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Non-adiabatic energization and transport of planetary ions in the magnetospheric flanks of Mercury

Abstract : We investigate the acceleration and transport of planetary ions within Kelvin-Helmholtz (KH) vortices that develop in the magnetospheric flanks of Mercury, using single-particle trajectory calculations in a field model obtained from MHD simulations. Due to the presence of heavy ions of planetary origin (e.g., O+, Na+, and K+) following ionization of exospheric neutrals and the complicated field structure during the KH vortex development, the scale of electric field variation may be comparable with ion gyration motion. Therefore ions may experience non-adiabatic energization as they drift across the magnetopause. In this study, we consider realistic configurations for both dawn and dusk magnetospheric flanks, and we focus on the effect of the spatial and temporal variations of the electric field magnitude and orientation along the ion path on the ion dynamics. We show that the intensification rather than the change of orientation is responsible for large non-adiabatic energization of heavy ions of planetary origin. This energization systematically occurs for ions with low initial energies in the direction perpendicular to the magnetic field, the energy gain being of the order of the energy corresponding to the maximum ExB drift speed, ɛmax, in a like manner to a pickup ion process. It is also found that ions that have initial energies comparable to ɛmax may be decelerated depending upon gyration phase. We find that ions with initial perpendicular energies much larger than ɛmax are little affected along the ion path through KH vortices. By comparing dynamical regimesin the dawn versus dusk regions, and also by considering different IMF directions, we show that the ion transport across the magnetopause is controlled by the orientation of the magnetosheath electric field and that the rate of energization depends upon the scale of KH vortices versus Larmor radii.
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Submitted on : Friday, February 11, 2022 - 8:59:21 AM
Last modification on : Saturday, June 25, 2022 - 10:53:31 PM

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S. Aizawa, Dominique Delcourt, N. Terada, y. Kasaba, y. Katoh. Non-adiabatic energization and transport of planetary ions in the magnetospheric flanks of Mercury. American Geophysical Union, 2018, San Francisco, United States. pp. 10. ⟨insu-03565534⟩

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