Implementing a physical initialization procedure in a regional spectral model: impact on the short-range rainfall forecasting over South America

In this paper we describe the implementation of a physical initialization procedure in the recently developed Florida State University nested regional spectral model, and its impact on short-term forecasting over South America. Because the regional model forecasts perturbations to the global model results, we seek to determine the impact of the boundary condition on the regional model assimilation. The regional model is able to assimilate the satellite-derived rain rates rather well, regardless of whether the global model, providing the boundary conditions, has been physically initialized. The regional model is able to assimilate higher-resolution precipitation data, and also the global model assimilates coarser resolution data as reported in earlier studies. Ten experiments are performed over the northern part of South America during the tropical rainy season of January and February 1999. The initial correlation coefficients of the rain rates exceed 0.9 for all physically initialized cases. The subsequent 24-h forecast is also improved, as measured by spatial correlation coefficients and equitable threat scores.