Tail Plasma Domains and the Auroral Oval-Results of Mapping Based on the Tsyganenko 1989 Magnetosphere Model.

Abstract

We apply the magnetosphere model of TSYGANENKO (1989) to project into the ionosphere the tail plasma domains (with density >0.1cm-3) as measured by PROMICS-2 on Prognoz-8. The Plasma Sheet Boundary Layer (the separatrix layer) in our data is easily recognizable as a region distinct from the Central Plasma Sheet only when the plasma sheet expands at the beginning of substorm recovery. During weakly disturbed and quiet periods and at flanks the separatrix layer is not seen by our plasma instrument. However, when both the electron temperature and ion mass composition are taken into account we usually see three distinctly different plasma domains in the tail: the region A (we call it tentatively the warm envelope of the plasma sheet) dominated by the solar wind originated plasma with cold electrons (Te≤100eV), the region B (called here the high-latitude plasma sheet) with the electron temperature less than 1keV, density fluctuations, irregular spectra and presence of cold oxygen ion beams (field aligned and/or conical) and the region C (called here the hot core of the plasma sheet) with electron energy density≈1keV/cm3 where the hot oxygen ions dominate over the doubly ionized helium. This classification of plasma sheet subregions is similar to the one discussed by FELDSTEIN and GALPERIN (1985). We suggest that the warm envelope originates from the stagnating Low Latitude Boundary Layer. The warm envelope of the plasma sheet maps in most cases poleward of the statistical auroral oval of Feldstein-Starkov. The hot core of the plasma sheet maps into the equatorward half of the statistical oval and is connected to R<15 RE in the equatorial plane. The high latitude plasma sheet with the field aligned and/or conical O+ beams maps immediately poleward and/or into the poleward half of the F-S oval and is mostly on the field lines which close at R<60RE.