A local grid refinement approach for the lithosphere and upper mantle in 3-D spherical mantle convection models

High resolution mantle convection models have made great progress over the past years owing in large part to the rapid increase in computational resources. However, fully resolving Earth's upper thermal boundary layer, the lithosphere, in 3-D spherical convection simulations is still beyond the reach of even the most powerful supercomputers currently available. Here we address the problem using the 3-D spherical mantle convection code TERRA. Applying a non-uniform computational grid with local mesh refinements concentrated into the lithosphere and the upper mantle, we are able to achieve grid point resolutions of less than 20 km in the low viscosity upper mantle allowing us to model highly vigorous mantle convection at Rayleigh numbers exceeding 10⁹. Our non-uniform mesh implementation also allows a drastic reduction in computational cost, which is decreased by an order of magnitude compared to convection models having a uniform grid point resolution throughout the mantle. We will show basic numerical calculations performed at Rayleigh number 10⁹ that exhibit Earth-like surface veocities and Nusselt number.