Regular Density Inhomogeneities in the Boundary Layer of the Plasmasphere

Abstract

Based on thermal plasma measurements on the MAGION-5 and INTERBALL-1 satellites in the plasmasphere boundary layer, similar recurring changes in the proton density were identified depending on the L-shell. Such density variations have the following characteristic features: (a) density variations occur sharply, on the density profile—the dependence of density on L or on geomagnetic latitude λ—they have a sawtooth nature, and the density of protons at the peaks (maxima) of variations exceeds that at the minima of variations by two to eight times; (b) the characteristic size of variations in the radial direction in the plane of the geomagnetic equator is ~0.15 RE or ~1000 km; (c) sawtooth changes in proton density in the plasmasphere boundary layer can span at least 90° in longitude; (d) regular variations in plasma density were observed at geomagnetic latitudes up to 30°, and this latitude is limited to the orbits of satellites whose data were used for the analysis. Sawtooth variations in thermal plasma density are apparently related to spatial structures that evolve but persist in the plasmasphere boundary layer, at least over the course of a day. Plasma inhomogeneities were observed in fairly quiet or slightly disturbed geomagnetic conditions. The considered inhomogeneities are probably a consequence of the interchange or quasi-interchange instability developing in the plasmasphere boundary layer.