Kelvin-Helmholtz instability at Saturn's magnetopause: Hybrid simulations

Abstract

[1] Recent observations of a plasma vortex in Saturn's dayside outer magnetosphere is evidence that the Kelvin-Helmholtz instability (KHI) is operating at Saturn's morning magnetospheric boundaries. Kelvin-Helmholtz vortices can mediate the transport of mass, momentum, energy and magnetic flux at the magnetospheric boundaries, making KHI an important mechanism through which the solar wind interacts with the magnetosphere. We derive plasma properties from the Cassini Plasma Spectrometer (CAPS) during the December 13, 2004 magnetopause boundary encounter. These plasma properties (ion temperature, density, composition, and plasma flow) are used as input parameters for a two-dimensional hybrid simulation of the KHI unstable planetward edge of Saturn's boundary layer region. We investigate the effect of heavy magnetospheric ions on the KHI evolution and test the growth rates as a function of magnetosonic Mach number. We compare our simulation results with the plasma data, estimate diffusion coefficients due to KHI plasma mixing (D > 1010 m2 s−1) and energy transported into Saturn's magnetosphere (∼40 GW) due to the KHI unstable boundaries and conclude that mass transfer processes at Saturn's magnetopause boundary can play a significant role in driving magnetospheric dynamics.