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 +/- 20 degrees) 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 similar to 4.8 R-E on the noon side and the other from a valley of plasma pressure which could arise near similar to 4.8 R-E on the night side. Plain Language Summary Large-scale current systems existing in space affect the magnetic field on the surface of Earth and the ring current has a dominant influence. Space weather drives large variations in these currents which disturb the surface magnetic fields. When the disturbance is violent, it is called a magnetic storm and may have a disastrous impact on satellite and ground systems. Using the high-precision magnetic field data of the four spacecraft in NASA's Magnetospheric Multiscale mission, by employing a multispacecraft analysis method, we calculate the distribution of local current density in space. Through statistical analysis of the current in the region, we study its morphology. We confirm the asymmetry of the ring current found in previous studies and suggest a new explanation for part of the asymmetry, that is, that the generally westward ring current is superimposed on closed, banana-like currents.