Derivation of Consistent Surface Fixed Fields for use in a Global NWP Model.

Abstract : This report describes a method for generating a consistent set of surface fixed fields for use in a global NWP model. These fields include orography, the land sea mask and the sea surface temperature. The method is based on two principles. First, the interpolation from the higher resolution data grid to the coarser resolution model grid is done with a local filtering or analysis technique. Second, the three analyzed fields are kept consistent by using the same method and filter parameters for each field. The basic orographic data set is the 1 X 1 degree Sripps data. This is used to produce the model grid values of orography and the land sea mask. The basic data for the sea surface temperature consists of monthly mean values on the 2.5 X 2.5 degree grid used by NMC. For the orography and land sea mask, we first use the basic data to generate values on the 2.5 X 2.5 degree grid. Then all three fields are interpolated to the model grid. The resulting land sea mask also allows for fractional land coverage at model grid points. Keywords: Land sea contrast; Numerical weather forecasting; Atmosphere models; Surface fields.