I.L. Ovchinnikov

Magnetostatically equilibrated plasma sheet with developed medium-scale turbulence: Structure and implications for substorm dynamics

A simple theory of the magnetostatic equilibrium of the magnetospheric plasma sheet is proposed. It takes into consideration the effects of the large-scale dawn-to-dusk electric field and developed medium-scale turbulence. This makes it possible to describe the main features of the plasma sheet dynamics. The suggested model assumes that the magnetic field lines are not equipotential and that the regular velocity of a plasma parcel is much lower than the chaotic velocity. Hence the plasma is intensely mixed. One of the main consequences of such mixing is the experimentally observed temperature equalization across the plasma sheet. The obtained dependence of plasma pressure on the magnetic vector potential permits one to solve the Grad-Shafranov equation and reconstruct, in the tail approximation, the magnetic field line configuration for the case of inhomogeneous distribution of the dawn-to-dusk electric field along the tail. The thickness of the plasma sheet in the model is determined by the magnitudes of the regular and stochastic electric fields, their scales, and plasma temperature. A quasi three-dimensional model of the plasma sheet is developed. The substorm dynamics of the plasma sheet is analyzed. The model can explain the thinning of the plasma sheet without variations in the plasma pressure at the tail axis (thinning without compression) during the substorm growth phase. The plasma sheet expansion during substorm expansion phase is related to the growth of turbulent fluctuations.

Determination of the Turbulent Diffusion Coefficient in the Plasma Sheet Using the Project INTERBALL Data

The results of an analysis of velocity fluctuations in the plasma sheet of the Earths magnetotail measured onboard INTERBALL Tail Probe satellite are presented. The hodographs of the velocity in directions (Y, Z) and correlation functions are presented for a number of passages when the satellite was in the plasma sheet for a long time. The turbulent diffusion coefficients are calculated. A comparison of the obtained diffusion coefficients with those predicted theoretically in [1] is carried out. It is shown that the results of observations confirm theoretical predictions.

Generation of unmagnetized motion of plasma sheet electrons and its possible causes

Results of experimental and theoretical studies of unmagnetized stochastic motion of the plasma sheet electrons and the mixing of plasma in the plasma sheet are presented. Analysis of the electron temperature distributions within the plasma sheet is undertaken using the data from Intercosmos-Bulgaria-1300 polar orbiting satellite. The electron temperature is obtained with consideration of acceleration of precipitating electrons by the field-aligned potential drop; this temperature is nearly constant in the meridional direction and has no longitudinal dependence during quiet geomagnetic conditions. Analysis of spacial fluctuations of precipitating electron fluxes for a fixed electron energy shows that fluctuation spectra of primary electrons have a power dependence and resemble the spectra of electric field fluctuations observed within the plasma sheet. The satellite observations are interpreted in terms of stochastic motion of the plasma sheet electrons and intensive mixing of plasma in the sheet. It is suggested that the electron motion in the electric field with a characteristic scale comparable with the electron Larmor radius is a source of stochastization; chaotization of the particle trajectories could be a part of stochastization process. The particle motion in a homogeneous magnetic field and in a regular inhomogeneous electric field with a sinusoidal distribution in one direction and a homogeneous distribution in the perpendicular direction is analyzed as an example of the chaotic motion.

Topology of High-Latitude Magnetospheric Currents

The structure and localization of high latitude transverse and field-aligned currents are analyzed using the data from the Themis satellite mission. A number of evidences resumed in this paper, including daytime compression of magnetic field lines and the existence of magnetic field minima far from the equatorial plane make necessary to reanalyze the traditional points of view about the topology of high-latitude magnetospheric currents. Comparison between the dayside integral transverse currents at the geocentric distances 7–10R E , calculated assuming the validity of the condition of magnetostatic equilibrium and the nighttime transverse currents, showed that ordinary ring current has the high latitude continuation until geocentric distances ∼10–13R E . The problem of the location of Region 1 field-aligned current of Iijima and Potemra is discussed.

The model of turbulent plasma sheet during IMF Bz > 0

Abstract Theory of the plasma sheet with medium-scale developed turbulence gives the possibility to explain the main processes of plasma sheet bifurcation and theta-aurora formation during IMF B z > 0. The model suggests that during IMF B z > 0 small bulge structure in the plasma sheet center is formed. The polarization of the bulge due to dawnward electron motion and duskward ion motion decreases the large-scale electric field in the bulge region. The decrease of the large-scale field in the conditions of constant coefficient of diffusion leads to the bulge growth. The results of plasma sheet bifurcation and theta-aurora formation modelling are presented.

Current sheet with medium scale developed turbulence and the formation of the plasma sheet of Earth's magnetosphere and solar prominences

Abstract A current sheet model with developed medium scale turbulence has been constructed. It is suggested that regular plasma flow in the current sheet is compensated by diffusive flux and plasma mixing, leading to temperature equalization. The analyzed turbulence has the form of electrostatic vortices in which electrons and ions move with the same velocities and hence does not lead to anomalous resistivity and current dissipation. It is possible to determine the plasma pressure dependence on magnetic vector potential and to find the Grad—Shafranov equation solutions. The theory is used to explain the Earths magnetosphere plasma sheet characteristics. It is taken into account that experimentally observed plasma velocity fluctuations in the Earths plasma sheet and quiescent prominences are much higher than regular plasma flow velocities. The analysis of turbulent current sheet dynamics after the regular motion weakening allows to construct the prominence formation theory. The decreasing of plasma pressure in the sheet due to diffusion leads to field-aligned plasma flow and plasma tube filling by cold chromospheric plasma by the action of siphon mechanism.

Medium scale magnetospheric turbulence and quasi three-dimensional plasma sheet modeling

Abstract The role of the large- and medium-scale magnetospheric turbulence in the magnetospheric plasma dynamics is analyzed. The large scale convection electric field leads to plasma sheet compression which can be compensated by quasidiffusion flux directed against plasma pressure gradient. In the magnetostatic equilibrium regular and diffusion flux are compensated. On the basis of the developed theory the three dimensional solutions determining plasma sheet structure are modelled. The dependence of the plasma sheet structure on the interplanetary magnetic field (IMF) B z orientation is investigated. It is shown that southward IMF orientation create the concave plasma sheet structure and northward IMF orientation can lead to the formation of convex structure in the center of plasma sheet. Possible explanation of theta-aurora formation is discussed.

Quasi-three dimensional modelling of the plasma sheet including turbulence on medium scales

The analysis of electric field and plasma observations in the plasma sheet and auroral zone points to the existence of low frequency turbulence which leads to intensive plasma mixing and equilibration of the electron and ion temperatures across the plasma sheet. Particle transport by turbulent electric fields may be the main process of plasma sheet formation. The suggestion about local equality of large-scale convection transport and quasi-diffusive turbulence permits to solve the Grad-Shafranov problem and to determine the dependence of the plasma pressure from the magnetic vector potential. The main input parameter of the model is the large-scale distribution of the electrostatic potential. This is computed from the Volland-Stern model for the ionospheric electric field and Tsyganenkos model of the magnetic field. The plasma distribution across the tail at different geocentric distances is obtained. Its dependence on the interplanetary magnetic field component Bz is analyzed. It is shown that if interplanetary magnetic field is northward, the plasma sheet can become convex in the center of the tail which may cause bifurcation of plasma sheet and formation of theta-aurora.

Turbulence in the Plasma Sheet during Substorms: A Case Study for Three Events Observed by the INTERBALL Tail Probe

Variations of turbulence properties of the plasma sheet during geomagnetic substorms are investigated using observations of the INTERBALLTail Probe satellite. The periods are chosen when the satellite was inside the plasma sheet. Fluctuations of the plasma bulk velocity across the plasma sheet are studied for the growth, expansion, and recovery phases of geomagnetic substorms on October 14, 1997; October 30, 1997; and December 16, 1998. It was demonstrated that the level of turbulence increases considerably after the onset of the substorm expansion phase and slowly decreases nearly to the presubstorm level later. The correlation times of plasma fluctuations in the Z-direction are estimated, and diffusion coefficients in the Z-direction are calculated.

Reconnection in the conditions of developed turbulence

Abstract The results of many investigations have shown that equilibrium current structures are frequently formed in the presence of developed turbulence. Therefore internal current instabilities cannot be the cause of observed reconnection phenomena. However external factors may be responsible for the observed changes in the magnetic field topology (reconnection). Some possible sources of such a kind, which could result in the reconnection on the Earths magnetopause and in the near tail regions, are analyzed here. It is shown that an effective eastward ring current can lead to many of the observed reconnection phenomena.