Computation of clear-air radar backscatter from numerical simulations of turbulence: 3. Off-zenith measurements and biases throughout the lifecycle of a Kelvin-Helmholtz instability
Computation of clear-air radar backscatter from numerical simulations of turbulence: 3. Off-zenith measurements and biases throughout the lifecycle of a Kelvin-Helmholtz instability
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DOI：
10.1029/2011jd017179
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发表时间：
2012-09-05
影响因子：
4.4
通讯作者：
Lund, Tom
中科院分区：
文献类型：
--
作者：
Fritts, David C.;Wan, Kam;Lund, Tom
Franke等人（2011年）和Fritts等人（2011年）的先前论文描述了根据Kelvin-Helmholtz（KH）剪切不稳定性引起的湍流数值模拟计算雷达后向散射功率和垂直速度。后向散射功率和推断的速度与湍流的分布和真实速度的比较发现，在识别活跃或强烈的湍流和推断的多普勒频谱和垂直速度在整个流动演变的偏见。本文将这些分析扩展到典型的多波束MF，HF和VHF雷达的离天顶视角。这些揭示了类似的偏见，在识别湍流发生，多普勒频谱，并推断径向速度，与额外的敏感性，相对于平均剪切的离天顶角在整个湍流层。径向速度通常被低估湍流的产生和破裂的KH波涛，除了湍流折射率梯度是强的。多普勒光谱偏向于保留强折射率梯度的区域，这意味着在演化的后期阶段具有很强的方面敏感性。在演化的后期阶段，持续的倾斜结构有助于径向速度测量偏差，也是离天顶角和时间的函数。
Previous papers by Franke et al. (2011) and Fritts et al. (2011) described the computation of radar backscatter power and vertical velocities from numerical simulations of turbulence arising due to Kelvin-Helmholtz (KH) shear instability. Comparisons of backscatter power and inferred velocities with the distributions of turbulence and the true velocities revealed biases in the identification of active or intense turbulence and in the inferred Doppler spectrum and vertical velocities throughout the flow evolution. This paper extends these analyses to off-zenith viewing angles typical of multiple-beam MF, HF, and VHF radars. These reveal similar biases in the identification of turbulence occurrence, Doppler spectra, and inferred radial velocities, with additional sensitivity to the off-zenith angle relative to the mean shear across the turbulence layer. Radial velocities are typically underestimated during turbulence generation and breakdown of the KH billows, except where turbulence refractive index gradients are strong. Doppler spectra are biased toward regions retaining strong refractive index gradients, implying strong aspect sensitivity at later stages in the evolution. Persistent tilted structures at late stages of the evolution contribute to radial velocity measurement biases that also are functions of off-zenith angle and time.