Author name code: romashets ADS astronomy entries on 2022-09-14 author:"Romashets, Eugene P." ------------------------------------------------------------------------ Title: Euler Potentials for Dungey Magnetosphere With Axisymmetric Ring and Field-Aligned Currents Authors: Romashets, E.; Vandas, M. Bibcode: 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. Title: Euler Potentials for the Earth Magnetic Field With Field-Aligned Currents Authors: Romashets, E.; Vandas, M. Bibcode: 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. 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. Bibcode: 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, https://doi.org/10.1029/94JA01778) model and the Romashets and Vandas (2019, https://doi.org/10.1029/2006JA012072) model complemented with the Jelínek et al. (2012, https://doi.org/10.1029/2011JA017252) 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. Title: Modeling of magnetic field in the magnetosheath using elliptic coordinates Authors: Vandas, M.; Romashets, E. P. Bibcode: 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). Title: Interplanetary flux ropes of any twist distribution Authors: Vandas, M.; Romashets, E. P. Bibcode: 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.
Aims: Real flux ropes have varying twist. Therefore, analytical magnetic field configurations with prescribed twist distributions are searched for in cylindrical geometry.
Methods: Equations for the field solenoidality and for the force-free condition are solved for case when a twist profile is prescribed.
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. Title: Analytic Modeling of Magnetic Field in the Magnetosheath and Outer Magnetosphere Authors: Romashets, E. P.; Vandas, M. Bibcode: 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. Title: Magnetic cloud fit by uniform-twist toroidal flux ropes Authors: Vandas, M.; Romashets, E. Bibcode: 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.
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.
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.
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. Title: Toroidal Flux Ropes with Elliptical Cross Sections and Their Magnetic Helicity Authors: Vandas, M.; Romashets, E. Bibcode: 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). Title: Toroidal linear force-free magnetic fields with axial symmetry Authors: Vandas, M.; Romashets, E. Bibcode: 2016A&A...585A.108V Altcode:
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.
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.
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. Title: Euler potentials for a geomagnetic field which includes the Birkeland current Authors: Romashets, E.; Vandas, M. Bibcode: 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. Title: Modeling of magnetic cloud expansion Authors: Vandas, M.; Romashets, E.; Geranios, A. Bibcode: 2015A&A...583A..78V Altcode:
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.
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.
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.
Conclusions: Analysis of velocity components tests magnetic cloud models more strictly and may reveal information on magnetic cloud shapes. Title: Comparative study of a constant-alpha force-free field and its approximations in an ideal toroid Authors: Vandas, M.; Romashets, E. Bibcode: 2015A&A...580A.123V Altcode:
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.
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.
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.
Conclusions: The Miller & Turner solution is a reasonable substitute for the exact solution even for low aspect ratios (≈2). Title: Modeling of magnetic cloud expansion Authors: Vandas, Marek; Romashets, Eugene; Geranios, Athanassios Bibcode: 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. 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. Bibcode: 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. Title: Euler potentials for two current sheets of nonzero thickness along ambient uniform magnetic field Authors: Vandas, M. I.; Romashets, E. P. Bibcode: 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. Title: Magnetic field disturbance in front of a super-sonic toroidal magnetic cloud Authors: Vandas, M.; Romashets, E. P. Bibcode: 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. Title: Dynamics of a toroidal magnetic cloud: A semi-analytic approach Authors: Vandas, M.; Romashets, E. P. Bibcode: 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. Title: Modeling Irregularities in Solar Flux Ropes Authors: Romashets, E.; Vandas, M. Bibcode: 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. Title: Euler potentials for two current sheets along ambient uniform magnetic field Authors: Romashets, E. P.; Vandas, M. Bibcode: 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. Title: Euler potentials of two line currents in an ambient uniform magnetic field Authors: Romashets, E.; Vandas, M. Bibcode: 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. Title: Expansion of magnetic clouds in the solar wind Authors: Vandas, M.; Romashets, E. Bibcode: 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. Title: Euler potentials for two line currents aligned with an ambient uniform magnetic field Authors: Romashets, E. P.; Vandas, M. Bibcode: 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. Title: Analytical description of electric currents in the magnetosheath region Authors: Romashets, E.; Vandas, M.; Veselovsky, I. S. Bibcode: 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. Title: Magnetic clouds observed by STEREO Authors: Romashets, E.; Vandas, M.; Howard, T. Bibcode: 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. Title: Correction to “Modeling of the magnetic field in the magnetosheath region” Authors: Romashets, E. P.; Vandas, M. Bibcode: 2010JGRA..11511220R Altcode: No abstract at ADS Title: Magnetic Field Disturbance Produced by a Super-Sonic Toroidal Magnetic Cloud Authors: Vandas, Marek; Romashets, E. Bibcode: 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. Title: Evolution of Toroidal Magnetic Clouds Authors: Romashets, Eugene; Vandas, M. Bibcode: 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. Title: Modeling of Magnetic Field Disturbances in Sheath Region of Interplanetary Magnetic Clouds of Elliptical Shapes Authors: Vandas, M.; Romashets, E. P. Bibcode: 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. 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. Bibcode: 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. Title: Magnetic Clouds Fitted by a Constant-Alpha Force-Free Toroidal Solution Authors: Vandas, M.; Romashets, E. P. Bibcode: 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. Title: Modeling of Local Magnetic Field Enhancements within Solar Flux Ropes Authors: Romashets, E.; Vandas, M.; Poedts, S. Bibcode: 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. Title: Application of a constant-alpha force-free field in a toroid to fit magnetic clouds Authors: Vandas, M.; Romashets, E. Bibcode: 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. Title: Characteristics of magnetised plasma flow around stationary and expanding magnetic clouds Authors: Dalakishvili, G.; Poedts, S.; Fichtner, H.; Romashets, E. Bibcode: 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.
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.
Results: Subsequently, the plasma density and pressure are expressed as functions of the magnetic field and the velocity field.
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. Bibcode: 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. Bibcode: 2009GeoRL..3612107R Altcode: Abstract Available from http://www.agu.org Title: Linear force-free field of a toroidal symmetry Authors: Romashets, E.; Vandas, M. Bibcode: 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.
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.
Methods: The solution is found as a superposition of fields given by linear force-free cylinders tangential to a generating toroid.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.
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.
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.
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. Bibcode: 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.
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.
Methods: The method applied in this study consists of three steps. First, the r-component of the magnetic field at r=2.5 Rs 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 Rs 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.
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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 m = (8π n 1 m p)1/2( D - NV1), 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 m 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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=α0/(1+r/r0). Title: Asymmetric magnetic field inside a cylindrical flux rope Authors: Romashets, E. P.; Vandas, M. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2003ESASP.535..587V Altcode: 2003iscs.symp..587V Magnetic clouds are known as a possible source of strong geomagnetic storms due to a large southward Bz 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 Bz 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bmax/Bmin > 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. Bibcode: 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 Bz component of the draped field, even if there is no strong Bz component inside the cloud. Title: Propagation of a Toroidal Magnetic Cloud through the Inner Heliosphere Authors: Romashets, Eugene; Vandas, Marek Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 ~ repsilon in cylindrical co-ordinates. Title: Magnetic field in an elliptic flux rope: a generalization of the Lundquist solution Authors: Vandas, M.; Romashets, E. P. Bibcode: 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. Bibcode: 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. Bibcode: 2002SoSyR..36..499B Altcode: A database is compiled for the study of solar and heliospheric causes of geomagnetic perturbations with the daily average index Ar > 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 Nα-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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1992Ge&Ae..32...25I Altcode: No abstract at ADS Title: Force-free magnetic field in an asymmetric interplanetary cloud. Authors: Romashets, E. P. Bibcode: 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. Title: Interplanetary medium disturbances generated by a slow isolated magnetic cloud. Authors: Ivanov, K. G.; Romashets, E. P.; Kharshiladze, A. F. Bibcode: 1992Ge&Ae..32...85I Altcode: No abstract at ADS Title: Shape of the magnetic cloud in the solar wind. Authors: Romashets, E. P.; Ivanov, K. G. Bibcode: 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.