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 D0 state of 2FP dimer cation, HF
elimination is exothermic, but the process encounters a large barrier,
2.75 eV. However, in S1 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 S1 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
M ) 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 M 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 M 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 M 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" (2013, ApJL,
778, L8)
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-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.
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.
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.
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.
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.
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.
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.
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.