夏季中国东部降水季节内振荡的区域模式模拟

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

利用中国科学院大气物理研究所大气科学与地球流体力学国家重点实验室(LASG)发展的区域气候模式CREM,对中国东部夏季降水的季节内振荡(ISO)进行了模拟研究,通过与格点和卫星观测降水资料及NCEP2再分析资料的对比,评估了该模式的优缺点。结果表明,该模式对东部季风区ISO具有较强的模拟能力。模式能够模拟出中国东部夏季降水气候态的季节内振荡(CISO)信号,并能较好地再现其纬向上西传和经向上北传的传播特征,尽管模拟的CISO强度分布与观测相比大值中心位置偏西北。此外,模式也能够合理地再现出降水瞬变的季节内振荡(TISO)的局地振荡特征以及高频振荡周期,但模拟的TISO强度较观测偏强,且在长江流域,模拟的TISO显著周期较短,其传播也表现出过强的东传。分析表明,上述偏差与夏季平均环流场以及ISO对应的辐散场和湿度场自身垂直结构的模拟偏差有关。NCEP2再分析资料的降水产品难以准确描述观测的CI-SO和TISO特征,CREM的模拟结果相对于再分析资料具有明显的"增值"。

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.