Geotail observations of ion velocity distributions with multi‐beam structures in the post‐plasmoid current sheet

Abstract

Two unusual ion velocity distributions were observed by the Geotail LEP instrument in the distant current sheet just after the passage of plasmoids. These ion distributions are particular in that in each case there are two or three well‐ordered, cold and dense beams embedded in a hot, tenuous component. The beams are roughly aligned in the convection direction and flow duskward and tailward with large velocities. When those distributions were observed, the spacecraft was very close to the middle plane of the current sheet, where the Bx and Bz components of the magnetic field were quite small and at the same time Bx was the dominant component. The present observations reveal much more complicated pattern of the ion velocity distributions in the current sheet during the course of substorm than as expected.