First measurements of tides in the stratosphere and lower mesosphere by ground-based Doppler microwave wind radiometry

Artikel i vetenskaplig tidskrift, 2020

Atmospheric tides are important for vertical coupling in the atmosphere, from the stratosphere down to the troposphere and up to the thermosphere. They are planetary-scale gravity waves with well-known periods that are integer fractions of a day and can be observed in the temperature or wind fields in the atmosphere. Most lidar techniques and satellites measure atmospheric tides only in the temperature field and continuous measurements of the tides in the wind field of the stratosphere and lower mesosphere are rare, even though, with modern lidars, they would be feasible. In this study, we present measurements of the diurnal tide in the wind field in the stratosphere and lower mesosphere by ground-based microwave wind radiometry for two different campaigns in tropical and polar regions. Further, we compare our measurements to MERRA-2 reanalysis data. In the tri-monthly mean, we find a good correspondence in the amplitude and phase of the diurnal tide between measurements and reanalysis with the most important features of the diurnal tides represented in both data sets. When looking at shorter timescales, we find significant differences in the data sets. We make an attempt to examine these differences and discriminate between atmospheric variability and noise, and we present some hints for intermittent diurnal tides. We conclude that continuous ground-based observations of tides in the middle atmospheric wind field are feasible, and they deliver consistent results for the mean amplitude and phase of the diurnal tide in the tri-monthly mean. We further discuss the limitations in regards to short timescale observations of tides and the possibility to provide additional insight into middle atmospheric dynamics that is complementary to temperature observations and reanalysis data.