SELF-CONSISTENT KINETIC PHOTOELECTRON EFFECTS ON THE POLAR WIND

Anomalous electron heat fluxes and recent observations of day-night asymmetries in polar wind features indicate that photoelectrons may affect polar wind dynamics. These anomalous fluxes require a global kinetic description (le., mesoscale particle phase space evolution involving microscale interactions); their impact on the polar wind itself requires a self-consistent description. In this Letter, we discuss results of a self-consistent hybrid model that explains the dayside observations. This model represents the first global kinetic collisional description for photoelectrons in a self-consistent classical polar wind picture. In this model, photoelectrons are treated as test particles, ion properties are based on global kinetic collisional calculations, thermal electron features and the ambipolar field are determined by fluid calculations. The model provides the first global steady-state polar wind solution that is continuous from the subsonic collisional regime at low altitude to the supersonic collisionless regime at high altitude. Also, the results are consistent with experiments in several aspects, such as order of magnitude of the ambipolar electric potential, qualitative features of the ion outflow characteristics, electron anisotropy and upwardly directed electron heat flux on the dayside.