华南地处东亚季风区，其洪涝灾害很大程度与大气低频振荡及其传播联系密切。来自副热带和热带的大气低频信号从海洋带来低频对流和源源不断的水汽，并沿着不同方向传播至华南，促使华南上空低频对流发展加强。来自中高纬的大气环流低频振荡也是影响华南降水异常的原因之一。前汛期高、低纬度低频风场同时向华南地区传输水汽，会产生极强的降水。本文对1980年以来华南前汛期的多个涝、旱年，低频降水的水汽输送源地、关键水汽环流系统以及水汽输送通道进行对比研究，揭示其差异，并用HYSPLIT后向轨迹模式进行了验证，同时也寻找到一些有意义的预测信号。
旱涝年相同的特征包括:1) 主要低频水汽源地是贝加尔湖的南侧、日本海北部和黄海、南海和西太平洋。2)主要低频水汽环流系统是贝加尔湖反气旋(LBAC)、东北气旋(东北气旋)、菲律宾海反气旋(PSAC)和华南气旋(SCC)（图1）。旱涝年的不同特征包括:1)涝年，日本南部海域另一个水汽源地，澳大利亚反气旋是另一个重要的低频水汽环流系统（图1）。2)涝年有两个西南暖水汽流和一个东南越赤道水汽流，而旱年只有一个西南暖水汽流。此外，大部分显著的预测信号在涝年和旱年的大约-4 d时开始出现，但类似的预测信号出现的时间是有区别的，有些预测信号只出现在涝年（图2和图3）。
Figure 1. The composite 10–20-d LF column-integrated water vapor flux (vector,uint:105 g m-1s-1, significant at α =0.1 level) and the corresponding water vapor flux divergence (shaded, uint: g m-2s-1 ) based on the peak phase 3(a,b) and the valley phase 7 (c,d) of 10–20-d LF precipitation during the flood (a,c) and drought (b,d)years. A and C represent anticyclonic and cyclonic LF water vapor circulation, respectively.
Figure 2. Lead-lag correlation coefficient vector maps (significant at α=0.05 level) for the flood years, produced based on 10–20-d LF column-integrated water vapor fluxes 8–0 d before LF precipitation and time intervals of 2 d. A and C represent anticyclonic and cyclonic LF water vapor circulation systems, respectively, and the long red vector represents wet-warm water vapor transport channel.
Figure 3. As in Fig. 2, but for the drought years.
文章信息：
Liping Li，Chenyu Ma，Chunyan Yang. 2020. Study on the differences in water vapor characteristics and predictive signals of low-frequency precipitation in the pre-flood season of South China between flood and drought years. International Journal of Climate. 2020,40:6587-6602