NUMERICAL-SIMULATION OF AN IONOSPHERIC DISTURBANCE OVER EISCAT USING A GLOBAL IONOSPHERIC MODEL

A global numerical model of the Earth's upper atmosphere has been used to simulate numerically the behaviour of the ionosphere observed by E ISCAT on 24-25 March 1987 when the quiet day of 24 March was followed by the disturbed day of 25 March, with a Sudden Commencement (SC) star ting about 1540 UT. We have selected the model input data for the auro ral precipitating particle fluxes and the field-aligned currents to ob tain an acceptable agreement between the calculated and observed ionos pheric variations. A rather good similarity between the calculated and observed variations of the electric field, E-region electron concentr ation, F2-region ion temperature and electron concentration has been f ound. Spatial distributions of the electric potential and F2-region el ectron concentration and ion temperature have been obtained. The dynam ics of the main ionospheric trough during the disturbed period has bee n investigated. It has been found that the equatorward movement of the midnight part of the trough is connected with the enhanced plasma tra nsport, while the apparent westward and eastward movements of the even ing and morning edges of the trough are connected with the ''hot spots '' caused by Joule heating of the ion gas.