2013年冬季广东罕见持续暴雨过程特点及成因

Causal Analysis of a Unusual Continuous Torrential Rainfall Event in Guangdong in Winter 2013

利用常规气象观测站、区域自动站资料和NCEP/NCAR客观分析资料等,对2013年12月13—17日广东出现的持续时间长、影响范围广和累计雨量大的罕见暴雨过程特征及成因进行了分析;对比分析了此过程与2008年年初持续低温雨雪冰冻过程形成的异同条件。结果表明:500hPa上在青藏高原附近建立"北脊南槽"的环流形势,促使北方冷空气沿脊前东移南下和来自南海、孟加拉湾沿南支槽前向东向北推进的暖湿气流在广东持续交绥,并在局地形成异常经向垂直环流,为持续性暴雨提供有利的环流背景条件;广东位于200hPa高空槽前部,处于高空急流入口区南侧的辐散、中低层辐合的区域中,也十分利于中低层水汽辐合抬升、凝结而产生暴雨。同2008年初持续低温雨雪冰冻过程相比较,这两次过程均发生在相似的"北脊南槽"形势下,但本次过程槽脊经向度大、南支槽位置偏南、降雨强度大;而2008年初过程则雨雪冰冻影响范围广和持续时间长;两过程虽同是在冬季低温背景下发生,而本次过程没有像2008年初过程那样在中层建立一强逆温层和低层形成一过冷却层,因而降水相态以雨为主,2008年初过程则以降雪冰冻(冻雨)天气为主。

Guangdong suffered the heaviest continuous torrential rainfall from 13 to 17 December 2013, according to the winter records since 1951. Based on the data of conventional meteorological observation, automatic weather station, and NCEP reanalysis, the characteristics and the possible causes of the continuous torrential rain are analyzed. The results show that the circulation situation at middle and high levels in Asia shows a ＂ridge in north and trough in south＂ pattern, which was favorable for the southward moving of cold air and the persistent meeting with the moist southerly from the Bay of Bengal and the South China Sea, and resulted in an unusual local meridional circulation above Guangdong. There appeared intense divergence at upper levels and intense convergence at lower levels, a favorable condition for torrential rainfall. Compared with the continuous freezing rain and snow weather in Guangdong at the beginning of 2008, the meridional wavelength of the ridge and trough was larger, and the extension of the trough was farther south than normal; therefore, the cumulative precipitation in this event was stronger without freezing rainfall.