Ac Fields and Wave Particle Interactions

Abstract

Several new experiments provide detailed information about electrostatic and electromagnetic plasma waves in the outer magnetosphere, magnetosheath, and solar wind. Dipole antennas now commonly detect the electric components of whistler mode chorus and triggered emissions near 20 to 50 % of the local or equatorial gyrofrequency, and purely electrostatic bursts are sometimes found in the same frequency range. Non whistler mode electrostatic noise with f>f _c (local) is very frequently detected on the nightside auroral lines of force, and strong emissions that appear to be related to the Bernstein modes are found beyond the plasmapause very near the magnetic equator. These electrostatic signals, as well as the chorus bursts, represent strong sources of turbulence that can produce significant pitch angle scattering, particle precipitation, and acceleration. On Pioneer 8 and 9 low frequency electrostatic waves are found near the nightside magnetopause boundary; these signals may be associated with fast diffusion and with the ‘viscous’ interaction that produces the geomagnetic tail. In the magnetosheath and solar wind other types of wave particle interactions are observed. Magnetic ‘null’ regions at filament boundaries generally involve excitation of intense high frequency electrostatic noise and locally trapped electromagnetic waves are sometimes detected in density troughs. The modern comprehensive payloads allow some wave modes to be identified completely and in-orbit verification of the E field amplitude measurements is obtained.