PRECIPITATING ELECTRONS ASSOCIATED WITH THE DIFFUSE AURORA - EVIDENCE FOR ELECTRONS OF ATMOSPHERIC ORIGIN IN THE PLASMA SHEET

Observations were made of precipitating electrons associated with the proton, or diffuse, aurora. At energies greater than about 1 keV the electron energy distribution was Maxwellianlike, and pitch angle distribution was isotropic over the precipitation hemisphere but displayed a well-developed atmospheric loss cone over the upgoing hemisphere. In contrast, the energy distribution of the lower-energy electrons more nearly approached a power law, while the pitch angle distribution approached isotropy. The symmetry between the downgoing and upgoing low-energy electron intensities shows that at these energies the downgoing electrons have their origin as backscattered and secondary electrons from an atmosphere. It is proposed that backscattered and secondary electrons, produced as a result of the general precipitation, are pitch angle scattered into stably trapped orbits while in transit along the magnetic field line by the same turbulent wave fields generally invoked to account for the precipitation. The reservoir of trapped electrons thus becomes a combination of some primordial population and the electrons produced from the atmosphere by precipitation from this reservoir. Numerical models of the equilibrium electron energy spectrum expected to exist in this situation were developed.