Space Physics Seminar spring-2014

The Kelvin-Helmholtz instability (KHI) is a key process for the transport of solar wind plasma across the Earth’s magnetospheric boundary (magnetopause). When both magnetic and velocity shears coexists within a boundary as commonly seen at the magnetopause, the resulting KHI leads to generation of vortices and subsequent triggering of magnetic reconnection. Our recent large-scale 3D fully kinetic simulations of this so-called vortex-induced reconnection (VIR) process for symmetric boundary layers demonstrated the copious formation of oblique flux ropes, which leads to a chaotic mixing of the plasma within the vortex layer. THEMIS observations at the dusk-flank magnetopause indeed show similar features of flux ropes between observed KH vortices. More recently, we performed additional 3D fully kinetic simulations considering the effects of density and temperature asymmetries, which also commonly exist across the magnetopause. Past 2D simulations have shown that such asymmetries can lead to an excitation of secondary instabilities along the edge of the vortex in the absence of a finite magnetic field component parallel to the k-vector of the KHI (B_k). Since B_k is expected to be finite at the magnetopause, here we explore the effect of B_k on secondary instabilities in 3D. We find that the suppression of the secondary instabilities due to B_k is an artifact of the 2D simulations, whereas in 3D the instabilities can grow over a range of oblique angles even when there is a finite B_k. The non-linear growth of these instabilities disturbs the structure of the edge layer of the vortex and transports the mixed plasmas produced by VIR more deeply into the magnetospheric region. The estimated mixing and transport rates are enough to form the tail-flank low-latitude boundary layer (LLBL) and the cold-dense plasma sheet (CDPS) both of which contain a mixture of plasmas of solar wind (magnetosheath) and magnetosphere origins. In this presentation, we will show detailed results of these 3D simulations as well as a brief history of theoretical, numerical and observational studies on the KHI at the magnetopause.