Semi-Lagrangian advection on a Gaussian grid.

Abstract

In recent years, tests with gridpoint models have shown that semi-Lagrangian schemes permit the use of large time steps (roughly 3 to 6 times those permitted by the CFL criterion for the corresponding Eulerian models), without reducing the accuracy of the forecasts. This leads to improved model efficiency, since fewer steps are needed to complete the forecast. This paper examines the semi-Lagrangian treatment of advection on the Gaussian grid used in spectral models. Interpolating and noninterpolating versions of the semi-Lagrangian scheme are applied to the problem of solid body rotation on the globe, and their performance is compared with that of an Eulerian spectral treatment. It is shown that the semi-Lagrangian models produce stable, accurate integrations using time steps that far exceed the CFL limit for the Eulerian spectral model.-from Author