Abstract
Abstract. The variability in the middle atmosphere is driven by a variety of waves covering different spatial and temporal scales. We diagnose the variability in the thermal tides due to changes in the background wind by an adaptive spectral filter, which takes the intermittency of tides into account. We apply this diagnostic to temperature observations from daylight-capable lidar at midlatitudes (54∘ N, 12∘ E) as well as to reanalysis data of horizontal winds from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). These reanalysis data provide additional wind information in the altitude range between 30 and 70 km at the location of the lidar as well as on a global scale. Using the global data gives information on the tidal modes seen at one location. A comparison of the temperature and wind information affirms whether there is a fixed phase relation of the tidal waves in the temperature and the wind data. We found that in general the local tidal signatures are dominated by migrating tidal modes, and the signature is weaker in temperatures than in winds. While the meridional wind tide leads the zonal wind tide by 90∘, the phase relation between the temperature and the wind tide is more complex. At certain altitudes the temperature tide follows the zonal wind tide. This knowledge helps in improving the interpretation of the seasonal variation in tides from different observables, especially when only data from single locations are used. The findings provide additional information about the phase stability of tidal waves, and the results clearly show the importance of a measurement acquisition on a routine basis with high temporal and spatial resolution.
Highlights
Atmospheric waves play a major role in the circulation of the Earth’s atmosphere, as they couple the different atmospheric layers
The adaptive spectral filtering leads to more information about the amplitudes and phases in time and space, which is an enhancement compared to using the one-dimensional filtering approach
This paper addresses the relationship between tidal fluctuations observed in temperatures and winds in the stratosphere and mesosphere during 10 d in May 2016 using the ground-based, daylight-capable RMR lidar located at Kühlungsborn (54◦ N, 12◦ E) together with reanalysis data provided by MERRA-2
Summary
Atmospheric waves play a major role in the circulation of the Earth’s atmosphere, as they couple the different atmospheric layers These waves are often generated in the troposphere and propagate to higher altitudes, where they become dynamically unstable and break and deposit their momentum and energy to the mean flow (e.g., Fritts and Alexander, 2003). Such waves driven by the absorption of solar radiation are one of the strongest perturbations in the middle atmosphere. Such tides are assumed to be excited mainly by zonally asymmetric variations in topography or time-varying heat sources (Lieberman et al, 2015; Sakazaki et al, 2015)
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