Impact of the spectral nudging on the simulation of a regional climate model: Different weight function

The spectral nudging technique is incorporated into wind fields in the regional climate model, RegCM3, and validated with the 2003 meiyu event. The results show that, with the spectral nudging, the ability of the model to simulate a local short time scale climate scenario, such as the meiyu event, can be improved obviously. It can correct efficiently the circulation and meiyu front northward biases which induce the precipitation northward biases during the meiyu produced by the model. Furthermore, two key variables to the spectral nudging: the weight function and the intensity index are tested. From the comparison among two weight functions and two corresponding intensity indices respectively, we find that the improvement of the spectral nudging depend mainly on the intensity coefficient. The spectral nudging with the weight function designed by von Stortch，et al.in 2000 and the intensity coefficient set to 0.05, gets the greatest improvement in the simulation of 2003 meiyu among the five experiments. Although the spectral nudging can make simulated circulation close to the forcing fields and the position and intensity of meiyu rainbelt close to the observation, respectively, this technique can not eliminate all the biases of the model. The better simulation of those variables that are closely related to physics processes, such as the positions of the low level temperature and the high temperature and high humid areas, should be relied on the further physics process improvement.