Study of the Relationship Between Diffuse Auroral and Plasma Sheet Electron Distributions.

This thesis deals with the relationship between the diffuse auroral and plasma sheet electron distributions in the midnight region (+/-2 hrs MLT) of the earth's magnetosphere. Past studies have suggested that electron cyclotron harmonic (ECH) waves in resonance are responsible for the pitch angle diffusion of low energy plasma sheet electrons into the atmospheric loss cone and the resulting precipitation into the diffuse auroral ionosphere. However, the adequacy of ECH waves as the principal diffusion mechanism is currently in controversy and is tested empirically in this study. The data base used consisted of low energy (50 eV to 25 keV) differential electron flux measurements from the low altitude polar-orbiting P78-1 satellite and the near-geosynchronous SCATHA satellite taken when the two spinning satellites were in conjunction, i.e., located at points along the same geomagnetic field line. The P78 -1 measurements provided electron pitch angle distribution information within the loss cone during the conjunction events. (Direct measurements within the equatorial loss cone have never been made because of the inadequate angular resolution of the electron detectors.) One and a half years of electron data yielded 14 useful conjunction events that were used to calculate precipitation lifetimes and pitch angle diffusion coefficients as functions of energy and magnetic activity (Kp). By using the empirically determined diffusion coefficients within the framework of quasi-linear pitch angle diffusion theory, ECH wave amplitudes required to scatter trapped plasma sheet electrons into the atmospheric loss cone were determined. The results were compared to past analyses and to measured wave amplitudes from the OGO 1 and GEOS 2 satellites. Unfortunately, an unequivocal interpretation is not possible. The empirical requirements of this study are compatible with the OGO 1 measurements but exceed the wave amplitudes reported from the GEOS 2 observations.