山区地形对暴雨的影响

利用常规气象观测资料、卫星云图、多普勒天气雷达资料、区域自动气象站资料与NECP/NCAR 1°×1°逐6 h全球再分析资料，对2016年7月3—4日梵净山东南侧暖区特大暴雨的中尺度系统演变与环境场特征进行了分析。结果表明：（1）该过程暴雨发生在副热带高压西北侧高空槽区、低层暖切变南侧、低空急流左前端及高空200 hPa分流辐散区，主要影响系统为500 hPa高空槽和850 hPa暖切变线，地面无明显冷空气影响，属贵州暖区极端暴雨。（2）此次暖区暴雨是由4个对流云团连续影响直接造成，强降雨出现在对流云团中心附近及其后侧云顶亮温（T_BB）等值线梯度大值区。（3）暴雨由积状云为主的混合降水回波造成；暖云层和湿层深厚、低层水汽输送充沛、异常偏低的自由对流高度（LFC）和抬升凝结高度（LCL）及中等强度“瘦高”型对流有效位能分布，是形成高效率降水的有利环境条件。（4）梵净山对水汽向北输送具有阻挡作用，使水汽通量大值带和水汽辐合中心集中在其东南侧；边界层偏东风在山前转向南流与南来偏南气流在暴雨区形成东西向稳定中尺度辐合线，对流在辐合线附近触发、合并、加强和东移是造成特大暴雨的重要原因；迎风坡和喇叭口地形的中小尺度动力强迫有利于边界层水汽输送和抬升凝结。

Analysis on mesoscale system evolution and environmental field characteristics of a warm-sector heavy rainfall event in summer in the southeast of Fanjing Mountains

Using routine upper-air and surface weather observations, satellite images, Doppler weather radar products, the observations from regional automatic weather stations and NCEP 6-hourly reanalysis data with 1°×1° resolution, we have conducted an analysis of the mesoscale system evolution and environmental field characteristics of a warm-sector heavy rainfall event occurred in the southeast of Fanjing Mountain from July 3 to 4 in 2016. Results are as follows. (1) This event, whose main influencing systems are westerly trough at 500 hPa and warm shear line at 850 hPa, occurred in the upper trough area to the northwest of the subtropical high, the south side of low-level warm shear, the left front of low-level jet and the divergence zone at 200 hPa. As a result, this event is a warm-sector extreme heavy rainfall event in Guizhou without the affecting of obvious cold air in the ground level. (2) This warm-sector heavy rainfall event is directly caused by four continuous convective cloud clusters, in which the severe precipitation occurred near the center of the convective cloud clusters and in the area of big values of TBB gradient at their back side. (3) The heavy rain was caused by the mixed precipitation echoes of cumuliform clouds. Favorable environmental conditions causing such a high efficient precipitation include warm clouds, deep wet layer, low-level abundant water vapor transport, abnormal low level of free convection (LFC) and level of condensation lifting (LCL), and