Quantification of waves in lidar observations of noctilucent clouds at scales from seconds to minutes

• Published in: Atmospheric Chemistry and Physics
• Main Authors: N. Kaifler, G. Baumgarten, J. Fiedler, F.-J. Lübken
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2013
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Norway; Alomar; Northern Norway
• Online Access: https://doi.org/10.5194/acp-13-11757-2013; https://doaj.org/article/f97526e7ed3446d2a87a6eb4123538b4

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.