CALIBRATION OF A NUMERICAL IONOSPHERIC MODEL WITH EISCAT OBSERVATIONS

A set of EISCAT UHF and VHF observations is used for calibrating a cou pled fluid-kinetic model of the ionosphere. The data gathered in the p eriod 1200-2400 UT on 24 March 1995 had various intervals of interest for such a calibration. The magnetospheric activity was very low durin g the afternoon, allowing for a proper examination of a case of quiet ionospheric conditions. The radars entered the auroral oval just after 1900 UT: a series of dynamic events probably associated with rapidly moving auroral arcs was observed until after 2200 UT. No attempts were made to model the dynamical behaviour during the 1900-2200 UT period. In contrast, the period 2200-2400 UT was characterised by quite stead y precipitation: this latter period was then chosen for calibrating th e model during precipitation events. The adjustment of the model on th e four primary parameters observed by the radars (namely the electron concentration and temperature and the ion temperature and velocity) ne eded external inputs (solar fluxes and magnetic activity index) and th e adjustments of a neutral atmospheric model in order to reach a good agreement. It is shown that for the quiet ionosphere, only slight adju stments of the neutral atmosphere models are needed. In contrast, adju sting the observations during the precipitation event requires strong departures from the model, both for the atomic oxygen and hydrogen. Ho wever, it is argued that this could well be the result of inadequately representing the vibrational states of Nz during precipitation events , and that these factors have to be considered only as ad hoc correcti ons.