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Author name code: getling
ADS astronomy entries on 2022-09-14
author:"Getling, Alexander"
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Title: Spatial Scales and Time Variation of Solar Subsurface
Convection
Authors: Getling, Alexander V.; Kosovichev, Alexander G.
2022arXiv220804642G Altcode:
Spectral analysis of the spatial structure of solar subphotospheric
convection is carried out for subsurface flow maps constructed
using the time--distance helioseismological technique. The source
data are obtained from the Helioseismic and Magnetic Imager
(HMI) onboard Solar Dynamics Observatory (SDO) from 2010 May to
2020 September. A spherical-harmonic transform is applied to the
horizontal-velocity-divergence field at depths from 0 to 19~Mm. The
range of flow scales is fairly broad in shallow layers and narrows
as the depth increases. The horizontal flow scales rapidly increase
with depth, from supergranulation to giant-cell values, and indicate
the existence of large-scale convective motions in the near-surface
shear layer. The results can naturally be interpreted in terms of
a superposition of differently scaled flows localized in different
depth intervals. There is some tendency toward the emergence of
meridionally elongated (banana-shaped) convection structures in the
deep layers. The total power of convective flows is anticorrelated
with the sunspot-number variation over the solar activity cycle in
shallow subsurface layers and positively correlated at larger depths,
which is suggestive of the depth redistribution of the convective-flow
energy due to the action of magnetic fields.
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Title: Helioseismic Monitoring of Solar Subsurface Dynamics and
Activity
Authors: Kosovichev, Alexander; Pipin, Valery; Getling, Alexander;
Stejko, Andrey; Stefan, John; Guerrero, Gustavo
2022cosp...44.3215K Altcode:
Uninterrupted helioseismic data from Michelson Doppler Imager (MDI)
onboard Solar and Heliospheric Observatory (SoHO) and from Helioseismic
and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO)
have provided unique information about flows and structures evolving
on various temporal and spatial scales inside the Sun. The data
cover the past two solar cycles and the rising phase of the current
solar cycle. In particular, our analysis of variations of the internal
differential rotation reveals "extended" cyclic variations of migrating
zonal flows ("torsional oscillations") through the whole convection
zone. The observed patterns of subsurface flow acceleration provide
evidence of hydromagnetic dynamo waves, which control the strength
of sunspot cycles, and potentially carry information about the future
solar cycles. Similarly, "extended" cyclic variations of the subsurface
meridional circulation, detected by local helioseismic techniques,
reflect the evolution of subsurface magnetic fields and emerging
magnetic flux. Furthermore, to monitor emerging active regions, we
develop a "deep-focus" helioseismic diagnostics, which allows us to
detect large emerging active regions before they become visible on
the surface. We present recent advances in helioseismic monitoring
of solar activity and discuss helioseismic constraints on models of
global solar variability and space weather forecasting.
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Title: Advances and Challenges in Observations and Modeling of the
Global-Sun Dynamics and Dynamo
Authors: Kosovichev, A. G.; Guerrero, G.; Stejko, A. M.; Pipin, V. V.;
Getling, A. V.
2022arXiv220310721K Altcode:
Computational heliophysics has shed light on the fundamental physical
processes inside the Sun, such as the differential rotation, meridional
circulation, and dynamo-generation of magnetic fields. However,
despite the substantial advances, the current results of 3D MHD
simulations are still far from reproducing helioseismic inferences
and surface observations. The reason is the multi-scale nature of
the solar dynamics, covering a vast range of scales, which cannot be
solved with the current computational resources. In such a situation,
significant progress has been achieved by the mean-field approach,
based on the separation of small-scale turbulence and large-scale
dynamics. The mean-field simulations can reproduce solar observations,
qualitatively and quantitatively, and uncover new phenomena. However,
they do not reveal the complex physics of large-scale convection,
solar magnetic cycles, and the magnetic self-organization that causes
sunspots and solar eruptions. Thus, developing a synergy of these
approaches seems to be a necessary but very challenging task.
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Title: Spatial Spectrum of Solar Convection from Helioseismic Data:
Flow Scales and Time Variations
Authors: Getling, Alexander V.; Kosovichev, Alexander G.
2022arXiv220100638G Altcode:
We analyze spectral properties of solar convection in the range of
depths from 0 to 19~Mm using subsurface flow maps obtained by the
time-distance heiioseismology analysis of solar-oscillation data from
the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics
Observatory (SDO) from May 2010 to September 2020. The results reveal
a rapid increase of the horizontal flow scales with the depth, from
supergranulation to giant-cell scales, and support the evidence of
large-scale convection, previously detected by tracking the motion of
supergranular cells on the surface. The total power of convective flows
correlates with the solar activity cycle. During the solar maximum,
the total power decreases in shallow subsurface layers and increases
in the deeper layers.
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Title: Large-Scale Dynamics of Solar Subsurface Shear Layer:
Theoretical Predictions and Helioseismic Inferences
Authors: Kosovichev, Alexander; Getling, Alexander; Guerrero, Gustavo;
Pipin, Valery; Stejko, Andrey
2021AGUFMSH53C..03K Altcode:
Helioseismic observations show that the solar rotation rate sharply
increases with depth in the outer 30 Mm-deep layers of the solar
convection zone. This subsurface shear layer (SSL) plays a critical role
in the formation of migrating activity belts (the butterfly diagram)
and the emergence of active regions. Measurements of the rotation
rate indicate that the magnetic field of sunspots and active regions
is anchored in the subsurface shear layer. The magnetic structure of
the SSL has not been directly measured by helioseismology, but it can
be inferred by comparing variations of subsurface flows and sound-speed
variations predicted by dynamo models with helioseismic measurements. To
establish the connections between the flows and fields, we construct
and analyze synoptic maps of subsurface flows in the SSL, obtained
from time-distance helioseismic inversion during the whole Solar Cycle
24 and the rising phase of Cycle 25. The results reveal the extended
solar-cycle pattern of variations of the meridional circulation,
predicted by the dynamo models and previously known from surface and
subsurface observations of zonal flows. We discuss the origin of the
observed variations and their links to the magnetism and dynamics of
the subsurface shear layer.
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Title: Multiscale Organization of Turbulent Convection in Global-Sun
Simulations
Authors: Guerrero, Gustavo; Stejko, Andrey; Kosovichev, Alexander;
Getling, Alexander; Smolarkiewicz, Piotr
2021AGUFMSH55D1885G Altcode:
Solar convection is at the core of fundamental phenomena such as
differential rotation and meridional circulation and, ultimately, the
solar dynamo. The governing mechanisms, amplitude, and dominant scales
of convection in the solar interior remain under debate. Furthermore,
the large Reynolds and Rayleigh numbers involved make it implausible
to resolve all relevant scales using direct numerical simulation. In
this work, we study solar convection through global, non-rotating, and
non-magnetic implicit large-eddy simulations (ILES), using the 3D global
hydrodynamic code EULAG. Our simulations exhibit a pattern of multiscale
convection, clearly visible on the domain surface (~0.96 R), generated
by a solar-like density and entropy stratification. Scale-splitting
is evident at various depths throughout the model, with the upper
boundary of convective cells penetrating surface layers, resembling
solar-like convection. A continuous and coherent multiscale structure
of convective cells is observed throughout the convective interior. The
power peak of convective scales continuously shrinks with height to a
maximum spherical harmonic degree of l = 40-50 on the model surface,
compatible with reports of giant cell observations. Simulations are
performed from low to high resolution to explore whether integral
properties of convection, such as the RMS velocity, temperature
profiles, and turbulent spectra, become independent of the mesh
size. Results are compared with current observations of surface and
sub-surface solar convection.
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Title: 3D Helioseismic Forward-Modeling and Analysis of Meridional
Circulation
Authors: Stejko, Andrey; Kosovichev, Alexander; Pipin, Valery;
Guerrero, Gustavo; Getling, Alexander; Smolarkiewicz, Piotr
2021AGUFMSH55D1870S Altcode:
The 3D Global Acoustic Linearized Euler (GALE) code is used to explore
the variance in helioseismic signatures that result from various
profiles of meridional circulation. The structure of meridional
circulation regulates the redistribution of angular momentum and
magnetic flux that governs the solar cycle. Forward-modeling is a useful
tool in exploring the structure of meridional circulation and its impact
on global parameters and can help resolve the current controversy
between single and double-cell circulation profiles. Profiles of
meridional circulation are generated using mean-field dynamo models,
which induce a reverse flow near the base of the convection zone,
characteristic of double-cell meridional circulation, with the inclusion
of turbulent pumping (-effect) resulting from a strong rotational
gradient in the region. These models provide physics-based mechanisms
for the low-end in potential differences between single- and double-cell
meridional circulation profiles. The resulting flows are used as
background velocities in the linearized acoustic GALE codesimulating the
stochastic excitation of acoustic perturbations. Techniques in local
helioseismology are then applied to measure flow signatures, showing
that within the observational time-period of the HMI instrument onboard
Solar Dynamics Observatory, it may not be possible to definitively
distinguish between single-cell and double-cell meridional circulation
structure. This analysis is extended to models of meridional circulation
generated in convectively-driven non-linear 3D global-Sun simulations
to explore the helioseismic differences generated by these models and
compare them with observations.
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Title: The Origin Of The Extended Solar Cycle
Authors: Kosovichev, A.; Pipin, V.; Getling, A.
2021AAS...23830405K Altcode:
The extended 22-year solar cycle phenomenon, discovered in observations
of the solar corona and variations of the solar differential rotation
(torsional oscillations), represents a fundamental heliophysics problem
linked to dynamo processes inside the Sun. As observed on the surface,
the extended solar cycle starts during a sunspot maximum at high
latitudes and consists of a relatively short polar branch (described
as "rush to the poles") and a long equatorward branch that continues
through the solar minimum and the next sunspot cycle. Helioseismic
observations of the internal dynamics of the Sun during the last two
solar activity cycles allow us to identify the dynamical processes
associated with the extended solar cycle throughout the depth of the
convective zone and to link them with dynamo models. Observational
data obtained from the SoHO (1996-2010) and SDO (2010-2020) spacecraft
represent measurements of the internal differential rotation, meridional
circulation, and thermodynamic parameters. The data indicate that the
development of a new extended solar cycle begins at about 60 degrees
latitude at the base of the convective zone during the maximum of
the previous cycle. Then, the process of magnetic field migration to
the Sun's surface is divided into two branches: fast (in 1-2 years)
migration to the poles in the high-latitude zone and slow migration to
the equator at middle and low latitudes for ~ 10 years. The subsurface
rotational shear layer (leptocline) plays a key role in the formation
of the magnetic butterfly diagram. Both the zonal flows (torsional
oscillations) and the meridional circulation reveal the 22-year
pattern of the extended solar cycle. A self-consistent MHD model
of the solar dynamo developed in the mean-field theory framework is
in good qualitative and quantitative agreement with the helioseismic
observations. The model shows that the extended solar-cycle phenomenon
is caused by magnetic field quenching of the convective heat flux
and modulation of the meridional circulation induced by the heat
flux variations. The model explains why the solar minimum polar field
predicts the next sunspot maximum and points to new possibilities for
predicting solar cycles from helioseismological data.
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Title: Helioseismic Observations and Modeling of Solar Dynamo
Authors: Kosovichev, Alexander G.; Getling, Alexander V.; Pipin,
Valery V.
2021csss.confE.115K Altcode:
Helioseismological observations of the internal dynamics of the
Sun during the last two solar activity cycles make it possible
to trace the development of solar dynamo processes throughout the
depth of the convective zone and to link them with models of solar
cycles. Observational data obtained from the SoHO (1996-2010) and
SDO (2010-2020) spacecraft represent measurements of the internal
differential rotation, meridional circulation, and thermodynamic
parameters. The structure and dynamics of zonal and meridional
plasma flows reveal the processes of generation and transfer of
magnetic fields inside the Sun. The data analysis shows that active
latitudes and regions of a strong polar field on the Sun's surface
coincide with regions of deceleration of zonal currents ("torsional
oscillations"). The observed structure of zonal flows and their
latitudinal and radial migration in deep layers of the convective
zone correspond to dynamo waves predicted by dynamo theories and
numerical MHD models. The data indicate that the development of a new
solar cycle begins at about 60 degrees latitude at the base of the
convective zone during the maximum of the previous cycle. Then, the
process of magnetic field migration to the Sun's surface is divided
into two branches: fast (in 1-2 years) migration in the high-latitude
zone and slow migration at middle and low latitudes for ~ 10 years. The
subsurface rotational shear layer ("leptocline") plays a key role in
the formation of the magnetic "butterfly diagram". Both the zonal
flows ("torsional oscillations") and the meridional circulation
reveal the 22-year pattern of the "extended" solar cycle, initially
discovered from observations of Doppler velocities and the structure
of the solar corona.A self-consistent MHD model of the solar dynamo
developed in the mean-field theory framework is in good qualitative
and quantitative agreement with the helioseismic observations. The
model shows that the observed variations of the solar dynamics are
associated with a magnetic field effect on convective heat transfer
and the corresponding modulation of the meridional circulation. The
model explains why the solar minimum polar field predicts the next
sunspot maximum and points to new possibilities for predicting solar
cycles from helioseismological data.
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Title: Evolution of Subsurface Zonal and Meridional Flows in Solar
Cycle 24 from Helioseismological Data
Authors: Getling, Alexander V.; Kosovichev, Alexander G.; Zhao, Junwei
2021ApJ...908L..50G Altcode: 2020arXiv201215555G
The results of determinations of the azimuthal and meridional
velocities by time-distance helioseismology from Helioseismic and
Magnetic Imager on board Solar Dynamics Observatory from 2010 May to
2020 September at latitudes and Stonyhurst longitudes from - 60° to
+ 60° and depths to about 19 Mm below the photosphere are used to
analyze spatiotemporal variations of the solar differential rotation
and meridional circulation. The pattern of torsional oscillations,
or latitudinal belts of alternating "fast" and "slow" zonal flows
migrating from high latitudes toward the equator, is found to extend in
the time-latitude diagrams over the whole time interval. The oscillation
period is comparable with a doubled solar-activity-cycle and can be
described as an extended solar cycle. The zonal-velocity variations
are related to the solar-activity level, the local-velocity increases
corresponding to the sunspot-number increases and being localized at
latitudes where the strongest magnetic fields are recorded. The dramatic
growth of the zonal velocities in 2018 appears to be a precursor of
the beginning of Solar Cycle 25. The strong symmetrization of the
zonal-velocity field by 2020 can be considered another precursor. The
general pattern of poleward meridional flows is modulated by latitudinal
variations similar to the extended-solar-cycle behavior of the zonal
flows. During the activity maximum, these variations are superposed
with a higher harmonic corresponding to meridional flows converging to
the spot-formation latitudes. Our results indicate that variations of
both the zonal and meridional flows exhibit the extended-solar-cycle
behavior, which is an intrinsic feature of the solar dynamo.
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Title: Peculiarities of the Dynamics of Solar NOAA Active Region 12673
Authors: Getling, A. V.
2019ApJ...878..127G Altcode: 2019arXiv190408367G
The dynamics of active region (AR) 12673 is qualitatively studied using
observational data obtained with the Helioseismic and Magnetic Imager
of the Solar Dynamics Observatory on 2017 August 31-September 8. This
AR was remarkable for its complex structure and extraordinary flare
productivity. The sunspot group in this AR consisted of (1) an old,
well-developed and highly stable, coherent sunspot, which had also been
observed two solar rotations earlier, and (2) a rapidly developing
cluster of umbral and penumbral fragments. Cluster (2) formed two
elongated, arc-shaped chains of spot elements, skirting around the
major sunspot (1), with two chains of magnetic elements spatially
coinciding with the arcs. AR components (1) and (2) were in relative
motion, cluster (2) overtaking spot (1) in westward motion, and their
relative velocity agrees in order of magnitude with the velocity jump
over the near-surface shear layer, or leptocline. The pattern of motion
of the features about the main spot bears amazing resemblance to the
pattern of a fluid flow about a roundish body. This suggests that spot
(1) was dynamically coupled with the surface layers, while cluster (2)
developed in deeper layers of the convection zone. The magnetic-flux
emergence in cluster (2) appeared to be associated with fluid motions
similar to roll convection. The mutual approach of components (1)
and (2) gave rise to light bridges in the umbrae of sunspots with the
magnetic field having the same sign on both sides of the bridge.
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Title: The Origin and Early Evolution of a Bipolar Magnetic Region
in the Solar Photosphere
Authors: Getling, A. V.; Buchnev, A. A.
2019ApJ...871..224G Altcode: 2018arXiv180506486G
Finding the formation mechanisms for bipolar configurations of a
strong local magnetic field under control of the relatively weak
global magnetic field of the Sun is a key problem of the physics of
solar activity. This study is aimed at discriminating whether the
magnetic field or fluid motion plays a primary, active role in this
process. The very origin and early development stage of Active Region
12548 are investigated based on Solar Dynamics Observatory/Helioseismic
and Magnetic Imager observations of 2016 May 20-25. Full-vector
magnetic and velocity fields are analyzed in parallel. The leading
and trailing magnetic polarities are found to grow asymmetrically in
terms of their amplitude, magnetic flux, and the time variation of
these quantities. The leading-polarity magnetic element originates
as a compact feature against the background of a distributed
trailing-polarity field, with an already existing trailing-polarity
magnetic element. No signs of strong horizontal magnetic fields
are detected between the two magnetic poles. No predominant upflow
between their future locations precedes the origin of this bipolar
magnetic region (BMR); instead, upflows and downflows are mixed, with
some prevalence of downflows. Any signs of a large-scale horizontal
divergent flow from the area where the BMR develops are missing;
in contrast, a normal supergranulation and mesogranulation pattern
is preserved. This scenario of early BMR evolution is in strong
contradiction with the expectations based on the model of a rising
Ω-shaped loop of a flux tube of strong magnetic field, and an in
situ mechanism of magnetic-field amplification and structuring should
operate in this case.
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Title: Effects of variable thermal diffusivity on the structure
of convection
Authors: Shcheritsa, O. V.; Getling, A. V.; Mazhorova, O. S.
2016arXiv160402543S Altcode:
The multiscale flow structure in the solar convection zone -
the coexistence of such features as the granules, mesogranules,
supergranules and giant cells - has not yet been properly
understood. Here, the possible role of one physical factor - variations
in the thermal diffusivity - in the formation of a multiscale convection
structure is investigated. Thermal convection in a plane horizontal
fluid layer is numerically simulated. The temperature dependence of
thermal diffusivity is chosen so as to produce a sharp kink in the
static temperature profile near the upper layer boundary. As a result,
the magnitude of the (negative) static temperature gradient dTs/dz,
being small over the most part of the layer thickness, reaches large
values in a thin boundary sublayer. To identify the structures on
different scales, we apply a smoothing procedure, computational-homology
techniques and spectral processing to the temperature field. The flow
is found to be a superposition of three cellular structures with three
different characteristic scales. The largest (first-scale) convection
cells, with central upflows, fill the whole layer thickness; most of
these cells are divided by bridges, or isthmuses, into a few smaller
(second-scale) ones, which are localised in the upper portion of the
layer; finally, there are numerous tiny (third-scale) features that dot
the horizontal sections of the layer located near its upper boundary
and exhibit a tendency of gathering in the intercellular lanes of the
first-scale cells. The third-scale cellular structures are advected
by the first-scale and second-scale convective flows. The spatial
spectrum of the flow does not directly indicate the presence of the
second-scale and third-scale structures; however, they can be selected
by using our processing techniques. On the whole, the simulated flow
pattern qualitatively resembles that observed on the Sun.
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Title: Development of Active Regions: Flows, Magnetic-Field Patterns
and Bordering Effect
Authors: Getling, A. V.; Ishikawa, R.; Buchnev, A. A.
2016SoPh..291..371G Altcode: 2016SoPh..tmp....9G; 2015arXiv150601848G
A qualitative analysis is given of the data on the full magnetic
and velocity vector fields in a growing sunspot group, recorded
nearly simultaneously with the Solar Optical Telescope on the Hinode
satellite. Observations of a young bipolar subregion developing within
AR 11313 were carried out on 9 - 10 October 2011. Our aim was to form an
idea about the consistency of the observed pattern with the well-known
rising-tube model of the formation of bipolar active regions and sunspot
groups. We find from our magnetograms that the distributions of the
vertical [B<SUB>v</SUB>] and the horizontal [B<SUB>h</SUB>] component
of the magnetic field over the area of the magnetic subregion are
spatially well correlated; in contrast, the rise of a flux-tube loop
would result in a qualitatively different pattern, with the maxima of
the two magnetic-field components spatially separated: the vertical
field would be the strongest where either spot emerges, while the
maximum horizontal-field strengths would be reached in between them. A
specific feature, which we call the bordering effect, is revealed:
some local extrema of B<SUB>v</SUB> are bordered with areas of locally
enhanced B<SUB>h</SUB>. This effect suggests a fountainlike spatial
structure of the magnetic field near the B<SUB>v</SUB> extrema, which
is also hardly compatible with the emergence of a flux-tube loop. The
vertical-velocity field in the area of the developing active subregion
does not exhibit any upflow on the scale of the whole subregion, which
should be related to the rising-tube process. Thus, our observational
data can hardly be interpreted in the framework of the rising-tube
model.
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Title: Stratification-induced scale splitting in convection
Authors: Shcheritsa, O. V.; Getling, A. V.; Mazhorova, O. S.
2015AdSpR..55..927S Altcode: 2014arXiv1401.8137S
The coexistence of motions on various scales is a remarkable feature of
solar convection, which should be taken into account in analyses of the
dynamics of magnetic fields. Therefore, it is important to investigate
the factors responsible for the observed multiscale structure of solar
convection. In this study, an attempt is made to understand how the
scales of convective motions are affected by the particularities of
the static temperature stratification of a fluid layer. To this end,
simple models are considered. The equations of two-dimensional thermal
convection are solved numerically for a plane horizontal fluid layer
heated from below, in an extended Boussinesq approximation that
admits thermal-diffusivity variations. These variations specify
the stratification of the layer. The static temperature gradient
in a thin sublayer near the upper surface of the layer is assumed
to be many times larger than in the remainder of the layer. In
some cases, distributed heat sinks are assumed to produce a stably
stratified region overlying the convective layer. Manifestations of
the scale-splitting effect are noted, which depend on the boundary
conditions and stratification; it becomes more pronounced with the
increase of the Rayleigh number. Small-scale convection cells are
advected by larger-scale flows. In particular, the phase trajectories
of fluid particles indicate the presence of complex attractors, which
reflect the multiscale structure of the flow. The effect of the stably
stratified upper sublayer on the flow scales is also considered.
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Title: Doubts about the crucial role of the rising-tube mechanism
in the formation of sunspot groups
Authors: Getling, A. V.; Ishikawa, R.; Buchnev, A. A.
2015AdSpR..55..862G Altcode: 2014arXiv1401.8077G
Some preliminary processing results are presented for a dataset obtained
with the Solar Optical Telescope on the Hinode satellite. The idea of
the project is to record, nearly simultaneously, the full velocity and
magnetic-field vectors in growing active regions and sunspot groups at
a photospheric level. Our ultimate aim is to elaborate observational
criteria to distinguish between the manifestations of two mechanisms
of sunspot-group formation - the rising of an Ω -shaped flux tube of
a strong magnetic field and the in situ amplification and structuring
of magnetic field by convection (the convective mechanism is briefly
described). <P />Observations of a young bipolar subregion developing
within AR 11313 were carried out on 9-10 October 2011. During each
2-h observational session, 5576-Å filtergrams and Dopplergrams
were obtained at a time cadence of 2 min, and one or two 32-min-long
spectropolarimetric fast-mode scans were done. Based on the series of
filtergrams, the trajectories of corks are computed, using a technique
similar to but more reliable than local correlation tracking (LCT),
and compared with the magnetic maps. At this stage of the investigation,
only the vertical magnetic field and the horizontal flows are used for
a qualitative analysis. <P />According to our preliminary findings,
the velocity pattern in the growing active region has nothing to do
with a spreading flow on the scale of the entire bipolar region, which
could be expected if a tube of strong magnetic field emerged. No violent
spreading flows on the scale of the entire growing magnetic region can
be identified. Instead, normal mesogranular and supergranular flows
are preserved. Signs of small-scale structuring of the magnetic field
can be detected in the area where new spots develop, and signs of
the presence of separatrices between the magnetic polarities can be
found, such that the surface flows converge to but not diverge from
these separatrix curves. The observed scenario of evolution seems to
agree with Bumba's inference that the development of an active region
does not entail the destruction of the existing convective-velocity
field. The convective mechanism appears to be better compatible with
observations than the rising-tube mechanism. <P />In the umbras of
the well-developed sunspots, flows converging to the umbra centres
are revealed. Spreading streams are present around these spots.
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Title: Can subphotospheric magnetic fields be amplified and structured
by a convective mechanism?
Authors: Getling, Alexander; Mazhorova, Olga; Kolmychkov, Vyacheslav
2014cosp...40E.975G Altcode:
Strong photospheric magnetic fields frequently originate at the knots
of the network formed by intercellular lanes -- the peripheral parts
of convection cells on various scales. This phenomenon is normally
interpreted as a result of the “sweeping” of magnetic field lines by
convective motions. On the other hand, magnetic elements can emerge in
the inner parts of supergranules (Title, 2006), which may be an effect
of the “winding” of magnetic field lines by circulating matter, as
suggested by Tverskoi (1966) based on a simple kinematic model. In this
study, magnetoconvection in a horizontal layer of incompressible fluid
is simulated numerically. The initial magnetic field is assumed to be
weak, uniform throughout the layer and horizontal. The interaction of
quasi-ordered cellular convection with the magnetic field is shown to be
able to produce bipolar (and also diverse more complex) configurations
of a substantially amplified magnetic field. In some cases, bipolar
magnetic structures change into unipolar ones. Such transitions are
analysed. The formation of the magnetic features can be attributed to
either the “winding” or “sweeping” of magnetic field lines. The
operation of this mechanism is controlled by the very topology of the
cellular flow and does not require strong initial fields. Under solar
conditions, it should be manifest on various spatial scales. This
work was supported by the Russian Foundation for Basic Research,
project no. 12-02-00792-a.
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Title: Formation of sunspot groups: Do we see manifestations of the
rising-tube mechanism?
Authors: Getling, Alexander; Ishikawa, Ryohko; Buchnev, Aleksei
2014cosp...40E.974G Altcode:
A comparison is made between the expected manifestations of two
mechanisms suggested to account for the formation of local photospheric
magnetic fields, viz., the rising of an Omega-shaped flux tube of
a strong magnetic field and the emph{in situ} amplification and
structuring of magnetic field by convection. The ultimate aim of
the study is to elaborate observational criteria to find out which
mechanism controls the process in any given case. To this end, the
full velocity and magnetic-field vectors in growing active regions
and sunspot groups at a photospheric level were recorded nearly
simultaneously. Observations of a young bipolar subregion developing
within AR 11313 were carried out on 9-10 October 2011, with the Solar
Optical Telescope on the emph{Hinode} satellite, which yielded 5576-Å
filtergrams and Dopplergrams and also spectropolarimetric records of
the magnetic-field vector. To determine the tangential-velocity field,
a technique similar to but more reliable than local correlation tracking
(LCT) was applied to the series of filtergrams, and the trajectories
of corks were computed. According to our preliminary findings, the
velocity pattern in the growing active region cannot be described
as a spreading flow on the scale of the entire bipolar region, which
could be expected if a tube of strong magnetic field emerged. Instead,
normal mesogranular and supergranular flows are observed in agreement
with Bumba’s inference that the development of an active region
does not entail the destruction of the existing convective-velocity
field. Between the magnetic polarities, curves can be found to which
the surface flows converge rather than diverging from them under
the action of a rising tube. The convective mechanism appears to be
better compatible with observations than the rising-tube mechanism. In
the umbras of the well-developed sunspots, flows converging to the
umbra centres are revealed. Spreading streams are present around these
spots. Hinode is a Japanese mission developed and launched by ISAS/JAXA,
with NAOJ as domestic partner and NASA and STFC (UK) as international
partners. It is operated by these agencies in cooperation with ESA
and NSC (Norway). This work was supported by the Russian Foundation
for Basic Research (project no. 12-02-00792-a).
---------------------------------------------------------
Title: Why can different flow scales coexist in solar convection?
Authors: Getling, Alexander; Shcheritsa, Olga; Mazhorova, Olga
2014cosp...40E.976G Altcode:
Solar convection demonstrates a remarkable multiscale structure (the
coexistence of granules, mesogranules, supergranules and giant cells),
which largely controls the structure and dynamics of photospheric
magnetic fields. With the aim of comprehending the possible mechanisms
of such scale splitting, the effect of particularities of the static
temperature profile on the structure of convection are considered
here. To this end, two-dimensional convection in a plane horizontal
layer of an incompressible fluid heated from below is simulated
numerically. The stratification of the layer is controlled by
thermal-diffusivity variations. The static temperature gradient in
a thin sublayer near the upper surface of the layer is assumed to be
many times larger than in the remainder of the layer. In some cases,
distributed heat sinks are assumed to produce a stably stratified region
overlying the convective layer. Manifestations of the scale-splitting
effect are observed, which depend on the boundary conditions and
stratification. The multiscale structure of the flow is manifest most
clearly in the presence of complex attractors in the pattern of phase
trajectories of fluid particles. Small-scale convection cells are
carried by larger-scale flows. This work was supported by the Russian
Foundation for Basic Research, project no. 12-02-00792-a.
---------------------------------------------------------
Title: Concerning the multiscale structure of solar convection
Authors: Getling, A. V.; Mazhorova, O. S.; Shcheritsa, O. V.
2013Ge&Ae..53..904G Altcode:
The discrete scale spectrum of the convective flows observed on the
Sun has not yet received a convincing explanation. Here, an attempt
is made to find conditions for the coexistence of convective flows on
various scales in a horizontal fluid layer heated from below, where
the thermal diffusivity varies with temperature in such a way that the
static temperature difference across a thin sublayer near the upper
surface of the layer is many times larger than the temperature variation
across the remainder of the layer. The equations of two-dimensional
thermal convection are solved numerically in an extended Boussinesq
approximation, which admits thermal-diffusivity variations. The
no-slip conditions are assumed at the lower boundary of the layer;
either no-slip or free-slip conditions, at the upper boundary. In the
former case, stable large-scale rolls develop, which experience small
deformations under the action of small structures concentrated near
the horizontal boundaries. In the latter case, the flow structure is
highly variable, different flow scales dominate at different heights,
the number of large rolls is not constant, and a sort of intermittency
occurs: the enhancement of the small-scale flow component is frequently
accompanied by the weakening of the large-scale one, and vice versa. The
scale-splitting effects revealed here should manifest themselves in
one way or another in the structure of solar convection.
---------------------------------------------------------
Title: Convective mechanism of amplification and structuring of
magnetic fields
Authors: Getling, A. V.; Kolmychkov, V. V.; Mazhorova, O. S.
2013IAUS..294..137G Altcode:
Magnetoconvection in a horizontal layer of incompressible fluid
is simulated numerically. The initial magnetic field is assumed
to be uniform and horizontal. The interaction of quasi-ordered
cellular convection with the magnetic field is shown to be able to
produce bipolar (and also diverse more complex) configurations of a
substantially amplified magnetic field. The operation of this mechanism,
which can be regarded as a modification of the mechanism suggested by
Tverskoi (1966), is controlled by the very topology of the cellular
flow, should be manifest on various spatial scales, and does not
require strong initial fields. Magnetic configurations develop both in
the central parts of convection cells, where circulatory fluid motion
“winds” magnetic field lines, and in the network formed by their
peripheral regions due to the “sweeping” of magnetic field lines.
---------------------------------------------------------
Title: The flow helicity in quasi-orderedcellular convection
Authors: Getling, A. V.
2013IAUS..294..359G Altcode:
The helicity of cellular convective flows in a horizontal layer of
compressible fluid (gas) heated from below and rotating about a vertical
axis is studied using finite-difference numerical simulations. The
medium is assumed to be polytropically stratified. An initial thermal
perturbation is introduced so as to produce a system of Bénard-type
hexagonal convection cells. The flow gradually becomes less ordered,
and the mean helicity grows initially and decreases sharply after the
substantial chaotisation of the flow. Given the Rayleigh and Prandtl
numbers, the maximum value reached by the mean helicity increases with
the decrease of the polytrope index and has a maximum at a certain
rotational velocity of the layer.
---------------------------------------------------------
Title: Toward understanding the multiscale spatial spectrum of
solar convection
Authors: Getling, A. V.; Mazhorova, O. S.; Shcheritsa, O. V.
2013IAUS..294..361G Altcode:
Convection is simulated numerically based on two-dimensional Boussinesq
equations for a fluid layer with a specially chosen stratification such
that the convective instability is much stronger in a thin subsurface
sublayer than in the remaining part of the layer. The developing
convective flow has a small-scale component superposed onto a basic
large-scale roll flow.
---------------------------------------------------------
Title: The helicity of the velocity field for cellular convection
in a rotating layer
Authors: Getling, A. V.
2012ARep...56..395G Altcode: 2012AZh....89..441G
The helicity of a cellular convective flow in a horizontal layer
of a compressible fluid (gas) heated from below and rotating about
the vertical axis is studied using finite-difference numerical
simulations. The medium is assumed to be polytropically stratified. A
thermal perturbation that produces a system of Bénard-type hexagonal
convection cells is introduced at the initial time. Next, the cells
are deformed by the action of the Coriolis force; however, at some
stage of the evolution, the flow is nearly steady (at later times,
the cells break down). For given Rayleigh and Prandtl numbers, the
velocity-field helicity for this stage averaged over the layer increases
with decreasing polytrope index (i.e., with increasing the curvature of
the static entropy profile) and has a maximum at a certain rotational
velocity of the layer. Numerical simulations of such quasi-ordered
convective flows should reduce the uncertainties in estimates of the
helicity, a quantity important for the operation of MHD dynamos.
---------------------------------------------------------
Title: Some structural features of the convective-velocity field in
the solar photosphere
Authors: Getling, A. V.; Buchnev, A. A.
2010ARep...54..254G Altcode: 2010AZh....87..286G
An algorithm for measuring horizontal photospheric velocities previously
employed to process aerospace images is adapted for problems in solar
physics and realized in a computational code. It differs from the
standard procedure of local correlation tracking in a special choice
of trial areas (“targets”), whose displacements are determined
bymaximizing the correlation between the original and various shifted
positions of the target. Specifically, an area is chosen as a target
in a certain neighborhood of each node of a predefined grid if either
the contrast or the entropy of the brightness distribution reaches
its maximum in this area. The horizontal velocities obtained are then
interpolated to the positions of imaginary “corks” using the
Delaunay triangulation and affine transformations specified by the
deformation of the obtained triangles at the time step considered. The
motion of the corks is represented by their trajectories. A
superposition of flows on different scales, from mesogranular to
supergranular, can clearly be seen. “Large mesogranules” with
sizes of order 15 Mm are revealed. In many cases, these are stellate in
shape. Areas of strong convergence of the horizontal flows are detected;
this convergence is sometimes accompanied by swirling. Evidence is
found for the possible coexistence of convection cells with different
circulation directions, so-called l-type and g-type cells.
---------------------------------------------------------
Title: Do Long-Lived Features Really Exist in the Solar
Photosphere? II. Contrast of Time-Averaged Granulation Images
Authors: Brandt, P. N.; Getling, A. V.
2008SoPh..249..307B Altcode: 2008arXiv0802.0204B; 2008SoPh..tmp...64B
The decrease in the rms contrast of time-averaged images with the
averaging time is compared between four data sets: (1) a series of
solar granulation images recorded at La Palma in 1993, (2) a series
of artificial granulation images obtained in numerical simulations
by Rieutord et al. (Nuovo Cimento25, 523, 2002), (3) a similar
series computed by Steffen and his colleagues (see Wedemeyer et
al. in Astron. Astrophys.44, 1121, 2004), (4) a random field with
some parameters typical of the granulation, constructed by Rast
(Astron. Astrophys.392, L13, 2002). In addition, (5) a sequence of
images was obtained from real granulation images by using a temporal
and spatial shuffling procedure, and the contrast of the average of n
images from this sequence as a function of n is analysed. The series
(1) of real granulation images exhibits a considerably slower contrast
decrease than do both the series (3) of simulated granulation images
and the series (4) of random fields. Starting from some relatively
short averaging times t, the behaviour of the contrast in series (3)
and (4) resembles the t<SUP>−1/2</SUP> statistical law, whereas
the shuffled series (5) obeys the n<SUP>−1/2</SUP> law from n=2
on. Series (2) demonstrates a peculiarly slow decline of contrast,
which could be attributed to particular properties of the boundary
conditions used in the simulations. Comparisons between the analysed
contrast-variation laws indicate quite definitely that the brightness
field of solar granulation contains a long-lived component, which could
be associated with locally persistent dark intergranular holes and/or
with the presence of quasi-regular structures. The suggestion that the
random field (4) successfully reproduces the contrast-variation law
for the real granulation (Rast in Astron. Astrophys.392, L13, 2002)
can be dismissed.
---------------------------------------------------------
Title: Widespread Occurrence of Trenching Patterns in the Granulation
Field: Evidence for Roll Convection?
Authors: Getling, A. V.; Buchnev, A. A.
2008SoPh..248..233G Altcode: 2007arXiv0709.3251G
Time-averaged series of granulation images are analysed using
COLIBRI, a purpose-adapted version of a code originally developed
to detect straight or curvilinear features in aerospace images. The
image-processing algorithm utilises a nonparametric statistical
criterion that identifies a straight-line segment as a linear feature
(lineament) if the photospheric brightness at a certain distance
from this line on both sides is stochastically lower or higher than
at the line itself. Curvilinear features can be detected as chains
of lineaments, using a modified criterion. Once the input parameters
used by the algorithm are properly adjusted, the algorithm highlights
"ridges" and "trenches" in the relief of the brightness field, drawing
white and dark lanes. The most remarkable property of the trenching
patterns is a nearly universally present parallelism of ridges and
trenches. Since the material upflows are brighter than the downflows,
the alternating, parallel light and dark lanes should reflect the
presence of roll convection in the subphotospheric layers. If the
numerous images processed by us are representative, the patterns
revealed suggest a widespread occurrence of roll convection in the
outer solar convection zone. In particular, the roll systems could form
the fine structure of larger scale, supergranular and/or mesogranular
convection flows. Granules appear to be overheated blobs of material
that could develop into convection rolls owing to instabilities of
roll motion.
---------------------------------------------------------
Title: Generation of coupled global and local magnetic fields by a
cellular MHD dynamo
Authors: Getling, A. V.; Simitev, R. D.; Busse, F. H.
2007IAUS..239..482G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Is solar convection responsible for the local amplification and
structuring of magnetic fields? (Observational test of the hypothesis)
Authors: Getling, A. V.; Bao, X. M.
2007IAUS..239..496G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Quasi-regular structures in the solar photosphere (trenching
in the brightness relief): Algorithmic treatment
Authors: Getling, A. V.; Buchnev, A. A.
2007IAUS..239..499G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Can cellular convection in a rotating spherical shell maintain
both global and local magnetic fields?
Authors: Getling, A. V.; Simitev, R. D.; Busse, F. H.
2007IJGA....7.1004G Altcode: 2007IJGA....7I1004G; 2006astro.ph.10753G
[1] A convection-driven MHD dynamo in a rotating spherical shell, with
clearly defined structural elements in the flow and magnetic field,
is simulated numerically. Such dynamos can be called deterministic,
in contrast to those explicitly dependent on the assumed properties of
turbulence. The cases most interesting from the standpoint of studying
the nature of stellar magnetism demonstrate the following features. On
a global scale, the convective flows can maintain a "general" magnetic
field with a sign-alternating dipolar component. Local (in many
cases, bipolar) magnetic structures are associated with convection
cells. Disintegrating local structures change into background fields,
which drift toward the poles. From time to time, reversals of the
magnetic fields in the polar regions occur, as "new" background fields
expel the "old" fields.
---------------------------------------------------------
Title: Do Quasi-Regular Structures Really Exist in the Solar
Photosphere? I. Observational Evidence
Authors: Getling, A. V.
2006SoPh..239...93G Altcode: 2006SoPh..tmp...82G; 2006astro.ph.10698G
Two series of solar-granulation images - the La Palma series of 5 June
1993 and the SOHO MDI series of 17 - 18 January 1997 - are analysed
both qualitatively and quantitatively. New evidence is presented for
the existence of long-lived, quasi-regular structures (first reported
by Getling and Brandt, Astron. Astrophys. 382, L5 (paper I), 2002),
which no longer appear unusual in images averaged over 1 - 2-hour
time intervals. Such structures appear as families of light and dark
concentric rings or families of light and dark parallel strips ("ridges"
and "trenches" in the brightness distributions). In some cases, rings
are combined with radial "spokes" and can thus form "web" patterns. The
characteristic width of a ridge or trench is somewhat larger than
the typical size of granules. Running-average movies constructed from
the series of images are used to seek such structures. An algorithm
is developed to obtain, for automatically selected centres, the
radial distributions of the azimuthally averaged intensity, which
highlight the concentric-ring patterns. We also present a time-averaged
granulation image processed with a software package intended for the
detection of geological structures in aerospace images. A technique of
running-average-based correlations between the brightness variations
at various points of the granular field is developed and indications
are found for a dynamical link between the emergence and sinking of hot
and cool parcels of the solar plasma. In particular, such a correlation
analysis confirms our suggestion that granules - overheated blobs -
may repeatedly emerge on the solar surface. Based on our study, the
critical remarks by Rast (Astron. Astrophys. 392, L13, 2002) on the
original paper by Getling and Brandt (paper I) can be dismissed.
---------------------------------------------------------
Title: Cellular dynamo in a rotating spherical shell
Authors: Getling, A. V.; Simitev, R. D.; Busse, F. H.
2005AN....326..241G Altcode:
Magnetoconvection in a rotating spherical shell is simulated numerically
using a code developed by Tilgner and Busse. The thermal stratification
is convectively unstable in the outer part and stable in the inner
part of the shell. Regimes are found in which the convective flow is
weakly affected by rotation and preserves its cellular structure. The
dipolar component of the large-scale magnetic field exhibits undamped
oscillations. It appears that convection cells slightly modified by
rotation can be building blocks of the global dynamo. The generation
of the magnetic field is thus due to regular “macroscopic” flows,
and their structure itself may ensure the presence of the α effect
responsible for the action of the dynamo. Such dynamos can be called
deterministic, in contrast to those in which the maintenance of the
magnetic field is related to the statistical predominance of a certain
sign of helicity in the turbulent velocity field. Investigation of
conditions under which dynamos of this sort can operate could suggest
a more definite answer to the question of the origin of solar and
stellar magnetic fields.
---------------------------------------------------------
Title: Contrast of time-averaged images of the solar granulation
Authors: Brandt, P. N.; Getling, A. V.
2004IAUS..223..231B Altcode: 2005IAUS..223..231B
The time-averaged images of the solar granulation exhibit a slower
decrease in contrast with the averaging time than do time-averaged
images of numerically simulated granulation and time-averaged random
fields with some parameters typical of granulation. This confirms the
hints for long-lived structures in the granulation pattern.
---------------------------------------------------------
Title: Compressible magnetoconvection as the local producer of
solar-type magnetic structures
Authors: Dobler, W.; Getling, A. V.
2004IAUS..223..239D Altcode: 2005IAUS..223..239D
Simulations of cellular magnetoconvection in a compressible fluid
reveal the formation of magnetic structures with a substantial bipolar
component as an inherent property of the topology of cellular flows.
---------------------------------------------------------
Title: Structure of solar convection: guesses and observational
evidence
Authors: Getling, A. V.
2004IAUS..223..247G Altcode: 2005IAUS..223..247G
Signs of quasi-regular structures in time-averaged photospheric images
are described.
---------------------------------------------------------
Title: Regular Photospheric Patterns (Trenching in the Brightness
Relief) and Persistence of the Granular Field
Authors: Getling, A. V.; Brandt, P. N.
2003ASPC..286..185G Altcode: 2003ctmf.conf..185G
No abstract at ADS
---------------------------------------------------------
Title: Convective Mechanism for Formation of Solar Magnetic Bipoles
Authors: Getling, A. V.; Ovchinnikov, I. L.
2003ASPC..286..139G Altcode: 2003ctmf.conf..139G
No abstract at ADS
---------------------------------------------------------
Title: Quasi-regular structures of the solar photosphere
Authors: Getling, A. V.; Brandt, P. N.
2002ESASP.506..617G Altcode: 2002ESPM...10..617G; 2002svco.conf..617G
As we already reported, the simple procedure of time averaging, when
applied to the photospheric brightness field, reveals quasi-regular
structures of the photospheric and subphotospheric flows. Our analysis
presented here shows that the decrease in the rms contrast of the
averaged images with the increase of the averaging time τ is slower
compared to the √τ law, which argues for the real persistence
of the revealed structures as physical entities. The procedure of
running-average-based correlation is suggested to seek coherence
between the brightness variations at the points of emergence and
sinking of granules. Some results of the correlation analysis confirm
the notion that granules are overheated blobs of material carried by
the convective circulation.
---------------------------------------------------------
Title: Solar convection as the producer of magnetic bipoles
Authors: Getling, A. V.; Ovchinnikov, I. L.
2002ESASP.506..819G Altcode: 2002svco.conf..819G; 2002ESPM...10..819G
A mechanism for the in situ formation of bipolar magnetic
configurations, alternative to the well-known rising-tube mechanism, is
considered. Cellular magnetoconvection is simulated numerically. The
initial magnetic field is assumed to be fairly weak and directed
horizontally. A pattern of small-amplitude hexagonal cells is specified
initially. A hexagonal convection cell can substantially amplify the
magnetic field and impart bipolar configurations to it. Depending on
the parameters, the amplified field may form either a simple pair of
magnetic islands, opposite in polarity, or a more complex superposition
of bipoles. In particular, very compact magnetic elements of strong
field can form. The resulting pattern of magnetic-field evolution is
in better agreement with observations than the rising-tube model.
---------------------------------------------------------
Title: Regular structures of the solar photosphere. (Persistence of
the granular field and trenching in the brightness relief)
Authors: Getling, A. V.; Brandt, P. N.
2002A&A...382L...5G Altcode:
The simple procedure of time averaging, when applied to the
photospheric brightness field, reveals quasi-regular structures of
the photospheric and subphotospheric flows. We use an 8-h sub-set of
the series of photospheric images obtained on 5 June 1993 with the
Swedish Vacuum Solar Telescope, La Palma. First, the averaged images
are far from completely smeared and contain a multitude of bright,
granular-sized blotches even if the averaging period is as long as 8
h. This suggests that granules prefer to originate at certain sites,
where they emerge repeatedly, and the granular field demonstrates a
sort of persistence for many hours. Second, the resulting patterns
display relatively regular structures, which can be revealed only if
the averaging period is sufficiently long (the optimum seems to lie
between 2 and 3 h). The averaged brightness relief is “trenched”:
it comprises systems of concentric rings and arcs as well as straight
or slightly wavy lines and systems of parallel strips. The trenching
patterns resemble the so-called target patterns observed in experiments
on Rayleigh-Bénard convection. In addition, the brightness values
at a local averaged-field maximum and at a nearby minimum exhibit a
distinct tendency to vary in antiphase. Thus, a previously unknown
type of self-organization is manifest in the solar atmosphere, and
our findings support the suggestion that granules are associated with
overheated blobs carried by the convective circulation.
---------------------------------------------------------
Title: Solar convection and sunspot formation mechanishm
Authors: Getling, A. V.
2001A&AT...20..433G Altcode:
The rising-flux-tube model of the formation of a bipolar sunspot
group sharply disgrees with the normally observed features of the
process. Meanwhile, these features can be successfully accounted
for in terms of local magnetic-field amplification due to zellular
convective motions of the solar plasma. Here, magnetoconvection in a
plane horizontal fluid layer is simulated numberically magnetic field
and a weak cellular flow are present. Convention can produce bipolar
configurations of strongly amplified magnetic field. Indications are
found for the nontrivial effect of flow freezing. The action of the
convective mechanism may be controlled by the large-scale toroidal
magnetic field of the Sun.
---------------------------------------------------------
Title: Convective Mechanism for the Formation of Photospheric
Magnetic Fields
Authors: Getling, A. V.
2001ARep...45..569G Altcode:
The well-known model that attributes the formation of a bipolar sunspot
group to the emergence of a flux tube disagrees sharply with the
usual observed pattern of phenomena. At the same time, the observed
patterns can be accounted for quite convincingly in terms of local
magnetic-field amplification due to cellular convective motions of the
solar plasma. In this study, magnetoconvection in a plane horizontal
fluid layer is simulated numerically in the framework of the fully
nonlinear, three-dimensional problem. A weak horizontal magnetic field
and weak cellular flow are assumed to be present initially. Convection
is shown to be capable of producing bipolar magnetic configurations of
the strongly amplified magnetic field. Indications of magnetic freezing
of the flow in the cell are found. The action of the amplification
mechanism under study may be controlled by the large-scale toroidal
magnetic field of the Sun.
---------------------------------------------------------
Title: Hydrodynamic Instabilities and Photospheric Structures
Authors: Getling, A. V.
2000ARep...44...56G Altcode:
The possible role of convective-flow instabilities in the formation
of certain structures observed in the solar photospheric and
subphotospheric layers is discussed. High-resolution video records
suggest that the granulation field is structurally and dynamically
ordered in accordance with the mesogranulation pattern. Thus, it
strikingly resembles the so-called spoke patterns of convection
observed experimentally. These patterns could be produced by some
instability of the mesogranular flow. Mesogranules seem to be the main
structural features of the velocity field, whereas granules behave
as relatively passive elements—blobs of overheated material carried
by the mesogranular flow. One possible mechanism for their origin is
the development of a three-dimensional analogue of the one-blob or the
two-blob instability known from studies of convection. In particular,
if this interpretation is adopted, the phenomenon of exploding granules
can be accounted for in a natural way.
---------------------------------------------------------
Title: Numerical modelling of the magnetospheric convection in the
region of closed force lines of the magnetic field.
Authors: Alekseeva, L. M.; Getling, A. V.; Savelev, V. V.
1982Ge&Ae..22..612A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The convective zone of the sun.
Authors: Getling, A. V.
1982IGAFS..61....3G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the scales of convection flows in a horizontal layer with
radiative energy transfer
Authors: Getling, A. V.
1980FizAO..16..529G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Theories of solar activity.
Authors: Getling, A. V.; Tverskoi, B. A.
1980IzSSR..44.2560G Altcode:
A solar dynamo model is developed which takes into account the
relationship between global and local magnetic fields. It is shown that
the model can explain certain aspects of solar activity. In particular,
local magnetic fields intensified by convection cells can be the cause
of sunspot groups. The basic features of the dynamo model are in accord
with the features of the solar cycle: i.e., the model indicates changes
of the sign of background fields in polar regions in each 11-year cycle,
as well as a correlation between spot-forming activity and toroidal
fields (whose existence in subphotospheric layers is highly probable).
---------------------------------------------------------
Title: Standing acoustic-gravity waves in the high-latitude atmosphere
with allowance for the rotation of the earth
Authors: Alekseeva, L. M.; Getling, A. V.; Magnitskii, B. V.
1980Ge&Ae..20...72A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Model of an Oscillatory Hydromagnetic Dynamo. II
Authors: Getling, A. V.; Tverskoy, B. A.
1971Ge&Ae..11..330G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A model of an oscillating hydromagnetic dynamo. II.
Authors: Getling, A. V.; Tverskoj, B. A.
1971GeA....11..389G Altcode: 1971Ge&Ae..11..389G
No abstract at ADS
---------------------------------------------------------
Title: Model of an Oscillatory Hydromagnetic Dynamo. I
Authors: Getling, A. V.; Tverskoy, B. A.
1971Ge&Ae..11..176G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A model of an oscillating hydromagnetic dynamo. I.
Authors: Getling, A. V.; Tverskoj, B. A.
1971GeA....11..211G Altcode: 1971Ge&Ae..11..211G
No abstract at ADS
---------------------------------------------------------
Title: Criteria of thermal (overheat) instability of a transparent
radiating gas.
Authors: Getling, A. V.; Kuzmin, V. V.; Tverskoj, B. A.
1971DoSSR.196...71G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Fields in the Convection Cells of the Supergranulation
Zone.
Authors: Getling, A. V.
1969SvA....12..967G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solution of a class of magnetohydrodynamic problems with
strengthening of the magnetic field.
Authors: Getling, A. V.
1969DoSSR.187..301G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Possible Mechanism for Producing Sunspot Magnetic Fields.
Authors: Getling, A. V.; Tverskoi, B. A.
1968SvA....12..481G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Fields in the Convection Cells of the Supergranulation
Zone.
Authors: Getling, A. V.
1968AZh....45.1222G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Possible Mechanism for Producing Sunspot Magnetic Fields.
Authors: Getling, A. V.; Tverskoi, B. A.
1968AZh....45..606G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Propagation of Hydromagnetic Waves in a Slightly Inhomogeneous
Medium
Authors: Getling, A. V.
1967SvA....11..410G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Propagation of Hydromagnetic Waves in a Slightly Inhomogeneous
Medium
Authors: Getling, A. V.
1967AZh....44..513G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hydromagnetic Waves in a Nonisentropic Medium in the Presence
of a Gravitational Field
Authors: Getling, A. V.
1965SvA.....9..451G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hydromagnetic Waves in a Nonisentropic Medium in the Presence
of a Gravitational Field
Authors: Getling, A. V.
1965AZh....42..568G Altcode:
No abstract at ADS
