ELECTRON-PRECIPITATION ACCOMPANYING PC-5 PULSATIONS OBSERVED BY THE DE SATELLITES AND AT A GROUND STATION

Using data from the polar orbiting Dynamic Explorer (DE) -1 and -2 sat ellites and a ground-based station, we investigated electron precipita tion phenomena accompanying Pc 5 pulsations. DE-2 observed oscillatory disturbances in the magnetic and electric fields in the upper ionosph ere at the geomagnetic footprint of the high altitude region in which transverse Pc 5 pulsations were detected by DE-1. DE-2 observed electr ons precipitating into the ionosphere with energies of several keV to several tens of keV, These electrons were accelerated in the direction of the ambient magnetic field. When Pc 5 pulsations in the H-componen t and periodic variations of cosmic radio noise absorption (CNA pulsat ions) were observed at Syowa Station, DE-2 which was in geomagnetic co njunction with Syowa Station also observed oscillatory disturbances in the magnetic and electric fields. These oscillatory disturbances are caused by small-scale field-aligned currents each with. width of 0.5 d egrees-1.4 degrees invariant latitude. This suggests that Pc 5 pulsati ons have a small-scale resonance structure in the radial direction. Th e resonance structure has a small scale comparable to the ion acoustic gyroradius, then kinetic Alfven waves having electric fields parallel to the ambient magnetic field can arise. The parallel electric field generates a field-aligned potential drop of about 3-5 kV. Electrons ac celerated by these kinetic Alfven waves would cause CNA pulsations, th e phase of which leads that of the B-component of the Pc 5 pulsations by 90 degrees in the southern hemisphere. This is consistent with the observations at Syowa Station.