Observational study on the three-dimensional structure of a drainage flow

(1)提出了考虑动量输送和感热输送的排水流“包裹模型”。根据坡长、坡体垂向落差、坡体与周围大气的位温差、坡体平均体积系数所表示的坡面空气动力条件和周围环境稳定度等参数，分别推导出坡体厚度h和坡体速度u，分别对应于实际排水流的逆温高度和最大速度。平均体积系数不仅取决于粗糙长度（z_0和z_&lt;<theta>&gt;），而且还取决于坡长。在几十米到几百公里长的斜坡上，预测的排水厚度和流速与观测结果一致。(2)连续观测了V型河谷内风速和温度的三维分布。通过对79个典型排水流场的分析，得出以下特征：河谷冷层由漂流冷层和原生冷层两部分组成，漂流冷层温度梯度恒定，排水流风速廓线呈抛物线型，最大流速与冷却强度的平方根成正比，厚度随冷却强度略有增加。在两个单独的横截面上估算了由于排水流引起的水平热通量，从而导致C_H和B_H^的值<-1>分别为0.01和20。

(1) The "Parcel Model" of drainage flow was proposed by considering its momentum and sensible heat transports. The thickness h and velocity u of the Parcel, corresponding to the inversion height and maximum velocity of actual drainage fow, respectively, were derived in terms of the following parameters: the length and vertical drop of the slope, potential temperature difference between the ambient atmosphere and the Parcel, aerodynamic condition of the slope surface expressed by the mean bulk coefficients, and ambient stability. The mean bulk coefficients depend not only on the roughness lengths (z_o and z_<<theta>>) but also on the slope length. The predicted thickness and velocity of drainage flow agree with the observations on slopes several tens of meters to several hundred kilometers long.(2) Three-dimensional distributions of wind speed and temperature in a V-shaped valley were continuously observed. Analyzed typical drainage flows (79 cases) show the following features: The cold layer in the valley consists of two parts (drifted cold layer and primary cold layer); temperature gradient is constant in the drifted cold layer; wind profile of drainage flow is parabolic; maximum velocity is proportional to a square root of cooling strength and the thickness slightly increases with cooling strength. Horizontal heat fluxes due to drainage flow were estimated at two separate cross sections, leading to the values of C_H and B_H^<-1> to be 0.01 and 20, respectively.