季节预测模式对东亚夏季环流的预测能力及其对热带海洋的响应分析

摘要

东亚夏季环流变化对中国夏季降水的年际变化有重要影响,因此需要进一步理解季节预测模式对东亚夏季环流的预测能力.利用1991～2013年美国国家环境预测中心(NCEP)、中国气象局国家气候中心(NCC)和日本东京气候中心(TCC)的三个季节预测模式(CFS V2、BCC_CSM V2和MRI-CGCM)以及NCEP/NCAR再分析资料,定量评估了模式对东亚夏季风(EASM)和夏季西太平洋副热带高压(WPSH)强度的预测能力.在此基础上,分析了模式预测的EASM和WPSH对热带海温异常的响应能力,以及ENSO事件对EASM和WPSH预测的影响,阐述了预测误差产生的原因.结果表明:整体而言,三个模式对EASM和WPSH的预测技巧较高,但TCC模式对WPSH的预测技巧相对较低.三个模式预测的850hPa风场在西北太平洋存在一个异常气旋,使得预测的EASM偏强和WPSH偏弱.同时,二者的年际变率整体比观测小.三个模式预测的EASM和WPSH对热带海洋海温异常的响应随季节演变特征与观测比较接近,但NCEP模式和TCC模式预测的EASM对前期热带太平洋和前期、同期热带印度洋的海温异常响应要强于观测,NCC模式预测的EASM对前期和同期的热带太平洋的海温异常响应明显比观测强.此外,三个模式预测的WPSH对前期和同期的热带太平洋、热带印度洋和热带大西洋的海温异常响应明显强于观测.三个模式预测的EASM和WPSH在ENSO年的平均绝对误差(MAE)整体而言要比正常年的小很多,NCEP模式和NCC模式预测的EASM和WPSH的MAE在La Ni(n)a年和E1 Ni(n)o年差别不大,而TCC模式预测的EASM和WPSH的MAE在E1 Ni(n)o年比在La Ni(n)a年大很多,表明ENSO事件是东亚夏季环流重要的可预报源.%Changes in the East Asian summer circulation have great impacts on summer rainfall in China.It is necessary to better understand the forecasting capacity of seasonal forecast models.In this study,we evaluated the capacity of seasonal forecast models for the forecast of the intensity of East Asian Summer Monsoon (EASM) and Western Pacific Subtropical High (WPSH) in the summer based on the NCEP/NCAR reanalysis and simulations for 1991-2013 from three seasonal forecast models,i.e.CFS V2,BCC_CSM V2 and MRI-CGCM.These models are from National Centers for Environmental Prediction (NCEP),National Climate Center (NCC) and Tokyo Climate Center (TCC) respectively.To illustrate the origin of forecast errors,we analyzed responses of the EASM and WPSH to tropical sea surface temperature (SST) anomaly in these models and impacts of ENSO events on the forecast of the EASM and WPSH.Analysis results indicated that the forecast skills for the EASM and WPSH were high in all models,while those of the TCC model are relatively low.An anomalous cyclone was simulated over western North Pacific,resulting in stronger EASM and weaker WPSH compared to that of observations in all models.Meanwhile,the annual variability of the EASM and WPSH was weaker than that of observations.Characteristic responses of the EASM and WPSH to tropical SST anomaly and its seasonal evolution were close to those of observations in all models.The response of the EASM to the preceding tropical Pacific Ocean SST anomaly and the preceding and simultaneous tropical Indian Ocean SST anomaly in NCEP model and TCC model were stronger than those in observations,and the responses of the EASM to the preceding and simultaneous tropical Pacific Ocean SST anomaly in NCC model were obviously stronger than those in observations.Besides,the responses of the WPSH to the preceding and simultaneous SST anomalies over tropical Pacific Ocean,tropical Indian Ocean and tropical Atlantic Ocean were obviously stronger in all the models than those in observations.The mean absolute errors (MAE) of the EASM and WPSH forecasted by the three models in ENSO events overall were much smaller than those in normal years.The MAEs of the EASM and WPSH forecast by NCEP model and NCC model in La Ni（n）a events were close to that in E1 Ni（n）o events,while The MAEs of EASM and WPSH forecasted by TCC in E1 Ni（n）o events were much higher than that in La Nif（n）a events.This result also indicated that ENSO event was an important source of forecast for the East Asian summer circulation.