The topside equatorial ionosphere during daytime: Elevated plasma temperatures, the transequatorial O + breeze and the dynamics of minor ions

Abstract

Steady-state calculations are performed for the daytime equatorial F2-region and topside ionosphere. Values are calculated of the electron and ion temperatures and the concentrations and field-aligned velocities of the ions O +, H + and He +. Account is taken of upward E × B drift, a summer-winter horizontal neutral air wind and heating of the electron gas by thermalization of fast photoelectrons. The calculated plasma temperatures are in accord with experiment: at the equator there is an isothermal region from about 400–550 km altitude, with temperatures of about 2400 K around 800 km altitude. The transequatorial O + breeze flux from summer to winter in the topside ionosphere is not greatly affected by the elevated plasma temperatures. The field-aligned velocities of H + and He + depend strongly on the O + field-aligned velocity and on the presence of large temperature gradients. For the minor ions, ion-ion drag with O + cannot be neglected for the topside ionosphere.