A planetary wave model for Saturn’s 10.7-h periodicities

Abstract

A proposed resolution of the unexplained 10.7-h periodicities in Saturn’s magnetosphere is a system of atmospheric vortices in the polar regions of the planet. We investigate a description of such vortices in terms of planetary-scale waves. Approximating the polar regions as flat, we use theory developed originally by Haurwitz (Haurwitz, B. [1975]. Geophys. Bioklimatol. 24, 1–18) to find circumpolar Rossby wave solutions for Saturn’s upper stratosphere and lower thermosphere. We find vertically propagating twin vortex solutions that drift slowly westwards at <1% of the deep planetary angular velocity and are thus ideal candidates for explaining the observed periodicities. To produce integrated field-aligned currents of the order of 1MA we require wind velocities of ∼70ms-1. A particular class of vertically propagating solutions are potentially consistent with wave energy being ‘trapped’ between the deep atmosphere and lower thermosphere, at altitudes suited to the production of the necessary field-aligned current systems.