Satellite observations of the average properties of auroral particle precipitations: Latitudinal variations

Abstract

The results of a statistical study of the auroral particle data from satellite 1963-42A have shown some interesting systematics in the averaged properties of the low-energy particles. When data from 216 traversals of the auroral zones were averaged over 1° intervals of invariant latitude, a statistically significant ‘soft’ electron zone was found at high latitudes at local times near midnight and noon. Both the averaged pitch-angle distributions and energy spectral distributions of the auroral electrons were found to vary systematically with latitude. The averaged energy distributions in the ‘hard’ zone hardened dramatically with decreasing latitude on the dayside, in reasonably good agreement with expectations assuming they were precipitated from a quasi-trapped parent population that was drifting in L under conservation of the first two adiabatic invariants. This process could be a source for energetic outer belt electrons. On the nightside, the dependence on latitude was less pronounced, but there was evidence for a maximum in the spectral hardness near the center of the zone. The averaged angular distributions were almost isotropic near the center of the zone and became highly anisotropic in the wings, with the maximum flux at high pitch angles. The auroral proton precipitation zone consisted of a single peak that exhibited a diurnal variation of 8½°.