CROSS-L MOTION OF A RELATIVISTIC ELECTRON BELT FORMED IN THE SLOT REGION

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 (E(el) > 15 MeV and E(prot) > 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 DELTAL = 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, approximately 6 x 10(-4) and approximately 3 X 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: N(t), = N0e(k)(1-t/t0), where k is 0.069.