2019年汛期气候预测效果评述及降水预测先兆信号分析

Overview of Climate Prediction for the Summer 2019 and the Precursory Signals

2019年汛期降水呈南多北少分布,主要多雨区位于东北和江南等地。3月发布的预报对江南、西南东部、东北东部、西北中部地区降水偏多和内蒙古中部及东北部的偏少均做了较好预测;5月发布的滚动预测将南方主要多雨中心南移,订正结果与实况更为一致。6月发布的盛夏预报及时加强了对东北地区降水趋势的订正,准确预测了东北地区降水明显偏多的特征。对南海夏季风、西南雨季、梅雨及华北雨季的季节进程预测也和实况一致。但2019年汛期降水预测也存在明显的不足之处:对长江中下游沿江降水异常偏少预测错误;对东北地区多雨的范围和异常程度估计不足。初步分析了2018—2019年冬季青藏高原积雪面积异常偏多、2018—2019年厄尔尼诺事件以及热带印度洋海温持续偏暖对长江中下游降水预测指示意义的失败,并与2018年外强迫信号及大气环流做了简单对比,指出汛期降水和传统影响因子不匹配、非对称的复杂性研究还需要深入开展。

In summer 2019,precipitation in south of China was above normal,but below normal in north of China.Much more precipitation was found in Northeast China and the south of the Yangtze River.The precipitation above normal in the south of the Yangtze River,the east of Southwest China,the east of Northeast China,the central part of the Northwest China,and the precipitation below normal in central and northeastern Inner Mongolia were well predicted in March.The updated forecast released in May predicted the main rainy centers in southern China would move southward,and this corrected forecast is more consistent with the observation.The prediction for July-August released in June modified the precipitation prediction trend for Northeast China,and accurately predicted the characteristics of much more precipitation in this region.The predictions on the onset of the South China Sea summer monsoon,the rainy season in Southwest China,Meiyu,and the rainy season in North China were predicted well.However,there were deficiencies in the precipitation prediction in summer 2019.The prediction of precipitation anomaly along the middle and lower reaches of the Yangtze River was wrong.The range and the anomaly degree of the precipitation above normal in Northeast China were underestimated.In addition,this paper preliminarily analyzes the failure of the snow area anomaly of Qinghai-Tibetan Plateau,the El Ni?o event and the tropical Indian Ocean warming in winter 2018—2019 indicating the precipitation anomaly in the middle and lower reaches of the Yangtze River.The external-forcing factors and the associated atmospheric circulation between 2018 and 2019 are compared.It is pointed out that the research on the complexity of the mismatch and asymmetry between the summer precipitation and the traditional impact factors needs to be further carried out.