On the relevance of the MHD approach to study the Kelvin-Helmholtz instability of the terrestrial magnetopause

Abstract

It is shown that the usual MHD approximation is not suitable for the description of the Kelvin-Helmholtz instability of the terrestrial magnetopause. Indeed such a description implies an ideal magnetopause with a smooth continuous variation of the plasma and field parameters occuring in an extended current sheet. However, the actual magnetopause and its adjacent plasma boundary layer are highly irregular, both spatially and temporally. Therefore, finite ion Larmor radius effects do not represent small corrections. It is argued that these small-scale inhomogeneities can change drastically the usual large-scale description of the magnetopause oscillations.