The interplanetary modulation and transport of Jovian electrons

Abstract

Simultaneous measurements by Pioneer 11 of the 3‐ to 6‐MeV Jovian electron flux, interplanetary magnetic field magnitude, and solar wind speed during the pre‐Jupiter encounter period reveal that electron transport across the average field direction was greatly inhibited in corotating interaction regions (CIR's) and enhanced in rarefaction regions. Since CIR's are regions of compressed solar wind plasma, these results suggest that cross‐field transport is affected by the degree of compression of the solar wind. The ‘stochastic field’ model of cross‐field diffusion provides a plausible explanation of the effect of compression on the cross‐field diffusion coefficient K⊥. The solution of a convection‐diffusion equation for a model that includes the effects of CIR's and assumes that Jupiter is a time‐independent point source of electrons describes the spatial dependence of the peak electron fluxes and the time‐intensity profiles of individual electron flux increases. It has been noted that Jovian electrons are detected at the earth even when the interplanetary magnetic field does not appear to connect the earth directly to Jupiter. By extending the above model to 1 AU from the sun we find that cross‐field diffusion of the electrons provides a plausible explanation for this observation.