explanation blue bibcodes open ADS page with paths to full text
Author name code: chatterjee
ADS astronomy entries on 2022-09-14
author:"Chatterjee, Piyali"
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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
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.
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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
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.
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Title: Configuration files for simulations of the solar spicule forest
Authors: Chatterjee, Piyali; Dey, Sahel
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
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file setup_fig2b contains the run directory used to produce Fig 2 b
and c in Dey et al (2022, Nature Physics).
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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
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.
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Title: Modeling the solar spicule forest and the coronal swirls
Authors: Chatterjee, Piyali
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.
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Title: Testing Alfvén wave propagation in a "realistic" set-up of
the solar atmosphere
Authors: Chatterjee, Piyali
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.
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Title: Dimerization Effect on HF Elimination from the Photoionized
Fluorophenols
Authors: Chatterjee, Piyali; Biswas, Souvick; Chakraborty, Tapas
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.
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Title: Testing Alfvén wave propagation in a "realistic" set-up of
the solar atmosphere
Authors: Chatterjee, Piyali
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.
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Title: Applying the Weighted Horizontal Magnetic Gradient Method to
a Simulated Flaring Active Region
Authors: Korsós, M. B.; Chatterjee, P.; Erdélyi, R.
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.
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Title: Strong nonlocality variations in a spherical mean‑field
dynamo
Authors: Brandenburg, Axel; Chatterjee, Piyali
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.
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Title: Modeling Repeatedly Flaring δ Sunspots
Authors: Chatterjee, Piyali; Hansteen, Viggo; Carlsson, Mats
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.
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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.
2015sac..book..191B Altcode:
No abstract at ADS
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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.
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.
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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
2014ApJ...792L..24C Altcode:
No abstract at ADS
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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
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.
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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.
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.
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Title: MHD simulations of homologous and cannibalistic coronal
mass ejections
Authors: Fan, Yuhong; Chatterjee, Piyali
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.
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Title: MHD Simulations of the Initiation of Coronal Mass Ejections
Authors: Fan, Yuhong; Chatterjee, Piyali
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.
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Title: Homologous and cannibalistic coronal mass ejections from
twisted magnetic flux rope simulations
Authors: Chatterjee, Piyali; Fan, Yuhong
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
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.
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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
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.
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Title: Formation of hot channels in pre-CME coronal flux ropes and
their role in the onset of eruptions
Authors: Fan, Yuhong; Chatterjee, P.
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.
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Title: Modelling of delta-spots with a focus on multiple eruptions
Authors: Chatterjee, Piyali
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.
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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
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.
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Title: Alpha effect due to buoyancy instability of a magnetic layer
Authors: Chatterjee, P.; Mitra, D.; Rheinhardt, M.; Brandenburg, A.
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
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
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.
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
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&A (in press).
---------------------------------------------------------
Title: Magnetic helicity fluxes in interface and flux transport
dynamos
Authors: Chatterjee, P.; Guerrero, G.; Brandenburg, A.
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
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 & 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.
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.
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>
< 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
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.
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.
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.
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
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
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
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.
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
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&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
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
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
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.
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
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.
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.
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.
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.
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.
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.
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
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
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.
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Title: The Origin of Helicity in Solar Active Regions
Authors: Choudhuri, Arnab Rai; Chatterjee, Piyali; Nandy, Dibyendu
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.
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Title: On Solar Radius Variation with Magnetic Field
Authors: Choudhuri, Arnab Rai; Chatterjee, Piyali
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.
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Title: Space-Time Torsion, Broken Lorentz Symmetry and Inflation in
the Early Universe
Authors: Chatterjee, P.; Bhattacharya, B.
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.