Calculated and observed photoelectron-flux spectra at dawn

Electron-flux spectra have been calculated for dawn conditions at altitudes of 180, 200 and 250 km and compared with recent observations by Hays and Sharp (1973). A discrete energy-loss model was used in the calculations and good agreement is found between the calculated and measured spectra. A discrepancy is found between the calculated rate of electron formation by photoionization and collisional ionization and the loss rate deduced from the measured electron and ion densities. No definitive explanation of this discrepancy has been found.