Self‐consistent kinetic photoelectron effects on the polar wind

Abstract

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 (i.e., 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.

Survey of cold ionospheric outflows in the magnetotail

“…This could be explained by orbital asymmetry and seasonal variations; the measurements are centred on 3 September, which means that the data are shifted by around 20 days from autumnal equinox towards northern summer. During summer the amount of escaping photoelectrons from the upper atmosphere increases, resulting in a larger ambipolar electric field and thus also a larger ion outflow (Tam et al, 1995). Large seasonal variations of the electron density have been seen at high altitude above the polar cap with Polar, and the variations are particularly steep around the equinoxes (Laakso et al, 2002).…”

Heating of the sunlit polar cap ionosphere by reflected photoelectrons

“…The second option is heavy ion outflow. Using kinetic simulations which include photoelectrons, Tam et al [1995Tam et al [ , 1998] have produced supersonic O + outflow. However, these simulations also predict electron temperatures well over 10 4 K, which are much higher than Akebono measurements [Yau et al, 1995].…”

Self‐consistent simulation of the photoelectron‐driven polar wind from 120 km to 9 RE altitude

“…In the past 10 years, attention has been focused on studying the temporal characteristics of the polar wind. However, these models [Tam et al, 1995; adopted 500 km altitude boundary conditions, and since ionospheric ions and electrons are produced in large part by photoionization of the neutral atmosphere at lower altitudes, the models are incomplete and not self-consistent. These photoionization processes occur primarily below 500 km altitude, and the maximum photoelectron production rate occurs in the 130-140 km altitude range.…”