Numerical modelling of the thermospheric and ionospheric effects of magnetospheric processes in the cusp region

[摘要] The thermospheric and ionospheric effects ofthe precipitating electron flux and field-aligned-current variations in the cusphave been modelled by the use of a new version of the global numerical model ofthe Earth's upper atmosphere developed for studies of polar phenomena. Theresponses of the electron concentration, ion, electron and neutral temperature,thermospheric wind velocity and electric-field potential to the variations ofthe precipitating 0.23-keV electron flux intensity and field-aligned currentdensity in the cusp have been calculated by solving the correspondingcontinuity, momentum and heat balance equations. Features of the atmosphericgravity wave generation and propagation from the cusp region after the electronprecipitation and field-aligned current-density increases have been found forthe cases of the motionless and moving cusp region. The magnitudes of thedisturbances are noticeably larger in the case of the moving region of theprecipitation. The thermospheric disturbances are generated mainly by thethermospheric heating due to the soft electron precipitation and propagate tolower latitudes as large-scale atmospheric gravity waves with the meanhorizontal velocity of about 690 m s^–1. They reveal appreciablemagnitudes at significant distances from the cusp region. The meridional-wind-velocitydisturbance at 65^° geomagnetic latitude is of the same order (100 ms^–1) as the background wind due to the solar heating, but isoppositely directed. The ionospheric disturbances have appreciable magnitudes atthe geomagnetic latitudes 70^°–85^°. Theelectron-concentration and -temperature disturbances are caused mainly by theionization and heating processes due to the precipitation, whereas theion-temperature disturbances are influence strongly by Joule heating of the iongas due to the electric-field disturbances in the cusp. The latter stronglyinfluence the zonal- and meridional-wind disturbances as well via the effects ofion drag in the cusp region. The results obtained are of interest because of thelocation of the EISCAT Svalbard Radar in the cusp region and the associatedobservations at lower latitudes that will be possible using the existing EISCATUHF and VHF radars. The paper makes predictions for both these regions, andthese predictions will be tested by joint observations by ESR, EISCAT UHF/VHFand other ground-based ionosphere/thermosphere observations.

[学科分类] 地球科学(综合)