can also evolve Lagrangian (inertial and noninertial) particles,
  their coagulation and condensation, as well as their interaction with
  the fluid.

Title: Modeling the solar spicule forest and the coronal swirls
Authors: Chatterjee, Piyali
Bibcode: 2021cosp...43E1797C
Altcode:
  Solar spicules, which can be observed when imaging the Sun using the Ca
  II H (396.9 nm) line, Mg II k(279.6 nm) line or the H Alpha (656.28 nm)
  spectral line filters, are thin cylindrical structures comprising of
  cold and dense plasma from the chromosphere making incursions -all the
  time- into the much hotter solar coronal plasma. Spicules seen in Ca II
  H filter are loosely classified by solar astronomers into two classes --
  type-I and type-II, the latter being more energetic than the former. Our
  numerical magneto-hydrodynamic (MHD) experiments in two dimensions
  establishes that periodic forcing due to formation and destruction of
  convective granules on the visible solar surface is sufficient to form
  the forest of spicules with physical characteristics similar to the
  observed spicules. In our unified model of the spicule forest, the more
  energetic spicules are formed when this periodic forcing is further
  aided by magnetic reconnection. Therefore our simulations further
  contribute to unveiling the subtleties of spicule formation. We also
  study the characteristics of spicules formed in coronal holes versus
  in quiet sun or the active region. It is to be noted that spicules
  are not dependent on the 2-dimensionality of our model. We obtain
  spicules of similar characteristics in a 3-dimensional version of the
  same model. The behavior only gets richer because now the spicules can
  also have a torsional mode apart from the transverse kink and sausage
  modes also seen in the 2-dimensional model. New interesting features
  like short lived coronal swirls also appear in the 3-dimensional model
  alongside spicules but with a very small spatial overlap even though
  there exists striking temporal coincidence. We explore the presence
  of Kelvin-Helmholtz instability and its effect on the multi-stranded
  structure of spicules. Finally, we analyze different oscillation modes
  of the synthetic spicules using time-distance diagrams and estimate
  the energy in the modes.

Title: Testing Alfvén wave propagation in a "realistic" set-up of
    the solar atmosphere
Authors: Chatterjee, Piyali
Bibcode: 2020GApFD.114..213C
Altcode:
  We present a radiative magneto-hydrodynamic simulation set-up using
  the pencil code to study the generation, propagation and dissipation
  of Alfvén waves in the solar atmosphere which includes a convective
  layer, photosphere below and chromosphere, transition region and the
  corona above. We prepare a set-up of steady-state solar convection
  where the imposed external magnetic field also has reached the final
  value gradually starting from a very small value. From that state,
  we start several simulations by varying the magnetic Prandtl number
  and the forcing strengths. We find the propagation characteristics of
  waves excited in this simulation run depend strongly on the magnetic
  Prandtl number and the wave number of the forcing. For magnetic
  Prandtl number of unity, we obtain localised heating in the corona
  due to shock dissipation.

Title: Dimerization Effect on HF Elimination from the Photoionized
    Fluorophenols
Authors: Chatterjee, Piyali; Biswas, Souvick; Chakraborty, Tapas
Bibcode: 2019isms.confEFC06C
Altcode:
  A time of flight mass spectrometry study for multi-photon ionization
  dissociation of monomers and dimers of 2- and 3-fluorophenols (2FP
  and 3FP) by a pulsed UV laser light of wavelength 266 nm will be
  presented. For these molecules, HF elimination from the excited and
  ionic states is a vital reaction channel. Our measurements reveal
  that the reaction does not occur from the monomer of 3FP, but it does
  occur with a measurable yield from the monomer cation of 2FP. On the
  other hand, upon formation of hydrogen bonded dimers, this reaction is
  triggered in the cation of 3FP, but for 2FP dimer cation the reaction
  is so facile that no intact dimer cation survives and only the HF
  eliminated dimer ion shows up in the mass spectrum. Electronic structure
  theory predicts that in the D<SUB>0</SUB> state of 2FP dimer cation, HF
  elimination is exothermic, but the process encounters a large barrier,
  2.75 eV. However, in S<SUB>1</SUB> state of the dimer the reaction is
  predicted to be barrierless. Thus, we propose that for this dimer,
  HF elimination takes place in the intermediate S<SUB>1</SUB> state,
  and the remaining fragment that has relatively lower ionization energy
  is ionized effectively by an overall two-photon (1+1) process. For the
  reaction to occur from 3FP dimer cation, a rearrangement of the dimer
  geometry and formation of an intermediate adduct has been suggested, and
  it is argued that the latter could be produced by nucleophilic attack
  of the neutral moiety at the ortho site of the cationic counterpart,
  and the whole process requires 3-photon (2+1) absorption.

Title: Testing Alfvén wave propagation in a "realistic" set-up of
    the solar atmosphere
Authors: Chatterjee, Piyali
Bibcode: 2018arXiv180608166C
Altcode:
  We present a radiative magneto-hydrodynamic simulation set-up using
  the PENCIL CODE to study the generation, propagation and dissipation
  of Alfvén waves in the solar atmosphere which includes a convective
  layer, photosphere below and chromosphere, transition region and the
  corona above. We prepare a setup of steady-state solar convection
  where the imposed external magnetic field also has reached the final
  value gradually starting from a very small value. From that state,
  we start several simulations by varying the magnetic Prandtl number
  and the forcing strengths. We find the propagation characteristics of
  waves excited in this simulation run depend strongly on the magnetic
  Prandtl number and the wave number of the forcing. For magnetic
  Prandtl number of unity, we obtain localized heating in the corona
  due to shock dissipation.

Title: Applying the Weighted Horizontal Magnetic Gradient Method to
    a Simulated Flaring Active Region
Authors: Korsós, M. B.; Chatterjee, P.; Erdélyi, R.
Bibcode: 2018ApJ...857..103K
Altcode: 2018arXiv180410351K
  Here, we test the weighted horizontal magnetic gradient (WG<SUB>
  M </SUB>) as a flare precursor, introduced by Korsós et al., by
  applying it to a magnetohydrodynamic (MHD) simulation of solar-like
  flares. The preflare evolution of the WG<SUB> M </SUB> and the behavior
  of the distance parameter between the area-weighted barycenters of
  opposite-polarity sunspots at various heights is investigated in the
  simulated δ-type sunspot. Four flares emanated from this sunspot. We
  found the optimum heights above the photosphere where the flare
  precursors of the WG<SUB> M </SUB> method are identifiable prior
  to each flare. These optimum heights agree reasonably well with the
  heights of the occurrence of flares identified from the analysis of
  their thermal and ohmic heating signatures in the simulation. We also
  estimated the expected time of the flare onsets from the duration of the
  approaching-receding motion of the barycenters of opposite polarities
  before each single flare. The estimated onset time and the actual time
  of occurrence of each flare are in good agreement at the corresponding
  optimum heights. This numerical experiment further supports the use
  of flare precursors based on the WG<SUB> M </SUB> method.

Title: Strong nonlocality variations in a spherical mean‑field
    dynamo
Authors: Brandenburg, Axel; Chatterjee, Piyali
Bibcode: 2018AN....339..118B
Altcode: 2018arXiv180204231B
  To explain the large-scale magnetic field of the Sun and other
  bodies, mean-field dynamo theory is commonly applied where one
  solves the averaged equations for the mean magnetic field. However,
  the standard approach breaks down when the scale of the turbulent
  eddies becomes comparable to the scale of the variations of the mean
  magnetic field. Models showing sharp magnetic field structures have
  therefore been regarded as unreliable. Our aim is to look for new
  effects that occur when we relax the restrictions of the standard
  approach, which becomes particularly important at the bottom of the
  convection zone where the size of the turbulent eddies is comparable
  to the depth of the convection zone itself. We approximate the
  underlying integro-differential equation by a partial differential
  equation corresponding to a reaction-diffusion type equation for the
  mean electromotive force, making an approach that is nonlocal in
  space and time feasible under conditions where spherical geometry
  and nonlinearity are included. In agreement with earlier findings,
  spatio-temporal nonlocality lowers the excitation conditions of the
  dynamo. Sharp structures are now found to be absent. However, in the
  surface layers the field remains similar to before.

Title: Modeling Repeatedly Flaring δ Sunspots
Authors: Chatterjee, Piyali; Hansteen, Viggo; Carlsson, Mats
Bibcode: 2016PhRvL.116j1101C
Altcode: 2016arXiv160100749C
  Active regions (ARs) appearing on the surface of the Sun are classified
  into α , β , γ , and δ by the rules of the Mount Wilson Observatory,
  California on the basis of their topological complexity. Amongst these,
  the δ sunspots are known to be superactive and produce the most
  x-ray flares. Here, we present results from a simulation of the Sun
  by mimicking the upper layers and the corona, but starting at a more
  primitive stage than any earlier treatment. We find that this initial
  state consisting of only a thin subphotospheric magnetic sheet breaks
  into multiple flux tubes which evolve into a colliding-merging system
  of spots of opposite polarity upon surface emergence, similar to those
  often seen on the Sun. The simulation goes on to produce many exotic δ
  sunspot associated phenomena: repeated flaring in the range of typical
  solar flare energy release and ejective helical flux ropes with embedded
  cool-dense plasma filaments resembling solar coronal mass ejections.

Title: The Sun's Interior Structure and Dynamics, and the Solar Cycle
Authors: Broomhall, A. -M.; Chatterjee, P.; Howe, R.; Norton, A. A.;
   Thompson, M. J.
Bibcode: 2015sac..book..191B
Altcode:
  No abstract at ADS

Title: The Sun's Interior Structure and Dynamics, and the Solar Cycle
Authors: Broomhall, A. -M.; Chatterjee, P.; Howe, R.; Norton, A. A.;
   Thompson, M. J.
Bibcode: 2014SSRv..186..191B
Altcode: 2014arXiv1411.5941B
  The Sun's internal structure and dynamics can be studied with
  helioseismology, which uses the Sun's natural acoustic oscillations
  to build up a profile of the solar interior. We discuss how solar
  acoustic oscillations are affected by the Sun's magnetic field. Careful
  observations of these effects can be inverted to determine the
  variations in the structure and dynamics of the Sun's interior as
  the solar cycle progresses. Observed variations in the structure and
  dynamics can then be used to inform models of the solar dynamo, which
  are crucial to our understanding of how the Sun's magnetic field is
  generated and maintained.

Title: Erratum: "Simulation of Homologous and Cannibalistic Coronal
    Mass Ejections Produced by the Emergence of a Twisted Flux Rope into
    the Solar Corona" <A href="/abs/2013ApJL..778L...8C">(2013, ApJL,
    778, L8)</A>
Authors: Chatterjee, Piyali; Fan, Yuhong
Bibcode: 2014ApJ...792L..24C
Altcode:
  No abstract at ADS

Title: Bifurcations of ion acoustic solitary and periodic waves in
    an electron-positron-ion plasma through non-perturbative approach
Authors: Saha, Asit; Chatterjee, Prasanta; Chatterjee
Bibcode: 2014JPlPh..80..553S
Altcode:
  Ion acoustic solitary waves and periodic waves in an unmagnetized
  plasma with superthermal (kappa-distributed) electrons and positrons
  are investigated through a non-perturbative approach. Model equations
  are transformed to a planar dynamical system. Then by using the
  bifurcations of phase portraits of this planar dynamical system, we
  have established that our model has solitary wave and periodic wave
  solutions. We have obtained two analytical solutions for these solitary
  and periodic waves depending on the parameters. From these solitary
  wave and periodic wave solutions, we have shown the combined effects of
  temperature ratio (σ) of electrons and positrons, spectral index (κ),
  speed of the traveling wave (v), and density ratio (p) of positrons and
  electrons on the characteristics of ion acoustic solitary and periodic
  waves. The spectral index, density ratio, speed of the traveling wave,
  and temperature ratio significantly affect the characteristics of ion
  acoustic solitary and periodic structures. The present study might be
  helpful to understand the salient features of nonlinear ion acoustic
  solitary and periodic structures in the interstellar medium.

Title: Head-on collisions of two types of dust-acoustic solitons in
    a magnetized quantum plasma
Authors: Ghorui, M. K.; Samanta, U. K.; Maji, T. K.; Chatterjee, P.
Bibcode: 2014Ap&SS.352..159G
Altcode:
  The head-on collisions of dust-acoustic waves (DAWs) in a dense
  magnetized quantum dusty plasma are investigated by using the extended
  version of the Poincaré-Lighthill-Kuo (PLK) method. We discuss the
  theoretical predictions as regards the existence of compressive and
  rarefactive DAWs in the model. We also observe that, in the generic
  case, collisions are possible among the same polarity solitons,
  whereas in the special case, collisions are possible among the same
  or opposite polarity solitons. It is also observed that the phase
  shifts are significantly affected by the quantum diffraction parameter
  and the dust cyclotron frequency. The interesting observations of
  this manuscript are that the waves reach a maximum amplitude which
  is a superposition of the initial amplitude and they suffer a time
  delay during their collision. Our results may be useful in space and
  laboratory plasmas as well as in plasma applications.

Title: MHD simulations of homologous and cannibalistic coronal
    mass ejections
Authors: Fan, Yuhong; Chatterjee, Piyali
Bibcode: 2014AAS...22421203F
Altcode:
  We present magneto-hydrodynamic simulations of the development of a
  homologous sequence of coronal mass ejections (CMEs) and demonstrate
  their so-called cannibalistic behavior. These CMEs originate from
  the repeated formations and partial eruptions of kink unstable flux
  ropes as a result of the continued emergence of a twisted flux rope
  across the lower boundary into a pre-existing coronal potential arcade
  field. The simulations show that a CME erupting into the open magnetic
  field created by a preceding CME has a higher speed, and therefore
  tends to be cannibalistic, catching up and merging with the preceding
  one into a single fast CME. All the CMEs attained speeds of about
  1000 km/s as they exit the domain. The reformation of a twisted flux
  rope after each CME eruption during the sustained flux emergence can
  naturally explain the X-ray observations of repeated reformations of
  sigmoids and “sigmoid-under-cusp” configurations at a low-coronal
  source of homologous CMEs.

Title: MHD Simulations of the Initiation of Coronal Mass Ejections
Authors: Fan, Yuhong; Chatterjee, Piyali
Bibcode: 2014cosp...40E.833F
Altcode:
  Using three-dimensional MHD simulations, we model the quasi-static
  evolution and the onset of eruption of twisted magnetic flux ropes in
  the solar corona. We present simulations where the eruption is triggered
  by either the onset of the torus instability or the helical kink
  instability of the line-tied coronal flux rope. The simulations show
  that S (or inverse S) shaped current sheets develop along topological
  structures identified as Quasi Separatrix Layers (QSLs), during the
  quasi-static phase before the eruption. Reconnections in the current
  sheets effectively add twisted flux to the flux rope and thus allow
  it to rise quasi-statically to the critical height for the onset of
  the torus instability. We examine the thermal features produced by the
  current sheet formation and the associated reconnections and found that
  they can explain some of the observed features in coronal prominence
  cavities as well as in pre-eruption active regions. We also present
  simulations of the development of a homologous sequence of CMEs caused
  by the repeated formation and partial eruption of kink unstable flux
  ropes as a result of continued flux emergence. It is found that such
  homologous CMEs tend to be cannibalistic, leading to the formation of
  more energetic, highly twisted ejecta.

Title: Homologous and cannibalistic coronal mass ejections from
    twisted magnetic flux rope simulations
Authors: Chatterjee, Piyali; Fan, Yuhong
Bibcode: 2014cosp...40E.487C
Altcode:
  We present results from magnetohydrodynamic simulations of the
  development of homologous sequence of coronal mass ejections (CMEs) and
  demonstrate their so-called cannibalistic behavior. These CMEs originate
  from the repeated formations and partial eruptions of kink unstable
  flux ropes as a result of continued emergence of a twisted flux rope
  across the lower boundary into a pre-existing coronal potential arcade
  field. Our simulation shows that a CME erupting into the open magnetic
  field created by a preceding CME has a higher speed. The second of
  the three successive CMEs in one of the simulations is cannibalistic,
  catching up and merging with the first into a single fast CME before
  exiting the domain. All the CMEs including the leading merged CME,
  attained speeds of about 1000 km s-1 as they exit the domain. The
  reformation of a twisted flux rope after each CME eruption during the
  sustained flux emergence can naturally explain the X-ray observations
  of repeated reformations of sigmoids and "sigmoid-under-cusp"
  configurations at a low-coronal source of homologous CMEs. We also
  investigate the initiation mechanism and ejecta topology of these
  energetic CMEs as a function of the twist parameter of the flux rope.

Title: Simulation of Homologous and Cannibalistic Coronal Mass
    Ejections produced by the Emergence of a Twisted Flux Rope into the
    Solar Corona
Authors: Chatterjee, Piyali; Fan, Yuhong
Bibcode: 2013ApJ...778L...8C
Altcode: 2013arXiv1309.4785C
  We report the first results of a magnetohydrodynamic simulation of the
  development of a homologous sequence of three coronal mass ejections
  (CMEs) and demonstrate their so-called cannibalistic behavior. These
  CMEs originate from the repeated formations and partial eruptions
  of kink unstable flux ropes as a result of continued emergence of
  a twisted flux rope across the lower boundary into a pre-existing
  coronal potential arcade field. The simulation shows that a CME
  erupting into the open magnetic field created by a preceding CME
  has a higher speed. The second of the three successive CMEs is
  cannibalistic, catching up and merging with the first into a single
  fast CME before exiting the domain. All the CMEs including the
  leading merged CME, attained speeds of about 1000 km s<SUP>-1</SUP>
  as they exit the domain. The reformation of a twisted flux rope after
  each CME eruption during the sustained flux emergence can naturally
  explain the X-ray observations of repeated reformations of sigmoids
  and "sigmoid-under-cusp" configurations at a low-coronal source of
  homologous CMEs.

Title: Effect of non-extensivity during the collision between inward
    and outward ion acoustic solitary waves in cylindrical and spherical
    geometry
Authors: Ghosh, Uday Narayan; Chatterjee, Prasanta; Chatterjee
Bibcode: 2013JPlPh..79..789G
Altcode:
  The head-on collision between two cylindrical/spherical ion acoustic
  solitary waves (IASWs) in un-magnetized plasmas comprising inertial ions
  and q-non-extensive electrons and positrons is investigated using the
  extended version of the Poincaré-Lighthill-Kuo perturbation method. How
  the interactions are taking place in cylindrical and spherical geometry
  are studied, and the collision is shown at different times. The
  non-planar geometry can modify analytical phase shifts following the
  head-on collision are derived. The effects of q-non-extensive electrons
  and positrons on the phase shift are studied. It is shown that the
  properties of the interaction of IASWs in cylindrical and spherical
  geometry are very different.

Title: Formation of hot channels in pre-CME coronal flux ropes and
    their role in the onset of eruptions
Authors: Fan, Yuhong; Chatterjee, P.
Bibcode: 2013SPD....4410302F
Altcode:
  Using 3D magneto-hydrodynamic simulations of the eruption of
  coronal flux ropes, we examine the thermal features produced by
  current sheet formation and the associated “tether-cutting”
  reconnections. We find that current sheets form along topological
  structures identified as quasi-separatrix layers (QSLs) during the
  pre-eruption stage. Tether-cutting reconnections in the current sheets
  produce a hot channel containing reconnected, twisted flux threading
  under the axis of the flux rope. This accumulation of twisted flux
  allows the flux rope to rise quasi-statically to the critical height for
  the onset of the torus instability, which leads to the dynamic eruption
  of the flux rope. The current sheet morphology and the hot channel that
  forms above it may explain the observed prominence “horns” enclosing
  a central cavity seen in AIA observations of coronal cavities. They
  may also be the cause of the X-ray emitting cores observed in some
  coronal cavities. We present a sequence of simulations to examine how
  the temperature and density of the hot channel depend on the properties
  of the coronal flux rope, and compare the results with multi-wavelength
  coronal observations of CMEs.

Title: Modelling of delta-spots with a focus on multiple eruptions
Authors: Chatterjee, Piyali
Bibcode: 2013SPD....44...08C
Altcode:
  It is a generally accepted idea from observations that delta-spot
  regions are harbingers of 'super activity' in the Solar atmosphere. In
  this computational study we model a typical delta spot region by
  emerging two independent twisted flux ropes into the Solar corona. We
  support the above idea by invoking existing statistical studies of
  delta-spot regions and the associated flares. It has been found from
  observations that component sunspots locked into a delta-spot region
  often have different sizes, fluxes and evolutionary history. Also
  supporting the above idea is the fact that the connectivity between the
  two component spots is found to be stronger after a flare than before
  it. The two colliding bipoles can give rise to steep magnetic gradients
  and shear at the neutral line. Such collisions have the potential
  to increase the magnetic free energy available for not just one but
  multiple eruptions. In our isothermal compressible MHD simulations
  we vary the relative magnetic flux as well as the twist of the two
  emerging flux ropes. For colliding bipoles we do find signatures of
  multiple eruptions as well as intense current sheets. Further, we also
  find evidence of new magnetic connections between the components of
  the delta-spot after eruption.

Title: Non-planar ion acoustic Gardner solitons in
    electron-positron-ion plasma with superthermal electrons and positrons
Authors: Ghosh, Deb Kumar; Ghosh, Uday Narayan; Chatterjee, Prasanta;
   Chatterjee
Bibcode: 2013JPlPh..79...37G
Altcode:
  The properties of non-planar (cylindrical and spherical) ion
  acoustic solitary waves (IASWs) in an unmagnetized collisionless
  electron-positron-ion (e-p-i) plasma, whose constituents are
  inertial ions and superthermal/non-Maxwellian electrons and positrons
  (represented by the kappa (κ) distribution), are investigated by
  deriving the modified Gardner (MG) equation. The well-known reductive
  perturbation method is employed to derive the MG equation. The basic
  features of non-planar IA Gardner solitons (GSs) are discussed. It is
  seen that the properties of non-planar IAGSs (positive and negative)
  differ significantly as the value of spectral index kappa changes.

Title: Alpha effect due to buoyancy instability of a magnetic layer
Authors: Chatterjee, P.; Mitra, D.; Rheinhardt, M.; Brandenburg, A.
Bibcode: 2011A&A...534A..46C
Altcode: 2010arXiv1011.1218C
  Context. A strong toroidal field can exist in form of a magnetic
  layer in the overshoot region below the solar convection zone. This
  motivates a more detailed study of the magnetic buoyancy instability
  with rotation. <BR /> Aims: We calculate the α effect due to
  helical motions caused by an unstable magnetic layer in a rotating
  density-stratified system with angular velocity Ω making an angle
  θ with the vertical. We also study the dependence of the α effect
  on θ and the strength of the initial magnetic field. <BR /> Methods:
  We carry out three-dimensional hydromagnetic simulations in Cartesian
  geometry. A turbulent electromotive force (EMF) due to the correlations
  of the small scale velocity and magnetic field is generated. We use
  the test-field method to calculate the transport coefficients of
  the inhomogeneous turbulence produced by the layer. <BR /> Results:
  We show that the growth rate of the instability and the twist of the
  magnetic field vary monotonically with the ratio of thermal conductivity
  to magnetic diffusivity. The resulting α effect is non-uniform and
  increases with the strength of the initial magnetic field. It is thus
  an example of an "anti-quenched" α effect. The α effect is also
  nonlocal, i.e. scale dependent, requiring around 8-16 Fourier modes
  to reconstruct the actual mean EMF based on the actual mean field.

Title: A theoretical model of torsional oscillations from a flux
    transport dynamo model
Authors: Chatterjee, Piyali; Chakraborty, Sagar; Choudhuri, Arnab Rai
Bibcode: 2011IAUS..273..366C
Altcode: 2010arXiv1008.2161C
  Assuming that the torsional oscillation is driven by the Lorentz
  force of the magnetic field associated with the sunspot cycle, we use
  a flux transport dynamo to model it and explain its initiation at a
  high latitude before the beginning of the sunspot cycle.

Title: Spontaneous chiral symmetry breaking by hydromagnetic buoyancy
Authors: Chatterjee, Piyali; Mitra, Dhrubaditya; Brandenburg, Axel;
   Rheinhardt, Matthias
Bibcode: 2011PhRvE..84b5403C
Altcode: 2010arXiv1011.1251C
  Evidence for the parity-breaking nature of the magnetic buoyancy
  instability in a stably stratified gas is reported. In the absence
  of rotation, no helicity is produced, but the nonhelical state
  is found to be unstable to small helical perturbations during the
  development of the instability. The parity-breaking nature of this
  magnetohydrodynamic instability appears to be the first of its kind
  and has properties similar to those in chiral symmetry breaking in
  biochemistry. Applications to the production of mean fields in galaxy
  clusters are discussed.

Title: Reynolds stress and heat flux in spherical shell convection
Authors: Käpylä, P. J.; Mantere, M. J.; Guerrero, G.; Brandenburg,
   A.; Chatterjee, P.
Bibcode: 2011A&A...531A.162K
Altcode: 2010arXiv1010.1250K
  Context. Turbulent fluxes of angular momentum and enthalpy or heat due
  to rotationally affected convection play a key role in determining
  differential rotation of stars. Their dependence on latitude and
  depth has been determined in the past from convection simulations
  in Cartesian or spherical simulations. Here we perform a systematic
  comparison between the two geometries as a function of the rotation
  rate. <BR /> Aims: Here we want to extend the earlier studies by
  using spherical wedges to obtain turbulent angular momentum and
  heat transport as functions of the rotation rate from stratified
  convection. We compare results from spherical and Cartesian models
  in the same parameter regime in order to study whether restricted
  geometry introduces artefacts into the results. In particular,
  we want to clarify whether the sharp equatorial profile of the
  horizontal Reynolds stress found in earlier Cartesian models is
  also reproduced in spherical geometry. <BR /> Methods: We employ
  direct numerical simulations of turbulent convection in spherical
  and Cartesian geometries. In order to alleviate the computational
  cost in the spherical runs, and to reach as high spatial resolution
  as possible, we model only parts of the latitude and longitude. The
  rotational influence, measured by the Coriolis number or inverse Rossby
  number, is varied from zero to roughly seven, which is the regime
  that is likely to be realised in the solar convection zone. Cartesian
  simulations are performed in overlapping parameter regimes. <BR />
  Results: For slow rotation we find that the radial and latitudinal
  turbulent angular momentum fluxes are directed inward and equatorward,
  respectively. In the rapid rotation regime the radial flux changes sign
  in accordance with earlier numerical results, but in contradiction with
  theory. The latitudinal flux remains mostly equatorward and develops
  a maximum close to the equator. In Cartesian simulations this peak
  can be explained by the strong "banana cells". Their effect in the
  spherical case does not appear to be as large. The latitudinal heat
  flux is mostly equatorward for slow rotation but changes sign for
  rapid rotation. Longitudinal heat flux is always in the retrograde
  direction. The rotation profiles vary from anti-solar (slow equator) for
  slow and intermediate rotation to solar-like (fast equator) for rapid
  rotation. The solar-like profiles are dominated by the Taylor-Proudman
  balance. <P />Movies and Appendix A are available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

Title: Alpha effect due to magnetic buoyancy instability of a
    horizontal magnetic layer
Authors: Chatterjee, Piyali
Bibcode: 2011ASInC...2..137C
Altcode:
  In this paper we study the hydromagnetic instability of a toroidal
  magnetic layer such as that thought to be located in the solar
  tachocline. The magnetic layer is located in a convectively stable layer
  and is subject to what is known as the magnetic buoyancy instability
  (MBI) and under suitable conditions breaks up into twisted and arching
  magnetic flux tubes. The MBI gives rise to an anti-quenched α effect
  which can be measured by using the sophisticated quasi-kinematic test
  field method. This paper aims at summarizing the main results of a
  much longer paper by Chatterjee et al. 2011, A&amp;A (in press).

Title: Magnetic helicity fluxes in interface and flux transport
    dynamos
Authors: Chatterjee, P.; Guerrero, G.; Brandenburg, A.
Bibcode: 2011A&A...525A...5C
Altcode: 2010arXiv1005.5335C
  Context. Dynamos in the Sun and other bodies tend to produce magnetic
  fields that possess magnetic helicity of opposite sign at large
  and small scales, respectively. The build-up of magnetic helicity
  at small scales provides an important saturation mechanism. <BR />
  Aims: In order to understand the nature of the solar dynamo we need
  to understand the details of the saturation mechanism in spherical
  geometry. In particular, we aim to understand the effects of magnetic
  helicity fluxes from turbulence and meridional circulation. <BR />
  Methods: We consider a model with only radial shear confined to a
  thin layer (tachocline) at the bottom of the convection zone. The
  kinetic α owing to helical turbulence is assumed to be localized in a
  region above the convection zone. The dynamical quenching formalism is
  used to describe the build-up of mean magnetic helicity in the model,
  which results in a magnetic α effect that feeds back on the kinetic α
  effect. In some cases we compare these results with those obtained from
  a model with a simple algebraic α quenching formula. <BR /> Results: In
  agreement with earlier findings, the magnetic α effect has the opposite
  sign compared with the kinetic α effect and leads to a catastrophic
  decrease of the saturation field strength proportional to the inverse
  magnetic Reynolds number. At high latitudes this quenching effect
  can lead to secondary dynamo waves that propagate poleward because
  of the opposite sign of α. These secondary dynamo waves are driven
  by small-scale magnetic helicity instead of the small-scale kinetic
  helicity. Magnetic helicity fluxes both from turbulent mixing and from
  meridional circulation alleviate catastrophic quenching. Interestingly,
  supercritical diffusive helicity fluxes also give rise to secondary
  dynamo waves and grand minima-like episodes.

Title: What do global p-modes tell us about banana cells?
Authors: Chatterjee, Piyali
Bibcode: 2011JPhCS.271a2066C
Altcode: 2010arXiv1010.4204C
  We have calculated the effects of giant convection cells also know as
  sectoral rolls or banana cells, on p-mode splitting coefficients. We
  use the technique of quasi-degenerate perturbation theory formulated by
  Lavely &amp; Ritzwoller in order to estimate the frequency shifts. A
  possible way of detecting giant cells is to look for even splitting
  coefficients of 'nearly degenerate' modes in the observational data
  since these modes have the largest shifts. We find that banana cells
  having an azimuthal wave number of 16 and maximum vertical velocity
  of 180 m s<SUP>-1</SUP> cannot be ruled out from GONG data for even
  splitting coefficients.

Title: Turbulent transport in hydromagnetic flows
Authors: Brandenburg, A.; Chatterjee, P.; Del Sordo, F.; Hubbard,
   A.; Käpylä, P. J.; Rheinhardt, M.
Bibcode: 2010PhST..142a4028B
Altcode: 2010arXiv1004.5380B
  The predictive power of mean-field theory is emphasized by comparing
  theory with simulations under controlled conditions. The recently
  developed test-field method is used to extract turbulent transport
  coefficients both in the kinematic and the nonlinear or quasi-kinematic
  cases. A striking example of the quasi-kinematic method is provided by
  magnetic buoyancy-driven flows that produce an α effect and turbulent
  diffusion.

Title: Shear-driven and diffusive helicity fluxes in αΩ dynamos
Authors: Guerrero, G.; Chatterjee, P.; Brandenburg, A.
Bibcode: 2010MNRAS.409.1619G
Altcode: 2010MNRAS.tmp.1434G; 2010arXiv1005.4818G; 2010MNRAS.tmp.1451G
  We present non-linear mean-field αΩ dynamo simulations in spherical
  geometry with simplified profiles of kinetic α effect and shear. We
  take magnetic helicity evolution into account by solving a dynamical
  equation for the magnetic α effect. This gives a consistent description
  of the quenching mechanism in mean-field dynamo models. The main goal
  of this work is to explore the effects of this quenching mechanism
  in solar-like geometry, and in particular to investigate the role of
  magnetic helicity fluxes, specifically diffusive and Vishniac-Cho (VC)
  fluxes, at large magnetic Reynolds numbers (R<SUB>m</SUB>). For models
  with negative radial shear or positive latitudinal shear, the magnetic
  α effect has predominantly negative (positive) sign in the Northern
  (Southern) hemisphere. In the absence of fluxes, we find that the
  magnetic energy follows an R<SUP>-1</SUP><SUB>m</SUB> dependence, as
  found in previous works. This catastrophic quenching is alleviated in
  models with diffusive magnetic helicity fluxes resulting in magnetic
  fields comparable to the equipartition value even for R<SUB>m</SUB>=
  10<SUP>7</SUP>. On the other hand, models with a shear-driven
  Vishniac-Cho flux show an increase in the amplitude of the magnetic
  field with respect to models without fluxes, but only for R<SUB>m</SUB>
  &lt; 10<SUP>4</SUP>. This is partly a consequence of assuming a
  vacuum outside the Sun which cannot support a significant VC flux
  across the boundary. However, in contrast to the diffusive flux, the
  VC flux modifies the distribution of the magnetic field. In addition,
  if an ill-determined scaling factor in the expression for the VC flux
  is large enough, subcritical dynamo action is possible that is driven
  by the action of shear and the divergence of magnetic helicity flux.

Title: Can catastrophic quenching be alleviated by separating shear
    and α effect?
Authors: Chatterjee, Piyali; Brandenburg, Axel; Guerrero, Gustavo
Bibcode: 2010GApFD.104..591C
Altcode: 2010arXiv1005.5708C
  The small-scale magnetic helicity produced as a by-product of
  the large-scale dynamo is believed to play a major role in dynamo
  saturation. In a mean-field model the generation of small-scale
  magnetic helicity can be modelled by using the dynamical quenching
  formalism. Catastrophic quenching refers to a decrease of the
  saturation field strength with increasing Reynolds number. It has
  been suggested that catastrophic quenching only affects the region of
  non-zero helical turbulence (i.e. where the kinematic α operates) and
  that it is possible to alleviate catastrophic quenching by separating
  the region of strong shear from the α layer. We perform a systematic
  study of a simple axisymmetric two-layer αΩ dynamo in a spherical
  shell for Reynolds numbers in the range 1 ≤ R <SUB>m</SUB> ≤
  10<SUP>5</SUP>. In the framework of dynamical quenching we show that
  this may not be the case, suggesting that magnetic helicity fluxes
  would be necessary.

Title: Equatorial magnetic helicity flux in simulations with
    different gauges
Authors: Mitra, D.; Candelaresi, S.; Chatterjee, P.; Tavakol, R.;
   Brandenburg, A.
Bibcode: 2010AN....331..130M
Altcode: 2009arXiv0911.0969M
  We use direct numerical simulations of forced MHD turbulence with a
  forcing function that produces two different signs of kinetic helicity
  in the upper and lower parts of the domain. We show that the mean
  flux of magnetic helicity from the small-scale field between the
  two parts of the domain can be described by a Fickian diffusion law
  with a diffusion coefficient that is approximately independent of the
  magnetic Reynolds number and about one third of the estimated turbulent
  magnetic diffusivity. The data suggest that the turbulent diffusive
  magnetic helicity flux can only be expected to alleviate catastrophic
  quenching at Reynolds numbers of more than several thousands. We
  further calculate the magnetic helicity density and its flux in the
  domain for three different gauges. We consider the Weyl gauge, in which
  the electrostatic potential vanishes, the pseudo-Lorenz gauge, where
  the speed of light is replaced by the sound speed, and the `resistive
  gauge' in which the Laplacian of the magnetic vector potential acts
  as a resistive term. We find that, in the statistically steady state,
  the time-averaged magnetic helicity density and the magnetic helicity
  flux are the same in all three gauges.

Title: Why Does the Torsional Oscillation Precede the Sunspot Cycle?
Authors: Chatterjee, P.; Chakraborty, S.; Choudhuri, A. R.
Bibcode: 2010ASSP...19..500C
Altcode: 2010mcia.conf..500C
  The Sun's rotation shows a periodic variation with the sunspot cycle,
  called torsional oscillations, the nature of which inside the solar
  convection zone has been determined from helioseismology. Several
  authors developed theoretical models of torsional oscillations by
  assuming that they are driven by the Lorentz force of the Sun's
  cyclically varying magnetic field. If this is true, then one would
  expect the torsional oscillations to follow the sunspot cycles. However,
  the torsional oscillations of a cycle begin a couple of years before
  the sunspots of that cycle appear and at a latitude higher than where
  the first sunspots are subsequently seen. Our aim in this paper is to
  provide an explanation for this seemingly causality defying phenomenon.

Title: Solar Flows and Their Effect on Frequencies of Acoustic Modes
Authors: Chatterjee, Piyali; Antia, H. M.
Bibcode: 2009ApJ...707..208C
Altcode: 2009arXiv0910.4137C
  We have calculated the effects of large-scale solar flows, such as the
  meridional circulation, giant convection cells, and solar rotation
  on the helioseismic splitting coefficients using quasi-degenerate
  perturbation theory (QDPT). Our investigation reveals that the effect of
  poloidal flows like the large-scale meridional circulation are difficult
  to detect in observational data of the global acoustic modes since the
  frequency shifts are much less than the errors. However, signatures
  of large-scale convective flows may be detected if their amplitude
  is sufficiently large by looking for frequency shifts due to nearly
  degenerate modes coupled by convection. In this comprehensive study,
  we attempt to put limits on the magnitude of flow velocities in giant
  cells by comparing the splitting coefficients obtained from the QDPT
  treatment with observational data.

Title: Small-scale magnetic helicity losses from a mean-field dynamo
Authors: Brandenburg, Axel; Candelaresi, Simon; Chatterjee, Piyali
Bibcode: 2009MNRAS.398.1414B
Altcode: 2009MNRAS.tmp..979B; 2009arXiv0905.0242B
  Using mean-field models with a dynamical quenching formalism, we
  show that in finite domains magnetic helicity fluxes associated
  with small-scale magnetic fields are able to alleviate catastrophic
  quenching. We consider fluxes that result from advection by a mean flow,
  the turbulent mixing down the gradient of mean small-scale magnetic
  helicity density or the explicit removal which may be associated with
  the effects of coronal mass ejections in the Sun. In the absence of
  shear, all the small-scale magnetic helicity fluxes are found to be
  equally strong for both large- and small-scale fields. In the presence
  of shear, there is also an additional magnetic helicity flux associated
  with the mean field, but this flux does not alleviate catastrophic
  quenching. Outside the dynamo-active region, there are neither sources
  nor sinks of magnetic helicity, so in a steady state this flux must
  be constant. It is shown that unphysical behaviour emerges if the
  small-scale magnetic helicity flux is forced to vanish within the
  computational domain.

Title: Erratum: Why Does the Sun's Torsional Oscillation Begin before
    the Sunspot Cycle? [Phys. Rev. Lett. 102, 041102 (2009)]
Authors: Chakraborty, Sagar; Choudhuri, Arnab Rai; Chatterjee, Piyali
Bibcode: 2009PhRvL.103i9902C
Altcode:
  No abstract at ADS

Title: Why Does the Sun's Torsional Oscillation Begin before the
    Sunspot Cycle?
Authors: Chakraborty, Sagar; Choudhuri, Arnab Rai; Chatterjee, Piyali
Bibcode: 2009PhRvL.102d1102C
Altcode: 2009arXiv0907.4842C
  Although the Sun’s torsional oscillation is believed to be driven by
  the Lorentz force associated with the sunspot cycle, this oscillation
  begins 2 3 yr before the sunspot cycle. We provide a theoretical
  explanation of this with the help of a solar dynamo model having a
  meridional circulation penetrating slightly below the bottom of the
  convection zone, because only in such dynamo models does the strong
  toroidal field form a few years before the sunspot cycle and at a
  higher latitude.

Title: How Do f-Mode Frequencies Change with Solar Radius?
Authors: Chatterjee, Piyali; Antia, H. M.
Bibcode: 2008ApJ...688L.123C
Altcode: 2008arXiv0810.4213C
  We test the relation between relative f-mode frequency variation
  (δ ν/ν) and Lagrangian perturbation in the solar radius (δ r/r)
  obtained by Dziembowski and Goode using several pairs of solar models
  and show that it does not hold true for any of the model pairs we
  have used. We attempt to derive a better approximation for the kernel
  linking the relative frequency changes and the solar radius variation
  in the subsurface layers.

Title: A theoretical model for the magnetic helicity of solar
    active regions
Authors: Chatterjee, Piyali; Choudhuri, Arnab Rai; Petrovay, Kristof;
   Nandy, Dibyendu
Bibcode: 2008AdSpR..41..893C
Altcode:
  Active regions on the solar surface are known to possess magnetic
  helicity, which is predominantly negative in the northern hemisphere
  and positive in the southern hemisphere. Choudhuri et al. [Choudhuri,
  A.R. On the connection between mean field dynamo theory and flux
  tubes. Solar Phys. 215, 31 55, 2003] proposed that the magnetic helicity
  arises due to the wrapping up of the poloidal field of the convection
  zone around rising flux tubes which form active regions. Choudhuri
  [Choudhuri, A.R., Chatterjee, P., Nandy, D. Helicity of solar active
  regions from a dynamo model. ApJ 615, L57 L60, 2004] used this idea to
  calculate magnetic helicity from their solar dynamo model. Apart from
  getting broad agreements with observational data, they also predict
  that the hemispheric helicity rule may be violated at the beginning
  of a solar cycle. Chatterjee et al. [Chatterjee, P., Choudhuri, A.R.,
  Petrovay, K. Development of twist in an emerging magnetic flux tube
  by poloidal field accretion. A&amp;A 449, 781 789, 2006] study the
  penetration of the wrapped poloidal field into the rising flux tube
  due to turbulent diffusion using a simple 1-d model. They find that
  the extent of penetration of the wrapped field will depend on how
  weak the magnetic field inside the rising flux tube becomes before
  its emergence. They conclude that more detailed observational data
  will throw light on the physical conditions of flux tubes just before
  their emergence to the photosphere.

Title: Solar activity forecast with a dynamo model
Authors: Jiang, Jie; Chatterjee, Piyali; Choudhuri, Arnab Rai
Bibcode: 2007MNRAS.381.1527J
Altcode: 2007arXiv0707.2258J; 2007MNRAS.tmp..899J
  Although systematic measurements of the Sun's polar magnetic field exist
  only from mid-1970s, other proxies can be used to infer the polar field
  at earlier times. The observational data indicate a strong correlation
  between the polar field at a sunspot minimum and the strength of the
  next cycle, although the strength of the cycle is not correlated
  well with the polar field produced at its end. This suggests that
  the Babcock-Leighton mechanism of poloidal field generation from
  decaying sunspots involves randomness, whereas the other aspects of
  the dynamo process must be reasonably ordered and deterministic. Only
  if the magnetic diffusivity within the convection zone is assumed to
  be high (of order 10<SUP>12</SUP>cm<SUP>2</SUP>s<SUP>-1</SUP>), we can
  explain the correlation between the polar field at a minimum and the
  next cycle. We give several independent arguments that the diffusivity
  must be of this order. In a dynamo model with diffusivity like this,
  the poloidal field generated at the mid-latitudes is advected toward
  the poles by the meridional circulation and simultaneously diffuses
  towards the tachocline, where the toroidal field for the next cycle
  is produced. To model actual solar cycles with a dynamo model having
  such high diffusivity, we have to feed the observational data of the
  poloidal field at the minimum into the theoretical model. We develop a
  method of doing this in a systematic way. Our model predicts that cycle
  24 will be a very weak cycle. Hemispheric asymmetry of solar activity
  is also calculated with our model and compared with observational data.

Title: Predicting Solar Cycle 24 With a Solar Dynamo Model
Authors: Choudhuri, Arnab Rai; Chatterjee, Piyali; Jiang, Jie
Bibcode: 2007PhRvL..98m1103C
Altcode: 2007astro.ph..1527C
  Whether or not the upcoming cycle 24 of solar activity will be strong
  is being hotly debated. The solar cycle is produced by a complex
  dynamo mechanism. We model the last few solar cycles by “feeding”
  observational data of the Sun’s polar magnetic field into our solar
  dynamo model. Our results fit the observed sunspot numbers of cycles
  21 23 reasonably well and predict that cycle 24 will be about 35%
  weaker than cycle 23.

Title: On Magnetic Coupling Between the Two Hemispheres in Solar
    Dynamo Models
Authors: Chatterjee, Piyali; Choudhuri, Arnab Rai
Bibcode: 2006SoPh..239...29C
Altcode: 2006SoPh..tmp...77C
  By introducing an asymmetry between the two hemispheres, we study
  whether the solar dynamo solutions in the two hemispheres remain
  coupled with each other. Our calculations are based on the solar
  dynamo code SURYA, which incorporates the helioseismically-determined
  solar-rotation profile, a Babcock-Leighton α effect concentrated near
  the surface, and a meridional circulation. When the magnetic coupling
  between the hemispheres is enhanced by either increasing the diffusion
  or introducing an α effect distributed throughout the convection zone,
  we find that the solutions in the two hemispheres evolve together with
  a single period even when we make the meridional circulation or the
  α effect different in the two hemispheres. On the other hand, when
  the hemispheric coupling is weaker for other values of parameters,
  an asymmetry between the hemispheres can make solutions in the two
  hemispheres evolve independently with different periods.

Title: Forecasting Cycle 24 with a Solar Dynamo Model
Authors: Jiang, Jie; Chatterjee, P.; Choudhuri, A. R.
Bibcode: 2006ihy..workE..28J
Altcode:
  A challenge before solar physicists right now is to forecast the
  strength of the next solar cycle (Cycle 24). Several contrary forecasts
  have already been made. Most of the forecasts are based on various
  precursor methods. Only one forecast is based on a dynamo model (Dikpati
  and Gilman 2006). Since we find some aspects of this work questionable,
  it is desirable to have another independent forecast based on a dynamo
  model. We are carrying out an analysis based on our dynamo model,
  using a methodology different from what was used by Dikpati and
  Gilman (2006). We shall present the methodology of our approach and,
  most probably, we shall also have some results by the time of the
  IHY meeting.

Title: Helicity of Solar Active Regions from a Dynamo Model
Authors: Chatterjee, Piyali
Bibcode: 2006JApA...27...87C
Altcode:
  We calculate helicities of solar active regions based on the idea that
  poloidal flux lines get wrapped around a toroidal flux tube rising
  through the convection zone, thereby giving rise to the helicity. We
  use our solar dynamo model based on the Babcock-Leighton α-effect to
  study how helicity varies with latitude and time.

Title: On the Origin of Current Helicity in Active Regions
Authors: Petrovay, K.; Chatterjee, P.; Choudhuri, A.
Bibcode: 2006ESASP.617E..67P
Altcode: 2006soho...17E..67P
  No abstract at ADS

Title: Development of twist in an emerging magnetic flux tube by
    poloidal field accretion
Authors: Chatterjee, P.; Choudhuri, A. R.; Petrovay, K.
Bibcode: 2006A&A...449..781C
Altcode: 2005astro.ph.12472C
  Aims.Following an earlier proposal for the origin of twist in the
  magnetic fields of solar active regions, we model the penetration of
  a wrapped up background poloidal field into a toroidal magnetic flux
  tube rising through the solar convective zone. Methods.The rise of the
  straight, cylindrical flux tube is followed by numerically solving the
  induction equation in a comoving Lagrangian frame, while an external
  poloidal magnetic field is assumed to be radially advected onto the
  tube with a speed corresponding to the rise velocity. Results.One
  prediction of our model is the existence of a ring of reverse current
  helicity on the periphery of active regions. On the other hand, the
  amplitude of the resulting twist depends sensitively on the assumed
  structure (diffuse vs. concentrated/intermittent) of the active
  region magnetic field right before its emergence, and on the assumed
  vertical profile of the poloidal field. Nevertheless, in the model
  with the most plausible choice of assumptions a mean twist comparable
  to the observations results. Conclusions.Our results indicate that the
  contribution of this mechanism to the twist can be quite significant,
  and under favourable circumstances it can potentially account for most
  of the current helicity observed in active regions.

Title: Theoretical model for calculation of helicity in solar
    active regions
Authors: Chatterjee, P.
Bibcode: 2006ilws.conf...30C
Altcode:
  We (Choudhuri, Chatterjee and Nandy, 2005) calculate helicities of
  solar active regions based on the idea of Choudhuri (2003) that poloidal
  flux lines get wrapped around a toroidal flux tube rising through the
  convection zone, thereby giving rise to the helicity. Rough estimates
  based on this idea compare favourably with the observed magnitude of
  helicity. We use our solar dynamo model based on the Babcock--Leighton
  α-effect to study how helicity varies with latitude and time. At the
  time of solar maximum, our theoretical model gives negative helicity
  in the northern hemisphere and positive helicity in the south, in
  accordance with observed hemispheric trends. However, we find that,
  during a short interval at the beginning of a cycle, helicities tend to
  be opposite of the preferred hemispheric trends. Next we (Chatterjee,
  Choudhuri and Petrovay 2006) use the above idea along with the sunspot
  decay model of Petrovay and Moreno-Insertis, (1997) to estimate the
  distribution of helicity inside a flux tube as it keeps collecting
  more azimuthal flux during its rise through the convection zone and
  as turbulent diffusion keeps acting on it. By varying parameters over
  reasonable ranges in our simple 1-d model, we find that the azimuthal
  flux penetrates the flux tube to some extent instead of being confined
  to a narrow sheath outside.

Title: A theoretical model for the magnetic helicity of solar
    active regions
Authors: Choudhuri, A. R.; Chatterjee, P.; Petrovay, K.; Nandy, D.
Bibcode: 2006cosp...36..714C
Altcode: 2006cosp.meet..714C
  Active regions on the solar surface are known to possess magnetic
  helicity which is predominantly negative in the northern hemisphere
  and positive in the southern hemisphere Choudhuri 2003 Sol Phys 123 217
  proposed that the magnetic helicity arises due to the wrapping up of the
  poloidal field of the convection zone around rising flux tubes which
  form active regions Choudhuri Chatterjee and Nandy 2004 ApJ 615 L57
  used this idea to calculate magnetic helicity from their solar dynamo
  model and found broad agreements with observational data Chatterjee
  Choudhuri and Petrovay 2006 A A in press have studied the penetration
  of the wrapped poloidal field into the rising flux tube and concluded
  that more detailed observational data will throw light on the physical
  conditions of flux tubes just before their emergence to the photosphere

Title: Reply to the Comments of Dikpati et al.
Authors: Choudhuri, A. R.; Nandy, D.; Chatterjee, P.
Bibcode: 2005A&A...437..703C
Altcode: 2005astro.ph..5232C
  We respond to Dikpati et al.'s criticism of our recent solar dynamo
  model. A different treatment of the magnetic buoyancy is the most
  probable reason for their different results.

Title: Full-sphere simulations of a circulation-dominated solar
dynamo: Exploring the parity issue
Authors: Chatterjee, P.; Nandy, D.; Choudhuri, A. R.
Bibcode: 2004A&A...427.1019C
Altcode: 2004astro.ph..5027C
  We explore a two-dimensional kinematic solar dynamo model in a full
  sphere, based on the helioseismically determined solar rotation
  profile and with an α effect concentrated near the solar surface,
  which captures the Babcock-Leighton idea that the poloidal field is
  created from the decay of tilted bipolar active regions. The meridional
  circulation, assumed to penetrate slightly below the tachocline, plays
  an important role. Some doubts have recently been raised regarding
  the ability of such a model to reproduce solar-like dipolar parity. We
  specifically address the parity issue and show that the dipolar mode
  is preferred when certain reasonable conditions are satisfied, the
  most important condition being the requirement that the poloidal field
  should diffuse efficiently to get coupled across the equator. Our model
  is shown to reproduce various aspects of observational data, including
  the phase relation between sunspots and the weak, diffuse field.

Title: Helicity of Solar Active Regions from a Dynamo Model
Authors: Choudhuri, Arnab Rai; Chatterjee, Piyali; Nandy, Dibyendu
Bibcode: 2004ApJ...615L..57C
Altcode:
  We calculate helicities of solar active regions based on the idea that
  poloidal flux lines get wrapped around a toroidal flux tube rising
  through the convection zone, thereby giving rise to the helicity. Rough
  estimates based on this idea compare favorably with the observed
  magnitude of helicity. We use our solar dynamo model based on the
  Babcock-Leighton α-effect to study how helicity varies with latitude
  and time. At the time of solar maximum, our theoretical model gives
  negative helicity in the northern hemisphere and positive helicity in
  the south, in accordance with observed hemispheric trends. However,
  we find that during a short interval at the beginning of a cycle,
  helicities tend to be opposite of the preferred hemispheric trends.

Title: Full Sphere Axisymmetric Simulations of the Solar Dynamo
Authors: Nandy, Dibyendu; Chatterjee, Piyali; Choudhuri, Arnab Rai
Bibcode: 2004IAUS..223..133N
Altcode: 2005IAUS..223..133N
  We explore a full sphere (2D axisymmetric) kinematic solar dynamo
  model based on the Babcock-Leighton idea that the poloidal field is
  generated in the surface layers from the decay of tilted bipolar solar
  active regions. This model incorporates the helioseismically deduced
  solar rotation profile and an algorithm for buoyancy motivated from
  simulations of flux tube dynamics. A prescribed deep meridional
  circulation plays an important role in the advection of magnetic
  flux. We specifically address the parity issue and show that -
  contrary to some recent claims - the Babcock-Leighton dynamo can
  reproduce solar-like dipolar parity if certain reasonable conditions
  are satisfied in the solar interior, the most important requirement
  being that the poloidal field of the two hemispheres be efficiently
  coupled across the equator.

Title: The Origin of Helicity in Solar Active Regions
Authors: Choudhuri, Arnab Rai; Chatterjee, Piyali; Nandy, Dibyendu
Bibcode: 2004IAUS..223...45C
Altcode: 2005IAUS..223...45C; 2004astro.ph..6598C
  We present calculations of helicity based on our solar dynamo model
  and show that the results are consistent with observational data.

Title: On Solar Radius Variation with Magnetic Field
Authors: Choudhuri, Arnab Rai; Chatterjee, Piyali
Bibcode: 2003astro.ph.11028C
Altcode:
  In response to the claim by Dziembowski et al. (2001) that the solar
  radius decreases with magnetic activity at the rate of 1.5 km/yr, we
  consider the theoretical question whether a radius variation is expected
  with the solar cycle. If the radius variation is caused by the magnetic
  pressure of toroidal flux tubes at the bottom of the convection zone,
  then the dynamo model of Nandy and Choudhuri (2002) would suggest a
  radius decrease with magnetic activity, in contrast to other dynamo
  models which would suggest a radius increase. However, the radius
  decrease is estimated to be only of the order of hundreds of metres.

Title: Space-Time Torsion, Broken Lorentz Symmetry and Inflation in
    the Early Universe
Authors: Chatterjee, P.; Bhattacharya, B.
Bibcode: 1993MPLA....8.2249C
Altcode:
  We have shown here, a possible scheme of inflationary scenario at
  an early stage of the universe during the radiation dominated era by
  introducing a local Lorentz symmetry violating term in the space-time
  torsion of Einstein-Cartan action in E(4,1) space. This 'additional'
  mechanism for producing inflation may also suggest the answer to the
  question of the local relative abundance of particles over antiparticles
  in the observed universe.

