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Author name code: romashets
ADS astronomy entries on 2022-09-14
author:"Romashets, Eugene P."
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Title: Euler Potentials for Dungey Magnetosphere With Axisymmetric
Ring and Field-Aligned Currents
Authors: Romashets, E.; Vandas, M.
2022JGRA..12730171R Altcode:
Euler potentials are found for the magnetic field in the inner
magnetosphere, consisting of the Earth's dipole field, the Dungey term,
ring current (RC), and field-aligned current (FAC). The magnetic field
in this approximation is axially symmetric. One Euler potential for the
dipole, Dungey term, and RC is the same, while that for the magnetic
field induced by FAC is different and calculated in this work under
the condition that all four field contributions have the same second
Euler potential. The Euler potentials are determined for quiet, severe,
and superstorm geomagnetic conditions. The restriction of the model
is its axial symmetry, so changes of the location and intensity of
the currents with azimuthal angle are not explicitly present. On the
other hand, these parameters can be changed in the model, and one can
study local distributions.
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Title: Euler Potentials for the Earth Magnetic Field With
Field-Aligned Currents
Authors: Romashets, E.; Vandas, M.
2020JGRA..12528153R Altcode:
Euler potentials of the Earth's dipole magnetic field with field-aligned
currents are found. The results generalize ones obtained earlier for
systems of plane currents parallel to an ambient uniform magnetic
field. A real current system corresponding to an observed increase of
the magnetic field measured by a low-altitude spacecraft is used in
this modeling. Parameters of charged particle trajectories, such as
length and period, are determined for typical and strongly disturbed
conditions. A particle distribution function is calculated.
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Title: Comparison of Observed and Modeled Magnetic Fields in the
Earth's Magnetosheath
Authors: Vandas, M.; Němeček, Z.; Å afránková, J.; Romashets,
E. P.; Hajoš, M.
2020JGRA..12527705V Altcode:
Observations of the magnetic field for two passages through
the Earth's magnetosheath are used for comparison with two
simple models of the magnetosheath field that describe it as
a potential field. We apply the Kobel and Flückiger (1994, <A
href="https://doi.org/10.1029/94JA01778">https://doi.org/10.1029/94JA01778</A>)
model and the Romashets and Vandas (2019, <A
href="https://doi.org/10.1029/2006JA012072">https://doi.org/10.1029/2006JA012072</A>)
model complemented with the Jelínek et al. (2012, <A
href="https://doi.org/10.1029/2011JA017252">https://doi.org/10.1029/2011JA017252</A>)
empirical determination of the bow shock and magnetopause shapes and
positions. The models yield a satisfactory match to observations when
the positions and shapes of the bow shock and the magnetopause are
controlled by the instantaneous solar wind upstream dynamic pressure
and the instantaneous upstream interplanetary magnetic field vector
is taken into account.
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Title: Modeling of magnetic field in the magnetosheath using elliptic
coordinates
Authors: Vandas, M.; Romashets, E. P.
2019P&SS..17804692V Altcode:
Magnetosheath is a region between the bow shock and the
magnetopause. Knowledge of its magnetic field is important for many
studies, e.g., on reconnection processes at the magnetopause. Shape
of the magnetopause is often described as an ellipsoid in empirical
models. We derive here analytic model of the magnetosheath field
for case when both the magnetopause and the bow shock are axially
symmetric ellipsoids. The field is assumed to be potential and to
fulfill obvious conditions at the magnetopause (tangentiality) and
the bow shock (continuity of the normal component).
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Title: Interplanetary flux ropes of any twist distribution
Authors: Vandas, M.; Romashets, E. P.
2019A&A...627A..90V Altcode:
Context. Recent investigations indicate that the magnetic field
configuration in interplanetary flux ropes is in contrast with
the common magnetic field models that are used to fit them, namely
constant-alpha force-free fields, whose twist increases without limits
toward the flux-rope boundary. Therefore, magnetic field configurations
with a constant twist are now being employed in fits. <BR /> Aims:
Real flux ropes have varying twist. Therefore, analytical magnetic
field configurations with prescribed twist distributions are searched
for in cylindrical geometry. <BR /> Methods: Equations for the field
solenoidality and for the force-free condition are solved for case
when a twist profile is prescribed. <BR /> Results: A model of a
force-free magnetic field configuration with an arbitrarily given
twist distribution in a cylinder and its relative helicity per unit
length are presented. It is applied to a core-envelope model recently
suggested in studies of twist in magnetic clouds.
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Title: Analytic Modeling of Magnetic Field in the Magnetosheath and
Outer Magnetosphere
Authors: Romashets, E. P.; Vandas, M.
2019JGRA..124.2697R Altcode:
Magnetosheath is a region surrounded by the bow shock and the
magnetopause. According to statistical analysis, the boundaries can
be treated as nonconfocal paraboloids of rotations. It is not easy to
meet boundary conditions simultaneously on both sides. This problem
is treated here and its solution is presented. A linear combination of
harmonics that satisfy the condition on the magnetopause are selected
in order to meet the condition on the bow shock. The method allows
to calculate surface currents on the magnetopause. It is applied for
typical conditions in solar wind. A modified magnetic dipole is used as
a model of the magnetospheric field. Its modification is found by the
method of potentials using cylindrical harmonics. Magnetopause currents
are compared with results from a model with confocal paraboloids,
which is commonly used in literature.
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Title: Magnetic cloud fit by uniform-twist toroidal flux ropes
Authors: Vandas, M.; Romashets, E.
2017A&A...608A.118V Altcode:
Context. Detailed studies of magnetic cloud observations in the solar
wind in recent years indicate that magnetic clouds are interplanetary
flux ropes with a low twist. Commonly, their magnetic fields are
fit by the axially symmetric linear force-free field in a cylinder
(Lundquist field), which in contrast has a strong and increasing
twist toward the boundary of the flux rope. Therefore another field,
the axially symmetric uniform-twist force-free field in a cylinder
(Gold-Hoyle field) has become employed to analyze magnetic clouds. <BR
/> Aims: Magnetic clouds are bent, and for some observations, a
toroidal rather than a cylindrical flux rope is needed for a local
approximation of the cloud fields. We therefore try to derive an
axially symmetric uniform-twist force-free field in a toroid, either
exactly, or approximately, and to compare it with observations. <BR
/> Methods: Equations following from the conditions of solenoidality
and force-freeness in toroidally curved cylindrical coordinates were
solved analytically. The magnetic field and velocity observations of a
magnetic cloud were compared with solutions obtained using a nonlinear
least-squares method. <BR /> Results: Three solutions of (nearly)
uniform-twist magnetic fields in a toroid were obtained. All are exactly
solenoidal, and in the limit of high aspect ratios, they tend to the
Gold-Hoyle field. The first solution has an exactly uniform twist,
the other two solutions have a nearly uniform twist and approximate
force-free fields. The analysis of a magnetic cloud observation showed
that these fields may fit the observed field equally well as the
already known approximately linear force-free (Miller-Turner) field,
but it also revealed that the geometric parameters of the toroid might
not be reliably determined from fits, when (nearly) uniform-twist model
fields are used. Sets of parameters largely differing in the size of
the toroid and its aspect ratio yield fits of a comparable quality.
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Title: Toroidal Flux Ropes with Elliptical Cross Sections and Their
Magnetic Helicity
Authors: Vandas, M.; Romashets, E.
2017SoPh..292..129V Altcode:
Axially symmetric constant-alpha force-free magnetic fields in
toroidal flux ropes with elliptical cross sections are constructed in
order to investigate how their alphas and magnetic helicities depend
on parameters of the flux ropes. Magnetic configurations are found
numerically using a general solution of a constant-alpha force-free
field with an axial symmetry in cylindrical coordinates for a wide
range of oblatenesses and aspect ratios. Resulting alphas and magnetic
helicities are approximated by polynomial expansions in parameters
related to oblateness and aspect ratio. These approximations hold for
toroidal as well as cylindrical flux ropes with an accuracy better than
or of about 1%. Using these formulae, we calculate relative helicities
per unit length of two (probably very oblate) magnetic clouds and
show that they are very sensitive to the assumed magnetic cloud shapes
(circular versus elliptical cross sections).
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Title: Toroidal linear force-free magnetic fields with axial symmetry
Authors: Vandas, M.; Romashets, E.
2016A&A...585A.108V Altcode:
<BR /> Aims: Interplanetary magnetic flux ropes are often described
as linear force-free fields. To account for their curvature, toroidal
configurations must be used. The aim is to find an analytic description
of a linear force-free magnetic field of the toroidal geometry in
which the cross section of flux ropes can be controlled. <BR />
Methods: The solution is found as a superposition of fields given by
linear force-free cylinders tangential to a generating toroid. The
cylindrical field is expressed in a series of terms that are not
all cylindrically symmetric. <BR /> Results: We found the general
form of a toroidal linear force-free magnetic field. The field is
azimuthally symmetric with respect to the torus axis. It depends on
a set of coefficients that enables controlling the flux rope shape
(cross section) to some extent. By varying the coefficients, flux ropes
with circular and elliptic cross sections were constructed. Numerical
comparison suggests that the simple analytic formula for calculating
the helicity in toroidal flux ropes of the circular cross section
can be used for flux ropes with elliptic cross sections if the minor
radius in the formula is set to the geometric mean of the semi-axes
of the elliptic cross section.
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Title: Euler potentials for a geomagnetic field which includes the
Birkeland current
Authors: Romashets, E.; Vandas, M.
2015AGUFMSH11A2379R Altcode:
Pairs of Euler potentials, alpha and beta, are known for symmetric
configurations, like dipole field (Stern, 1964) or ring current
field (Schulz and Chen, 2008), but it is much more difficult to
model with this approach a combination of the Earth dipole field and
fields generated by the Birkeland and ring currents. In this work we
semi-analytically construct Euler potentials for this system and study
dynamics of charged particles in the vicinity of field aligned current
layers. Results of the calculations can be compared with spacecraft
FAC and charged particle observations.
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Title: Modeling of magnetic cloud expansion
Authors: Vandas, M.; Romashets, E.; Geranios, A.
2015A&A...583A..78V Altcode:
<BR /> Aims: Magnetic clouds are large interplanetary flux ropes
that propagate in the solar wind from the Sun and that expand during
their propagation. We check how magnetic cloud models, represented by
cylindrical magnetic flux ropes, which include expansion, correspond
to in situ observations. <BR /> Methods: Spacecraft measurements of
magnetic field and velocity components inside magnetic clouds with
clearly expressed expansion are studied in detail and fit by models. The
models include expanding cylindrical linear force-free flux ropes with
circular or elliptic cross sections. <BR /> Results: From the period of
1995-2009, 26 magnetic clouds were fit by the force-free model of an
expanding circular cylindrical flux rope. Expansion velocity profiles
qualitatively correspond to model ones in the majority of cases (81%)
and quantitatively in more than half of them (58%). In four cases an
elliptic cross section significantly improved a match between observed
and modeled expansion velocity profiles. <BR /> Conclusions: Analysis
of velocity components tests magnetic cloud models more strictly and
may reveal information on magnetic cloud shapes.
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Title: Comparative study of a constant-alpha force-free field and
its approximations in an ideal toroid
Authors: Vandas, M.; Romashets, E.
2015A&A...580A.123V Altcode:
<BR /> Aims: Magnetic clouds in the solar wind are large, loop-like
interplanetary flux ropes and may be locally approximated by a toroidal
flux rope. We compare approximate constant-alpha force-free fields
in an ideal toroid, used in magnetic cloud analysis, with the exact
solution, and examine their validity for low aspect ratios, which can
be found in magnetic clouds. The approximate toroidal solutions were
originally derived under the assumption of large aspect ratios. <BR />
Methods: Three analytic simple approximate constant-alpha force-free
solutions and the exact analytic solution are compared with respect
to magnetic field profiles, magnetic field magnitude distributions,
and magnetic helicity, with moderate (2-3) and very low (<2) aspect
ratios. <BR /> Results: The Miller & Turner (1981, Phys. Fluids,
24, 363) field and its modification (to satisfy exact solenoidality)
match the position of the magnetic axis in the toroidal flux rope
well even for very low aspect ratios. The same can be said for the
modified field and the position of the magnetic field maximum. When
calculating helicity of the toroidal flux rope, the Miller &
Turner field yields better results. A simple formula for magnetic
helicity derived from the Miller & Turner solution is valid with
a good accuracy even for very low aspect ratios. <BR /> Conclusions:
The Miller & Turner solution is a reasonable substitute for the
exact solution even for low aspect ratios (≈2).
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Title: Modeling of magnetic cloud expansion
Authors: Vandas, Marek; Romashets, Eugene; Geranios, Athanassios
2015TESS....121003V Altcode:
A model of an expanding elliptic cylindrical force-free flux
rope is used to interpret in-situ magnetic cloud observations by
spacecraft. Input quantities are measurements of magnetic field
components and velocity magnitudes along a spacecraft trajectory inside
a magnetic cloud. During the fitting procedure flux-rope geometric
parameters and cloud expansion velocity are determined. Observed
separate velocity components are not used in the fitting procedure,
but in radial (expansion) velocity construction which is compared to
model one to test our model more strictly. 24 magnetic clouds with
clearly expressed expansion were fitted by the model. Radial velocity
profiles qualitatively correspond to model ones in majority of cases
(83%), in more than half of them (58%) quantitatively.
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Title: An Ensemble Study of a January 2010 Coronal Mass Ejection
(CME): Connecting a Non-obvious Solar Source with Its ICME/Magnetic
Cloud
Authors: Webb, D. F.; Bisi, M. M.; de Koning, C. A.; Farrugia, C. J.;
Jackson, B. V.; Jian, L. K.; Lugaz, N.; Marubashi, K.; Möstl, C.;
Romashets, E. P.; Wood, B. E.; Yu, H. -S.
2014SoPh..289.4173W Altcode: 2014SoPh..tmp..114W
A distinct magnetic cloud (MC) was observed in-situ at the Solar
TErrestrial RElations Observatory (STEREO)-B on 20 - 21 January
2010. About three days earlier, on 17 January, a bright flare and
coronal mass ejection (CME) were clearly observed by STEREO-B,
which suggests that this was the progenitor of the MC. However, the
in-situ speed of the event, several earlier weaker events, heliospheric
imaging, and a longitude mismatch with the STEREO-B spacecraft made this
interpretation unlikely. We searched for other possible solar eruptions
that could have caused the MC and found a faint filament eruption
and the associated CME on 14 - 15 January as the likely solar source
event. We were able to confirm this source by using coronal imaging
from the Sun Earth Connection Coronal and Heliospheric Investigation
(SECCHI)/EUVI and COR and Solar and Heliospheric Observatory
(SOHO)/Large Angle and Spectrometric Coronograph (LASCO) telescopes
and heliospheric imaging from the Solar Mass Ejection Imager (SMEI)
and the STEREO/Heliospheric Imager instruments. We use several empirical
models to understand the three-dimensional geometry and propagation of
the CME, analyze the in-situ characteristics of the associated ICME, and
investigate the characteristics of the MC by comparing four independent
flux-rope model fits with the launch observations and magnetic-field
orientations. The geometry and orientations of the CME from the
heliospheric-density reconstructions and the in-situ modeling are
remarkably consistent. Lastly, this event demonstrates that a careful
analysis of all aspects of the development and evolution of a CME is
necessary to correctly identify the solar counterpart of an ICME/MC.
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Title: Euler potentials for two current sheets of nonzero thickness
along ambient uniform magnetic field
Authors: Vandas, M. I.; Romashets, E. P.
2014JGRA..119.2579V Altcode:
Euler potentials of two current sheets of nonzero thickness parallel
or antiparallel to each other and aligned with a uniform ambient
magnetic field are constructed analytically. The results generalize
ones obtained earlier for systems of two line currents and of two
current sheets with zero thickness. Conditions for particle mirroring
in this field structure are investigated. The results can be applied
to Birkeland currents.
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Title: Magnetic field disturbance in front of a super-sonic toroidal
magnetic cloud
Authors: Vandas, M.; Romashets, E. P.
2013AIPC.1539..283V Altcode:
An analytical model is presented of a fast moving magnetic cloud with a
bow shock ahead. The magnetic cloud is treated as a toroid. The model
describes magnetic field structure in the area between the bow shock
and the cloud's boundary (magnetosheath). The bow shock surface is
set a priori, determined by a number of parameters to be found when
interpreting a given event. Magnetic field is constructed from the
following constrains: the normal component is continuous across the
bow shock and absent on the boundary; the co-planarity condition is
fulfilled on the boundary.
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Title: Dynamics of a toroidal magnetic cloud: A semi-analytic approach
Authors: Vandas, M.; Romashets, E. P.
2013AIPC.1539..287V Altcode:
Magnetic clouds are a subset of coronal mass ejections with a
well-defined magnetic structure. They are modeled as toroids in
the present study and their dynamics in the inner heliosphere
is investigated under the influence of external forces, namely
gravitational, drag, and diamagnetic ones. The forces cause not only
changes in radial motion, but also a rotation of the toroid. The
diamagnetic force and its moment acting on the toroid in an
inhomogeneous magnetic field are expressed analytically. Resulting
equations of motion are solved numerically and typical solutions
are presented.
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Title: Modeling Irregularities in Solar Flux Ropes
Authors: Romashets, E.; Vandas, M.
2013SoPh..284..235R Altcode:
To model irregularities in the magnetic structure of solar flux
ropes or in interplanetary magnetic clouds, we propose the following
approach. A local irregularity in the form of a compact toroid is added
into a cylindrical linear force-free magnetic structure. The radius of
the cylinder and the small radius of the toroid are the same, since
the force-free parameter α is constant, that is, we have in total a
linear force-free configuration, too. Meanwhile, the large radius of
the toroid can be smaller. The effect of such modeling depends on the
aspect ratio of the compact toroid, its location and orientation, and
on its magnetic field magnitude in comparison with that of the cylinder.
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Title: Euler potentials for two current sheets along ambient uniform
magnetic field
Authors: Romashets, E. P.; Vandas, M.
2012JGRA..117.7221R Altcode: 2012JGRA..11707221R
Euler potentials of two current sheets of finite width parallel
or antiparallel to each other and aligned with a uniform ambient
magnetic field are constructed analytically. It is shown how analytic
treatment can be simplified using complex number analysis. Our approach
generalizes results obtained earlier for a system of two line currents
(wires). In the present solution the latter system represents a
limiting case, and differences between results from configurations
with sheets/wires are discussed. The solution is applied for study
of bouncing motion of particles trapped between mirror points of this
field structure. The result can be applied to Birkeland currents and
to laboratory plasma experiments.
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Title: Euler potentials of two line currents in an ambient uniform
magnetic field
Authors: Romashets, E.; Vandas, M.
2011AGUFMSM31A2080R Altcode:
Euler potentials of two line currents parallel or antiparallel
to each other and aligned with a uniform ambient magnetic field
are constructed. Explicit expressions for magnetic field lines are
found. The solution is used for study of bouncing motion of particles
trapped between mirror points of this field structure. The result
can be applied to Birkeland currents and also to laboratory plasma
experiments. The next step will be generalization of the approach
by modelling in the same manner magnetic field of of two zero-width
current sheets.
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Title: Expansion of magnetic clouds in the solar wind
Authors: Vandas, M.; Romashets, E.
2011AGUFMSH23A1943V Altcode:
Magnetic clouds are supposed to be large interplanetary flux
ropes propagating away from the Sun. Due to enhanced inner magnetic
pressure, they expand during their travel. We analyze magnetic cloud
observations using OMNI database and fit them by our models with
cylindrical or toroidal geometry. Comparison of the time-dependent
models with observations is shown for several cases with a detailed
discussion. In addition to magnetic field vectors, also velocity vectors
are modeled, and it is found that the radial velocity component behaves
as expected. In some cases, analysis of velocity components helps up
to determine, which model is more appropriate, cylindrical or toroidal
one, that is, if curvature plays a role.
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Title: Euler potentials for two line currents aligned with an ambient
uniform magnetic field
Authors: Romashets, E. P.; Vandas, M.
2011JGRA..116.9227R Altcode:
Euler potentials of two line currents parallel or antiparallel
to each other and aligned with a uniform ambient magnetic field
are constructed. Explicit expressions for magnetic field lines are
found. The solution is applied for study of bouncing motion of particles
trapped between mirror points of this field structure. The result can be
applied to Birkeland currents and also to laboratory plasma experiments.
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Title: Analytical description of electric currents in the
magnetosheath region
Authors: Romashets, E.; Vandas, M.; Veselovsky, I. S.
2010JASTP..72.1401R Altcode:
Volume currents in the magnetosheath region are calculated within the
framework of a new analytical model. Magnetic field structure in the
region is found, satisfying boundary conditions on the bow shock and the
magnetopause, and then volume currents are calculated using the Maxwell
equation. Surface bow shock and magnetopause currents are calculated,
too. Free parameters of the model are interplanetary magnetic field,
Mach number of the solar wind flow, distances to the bow shock and to
the magnetopause, and field compression at the magnetopause.
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Title: Magnetic clouds observed by STEREO
Authors: Romashets, E.; Vandas, M.; Howard, T.
2010AGUFMSH51C1693R Altcode:
We present the results from an attempt to merge in-situ magnetic
cloud reconstruction techniques with white light heliospheric imager
3-D reconstruction techniques. This has been accomplished to serve
two purposes: 1) to identify which features of interplanetary coronal
mass ejections (ICMEs) are most prominent in heliospheric imagers; 2)
to set some standards from which scientific revelations about ICMEs
may be achieved. We combine the magnetic cloud model of Romashets et
al. (A&A, 2007) with the elliptical force-free solution (Vandas
& Romashets, A&A, 2003) and the recently-developed Tappin-Howard
(TH) model (Tappin & Howard, SSR, 2009) for heliospheric imager
ICMEs. Along with an analysis of the kinematic evolution of the CME we
compare the 3-D structures of each of the features in the heliospheric
imagers with those of the magnetic cloud.
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Title: Correction to “Modeling of the magnetic field in the
magnetosheath region”
Authors: Romashets, E. P.; Vandas, M.
2010JGRA..11511220R Altcode:
No abstract at ADS
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Title: Magnetic Field Disturbance Produced by a Super-Sonic Toroidal
Magnetic Cloud
Authors: Vandas, Marek; Romashets, E.
2010AAS...21640608V Altcode: 2010BAAS...41..881V
Magnetic clouds are commonly interpreted as manifestations of large
interplanetary magnetic flux ropes. The flux ropes have a loop like
shape, i.e., they are curved, and they are approximated by a toroidal
shape in the present work. Magnetic clouds near Earth have impacts on
geomagnetic activity, the strongest influence on the magnetosphere
is usually caused by very fast, super-sonic clouds. To find a bow
shock surface and magnetic field structure in the area between the bow
shock and the cloud's boundary is a difficult task. Our approach to the
problem is to set a priori a bow shock surface, which is determined by a
number of parameters to be found when interpreting a given event. Then
magnetic field is constructed from the following constrains: the
normal component is continuous across the bow shock and absent on
the boundary. Additionally, there is also a co-planarity condition
to be fulfilled on the boundary. We shall show example calculations
and interpretations.
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Title: Evolution of Toroidal Magnetic Clouds
Authors: Romashets, Eugene; Vandas, M.
2010AAS...21640611R Altcode: 2010BAAS...41..881R
It was shown by numerical MHD simulation (Detman et al., JGR, 1991,
Vandas et al., JGR, 1997, 1998) that spherical spheromaks can evolve
into toroidal ones. In terms of toroid's aspect ratios the phenomenon
can be treated as transformation from less than unity value to greater
than unity. Until recently, there were no linear force-free solutions
known for very small aspect ratios. It was found by Romashets and
Vandas (A&A, 2009) and used for interpretation of solar flux ropes
instabilities (Romashets, Vandas, and Poedts, Solar Phys., 2010). The
shape is of a toroidal form, but it is not an ideal toroid, since
its cross-section is not circular. It is a tear drop shape for some
parameters. The solution of Tsuji (Phys. Fluids, 1991) is an ideal
toroid, on the other hand it is applicable only for aspect ratio more
than 1. We shall demonstrate that the magnetic structure in the range
0.5-2.5 transforms from a sphere into a toroid.
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Title: Modeling of Magnetic Field Disturbances in Sheath Region of
Interplanetary Magnetic Clouds of Elliptical Shapes
Authors: Vandas, M.; Romashets, E. P.
2010AIPC.1216..399V Altcode:
It is widely accepted that magnetic disturbances around fast
interplanetary magnetic clouds can play an important role in their
geo-effectiveness. An analytical solution for magnetic field in
the sheath region of a cylindrical magnetic cloud with an elliptical
cross-section is proposed. Upstream magnetic field can have an arbitrary
direction. Normal magnetic field components are conserved through the
bow shock with a high accuracy.
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Title: A new time-dependent ionosphere-magnetosphere coupling model:
Comparison of field-aligned currents against ST5 observations
Authors: Huang, T. S.; Romashets, E.; Le, G.; Wang, Y.; Slavin, J. A.
2010JASTP..72..369H Altcode:
By using Tsyganenko's model for the magnetosphere's magnetic field,
which links two hemispheres of the ionosphere, and adopting a practical
boundary condition for the electric potential around the polar cap, we
developed a new ionosphere-magnetosphere coupling model based on prairie
view dynamo code (PVDC). The new model takes the variations in solar
wind and interplanetary magnetic field, as well as the geomagnetic
activity, into account. Rather than the previous version of PVDC
that is useful only for quiet conditions, the new model enables to
calculate the electric potential and currents in the ionosphere and the
field-aligned current (FAC) off the ionosphere in quiet and disturbed
times. Comparison of the calculated FAC with the measurements of Space
Technology 5 (ST5) mission shows a good agreement.
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Title: Magnetic Clouds Fitted by a Constant-Alpha Force-Free Toroidal
Solution
Authors: Vandas, M.; Romashets, E. P.
2010AIPC.1216..403V Altcode:
Magnetic clouds have been defined as special regions in the solar wind
with higher magnetic field magnitude, lower proton temperature, and
large rotation of the magnetic field vector. In some cases, the rotation
exceeds 180° and it is interpreted as a signature that a magnetic
cloud/flux rope is curved. It corresponds to common understanding
that magnetic clouds are large interplanetary flux ropes, which have
loop-like shapes in the heliosphere. In such cases, magnetic clouds are
fitted by approximate linear force-free toroidal solutions (derived
for large aspect ratios). Here an exact constant-alpha force-free
toroidal solution is compared with approximate ones and it is found
a reasonable agreement even for low aspect ratios.
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Title: Modeling of Local Magnetic Field Enhancements within Solar
Flux Ropes
Authors: Romashets, E.; Vandas, M.; Poedts, S.
2010SoPh..261..271R Altcode: 2010SoPh..tmp....7R
To model and study local magnetic-field enhancements in a solar flux
rope we consider the magnetic field in its interior as a superposition
of two linear (constant α) force-free magnetic-field distributions,
viz. a global one, which is locally similar to a part of the
cylinder, and a local torus-shaped magnetic distribution. The newly
derived solution for a toroid with an aspect ratio close to unity is
applied. The symmetry axis of the toroid and that of the cylinder may or
may not coincide. Both the large and small radii of the toroid are set
equal to the cylinder's radius. The total magnetic field distribution
yields a flux tube which has a variable diameter with local minima and
maxima. In principle, this approach can be used for the interpretation
and analysis of solar-limb observations of coronal loops.
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Title: Application of a constant-alpha force-free field in a toroid
to fit magnetic clouds
Authors: Vandas, M.; Romashets, E.
2009AGUFMSH13B1514V Altcode:
Magnetic clouds are large interplanetary flux ropes. Commonly their
magnetic field configuration is fitted by a constant-alpha force-free
field in a cylinder (Lundquist solution). A characteristic feature of
magnetic clouds is a large rotation of the magnetic field vector. In
some cases, the rotation exceeds 180 degrees and it is interpreted
as a signature that the flux rope is curved. Here fits by the above
mentioned solution fail and another solution is needed, a constant-alpha
force-free solution in a toroid. A rather complex exact analytical
solution (Tsuji solution) is compared with approximate simpler ones
and fits of several magnetic clouds are presented.
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Title: Characteristics of magnetised plasma flow around stationary
and expanding magnetic clouds
Authors: Dalakishvili, G.; Poedts, S.; Fichtner, H.; Romashets, E.
2009A&A...507..611D Altcode:
Aims: Studies of interplanetary magnetic clouds have shown that the
characteristics of the region ahead of these objects, which are moving
away from the Sun in the solar wind, play a role in determining their
geo-efficiency, i.e. the kind and the degree of their effects on the
Earth environment. Therefore, our main goal is to model and study
the plasma parameters in the vicinity of interplanetary magnetic
clouds. <BR />Methods: To this end we present a model in which
the magnetic clouds are immersed in a magnetised plasma flow with a
homogeneous magnetic field. We first calculate the resulting distortion
of the external magnetic field and then determine the plasma velocity
by employing the frozen-in condition. <BR />Results: Subsequently,
the plasma density and pressure are expressed as functions of the
magnetic field and the velocity field. <BR />Conclusions: The plasma
flow parameters are determined by solving the time-independent ideal
MHD equations for both the stationary regime and for the case of an
expanding cylindrical magnetic cloud, thus extending previous results
that appeared in the literature.
---------------------------------------------------------
Title: On expansion of magnetic clouds in the solar wind
Authors: Vandas, M.; Geranios, A.; Romashets, E.
2009ASTRA...5...35V Altcode:
Magnetic clouds are supposed to be large interplanetary flux ropes
propagating away from the Sun. Due to enhanced inner magnetic pressure,
they expand during their travel. We have analyzed 21 magnetic clouds
from Wind observations and fitted them by our model. Comparison of
the time-dependent model with observations is shown for several cases
with a detailed discussion. The model describes behavior of compared
quantities satisfactorily. In addition to magnetic field vectors, also
velocity vectors were modeled and it was found that radial velocity
component behaves as expected. Analysis of velocity components put
models under a more strict test and yields more confidence into models
and derived magnetic cloud parameters.
---------------------------------------------------------
Title: Correction to “Force-free field inside a toroidal magnetic
cloud”
Authors: Romashets, E. P.; Vandas, M.
2009GeoRL..3612107R Altcode:
<A href="/journals/gl/gl0912/2009GL038341/">Abstract Available</A>
from <A href="http://www.agu.org">http://www.agu.org</A>
---------------------------------------------------------
Title: Linear force-free field of a toroidal symmetry
Authors: Romashets, E.; Vandas, M.
2009A&A...499...17R Altcode:
Context: Interplanetary flux ropes are often described by linear
force-free fields. To account for their curvature, toroidal
configurations valid for large aspect ratios are used. However,
in some cases, flux ropes need to be approximated by a toroid with
a low aspect ratio. <BR />Aims: The aim is to find an analytical
description of a linear force-free magnetic field of toroidal geometry,
not restricted to large aspect ratios. <BR />Methods: The solution is
found as a superposition of fields given by linear force-free cylinders
tangential to a generating toroid. <BR />Results: The obtained solution
describes toroidal flux ropes with reasonable shapes and magnetic field
values. The field is exactly linear force-free for arbitrary aspect
ratios. The new solution can be applied for solar and interplanetary
flux ropes, astrophysical objects, and laboratory plasma.
---------------------------------------------------------
Title: Modeling of the magnetic field in the magnetosheath region
Authors: Romashets, E. P.; Poedts, S.; Vandas, M.
2008JGRA..113.2203R Altcode:
In recent years, many advanced numerical techniques and codes have
been developed to calculate the location of the bow shock and the
magnetohydrodynamic parameters in the sheath region for various types
of inflows and obstacle shapes. Some of these methods are applicable
to the Earth's magnetosphere. On the other hand, only a few attempts
have been made to describe the problem analytically. In this paper,
we consider the discontinuities at the bow shock surface and at the
magnetopause as boundary conditions for the construction of the magnetic
field in the region between these two surfaces. The locations and the
(parabolic) shapes of the two surfaces are specified depending on the
solar wind parameters, viz. velocity, density, temperature, and magnetic
field. In the inner magnetosphere, i.e., below the magnetopause,
the magnetic field is considered as given by a modified dipole. The
solution is derived in parabolic coordinates.
---------------------------------------------------------
Title: Effects of the field-aligned currents and potential drops
in the magnetosphere on the coupling of the ionosphere with the
magnetosphere
Authors: Huang, T.; Romashets, E.
2007AGUFMSA51A0241H Altcode:
Models for the field-aligned currents and electric potential drops in
the magnetosphere are presented on the basis of observational data, and
are introduced in the upgraded Prairie View Dynamo Code, by adding extra
field- aligned current term and potential drop term into the Poisson
equation. The effects of the field-aligned currents and potential drops
on the coupling of the ionosphere with the magnetosphere are examined
under different solar wind and geomagnetic conditions for different
dates and diurnal times.
---------------------------------------------------------
Title: Electric potential in low latitude ionosphere: Influence of
neutral wind.
Authors: Romashets, E.; Huang, T.
2007AGUFMSA51A0240R Altcode:
Upgraded Prairie View Dynamo Code is utilized to study the dependence
of electric potential in low latitude ionosphere on the intensity of
neutral wind. As a matter of fact, the wind and Hall and Pedersen
conductances are the main internal parameters that determine the
electric potential in the ionosphere, in response to the changes in
polar cap caused by interplanetary magnetic field and solar wind plasma
variations, and by associated substorms in the magnetosphere. In
this work, we consider the solution of the Poisson equation for
electric potential, with boundary condition imposed on the division
line between the open and closed field lines of IGRF- 10+T89 model
field. The boundary conditions and results are dependent also on
universal time, since mutual orientation of the ionospheric and the
magnetospheric field is changing diurnally. The electric potential on
the boundary is set from Weimer's empirical model. We present results
of calculations of electric potential, for strong and moderate storms,
as well as for quiet times. For better accuracy it is more important
to set correctly neutral wind in quiet times, while in disturbed and
stormy ones the result becomes sensitive only to boundary conditions
and the ionospheric conductances distributions used in the calculation.
---------------------------------------------------------
Title: Plasma flows around magnetic obstacles in the solar wind
Authors: Romashets, E.; Poedts, S.
2007A&A...475.1093R Altcode:
Context: Recent numerical simulations and data analysis have shown
that the area in front of magnetic clouds is very important from the
point of view of its geo-efficiency. This area has very complicated
magnetic and plasma structures. It is necessary to describe the plasma
parameter distributions in the vicinity of magnetic clouds and other
stable structures in the solar wind. Assuming that the magnetic field
around the object is determined or measured, the velocity field is
calculated from the frozen-in equation, while the density and pressure
are given by explicit formulas expressing P and ρ as functions of only
{B} and {V}. An alternative method is to solve the full system of MHD
equations numerically, but even in this case the analytical estimates
determined here are also useful when formulating initial and boundary
conditions. <BR />Aims: The aim is to treat the region in front of
interplanetary magnetic clouds in terms of analytical functions for
a detailed consideration of general phenomena and also for particular
phenomena of specific clouds. <BR />Methods: First, the velocity and
magnetic field distributions satisfying the boundary conditions and
the frozen-in condition are determined. Next, the plasma density and
pressure are calculated. <BR />Results: The three-dimensional plasma
parameter distributions are found for the general case of an inclined
cylindrical cloud.
---------------------------------------------------------
Title: Modeling of the three-dimensional motion of toroidal magnetic
clouds in the inner heliosphere
Authors: Romashets, E.; Vandas, M.; Poedts, S.
2007A&A...466..357R Altcode:
Context: The motion of a magnetic cloud through the heliosphere
is governed by three main forces, viz. the diamagnetic force, the
drag force, and gravity. Some recently derived formulas enabling the
calculation of the ambient magnetic field around a toroidal magnetic
cloud are applied to calculate the diamagnetic force acting on the
cloud and to determine the cloud dynamics. <BR />Aims: The aim is to
determine the three dimensional velocity profiles and the trajectory
of the magnetic cloud, as well as the evolution of the orientation of
the cloud axis from the calculated moment of the force. <BR />Methods:
The method applied in this study consists of three steps. First, the
r-component of the magnetic field at r=2.5 R<SUB>s</SUB> is derived
from a spherical harmonic analysis. Next, the field distribution in the
entire heliosphere, including the spiral structure, is reconstructed
in a way that is consistent with this boundary condition at r=2.5
R<SUB>s</SUB> as well as with actual measurements at 1 AU. Then,
a toroid is launched at a point obtained from solar observations of
a specific event and the initial size, orientation, and velocity of
this toroid is estimated from these observational data as well. <BR
/>Results: The three dimensional velocity profiles and the trajectory of
the magnetic cloud, as well as the evolution of the orientation of the
cloud axis have been determined for a toroidally shaped cloud moving in
the interplanetary medium taking into account a spiral magnetic field.
---------------------------------------------------------
Title: Field-aligned currents calculated based on the upgraded
Prairie View Magnetosphere- ionosphere Coupling Model
Authors: Romashets, E.; Huang, T.
2006AGUFMSM11A0303R Altcode:
Using the experimental magnetic field and the newly defined Eular
Potentials, we upgraded Prairie View Magnetosphere-ionosphere
Coupling Model that was originally created in the frame of IGRF. The
electric fields in the ionosphere and the field-aligned currents in the
magnetosphere are calculated with the upgraded magnetosphere-ionosphere
coupling model, and a preliminary comparison of the calculations with
the measurements from ST5 will be presented.
---------------------------------------------------------
Title: Discontinuity of Euler potentials and particle drift motion
in a magnetic field with field- aligned currents
Authors: Huang, T.; Romashets, E.; Petrov, Y.
2006AGUFMSM11B0314H Altcode:
In the presence of field-aligned currents, a magnetic field may have no
continuous Euler potentials alpha and beta though physics quantities B
and A are continuous. As a consequence, the standard canonic equations
for particle drift motion may fail to apply in the area adjacent to
the alpha and beta-discontinuity area. As an example, we inspect the
Euler potentials and the particle drift motion in a magnetic field
resulted from combining a 2D dipole with the field produced by two
circular currents.
---------------------------------------------------------
Title: On the Motion of Toroidal Magnetic Clouds in the Solar Corona
and Inner Heliosphere
Authors: Romashets, E.; Vandas, M.; Poedts, S.
2006ESASP.617E.144R Altcode: 2006soho...17E.144R
No abstract at ADS
---------------------------------------------------------
Title: Solar-terrestrial storm of November 18 20, 2003. 1. Near-Earth
disturbances in the solar wind
Authors: Ivanov, K. G.; Romashets, E. P.; Kharshiladze, A. F.
2006Ge&Ae..46..275I Altcode:
The structure, configuration, dynamics, and solar sources of the
near-Earth MHD disturbance of the solar wind on November 20, 2003,
is considered. The disturbances of October 24 and November 22 after
flares from the same AR 10484 (10501) are compared. The velocity
field in the leading part of the sporadic disturbance is for the first
time studied in the coordinate system stationary relative to the bow
shock. A possible scenario of the physical processes in the course
of this solar-terrestrial storm is discussed in comparison with the
previously developed scenario for the storm of July 15, 2000. It has
been indicated that (1) the near-Earth disturbance was observed at the
sector boundary (HCS) and in its vicinities and (2) the disturbance
MHD structure included: the complicated bow shock, wide boundary layer
with reconnecting fields at a transition from the shock to the magnetic
cloud, magnetic cloud with a magnetic cavity including packed substance
of an active filament, and return shock layer (supposedly). It has been
found out that the shock front configuration and the velocity field
are reproduced at an identical position of AR and HCS relative to the
Earth on November 20 and 24. It has been indicated that the maximal
magnetic induction in the cloud satisfied the condition B <SUB>m</SUB> =
(8π n <SUB>1</SUB> m <SUB>p</SUB>)<SUP>1/2</SUP>( D - NV<SUB>1</SUB>),
i.e., depended on the dynamic impact on the cloud during all three
storms [Ivanov et al., 1974]. When the disturbance was related to solar
sources, the attention has been paid to the parallelism of the axes of
symmetry of the active filament, transient coronal hole, coronal mass
ejection, zero line of the open coronal field (HCS), and the axis of
the near-Earth magnetic cloud: the regularity previously established in
the scenario of the storm of July 15, 2000 [Ivanov et al., 2005]. It
has been indicated that the extremely large B <SUB>m</SUB> value in
the cloud of October 20 was caused by a strong suppression of the
series of postflare shocks reflected from the heliospheric streamer.
---------------------------------------------------------
Title: Comparison of force-free flux rope models with observations
of magnetic clouds
Authors: Vandas, M.; Romashets, E. P.; Watari, S.; Geranios, A.;
Antoniadou, E.; Zacharopoulou, O.
2006AdSpR..38..441V Altcode: 2004AdSpR..38..441V
Recently, we have found a force-free solution inside an elliptic
cylinder for magnetic cloud models. For a diminishing oblateness, the
solution tends to the widely used Lundquist constant-alpha force-free
solution inside a circular cylinder. The solution may include effects
of a flux rope expansion. A comparison of this new solution and
the Lundquist solution with magnetic cloud observations is done for
magnetic clouds with flat magnetic field magnitude profiles. In such
cases, oblateness improves fits of magnetic field magnitude profiles
in clouds significantly.
---------------------------------------------------------
Title: Field configuration around large flux ropes in the solar
corona and inner heliosphere
Authors: Romashets, E. P.; Vandas, M.
2006AdSpR..38..447R Altcode:
Our recently developed method, how to determine analytically a
magnetic field distribution in the vicinity of a large flux rope,
is used to describe field disturbances for few typical examples. The
disturbed field is treated as a combination of a pre-existing one and
an additional current-free part.
---------------------------------------------------------
Title: Field Structure Around a Super-Sonic Interplanetary Magnetic
Clouds with Forward and Reverse Shocks
Authors: Romashets, E.; Vandas, M.
2005ESASP.592..763R Altcode: 2005ESASP.592E.156R; 2005soho...16E.156R
No abstract at ADS
---------------------------------------------------------
Title: Plasma Flows Inside Magnetic Clouds
Authors: Vandas, M.; Romashets, E.; Watari, S.
2005ESASP.592..775V Altcode: 2005soho...16E.159V; 2005ESASP.592E.159V
No abstract at ADS
---------------------------------------------------------
Title: Magnetic clouds of oblate shapes
Authors: Vandas, M.; Romashets, E.; Watari, S.
2005P&SS...53...19V Altcode:
There is a growing evidence that cross-sections of magnetic clouds
(interplanetary magnetic flux ropes) have oblate shapes. This follows
from theoretical results as well as from interpretation of in situ
measurements. MHD simulations show that a leading part of a cloud,
an apex, has an oblate cross-section, and this may be very extreme
in some cases. Interpretations of magnetic cloud observations by
non-force-free models, multispacecraft observations, and analyses of the
cloud bow shock stand-off distance also indicate that a cross-section
of some magnetic clouds is oblate. Recently we have found a force-free
solution with constant alpha in an elliptic cylinder. It is a direct
generalization of the widely used Lundquist constant-alpha force-free
solution inside a circular cylinder. Comparisons of this solution and
the Lundquist solution with observations are shown.
---------------------------------------------------------
Title: Solar origins of intense geomagnetic storms in 2002 as seen
by the CORONAS-F satellite
Authors: Panasenco, O.; Veselovsky, I. S.; Dmitriev, A. V.; Zhukov,
A. N.; Yakovchouk, O. S.; Zhitnik, I. A.; Ignat'ev, A. P.; Kuzin,
S. V.; Pertsov, A. A.; Slemzin, V. A.; Boldyrev, S. I.; Romashets,
E. P.; Stepanov, A.; Bugaenco, O. I.; Bothmer, V.; Koutchmy, S.;
Adjabshirizadeh, A.; Fazel, Z.; Sobhanian, S.
2005AdSpR..36.1595P Altcode:
We analyze solar origins of intense geomagnetic perturbations recorded
during 2002. All of them were related to coronal mass ejections
(CMEs). The initiation of CMEs was documented using the SPIRIT
instrument (SPectrohelIographic Soft X-Ray Imaging Telescope) onboard
the CORONAS-F satellite. Monochromatic full Sun images taken in the Mg
XII doublet at 8.418 and 8.423 Å showed the appearance of free energy
release sites at altitudes up to 0.4 solar radii. CMEs were initiated
at these sites and propagated in interplanetary space under appropriate
local conditions including the geometry of the magnetic fields.
---------------------------------------------------------
Title: New Force-Free Models of Magnetic Clouds
Authors: Vandas, M.; Romashets, E. P.; Watari, S.
2005HiA....13..133V Altcode:
Magnetic clouds are thought to be large flux ropes propagating through
the heliosphere. Their twisted magnetic fields are mostly modeled
by a constant-alpha force-free field in a circular cylindrical flux
rope. However the interplanetary flux ropes are three dimensional
objects. In reality they possibly have a curved shape and an oblate
cross section. Recently we have found two force-free models of flux
ropes which takes into account the mentioned features. These are (i)
a constant-alpha force-free configuration in an elliptic flux rope and
(ii) a force-free field in a toroid with arbitrary aspect ratio. Their
nature will be described and their ability to fit observed unusual
magnetic field profiles will be demonstrated.
---------------------------------------------------------
Title: Magnetic storm cessation during sustained northward IMF
Authors: Veselovsky, I. S.; Bothmer, V.; Cargill, P.; Dmitriev, A. V.;
Ivanov, K. G.; Romashets, E.; Zhukov, A. N.; Yakovchouk, O. S.
2005AdSpR..36.2460V Altcode:
Times of sustained strong northward IMF can interrupt the magnetic
storm development and lead to lower levels of geomagnetic activity
for many hours. During 1997-2000 we have found two events of this
kind observed on November 8, 1998 and October 13, 2000. In both
cases, the storms started as usual after arrival of ejecta with a
southward IMF component from the Sun to the Earth, but ceased after
several hours due to the onset of sustained northward IMF leading
to the faster recovery process. After the passage of this so-called
positive domain, the storm development started again. The heliospheric
magnetic field intensity remained enhanced and nearly constant. The
solar origins of the geomagnetic storm interruptions have been
investigated. Tentatively they may be related to strong nonlinear
Alfvйn type solitary waves excited by non-stationary coronal current
variations with a characteristic time-scale of about a day.
---------------------------------------------------------
Title: Force-free magnetic field in a cylindrical flux rope without
a constant alpha
Authors: Romashets, E.; Vandas, M.
2005AdSpR..36.2268R Altcode:
It is generally assumed that magnetic fields inside interplanetary
magnetic clouds and flux ropes in the solar photosphere are
force-free. In order to model such fields, the solution of rot B = αB
is commonly used where α = const. But comparisons of this solutions
with observations show significant difference. To treat this problem,we
examine the solutions with α=α<SUB>0</SUB>/(1+r/r<SUB>0</SUB>).
---------------------------------------------------------
Title: Asymmetric magnetic field inside a cylindrical flux rope
Authors: Romashets, E. P.; Vandas, M.
2005AdSpR..35.2167R Altcode:
In order to consider an asymmetric field distribution inside
a cylindrical tube with a circular cross section, with the field
magnitude maximum reached at a point different from the geometrical
centre of the tube, we propose a new solution obtained in bi-cylindrical
coordinates. If the parameter α of the system is very large, the
solution approaches the well known symmetric Lundquist solution. The
new solution models a field magnitude shift due to relative motion of
the cylinder and the ambient solar wind. If the cylinder is moving much
faster than the ambient medium, its field maximum is shifted forward,
otherwise it is shifted in the opposite direction.
---------------------------------------------------------
Title: Modelling of magnetic field near the magnetopause
Authors: Romashets, E.; Vandas, M.; Nagatsuma, T.
2005P&SS...53..127R Altcode:
There are many reliable phenomenological and theoretical methods
to model conditions on the outer and inner sides of magnetopause
during quiet and disturbed periods. We present here, in this paper,
an approximate analytical description of magnetic field distribution
between the bow shock and the magnetopause, and on the inner side of
the magnetopause. The approach is the following: (i) the field near
the Earth's surface is equal to one of an inclined dipole located
at the center; (ii) on the magnetopause the normal component of the
magnetic field is zero; (iii) on the bow shock the normal component is
continuous. The solution, obtained in coordinates of a paraboloid of
rotation, is a function of dipole orientation and distance to the bow
shock, which is determined by the solar wind parameters. Magnetic fields
induced by the ring current are also considered. The intensity of the
ring current is determined by a magnetic field jump at the magnetopause.
---------------------------------------------------------
Title: Magnetic Field Configuration Around Large Flux Ropes
Authors: Romashets, E.; Vandas, M.
2005IAUS..226..428R Altcode:
An analytical method is used to model a magnetic field distribution in
the vicinity of a large interplanetary or solar flux rope. The field is
a sum of the pre-existing one and an additional current-free part. An
example using real data is shown.
---------------------------------------------------------
Title: Solar and Heliospheric Phenomena in October-November 2003:
Causes and Effects
Authors: Veselovsky, I. S.; Panasyuk, M. I.; Avdyushin, S. I.;
Bazilevskaya, G. A.; Belov, A. V.; Bogachev, S. A.; Bogod, V. M.;
Bogomolov, A. V.; Bothmer, V.; Boyarchuk, K. A.; Vashenyuk, E. V.;
Vlasov, V. I.; Gnezdilov, A. A.; Gorgutsa, R. V.; Grechnev,
V. V.; Denisov, Yu. I.; Dmitriev, A. V.; Dryer, M.; Yermolaev,
Yu. I.; Eroshenko, E. A.; Zherebtsov, G. A.; Zhitnik, I. A.;
Zhukov, A. N.; Zastenker, G. N.; Zelenyi, L. M.; Zeldovich,
M. A.; Ivanov-Kholodnyi, G. S.; Ignat'ev, A. P.; Ishkov, V. N.;
Kolomiytsev, O. P.; Krasheninnikov, I. A.; Kudela, K.; Kuzhevsky,
B. M.; Kuzin, S. V.; Kuznetsov, V. D.; Kuznetsov, S. N.; Kurt, V. G.;
Lazutin, L. L.; Leshchenko, L. N.; Litvak, M. L.; Logachev, Yu. I.;
Lawrence, G.; Markeev, A. K.; Makhmutov, V. S.; Mitrofanov, A. V.;
Mitrofanov, I. G.; Morozov, O. V.; Myagkova, I. N.; Nusinov, A. A.;
Oparin, S. N.; Panasenco, O. A.; Pertsov, A. A.; Petrukovich, A. A.;
Podorol'sky, A. N.; Romashets, E. P.; Svertilov, S. I.; Svidsky, P. M.;
Svirzhevskaya, A. K.; Svirzhevsky, N. S.; Slemzin, V. A.; Smith, Z.;
Sobel'man, I. I.; Sobolev, D. E.; Stozhkov, Yu. I.; Suvorova, A. V.;
Sukhodrev, N. K.; Tindo, I. P.; Tokhchukova, S. Kh.; Fomichev, V. V.;
Chashey, I. V.; Chertok, I. M.; Shishov, V. I.; Yushkov, B. Yu.;
Yakovchouk, O. S.; Yanke, V. G.
2004CosRe..42..435V Altcode:
We present new observational data on the phenomena of extremely
high activity on the Sun and in the heliosphere that took place
in October-November 2003. A large variety of solar and heliospheric
parameters give evidence that the interval under consideration is unique
over the entire observation time. Based on these data, comparing them
with similar situations in the past and using available theoretical
concepts, we discuss possible cause-and-effect connections between
the processes observed. The paper includes the first results and
conclusions derived by the collaboration “Solar Extreme Events-2003”
organized in Russia for detailed investigations of these events. As a
result of our consideration, it is beyond question that the physical
causes of solar and heliospheric phenomena in October-November 2003
are not exclusively local and do not belong only to the active regions
and solar atmosphere above them. The energy reservoirs and driving
forces of these processes have a more global nature. In general, they
are hidden from an observer, since ultimately their sources lie in
the subphotospheric layers of the Sun, where changes that are fast
and difficult to predict can sometimes take place (and indeed they
do). Solar flares can serve as sufficiently good tracers of these sudden
changes and reconstructions on the Sun, although one can still find
other diagnostic indicators among the parameters of magnetic fields,
motions of matter, and emission characteristics.
---------------------------------------------------------
Title: The modelling of the field structure in the day and night
side parts of the magnetosphere
Authors: Romashets, E.; Vandas, M.; Nagatsuma, T.
2004cosp...35...39R Altcode: 2004cosp.meet...39R
The main contributors to the global magnetospheric field are: i) the
central dipole; ii) the ring current; iii) the tail current; iiii)
currents on the magnetopause. In order to take into account all four
parts in the calculation one can use the following approach: at first to
find fields induced by i)-iii) and then to modify these fields in such
a way which excludes the normal component on the magnetopause. This
modification is equivalent to introducing the magnetopause surface
currents. The intensities of the ring and tail currents are determined
by the jump of tangential component at the sub-sonic point of the
magnetopause. The three-dimensional magnetospheric field distribution
is governed by a few main parameters: a) dipole orientation (season);
b) distances to the magnetopause and to the bow shock - functions
of velocity and density of solar wind; c) intensity and direction of
interplanetary magnetic field. Having measurements on b) and c) the
proposed model gives field distribution in the entire magnetosphere
and in the magnetosheath.
---------------------------------------------------------
Title: Comparison of Force-Free Flux Rope Models with Observations
of Magnetic Clouds
Authors: Vandas, M.; Romashets, E. P.; Watari, S.; Geranios, A.
2004cosp...35.2160V Altcode: 2004cosp.meet.2160V
In recent years we have found force-free solutions inside an elliptic
cylinder (A&A, 2002) and inside a toroid (GRL, 2003) for magnetic
cloud models. The solutions tend to the widely used Lundquist
constant-alpha force-free solution inside a circular cylinder in
their appropriate limits. The both solutions may include effects of a
flux rope expansion. Comparisons of these solutions and the Lundquist
solution with magnetic cloud observations will be done for a larger
set of magnetic clouds and it will be investigated, how oblateness and
curvature of flux ropes, in addition to expansion, can improve model
fits. We shall also examine, how the modelled flux rope expansion
is consistent with three dimensional plasma flows inside observed
magnetic clouds.
---------------------------------------------------------
Title: Magnetic field inside asymmetric cylindrical flux ropes
Authors: Romashets, E.; Vandas, M.
2004cosp...35...38R Altcode: 2004cosp.meet...38R
In order to consider an asymmetric field distribution inside a
cylindrical tube with a circular cross section, with the field's
magnitude maximum reached in a point different from the geometrical
center of the tube, we propose a new solution obtained in so-called
bi-cylindrical coordinates. If the parameter alpha of the system
is very large, then the solution approaches the well known symmetric
Lundquist solution. The new solution models a field magnitude shift due
to relative motion of the cylinder and the ambient solar wind. If the
cylinder is moving much faster than the ambient medium, its field's
maximum is shifted forward, otherwise - in opposite direction. Quiet
clouds, with velocities of ambient solar wind may have a symmetric
structure. We present interplanetary clouds interpretation based on
the new solution. There are criteria for such clouds: 1) asymmetric
profile; 2) negligible expansion; 3) nearly central crossing.
---------------------------------------------------------
Title: Field configuration around and inside large flux ropes in
the solar corona and inner heliosphere
Authors: Romashets, E.; Vandas, M.
2004cosp...35...60R Altcode: 2004cosp.meet...60R
We shall present a method how to describe analytically a magnetic
field distribution in the vicinity and within a large interplanetary
flux rope with its roots on the Sun. The field is nearly force-free
inside the loop and current-free outside it. To construct a solution
for case of an arbitrarily shaped axial line of the tube (which can be
non-planar), as well as for arbitrary thickness of the tube (which is
a function of the heliodistance), the solutions for a field drapery
around a toroid (Vandas et al. [A&A, 2004]) and for a force-free
field inside a toroid (Romashets and Vandas [GRL, 2003]) are used
locally in their magnetic vector potential representations. Such an
approach ensures that the field has no normal component to the boundary
of the loop. Implications of this solution for interpretation of real
magnetic cloud observations will be given and some examples shown.
---------------------------------------------------------
Title: Toroidal flux ropes
Authors: Romashets, E.; Vandas, M.
2004IAUS..223..395R Altcode: 2005IAUS..223..395R
We present a method how to describe analytically a magnetic field
distribution in the vicinity of a large interplanetary flux rope. The
field consists of the pre-existing one and an additional current-free
part. This work was supported by INTAS grant 03-51-6206, AV CR project
S1003006, and RFBR grant 03-02-16340.
---------------------------------------------------------
Title: Potential magnetic fields around flux ropes
Authors: Vandas, M.; Romashets, E. P.; Watari, S.
2003A&A...412..281V Altcode:
A method of calculation of potential magnetic fields around cylindrical
and toroidal flux ropes is presented. The flux rope has an arbitrary
orientation with respect to ambient field. The problem is solved
analytically. Expressions for the magnetic field components, diamagnetic
force, and its moment are found. Results obtained can be used for
estimations of magnetic forces in systems where magnetic flux ropes
and potential fields coexist, e.g., in the solar corona.
---------------------------------------------------------
Title: Force-free field inside a toroidal magnetic cloud
Authors: Romashets, E. P.; Vandas, M.
2003GeoRL..30.2065R Altcode: 2003GeoRL..30tSSC8R
An analytical solution of force-free magnetic fields inside a toroid
with an arbitrary aspect ratio was found. A scalar equation was
derived which when solved gives the heart of the solution of the
vector field in toroidal coordinates, in closed form in terms of
hypergeometric functions. The solution can be used for interpretation
of magnetic cloud measurements in the interplanetary space. If it is
assumed that a magnetic cloud is a large loop with roots at the Sun,
then its part can be locally treated as a part of a toroid. The former
solution by Miller and Turner [1981] was limited only to larger aspect
ratios. The presented solution coincides with the Lundquist [1950]
one for cylindrical clouds in case of a very large aspect ratio torus.
---------------------------------------------------------
Title: Fields around magnetic clouds: comparison between theoretical
solutions and measurements
Authors: Vandas, M.; Watari, S.; Romashets, E. P.
2003ESASP.535..587V Altcode: 2003iscs.symp..587V
Magnetic clouds are known as a possible source of strong geomagnetic
storms due to a large southward B<SUB>z</SUB> component located in their
interior. Magnetic clouds as magnetically isolated bodies also disturb
the ambient magnetic field around them during their propagation. This
draped field may contain significantly large southward B<SUB>z</SUB>
component and thus it may also cause a geomagnetic storm. Therefore
the knowledge on the draped field is important for space weather
predictions. Theoretical external magnetic field profiles (assumed to
be potential) are compared with real measurements of magnetic fields
near magnetic clouds for several events. From 15 analyzed cases about
one half was found to be consistent with the model, one fifth not, and
remaining cases were not able to be evaluated due to large fluctuations.
---------------------------------------------------------
Title: Interaction Of Magnetic Clouds In The Inner Heliosphere
Authors: Romashets, E.; Cargill, P.; Schmidt, J.
2003AIPC..679..794R Altcode:
A method of potentials has been used in the past for the calculation of
the force acting on isolated magnetic bodies in solar corona and inner
heliosphere, where large gradients of magnetic pressure exist. Since
recent observations showed that coronal mass ejections (CME) can leave
the Sun more frequently than was expected before 1995, it is clear that
interactions between CMEs can play important role in the formation of
geo-effective structures near the Earth's orbit. We present here an
evaluation of two interacting CMEs and the field distribution around
them, using potential solution in bi-cylindrical coordinates.
---------------------------------------------------------
Title: Solar Wind Disturbances and Their Sources in the EUV Solar
Corona
Authors: Zhukov, A. N.; Veselovsky, I. S.; Clette, F.; Hochedez,
J. -F.; Dmitriev, A. V.; Romashets, E. P.; Bothmer, V.; Cargill, P.
2003AIPC..679..711Z Altcode:
We investigate possible links between the activity manifestations in the
solar corona and conditions in the solar wind. For the reduction of this
immense task we have selected 206 events in the solar wind in 1997 -
2000 corresponding to geomagnetic events with Ap > 20 (compiled into
a database at <emph TYPE="46">http://alpha.sinp.msu.ru/apev). Up
to now, 24 events during the epoch of low solar activity (January 1997 -
January 1998) are investigated. The solar wind conditions monitored by
ACE and WIND spacecraft were traced back to the solar corona observed
by SOHO/EIT. The search for coronal signatures which are probably
associated with the disturbed solar wind conditions was performed. The
coronal sources of these 24 events are identified, namely: eruptions in
active regions, filament eruptions and coronal holes. It is shown that
halo and partial halo CMEs observed within the SOHO/LASCO sensitivity
limits are not necessary indicators of Earth-directed eruptions, and
coronal EUV dimmings can be used as a complementary indicator. We also
found that a structure now conventionally called a “sigmoid” cannot
be represented as a single S-shaped loop (flux tube), but exhibits an
assembly of many smaller structures. It could be formed and destroyed
via eruptions.
---------------------------------------------------------
Title: Interplanetary magnetic clouds of toroidal shapes
Authors: Romashets, E. P.; Vandas, M.
2003ESASP.535..535R Altcode: 2003iscs.symp..535R
Analytical solutions of force-free equation inside a toroid are
derived for constant and non-constant alpha. They can be used for
interpretation of solar flux ropes and interplanetary magnetic
clouds. The solution with non-constant alpha is valid for arbitrary
aspect ratio torus. Magnetic fiels inside toroids with low aspect
ratios give very high ratios B<SUB>max</SUB>/B<SUB>min</SUB> > 10,
while for high aspect ratios this value is about 2.
---------------------------------------------------------
Title: Modeling magnetic fields around magnetic clouds of different
geometries
Authors: Vandas, M.; Romashets, E. P.; Watari, S.
2003ESASP.535..583V Altcode: 2003iscs.symp..583V
In-situ observations show that the maximum strength of the magnetic
field draping around a magnetic cloud is of the order of the field
inside the cloud. We investigate theoretically how this strength
depends on geometrical parameters of magnetically closed bodies like
cylinders, spheroids, or toroids. These bodies are inserted into an
intially homogeneous ambient magnetic field and then a distortion of the
external field is calculated under the assumption that the normal field
component vanishes at the boundary of the body. If the external field
is supposed to be potential, then the maximum increase in the magnetic
field magnitude is around 2 times. Non-potential fields yield larger
maxima and such increases may explain a trigger of a strong geomagnetic
storm only by the B<SUB>z</SUB> component of the draped field, even
if there is no strong B<SUB>z</SUB> component inside the cloud.
---------------------------------------------------------
Title: Propagation of a Toroidal Magnetic Cloud through the Inner
Heliosphere
Authors: Romashets, Eugene; Vandas, Marek
2003AIPC..679..180R Altcode:
An analytical solution for a potential magnetic field with arbitrary
intensity around a toroidal magnetic cloud has been found. The
background external field may have a gradient. The solution is used for
calculation of magnetic cloud propagation. Obtained velocity profiles
show a good agreement with in situ observations near the Earth's orbit.
---------------------------------------------------------
Title: How to forecast geomagnetic storms reliably - The
characteristics of storms in the rising phase of solar cycle 23
Authors: Bothmer, V.; Cargill, P.; Dmitriev, A.; Romashets, E.;
Veselovsky, I.; Zhukov, A.
2003EAEJA.....2018B Altcode:
The solar wind input parameters were studied for geomagnetic disturbed
days in which Ap exceeded its average value by using plasma and magnetic
field data from various near-Earth satellites. More than 270 events
occurred during the time-period 1997 to 2002. The interplanetary
and solar characteristics of these events have been summarised
at http://alpha.sinp.msu.ru/apev. A unique identification of the
corresponding solar sources was not possible for all of the events,
but in general they could be classified based on SOHO white-light and
EUV observations taken by the LASCO/EIT telescopes into disturbances
caused by coronal hole flows and coronal mass ejections or interactions
between them. Compression regions caused by stream interactions
effects including compressed Alfven-waves are also an important
cause of enhanced geomagnetic activity. Our results imply that the
forecast of an individual storms does not only require sufficient
real-time observations of the solar corona, but as well modelling of
the heliospheric situation, finally taking into account a seasonal
dependence of the coupling efficiency of the IMF with the Earth’s
magnetosphere. The work is supported by grants INTAS-ESA 99-00727 and
INTAS 00-752 .
---------------------------------------------------------
Title: Solar wind disturbances and their sources in the EUV solar
corona
Authors: Zhukov, A.; Veselovsky, I.; Bothmer, V.; Dmitriev, A.;
Clette, F.; Romashets, E.; Cargill, P.
2003EAEJA.....2682Z Altcode:
We investigate possible links between the activity manifestations in
the solar corona and conditions in the solar wind. For the reduction
of this immense task we have selected 206 events in the solar wind
in 1997 -- 2000 corresponding to geomagnetic events with Ap > 20
(compiled into a database at http://alpha.sinp.msu.ru/apev). The solar
wind conditions monitored by ACE and WIND spacecraft were traced back to
the solar corona observed by SOHO/EIT. The search for coronal signatures
that are probably associated with the disturbed solar wind conditions
was performed. The coronal sources of the events are identified, namely:
eruptions in active regions, filament eruptions and coronal holes. It is
shown that halo and partial halo CMEs observed within the SOHO/LASCO
sensitivity limits are not necessary indicators of Earth-directed
eruptions, and coronal EUV dimmings can be used as a complementary
indicator. We also found that a structure now conventionally called a
”sigmoid” cannot be represented as a single S-shaped loop (flux tube),
but exhibits an assembly of many smaller structures. It could be formed
and destroyed via eruptions.
---------------------------------------------------------
Title: A force-free field with constant alpha in an oblate cylinder:
A generalization of the Lundquist solution
Authors: Vandas, M.; Romashets, E. P.
2003A&A...398..801V Altcode:
A force-free magnetic field with constant alpha for a circular
cylindrical flux rope (Lundquist solution) is widely used to
describe the magnetic field configuration in interplanetary
flux ropes. Observations as well as MHD simulations indicate
that interplanetary flux ropes are not circular but have an oblate
shape. Here we present an analytical solution for a force-free magnetic
field with constant alpha in an elliptic flux rope which may be regarded
as a direct generalization of the Lundquist solution. An alternative
simpler solution for a force-free magnetic field with constant alpha
in an oblate flux rope is discussed.
---------------------------------------------------------
Title: The development of the Russian Space Weather Initiatives
Authors: Dmitriev, A.; Belov, A.; Gorgutsa, R.; Ishkov, V.; Kozlov,
V.; Nymmik, R.; Odintsov, V.; Petrukovich, A.; Popov, G.; Romashets,
E.; Shevchenko, M.; Troshichev, O.; Tverskaya, L.; Zaitzev, A.
2003AdSpR..31..855D Altcode:
Russian Space Weather Initiatives (RSWI) support different models for
space weather forecastin (http://alpha.npi.msu.su/RSWI/rswi.html). The
models give the long-time (months-years) and short-time (days)
predictions of the solar activity, heliospheric conditions, and dynamics
of the Earth's magnetic field and radiation. Many different parameters
measured from the Sun to the Earth's magnetosphere are used as inputs
to the space weather models. The paper is devoted to a short overview
of these models.
---------------------------------------------------------
Title: New Force-Free Models of Magnetic Clouds
Authors: Vandas, Marek; Romashets, Eugene P.; Watari, Shinichi
2003IAUJD...3E...6V Altcode:
Magnetic clouds are thought to be large flux ropes propagating through
the heliosphere. Their twisted magnetic fields are mostly modeled
by a constant-alpha force-free field in a circular cylindrical flux
rope. However the interplanetary flux ropes are three dimensional
objects. In reality they possibly have a curved shape and an oblate
cross section. Recently we have found two force-free models of flux
ropes which takes into account the mentioned features. These are (i)
a constant-alpha force-free configuration in an elliptic flux rope and
(ii) a force-free field in a toroid with arbitrary aspect ratio. Their
nature will be described and their ability to fit observed unusual
magnetic field profiles will be demonstrated.
---------------------------------------------------------
Title: Effects of coronal hole flows loaded by material from a
disappearing filament
Authors: Romashets, E. P.; Vandas, M.; Ivanov, K. G.
2003AdSpR..31..907R Altcode:
MHD self-consistent simulation results are presented for the case of
a sequence of pulses with increases in velocity and density of the
solar wind at small heliodistances, where they are introduced as lower
boundary conditions. These pulses model coronal hole dynamics (velocity
increase) and a disappearing filament (density increase). To support
the model results, the observations of May 17-19, 1999, event are
used. It was concluded, on the basis of simulations, that a strong
geomagnetic storm can result from an interaction between fast and
dense fluxes in the heliosphere, even if each flux separately is not
geoeffective at all.
---------------------------------------------------------
Title: Force-free magnetic fields with not constant alpha
Authors: Romashets, Eugene; Vandas, Marek
2002ESASP.506...17R Altcode: 2002svco.conf...17R; 2002ESPM...10...17R
It is generally assumed that magnetic fields inside interplanetary
magnetic clouds are force-free. In order to interpret such fields, the
solution of rotB = αB is used where α = const. Direct comparisons
of this solution with observations show significant differences in
magnetic field magnitude profiles in magnetic clouds. To treat this
problem, we examine the solution with α ~ r<SUP>epsilon</SUP> in
cylindrical co-ordinates.
---------------------------------------------------------
Title: Magnetic field in an elliptic flux rope: a generalization of
the Lundquist solution
Authors: Vandas, M.; Romashets, E. P.
2002ESASP.506..217V Altcode: 2002svco.conf..217V; 2002ESPM...10..217V
Magnetic fields in interplanetary flux ropes are commonly described
by a force-free solution with constant alpha in a circular cylinder
found by Lundquist (1950). However, both MHD simulations (Vandas
et al., 1995, 2002; Cargill et al., 1996) and detailed analyses of
spacecraft measurements (Mulligan & Russell, 2001) indicate that
interplanetary flux ropes have not a circular cross section, but they
are quite oblate. We present a solution for force-free magnetic field
with constant alpha in an elliptic cylinder. This analytical solution
can be regarded as a generalization of the Lundquist solution.
---------------------------------------------------------
Title: Dynamics of open solar magnetic fields, active longitudes,
and near earth disturbances
Authors: Ivanov, K.; Bothmer, V.; Kharshiladze, A.; Romashets, E.;
Veselovsky, I.
2002ESASP.506..141I Altcode: 2002ESPM...10..141I; 2002svco.conf..141I
Open magnetic field lines in the solar corona are calculated in order to
study their relationship to solar activity and near Earth disturbances
in 2000. Slow, rotation by rotation, dynamics of photospheric regions
with open fields show a correlation with generating and decay of
active complexes located at longitudes 280-360 degrees, and with the
series of the near Earth recurrent extra storms on May 24, July 15,
August 12, and October 5.
---------------------------------------------------------
Title: Solar and Heliospheric Causes of Geomagnetic Perturbations
during the Growth Phase of Solar Cycle 23
Authors: Bothmer, V.; Veselovsky, I. S.; Dmitriev, A. V.; Zhukov,
A. N.; Cargill, P.; Romashets, E. P.; Yakovchouk, O. S.
2002SoSyR..36..499B Altcode:
A database is compiled for the study of solar and heliospheric causes
of geomagnetic perturbations with the daily average index A<SUB>r</SUB>
> 20 that were observed in the period 1997-2000. The number of such
events (more than 200) progressively increased and fluctuated as the
current solar cycle developed. It is established that geomagnetic
storms are generated by dynamical processes and structures near
the center of the solar disk in a zone of several tens of degrees,
and these processes are responsible for the appearance in the Earth's
region, within several tens of hours, of quasistationary and transient
solar wind streams with a sufficiently strong southward component of
the heliospheric magnetic field. These streams lasted more than a few
hours. The following structures can serve as morphological indicators
for the prediction of the appearance of such streams: (1) active and
disappearing filaments derived from synoptic N<SUB>α</SUB>-maps of the
Sun, (2) solar flares, (3) coronal holes and evolving active regions,
and (4) the heliospheric current sheet. The geometry of coronal mass
ejections needs further observational study.
---------------------------------------------------------
Title: Toroidal Force Free Structure Inside Interplanetary Magnetic
Clouds
Authors: Romashets, E. P.
2002AAS...200.3721R Altcode: 2002BAAS...34..950R
A solution of equation for force free magnetic field inside toroid
is used to identify size, location, and orientation of interplanetary
clouds of this geometry associated with a series of strong geomagnetic
storms in 1999. The solution obtained in toroidal coordinates μ ,
η , and ϕ for arbitrary aspect ratio torus and for not constant
alpha. This work was supported by EU-INTAS-ESA grant 99-00727
---------------------------------------------------------
Title: Modification of interplanetary magnetic field by the Earth's
magnetosphere a - SOLSPA 2001
Authors: Romashets, Eugene; Nagatsuma, Tsutomu
2002ESASP.477..475R Altcode: 2002scsw.conf..475R
We present an analytical solution for drapery around magnetosphere of
interplanetary magnetic field which has an arbitrary direction far from
the Earth. Extra assumptions about the manner of modification were used
(i) the field is potential and (ii) there is no normal component on the
magnetopause. The solution was constructed by selection of harmonics
satisfying these conditions. The formula was used for estimations of
maximums of Bz and B outside the surface depending on the direction
and the value of initial field and for description of strong g/m storms
of 1999-2000.
---------------------------------------------------------
Title: Solar and heliospheric origins of geomagnetic perturbations
in the rising phase of Solar Cycle 23
Authors: Bothmer, V.; Cargill, P.; Romashets, E. P.; Veselovsky, I. S.
2002ESASP.477..331B Altcode: 2002scsw.conf..331B
Solar sources of strong geomagnetic perturbations are connected
to coronal mass ejections and corotating inhomogeneities in the
heliosphere. Geomagnetic perturbations with Ap > 20 in 1997-2000 were
produced by heliospheric magnetic fields and solar wind plasma streams
related to the following morphological features observed at the Sun:
1) active and disappearing filaments and prominences (sdf) seen in Hα
synoptic maps; 2) solar flares; 3) evolving active regions and coronal
holes (CH); 4) heliospheric current sheet (HCS) positions deduced from
photospheric magnetic field measurements. Strong geomagnetic storms
during this period of time were observed when compound plasma streams
from several sources on the Sun reached the Earth's magnetosphere. The
combination of the transient processes and corotating inhomogeneities
in the solar corona and deeper layers of the solar atmosphere not far
from the center of the solar disk (first tens of degrees) represent
a sufficient condition for the formation of such compound streams
exemplified by sdf-CH-HCS passage.
---------------------------------------------------------
Title: Subsector structure of the interplanetary space - SOLSPA 2001
Authors: Ivanov, K. G.; Bothmer, V.; Cargill, P.; Kharshiladze, A. F.;
Romashets, E. P.; Veselovsky, I. S.
2002ESASP.477..317I Altcode: 2002scsw.conf..317I
A new conception about sub-sector structure of the interplanetary
space is introduced. It is shown that in a potential model of the
solar magnetic field there exist direct relations between photospheric
regions of open magnetic field lines and corresponding magnetic domains
at the source surface and in the interplanetary magnetic field. These
domains generate a large-scale sub-sector structure of the solar and
interplanetary magnetic field, with boundaries between domains of the
same polarities. Solar, interplanetary, and ground-based observations
of 1999-2000 were used to test this conclusion.
---------------------------------------------------------
Title: Modeling of IMF draping around a supersonic magnetic cloud
Authors: Romashets, Eugene; Vandas, Marek
2002ESASP.477..297R Altcode: 2002scsw.conf..297R
We have found an approximate analytical solution of magnetic field
distribution around a flux rope. The obtained solution shows a behavior
of magnetic field lines around a cylindrical magnetically closed
body with a bow shock ahead. The bow shock shape was assumed to be
a parabolic cylinder. The resulting field is described by a sum of a
few functions with coefficients, which are obtained from the following
conditions: (i) no normal field component at the flux rope surface;
(ii) normal components are continuous at the bow shock; and (iii)
the field approaches undisturbed values at large distances from the
center of the body.
---------------------------------------------------------
Title: Force-free magnetic fields with not constant alpha.
Authors: Romashets, E.; Vandas, M.
2002cosp...34E.534R Altcode: 2002cosp.meetE.534R
The equation rmrot bf B = bf B withrn is solved in cylindrical
coordinates r, , Z . The case n = 0 corresponds to the well known field
distribution with= rmconst (the Lundquist solution), which is often used
for interpretation of interplanetary magnetic cloud observations as
well as of eruptive processes on the Sun. A hypothesis is that stable
bodies can be described by solutios with n = 0 or n = 1, while active,
evolving ones -- by n = 5 and higher.
---------------------------------------------------------
Title: The Force Free Magnetic Structure Inside A Toroid
Authors: Romashets, E. P.
2002mwoc.conf..311R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic storm cessation during sustained Northward IMF
Authors: Veselovsky, I.; Bothmer, V.; Cargill, P.; Ivanov, K.;
Romashets, E.; Yakovchouk, O.
2002cosp...34E.420V Altcode: 2002cosp.meetE.420V
Times of sustained strong Northward IMF can interrupt the magnetic
storm development and lead to lower levels of geomagnetic activity
for many hours. During 1997-2000 we have found two events of this kind
observed on November 8, 1998 and October 13, 2000. In both cases, the
storms started as usual after arrival of ejecta with a southward IMF
component from the Sun to the Earth, but ceased after several hours
due to the onset of sustained Northward IMF. After the passage of
this so called positive domain storm development started again. The
heliospheric magnetic field intensity remained enhanced and nearly
constant. The solar origins of the geomagnetic storm interruptions have
been investigated. Tentatively they may be related to strong nonlinear
Alfven type solitary waves excited by nonstationary coronal current
variations with a characteristic time-scale of about a day.
---------------------------------------------------------
Title: Propagation of a toroidal magnetic cloud in interplanetary
space
Authors: Romashets, E. P.; Vandas, M.
2002AdSpR..29..313R Altcode:
We studied dynamics of a compact toroid in interplanetary space
considering the diamagnetic force, gravity, and the drag force of the
ambient solar wind. Magnetic cloud velocity profiles were calculated
for different initial speeds using an expression of the diamagnetic
force in purely toroidal coordinates.
---------------------------------------------------------
Title: Dynamics of magnetic cloud of arbitrary shape in the solar wind
Authors: Romashets, E.; Cargill, P.
2001AGUFMSH12A0742R Altcode:
The method of potentials is used for the study of the modification of
the interplanetary magnetic field by the propagation of magnetic clouds
through the inner helioosphere. The evolution of ambient field will be
shown for magnetic clouds of different geometries. The compression of
the ambient field is much stronger if the magnetic cloud is supersonic
and a bow shock was formed in front of it. However, geoeffectiveness is
very sensitive to the value of Bz in pre-existing undisturbed medium. If
we solve the problem in bicylindrical co-ordinates, we can consider
also the mutual force acting on two CMEs by each other, and evaluate
deceleration/acceleration when slow and fast bodies interact. The
results will be used for explanation of outstanding events of 1997
and 1999. The work is supported by EU/INTAS-ESA grant 99-00727.
---------------------------------------------------------
Title: Dynamics of a toroidal magnetic cloud in the solar wind
Authors: Romashets, E. P.; Vandas, M.
2001JGR...10610615R Altcode:
Knowledge about the behavior of compact toroidal magnetic force-free
objects in ambient magnetic field may help to better understand
dynamical processes in association with coronal mass ejections and
their interplanetary counterparts. The problem to find the diamagnetic
force acting on a toroidal object in an inhomogeneous magnetic field is
solved analytically. At first the drapery of the inhomogeneous magnetic
field caused by an insertion of a toroid was found, and then the force
acting on the toroid by this disturbed magnetic field was obtained. The
problem is considered in purely toroidal coordinates. The obtained
solution can be used for calculations of the repulsing diamagnetic
force acting on isolated objects in the solar corona such as magnetic
clouds of a toroidal shape and for the determination of their velocity
profiles. Deformations of toroidal transients due to this melon seed
force are not investigated here. Only the force acting on the toroid
as a whole is taken in consideration.
---------------------------------------------------------
Title: Heliospheric current sheet effect on propagation of type II
interplanetary radio bursts from coronal mass ejections
Authors: Ivanov, Kim G.; Romashets, Eugene P.
2001RaSc...36.1739I Altcode:
In this paper, we present our hypothesis that a disturbed heliospheric
current sheet and heliospheric plasma sheet can exert a very strong
influence on propagation of type II radio waves through interplanetary
space. We make a conjecture that these layers become more dense and
the critical frequency becomes higher, so radio emission induced in the
bow shock region in front of the coronal mass ejection is reflected or
deflected more strongly. The idea is illustrated by two examples of type
II radio bursts: in January 1997 and in May 1997. In the first case,
the effect of the heliospheric current sheet and heliospheric plasma
sheet was minimal because they were some 30° below the ecliptic plane
and did not play an important role in the propagation of radio waves
to the Earth, while during the second event the layers were located
in the way of radio waves, and attenuated them strongly.
---------------------------------------------------------
Title: January 5-12, 1997 Heliospheric Substorm: Morphology and
Interpretation
Authors: Ivanov, K.; Romashets, E.
1997SPD....28.0266I Altcode: 1997BAAS...29..905I
The solar sources, dynamics, MHD-structure and geometry of the January,
9-12 1997 near-Earth interplanetary disturbances were con sidered in
the lights of SOHO, WIND, and INTERBALL plasma and IMF data. The solar
magnetic field data (T.Hoeksema, Internet) and preliminary analises of
the disturbances given by D.F.Webb and L.F.Burlaga (Internet) were taken
into account. The brief summary of our findings is here outlined. The
solar sources. The two coronal mass ejections (filament- associated)
and the heliospheric current sheet (HCS) were strongly involved into a
scenario of the event. Dynamics. It was a typical (as in Ivanov et al.,
1995, Solar Wind Eight, p.575) heliospheric substorm (HS) with three-
phase IMF and plasma dynamics. The onset of the growth phase of the HS
at 1 AU was on Jan. 9 at 0930 UT, long before the forward shock wave
arrival to the WIND location. MHD-structure. Preliminary, at least
seven specific bounda- ries were identified. Some of them were shock
waves and rotational discontinuities. They say about the common featu-
res of the event and its origin, and evolution. Interpretation. The
near-Earth plasma and IMF variations during this event were tentatively
explained in terms of HCS current jets (Ivanov and Romashets, 1997, in
press) and Ma et. al. (1991,JGR) solution on a plasma cylinder inter-
action with a tangential discontinuity.
---------------------------------------------------------
Title: Twin Phobos 1 and Phobos 2 observations of heliospheric
disturbances near the heliospheric current sheet
Authors: Ivanov, K. G.; Styazkin, V. A.; Eroshenko, E. G.; Romashets,
E. P.
1996AIPC..382..575I Altcode:
The structure, geometry, and dynamics of the two moderate IMF
disturbances on July 25-28, and August 5-7, 1988 were considered
using the measurements obtained by the twin Phobos 1 and Phobos 2
spacecraft. Rather regular three-phase dynamics of the disturbances
suggested. The disturbances occurred in the vicinity of HCS and we
name them heliospheric substorms. A theoretical model of a rotational
electrojet flowing over the HCS was tested to explain growth phase of
the substorms.
---------------------------------------------------------
Title: The interplanetary magnetic field as measured by Phobos-1 and
Phobos-2 spacecraft. 2. Disturbance near the sector boundary on July
25 - 28, 1988.
Authors: Ivanov, K. G.; Styazhkin, V. A.; Eroshenko, E. G.; Romashets,
E. P.
1994Ge&Ae..34...52I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar flares, magnetic clouds, and geomagnetic storms
Authors: Ivanov, K. G.; Kharshiladze, A. F.; Romashets, E. P.
1993SoPh..143..365I Altcode:
Firstly, semi-empirical distributions of solar wind proton number
density and velocity ordered around the Heliospherical Current Sheet
(HCS) of the inner heliosphere are considered. Then, the velocity
profiles of flare-generated Coronal Mass Ejections (CMEs) running
through the inhomogeneous heliosphere are calculated. They show that
the velocities strongly depend on flare positions with respect to the
HCS. Finally, a specific mutual flare-HCS-Earth location leading to
a strong geomagnetic storm is deduced from calculations and supported
by a few real events of solar-terrestrial physics.
---------------------------------------------------------
Title: Manifestation of the magnetic cloud deceleration effect from
data on the interplanetary plasma velocity near the earth
Authors: Ivanov, K. G.; Kharshiladze, A. F.; Romashets, E. P.
1993Ge&Ae..33...90I Altcode:
Observations aboard spacecraft passing through interplanetary magnetic
clouds on the earth orbit showed signs of a monotonic deceleration of
plasma filling these clouds. This paper presents a formula describing
local deceleration of a cloud on the earth orbit, together with
examples indicating that the expected cloud deceleration effect can
be detected, at least qualitatively, within the velocity data obtained
for interplanetary plasma. The deceleration effect explains the Lepping
paradox (Lepping et al., 1990), according to which the average velocity
of a magnetic cloud measured on one spacecraft is less than the velocity
of the solar wind ahead of the spacecraft.
---------------------------------------------------------
Title: Mutual location of a powerful flare, heliospheric current sheet
and the Earth favourable for the onset of a strong geomagnetic storm.
Authors: Ivanov, K. G.; Kharshiladze, A. F.; Romashets, E. P.
1992Ge&Ae..32...25I Altcode:
No abstract at ADS
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Title: Force-free magnetic field in an asymmetric interplanetary
cloud.
Authors: Romashets, E. P.
1992Ge&Ae..32...29R Altcode:
Approaches and solutions for determining the distribution of a
force-free magnetic field inside a perfectly conducting tube of
arbitrary cross section are examined. The magnetic field distribution
inside a cloud whose boundary is a perfectly conducting parabolic
cylinder is found; this situation corresponds to the possible
deformation of a magnetic flux of solar origin moving in interplanetary
space. The solutions obtained can be used to interpret satellite data
on magnetic clouds.
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Title: Interplanetary medium disturbances generated by a slow isolated
magnetic cloud.
Authors: Ivanov, K. G.; Romashets, E. P.; Kharshiladze, A. F.
1992Ge&Ae..32...85I Altcode:
No abstract at ADS
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Title: Shape of the magnetic cloud in the solar wind.
Authors: Romashets, E. P.; Ivanov, K. G.
1991Ge&Ae..31..583R Altcode:
A self-consistent theoretical method is used to determine the shape
of a magnetic cavity arising in the solar wind under the effect of the
motion of a toroidal flare-generated magnetic cloud. Under the effect of
solar-wind dynamic pressure, the cloud is compressed in the front part,
while a magnetic tail is formed in the rear part. When the hydrostatic
pressure of the solar wind is taken into account, the study indicates
that collapse of the tail can occur and that a closed magnetic cavity
of nonaxisymmetric toroidal configuration can be formed.
