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Solar and lunar tides in noctilucent clouds as determined by ground-based lidar
摘要： 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.
关键词： lunar tides,ALOMAR,solar tides,Noctilucent clouds,lidar observations
更新于2025-09-23 15:21:01
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The OH<sup>*</sup>(3&ndash;1) layer emission altitude cannot be determined unambiguously from temperature comparison with lidars
摘要： I investigate the nightly mean emission height and width of the OH?(3–1) layer by comparing nightly mean temperatures measured by the ground–based spectrometer GRIPS9 and the Nalidar at ALOMAR. The dataset contains 42 coincident measurements between November 2010 and February 2014, when GRIPS9 was in operation at the ALOMAR observatory (69.3?N, 16.0?E) in northern Norway. To closely resemble the mean temperature measured by GRIPS9, I weighted each nightly mean temperature profile measured by the lidar using Gaussian distributions with 40 different centre altitudes and 40 different full widths at half maximum. In principle, one can thus determine the altitude and width of the OH?(3–1) layer by finding the minimum temperature difference between the two instruments. On most nights, several combinations of centre altitude and width yield a temperature difference of ±2 K. The generally assumed altitude of 87 km and width of 8 km is never an unambiguous, good solution for any of the measurements. Even for a fixed width of ～8.4 km, one can sometimes find several centre altitudes that yield equally good temperature agreement. Weighted temperatures measured by lidar are not suitable to determine unambiguously the emission height and width of an OH? layer. If the OH?(3–1) rotational temperature is used as a proxy for the temperature at an altitude of 87 km with a width of 8.4 km, this proxy is representative to within ±16 K.
关键词： emission altitude,OH?(3–1) layer,Nalidar,ALOMAR,lidar,GRIPS9,temperature comparison
更新于2025-09-04 15:30:14