[P-EM14] 太陽圏・惑星間空間

[PEM14-09] Kaguya Observations of Solar Wind Electron Modification by Electrostatic Waves Above the Lunar Day Side: Preliminary Results

*原田 裕己¹、笠原 禎也²、西野 真木³、栗田 怜⁴、斎藤 義文³、横田 勝一郎⁵、高橋 太⁶、清水 久芳⁷ (1.京都大学大学院理学研究科、2.金沢大学総合メディア基盤センター、3.宇宙航空研究開発機構宇宙科学研究所、4.京都大学生存圏研究所、5.大阪大学・理学研究科、6.九州大学大学院理学研究院、7.東京大学地震研究所)

キーワード：月、太陽風電子、静電波

Despite the lack of a global intrinsic magnetic field and a dense atmosphere, the Moon drives many observable effects on the upstream solar wind plasma through absorption, scattering, reflection, and emission of charged particles by the surface and crustal magnetic fields. As a result, a variety of plasma waves are excited in the upstream solar wind in a similar manner to planetary foreshocks, though a global bow shock is absent at the Moon. Recently, Chu et al. (2020) reported two case studies of THEMIS-ARTEMIS observations above lunar crustal magnetic anomalies, thereby proposing two sources of electrostatic waves around the Moon: (i) counter-streaming electron beams consisting of incoming solar wind electrons and reflected electrons, and (ii) relative drift across the magnetic field between reflected ions and solar wind electrons. The former drives electron two stream instability generating electric field structures parallel to the background magnetic field, while the latter drives electron cyclotron drift instability leading to perpendicular electric field waves. They also proposed that these electrostatic instabilities cause substantial heating of solar wind electrons. However, the global nature of these electrostatic waves and resulting solar wind electron modification remains largely unexplored, partly because of the nearly equatorial orbits of the THEMIS-ARTEMIS probes.

In this study, we generate global selenographic maps of electric field waves and solar wind electron modification from Kaguya data obtained on the lunar dayside at ~100 km altitude polar orbits. The global maps clearly demonstrate the lunar crustal field control of electrostatic wave generation and incoming solar wind electron modification. Additionally, we identify IMF cone angle dependence of the waves and electron modification above strong magnetic anomalies. We discuss these preliminary results in the context of the proposed electrostatic instabilities.