[P-EM12] 太陽地球系結合過程の研究基盤形成

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

*藤原 均¹、野澤 悟徳²、小川 泰信³、三好 勉信⁴ (1.成蹊大学サステナビリティ教育研究センター/理工学部、2.名古屋大学宇宙地球環境研究所、3.国立極地研究所、4.九州大学大学院理学研究院地球惑星科学部門)

キーワード：熱圏、電離圏、極冠域、EISCATレーダー、モデリング

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.