New snow-physics to complement SSiB part II: Effects on soil moisture initialization and simulated surface fluxes, precipitation and hydrology of GEOS II GCM

The SSiB model, which was forced with GSWP ISLSCP Initiative I surface data , was modified to include more realistic snow physics and snow-melt infiltr ation. The new snow model in SSiB was again integrated with the GSWP data. The new SSiB simulation produced wetter and warmer soil, with more realisti c snow-melt timing and runoff, in regions of significant snow-melt. The sim ulation was used for initializing land-surface temperature, soil moisture, and snow cover for the GEOS II GCM, which was integrated for JJA to generat e an ensemble of runs for both 1987 and 1988. Each ensemble contained six c ases starting from an ECMWF analysis for each day starting from 29 May thro ugh 3 June of each year. As compared to the old SSiB GCM, the new SSiB GCM with new initial hydrolog ic conditions significantly improved the prediction of precipitation in mid -to-high-latitude regions of Canada and Russia. Evapotranspiration, soil mo isture, and runoff also compared more favorably in the new SSiB GCM simulat ion than the old SSiB GCM. Also, the 1988-1987 difference in northern India precipitation was more pronounced in the new SSiB GCM. In the U.S., where the old SSiB GCM had failed to simulate the 1988 drought circulation, the n ew SSiB GCM performed only slightly better. This was also evident in the 19 88-1987 differences. In this region, the influence of initial conditions wa s mostly lost in about one month's time to the evolution of an unrealistic circulation.