Ring Current Morphology From MMS Observations

Abstract

The Earth's ring current (RC) plays an important role in the inner magnetosphere as it has a dominant effect on the Earth's geomagnetic field. It is therefore very important to study its distribution to better understand the inner magnetospheric current system and its dynamics. The RC is primarily formed by charged particles with energies from ∼1 keV to hundreds of keV, captured by the Earth's magnetic field, which have gyration and drift motion caused by magnetic gradients and curvature (Parker, 1957). The RC typically lies between 2 and 8 R E and previously has been found to be reasonably well ordered within ±30° latitude. During magnetic storms, ionospheric particles may inject into the RC, dominating its morphology and dynamics (Daglis et al., 1999).Preceding work has shown a pronounced asymmetry and other effects through the analysis of a variety of observation data, often related to the effects of the RC in adjacent regions. For example, Le and Russell (1998) pointed out that residual magnetic field measurements from low-altitude polar orbiting spacecraft are potentially useful as monitors of RC strength when they cross the polar cap. Le et al. (2011) studied its asymmetry by analyzing the influence on the distribution of the residual normal components of the magnetic field at LEO (low Earth orbit). In situ magnetic data, covering many years and a number of earlier missions, were used by Le et al. (2004); Jorgensen (2004) estimated the RC distribution for different levels of geomagnetic activity. These studies, however, have generally used only single spacecraft to extract components of the current density, J (so that assumptions have to be made to obtain J from magnetic residuals) and indeed discrepancies exist between the morphology implied from low altitudes (to which other influences may contribute, such as field-aligned currents, FACs) and that seen in situ. The phased multispacecraft arrays of Cluster and THEMIS allowed direct estimates

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.…”