武汉市一次污染过程的局地流场和边界层结构的数值模拟

利用2013年11月武汉市逐日空气质量资料、地面气象观测资料、NCEP/NCAR再分析资料和L波段雷达探空资料，通过WRF模式模拟空气污染生消过程中的局地气象条件变化，探讨特殊地形条件下边界层结构变化和局地环流在污染物生消过程中的作用和影响。结果表明：（1）武汉地区当背景环流场强的时候，由地形引起的局地流场对污染物扩散的影响就弱，反之当背景环流场弱的时候, 地形对流场影响明显:夜间为山风，白天为谷风。夜间山风与偏西北气流及偏东气流在武汉及周边地区辐合，形成气流汇聚带，在武汉地区形成一个反复污染带,即由地形引起的局地流场对污染物扩散的贡献就大；（2）武汉地区发生空气污染时，地面湿度较高，边界层呈上干下湿状态，其特征为暖而干且有偏东小风，这导致污染物不断堆积和重污染过程的形成。

Numerical Simulation of the Local Flow Field and the Boundary Layer Structure in the Pollution Process in Wuhan

This study were carried out based on the daily air quality data, ground meteorological data, NCEP / NCAR reanalysis data and L band radar sounding data of Wuhan city in November, 2013. The WRF model was used to simulate the change of local meteorological conditions in the air pollution process, and the influence of boundary layer structure and local flow in the whole process of pollutant generation and elimination were also discussed. The results show that: (1) when the background large scale circulation is strong, the influence of the local flow caused by the terrain on pollutant diffusion will be weak in Wuhan; on the contrary, when the background large scale circulation field is weak, the local flow caused by the topography is found to have a large contribution to the diffusion of pollutants in Wuhan. Since Wuhan is surrounded by mountains on three sides, the impact of the topography on the flow field is obvious. When the background circulation field is weak, wind field is dominated by mountain wind at night and by valley wind in the daytime. At night, mountain winds, northwest airflow and easterly airflow converge in Wuhan and the surrounding areas, forming a convergence zone of airflow, which has been continually contaminating Wuhan. (2) When air pollution occurs in Wuhan, the humidity of earth surface is high, and the boundary layer is dry in the high altitude and wet in the low altitude. Moreover, the boundary structure features warm and dry air with easterly breeze which contributes a lot to the continuous accumulation of pollutants and the formation of heavy pollution process.