Solar cyclic behavior of trapped energetic electrons in Earth's inner radiation belt

Abstract

Magnetic electron spectrometer data from six satellites (OV3‐3, OV1‐14, OGO 5, S3‐2, S3‐3, and CRRES) have been used to study long‐term (1966‐1991) behavior of trapped energetic electrons in the inner radiation belt. Comparison of the observed energy spectra at L ≥ 1.35 for different phases of the solar cycle reveals a clear trend toward enhanced fluxes during periods of solar maximum for energies below a few hundred keV; we suggest that this is caused by an increase in the rate of inward radial diffusion from a source at higher L . In contrast, for L < 1.30, where atmospheric collisions become increasingly important, the electron flux is reduced during solar maximum; we attribute this to the expected increase in upper atmospheric densities. The electron flux above 1 MeV exhibits a systematic decay beyond 1979 to values well below the current NASA AE‐8 model. This indicates that the natural background of high‐energy electrons has previously been overestimated due to the long lasting presence of electrons produced by nuclear detonations in the upper atmosphere in the late 1950s and early 1960s.