Abstract:

Based on the observation data from automatic weather stations and conventional weather stations in Hubei Province and NCEP/NCAR reanalysis data with 6-hour resolution during 2003-2013, the sudden mesoscale rainstorms in Sanxia valley were classified, firstly. Then, every type of rainstorm process was elaborated in detail from configuration of atmospheric circulation situation and weather system, environment field and terrain effect, respectively, and the concept model  with great significance of forecast for every type of rainstorm was established. The results show that the sudden mesoscale rainstorm processes in Sanxia valley during 2003-2013 were divided into three types, namely the combined warm and cold shear type in front of the Southwest Vortex, intersected northerly and southerly airflow type in tail of northeast cold trough and convergence type over the boundary layer inside the subtropical high, respectively. For the first type, the binding domain of cold and warm shear in lower layers had good significance on mesoscale rainstorm forecast. The northerly wind dominated on the surface, the terrain uplift in southern slope (windward slope) of the valley entrance was strong, and the temperature field presented Ω-shape near the valley. The mesoscale convective systems (MCS) moved eastward along the valley. For the second type, the synoptic scale system was significant, and the convergence area in tail of cold shear in lower layers had good significance on mesoscale rainstorm forecast. The northerly and southerly airflows existed on the surface, two airflows intersected in the entrance of Sanxia Gorge and entered into the Gorge. The most of MCS moved from north to south due to the larger temperature gradient in southern slope of the valley. For the third type, the weak shear in the boundary layer had good significance on mesoscale rainstorm forecast. The southerly wind dominated on the surface. The southerly wind changed direction and formed the mesoscale convergence center under the forcing of terrain condition after it entered into the valley, and combined with the uplifting of windward slope in the north of the valley entrance, the dynamic forcing was stronger. The most of MCS moved northward due to terrain blocking. Finally, three kinds of concept model and prediction indexes of sudden mesoscale rainstorms were built in Sanxia valley based on the above research.

Key words: Sanxia valley, mesoscale rainstorm, terrain forcing, concept model

摘要：

利用2003—2013年湖北省三峡谷地加密自动站资料、常规观测资料、NCEP/NCAR逐6 h再分析资料，对三峡谷地突发性中尺度暴雨过程进行分型，并从环流背景及天气系统、环境场、地形影响等方面分别进行分析阐述，确立有预报意义的概念模型。结果如下：2003—2013年间，三峡谷地突发性中尺度暴雨过程分为西南低涡前冷暖切变结合型、东北冷槽尾部南北气流汇合型和副高内部边界层辐合型三类。其中，西南低涡前冷暖切变结合型，以天气尺度强迫为主，低层冷暖切变结合区对中尺度暴雨预报指示意义强，地面上以北风气流为主，峡谷入口处南侧迎风坡抬升作用强，峡谷附近温度场呈Ω型，中尺度对流系统(MCS)形成后多沿峡谷向东移动；东北冷槽尾部南北气流汇合型，天气尺度系统明显，低层冷切变尾部辐合区对中尺度暴雨预报指示意义强，地面上南、北两支气流并存，在峡谷入口处交汇进入峡谷，MCS形成后多由北向南移动；副高内部边界层辐合型，以边界层辐合和地形强迫抬升为主，边界层弱切变对预报指示意义强，地面上以偏南气流为主，进入峡谷后受地形阻挡作用，形成逆时针旋转的中尺度辐合中心，配合峡谷入口北侧迎风坡地形抬升作用，动力强迫达到最强，MCS形成后多由南向北移。在上述分析基础上，建立了三峡谷地三类中尺度暴雨概念模型。

关键词: 三峡谷地, 中尺度暴雨, 地形强迫, 概念模型