[P-EM12] Study of coupling processes in solar-terrestrial system

[PEM12-P19] Changes in the polar cap thermosphere/ionosphere during geomagnetically quiet periods

*Hitoshi Fujiwara¹, Satonori Nozawa², Yasunobu Ogawa³, Yasunobu Miyoshi⁴ (1.Education and Research Center for Sustainable Development/Faculty of Science and Technology, Seikei University, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.National Institute of Polar Research, 4.Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University)

Keywords:thermosphere, ionosphere, polar cap, EISCAT radar, modeling

Even during geomagnetically quiet periods, the European Incoherent Scatter (EISCAT) radar system has frequently observed significant disturbances in the dayside polar cap ionosphere. For example, high speed ion flows (> 800 m/s) with strong shears were observed at latitude higher than 80 deg on March 11, 2021. At that time, the flow directions were changed, and enhancements of the ion temperature (> 1000 K) were seen within several minutes under the condition of geomagnetically quiet (Kp~ 0-1). Some questions arise: (1) What are the maximum values or upper limits of the ion flow speed and ion temperature during geomagnetically quiet periods? (2) Where is the region of such a significant ionospheric variation? (3) What are the thermospheric variations in association with such an ionospheric variation? In order to answer the questions, we have made observations of the polar ionosphere with the EISCAT radar system and carried out modeling studies for global thermospheric and ionospheric simulations. In this presentation, we will introduce some of our previous results and our research projects with the EISCAT/EISCAT_3D radar system and a global model.