[P-EM14] 太陽地球系結合過程の研究基盤形成

[PEM14-11] High-Latitude Ionospheric Electron Density Depletion in Response to Negative Solar Wind Pressure Pulses

*Geetashree KAKOTI¹、Kazuo Shiokawa¹、Mala S Bagiya²、Geeta Vichare²、Shreedevi P.R.¹、Nozomu Nishitani¹、Yuichi Otsuka¹、Atsuki Shinbori¹、Michi Nishioka³、Septi Perwitasari³ (1.Institute for Space-Earth Environmental Research, Nagoya University, 、2.Indian Institute of Geomagnetism, Navi Mumbai, India、3.National Institute of Information and Communications Technology (NICT), Japan)

キーワード：Negative Solar Wind Pressure Pulses, Magnetosphere-Ionosphere-Thermosphere (MIT) system, Total Electron Content , High-Latitude Ionosphere

Negative solar wind pressure pulses can induce significant disturbances in the coupled Magnetosphere-Ionosphere-Thermosphere (MIT) system, impacting its structure, currents, and plasma distributions. This study examines two distinct negative pressure pulse events: one occurring under disturbed interplanetary magnetic field (IMF Bz) conditions on 23 March 2023 and another under nearly steady IMF Bz conditions on 23 March 2024. The 2023 event, associated with a G3-G4 class geomagnetic storm, was marked by a sudden ~20 nPa drop in solar wind dynamic pressure after the storm onset. In contrast, the 2024 event occurred during a geomagnetically quiet period before the onset of G2/G4-class storms and featured a sharp ~10 nPa pressure drop. Using Global Navigation Satellite System (GNSS)-Total Electron Content (TEC), ground magnetometer data, and AMPERE observations, we analyzed the impacts of these pressure pulses on the coupled M-I system. In both cases, the sudden decrease in solar wind dynamic pressure caused a rapid magnetopause expansion, leading to reduced magnetospheric currents and weakened magnetospheric fields. This, in turn, triggered a global depletion in ground magnetic fields and field-aligned currents. A novel finding of this study is the substantial reduction in TEC at high latitudes following the pressure drop. Under the disturbed geomagnetic conditions of the 2023 event, TEC reduction was observed across all local time sectors, whereas for the 2024 event, it was primarily concentrated in the European afternoon sector. This significant perturbation in ionospheric electron density is postulated to result from magnetospheric expansion triggered by the negative pressure pulse. To further investigate the physical processes involved, we utilized a comprehensive set of ground-based and satellite observations, including data from EISCAT, SuperDARN radars, and the Global-scale Observations of the Limb and Disk (GOLD) mission. Our findings highlight the critical role of negative solar wind pressure pulses as independent drivers capable of inducing rapid and widespread perturbations in the M-I system, regardless of IMF conditions.