摘要:利用国家气象信息中心提供的1960～2015年中国753站汛期（4～9月）逐日降水资料，对华南地区汛期旱涝急转现象进行了分析，定义了一个旱涝急转评价指标，分析了旱涝急转事件的特点及其大气环流特征。结果表明：华南在56年汛期中共发生了17次旱涝急转事件，发生频率由1960年代的3次下降到1970年代、1980年代的1次，后迅速增加到1990年代的4次、21世纪初的8次。将其按急转时间分为春末初夏旱转涝事件和盛夏涝转旱事件。春末初夏旱转涝事件，旱期西太平洋副热带高压主体偏南，中国东部主要受干冷高压脊控制，华南低层负涡度发展伴随着辐散、下沉运动的加强和水汽输送的减弱，降水偏少；涝期西太平洋副热带高压北抬，孟加拉湾南支槽异常偏强，华南位于副热带高压西侧和南亚高压东南侧，低层正涡度发展伴随着辐合、上升运动和水汽输送的加强，降水偏多。盛夏涝转旱事件，涝期西太平洋副热带高压主体偏西，华南处于副热带高压西北侧和南亚高压东南侧，低层水汽输送、辐合和上升运动均加强，正涡度发展，降水增多；旱期西太平洋副热带高压显著北跳，南亚高压向东向北扩展至长江中下游地区, 华南为西太平洋副热带高压和高空东风急流所控制，低层水汽输送减弱，辐散和下沉运动加强，负涡度发展，干旱少雨。
关键词:旱涝急转/
华南/
标准化降水指数/
汛期
Abstract:Based on the daily precipitation data of the 753 Chinese stations provided by the National Meteorological Information Center, the drought-flood abrupt alternation phenomenon during the 1960-2015 flood seasons (April to September) was investigated, an evaluation index of drought-flood abrupt alternation was defined, and the atmospheric circulation characteristics of the drought-flood abrupt alternation events were studied. The results show that the drought-flood abrupt alternation events happened 17 times in southern China during the flood seasons of 1960 to 2015, and the frequency of their occurrences declined from three times in the 1960s to once in the 1970s and the 1980s, and then increased rapidly to four times in the 1990s and eight times in the early 21st century. According to the abrupt alternation time, the events are divided into two groups: Drought-to-flood events in late spring and early summer and flood-to-drought events in midsummer. During the drought period of drought-to-flood events in late spring and early summer, the location of the western Pacific subtropical high was more southerly; the eastern part of China was mainly affected by a dry and cold ridge, and the negative vorticity development in the lower-level southern China was accompanied by the strengthening of divergence and descending movement and the weakening of the water vapor transport, which caused less rainfall in southern China. During the flood period of drought-to-flood events in late spring and early summer, the western Pacific subtropical high stretched toward the north; the southern branch trough of the Bay of Bengal was abnormally stronger; southern China was located in the west side of the subtropical high and southeast side of the South Asia high; and the positive vorticity development in the lower-level southern China was accompanied by the strengthening of convergence, ascending movement, and water vapor transport, which caused more rainfall in southern China. During the flood period of drought-to-flood events in midsummer, the location of the western Pacific subtropical high was more westerly; southern China was located in the northwest side of the subtropical high and the southeast side of the South Asia high; and the positive vorticity developed in the lower-level southern China with the strengthening of convergence, ascending movement, and water vapor transport, which caused the precipitation in southern China to increase. During the drought period of drought-to-flood events in midsummer, the western Pacific subtropical high jumped significantly to the north; the South Asia high extended eastward and northward to the middle and lower reaches of the Yangtze River; southern China was controlled by the subtropical high and the upper east wind jets; negative vorticity developed in the lower-level southern China with the strengthening of divergence and descending movement and the weakening of the water vapor transport, which caused the precipitation in southern China to decrease.
Key words:Drought-flood abrupt alternation/
Southern China/
Standardized precipitation index/
Flood season
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