Effect of a buried stably stratified layer on the zonal jets of Jupiter and Saturn

Recent gravity observations from Cassini and Juno have confirmed the idea that the cloud level jet streams of

Jupiter and Saturn plunge deeply into their molecular envelopes. In addition it is understood that the electrically

conducting interiors of the gas giants cannot support fast zonal flow.

Recent analyses of Juno and Cassini gravity and magnetic field data have indicated that the dynamos of Jupiter

and Saturn are quite deeply seated, even though estimates of electrical conductivity structure indicate that the

dynamos could be supported at shallower levels. Deeper than expected dynamos may be explained by buried

stably stratified layers in the gas giants, which could be associated with the radial distribution of Helium precipitation.

The phenomenological consequences of interior models of composition and structure on global dynamics has been extensively

discussed in the literature. However, from a dynamical perspective,

it remains a challenge to understand the nature of the transition from fast zonal flow with multiple jets

to the deeper interior, in which dynamo action generates the global magnetic field. As a stepping stone toward

understanding the jet/dynamo problem, we explore the effect of a buried stably stratified layer on this transition,

using the open-source computational dynamo code MagIC (magic-sph.github.io), in non-magnetic rotating convection mode.

Previous deep convection models that support fast zonal flow and multiple jets have used free-slip top and bottom boundary conditions.

We use a stably stratified layer on top of a no-slip boundary, which represents the top of a dynamo.

We find that a stably stratified layer can promote multiple jets at mid-latitudes. In particular, the strength of zonal flow at shallow levels

inside the tangent cylinder depends significantly on the strength of stable stratification. Our work implies that a

stably stratified layer buried deeply within the molecular envelope of the gas giants can help explain the coupling

of zonal flow to the deeply seated dynamos of the gas giants.