夏季索马里越赤道气流垂直结构的变化特征及其与东亚夏季风活动的关系

采用NCEP/NCAR和ERA40再分析月平均资料,对比分析夏季垂直尺度上五层(1000 hPa、925 hPa、850 hPa、700 hPa、600 hPa)索马里越赤道气流(SMJ)的时空演变特征。指出对流层中低层SMJ存在不同的垂直结构,且具有年际、年代际变化特征。夏季SMJ垂直结构主要呈现出全区一致、上下反相两种分布型(“A”型和“B”型),细分为一致增强型(“A+”型)、一致减弱型(“A-”型)、上弱下强型(“B+”型)和上强下弱型(“B-”型)。进一步分析指出,SMJ垂直结构与东亚夏季风活动关系密切,SMJ“A+”(“A-”)型垂直结构对应东亚夏季风偏强(弱),我国内蒙古东部、华北地区降水偏多(少);夏季SMJ“B+”(“B-”)型垂直结构对应东亚夏季风偏弱(强),我国江南、日本地区降水偏少(多)。

Variation Characteristics of the Vertical Structure of the Summer Somali Cross-Equatorial Flow and Its Relationship with East Asia Summer Monsoon Activity

The spatiotemporal evolution of Somali cross-equatorial flow (SMJ) in summer at five levels (1000 hPa, 925 hPa, 850 hPa, 700 hPa, 600 hPa) are studied on the basis of National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data and ERA40 reanalysis monthly mean data. The results show that vertical structures of SMJ in the middle and lower troposphere differ, with interannual and interdecadal change characteristics. Two main vertical structure modes are clarified. The first is a consistent mode in the entire region ("A" mode), and the second is the vertically opposite mode ("B" mode). Thus, four vertical anomalous types of SMJ are observed to include consistently strong pattern ("A+" pattern), consistently week pattern ("A-" pattern), higher weak and lower strong pattern ("B+" pattern), and higher strong and lower weak pattern ("B-" pattern). It is also indicated that the vertical structures of SMJ are closely related to East Asia summer monsoon activity. Specifically, the "A+" pattern (“A-" pattern) correlates strongly to the strong (weak) East Asia summer monsoon with more (less) rainfall in eastern Inner Mongolia and North China. The "B+" pattern ("B-" pattern) correlates strongly to the weak (strong) East Asia summer monsoon with less (more) rainfall in the southern area of the Yangtze River and Japan.