影响华南地区西南低涡的频数及移动特征分析

利用中国气象局提供的MICAPS观测资料以及空间分辨率为1 °×1 °的ERA-Interim再分析资料，对1991—2010年3—8月影响华南地区的西南低涡的生成和移动进行统计分析。结果表明，影响华南地区的西南低涡在6、7月出现频率较高；随着月份推移其维持时间逐渐增加，3月的维持时间最短（48小时），8月最长（105小时）；将影响华南地区的西南低涡按不同移动路径分为四类:东移型、东南移型、南移型和停滞型。在频数方面，东移型西南低涡出现次数最多（33个），东南移型次数最少（12个）；在维持时间方面，停滞型西南低涡的维持时间最短（54小时），南移型维持时间最长（86小时）。四类移动路径西南低涡所对应的大尺度环流场表明，停滞型西南低涡其对流层中高层槽脊不明显且辐散运动较弱，下游地区对流层低层有冷平流及辐散运动，不利于西南低涡的发展和移出，而其他三类移出型的西南低涡在对流层中高层有明显的槽脊系统及较强的辐散运动，同时在对流层低层，不同移动路径的西南低涡在各自移动方向上均有风场辐合带和暖平流区与之对应，有利于西南低涡的移动和发展。 

Characteristics Analysis on Frequency and Movement of Southwest Vortex Influencing South China

Based on statistical analyses, the characteristics of frequency and movement of southwest vortex influencing south China from March to August in 20 years (1991—2010), are studied by using observational data from MICAPS system supplied by CMA and the gridded reanalysis data from ERA-Interim with a horizontal spatial resolution of 1 °× 1 °. The result shows that the frequency of southwest vortex influencing south China is higher in June and July than any other months. The average duration of southwest vortex increases by month, with the shortest in March (48 hours) and the longest in August (105 hours). According to different moving paths, such southwest vortex can be classified into four types: eastward, southeastward, southward and stagnated vortex. Among them, the eastward type counts the most (37) while the southeastward type counts the least (12). Meanwhile, the duration of stagnated type is the shortest (54 hours) and the maintenance of southward type is the longest (86 hours). Comparing different moving paths of southwest vortex and corresponding large scale circulations, it can be concluded that when southwest vortex is moving (stagnated), the troughs and ridges in middle-upper troposphere is (isn't) clearly seen with a stronger (weaker) divergence movement, also warm (cold) advection and wind convergence (divergence) in downstream of the cradle in the lower troposphere, which is (not) favorable to the development and movement of southwest vortex influencing south China.