Conservative Semi-Lagrangian Transport on a Sphere and the Impact on Vapor Advection in an Atmospheric General Circulation Model

Abstract

A conservative semi-Lagrangian scheme with rational function for interpolation is implemented in spherical geometry and tested in an atmospheric general circulation model (AGCM). The new scheme, different from the conventional semi-Lagrangian method, is conservative and oscillation free. By introducing polar mixing and a time split computation of divergence, the scheme can compute advection transport correctly over the polar regions. Idealized advection tests with various velocity fields were carried out to demonstrate numerical accuracy and conservation in comparison with the spectral schemes. The impact of the advection computation on water vapor circulation in an AGCM is also investigated with numerical simulations on the Earth Simulator. Both pure advection tests and general circulation experiments show that the presented scheme is effective in improving the tracer transport property and the precipitation field in comparison with the leapfrog-spectral method.