Impact of soil moisture on regional spectral model simulations for South America

Abstract

A regional simulation using the regional spectral model (RSM) with 50-km grid space increment over South America is described. NCEP/NCAR 28 vertical levels T62 spectral resolution reanalyses were used to initialize and force the regional model for a two-year period from March 1997 through March 1999. Initially, the RSM had a severe drying trend in the soil moisture that adversely impacted the precipitation. The drying trend was presumably a response to the positive feedback between imperfect model parameterization schemes and the soil moisture module in the model. This drying trend was corrected in two additional experiments by tempering the deep soil moisture in the model during the integration. The first experiment prescribed the daily soil moisture in the deep second layer from the driving reanalysis; the second experiment utilized observed precipitation, to interactively correct the deep soil moisture during the integration. The regional precipitation simulations were only as good as, if not marginally better than, the reanalysis precipitation when validated against observed 0.5 degree gridded data. Nevertheless, both experiments corrected the reanalysis wet bias precipitation. The experiment with interactively corrected soil moisture provided the best simulation and had better anomaly threat scores at all precipitation intensities than the one with the specified soil moisture values from the reanalysis.

Citation

Chen, Shyh-Chin, John Roads 2005: Impact of soil moisture on regional spectral model simulations for South America. Terrestrial, Atmospheric and Oceanics Sci. 16, 5, 935-957.