The Effects of IMF B_z Periodic Oscillations on Thermospheric Meridional Winds

Previous studies mostly focused on ionosphere and thermosphere responses to strong southward interplanetary magnetic field (IMF) B_z conditions. However, it is not clear how the ionosphere and thermosphere (IT) system responds to Alfvénic quasi-periodic oscillating IMF B_z conditions. In this article, simulations by the Coupled Magnetosphere Ionosphere Thermosphere model have been used to investigate the effects of IMF B_z temporal variations with 10-, 30-, and 60-min oscillation periods on the coupled IT system. The simulation results show that the cross polar cap potential and auroral peak electron energy flux are stronger when the IMF B_z oscillation frequency is lower. The relatively small periodic wind responses in the 10-min IMF oscillation case indicates a low-pass filter nature of the magnetosphere-ionosphere-thermosphere system. Two different thermospheric wind (Vn) responses are revealed. One is the almost simultaneous responses at all latitudes, and the other shows a typical traveling atmospheric disturbances signature with a time delay with respect to the latitude for all UTs. The simultaneous Vn responses at all latitudes appear in the daytime Northern Hemisphere, which are mainly caused by the ion drag force in association with penetration electric fields induced plasma density and ion drifts changes. The short-period traveling atmospheric disturbances occurring in the nighttime of both hemispheres and the daytime of the Southern Hemisphere propagate from high to low latitudes showing latitudinal dependence. Both responses oscillate with the same frequencies as those of IMF B_z oscillations.