Thin embedded current sheets: Cluster observations of ion kinetic structure and analytical models

Abstract. Kinetic structure of embedded thin horizontal current sheets is investigated. Current density estimated by curlometer technique is in general agreement with a sum of electron and proton currents. Embedding of observed thin current sheets in the much wider plasma sheet is apparent in the current density profiles. Ion velocity distributions consist of two parts: the cold non-drifting core likely belongs to the plasma sheet background, while the hotter asymmetric "wings" carry the main portion of the current. Oxygen ions (if present) and higher-energy tails of distribution function can contribute up to 30% of the total current. We compared current density profiles across sheets with three typical current sheet models. Models which allow embedding, describe observed structures equally well at the level of experimental accuracy.