The accuracy of linear theory for predicting mountain‐wave drag: Implications for parametrization schemes
The accuracy of linear theory for predicting mountain‐wave drag: Implications for parametrization schemes
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线性理论预测山波阻力的准确性：对参数化方案的影响
DOI：
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发表时间：
2010
期刊：
影响因子：
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通讯作者：
S. Vosper
中科院分区：
文献类型：
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作者：
H. Wells;S. Vosper
这项研究的重点是简单的方法，用于参数化方案的精度预测阻力由于地形激发重力波（山波）。线性和非线性模型模拟了一个长的、低的二维山脊上的水流，以评估内波反射和非线性的重要性。使用具有小的无因次山高和缓坡的长山脊，以便在风和稳定性背景剖面没有垂直变化的情况下，通过线性理论准确预测山波阻力。对背景稳定性具有两层（对流层-平流层）结构的简单理想剖面进行的模拟表明，虽然阻力可以通过线性解准确预测，但部分波反射引起的干扰效应可以显著改变阻力。仅基于风和稳定性的低水平测量值（例如当前运行的山波参数化中的测量值）的阻力估计无法解释这种影响。从无线电探空仪和预报模型获得的更复杂的真实剖面的模拟结果表明，线性和非线性阻力预测可以有很大的不同。这意味着即使是针对整个大气廓线（而不是基于低层平均量）计算线性解也可能不准确。据推测，在这种情况下，非线性是由于共振三重相互作用时发生的Scorer参数与占主导地位的垂直传播的山波的波长的一半的振荡。山波阻力参数化的结果的影响进行了讨论。© Crown Copyright 2010.出版社：John Wiley & Sons，Ltd
This study focuses on the accuracy of simple methods used in parametrization schemes for predicting the drag due to orographically excited gravity waves (mountain waves). Linear and nonlinear model simulations of flow over a long, low two‐dimensional ridge are used to evaluate the importance of internal wave reflection and nonlinearity. A long ridge with a small non‐dimensional mountain height and a gentle slope is used so that, in the absence of vertical variations in the background profile of wind and stability, the mountain‐wave drag is accurately predicted by linear theory. Simulations conducted for simple idealised profiles in which the background stability has a two‐layer (troposphere–stratosphere) structure show that whilst the drag is accurately predicted by linear solutions, interference effects due to partial wave reflection can alter the drag significantly. Estimates of the drag which are based solely on low‐level measurements of wind and stability, such as those in current operational mountain‐wave parametrizations, cannot account for this effect. Results from simulations based on more complex realistic profiles, obtained from both radiosondes and a forecast model, show that the linear and nonlinear drag predictions can differ significantly. This implies that linear solutions can be inaccurate even when they are calculated for the full atmospheric profile (rather than being based on low‐level average quantities). It is hypothesised that, in this case, the nonlinearity is due to resonant triad interactions which occur when there are oscillations in the Scorer parameter with a wavelength half that of the dominant vertically propagating mountain wave. The implications of the results for mountain‐wave drag parametrization are discussed. © Crown Copyright 2010. Published by John Wiley & Sons, Ltd.