Intraseasonal Oscillation of Summer Rainfall over Eastern China Simulated with a Regional Climate Model

Performance of a regional climate model CREM, which was developed at the State Key Laboratory of Numerical Modeling for Atmospherics Sciences and Geophysical Fluid Dynamics/ Institute of Atmospheric Physics (LASG/IAP), in simulating the intraseasonal oscillation (ISO) of summer rainfall over eastern China is assessed by comparing model results against the observations and reanalysis data sets. The model reasonably reproduces the observed intensity, period, and propagation features of summer rainfall climatological ISO (hereafter CISO) in eastern China, but the location of the maximum rainfall center associated with CISO shifts northwestward. The observed high-frequency and local oscillation characteristics of rainfall anomalies associated with the transient ISO (hereafter TISO) are also well simulated, although the amplitude of TISO rainfall center is stronger than the observation, and the location of maximum rainfall center shifts northward relative to the observations. The simulated TISO period along the Yangtze River valley is shorter than the observations, and the associated rainfall centers also shift eastward. The deficiencies in ISO simulation are closely related to the model's biases in both summer mean state and vertical structures of convergence and specific humidity fields associated with ISO, suggesting that the improvements in summer mean state and convection process are crucial for a realistic simulation of ISO. The rainfall data derived from the reanalysis fail in reproducing both CISO and TISO, however, added values are evident in the rainfall downscaled by the CREM model.