Yu.P.Maltsev (Polar Geophysical Institute, Apatity)

The magnetostatic equilibrium equation with the anisotropic pressure has been solved, the transverse pressure being assumed twice as large as the parallel pressure. The equation allows to restore the pressure up to some unknown function of the geocentric distance which seems to be not too large. The empirical model of the magnetic field by Ostapenko et al. [1996] plausible for the distances from 3 to 10 earth radii has been used. The model depends on Dst, Kp, and AE indices, as well as on IMF Bz and the solar wind dynamic pressure. The radial profile of the magnetospheric plasma pressure computed for quiet conditions is similar to that obtained from direct measurements. Influence of the four above-mentioned parameters on the profile has been studied.

A.V.Kustov, G.J.Sofko (ISAS, U. of Saskatchevan, Saskatun, Canada)

R.A.Greenwald, J.M.Ruohoniemi (APL/JHU, Laurel, Maryland, USA)

Y.I.Feldstein, L.I.Gromova, A.E.Levitin, V.O.Papitashvili, B.A.Belov (IZMIRAN, 142092Troitsk, Moscow Region, Russia)

IZMEM is a potentially very useful tool for forecasting of the electric field and plasma convection patterns and the field-aligned current distributions over the high latitude ionosphere. The SuperDARN HF radar network provides ample opportunities for comprehensive comparisons of measured ionospheric plasma drifts with the modeled electric fields (i.e., 2-D plasma convection) and field-aligned currents. Several events under the relatively stable and unstable IMF conditions are investigated and discussed. Situations with IMF Bz>0 and Bz<0 are considered. Correlation coefficients for the SuperDARN/ IZMEM comparisons for both the magnitude and direction of the fields are found to be of the order of 0.7. The IZMEM predictions of location, direction, and magnitude of the field-aligned currents are also in good agreement with the SuperDARN observations. As expected, the IZMEM model is less reliable in forecasting of localized ionospheric plasma inhomogeneities, especially during the non-stationary IMF conditions.

A.V.Runov, M.I.Pudovkin (Institute of Physics, St.-Petersburg University, 198904, Russia)

C.-V.Meister (Institute for Theoretical Physics and Astrophysics, Potsdam University, Germany)

The 2D problem of initial current layer evolution in a result of the development of local anomalous resistivity is solved by numerical integration of corresponding MHD equation system. Initial magnetic field configuration is described as the tail-like equilibria layer with nonzero normal component. The profile of anomalous resistivity at the start of process is given, further development of the resistivity is determined by current density configuration. In focus of our attention are processes occur actually in the diffusion region and on its boundary, so we consider the early phase of the process.

Obtained results include temporal and spatial variations of magnetic and electric fields, plasma motion topology and MHD wave-like disturbances in dependence of the normal component intensity.

This work was supported by RFFI-DFG project 436 RUS 113/77 "Reconnection and turbulence".

M.A.Shukhtina, V.A.Sergeev (Institute of Physics, University of St.Petersburg, St. Petersburg, Russia; e-mail shuckht@snoopy.niif.spb.su)

R.Rasinkangas (Dept. of Physical Sciences,University of Oulu, Finland)

G.Kremser, A.Korth (Max-Plank-Institute fur Aeronomie, Katlenburg-Lindau,Germany)

G.Reeves, M.Thomsen (Los Alamos National Laboratory, Los Alamos, USA)

N.C.Maynard (Mission Research Corporation, Nashua, USA)

E.M.Basinska (Center for Space Physics, U. Boston, USA)

H.Singer (Space Environment Laboratory, NOAA, Boulder, USA)

E.V.Voronov

The motion of ions in the magnetospheric tail is considered. An analysis shows that one-particle code describes adequately the acceleration and heating of heavy ionospheric ions up to magnetospheric temperatures. The plasma configuration in the tail is similar to plasma sheet. Results of simulation using 3-d particle code are presented. An abrupt increase of the magnetospheric electric field leads to formation of a hot plasma cloud in the distant plasma sheet, which convects earthward. Earthward field-align flows with very high velocities (more then 1000 km/s) are produced near the model plasma sheet boundaries. In contrast, if the electric field varies slowly in time, then the mean energy of ionospheric ions in the near-Earth tail remains almost independent on activity level. The interaction of one-particle code with model of plasma sheet as a collisionless shock wave is also considered.

This work was partly supported by Russian Foundation for Basic Research under grant 96-05-64478.

A.A.Arykov, Yu.P.Maltsev, A.A.Ostapenko (Polar Geophysical Institute, 184200, Apatity, Russia)

A.A.Ostapenko, Yu.P.Maltsev (Polar Geophysical Institute, Apatity, Russia)

D.G.Sibeck (Applied Physics Laboratory, John Hopkins University, Laurel, USA)

The magnetospheric magnetic field disturbance during the solar wind pressure impulse (SI) passing along the magnetosphere is imitated as moving of the imaginary dipole from the subsolar point toward the Sun. During the movement, magnetic moment of the imaginary dipole is varied to create fixed magnetic field disturbance in the subsolar point. The model allows to derive the electric field and field-aligned currents variations inside the magnetosphere during SI. The magnetic field disturbance results in the electric field generation inside the magnetosphere. Generated electric field leads to the magnetospheric plasma movement. At the initial stage of SI, the field-aligned currents result from the down-dusk asymmetry in the movement of the inner plasmasheet boundary. In high latitude these field-aligned currents may lead to ground-measured magnetic disturbance of order of 10-100 nT.

Yu.P.Maltsev (Polar Geophysical Institute, Apatity, Russia)

Generation of the field-aligned current in a hot magnetospheric plasma is studied for a case when the magnetospheric volume varies due to variations in the solar wind dynamic pressure. The generated field-aligned current impulse is shown to be proportional to both the pressure impulse and the current density before the impulse onset. If the field-aligned currents are absent before a leap in the solar wind pressure they do not appear after the leap. For typical parameters, the ground magnetic perturbation produced by the field-aligned current variation is about 10-100 nT.

L.V.Benkevitch, W.B.Lyatsky (Polar Geophysical Institute, Apatity, Russia)

By present a number of ionospheric travelling convection vortices (TCV) events are observed and described. It is commonly assumed that a vortex focus in the ionosphere is situated right above the point where ground magnetometer data indicate zero of its magnetic field horizontal component. This is the case for a symmetric Hall current vortex. However, in accordance with observation results real TCVs are usually asymmetric strongly and their horizontal magnetic field zeros on the Earth surface are shifted with respect to their foci's position in the ionosphere. Two theoretical models of Hall current vortices have been considered and they are presented here. The models allow estimation of magnetic field horizontal component zero and extremum positions under a TCV as a function of a degree of its asymmetry. The results obtained could help to indicate with better precision the magnetospheric origins of field-aligned currents whose footprints the vortex foci happen to be.

D.Sibeck (APL/JHU, Laurel, Maryland, USA)

Ion energy dispersion events observed onboard the DMSP F7 satellite are studied. The dispersion trace can be characterized by an apparent drift velocity of the precipitating particles calculated from their energy spectra. The apparent drift velocity as a function of the interplanetary magnetic field (IMF) & magnetic local time (MLT) is investigated. The results obtained are in good agreement with the traditional dayside magnetospheric convection patterns expected for the northward and southward direction of the IMF. But some features of the apparent drift velocity behavior give an evidence that the ionospheric convection is not a single factor controlling the ion dispersion trace formation. One more possible cause effecting the ion dispersion in the cusp/cleft region may be consequence of the cusp/cleft displacement due to the changes in the solar wind dynamic pressure and/or the IMF Bz (and By) component variations. The magnetic field lines for this case may be considered as being fixed in the ionosphere. The estimates show that the contributions of both these mechanisms, the former of those is proportional to the IMF Bz value, whereas the latter is proportional rather to the time derivatives of the IMF Bz and solar wind dynamic pressure, have approximately the same order of magnitude.

T.A.Yahnina, B.B.Gvozdevsky (Polar Geophysical Institute, Apatity, Russia)

On the basis of the low-altitude NOAA satellite data we studied the morphology of the energetic proton precipitation occurring equatorward of the isotropy boundary of >30 keV protons. Anisotropy of the particle flux allows to suggest the moderate pitch-angle diffusion into the loss cone. Unlike to the plasma sheet protons the considered population does not contain the particles with energies <20 keV. The intensity of the proton flux correlates with geomagnetic activity in all local time sectors. Independently on the activity, the flux intensity is higher in the night-evening sector. The dropout of the flux is found westward of the meridian of 18 MLT. The flux decreases to tenth of maximal value at around 06-09 MLT. These findings allow us to suggest that the injected in the night sector and westward drifting protons precipitate due to interaction with ion-cyclotron waves in the vicinity of the evening bulge of the cold plasmaspheric plasma. In such a case the low-latitudinal edge of proton precipitation region could be considered as an indicator of the position of plasmapause. Formation of the proton flux depletion due to the charge exchange is also discussed.