Preliminary Results from the Coupled Atmosphere-Ocean Regional Climate Model at the Meteorological Research Institute

抄録

A ten-year integration of the Meteorological Research Institute Coupled atmosphere-ocean Regional Climate Model (MRI-CRCM) was conducted to evaluate the model’s performance in reproducing the present climate around Japan (CRCM run). MRI-CRCM couples a 20 km-mesh atmosphere Regional Climate Model (RCM20), and a North Pacific Ocean General Circulation Model, whose horizontal resolution is 1/4° (longitude) × 1/6° (latitude). Multi-nesting method is used for calculating the atmospheric part. A 60 km-mesh atmosphere Regional Climate Model (RCM60) is nested in MRI Coupled General Circulation Model, and RCM20 is nested in RCM60. To verify the effect of coupling, an atmospheric RCM run, that specified SST from a global coupled model run, was also conducted (ARCM run). Compared with observations, sea surface temperatures (SSTs) are overestimated in both runs for the winter over the Japan Sea. In the CRCM run, the SST simulation is somewhat improved and surface air temperature (1.5 m above the ground) is also lower than in the ARCM run.
Japan is classified into seven regions according to climatic features. Compared with observational data, summer surface air temperatures in both runs are somewhat high in most of Japan, except for southern regions. This warm bias is reduced in the CRCM run as compared to the ARCM. The improvements in the CRCM run are especially large in northern Japan, where the differences between the runs exceed 1.5 K. The precipitation simulations are compared with radar-AMeDAS data. A typical winter pattern with much rainfall along the coast of the Japan Sea, compared to the coast of the Pacific Ocean, are well reproduced in both runs, but the simulated precipitation is overestimated on the Pacific coast in winter. Precipitation is generally overestimated in northern Japan, while underestimated in western Japan throughout the year. Precipitation is less in the CRCM than in the ARCM run, because of the reduced latent heat flux and lower SSTs. The MRI-CRCM is an effective means to reproduce the Japanese climate, but has still biases in temperature and precipitation. Further improvements are needed.