Nocturnal drainage flow on simple slopes
Nocturnal drainage flow on simple slopes
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DOI：
10.1007/bf00122382
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发表时间：
1986-02
影响因子：
4.3
通讯作者：
T. W. Horst;J. Doran
中科院分区：
文献类型：
--
作者：
T. W. Horst;J. Doran
在两个地形和植被完全不同的地点进行了夜间坡面流的观测。在这两种情况下，连续测量风和温度剖面是从塔，通过下降流的深度延伸。在较简单的场地，近似于一个倾斜的平面，三个塔位于不同的距离下的斜坡，以测量斜坡流的发展与下坡距离。斜坡流深度，下坡风速，和温度赤字的变化率与下坡距离的预测是一致的Manins和Sawford（1979年）的层平均模型的斜坡流。而实测的夹带率与Ellison和Turner（1959）的实验室实验预测的结果相当。坡面流的深度大约是从坡顶垂直落差的0.05倍，这种关系也是从结合Manins和Sawford的模型以及Ellison和Turner的实验室数据得出的。分析的风谱和一个简单的数值模型表明，湍流动能剖面在斜坡流是依赖于周围风的速度和方向，并可以从平坦的地形上发现有很大的不同。在更复杂的两个测量站点，斜坡流的发生被发现与无量纲数5，这是一个功能的脊顶风速和强度和深度的反转，这是一个估计的浮力赤字的比例外部水平压力梯度相关。
Observations of nocturnal slope flow have been made at two sites with quite different topography and vegetation. In both cases, continuous measurements of wind and temperature profiles were made from towers that extended through the depth of the katabatic flow. At the simpler site, which approximates a tilted plane, three towers were located at different distances down the slope to measure the development of slope flow with downslope distance.Slope flow depth, downslope wind speed, and temperature deficit are found to change with downslope distance at rates that are consistent with the predictions of Manins and Sawford's (1979) layer-averaged model of slope flow, while measured entrainment rates are found to be comparable to those predicted by Ellison and Turner's (1959) laboratory experiments. The depth of slope flow is found to be roughly 0.05 times the vertical drop from the top of the slope, a relationship that also follows from combining Manins and Sawford's model and Ellison and Turner's laboratory data. Analysis of the wind spectra and a simple numerical model suggest that the turbulent kinetic energy profiles in slope flow are dependent on the speed and direction of the ambient wind and can differ substantially from those found over flat terrain. At the more complex of the two measurement sites, the occurrence of slope flow was found to correlate well with a dimensionless number 5 that is a function of the ridge-top wind speed and of the strength and depth of the inversion and that is an estimate of the ratio of the buoyancy deficit to the external horizontal pressure gradient.