Signature of an overturning gravity wave in the mesospheric sodium layer: Comparison of a nonlinear photochemical‐dynamical model and lidar observations
Signature of an overturning gravity wave in the mesospheric sodium layer: Comparison of a nonlinear photochemical‐dynamical model and lidar observations
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DOI：
10.1029/2005jd006749
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发表时间：
2006-09
影响因子：
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通讯作者：
Jiyao Xu;Anne K. Smith;R. Collins;C. She
中科院分区：
文献类型：
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作者：
Jiyao Xu;Anne K. Smith;R. Collins;C. She
在本文中，我们研究了钠层的演变中存在的翻转（或对流不稳定）重力波使用模型模拟和激光雷达观测。模拟采用时间依赖性，非线性，光化学动力学模型。这些观测是来自科罗拉多柯林斯堡（北纬41度，西经105度）的一组为期9天（210小时）的钠密度和温度激光雷达测量。我们模拟大尺度（垂直波长为30公里）和小尺度（垂直波长为10公里）波的演变和相关的钠层的演变。我们使用滤波方法来识别激光雷达测量中相似尺度的波。半日潮是激光雷达观测中占主导地位的大尺度波。我们提出了所观察到的钠密度，混合比，温度，位温，浮力周期超过24小时的演变。我们发现，该模型和观测结果显示出类似的行为，在演化的钠密度，混合比，和潜在的温度响应大，小尺度波。模型和观测结果表明，钠密度扰动有一个更明显的翻转行为在层的底部比层的顶部。钠密度也比混合比和位温具有更显著的翻转行为。由于小尺度波，钠密度的翻转特征在波周期内周期性地发生，甚至在波本身变得完全不稳定之前。该研究表明，在钠密度的单一翻转事件的观察应谨慎解释，并可能不表明一个波的完全翻转。
In this paper we study the evolution of the sodium layer in the presence of an overturning ( or convectively unstable) gravity wave using model simulations and lidar observations. The simulations employ a time-dependent, nonlinear, photochemical-dynamical model. The observations are a 9-day (210-hour) set of sodium density and temperature lidar measurements from Fort Collins, Colorado ( 41 degrees N, 105 degrees W). We model the evolution of large-scale ( vertical wavelength of 30 km) and small-scale ( vertical wavelength of 10 km) waves and the associated evolution of the sodium layer. We use filtering methods to identify waves of similar scales in the lidar measurements. The semidiurnal tide is the dominant large-scale wave in the lidar observations. We present the observed evolution of sodium density, mixing ratio, temperature, potential temperature, and buoyancy period over 24-hour periods. We find that the model and observations show similar behavior in the evolution of the sodium densities, mixing ratios, and potential temperature in response to large- and small-scale waves. The model and observations indicate that the sodium density perturbation has a more pronounced overturning behavior in the bottomside of the layer than the topside of the layer. The sodium density also has a more pronounced overturning behavior than the mixing ratio and potential temperature. The overturning signatures in the sodium density due to small-scale waves occur periodically at the wave period even before the wave itself becomes completely unstable. The study suggests that observations of single overturning events in sodium densities should be interpreted with caution and may not indicate complete overturning of a wave.