NUMERICAL MODELING OF THE THERMOSPHERIC AND IONOSPHERIC EFFECTS OF MAGNETOSPHERIC PROCESSES IN THE CUSP REGION

The thermospheric and ionospheric effects of the precipitating electro n flux and field-aligned-current variations in the cusp have been mode lled by the use of a new version of the global numerical model of the Earth's upper atmosphere developed for studies of polar phenomena. The responses of the electron concentration, ion, electron and neutral te mperature, thermospheric wind velocity and electric-field potential to the variations of the precipitating 0.23-keV electron flux intensity and field-aligned current density in the cusp have been calculated by solving the corresponding continuity, momentum and heat balance equati ons. Features of the atmospheric gravity wave generation and propagati on from the cusp region after the electron precipitation and field-ali gned current-density increases have been found for the cases of the mo tionless and moving cusp region. The magnitudes of the disturbances ar e noticeably larger in the case of the moving region of the precipitat ion. The thermospheric disturbances are generated mainly by the thermo spheric heating due to the soft electron precipitation and propagate t o lower latitudes as large-scale atmospheric gravity waves with the me an horizontal velocity of about 690 m s(-1). They reveal appreciable m agnitudes at significant distances from the cusp region. The meridiona l-wind-velocity disturbance at 65 degrees geomagnetic latitude is of t he same order (100 m s(-1))as the background wind due to the solar hea ting, but is oppositely directed. The ionospheric disturbances have ap preciable magnitudes at the geomagnetic latitudes 70 degrees-85 degree s. The electron-concentration and -temperature disturbances are caused mainly by the ionization and heating processes due to the precipitati on, whereas the ion-temperature disturbances are influence strongly by Joule heating of the ion gas due to the electric-field disturbances i n the cusp. The latter strongly influence the zonal- and meridional-wi nd disturbances as well via the effects of ion drag in the cusp region . The results obtained are of interest because of the location of the EISCAT Svalbard Radar in the cusp region and the associated observatio ns at lower latitudes that will be possible using the existing EISCAT UHF and VHF radars. The paper makes predictions for both these regions , and these predictions will be tested by joint observations by ESR, E ISCAT UHF/VHF and other ground-based ionosphere/thermosphere observati ons.