冬季城市边界层风场和温度场结构分析

AN ANALYSIS ON FLOW AND TEMPERATURE STRUCTURE OF WINTERTIME URBAN BOUNDARY LAYER

本文根据沈阳地区大气环境容量研究中1984年12月所进行的观测,对沈阳城市边界层的流场和温度场结构做了分析。得出了冬季城市边界层的一些特征。当地面风速微弱时,热岛效应显著。边界层低层辐合抬升,在城市下风边缘可能出现反向气流。当风速较强时,城市的摩擦效应占优势,城市上风部分辐合抬升,下风部分辐散下沉。观测分析还表明,城市建筑对气流的阻滞作用可伸展到几百米的高度。夜间微风时,接地逆温层厚度可达200m,城市内边界层从上风边缘起开始发展,厚度可达100m。白天风力微弱时,重烟尘污染可导致城市冷岛,并推迟对流边界层的发展。

Flow and temperature structures in Shenyang City, Liaoning Province have been analysed according to the fields experiments carried out in December, 1984. Features of wintertime urban boundary layer are obtained. As surface wind is light the effects of urban heat island are best expressed. There are flow convergence and ascending in the lower part of boundary layer. Return flow may occur in the downwind suburb. While wind is strong the friction effect of urban dominates. Convergence and ascending occur in the upwind part of the city, while divergence and decending in the downwind part. The wind retardation by friction may extend to a few hundred meters. During nighttime with light wind the depth of ground inversion is about 200m. The depth of internal boundary layer increases with the distance from the upwind hedge to about 100m at the downwind fringe. In the daytime with light wind heavy pollution may cause cool island and retard the development of convective boundary layer.