Near Earth Vortices Driving of Field Aligned Currents Based on Magnetosphere Multiscale and Swarm Observations

Abstract

A long-standing mystery in the study of Field-Aligned Currents (FACs) has been that:how the currents are generated and why they appear to be much stronger at high altitudes than in the ionosphere.Here we present two events of magnetotail FACs observed by the Magnetospheric Multiscale Spacecraft (MMS) on 1st July and 14th July 2016,to show how the Substorm Current Wedges (SCW) were formed.The results show that particles were transferred heading towards the Earth during the expansion phase of substorms. The azimuthal flow formed clockwise (counter-clockwise) vortex-like motion,and then generated downward (upward) FACs on the tailward/poleward side of the distorted field with opposite vorticity on their Earthward/equatorward side.We also analyzed the Region 1 FACs observed by the Earth Explorer Swarm spacecraft on 1st July 2016 and found that they were associated with FACs observed by MMS,although differing by a factor of 10.This difference suggests that either there was the closure of the currents at altitudes above 500 km or the currents were not strictly parallel to B and closed at longitudes away from where they were generated.