Generation mechanisms and scales of eddies on Jupiter

Tracking cloud features shows that eddies in Jupiter's upper troposphere transport angular momentum meridionally from retrograde into prograde jets (Salyk et al. 2006). Here we demonstrate generation mechanisms of eddies and the role of eddies in jet formation using a energetically consistent general circulation model of Jupiter's outer atmosphere.

In the equatorial region, diabatic heating balances the vertical advection of entropy. For strong enough internal heating, convective heating fluctuations that cannot be balanced by slow radiative processes induce fluctuations in the large-scale horizontal divergence and imply a Rossby wave source. Rossby waves so excited transport angular momentum into the equatorial region when they propagate poleward. If surface friction is sufficiently weak, equatorial superrotation is induced. Consistent with this eddy generation mechanism, the energy-containing eddy length scale is approximately equal to the equatorial Rossby radius.

Away from equator, baroclinic eddies generated by differential solar heating, preferentially in the more baroclinically unstable prograde jets, transport angular momentum into the prograde jets. The energy-containing scale is closely approximated both by Rhines scale based on the barotropic eddy kinetic energy and by the extratropical Rossby radius. There is no evidence for an inverse cascade of barotropic kinetic energy in the energy spectra or in the spectral fluxes of energy.

Tranports of angular momentum by eddies generated by the above two mechanisms can compete with each other. Simulations with larger meridional insolation gradients require stronger internal heat fluxes (and thus convective heat fluxes) to generate equatorial superrotation.