NUMERICAL MODELING OF INTERMITTENT ION OUTFLOW EVENTS ABOVE EISCAT

EISCAT observations with the UHF and VHF radars of the dynamics of the upper ionosphere have revealed the occurrence of intermittent ion out flows with velocities reaching several hundred m s(-1). It was previou sly shown that, during such events, the topside downward electron heat flux, inferred from the analysis of the vertical (field-aligned) stru cture of the electron temperature profiles, increases drastically up t o values of about 10 mu W m(-2). The numerical models described in a c ompanion paper are used here to simulate the effects of energy inputs driven by the magnetosphere. Three main effects are simulated separate ly: effects of frictional heating related to E x B drifts, effects due to topside heat flux perturbations and effects of upward field-aligne d currents of a few tens of mu A m(-2). It is shown that field-aligned currents and topside heat flux perturbations produce very similar eff ects and that combining field-aligned currents with frictional heating allows us to model the overall characteristics of the perturbations o f the electron density, of the electron and ion temperatures, and of t he ion vertical velocity. A good agreement with observations is found.