Medium energy pitch angle distribution during substorm injected electron clouds

Abstract

An investigation of pitch angle resolved electron data of energy <47 keV made by the MPA instrument on LANL geosynchronous satellites reveals a signature of symmetric peaks in the pitch angle distributions, observed to expand from being nearly at perpendicular pitch angles (∼90°) to nearly field aligned at lower energies. This feature is seen in almost every interval of increased fluxes at geosynchronous orbit. A closer examination reveals the expansion of the peak in pitch angle to be such that the corresponding parallel velocity (along B) is constant. In some time intervals there are simultaneous symmetric peaks in more than one energy band and the parallel energy corresponding to the symmetric peaks is seen to vary as function of time. The observations might be explained by particles interacting with whistler mode chorus through Landau resonance, diffusing particles with parallel velocity near the phase velocity of the waves.