Variability of the total radiation belt electron content

Abstract

To quantify radiation belt variability, while de-emphasizing internal transport, the total number of electrons in the outer belt has been computed from data taken on the Polar satellite as a function of time throughout 1998 and of kinetic energy in the range 0.8 to 6.4 MeV. Changes in this electron content are resolved on timescales from ̃1 day to several months. The variability is greatest at the higher energies, with several distinct (factor ≲10 3) injections followed by extended (≲100 day) periods of decay. Time-dependent magnetic field models are unable to accurately remove changes caused by adiabatic variations, but calculations based on a modified dipole field show that this can be achieved. Corrections are also made for radial transport conserving an adiabatic invariant. They show that seemingly small injections at high L may really be of comparable magnitude to large injections at low L. © 2009.