地形与Ekman边界层中的气流

利用σ坐标讨论地形与边界层气流是有很多方便的地方,因为,在此坐标中,下边界条件较为简单。在本工作中,首先将混合长理论加以推广并将它用于σ坐标,于是导得了用以描述地形上空边界层气流的控制方程,对边界层气流的特征,特别是对于Ekman抽吸作用进行了详细分析。指出有三种因子影响边界层顶部的垂直运动,第一种因子是边界层内涡度分布,这是与边界层中由于摩擦作用所引起的辐合辐散有直接联系;第二种因子是由于边界层顶部的气流爬坡运动所引起的;第三种是由于边界层中跨越等压线的分量爬坡所引起的,它出现于当等压线与地形等高线相平行时,或地转风呈现绕流情况时,这一作用最为明显。

EFFECTS OF OROGRAHY AND AIR FLOW IN EKMAN BOUNDARY LAYER

It is convenient to use o-coordinate to discuss the dynamic effect of orography and the flow in Ekman boundary layer. Because the lower boundary condition in the coordinate is quite simple. In this paper, the theory of mixing length is generalized to the coordinate. Then the governing equations, describing tht motion in the boundary layer over the mountain are derived. The features of flow in the boundary layer, especially the effects of Ekman pumping are discussed in details. It is pointed out that there are three factors which influence the vertical motion at the top of the boundary layer. The first is vorticity distribution in the boundary layer. This is related with the divergence of air flow caused by the friction. The second is the climbing up or down of the air flow over the mountain slopes. The third is the geostrophic wind which flows along the mountain. This is due to the climbing of air flow components which deviate from the geotrophic wind, caused by the effect of friction.