Simulation of China summer precipitation with a regional air-sea coupled model

A regional air-sea coupled climate model based on the regional climate model RegCM3 and the regional oceanic model POM (Princeton Ocean Model) is developed and a series of experiments are performed to verify the simulation ability of the coupled model over China in summer from 1963 to 2002. The simulation results show that the space coefficients between GISST and SST (summer sea temperature) in RegCM3POM exceed 0.9, so the SST in RegCM3POM is reasonable and available. Compared with the uncoupled experiments, the regional air-sea coupled model RegCM3 POM has better simulation performance in simulating the mean summer (from June to August) precipitation over China, and the distribution of rainband in the coupled model is more reasonable than that in the uncoupled model. The improvement of the rainfall simulation is very remarkable over the Yangtze river valley and South China, and as for the rainbelt intraseasonal evolution over eastern China in summer, the simulation ability of RegCM3POM is evidently improved compared with the uncoupled model. The interannual summer rainfall variation over eastern China simulated by RegCM3POM is accordant to observation result, and the spatial pattern of the interannual summer rainfall variation in the uncoupled model is unreasonable. Further analysis indicates that the simulated correlation coefficient between the summer rainfall in uncoupled model RegCM3 and observation is 0.30 over the Yangtze river valley and 0.29 in South China, while the coefficient between the rainfall in RegCM3POM model and observation is 0.48 over the Yangtze river valley and 0.61 in South China, which are more believable than that in the uncoupled model RegCM3. The simulation results of the relationship between SSTA (sea surface temperature anomaly) over costal oceans and summer precipitation show that the regional air sea coupled model has good performance in simulating the correlation coefficients between summer rainfall in the Yangtze river valley and SSTA of the Bay of Bengal, South China Sea and Kuroshio area, and the uncoupled model RegCM3 fails to reproduce the relationship between the rainfall over the Yangtze river valley in summer and SSTA in coastal oceans. The uncoupled model’s deficiencies are somewhat to blame that, in the uncoupled experiments, the SST is prescribed as a forcing, but in fact, SST anomaly is determined by anomalous atmosphere conditions, so the uncoupled model can not reflect the atmospheric feedback to ocean, and of course, the uncoupled model cannot reflect the air sea interaction over the sea surface. The precipitation is greatly affected by the water vapor, and a large mount of water vapor is carried from the ocean to the monsoon region by the monsoon flow. The further study shows that the monsoon circulation and the path of the moisture transport flux simulated by RegCM3-POM are in good agreement with the NCEP/NCAR data, which improves the rainfall simulation in China. Therefore, the regional air-sea coupled model is more available for China.