[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-05] Atmospheric ionization of EMIC-wave driven energetic electron precipitation events

*村瀬 清華^1,2、片岡 龍峰^1,2、田中 良昌^1,2、西山 尚典^1,2、橋本 大志^1,2、佐藤 薫³ (1.総合研究大学院大学、2.国立極地研究所、3.東京大学)

キーワード：大気電離、プラズマ波動、高エネルギー電子降下

Electromagnetic ion cyclotron (EMIC) waves have been known as one of the main drivers of energetic electron precipitation (EEP) into the Earth’s atmosphere. EEP associated with EMIC wave activity have been shown to causes localized mesospheric ozone depletion, suggesting a non-negligible impact on atmospheric variabilities. However, it is difficult to quantitatively discuss the global impact of EMIC-wave driven EEPs due to the lack of comprehensive observations of the energy range (i.e., ionization altitude), ionization intensity, and spatial extent. In this study, we attempt to characterize these ionization profiles focusing on the evaluation of the ionization impact of EMIC-wave driven EEPs based on the intensity, duration, and spatial extent of the ionization captured by ground-based measurements. We use observational data of the imaging riometer, the atmospheric radar, PANSY, and the magnetometer at Syowa Station (CGMLAT=-66.5°) in 2016-2019, which provide information of ionization altitudes, and wave spectra, respectively. We have found at least 350 events of EMIC-EEP candidates in which the mesospheric ionization coincides with the EMIC wave activities. The MLT distribution of events peaks on the afternoon side (14 MLT). Ionization signatures at altitudes below 60 km, suggesting >MeV electron precipitation, are confirmed for 35 % of the events. So far, only these basic statistical investigations have been completed, while the evaluation of ionization impact is still ongoing. In this presentation, we will discuss the evaluation in terms of the characteristics of ionization profiles for different types of wave excitation and physical properties of waves, i.e., wave frequency and band.