Superrotation and Jet Migration in Simulations of Jupiter's Convective Zone and Weather Layer

The mean zonal flow observed on Jupiter consists of an intricate pattern of jets, or bands of zonal flow moving prograde or retrograde compared to the bulk planetary rotation. The strongest flow is a superrotating (prograde) jet near the equator, which is flanked by 6-7 retrograde/prograde pairs of weaker jets per hemisphere. The two primary drivers of Jupiter's zonal flows are thought to be "shallow" baroclinically driven quasi-two-dimensional turbulence in an outer, stably stratified weather layer (WL) and "deep" rotationally constrained buoyantly driven three-dimensional Busse columns in the convective zone (CZ) just underneath the WL. To study both driving mechanisms simultaneously, we implement two rotating, three-dimensional, spherical-shell, anelastic convection simulations of a Jovian-like planet. In one case, the CZ is isolated, whereas in the other case, the upflows are allowed to overshoot into a stably stratified near-surface region, representing an idealized weather layer. We find that in both cases, homogenization of potential vorticity (whose forms in the CZ and WL are distinct) initially creates multiple jets at high latitudes, whereas angular momentum transport by Busse columns drives equatorial superrotation at low latitudes. The presence of an idealized WL significantly alters the thermal wind balance, resulting in large deviations of the meridional contours of the zonal flow from alignment with the rotation axis. Although the superrotation remains stable, the weaker high-latitude jets slowly migrate poleward and/or merge on a very long time scale (O(10) diffusion time scales or thousands of eddy turnover times).