Abstract
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.
Highlights
Noctilucent clouds (NLCs) are a phenomenon of the mesopause region from midlatitudes to high latitudes
The measured hourly mean values with respect to lunar time are shown for reference. Comparing these curves with the simulations we find that NLC occurrence frequency as well as altitude are only little impacted during the lunar morning, whereas during the lunar afternoon solar impacts are large compared to the measured values
The 21-year data set of the ALOMAR RMR lidar contains the largest NLC archive acquired by ground-based lidar and was investigated regarding solar and lunar tides in NLCs
Summary
Noctilucent clouds (NLCs) are a phenomenon of the mesopause region from midlatitudes to high latitudes. Ground-based visual data can only be obtained around solar midnight hours when the lower troposphere is dark but sunlight still illuminates the upper mesosphere and is scattered at the ice particles This hampers the identification of both solar and lunar tidal signatures. Ground-based lidars can cover the entire solar diurnal cycle and are able to identify solar and lunar tides As they operate at fixed locations, the superposition of all tidal components above the instrument is measured, with the migrating components giving the distinct variations with solar time. For the first time, we will extract solar and lunar tidal signatures in NLCs simultaneously from a multiyear data set obtained using ground-based lidar.
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