[P-CG23] 惑星大気圏・電磁圏

[PCG23-03] Sodium ion dynamics in the magnetospheric flanks of Mercury

*相澤 紗絵^1,2、Delcourt Dominique³、寺田 直樹¹ (1.東北大学大学院理学研究科、2.Laboratoire de Physique des Plasmas, Ecole polytechnique-CNRS-UPMC、3.Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, Universite d'Orleans - CNRS)

キーワード：水星磁気圏、ケルビン−ヘルムホルツ不安定、非断熱加速

We investigate the transport of planetary ions in the magnetospheric flanks of Mercury. In situ measurements from the MESSENGER spacecraft show evidences of Kelvin-Helmholtz instability development in this region of space, due to the velocity shear between the downtail streaming flow of solar wind originating protons in the magnetosheath and the magnetospheric populations. Ions that originate from the planet exosphere and that gain access to this region of space may be transported across the magnetopause along meandering orbits. We examine this transport using single particle trajectory calculations in model MHD simulations of the Kelvin-Helmholtz instability. We show that heavy ions of planetary origin such as Na⁺ may experience prominent nonadiabatic energization as they ExB drift across large-scale rolled up vortices. This energization is controlled by the characteristics of the electric field burst encountered along the particle path, the net energy change realized corresponding to the maximum ExB drift energy. This nonadiabatic energization also is responsible for prominent scattering of the particles toward the direction perpendicular to the magnetic field.