广西前汛期典型旱涝急转及其大气环流特征

TYPICAL DROUGHT-FLOOD ABRUPT ALTERNATION AND ITS ATMOSPHERIC CIRCULATION CHARACTERISTICS OF THE FIRST FLOOD SEASON IN GUANGXI

基于1969~2018年广西地区85个气象格点逐日降水数据及NCEP/NCAR再分析资料,分析前汛期典型旱涝急转及其大气环流特征。结果表明:(1)广西前汛期典型旱涝急转具有高强度及隐蔽性的特点,旱转涝事件集中在桂中和桂西南地区,涝转旱事件则分布于桂西和桂东北地区。(2)典型涝转旱的涝期,广西处在水汽辐合区,南海上空气旋式异常环流使洋面暖湿水汽持续输送,降水偏多;旱期,广西受西太平洋副高控制,水汽输送减弱,降水偏少。(3)典型旱转涝的旱期,孟加拉湾季风槽偏弱使水汽输送异常,伴随下沉辐散运动增强,降水减少;涝期,西太平洋副高明显东退,利于热带低值系统活动,低层水汽辐合程度加强,降水增多。

Based on the daily precipitation data of 85 meteorological grid points in Guangxi from 1969 to 2018 and NCEP/NCAR reanalysis data, the characteristics of typical drought-flood abrupt alternation(DFA)and its atmospheric circulation in the first flood season were analyzed.The results showed that the typical DFA of first flood season in Guangxi had the characteristics of concealment and high intensity.Besides that, the drought-to-flood events was concentrated in central and southwest Guangxi, while the flood-to-drought events was distributed in west and northeast Guangxi.In addition, the flood period of typical flood-to-drought, Guangxi was in the region of water vapor convergence, and the anomalous cyclonic circulation over the South China Sea made the warm and wet water vapor continuously to transport, which caused more precipitation.The drought period of typical flood-to-drought, under the control of the West Pacific Subtropical High, the water vapor transport in Guangxi was weakened and the precipitation was less.The drought period of typical drought-to-flood, the weak monsoon trough in the Bay of Bengal led to abnormal water vapor transport, with the strengthening of descending and divergence movement, which caused the precipitation to decrease.The flood period of typical drought-to-flood, the western Pacific subtropical high retreated eastward obviously, which was conducive to the activity of tropical low value system, and the extent of moisture convergence in the lower-level was strengthened, and eventually the precipitation increased.