On the incidence of Kelvin-Helmholtz instability for mass exchange process at the Earth’s magnetopause

Abstract

Abstract. Due to the velocity shear imposed by the solar wind flowing around the magnetosphere, the magnetopause flanks are preferred regions for the development of a KelvinHelmholtz instability. Since its efficiency for momentum transfer across the magnetopause has already been established, we investigate its efficiency for mass transfer. Using nonresistive magnetohydrodynamic simulations to describe the magnetic field shape in the instability region, we use testparticle calculations to analyse particle dynamics. We show that the magnetopause thickness and the instability wavelength are too large to lead to nonadiabatic motion of thermal electrons from the magnetosphere.On the other hand, the large mass of H + , He + and O + ions leads to such nonadiabatic motion and we thus propose the Kelvin-Helmholtz instability as a mechanism for either magnetospheric ion leakage into the magnetosheath or solar wind ion entry in the magnetosphere. Test-particle calculations are performed in a dimensionless way to discuss the case of each type of ion. The crossing rate is of the order of 10%. This rate is anti-correlated with shear velocity and instability wavelength. It increases with the magnetic shear. The crossing regions at the magnetopause are narrow and localized in the vicinity of the instability wave front. As a KelvinHelmholtz instability allows for mass transfer through the magnetopause without any resistivity, we propose it as an alternate process to reconnection for mass transfer through magnetic boundaries.

Transient reconnection in the cusp during strongly negative IMFBy

“…However, solar wind pressure pulses and KH or TBL waves cannot explain the flows in GSE Y‐direction or the observed ion dispersion. It does not seem that these mechanisms are able to explain significant transport of plasma (especially electrons) into the MS [ Smets et al , 2002]. Thus once more we cannot exclude that indentation of the MP can be caused by one of these mechanisms, though we still would need reconnection to explain other observed features.…”

Survey of energetic O<Sup>+</sup> ions near the dayside mid-latitude magnetopause with Cluster

“…However, they do not spatially resolve the reconnection boundaries yet. Other MHD simulations have examined the acceleration of O + test particles in the presence of an KH instability developing at the MP (Smets et al, 2002), but without taking them into account self-consistently. Because all these MP physical processes have a significant impact on macroscopic scales, incorporating the effect of the O + component on such MP processes would be an important challenge.…”

Kelvin–Helmholtz Instability: Lessons Learned and Ways Forward

“…An analytical expression of this instability threshold can be obtained for an ideal MHD plasma in an incompressible media (e.g. Smets et al 2002). It can also be demonstrated that, in the incompressible media approximation, the component of the instability wave vector perpendicular to the interface is purely imaginary.…”