Energetic electron flux pulsations observed at geostationary orbit: Relation to magnetic pulsations

Abstract

Energetic electron data (30–300 keV) from Los Alamos National Laboratory charged particle analyzers on board geostationary satellites were compared with magnetic field data from the GOES 3 geostationary satellite to study electron flux pulsations in the Pc 4–5 frequency range. From particle data and magnetic field data obtained with the satellites located only a small spatial distance apart, it is found that 60% of electron flux pulsation events have clearly associated magnetic pulsations. The magnetic pulsations have three different polarization and frequency characteristics: radially polarized Pc 4, azimuthally polarized Pc 5, and compressional Pc 5. Based on theoretical work presented by Southwood and Kivelson, it is concluded that the possible causes of the observed flux modulations are convection of a particle density gradient for the radially polarized Pc 4; the mirror effect, adiabatic acceleration, or convection of a particle density gradient for the azimuthally polarized Pc 5; and the mirror effect for the compressional Pc 5. Using data from geostationary satellites located at different magnetic latitudes, it is also found that the occurrence probability increases with latitude for the Pc 4 electron flux pulsations, whereas the probability is independent of the latitude for the Pc 5 pulsations. This is interpreted as due to the fundamental (Pc 5) and second harmonic (Pc 4) structure of standing waves. The electron flux pulsations which do not accompany magnetic pulsations are attributed to azimuthally polarized fundamental standing waves that have a magnetic node very close to the satellites.