地形影响下四川暴雨的数值模拟分析

Numerical simulation and analysis of Sichuan rainstorm under terrain influence

本文以NCEP资料为初值场对2004年9月3日到5日地形作用下四川省一次暴雨过程进行数值模拟,并在模式中加入加密的观测资料(OBS)进行模拟,结合实况对这两种模拟结果进行分析表明:前者模拟出的降水强度与实况相比有较大偏差,而后者的降水与实际更为相符,这表明加密观测资料对再现暴雨强度具有重要的中尺度信息作用。对大巴山的地形敏感性试验和诊断分析表明:大巴山地形使得西南暖湿气流所带来的水汽和热量在迎风坡堆积,从而在迎风坡和山顶出现较强的降水中心;而地形降低为"平台"后,大巴山降水中心减弱消失,说明地形对降水的落区和强度有重要影响;中尺度物理量的诊断分析表明物理量场与降水有很好的对应关系,涡度、散度的高低层配置、垂直上升运动、水汽输送的方向和强度等对暴雨的落区和强度有着决定性意义;层结稳定度分析表明大巴山降水中心以非对流性降水为主。

The paper carries out a numerical simulation on a rainstorm process at northeast of Sichuan province, with NCEP data as the initial field. Then another simulation is done, with OBS data added in the model. Analyzing the above two results, it is found that precipitation intensity in the former is different from the actual; while the latter＇s is more similar to the actual. It indicates that intensive observational data improve description of storm intensity and provide important mesoscale information. Terrain-sensitivity experiment and diagnostic analysis of physical quantities of Daba mountain show that the Daba mountain makes the water vapor and heat brought by southwest warm moist flow accumulated at windward slope, thus the comparatively strong precipitation center appeared at windward slope and peak of mountain. When the terrain is reduced to ＂platform＂, the precipitation of Daba mountain decreases and disappears, which shows that terrain has much of importance on the location and intensity of precipitation. Physical quantity fields have nice correspondence with precipitation. The distribution of high level and low level vortex and divergence, ascending movement, the direction and intensity of vapor transportation and so on have definite meaning to the rainfall region and intensity. The analysis of stratification stability shows that the Daba mountain precipitation centre is mainly made up of non-convective precipifation.