Cross‐L motion of a relativistic electron belt formed in the slot region

Abstract

A series of large magnetic storms during the March‐June 1991 period produced major changes in energetic particle fluxes in the magnetosphere. The most significant change was the addition of a semidurable belt of extremely energetic particles (Eel > 15 MeV and Eprot > 40 MeV) at 2.2 < L < 2.5 after the late March magnetic storm. This belt slowly moved to lower L. The width of the belt at half‐intensity remained constant at ΔL = 0.43 from 1 day after its formation through the end of the observations 6 months later. We have used data from the medium electrons A (MEA) and medium electrons B (MEB) particle spectrometers on CRRES to obtain cross‐L motion rates for the fraction of these energetic particles that occur as a background effect in the MEA and in the MEB (>6.5 MeV and >1 MeV respectively). Cross‐L motion rates for the first week after the storm sudden commencement of March 24, for the first month, and for the next 6 months have been obtained. The long‐and short‐term average rates of motion across L, ∼6 × 10−4 and ∼3 × 10−2 per day at L = 2.0 to 2.3, are similar to radial diffusion rates obtained from the distribution functions of fission electrons (Farley, 1969) and of relativistic electrons after a major magnetic storm (Tomassian et al., 1972). It is inferred from the constancy in width of the belt that radial diffusion proceeded predominantly toward lower L. The long‐term apparent decay rate for the particle flux intensity as seen by these instruments is a simple exponential in time: Nt = N0ek(1‐t/t0), where k is 0.069.