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High‐resolution observations of the density structure of atomic sodium in the Earth's mesosphere and lower thermosphere, using a large‐aperture lidar system, reveal features of this dynamic region in greater detail. The sodium is highly structured, showing multiple layers that vary in density and altitude on timescales ranging from minutes to hours. Large‐scale instabilities and Kelvin‐Helmholtz billows are observed along with an overall downward propagation of the layers. Coherent short‐period gravity wave oscillations are sometimes seen extending over the entire sodium region. Individual meteor ablation trails produce transient density spikes that last at most a few seconds. The mean sodium altitude is found to have a temporal power spectrum proportional to the –1.9 power of the frequency, close to that expected for Kolmogorov turbulence.
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Pfrommer et al. (2009) studied this question.
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