Electric Current Structure And Plasma Kinetic Feature in the Closed Thin Magnetopause

Abstract:

The magnetopause (MP) forms a current sheet boundary between the Earth’s magnetospheric field and the shocked solar wind (in the magnetosheath). Using the curlometer method, the four spacecraft Cluster observations have previously revealed the large scale features of this current layer, typically for magnetopause thicknesses down to a few hundred (200) km. The scale size of the Cluster configuration and the low cadence of the plasma moments limited the special resolution possible. The four spacecraft Magnetospheric Multiscale (MMS) mission, with spacecraft at small separation distances of a few to tens of km has enabled the intimate detail of the current layer to probed as well as closely tracking the properties of the current carriers. Here, we show that current densities derived from the curlometer and the corresponding high resolution plasma data are often in close agreement. This certifies the accuracy of the plasma data and allows comparisons to be made between the plasm currents at individual spacecraft to be compared to mean current densities. We have analysed the detailed plasma, kinetic features associated with the current carriers at positions across thin (less than 100 km) tangential-discontinuity magnetopause encounters. Our results show that for thin layers and within the overall boundary layer, more complicated features than the classic Chapman-Ferraro current model exist, such as separation of the ion and electron perpendicular currents and strong electron parallel currents. This may deepen the understanding of the closed magnetopause current sheet and indicates that plasma separation on small spatial scales occurs across the magnetopause boundary layer, possibly as a result of non-gyrotropic ion response and the operation of electrostatic repulsion.