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

(1)考虑径流动量和感热输运，提出了径流的“包裹模型”。根据坡度长度和垂直落差、周围大气与包裹的位能温差、平均体积系数表示的坡面气动条件、环境稳定性等参数，分别推导出与实际降水逆温高度和最大流速对应的包裹厚度h和速度u。平均体积系数不仅与粗糙度长度（z_o和z_<<theta>>）有关，还与坡度长度有关。预测的排水厚度和流速与几十米至几百公里长的斜坡上的观测结果一致。(2)连续观测了v型山谷内风速和温度的三维分布。典型流域流（79例）分析表明：河谷冷层由漂移冷层和原生冷层两部分组成；漂移冷层的温度梯度是恒定的；排水流风廓线为抛物线型；最大速度与冷却强度的平方根成正比，厚度随冷却强度略有增加。在两个不同的截面上估算了排水引起的水平热通量，得到C_H和B_H^<-1>的值分别为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.