Research on the coupling process between the lower thermosphere and the mesosphere in the polar region by using radar observations and model predictions

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The lower thermosphere at high latitudes is a unique region in the earth's atmosphere, because the atmosphere there couples with the middle/lower atmosphere as well as the ionosphere and magnetosphere. The lower thermosphere is significantly influenced by atmospheric waves propagating below as well as by their dissipation. Furthermore, during geomagnetically disturbed periods, the lower thermosphere interacts with the ionosphere and magnetosphere through several physical processes. These coupling processes with upper or lower regions are, however, not yet fully understood. To understand such a coupling process more deeply, we have made studies by using EISCAT radars, other radars and model simulations. Major results are as follows. (1) We investigated the importance of the ion drag by using EISCAT radar(KST and ESR)data obtained for 11-19 November 2003. We showed the importance of the ion drag and also suggested the pressure gradient could play another important role. (2) We investigated the ion drag contribution to the diurnal tidal amplitude by analyzing the data obtained for 1-7 July 1999 by ESR. We presented that sixty percent of the diurnal tidal amplitude arose from the ion drag acceleration. (3)We conducted the DELTA rocket campaign for December 2004 to understand the effect of the anal activity to the lower thermospheric wind dynamics. By analyzing FISCAT data for 74 hours hi total, we showed the day-to-day variability of the sermidiunal tide. (4)We showed that the magnitude and the dissipation height of the turbulent and electromagnetic energy poured from the upper and lower regions seem to be strongly dependent on the neutral wind particularly below〜10 km based on ESR data Also, we derived the height distributions of the thermospheric heating rate at the F region height on 9 March 1999 in association with electromagnetic energy inputs into the dayside polar cap/cusp region.