During the summer of 2017 (June to August),the average precipitation over China was 348.6 mm,which is 8.1％ more than the climate mean (332.6 mm).Two rainfall belts were observed over eastern China.The average temperature in summer was 21.7℃,which is 0.8℃ higher than the climate mean (20.9℃).The summer of 2017 is the second warmest since 1961.The East Asian summer monsoon (EASM) was weaker than normal,while the West Pacific subtropical high (WPSH) was significantly stronger than normal with southward ridge position.The anomalous Philippine Sea anticyclone controlled the lower troposphere.The "-+-" circulation pattern was located in Eurasian mid-high latitude,with negative anomalous over Ural Mountain and near Japan and positive anomalous over Baikal Region.Circulation configuration of low latitudes and mid-high latitudes resulted in anomalous convergence of moisture flux and more precipitation over the south of the Yangtze River.Further analysis indicated that the interdecadal strengthening of West Pacific subtropical high and the sea surface temperature anomalies over the central and eastern tropical Pacific changing from negative to positive are the important cause for the significantly more precipitation over the south of the Yangtze River.%2017年夏季(6-8月),全国平均降水量348.6 mm,较常年同期(322.6 mm)偏多8.1％,呈现南、北两条多雨带.全国平均气温21.7℃,较常年同期(20.9℃)偏高0.8℃,为1961年以来第二高.东亚夏季风偏弱,西太平洋副热带高压显著偏强,脊线位置偏南,菲律宾附近对流层低层为反气旋环流控制;欧亚中高纬呈现“两槽一脊”环流型,乌拉尔山地区高度场为负距平,高压脊偏弱,贝加尔湖地区为正距平控制,日本附近高度场为负距平.低纬度和中高纬度的环流配置有利于冷暖气流在我国长江以南交汇,水汽通量辐合偏强,主要多雨带位于我国长江以南地区,降水显著偏多.西太平洋副热带高压的年代际增强和赤道中东太平洋由冷水向暖水发展是多雨带偏南的重要原因.
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