Finite-Larmor-radius equilibrium and currents of the Earth's flank magnetopause

TL;DR

This paper develops an extended Hall-MHD model incorporating finite Larmor radius effects to analyze Earth's flank magnetopause, revealing asymmetries and current structures consistent with observations.

Contribution

It provides a generalized analytic framework for FLR-influenced equilibrium configurations and demonstrates how FLR effects alter magnetopause current layers.

Findings

Reproduces dusk-dawn asymmetry of current layers

Shows double-peak current profiles with ion Larmor radii scale

Identifies adjacent current sheets with different directions

Abstract

We consider the one-dimensional equilibrium problem of a shear-flow boundary layer within an "extended Hall-MHD" (eHMHD) model of plasma that retains first-order finite Larmor radius (FLR) corrections to the ion dynamics. We provide a generalized version of the analytic expressions for the equilibrium configuration given in Cerri et al. (2013) [Cerri et al., Phys. Plasmas 20, 112112 (2013)], highlighting their intrinsic asymmetry due to the relative orientation of the magnetic field $\mathbf{b}=\mathbf{B}/|\mathbf{B}|$ and the fluid vorticity $\mathbf{\omega}=\mathbf{\nabla}\times\mathbf{u}$ ("$\mathbf{\omega b}$ asymmetry"). Finally, we show that FLR effects can modify the Chapman--Ferraro current layer at the flank magnetopause in a way that is consistent with the observed structure reported by Haaland et al. (2014) [Haaland et al., J. Geophys. Res. Space Phys. 119, 9019-9037 (2014)]. In particular, we are able to qualitatively reproduce the following key features: (i) the dusk-dawn asymmetry of the current layer, (ii) a double-peak feature in the current profiles, and (iii) adjacent current sheets having thicknesses of several ion Larmor radii and with different current directions.