A nearly continuous observation of the equatorial plasmasphere from the inner radiation belt to near a magnetopause reconnection site

TL;DR

This study provides nearly continuous observations of the equatorial plasmasphere's properties from the inner radiation belt to the magnetopause, revealing significant density and temperature changes during radial transport.

Contribution

It offers detailed in situ measurements of the plasmasphere's radial extent and its property variations, enhancing understanding of plasma dynamics near the magnetopause.

Findings

Density decreases by a factor of ~1000 from inner to outer regions.

Proton temperature increases by a factor of ~100, especially beyond L=7.

Plasma properties scale with L-shell as L^{-4.3±0.4}.

Abstract

On 22 October 2015, VAP and MMS obtained near-continuous observations of the full radial extent of the duskside equatorial plasmasphere and plume. The plume is evident in in situ plasma data and an equatorial mapping of the ionospheric total electron content. The properties of the equatorial plasmasphere change dramatically from its the inner radiation belt to its outermost boundary (the magnetopause, near a reconnection site). The density decreases by a factor of $\sim$1000 over this range and scales with $L$-shell as $L^{-4.3\pm0.4}$, in good agreement with with theoretical expectations of the expansion of a flux tube volume during outward radial transport. The proton temperature increases by a factor of $\sim$100 over this same range, with the most pronounced heating occurring at $L>7$, which was covered by the orbit of MMS.