East China Summer Rainfall during ENSO Decaying Years Simulated by a Regional Climate Model

Abstract

The performance of the Climate version of the Regional Eta-coordinate Model (CREM), a regional cli- mate model developed by State Key Laboratory of Nu- merical modeling for Atmospheric Science and Geo- physical Fluid Dynamics/Institute of Atmospheric Physics (LASG/IAP), in simulating rainfall anomalies during the ENSO decaying summers from 1982 to 2002 was evalu- ated. The added value of rainfall simulation relative to reanalysis data and the sources of model bias were studied. Results showed that the model simulated rainfall anoma- lies moderately well. The model did well at capturing the above-normal rainfall along the Yangtze River valley (YRV) during El Nino decaying summers and the below and above-normal rainfall centers along the YRV and the Huaihe River valley (HRV), respectively, during La Nina decaying summers. These features were not evident in rainfall products derived from the reanalysis, indicating that rainfall simulation did add value. The main limita- tions of the model were that the simulated rainfall anoma- lies along the YRV were far stronger and weaker in mag- nitude than the observations during El Nino decaying summers and La Nina decaying summers, respectively. The stronger magnitude above-normal rainfall during El Nino decaying summers was due to a stronger northward transport of water vapor in the lower troposphere, mostly from moisture advection. An artificial, above-normal rainfall center was seen in the region north to 35N, which was associated with stronger northward water va- por transport. Both lower tropospheric circulation bias and a wetter model atmosphere contributed to the bias caused by water vapor transport. There was a stronger southward water vapor transport from the southern boundary of the model during La Nina decaying summers; less remaining water vapor caused anomalously weaker rainfall in the model as compared to observations. Keywords: East China rainfall, ENSO decaying summers, regional climate model, water vapor Citation: Zeng, X.-F., B. Li, L. Feng, et al., 2011: East China summer rainfall during ENSO decaying years simulated by a regional climate model, Atmos. Oceanic Sci. Lett., 4, 91-97.