Turbulent mixing and transport of collisionless plasmas across a stratified velocity shear layer

Abstract

[1] Two-dimensional simulations of the Kelvin-Helmholtz (K-H) instability in a nonuniform density medium and with the transverse magnetic field show the strong development of turbulence through nonlinear instabilities. Ideal MHD simulation results have indicated that the difference in density between two media plays a crucial role on the fast turbulent mixing and transport. The onset of the turbulence is triggered not only by the secondary K-H instability but also by the Rayleigh-Taylor (R-T) instability at the density interface inside the normal K-H vortex. The secondary R-T instability alters macroscopic structure by transporting dense fluids to tenuous region, while the secondary K-H instability is just a seed for the turbulence. Full particle simulations are also conducted and reproduces the similar result of the ideal MHDs, except that the strong electrostatic field caused by the secondary R-T instability scatters ions and deforms the electron density interface. As a result, the mixing area increases anomalously fast and extends spatially as compared to the result in the uniform density case.Citation: Matsumoto, Y., and M. Hoshino (2006), Turbulent mixing and transport of collisionless plasmas across a stratified velocity shear layer,

Observation of three distinct ion populations at the Kelvin-Helmholtz-unstable magnetopause

“…(e.g. Wilber and Winglee;Jonhson and Cheng, 2001;Sibeck et al, 1999;Matsumoto and Hoshino, 2006;Smets et al, 2007). As proposed by several authors Nykyri et al, 2006;Nishino et al, 2007b, c) the development of KHI-driven vortices can induce magnetic reconnection in the vicinity of rolled-up structure and hence solar wind entry.…”

“…The Kelvin-Helmholtz instability is not a plasma entry mechanism per se, but its occurrence is believed to be important for plasma transport at the flank magnetopause, in particular under northward IMF as it may allow local plasma penetration by favoring both magnetic reconnection Nykyri and Otto, 2001) and diffusive processes (e.g. Matsumoto and Hoshino, 2006;Smets et al, 2007).…”

Temperature anisotropies of electrons and two-component protons in the dusk plasma sheet

“…In the velocity shear layer around the magnetopause, the Kelvin-Helmholtz (KH) instability is expected to develop under strongly northward IMF . Simulations Nykyri and Otto, 2001;Matsumoto and Hoshino, 2006;Nakamura et al, 2006), as well as observational studies (Hasegawa et al, 2004(Hasegawa et al, , 2006, have suggested the occurrence of KH instability and growth of vortical structures there. We note that the two events with the strong parallel anisotropy of the cold proton component in the tail flank (T C⊥ /T C <0.5 on 24 March 1995 and 13 April 1998) are those where Hasegawa et al (2006) showed the existence of the rolled-up KH vortical structures, and that other 9 tailflank cases with the weaker parallel anisotropy were not identified as the rolled-up KH vortices by them.…”

Waves on the dusk flank boundary layer during very northward interplanetary magnetic field conditions: Observations and simulation

“…Maximum mixing is often found in the simple, but unrealistic, case of uniform density and field across the velocity shear. Thomas and Winske [1993] find that a density change across the boundary suppresses vortex development and mixing, whereas Matsumoto and Hoshino [2006] find larger density changes leads to secondary instabilities and increased mixing. Fujimoto and Terasawa [1995] find that a B magnitude change across the boundary decreases mixing.…”

“…[5] Several hybrid [Thomas and Winske, 1993;Thomas, 1995;Terasawa, 1994, 1995] and particle [Matsumoto and Hoshino, 2006] KH simulations have been reported, again with periodic boundary conditions. These studies find results similar to those of MHD but often with structures breaking off of irregular vortices [e.g., Thomas and Winske, 1993].…”