山东省春季大暴雨天气的形成机制个例分析

应用T213数值预报产品的分析场和6h预报场资料对山东省春季一次暴雨天气的成因进行了分析，结果表明：这次春季暴雨主要是受850hPa低涡和地面气旋影响产生的，低涡中心和气旋中心北部的辐合上升运动触发对流不稳定能量释放，产生暴雨。低空西南风急流为暴雨提供了充足的水汽和不稳定能量。暴雨区低层有较大的正螺旋度和非地转Q^*矢量辐合，说明暴雨区有中尺度和大尺度上升运动相叠加。与夏季暴雨的不同在于副热带系统较弱而西风带系统起主导作用，暴雨前后冷暖空气活动剧烈。

Formation Mechanism Analysis of a Heavy Rain in Shandong Province in Spring

By using the analyzed and 6-hour prediction data provided by the T213 model, the causes of a heavy rain and the energy and moisture conditions were analyzed. The dynamic trigger mechanism was studied through analyzing the features of helicity and Q* vectors. The result shows that the heavy rain was influenced mainly by the low vortex at 850 hPa and the surface cyclone; the convergence and ascending motion in the center of the vortex and north of the cyclone center triggered convective instability energy release, resulting in the heavy rain. The low-level Southwest Jet provided sufficient moisture and instability energy. The strong positive helicity and the intensive convergence of Q* vectors at the low level in the raining area indicate that there was superposition of mesoscale and synoptic-scale ascending motions. Differing from summer heavy rains, the systems in the westerly belt played a dominant role in spring heavy rain formation, but the subtropical systems are weaker and cool and warm air motions were very active before and after the heavy rain.