Periodicities in the IUE Particle Radiation Data

Abstract

The magnetospheric charged particle flux measured serendipitously by the IUE satellite during perigee passages from February 1978 to February 1989 has been searched for periodicities using Fourier transform and correlation techniques. The analysis uncovers persistent modulations of the particle flux with periods of 28 to 33 days and 15 to 17 days. The particle flux seen by IUE in the outer van Allen belt is modulated to a significant extent by the magentosphere's interaction with high-speed solar wind streams from coronal holes, in agreement with analyses of fluxes at other altitudes and of geomagnetic disturbance indices. It is suggested that recurrent global solar surface activity, such as the 25.8 day periodicity discussed by Bai and Sturrock (1991) and the solar "hot spots" reported by Bai (1987, 1988, 1990), may play a role in modulating the particle flux near solar maximum. (SECTION: The Solar System)