Abel, Gary Alexander; (1999) Field aligned electron distributions in the inner magnetosphere. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Low energy (≤ 100 eV - 10 keV) field aligned electrons are often observed by the Low Energy Plasma Analyzer (LEPA) on the CRRES satellite. These electrons usually occur in bursts of less than 10 minutes duration and are mostly bi-directional though not always equally. The events can be seen from L-values of 5 outwards (to at least L=7) and over most of the MLT range covered by CRRES. Most events are seen at the outer edge of CRRES' coverage and in the evening and early morning sectors, when the apogee of CRRES was at higher latitudes. The bursts normally occur within 20 minutes of substorm onset. The counterstreaming electrons usually appear to be scattered out of the loss cone while gaining energy. The total increase in energy may be more than an order of magnitude while the pitch angle increases to about 60 degrees. Theoretical diffusion curves for the resonant interaction between electrons and parallel propagating whistler mode waves have been suggested by Summers et al, 1998. These curves are distinctly different from the scattering paths seen in the LEPA data. The diffusion paths suggested by Summers et al, 1998, assume that the dispersion relation of the plasma is dominated by the cold plasma. We show that in the case of counterstreaming beams the dispersion relation is markedly different from the isotropic cold plasma approximation, and that the diffusion curves may well be different under this regime. High latitude spacecraft often observe upgoing field aligned electron beams. We believe these to be the source of the field aligned electron beams seen by CRRES. We see magnetic field perturbations, around the time of the counterstreaming beams, consistent with field aligned currents. We suggest that the electrons populating the counterstreaming beams may be the current carriers.

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