Recent Changes Implemented into the Global Forecast System at NMC

Abstract

A number of improvements were implemented on 6 March 1991 into the National Meteorological Center's global model, which is used in the global data assimilation system (GDAS), the aviation (AVN) forecast, and the medium-range forecast (MRF): The horizontal resolution of the forecast model was increased from triangular truncation T80 to T126, which corresponds to an equivalent increase in grid resolution from 160 km to 105 km. The use of enhanced orography has been discontinued and replaced by mean orography. A new marine-stratus parameterization was introduced. A new mass-conservation constraint was implemented. The horizontal diffusion in the medium scales was reduced by adopting the Leith formulation. A new, more accurate sea-surface temperature analysis is now used. In this note, we discuss each of the changes and briefly review the new model performance.