青藏高原东侧特殊地形对低层风场调整作用对比分析

Analysis of Topographic Effect of Eastern Tibetan Plateau to Lower Level Wind Field

通过对比分析2013年7月四川盆地西部的两次大暴雨过程,重点分析地形对低层流场的调整作用,结果表明:两次过程都是在副高西侧的低值系统影响下发生的,过程发生前期盆地西部处于高能高湿和及其不稳定的情况下,系统影响时有冷空气配合,"7.3"日的冷空气势力强于"7.9"过程,但低层南风弱于"7.9"过程;地形对两次暴雨过程的850 h Pa流场起到调整作用,冷空气影响前东南气流与地形以接近90°的夹角相交,地形的强迫抬升触发对流不稳定能量释放,冷空气入侵后,偏东北气流配合复杂的地形作用,造成龙门山沿线的暴雨;上升速度的大值区域主要位于103.5°E^105.5°E的地形陡峭区域,东南(东北)气流越强上升速度就越大,上升速度的大值区主要位于700 h Pa。

The adjustment of topographic effect to lower level wind field has been studied by comparing and analyzing the two heavy rains happen in western part of Sichuan in July 2013. The conclusion is that the two heavy rains happen under the condition of low system activity in subtropical highs. Western part of the basin is at high temperature and high energy with unstable condition in the early stage of heavy rains. Cold air comes together with low system, which cold air on July 3rd is stronger than that on July 9th, while lower level south wind on July 3rd is weaker than that on July 9th. Topographic effect adjusts 850 hPa flow field during these two heavy rains. Southeastern Air flow comes across with terrain by nearly 90 degree before the cold air came, then the special shape of the terrain forced the air flow rises up and causes convection. When the cold air comes in, heavy rain starts at Longmen Mountain area by the force of northeastern air flow together with the complicated topographic effect. Air flow rises up majorly around steep area at 103.5 °E--105.5°E. The stronger southeastern （northeastern） air flow is, the quicker it rises up, with the biggest increase is around 700 hPa area.