Kelvin–Helmholtz-Related Turbulent Heating at Saturn's Magnetopause Boundary

One of the grand challenge problems of the giant planet magnetospheres is the issue of nonadiabatic plasma heating. Simple turbulent heating models consider the energy cascade rate from one scale to another where the energy density is based on perpendicular magnetic fluctuations of counterpropagating Alfvén waves. Analytical expressions from turbulence theory for the heating rate density have yielded promising results for the observed ion heating at Jupiter and Saturn. Here, we compare ion heating using hybrid simulations of the Kelvin–Helmholtz instability and analytical estimates in an effort to validate turbulence theory and further understand the nature of the ion heating. Heating rate densities ∼10−15 W/m3 are produced in our three-dimensional Kelvin–Helmholtz simulations during the nonlinear growth phase and compare favorably with analytical estimates. Results targeting Saturn will be discussed in the broader context of radial plasma transport in the rapidly rotating magnetospheres.

Plain Language Summary

One of the big mysteries in space plasma physics is heating. In many instances, plasma is observed to increase in temperature when, for example, simple considerations would predict cooling instead. Using a three-dimensional plasma simulation of the Kelvin–Helmholtz instability, we find plasma heating. One possible scenario to explain this heating is the nonlinear interaction of counterpropagating Alfven waves. This theory is applied to the simulation results and we find a very good agreement. The results can be applied generally to many different scenarios in space plasmas and, in particular, we discuss implications for radial plasma transport at Jupiter and Saturn.