Plasma Transport in Saturn’s Inner Magnetosphere: Transition from Small-scale to Large-scale Interchange Convection Cells

Abstract:

Rice Convection Model simulations of plasma transport in Saturn’s inner magnetosphere (2 < L < 12) with an imposed source of cool plasma distributed in the range 5 < L < 10 typically exhibit a chaotic interchange convection pattern with narrow outflow channels of cool dense plasma interspersed with even narrower inflow channels of hot tenuous plasma from the outer magnetosphere. We have now extended these simulations to a larger range of L (2 < L < 20) and to much longer simulation times, T ~ 1000 hours ~ 20 circulation time scales. At times greater than a few circulation time scales the simulations reveal a new type of behavior in the outer region, with many narrow fingers coalescing to form fewer but broader outflow fingers. The Fourier spectrum of the azimuthal convection structure, initially dominated by azimuthal wavenumbers m ~ 20 – 40, becomes dominated instead by wavenumbers m ~ 1. Work is in progress to understand this behavior at an analytical level, and to investigate its possible role in producing spin-periodic phenomena in Saturn’s otherwise symmetric magnetosphere.