Viscous coupling in a spherical body of temperature-dependent viscosity

Abstract

The finite-amplitude thermal convection in a spherical body with temperaturedependent viscosity is considered with emphasis on the coupling of different convection modes. An axisymmetric convection is assumed, where the lateral dependence of the variables are resolved through their harmonic presentations whereas the radial and timedependence of the variables are determined by a finite difference method. In the case of a constant or radially-dependent viscosity model the coupling is due to the non-linear term in the energy equation. The former model tends to cool throughout the body whereas the latter model provides a thicker lithosphere and higher mean temperature below. In a laterally heterogeneous viscosity model all of the convection modes couple in a complicated manner. But the coupling does not change the temperature distribution significantly in the case of a small, moon-type, planetary body.