广西一次冬季暴雨的水汽特征分析

为分析2012 年1 月13—15 日广西暴雨过程的水汽来源、急流的输送作用和水汽饱和程度等特征，使用天气学分析和动力诊断的方法分析NCEP/NCAR 1°×1°再分析资料、红外云图等资料。结果表明：孟加拉湾和南海是本次暴雨过程的2 个水汽源地，500~700 hPa 中低空西南急流的建立和加强使孟加拉湾成为主要水源地，加强了暴雨区的水汽供应。而这支急流的维持依赖于200 hPa加强的副热带锋区西风急流入口区南侧的强辐散作用。不同源地的水汽输送高度不同，水汽通量中心出现在700 hPa。600 hPa 以下为水汽通量辐合层，700~850 hPa 辐合强度远大于925~1000 hPa；水汽通量中心在暴雨区的上风方，水汽辐合中心在水汽通量中心沿气流去向的一侧，700~850 hPa 叠加的辐合中心处即为暴雨区，辐合高度的升高、湿层剧烈向上扩展都可作为暴雨征兆。以上分析得出了冬季暴雨过程中水汽条件的形成机制，得出预报着眼点，对提高此类暴雨预报准确率有较大作用。

Water Vapor Characteristics of a Winter Rainstorm in Guangxi

The paper aims to analyze the characteristics of water vapor source, vapor transport by jet stream and water vapor saturation of a winter rainstorm occurred from January13 to15 of 2012 in Guangxi, the authors used weather analysis and dynamic diagnostic methods to analyze the NCEP/NCAR 1°×1° reanalysis data, infrared imagery and other information. The results showed that: Bay of Bengal and the South China Sea were the two vapor sources of this rainstorm process, the establishment of low-level southwest jet stream at 500-700 hPa made the Bay of Bengal be the main source, strengthened the water vapor supply to the rainstorm area. The jet stream mainly depended on strong divergence effect of south side of west jet stream entrance of strengthening sub-tropical frontal area at 200 hPa. Different sources of water vapor transport had different heights, water vapor flux center appeared at 700 hPa. The vapor flux convergence layer was below 600 hPa, convergence at 700- 850 hPa was much larger than that at 925- 1000 hPa; the overlapping vapor flux convergence center at 700 hPa and 850 hPa was the rainstorm area, the increased height of convergence and the wet layer’severe scaling up could be the signal of the rainstorm. The conclusion contained the formation mechanism of water vapor conditions of a winter rainstorm, obtained prediction focus, and had a great effect on improving the accuracy of winter rainstorm’s forecast.