Doppler sounding as a tool for the study of the MHD wave structure in the magnetosphere

The results of the experiment conducted in 1987 near Kharkov to develop a technique for the study of the spatial structure of MHD waves at ionospheric heights are discussed. Simultaneous digital Doppler soundings for 6 radiopaths (1–6 MHz) and ULF magnetic recordings were performed. To retrieve the ionospheric signal induced by an MHD wave optimal filtering was applied. The ~2nT Pi2 pulsations recorded on the ground correspond to ~ 15 m/s Doppler velocity in the F-layer. Analytical expressions for the ULF-related ionospheric Doppler effect have been derived in the framework of the ‘thin’ ionosphere. Some modifications are needed to achieve satisfactory quantitative agreement between the present theoretical estimates and experimental results.