北京城市化进程对边界层风场结构影响的研究

A study of the influence of urbanization of Beijing on the boundary wind structure

随着近10年来北京城市化步伐的加快，城市规模迅速扩大，北京三环以外的地区已由20世纪七、八十年代的城郊非均匀下垫面发展成现在粗糙复杂的城区下垫面，市区建筑物相应增多、增密和增高，导致城区地面动力学粗糙度明显增大．本文统计分析了北京325m气象塔1994年和1997～2003年夏季平均场观测资料，结果表明：（1）在受下垫面影响最为剧烈的近地层，风向逐年趋于紊乱，现在气象塔周围近地面的流场已经具备了典型城市粗糙下垫面的流场特征；（2）近地面夏季平均风速呈现非常明显的逐年递减的趋势，而且距离地表越近，平均风速逐年递减的趋势也越为显著，这种风速逐年递减的趋势直到63m左右才不明显，说明现在气象塔47m以下的观测资料反映的是城市冠层的流场特征，城市冠层厚度约在47—63m之间；（3）随着北京城市化的发展，城区近地面的平均风速存在逐年递减的趋势，但阵风并不存在相似的递减趋势，表明城市冠层的抬升对阵风的影响并不显著．

With the fast urbanization of Beijing City, the dimension of the city has largely expanded during the past 10 years, so many areas outside the third ring road of Beijing City have greatly changed from outskirts to inner city. Many higher buildings were set up in the original inner city, which lead to a remarkable increase of the ground roughness in Beijing. Based on the statistic analysis of the average data measured at the Beijing 325 m meteorological tower in 1994 and from 1997 to 2003, we have reached several significant conclusions. Firstly, the direction of the wind became more and more disordered on the surface layer which is strongly impacted by the underlying surface. Nowadays the wind field cannot reflect the characteristics of inhomogeneous underlying surface of suburb but of the inner city. Secondly, its summer mean speed is decreasing yearly below 63 m. And the nearer the earth＇ s surface, the more remarkable decreasing trend was. A conclusion is drawn in this paper that the data of the tower below 47 m reflect the characteristics of urban canopy layer, and the height of the urban canopy layer may reach 47 m to 63 m. Finally, though the mean wind has a yearly decreasing trend with fast development of Beijing City, the influence on the gust is not obvious and the decreasing trend of the maximum wind speed does not exist below 47 m.