春季和夏季爆发型ENSO事件对夏季中国降水的影响

Impact of Spring and Summer Onset Type ENSO on Summer Precipitation in China

采用NCEP再分析资料、海温资料以及中国台站降水资料,借助统计方法,讨论了不同爆发型El Ni？o和La Ni？a事件对中国夏季（5-10月）降水分布的影响。根据定义,El Ni？o和La Ni？a事件分为两类：一类是在4-6月爆发,称为春季爆发型（分为ELSP1、ELSP2、ELSP3和LASP）;一类是在7-10月爆发,称为夏季爆发型（分为ELSU和LASU）。结果显示,ELSP1型当年夏季,中国夏季降水主要呈现负距平分布,其中显著降水偏少区集中在黄河流域,在其次年夏季,降水由南往北呈现＂-、＋、-＂异常分布,显著降水偏多区主要集中于中原地带。ELSP2型当年夏季和次年夏季,中国夏季降水基本呈现相反变化分布,即当年夏季,全国降水以偏少为主,次年夏季全国降水以偏多为主。ELSP3型当年夏季,以华南降水偏多、其余地区降水偏少为主,在其次年夏季,降水主要以长江流域和华北偏多。ELSU型当年夏季,长江以北降水偏少、西南以及华南沿海降水偏多;次年夏季,降水由南往北呈现＂-、＋、-、＋＂异常分布。LASP型当年夏季使得全国降水基本一致增多,尤其是长江流域;而在其次年夏季,除了淮河和长江下游地区降水略多异常,全国降水以基本偏少为主。LASU型当年夏季,降水呈现长江以南偏少、以北偏多的主要分布形势,在其次年夏季,除了长江中下游区域降水偏多以外,其余地区降水均偏少。降水的异常分布与Hadley环流和水汽异常分布密切相关。但LASU型所导致的环流变化对中国夏季降水预测指示意义比较弱。

The NCEP reanalysis data, SST data, and precipitation measured at 617 weather stations across China have been exploited to investigate influences of spring and summer onset types of ENSO events on the summertime precipitation in China. El Ni？o and La Ni？a events can be classified into two major types： The spring type ENSO events whose onset time is from April to June（hereafter ELSP1, ELSP2, ELSP3, and LASP） and the summer type ENSO events whose onset time is from July to October（hereafter ELSU and LASU）. During the summer of ELSP1 years, consistent negative precipitation anomalies are found in China. Large negative precipitation anomalies are particularly distinct in the Yellow River basin. In the summer of the following year, precipitation anomalies demonstrate a ＂-, ＋,-＂ meridional pattern from south to north. Precipitation anomalies are opposite in the summer of ELSP2 years and that of the following years, that is more precipitation occur in the summer of ELSP2 years and less precipitation occur in the summer of the following years. During the ELSP3 summers, less precipitation occur in South China, whereas more precipitation occur in other regions of China. In the summer of the following years, however, positive precipitation anomalies are concentrated in the Yangtze River valley and North China. In the summer of ELSU years, negative precipitation anomalies appear to the north of the Yangtze River while positive anomalies occur in Southwest China and coastal region of South China. In the summer of the following years, precipitation anomalies demonstrate a ＂-, ＋,-, ＋＂ meridional pattern from south to north. Different to precipitationanomalies corresponding to other spring type of El Ni？o events, less rain occur in the summer of the spring type of La Ni？a（LASP） years and more rain occur in the summer of the following years. In the summer of LASP years, less precipitation occur in southern Yangtze River basin while more precipitation occur in northern Yangtze River basin. In contrast, negative precipitation anomalies are found over most area of China except the middle and lower reaches of the Yangtze River areas, where precipitation is slightly higher than normal. These changes in precipitation are closely related to anomalies in ascending and descending branches of the Hadley circulation and water vapor transport caused by the different onset types of ENSO events. It is worth noting that the anomalous circulations induced by the summer type of La Ni？a events only present weak implications for the forecast of summer precipitation in China.