The Effects of a Stably Stratified Region on the Formation of Zonal Winds on Gas Planets

The outer regions of both Gas Giants in our Solar System, Jupiter and Saturn, feature strong, alternately Eastward and Westward moving zonal winds. Cloud tracking has yielded latitudinal profiles of these winds, which are longitudinally invariant and steady in time to a high degree and reach all the way to the polar regions. However, reproducing these features in numerical simulations has proved difficult as certain physical transitions at various depths are required to both enable winds to form and be maintained at the higher latitudes, and then be quenched at the depths inferred from gravity measurements.
A sub-adiabatic region in combination with an increase in electrical conductivity seems to be key, but makes the dynamics rather complex. In this study we analyse how the two transitions affect the zonal winds formed in an overlying convecting region, as well as how they then penetrate into the respective stably stratified and dynamo regions.
Particularly in the case of Jupiter evidence is accumulating for a stably stratified layer, shallower than where Helium rain may be expected, based on interior models and magnetic field modelling. However, the nature of such a shallower layer and its exact depth is still very undetermined. This study helps to constrain the depth at which this stratified region begins relative to the depth of the transition into the dynamo region. We find that when the transition to high electrical conductivity is much deeper than the transition into the stable region, zonal winds form at all latitudes. When the boundary of the dynamo region becomes shallower, high-latitude jets are diminished in amplitude and cease to reach the polar regions.