Rotor types associated with steep lee topography: influence of the wind profile
Rotor types associated with steep lee topography: influence of the wind profile
复制标题
与陡峭背风地形相关的转子类型：风廓线的影响
DOI：
10.3402/tellusa.v57i2.14625
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
J. Kuettner
中科院分区：
文献类型：
--
作者：
R. Hertenstein;J. Kuettner
在对流层低层中的湍流转子通常与高振幅的背风波有关。已经观察到两种类型的转子。第一种类型，通常是看起来无害的积云或平行于山脉的积云线，在共振山波的波峰下有一个明确的环流。这种类型的转子包含中等或严重的湍流，并且通常被限制在经常观察到的上游近山顶反转的高度以下。第二种不太常见的转子类型比上游反转延伸得高得多。这种类型已经被观察到包含严重或极端的湍流，并被认为是与类似于水跃的高振幅山波系统有关。这两种类型的旋翼都对航空造成了危险，尽管第二种类型的旋翼危险得多。我们提出了两种不同的转子类型，揭示了内部结构和湍流强度的显着差异的高分辨率二维模拟。背风侧水平涡度的演变提供了有关形成机制的见解。由于斜压的产生，当气流溢出背风坡时，初始上游逆温内的水平涡度被修改。修正后的水平涡度的大小在初始的上游逆温中受切变的调节。同时，在浅层形成相反符号的水平涡度。形成的转子类型取决于沿着背风坡发生近表面气流分离时主导水平涡度的符号。模拟点的上游近山顶逆温，其变形在背风的山，转子形成的逆温内的初始垂直剪切的重要作用。
Turbulent rotors in the lower troposphere are usually associated with high-amplitude lee waves. Two types of rotors have been observed. The first type, often visible as harmless-looking cumulus or cumulus fractus lines paralleling the mountain range, comprises a well-defined circulation under the crests of resonant mountain waves. This type of rotor contains moderate or severe turbulence and is often confined below the height of a frequently-observed upstream, near-mountain-top inversion. A second, less common, rotor type extends much higher than the upstream inversion. This type has been observed to contain severe or extreme turbulence, and is thought to be associated with a high-amplitude mountain-wave system resembling a hydraulic jump. Both rotor types present a hazard to aviation, although the second type of rotor is far more dangerous. We present high-resolution two-dimensional simulations of two distinct rotor types, which reveal dramatic differences in internal structure and turbulence intensity. The evolution of the lee-side horizontal vorticity provides insight into the formation mechanism involved. Horizontal vorticity within the initial upstream inversion is modified due to baroclinic generation as the flow spills down the lee slope. The magnitude of the modified horizontal vorticity is regulated by shear in the initial upstream inversion. At the same time, horizontal vorticity of the opposite sign forms in a shallow surface layer. The type of rotor that forms depends on the sign of the dominant horizontal vorticity as near-surface flow separation occurs along the lee slope. The simulations point to the vital role of an upstream near-mountain-top inversion, its deformation in the lee of the mountain, and the initial vertical shear within the inversion in rotor formation.