Better understanding the dynamics of the East Asian monsoon system is essential to address its climate variability and predictability. Regional climate models are useful tools for this endeavor, but require a rigorous evaluation to first establish a suite of physical parameterizations that best simulate observations. To this end, the present study focuses on the CWRF (Climate extension of WRF) simulation of the 1998 summer flood over east China and its sensitivity to cumulus parameterizations on CWRF performance. The CWRF using the Kain-Fritsch and Grell-Devenyi cumulus schemes both capture the observed major characteristics of geographic distributions and daily variations of precipitation, indicating a high credibility in downscaling the monsoon. Important regional differences, however, are simulated by the two schemes. The Kain-Fritsch scheme produces the better precipitation patterns with smaller root-mean-square errors and higher temporal correlation coefficients, while overestimating the magnitude and coverage. In contrast, the Grell-Devenyi ensemble scheme, using equal weights on all closure members, overall underestimates rainfall amount, suggesting for future improvement with varying weights depending on climate regimes.
The capability of the Climate extension of the Weather Research and Forecasting (CWRF) model in simulating the 1991 and 1998 summer floods in China is evaluated with 4-month continuous integrations as driven by the NCEP/NCAR observational reanalysis. It is shown that CWRF has a pronounced downscaling skill, capturing the key characteristics in the spatial patterns and temporal evolutions of precipitation in both severe anomalous monsoon cases. The result gives a high perspective for future CWRF applications in understanding and predicting China monsoon variability.
China is a country with complex topography, land surface conditions, coastlines with the world highest plateau in its west and the largest ocean at its east, and with large contribution from mesoscale phenomena, such as the mei-yu frontal systems and tropical storms. To study the regional climate in such a region, a highly resolved regional climate model (RegCM) has been recently developed at the International Pacific Research Center (IPRC). The distinct features of this model include direct feedback of cumulus detrained cloud ice and cloud water into the grid-resolved quantities; the effect of cloud buoyancy on turbulence production with mixed-ice phase clouds; an explicit coupling between the cloud microphysics and radiation via cloud properties; an explicit coupling between land surface and radiation via surface albedo, direct and diffuse radiation fluxes; and the effect of frictionally generated dissipative heating. The performance of RegCM3 is demonstrated by its simulation of the 2003 summer extreme climate event over the whole China region including Tibetan Plateau. There have not had so many studies about this region on this regard. With the use of the NCEP Reanalysis 2 data provided by the NOAA-CIRES Climate Diagnostic Center, Boulder, Colorado, USA, from their Web site at http://www.cdc.noaa.gov/, which is available at 6hr intervals with a resolution of 2.5°×2.5°, as both the initial and lateral boundary conditions, the model was integrated from 1 May to 31 August 2003 with a resolution of 60km×60km covering the area of 15°-55°N, 70°-140°E. It is demonstrated that the RegCM3 has a pronounced rainfall downscaling scale, producing more realistic regional details and overall smaller biases than the driving reanalysis data. The model simulated realistically not only the temporal evolution of the area-averaged precipitation and the monthly mean precipitation spatial pattern but also the daily precipitation intensity distribution.