Performance of RegCM2.5/NCAR-CSM Nested System for the Simulation of Climate Change in East Asia Caused by Global Warming

Regional climate in East Asia under 1CO2 and 2CO2 conditions, was simulated for continuous 10-year periods by the RegCM2.5 developed by NCAR, using the output of a CO2 transient run from NCAR-CSM as lateral and surface boundary conditions in order to evaluate the performance of the nested system for the use of climate change simulation caused by global warming for that region. In this study, January and June climates were analyzed. Through the validation of the simulated present climate, it was clarified that the typical precipitation phenomenon which occurs on the northwestern side of Japan during the winter monsoon is relatively well reproduced in the RegCM, but weakly in the CSM. It indicates that the RegCM is essential for the prediction of regional climate change for the East Asia region. Although the present climate reproduced by the RegCM has some marked biases, e.g. the large cold bias in the higher latitude in winter and the missing of the Bai-u front in mainland China, they are mainly due to the overstimation of sea ice area, and the northward shift of the NPH (North Pacific High) in the CSM, respectively. The SST bias in the CSM significantly contributes to the surface air temperature bias on the coast. In the climate change simulations, the large-scale distributions of SLP and temperature in the RegCM bear a resemblance to those of the CSM in both months. On the other hand, the regional scale precipitation change patterns are different between the RegCM and the CSM in June, because the precipitation band near Japan is well reproduced in the RegCM both in the 1CO2 and the 2CO2 climate. In this simulation, some notable climate change features are found, such as the temperature increase at higher latitudes in January, or intensification of the NPH extending to the southwest in June. Although these changes are statistically significant, they are mainly influenced by the bias in the CSM because the changes occur over the bias region, and their magnitudes do not necessarily exceed the bias of the simulated present climate. From these results, it should be stressed that it is of utmost importance that the AOGCM information is of good quality in the prediction of regional climate change.