Tuesday, 16 January 2007
A flow-following finite-volume icosahedral model
Exhibit Hall C (Henry B. Gonzalez Convention Center)
A flow-following finite-volume icosahedral model (FIM) over the global domain has been developed. The grid-point based global model is formulated on isentropic-sigma surface and icosahedral geodesic grid discretized with conservative finite-volume operators. The flow following isentropic-sigma vertical coordinate is an improved version of the re-gridding and re-mapping processes which have been successfully used in atmospheric and ocean models such as Rapid Update Cycle (RUC) and HYbrid Coordinate Ocean Model (HYCOM). The Icosahedral geodesic spherical grid consisting of hexagon grid points with 12 pentagons provides a quasi-uniform coverage of the sphere and allows hierarchical refinements of grid spacing. The tendency terms are approximated by the explicit 3rd order Adam-Bashforth
time differencing scheme. The monotonicity of the transport scheme is achieved by extending the original Zalesak (1979) flux correction transportation (FCT) scheme into multiple time levels for the 3rd order Adam-Bashforth scheme. The physical parameterizations in FIM are incorporated from those used operationally by Global Forecast System (GFS) at National Centers for Environmental (NCEP). The FIM global model is evaluated with both the two- and three-dimensional flows. For the two-dimensional flows, FIM is extensively evaluated using the standard tests of Williamson et. al.(1992) for shallow water models on the sphere. For the three-dimensional flows, FIM successfully simulates mid-latitude baroclinic wave developments. Results from these test cases as well as real data simulations will be shown in the symposium.