Photoelectron fluxes in the ionosphere computed by a Monte Carlo Method

Abstract

The motions of photoelectrons in the ionosphere were simulated by a Monte Carlo technique developed specifically for this purpose. The physical model adopted for these simulations included transport effects, photoelectron collisions (both elastic and inelastic) with the three major neutral gases, and a continuous energy loss to ambient thermal electrons. The Monte Carlo approach allowed angular scattering due to photoelectron-neutral collisions to be considered in a complete and natural fashion. Two model atmospheres corresponding to two levels of solar activity were treated. For each model, photoelectron fluxes were computed as functions of altitude, energy, and pitch angle. A photoelectron escape flux of 2.5×108 cm−2 sec−1, carrying 3.6×109 ev cm−2 sec−1, was calculated for the model having moderate solar activity. The pitch-angle distribution of the escaping flux was found to be skewed toward small pitch angles. The magnitudes of the computed fluxes and other features of the results, such as the albedo of the atmosphere, are discussed and are compared with satellite and radar measurements and with the results of other calculations.