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Title: Quantification of waves in lidar observations of noctilucent clouds at scales from seconds to minutes
Authors: Kaifler, N.Baumgarten, G.Fiedler, J.
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Issue Date: 2013
Published in: Atmospheric Chemistry and Physics Vol. 13 (2013), No. 23
Publisher: Göttingen : Copernicus
Abstract: We present small-scale structures and waves observed in noctilucent clouds (NLC) by lidar at an unprecedented temporal resolution of 30 s or less. The measurements were taken with the Rayleigh/Mie/Raman lidar at the ALOMAR observatory in northern Norway (69 N) in the years 2008-2011. We find multiple layer NLC in 7.9% of the time for a brightness threshold of δ β 12 × 10-10 m-1 sr-1. In comparison to 10 min averaged data, the 30 s dataset shows considerably more structure. For limited periods, quasi-monochromatic waves in NLC altitude variations are common, in accord with ground-based NLC imagery. For the combined dataset, on the other hand, we do not find preferred periods but rather significant periods at all timescales observed (1 min to 1 h). Typical wave amplitudes in the layer vertical displacements are 0.2 km with maximum amplitudes up to 2.3 km. Average spectral slopes of temporal altitude and brightness variations are-2.01 ± 0.25 for centroid altitude,-1.41 ± 0.24 for peak brightness and-1.73 ± 0.25 for integrated brightness. Evaluating a new single-pulse detection system, we observe altitude variations of 70 s period and spectral slopes down to a scale of 10 s. We evaluate the suitability of NLC parameters as tracers for gravity waves.
Keywords: amplitude; brightness temperature; displacement; gravity wave; lidar; Mie theory; polar mesospheric cloud; Raman spectroscopy; Rayleigh wave; Norway
DDC: 550
License: CC BY 3.0 Unported
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