Measurements of the ambient photoelectron spectrum from atmosphere explorer

The ambient photoelectron spectrum above 300 km has been measured for a sample of 500 AE-E orbits during the period 13 December 1975 to 24 February 1976 corresponding to solar minimum conditions. The average and maximum ΣKsub(p) were 19 and 35, respectively. The photoelectron flux above 300 km was found to have an intensity and energy spectrum characteristic of the 250-300 km production region only when there was a low plasma density at the satellite altitude. At altitudes of 600 km, the photoelectron fluxes ranged from severely attenuated to essentially unaltered-depending on the specific conditions. Comparison of the observed attenuations photoelectron line broadening, and energy loss due to coulomb scattering from the thermal plasma with rough calculations based on stopping power and transmission coefficients of thermal plasma for fast electrons yielded order of magnitude agreement-satisfactory in view of the large number of assumptions necessary for the calculations. overall, the impression of the high altitude photoelectron flux which emerges from this work is that the fluxes are extremely variable as a consequence of interactions with the thermal plasma whose density is in turn affected by electrodynamic and neutral wind processes in the underlying F region. (author)