西北东部一次暴雨天气过程的数值模拟研究

利用较高分辨率非静力中尺度数值模式MM5,对2003年8月28日西北东部一次致洪暴雨天气过程进行了数值模拟,重点研究了中-α和中-β尺度系统的发生发展和演变过程,对影响暴雨的物理量场进行了诊断分析.结果表明:中-α尺度低涡越山后迅速生成发展,历时约14 h,少动,并激发了多个中-β尺度系统,在这些不同尺度系统相互作用下,形成了这次区域性暴雨.强降水主要出现在低涡系统的发展与成熟阶段.700 hPa以上稳定的大气层结,抑制了水汽和能量的垂直扩散,有利于水汽和能量沿低空向雨区输送.在暴雨区上空,水汽和能量以垂直输送为主,同时伴有大量潜能释放.暴雨区上空有明显的正涡(位涡)柱和发展旺盛的上升气流区,低层辐合中心位于650 hPa,高层辐散中心位于400 hPa,无辐散层位于500 hPa.

Numerical simulation of a torrential rainfall

Using MM5, a better resolved non-hydrostatic MESO-scale numerical model, this paper simulates a flood-triggering torrential rain process in the east part of northwestern China in August 28, 2003. The research focused on the genesis, evolution and decaying process of a and ;3 MESO-scale systems as well as diagnostic analysis of physical parameters. The results indicated that a MESO-scale vorticity builds up rapidly to its stable stage in down side of the mountain within 14 hours and, at the mean time, it induces several ;3 MESO-scale systems. The interaction of all these systems in different scales makes this regional torrential rain possible. Heavy precipitation occurs mainly at the developing stage of the vorticity. The stable atmospheric stratification over 700 hPa prevents vertical divergence of energy and water vapor, which is favorable for energy and water vapor flowing through lower levels to the rainfall areas. Beyond rainfall location, vertical transportation dominates the above layers with a large release of latent heat. There exist a distinct potential vorticity, an active updraft area, a lower convergence center at 650 hPa, an upper divergence center at 400 hPa and a non-divergence layer at 500 hPa.