摘要:利用1959～2013年台站逐日降水观测资料和JRA-55逐6小时再分析资料，分析了长江中下游地区夏季强降水对应的前期三维环流结构。通过对长江中下游地区373个强降水样本的大气环流场合成分析发现，在长江中下游地区对流层中上层存在暖异常，暖中心位于300 hPa。在静力平衡和准地转平衡的作用下，高层暖异常上层存在反气旋式环流，下层存在气旋式环流。一方面，暖异常通过高层的反气旋式环流异常，使得其北侧的200 hPa西风增强，并促使高层急流东伸、南移到长江中下游地区北侧附近，增强了长江中下游地区高空辐散；另一方面，暖异常通过低层的气旋式环流异常，加强了吹向长江中下游地区的西南风，使低层水汽输送及辐合增强。暖异常所引起的高低空环流异常的有利配置，对长江中下游地区夏季强降水形成有重要作用。300 hPa 暖异常在降水前48小时已经存在于青藏高原东部的400～300 hPa 高空，700 hPa 气旋式环流提前24小时出现在四川盆地中低层。高低层的环流要素相互配合并随时间东移，暖异常率先到达长江中下游地区，并配合低层气旋式环流和水汽辐合区，导致了长江中下游地区的强降水。
关键词:强降水/
三维环流/
长江中下游
Abstract:Using daily station data and Japanese 55-year Reanalysis Project (JRA-55) data from 1959 to 2013, a three-dimensional background circulation structure of summer heavy rainfall in the middle–lower reaches of the Yangtze River (MLYR) was analyzed. Composite analyses of circulation in advance of 373 heavy rainfall days revealed that a prominent warm anomaly with a center at 300 hPa emerged in the upper troposphere over the MLYR. Because of hydrostatic and quasi-geostrophic equilibriums, an anticyclonic (cyclonic) anomaly formed above (below) the warm center. On the one hand, the warm anomaly strengthened the westerly winds to the north of the warm center by a high-level anticyclonic circulation anomaly, which resulted in the jet stream in the upper-level over East Asia shifting southward and eastward to the north side of the MLYR. This enhanced the upper-level divergent anomaly field over the MLYR. On the other hand, the cyclonic anomaly below the warm anomaly reinforced the low-level southwesterly winds to the MLYR, which transported more water vapor to it and strengthened convergence. The favorable configuration of high and low altitude circulation anomalies caused by warm anomalies played an important role in the formation of strong precipitation in the MLYR. The 300 hPa warm anomaly existed at 400–300 hPa in the eastern part of the Qinghai-Tibet Plateau 48 hours before the precipitation in the MLYR. The 700 hPa cyclonic circulation appeared in the middle and lower layers over the Sichuan Basin 24 hours ahead of schedule. The high and low circulation elements cooperated with each other and moved eastward with time. The warm anomaly first reached the MLYR, and cooperated with the low-level cyclonic circulation and water vapor convergence area, resulting in strong precipitation over the MLYR.
Key words:Heavy rainfall/
Three-dimensional circulation structure/
middle–lower reaches of the Yangtze River
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