Radial diffusion observations in the Earth's outer radiation belt

Abstract

We examined the intensities and differential energy spectra of electrons between 1 and 3.6 Mev obtained with an instrument flown on polar-orbiting AF Satellite OV1 9 during May and June 1967, which almost coincided with the time of maximum solar activity. We observed a severe depletion of the outer-belt electrons with Ee>0.94 Mev coincident with the onset of the magnetic storm of May 25, and the subsequent growth of the peak flux at L≃3.0 (pre-storm L≃3.8). Over the region 2.5≲L≲5, and on May 23, 24, and June 16, the e-folding energies (E0) versus L distributions were found to be characteristic of the bimodal diffusion process. After the May 25 storm, the E0 distributions were independent of L, and we observed a spectral hardening from 〈E0〉 = 482 ± 67 kev (May 27) to the pre-storm value of 〈E0〉 = 567 ± 57 kev (June 14). On June 5, a secondary electron maximum appeared at L=3.40, which then diffused outward across field lines, with a velocity ∝ L10.6±2.0.