Radiation belt electron flux variability during three CIR-driven geomagnetic storms

Abstract

Coronal holes produce high speed solar wind streams ( HSS) that subsequently interact with the slower downstream solar wind forming co-rotating interaction regions (CIRs). The CIR/ HSS combination drives geomagnetic storms that have a weak to moderate signature in D st . We simulate the behavior of relativistic (976 keV) electrons in the outer radiation belt and the slot region ( 2 ⩽ L ⩽ 7 ) during three CIR-driven storms associated with three consecutive rotations of a coronal hole that occurred just after solar maximum during June–August 1991. We use a 1d radial diffusion model (RADICAL) with losses due to pitch-angle scattering by plasmaspheric hiss. The losses are expressed through the electron lifetime calculated using the PADIE code driven by a global K p -dependent model of plasmaspheric hiss intensity and f pe / f ce . The outer boundary condition is time and energy-dependent and derived from observations. The model reproduces the observed flux at L = 5 to within about a factor of 3 suggesting that flux levels are well-described by radial diffusion to and from the outer boundary. At L = 3.5 and 4, the model overestimates the flux decay rates. This results in the observed flux exceeding the model flux, by up to a factor of 5 at L = 4 and by up to a factor of 8 at L = 3.5 , by the end of the recovery phase. Comparison with model results from a geomagnetically quieter interval suggest that the underestimation in flux may be due to the lack of representation of local wave acceleration in the model.