长江中下游地区暴雨"积成效应"

采用1960–2011年中国740站日降水观测数据, 以长江中下游地区为切入点, 提出暴雨"积成效应"这一概念, 旨在将暴雨这一天气尺度强降水过程拓展为类似中长期天气尺度过程来考虑, 研究它对季节尺度降水的贡献及影响. 通过统计分析从持续时间(L_d)、控制面积(A_r)、降水贡献率(Q_s) 等三个角度建立暴雨"积成效应"概念及判定标准, 并进一步结合上述指标建立暴雨"积成效应"强度指数. 从这一角度出发, 探讨长江中下游地区暴雨"积成效应"与夏季降水的时空对应关系, 发现强度指数与同期夏季降水量的年际和年代际变化具有很好的一致性; 强弱指数年合成分布以及指数与中国东部夏季降水相关系数的空间分布呈现出类似于中国东部夏季雨带的分布形式; 而利用EOF分解对暴雨"积成效应"空间范围分类, 发现其与该地区夏季降水具有相似的4种空间型, 总体而言, 长江中下游地区暴雨"积成效应"造成的降水极大地影响甚至决定整个夏季降水的多寡及空间分布. 关键词： 长江中下游 暴雨 "积成效应" 夏季降水

"Cumulative Effect" of torrential rain in the middle and lower reaches of the Yangtze River

To expand the torrential rain which is a meso-and-micro scale weather process to a meso-and-long scale weather process, in this paper we choose the middle and lower reaches of the Yangtze River (MLRYZ) as a sample region, and propose the conception of "Cumulative Effect" of torrential rain (CETR) by using the daily precipitation observational data from 740 stations in China. On the statistical analysis of observations, we define CETR as the cumulation or superposition of many torrential rain processes, and three indexes, which are continuous time (L_d), control area (A_r) and precipitation contribution rate (Q_s), which are used for explaining the conception of CETR. Then taking these three indexes into consideration, we establish the intensity index of CETR (BQDI) and study the relationship between the BQDI and the summer precipitation in MLRYZ. Results show that the interannual and interdecadal variations of BQDI are similar to those of summer precipitation in MLRYZ. The distribution of correlation coefficient between the BQDI and the summer precipitation in Eastern China and the composite analysis of representative years in BQDI show a large positive relation area in MLRYZ (significance test at the 95% level) and two large negative relation areas in North and South China (significance test at the 95% level), which reveals that the variations of BQDI not only correspond to the variations of summer precipitation in MLRYZ but also correlate with the distribution of summer precipitation in Eastern China to some extent. Besides, an empirical orthogonal analysis is performed on the frequency of torrential rain in MLRYZ, we find that the four major spatial modes of torrential rain are also similar to those of summer precipitation in MLRYZ. In conclusion, the precipitation caused by CETR greatly influences even determines the amount and distribution of summer rainfall, which is worth further investigating.