Global, collisional model of high-energy photoelectrons

A previously-developed colissional, interhemispheric flux tube model for photoelectrons (PE) [Khazanov et al., 1994] has been extended to three dimensions by including transport due to (E) over right arrow x (B) over right arrow and magnetic gradient-curvature drifts. Using this model, initial calculations of the high-energy (greater than or equal to 50 eV) PE distribution as a function of time, energy, pitch angle, and spatial location in the equatorial plane, are reported for conditions of low geomagnetic activity. To explore both the dynamic and steady behaviors of the model, the simulation starts with the abrupt onset of photoelectron excitation, and is followed to steady state conditions. The results illustrate several features of the interaction of photoelectrons with typical magnetospheric plasmas and fields, including collisional diffusion of photoelectons in pitch angle with flux tube filling, diurnal intensity and pitch angle asymmetries introduced by directional sunlight, and energization of the photoelectron distribution in the evening sector. Cross-field drift is shown to have a long time scale, taking 12 to 24 hours to reach a steady state distribution. Future applications of the model are briefly outlined.