[P-EM16] 太陽圏・惑星間空間

[PEM16-03] 2025年5月に発生したCME群の惑星間空間シンチレーション観測とMHDシミュレーションの比較

*岩井 一正¹、塩田 大幸²、藤木 謙一¹、磯貝 拓史¹ (1.名古屋大学 宇宙地球環境研究所、2.情報通信研究機構)

キーワード：コロナ質量放出(CME)、惑星間空間シンチレーション

Coronal mass ejections (CMEs) cause various disturbances in the solar-terrestrial system. However, their propagation in interplanetary space has not been understood well. In early May 2024, multiple CMEs were generated and some of them arrived at the Earth, that caused severe solar-terrestrial storms. We have investigated these CMEs using the Interplanetary scintillation (IPS) observations. The IPS is a radio scattering phenomenon generated by the disturbances in the solar wind. IPS observation has been one of the most important tools for observing CMEs propagating in interplanetary space. The Institute for Space and Earth Environmental Research (ISEE), Nagoya University has observed IPS at 327 MHz using an observation system consist of three large radio telescopes. We found that an increasing number of large-amplitude IPS responses on 10 May, just before the shock arrival at the Earth. Large-amplitude IPS responses were detected especially in the line of sight in the direction of large solar separation angles, where the ICMEs of interest supposed to be located. Enhancements on IPS responses can be associated with the high-density region where the fast-propagating ICMEs pile up the background solar wind. In addition, several CMEs were generated from the same active region and some of them merged in the interplanetary space. Multiple ICME merging can enhance compression of the solar wind plasma that can produce intense radio scattering. Therefore, the enhanced IPS amplitude can be caused by the CME-CME interaction. The propagation of CMEs observed during this period have been reproduced using the MHD simulations that suggests multiple CMEs were generated in a short period of time, forming a dense region with multiple CME-CME interactions.