西太平洋副热带高压东西位置变动特征分析

采用NCEP／NCAR再分析逐日资料，根据特定区域涡度值，定义描述西太平洋副高东西位置的指标，并利用该指标研究了6月副高东西位置变动特征。结果表明：该指标不仅避免了由于高度的逐年升高而引起的副高逐年西进的年代际变化，而且能很好地反映大尺度环流场的特征；副高偏西年，赤道西风减弱，越赤道气流减弱，南海夏季风偏弱，江南和华南地区南风增强，其东侧负涡度发展，引导副高西伸，长江流域被副高北侧异常西南风控制，有利于雨带在此维持，降水偏多易涝。西太平洋副高东西位置变化的周期分析表明，6月副高西伸指数最强的周期信号为2、4、8a。

Variation Features of the Longitudinal Position of the Western Pacific Subtropical High

In terms of the NCEP/NCAR daily reanalysis data,an index based on the vorticity value in the key area is defined to describe the longitudinal position of the western Pacific subtropical high(SH).An investigation is carried out of variation features of the longitudinal position of the SH in June.Results show that the index avoids the interdecadal change of the westward stretch of the SH resulted from the yearly geopotential height rising,and well reflects the character of large-scale circulation field.In the wester subtropical high year,the equatorial westerly and the cross-equatorial flow weaken,the South China Sea summer monsoon is weaker.The southerly enhances over the south of Changjiang River and South China areas,then the negative vorticity develops in the east of these areas leading to the westward stretch of the SH.The anomalous southwesterly in the north side of the SH dominates over the Changjiang River Valley in favor of the maintaining of rainbelt,bringing about more rainfall(flood).The wavelet analysis suggests that the strongest periodical signal of the index in June is 2,4,and 8-year.