3D conservative cascade semi-Lagrangian transport scheme using reduced latitude-longitude grid (CCS-RG)

The article presents conservative cascade scheme using reduced grid (CCS-RG) - a finite volume semi-Lagrangian (FVSL) algorithm for numerical solution of 3D advection equation on the sphere. The CCS-RG is based on the cascade approach that allows to split 3D advected quantity mass remapping between the Lagrangian and Eulerian grids onto 3 1D remappings. Another feature is using a quasi-uniform spaced reduced latitude-longitude grid on the sphere. The scheme is inherently mass-conservative, monotonic and stable with large time-steps. The CCS-RG performance is tested with the advection cases from the Dynamical Core Model Intercomparison Project test suite. The impact of the reduced grids and two different monotonic filters on the solution is investigated. The comparison with the results obtained by other schemes proves competitive accuracy of CCS-RG. In most cases, the numerical solution obtained with various reduced grids is as accurate as the regular grid solution.