Ring Current Morphology From MMS Observations

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. Through statistical analysis of data from September 2015 to the end of 2016, covering the region of 2–8 R_E (Earth radius, 6,371 km), we reveal an almost complete near-equatorial (within (Formula presented.)) RC morphology in terms of radial distance and magnetic 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 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 R_E on the noon side and the other from a valley of plasma pressure which could arise near ∼4.8 R_E on the night side.