THE BEHAVIOR OF H+-IONS AND HE+-IONS IN THE TOPSIDE IONOSPHERE DURING A SHORT-LIVED SUBAURORAL ION DRIFT

A model of the ionosphere and plasmasphere is used to investigate the effects of an imposed westward plasma drift on H+ and He+ behaviour in the nightside topside ionosphere. A closed subauroral tube of plasma is considered and the velocity spike, of maximum value 2 km s-1, persists for 10 min. The upward surge of O+ flow (caused by frictional heating of the ions in the F-region) gives rise to rapid upward H+ and He+ flows. The H+ and He+ velocities in the topside are comparable to those of O+ but the transient H+ and He+ flows are not significant contributors to the magnetospheric light ion population. Above 500 km altitude the ionospheric H+ and He+ densities decrease during the westward plasma drift.