An empirical evaluation of radial diffusion coefficients for electrons of 50-100 kev from L = 4 to L = 7

Empirical values for radial diffusion coefficients have been calculated for electrons in the range 50–100 kev from L = 4 to L = 7 on the basis of equilibrium fluxes determined from Explorer 12 data. It has been assumed that the principal loss mechanism for these electrons is pitch-angle scattering by whistlers. The diffusion coefficients derived from the data are several orders of magnitude larger than that expected from Kellogg-Parker diffusion. Typical values for D1 are 2 RE/day at L = 4.5, 85 RE/day at L = 5.5, and −25 RE/day at L = 6.5. Typical values for D2 are 3 RE²/day at L = 4.5, 63 RE²/day at L = 5.5, and 11 RE²/day at L = 6.5. Also, a sharp peak in the value of D2 occurs at L = 5.75, and D1 changes sign at this point. It is suggested that large-scale magnetospheric electric fields, of order 1 or 2 mv/m and possibly arising from field-line merging in the geomagnetic tail, may be responsible for much of this diffusion.