Regional Quasi-Geostrophic Convection on the Tilted f-Plane*

In planetary interiors, stellar interiors, and icy moons' underground oceans, turbulent convection is heavily constrained by rotation, which promotes anisotropy along its axis (the Taylor-Proudman theorem) and the formation of large scale structures via an inverse energy cascade mechanism.

The flow morphology and the related transport properties (of heat, momentum, etc.) thus depend crucially on the angle between the rotation axis and local gravity, therefore causing strong variations of the local heat flux with the colatitude q in spherical shells.

In order to characterize these regional variations, we present a local model, valid in the asymptotic limit of rapid rotation, for quasi-geotrophic Rayleigh-Bénard convection on the tilted f-plane. The influence of both the colatitude q and the Rayleigh number Ra are analyzed by performing a computational parametric study. We map out the parameter space by delimiting three regions associated with different morphologies of the large scale barotropic flow: large scale dipolar vortices (LSV, near polar regions), zonal jets (ZJ, towards the equator), and bistable states composed of both (at intermediate latitudes and moderate Ra). Concomitantly, we observe that heat transfer, as measured by the Nusselt number, decreases during the transition from LSV states to ZJ states.