Abstract
We directly estimate the in situ current density of the Earth’s ring
current (RC) using the curlometer method and investigate its morphology
using the small spatial separations and high accuracy of the
Magnetospheric Multiscale mission (MMS). Through statistical analysis of
data from September 2015 to the end of 2016, covering the region of 2-8
RE (Earth radius, 6371 km), we reveal an almost complete near-equatorial
(within ) RC morphology in terms of radial distance and local time (MLT)
which complements and extends that found from previous studies. We found
no evidence of RC enhancement on the dusk-side during geomagnetic active
periods, but details of local time (MLT) asymmetries in, and the
boundary between, the inner (eastward) and outer (westward) currents are
revealed. We propose that part of the asymmetry demonstrated here
suggests that in addition to the overall persistence of the westward RC,
two large banana-like currents are directly observed, one which could
arise from a peak of plasma pressure near ~4.8 RE on the
noon side and the other from a valley of plasma pressure which could
arise near ~4.8 RE on the night side.