Katabatic winds: A field case study
Katabatic winds: A field case study
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下降风：现场案例研究
DOI：
10.1002/qj.49710544618
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发表时间：
1979
影响因子：
8.9
通讯作者：
B. Sawford
中科院分区：
文献类型：
--
作者：
P. Manins;B. Sawford
利用系留气球剖面设备的下降风的案例研究的结果进行了介绍和讨论。这些数据是独一无二的，它们提供了矢量风和潜在的虚拟温度在整个流动的细节。
从数据中得出结论，目前文献中提出的一维模型是不合适的。直接计算表明，负责冷却空气的辐射发散度比这些模式中使用的地面辐射通量小得多。这些模型的不足之处并不在于时间不变性的基本假设，而在于流动是三维的。
使用表面应力作为动力平衡中的减速应力也是错误的，至少只要环境风不帮助下降气流。气流和周围空气之间的应力更为重要，这种应力与气流的下坡发展密不可分，因此推断气流的下坡发展在下吹风的动力学中起着重要作用。
下降流是内部混合过程的一个例子。数据表明，建议一个临界梯度理查森数约1/4的内部混合以上斜坡流的维护。
Results of a case study of katabatic winds utilizing tethered balloon profiling equipment are presented and discussed. The data are unique in the detail they provide of both vector wind and potential virtual temperature throughout the flow.
It is concluded from the data that the one-dimensional models so far proposed in the literature are inappropriate. Direct computation shows that the divergence of radiation responsible for cooling the air is much smaller than the surface radiation flux used in these models. The inadequacy of these models is not due to the underlying assumption of temporal invariance, but rather the implication is that the flow is significantly three dimensional.
Use of surface stress as the retarding stress in the dynamical balance is also shown to be erroneous, at least so long as ambient wind does not assist the katabatic flow. The stress between the flow and the ambient air is much more important and this stress is inextricably tied in with the downslope development of the flow which is thus inferred to play a major part in the dynamics of katabatic winds.
Katabatic flow is an example of an internal mixing process. The data are shown to suggest a critical gradient Richardson number of about 1/4 for the maintenance of internal mixing above slope flows.