“7.21”特大暴雨的地形影响分析

Analysis of the Impact of Topography on the‘721'Extreme Heavy Rainstorm

为了深入研究地形对暴雨的影响,提高暴雨预报的精准度,利用NCEP资料和WRF模式对"7.21"特大暴雨进行了数值模拟和分析。结果显示:"7.21"特大暴雨是在有利的环境场以及这一地区特殊地形作用下发生;强降水中心主要出现在山谷、山区与平原交界区域,与地形的影响密切相关。地形的影响主要表现热力和动力2个方面:风顺山谷而吹,形成明显的高温、高湿的水汽输送,同时形成辐合、上升运动;山区和平原交界地带温度梯度大,加上迎风坡作用,有利于对流的发生、发展。

In order to more deeply study the impact of topography to the heavy rain, improve the rainstorm forecast accuracy, the author used the NCEP data and WRF model, the numerical simulations and analysis were conducted for a heavy rainstorm event occurred on July 21 2012 in Beijing, Hebei. The results showed that： the heavy rainfall was in favorable environment and special terrain occurred under the action of this area. Heavy rain center main valley, the mountains and plains of border area, was closely related to the effects of topography. Two aspects of terrain effects mainly thermodynamic and dynamic： wind valley while blowing, obvious form of high temperature, high humidity and water vapor transport, ascending motion, formation of convergence; mountains and plains along the border between the temperature gradient in the windward slope, plus the role, was conducive to the development of convection.