Ten‐year east Asian summer monsoon simulation using a regional climate model (RegCM2)

This paper presents a 10‐year (1987–1996) summer climate simulation using a regional climate model. The National Center for Atmospheric Research Regional Climate Model (NCAR RegCM2) was designated over east Asia with a horizontal grid spacing of approximately 50 km. The model was initialized at June 1 and integrated up to the end of August for the 10 years. Initial and boundary conditions were the National Centers for Environmental Prediction/NCAR reanalysis data. The 10‐year summer mean biases of the simulated ground temperature and daily precipitation rate over the east Asian land area are about −0.1°C and 1.1 mm/d, respectively. Including the ocean area, the bias of the precipitaion rate is significantly reduced to about 0.05 mm/d. More precipitation is simulated in June over the central part of the model domain. The systematic cold biases of the simulated ground temperature take place over the northern part of the domain. The RegCM2 reproduces fairly well the large‐scale features associated with the east Asian summer monsoon system, including the subtropical high over the northwestern Pacific Ocean, the planetary‐scale trough over Manchuria, the upper level jet and lower‐level southerly or southwesterly flow and the precipitation band extended from south China to Japan. The evolution processes of the onset, break phases and abrupt jumps between two adjacent phases of the east Asian summer monsoon are also well simulated. On the other hand, the intensity and magnitude of the large‐scale features are not well reproduced. For example, the subtropical high over the ocean is too intensified, in association with the enhancement of the warm air advection in the lower level to the precipitation area. The maximum baroclinic zone and the planetary‐scale trough and thus the monsoon rainbelt are shifted northward by 2°–3° compared to reanalysis data. However, some of the systematic errors are hidden in the anomaly analysis over the 10‐year RegCM2 climate period.