上海城市对风速的影响

本文根据上海城市和郊区实测的风速资料,首先论证了由于上海城市的发展,建筑群增多、增密、增高,导致下垫面粗糙度加大,其摩擦阻障效应消耗了空气水平运动的动能,因而使城区的年和月平均风速减小。其次,分析了上海城市热岛效应与风速的相互影响:盛行风速小,有利于热岛的形成;热岛强时,容易发展垂直湍流,有使城区风速增大的效应;在背景风场微弱时,热岛温度场会导致热岛环流。最后,阐明上海城市与郊区的风速差异有一临界风速v_o。当盛行风速大于v_o时,城市下垫面粗糙度大,使风速减小的效应突出;相反,当盛行风速小于v_o时,热岛湍流使城区风速增大的效应显著。上海v_o的年平均值在2米/秒左右。

Shanghai Urban Influences on Wind Velocity

The rapid development of urbanization in Shanghai has caused a change in ground surface roughness. It effects a trend toward lower wind velocity in the urban wind field. The close interaction between urban heat island and wind velocity is discussed. Under clear sky and calm or very weak winds the Shanghai city area develops an urban heat island and the temperature field often induces a heat island circulation. When the prevailing regional wind velocity is very weak or less than the critical wind velocity v_(?), vertical turbulence develops due to the urban heat island effect. The transfer of the upper layer momentum to the lower nearsurface layer is enhanced and the wind velocity in urban area becomes higher th n that in rural area. When the prevailing wind blows with velocity above v_(?), the surface roughness effect dominates and the urban wind is weaker than rural. The annual mean critical wind velocity is about 2m/s.