2012年7月华北降水异常成因分析

Cause Analysis on the Precipitation Anomalies in North China in July 2012

2012年7月,我国华北地区降水较常年偏多近45%,期间出现了严重的洪涝灾害。本文利用中国台站降水等资料,对华北降水异常现象及其可能成因进行了分析。结果表明,多因子共同作用可能造成了7月华北降水异常偏多。2012年7月,欧亚中高纬地区维持两脊一槽环流型,贝加尔湖附近低槽活动造成冷空气频繁南下。同时,西太平洋副热带高压(以下简称副高)明显偏北带来的充沛水汽与北方冷空气持续交汇于华北地区,共同构成了华北地区降水偏多的大尺度环流形势。分析还发现,西太平洋暖池区海温偏暖,产生的强盛对流活动使西太平洋副高位置偏北。同时,受北太平洋地区海温偏暖影响,东亚东北部—北太平洋地区盛行低层反气旋异常环流,也造成副高位置偏北。

Precipitations in North China were 45% more than normal during July 2012,accompanied with serious flood disasters.Utilizing precipitation data in China and other data,the characteristics of the anomalies and the possible causes ware analyzed.The results show that it might be attributed to the influ-ence of multiple factors.On the 500 hPa level,the large-scale circulation exhibits “two ridges and one trough”pattern over mid-high latitude of Eurasian Continent.The northward shift of the western Pacific subtropical high is also detected.Under this circumstance,the cold and the warm air converge strongly over North China,causing the serious precipitation anomalies.Further study shows that the SST of the e-quatorial western Pacific Warm Pool remains abnormally warmer in July 2012,generating strong convec-tive activities and driving the subtropical high to north.As a result,the subtropical high shifts northward. On the other hand,affected by the positive SSTA in the North Pacific,an anomalous anticyclone circula-tion prevails over the northeast of East Asia and North Pacific region,causing the subtropical high stretc-hing towards north.