Comparative study of plasma wave activity in the plasma sheet boundary and near Earth plasma sheet

The general structure of low frequency wave activity in the Earth's plasma sheet and its boundary layer is studied on the basis of the measurements made by ‘Prognoz-8’ satellite in the northern night and morning parts of the magnetotail. Pronounced wave activity is permanently observed in the high latitude parts of the plasma sheet boundary layer. The level of perturbations diminishes when a spacecraft moves towards tail lobes and drops rather sharply when it moves to the central plasma sheet. The peaks near the low hybrid resonance frequency (correlating with the local strength of the magnetic field) are evident in the electric field fluctuations spectra. A plasma instability of low hybrid type driven by transverse current is though to be the possible candidate for the excitation of these waves. Wave activity in tail lobes is related mainly to the isolated hot and cold plasma streams.