华南汛期持续性降水特征及其与30~90 d大气低频振荡的联系

利用全国756站逐日降水资料以及NCEP/NCAR再分析资料,研究了1961—2011年我国东部汛期持续性降水30~90 d低频变化特征及其与大气低频振荡的联系。结果表明,华南地区降水偏多型是汛期持续性降水低频变化的主导模态。对流层低层位势高度负异常和气旋型环流异常,以及高层略向北偏移的环流异常为华南汛期持续性降水低频变化提供了大尺度形势场。当西太平洋副热带高压脊线维持在22°N附近时,来自孟加拉湾和南海的水汽输送维持了华南地区汛期持续性降水活跃位相,向东北传播的副热带大气低频振荡系统对华南汛期持续性降水具有调制作用。此外,华南汛期降水低频变化还具有南北迁移的经向演变特征。

Characteristics of continuous precipitation during flood season of South China and its relationship with 30-90 day atmospheric low-frequency oscillation

Based on the daily precipitation data of 756 stations in China and NCEP/NCAR reanalysis data, the low-frequency variation characteristics of 30-90 d continuous precipitation in eastern China during flood season from 1961 to 2011 and its relationship with atmospheric low-frequency oscillation (LFO) are studied. The results show that the more frequent precipitation pattern is the dominant mode of the low frequency variation of the continuous precipitation in flood season in South China (SC). The negative geopotential height anomaly and cyclonic circulation anomaly in the lower troposphere and the circulation anomaly slightly shifted northward in the upper troposphere provide large-scale situation field for the low-frequency variation of continuous precipitation in flood season in SC. When the ridge line of the western Pacific subtropical high(WPSH) maintains around 22°N, the water vapor transport from the Bay of Bengal and South China Sea maintains the active phase of continuous precipitation in flood season in SC, and the LFO system of the subtropical atmosphere spreading to the northeast has a modulating effect on the continuous precipitation in flood season in SC. In addition, the low frequency variation of precipitation in flood season in SC also has the evolution characteristics of north-south migration.