Reynolds stress and heat flux in spherical shell convection
by
Petri Käpylä
→
Europe/Stockholm
122:026
122:026
Description
Turbulent fluxes of angular momentum and heat due to rotationally
affected convection play a key role in determining differential rotation
of stars. Aims. We compute turbulent angular momentum and heat transport
as functions of the rotation rate from stratified convection. We compare
results from spherical and Cartesian models in the same parameter regime
in order to study whether restricted geometry introduces artefacts into
the results.
We employ direct numerical simulations of turbulent convection
in spherical and Cartesian geometries. In order to alleviate
the computational cost in the spherical runs and to reach as high
spatial resolution as possible, we model only parts of the latitude
and longitude. The rotational influence, measured by the Coriolis
number or inverse Rossby number, is varied from zero to roughly
seven, which is the regime that is likely to be realised in the solar
convection zone. Cartesian simulations are performed in overlapping
parameter regimes.
For slow rotation we find that the radial and latitudinal turbulent
angular momentum fluxes are directed inward and equatorward,
respectively. In the rapid rotation regime the radial flux changes sign
in accordance with earlier numerical results, but in contradiction with
theory. The latitudinal flux remains mostly equatorward and develops
a maximum close to the equator. In Cartesian simulations this peak
can be explained by the strong 'banana cells'. Their effect in the
spherical case does not appear to be as large. The latitudinal heat
flux is mostly equatorward for slow rotation but changes sign for
rapid rotation. Longitudinal heat flux is always in the retrograde
direction. The rotation profiles vary from anti-solar (slow equator) for
slow and intermediate rotation to solar-like (fast equator) for rapid
rotation. The solar-like profiles are dominated by the Taylor-Proudman
balance.
