Ion cyclotron wave growth calculated from satellite observations of the proton ring current during storm recovery

Abstract

Using Explorer 45 observations of pitch angle distributions of ring current protons as a function of radial distance and energy during the recovery phase of a large geomagnetic storm, we have calculated wave, growth rates and the total wave energy gain of ion cyclotron waves propagating parallel to the geomagnetic field from high latitude toward the equator. We conclude that the observed proton fluxes and pitch angle anisotropies are sufficient to cause significant growth. In addition, we show that the observed patterns of proton pitch angle distributions as a function of energy, radial distance, and time (Williams and Lyons, 1974a, b) are a natural consequence of the spectrum of waves which can grow and propagate under the existing conditions of storm recovery.