Quantifying Kelvin-Helmholtz instability dynamics observed in noctilucent clouds: 1. Methods and observations
Quantifying Kelvin-Helmholtz instability dynamics observed in noctilucent clouds: 1. Methods and observations
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DOI：
10.1002/2014jd021832
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发表时间：
2014-08-16
影响因子：
4.4
通讯作者：
Fritts, David C.
中科院分区：
文献类型：
--
作者：
Baumgarten, Gerd;Fritts, David C.
在2009年夏季的两个晚上，从北方德国（K hlungsborn，54度N）和挪威中部（特隆赫姆，64度N）拍摄了夜光云（NLC）。这是第一次在云层高度（约83公里）达到10至20米的水平分辨率和约1秒的时间分辨率。使用较粗分辨率的其他成像提供了对云中观察到的较大尺度（类似于100公里）结构的监测。描述了两个系列的NLC图像，揭示了明显的开尔文-亥姆霍兹（KH）翻腾结构具有非常不同的形态和明显的过渡到湍流和混合。一个系列表现出深KH波涛和明显的二次不稳定性的波涛外部具有流向对齐（和展向波数），这表明一个小的初始理查森数（Ri）。第二个系列的图像表明，一个更大的和不太稳定的Ri，一个缓慢的KH巨浪演变，较浅的波涛，湍流和混合局限于波涛核心。我们建议，这些动态采用NLC成像系统的探索可能使表征和量化的KH不稳定性发生的统计数据，并在夏季中层顶环境中的湍流和混合的独特的敏感性，他们的小尺度动态的贡献。
Noctilucent clouds (NLCs) have been imaged during two nights in summer 2009 from northern Germany (K hlungsborn, 54 degrees N) and middle Norway (Trondheim, 64 degrees N). For the first time a horizontal resolution of 10 to 20 m at the altitude of the clouds (about 83 km) and a temporal resolution of about 1 s was achieved. Additional imaging using a coarser resolution provided monitoring of the larger-scale (similar to 100 km) structures observed in the clouds. Two series of NLC images are described that reveal apparent Kelvin-Helmholtz (KH) billow structures having very different morphologies and apparent transitions to turbulence and mixing. One series exhibits deep KH billows and apparent secondary instabilities in the billow exteriors having streamwise alignment (and spanwise wave number), suggesting a small initial Richardson number (Ri). A second series of images suggests a larger and less unstable Ri, a slower KH billow evolution, shallower billows, and turbulence and mixing confined to the billow cores. We suggest that systematic exploration of these dynamics employing NLC imaging may enable characterization and quantification of KH instability occurrence statistics and of their contributions to turbulence and mixing in the summer mesopause environment with unique sensitivity to their small-scale dynamics.