Abstract
Abstract. Noctilucent clouds (NLC) have been measured by the Rayleigh/Mie/Raman-lidar at the ALOMAR research facility in Northern Norway (69° N, 16° E). From 1997 to 2010 NLC were detected during more than 1850 h on 440 different days. Colocated MF-radar measurements and calculations with the Leibniz-Institute Middle Atmosphere (LIMA-) model are used to characterize the background atmosphere. Temperatures as well as horizontal winds at 83 km altitude show distinct differences during NLC observations compared to when NLC are absent. The seasonally averaged temperature is lower and the winds are stronger westward when NLC are detected. The wind separation is a robust feature as it shows up in measurements as well as in model results and it is consistent with the current understanding that lower temperatures support the existence of ice particles. For the whole 14-year data set there is no statistically significant relation between NLC occurrence and solar Lyman-α radiation. On the other hand NLC occurrence and temperatures at 83 km show a significant anti-correlation, which suggests that the thermal state plays a major role for the existence of ice particles and dominates the pure Lyman-α influence on water vapor during certain years. We find the seasonal mean NLC altitudes to be correlated to both Lyman-α radiation and temperature. NLC above ALOMAR are strongly influenced by atmospheric tides. The cloud water content varies by a factor of 2.8 over the diurnal cycle. Diurnal and semidiurnal amplitudes and phases show some pronounced year-to-year variations. In general, amplitudes as well as phases vary in a different manner. Amplitudes change by a factor of more than 3 and phases vary by up to 7 h. Such variability could impact long-term NLC observations which do not cover the full diurnal cycle.
Highlights
More than 125 years ago unusual clouds, visible as twilight phenomena after sunset, were documented for the first time (Leslie, 1885; Backhouse, 1885; Jesse, 1885)
We investigate how results from the Leibniz-Institute Middle Atmosphere (LIMA-)model are related to Noctilucent clouds (NLC) observations above Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR)
We presented results from a multi-year NLC data set obtained by ground-based lidar at ALOMAR
Summary
More than 125 years ago unusual clouds, visible as twilight phenomena after sunset, were documented for the first time (Leslie, 1885; Backhouse, 1885; Jesse, 1885). The following method is applied to each NLC parameter, because occurrence, altitude and brightness show different variation patterns over season as well as local time. Time resolution for both RMR-lidar and LIMA data is ∼150 seconds. Seasonal mean values of temperature and horizontal winds at 83 km altitude above ALOMAR are calculated with LIMA for times of confirmed absence as well as presence (βmax>4) of NLC within the lidar long-term data set. In combination with the wind results we conclude that LIMA seems to reproduce the background atmosphere to a sufficient degree even on hourly resolution
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