Observations and Numerical Simulations of Subrotor Vortices during T-REX
Observations and Numerical Simulations of Subrotor Vortices during T-REX
复制标题
T-REX 副旋翼涡流的观测与数值模拟
DOI：
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
M. Weissmann
中科院分区：
文献类型：
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作者：
J. Doyle;V. Grubišić;W. Brown;S. Wekker;A. Dörnbrack;Q. Jiang;S. Mayor;M. Weissmann
来自扫描多普勒和气溶胶激光雷达、风廓线雷达的高分辨率观测，以及地形诱导旋翼试验(T-REX)期间的地面和飞机测量，首次全面记录了与在山区背风面形成的大气旋翼有关的小尺度强烈旋涡。虽然旋翼已经被认为是飞机的潜在危险，但有人认为，由于强风切变和旋涡的瞬变性质，这些小尺度旋涡或副旋翼是最危险的特征。副旋翼事件的生命周期由扫描多普勒和气溶胶激光雷达在5分钟内捕获。激光雷达描绘了一个特征长度为500-1000m的放大涡旋，该涡旋翻转并增强到最大跨向涡度大于0.20 S−1。雷达风廓线观测记录了一系列涡旋，其特征是上升/下降气流耦合和增强的反向流区，这些涡旋是在强垂直风切变和亚临界理查森数层中产生的。观测和数值模拟表明，湍流副旋最常出现在水平涡度上升的前缘，这是边界层沿背风坡发生剪切和分离的表现。当副旋脱离涡片时，通过涡拉伸展和在某些情况下与三维湍流混合有关的倾斜过程发生强化。副旋翼和环境涡片通过上游逆温强度的适度增加而增强，这说明了旋翼湍流特征的可预报性挑战。
High-resolution observations from scanning Doppler and aerosol lidars, wind profiler radars, as well as surface and aircraft measurements during the Terrain-induced Rotor Experiment (T-REX) provide the first comprehensive documentation of small-scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain. Although rotors are already recognized as potential hazards for aircraft, it is proposed that these small-scale vortices, or subrotors, are the most dangerous features because of strong wind shear and the transient nature of the vortices. A life cycle of a subrotor event is captured by scanning Doppler and aerosol lidars over a 5-min period. The lidars depict an amplifying vortex, with a characteristic length scale of 500–1000 m, that overturns and intensifies to a maximum spanwise vorticity greater than 0.2 s−1. Radar wind profiler observations document a series of vortices, characterized by updraft/downdraft couplets and regions of enhanced reversed flow, that are generated in a layer of strong vertical wind shear and subcritical Richardson number. The observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes. As the subrotors break from the vortex sheet, intensification occurs through vortex stretching and in some cases tilting processes related to three-dimensional turbulent mixing. The subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength, which illustrates the predictability challenges for the turbulent characterization of rotors.