The Energization of Cold Ions around a Plasmoid in the Magnetotail
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We study numerically the interaction of cold ionospheric ions in the tail lobe with a plasmoid propagating steadily in the tailward direction. We have found that significant energization of cold ions occurs at the encounter with a plasmoid, where three types of the interaction processes are taking place: First, ions show gradient and curvature drift motions as the plasmoid approaches. These ions are accelerated up to ∼1 keV by the cross-tail electric field accompanying with the plasmoid motion (type-I energization). Second, some of the ions get large pitch angles after the type-I acceleration, and then mirror reflected by the plasmoid. These ions are accelerated up to 10 keV after the reflection (type-II energization). Third, the motions of the ions near the plasmoid become highly non-adiabatic, because their gyroradii become comparable to the field-line curvature radius after the type-I energization. Consequently the energy distribution of these ions is broadened in the trailing side of the plasmoid (type-III energization). These theoretical results are successfully compared with the recent GEOTAIL observation showing the dynamic interaction of cold ions with a plasmoid and their subsequent energization.
- Earth, Planets and Space
Earth, Planets and Space 47(2), 149-162, 1995-02
Society of Geomagnetism and Earth, Planetary and Space Sciences