Model studying the dynamics of tidal variations at altitudes of the middle thermosphere during geomagnetic disturbances

Results of the numerical computation of the tidal variation characteristics and of the average values of the horizontal components of the wind temperature and velocity at altitudes of 120-160 km are presented. The computations have been performed using the global self-consistent model of the thermosphere, ionosphere, and protonosphere (GSM TIP) for the conditions of August 22-30, 1998, when the strong geomagnetic disturbance was observed (August 26-27). The dynamics of the diurnal and semidiurnal tidal variations and of the average values of the wind and temperature horizontal components has been analyzed. It has been indicated that disturbances of tidal variation amplitudes depend on the phase of geomagnetic disturbance development, latitude, and longitude. The complex of physical processes governing the response of tidal variations in different latitudinal regions of the thermosphere at all stages of geomagnetic disturbance development has been determined. It has been indicated that the role of ion drag is important at the initial stage of a geomagnetic disturbance. In the periods of geomagnetic activity maximum and decay, the response of the thermosphere is governed by the processes initiated by Joule heating in the polar cap, as a result of which thermospheric disturbances exist for a long time.