Long‐Term Variations of Quasi‐Trapped and Trapped Electrons in the Inner Radiation Belt Observed by DEMETER and SAMPEX

Abstract

AbstractElectrons in the Earth's radiation belts can be categorized into three populations: precipitating, quasi‐trapped, and trapped. We use data from the Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) and Solar, Anomalous, and Magnetospheric Particle Explorer satellite (SAMPEX) missions and from ground‐based neutron monitors (NM) and sunspot observations to investigate the long‐term variation of quasi‐trapped and trapped sub‐MeV electrons on different L shells in the inner belt. DEMETER and SAMPEX measurements span over 17 years and show that at L ≤ 1.14 the electron flux is anticorrelated with sunspot number, but proportional to the cosmic ray intensity represented by NM count rates, which suggests that electrons at the inner edge of the inner belt are produced by Cosmic Ray Albedo Neutron Decay (CRAND). The solar cycle variation of cosmic rays increased the electron flux at L ≤ 1.14 by a factor of 2 from solar maximum at 2001 to solar minimum at 2009. At L ≥ 1.2, both quasi‐trapped and trapped electrons are enhanced during geomagnetic storms and decay to a background level during extended quiet times. At L > 2, quasi‐trapped electrons resemble trapped electrons, with correlation coefficients as high as 0.97, indicating that pitch angle scattering is the dominant process in this region.