Cluster statistics of thin current sheets in the Earth magnetotail: Specifics of the dawn flank, proton temperature profiles and electrostatic effects

Abstract

[1] In this paper we use the statistics of 70 crossings by the Cluster mission to study and compare properties of thin current sheets observed at the dawn and dusk flanks of the Earth magnetotail. Special attention is devoted to the current sheet embedding: we define the degree of the current sheet embedding as be = Bext/B0 (B0 and Bext are magnetic field magnitudes at the thin current sheet boundary and in the lobes). We determine the current density by curlometer technique and calculate the current sheet thickness. We demonstrate that the current sheets at the dawn flank have larger be, smaller magnitude of the current density and larger relative thicknesses in Larmor radii than the current sheets at the dusk flank. Protons in thin current sheets are divided into two populations (the current-carrying particles and the background) and the temperatures of these populations have been estimated. The distribution of the proton temperature p inside typical current sheet is approximated as p ≈ Tp(1 − αT(Bx/Bext)2), where Tp is the p value in the central region of the current sheet. The average value 〈αT〉 ≈ 0.8. The proton current density (flow velocity in Y) is positive at the dusk flank and negative at the dawn flank, while the electron current density is positive at both flanks. This difference of the proton current density at two flanks is explained by the E × B drift due to the presence of the earthward electrostatic field Ex. We develop a simple model of the earthward electrostatic field to incorporate the influence of the embedding and the dawn-dusk magnetic field component.