峡谷地形对两次大暴雨过程的增幅作用对比分析

利用湖北省加密自动站资料、常规观测资料、逐6h的NCEP／GFS再分析资料以及FY2E红外卫星云图资料，对2012年6月29日、7月4日湖北省两次大暴雨过程中峡谷地形的增幅机制进行对比分析。结果表明：两次过程均在有利的背景场及环境条件下受三峡谷地特殊地形影响而产生，冷暖空气相互对峙并配合峡谷地形的阻挡作用，迫使近地层水平流场、垂直流场发生改变，同时流入峡谷的地面气流与复杂地形相互作用，在峡谷内产生局地气旋性小环流或气流汇合区，地形性涡旋的生成对降水增幅起到关键作用；两次过程的不同之处是，前一过程中，冷空气作用更显著、不稳定能量累积更多、峡谷地形增幅作用更复杂，其中包括狭管效应、喇叭口效应及迎风坡地形效应，所以其降水效率更高、雨强更大。

Comparative analysis of valley topography effect on enhancement of two heavy rainstorms

Based on intensive automatic weather station observations in Hubei, conventional surface and upper data, 6-hourly reanalysis da-ta form NCEP and FY-2E infrared satellite images, a comparative analysis is made on enhancement mechanism of valley topography to two heavy rainstorms events occurred respectively on 29 June and on 4 July 2012. The results show that both heavy rainstorms occur in advanta-geous circulation patterns and environment conditions and are affected by valley topography in Yangtze River Three Gorges. Confronting of cold and warm air and coordinating with resistance effect from valley topography force the horizontal and vertical flow fields near the ground changed, meanwhile, the interaction between the ground airflow flowing into gorges and the complicated topography leads to a local cyclone micro-circulation or convergence zone in the gorges. As a result the formation of topographic vortexes plays a crucial role to increase precipi- tation. The difference between the two events is that in the former event, cold air has more significant effect, more instable energy is accumu-lated and more complicated enhancement of valley topography exists including the narrow-tube effect, bell mouthed topographic effect and windward slope effect, so that this event has more efficient precipitation and higher rainfall intensity.