Thin energetic O+ layer embedded in the magnetotail reconnection current sheet observed by Cluster

Abstract

In the classical picture of the magnetotail current sheet, the current carriers are mainly ions that undergo nonadiabatic motions. Oxygen ions could contribute a thicker current sheet than the protons due to their large gyroradii. In this paper, however, we report a thin energetic O+ layer embedded in the magnetotail proton current sheet observed by Cluster on 11 October 2001. The thickness of the O+ layer is estimated to be smaller than the half thickness of the local current sheet. And the layer is formed by energetic O+ with energy larger than 20 keV moving along the +Y direction in GSE coordinates. It is inferred that these energetic O+ are probably generated due to the selective acceleration effect of the thin reconnection electric field to the upstreaming ionospheric O+ ions with different initial condition.