Ring current morphology from MMS observations

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.

Dispersed Relativistic Electron Precipitation Patterns Between the Ion and Electron Isotropy Boundaries

“…We perform a simplified estimate: we fit the boundary of the isotropic precipitation (both the classical isotropy boundary and the equatorward dispersed pattern) to a function that depends on latitude, so we have E iso ( MLAT ). Then we use the typical equation for conditions of curvature scattering, R c / ρ = 8 (Sergeev & Tsyganenko, 1982), to determine the equatorial B z ( MLAT ) profile for a constant equatorial current density of 10 nA/m 2 (this is a large current density for the ring current ions, but still within the range of observations (see; C. Shen et al., 2014; Tan et al., 2022; Vallat et al., 2005; Yang et al., 2016) and model estimates (see Kubyshkina et al., 2009, 2011; Sergeev et al., 2023; Stephens et al., 2016)). The same B z ( MLAT ) profile is evaluated from the ion isotropy boundary.…”