Physical initialization for numerical weather prediction over the tropics

The current operational World Weather Watch over the tropical latitudes exhibits large data gaps. This paper proposes a detailed physical initialization procedure where the combined use of the World Weather Watch and detailed satellite data sets are used to enhance the definition of initial surface fluxes of water vapour and sensible heat, the initial rainfall rates and the earth’s radiation budget. The satellite radiances are used to unify the physical initializations of the fluxes, rainfall, and the clouds. This is carried out using a Newtonian relaxation during a-pre integration phase between day — 1 and day 0 where the fluxes, the rainfall rates, and the cloud distributions provide a consistent humidity analysis and a spin up of the diabatic heating and the divergent circulations. A comparison of medium range forecasts from a control experiment (that utilizes the standard nonlinear normal mode initialization, with physics, at day 0) with an experiment based on the unified physical initialization is carried out to demonstrate the effective enhancement of the World Weather Watch over the tropics by the proposed method. These experiments are carried out with a global spectral model which is run at a resolution of 106 wave triangular truncation.