Small Spatial-Scale Field-Aligned Currents in the Plasma Sheet Boundary Layer Surveyed by Magnetosphere Multiscale Spacecraft

Field-aligned currents play a significant role in the magnetosphere-ionosphere coupling. With the multipoint measurements and the advanced instruments of the four Magnetosphere Multiscale spacecraft, we estimate the fine structure of field-aligned currents in the plasma sheet boundary layer (PSBL) by using the plasma moment data from the Fast Plasma Investigation. Those fine field-aligned currents under higher temporal resolutions could be quite different from that under the lower temporal resolution: Bipolar current signals can be observed under higher resolutions, while no current signal appears under the lower resolution; higher current density magnitude and shorter time scale of the current layer under higher resolutions are observed than that under the lower resolution. The essential reason could be that the spatial scale of some field-aligned current layers in the PSBL is too small to be found by low temporal measurements; thus, our results demonstrate the necessity of high data resolutions in resolving the subproton-scale structure of the field-aligned current and dynamics in the PSBL.