Dynamic instability in the lower thermosphere inferred from irregular sporadic E layers
Dynamic instability in the lower thermosphere inferred from irregular sporadic E layers
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从不规则的零星E层推断出低层热层的动态不稳定性
DOI：
10.1029/2012ja017910
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发表时间：
2012
影响因子：
--
通讯作者：
S. González
中科院分区：
文献类型：
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作者：
D. Hysell;E. Nossa;M. Larsen;J. Munro;S. Smith;M. Sulzer;S. González
[1]本文介绍了位于圣克鲁瓦的阿雷西博非相干散射雷达和相干散射雷达对一个不规则零星Elayer的同时观测。层表现出周期性的结构，这是由于在中性流的剪切不稳定性。估计的随时间变化的矢量中性风廓线中，该层被嵌入的分析和剪切不稳定的理查森数的意义。除了计算Richardson数值外，我们还对Miles（1961）和霍华德（1961）的模式进行了特征值分析，用于观测的风廓线。计算出的本征模具有占主导地位的Kelvin-Helmholtz模式的估计流传播到西南部的相位速度接近50米/秒和水平波长之间的10-15公里。波的增长时间将短至约1分钟。这些特征与所观察到的Es层结构相一致。Miles-Howard模型在过去已经用解析和数值方法进行了广泛的分析，但是据我们所知，在背景风有转向和速度切变的情况下，方程的本征模的计算以前还没有进行过。与计算相关的困难与在满足方程的大量模式中识别增长最快的模式有关。本文叙述了这种方法及其解与观测到的零星E层波结构的关系。
[1] Simultaneous observations of an irregular sporadic Elayer from the Arecibo incoherent scatter radar and a coherent scatter radar located on St. Croix are presented. The layers exhibit periodic structuring which is attributed to shear instability in the neutral flow. Estimates of the time-varying vector neutral wind profiles in which the layer was embedded are analyzed and shown to be shear unstable in the Richardson number sense. In addition to the calculation of the Richardson number values, we present an eigenvalue analysis of the model of Miles (1961) and Howard (1961) for the observed wind profiles. The calculated eigenmodes have dominant Kelvin-Helmholtz modes for the estimated flow that are propagating to the southwest with phase speeds near 50 m/s and horizontal wavelengths between 10–15 km. The growth times for the waves would have been as little as about 1 min. These features are in reasonable agreement with the observed of Es-layer structure. The Miles-Howard model has been analyzed extensively in the past using both analytic and numerical techniques, but calculations of eigenmodes for the equations in a case with background winds that have turning and speed shear have not been carried out previously, as far as we know. The difficulties associated with the calculation are related to identifying the fastest growing modes among the large number of modes that satisfy the equations. The technique and the relationship of the solutions to the observed sporadicE layer wave structure are described.