ESD
Regional Climate Hindcast for the Western United States Using the RCSM
cal and were obtained from observational studies taken in the Great Plains.As the storm e nv i ronment and the resulting storm stru c t u re widely va ry according to location, existing parameters may not be suitable for the western United States. Hence, ri gorous evaluation of model results and sensitivity tests are important for a successful simulation of long-term re gional climate simulation. A preliminary evaluation of the RCSM is presented below.
January and February while the maximum snowmelt was in April and early May. The simulated snow c over wa s totally depleted at the end of June. Such variation of the snowcover is consistent with the observation in which snow remains only at high elevations after June.
Significance of Findings
The agreement betwe e n the observed and simu l a t e d climate fe a t u res in this preResults liminary experiment indicates that the RCSM is capaWe have completed an inible of long-term climate simFigure 2. Observed (solid line) and simulated (bars) daily-mean precipitation over tial evaluation of the RCSM California during the first 150 days of the simulation. ulation. Observed pre c i p i t afor a long-term climate simution events and the amount lation. In this study, we used the SAS scheme with the parameter of precipitation was well- simulated by the MAS. The surfa c e values currently employed by the NCEP for medium-range global s n ow budget by the SPS is also consistent with the observa t i o n . forecasts. U n d e restimation of spring precipitation could be part i a l ly corFigure 2 illustrates a comparison between the observed and rected by using the Anthes convection scheme instead of the SAS scheme. H oweve r, it needs more investigation to select a simulated daily-mean precipitation within California during the c o nvection scheme most suitable for the we s t e rn United States first 150 days of 1979.The observational data was from the co-op re gi o n . Long-term climate and streamfl ow simulation and deve lstations within California. For each month, 400-500 stations were opment of a high-performance ve rsion of the MAS are curre n t ly available for comparison.We interpolated the simulated precipiu n d e r way. tation to match the location of each station, as precipitation varies rapidly over a mountainous terrain. Related Publications The MAS has well-simulated the daily precipitation events in California. Figure 2 shows that eve ry observed precipitation Kim, J., N. Miller, K. Georgakakos and A. Guetter, River flow event is present in the simulated precipitation, except the last response to precipitation and snow budget in California durevent where the MAS has underestimated precipitation.This indiing the 1994-1995 winter, J. Climate, 11, pp. 2376-86, 1998. cates that the dynamic framework of the MAS is capable of accuKim, J., and N. Miller, Hydroclimate modeling of the western rately handling the tendency of the large-scale flows imposed through time-dependent lateral boundary conditions. United States: A hindcast and 2xCO2 impacts, Conference on detection and modeling of regional climate change, Trieste, The amount of precipitation is also generally well-simulated. Italy, June 1999. The agreement between the observed and simulated values are especially good for January and February (Julian days 1-60). Funding Precipitation was underestimated during the spring time from late March to May. This underestimation was partially corrected This work has been supported by the Laboratory Directed in the experiment using the Anthes scheme instead of the SAS R e s e a rch and Development Program of Law rence Berkeley scheme (not shown). National Laboratory under U.S. Department of Energy Contract The simulated snow budget was also consistent with the No. DE-AC03-76SF00098. observations. The simulated maximum snowfall occurred in
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