Solar and lunar tides in noctilucent clouds as determined by ground-based lidar
2018
Abstract. Noctilucent clouds (NLCs) occur during summer from midlatitudes to high latitudes. They consist of
nanometer-sized ice particles in an altitude range from 80 to 90 km and are
sensitive to ambient temperature and water vapor content, which makes them a
suitable tracer for variability on all timescales. The data set acquired by
the ALOMAR Rayleigh–Mie–Raman (RMR) lidar covers 21 years and is
investigated regarding tidal signatures in NLCs. For the first time solar and
lunar tidal parameters in NLCs were determined simultaneously from the same
data. Several NLC parameters are subject to persistent mean variations
throughout the solar day as well as the lunar day. Variations with lunar time
are generally smaller compared to variations with solar time. NLC occurrence
frequency shows the most robust imprint of the lunar semidiurnal tide. Its
amplitude is about 50 % of the solar semidiurnal tide, which is
surprisingly large. Phase progressions of NLC occurrence frequency indicate
upward propagating solar tides. Below 84 km altitude the corresponding
vertical wavelengths are between 20 and 30 km. For the lunar semidiurnal
tide phase progressions vary symmetrically with respect to the maximum of the
NLC layer.
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