Influence of atmospheric winds and tides on the propagation direction of mesospheric gravity waves observed in OH airglow in the Alpine region

Atmospheric gravity waves transport energy and momentum trough the different atmospheric layers from the troposphere up to the mesosphere and above. On the one hand this transport has influence on atmospheric circulation patterns and drives for example the meridional circulation in the mesosphere. On the other hand the prevailing wind field selectively influences the vertical propagation conditions of gravity waves of different phase speed and horizontal propagation direction.

The OH-airglow layer at ca. 86 km altitude (upper mesosphere / lower thermosphere, UMLT) is well-suited for the investigation of atmospheric dynamics, allowing continuous observations of the night-sky throughout the year. Especially, atmospheric gravity waves are prominent features in the data of airglow imaging systems. Furthermore, this altitude region is known to be a region where wave breaking occurs quite often making it particular interesting for quantifying the amount of energy and momentum released due to gravity waves.

Five years of airglow observations with three FAIM (Fast Airglow Imager) systems in and around the Alpine region are analysed regarding high-frequency gravity waves. Prevailing wind fields and tides from meteor radar wind data and ERA5 data are compared with the propagation direction of these waves and show patterns with high correlation. On seasonal timescales, the gravity waves clearly propagate predominantly to the East in summer and to the West in winter regarding the zonal direction. The meridional direction varies between the different years. On diurnal timescales, we find that atmospheric tides significantly impact the main propagation directions of the gravity waves.

We further present a case study of a stereoscopic reconstruction using two synchronized airglow-imagers with overlapping field-of-views. This allows deriving the wave amplitude and a 3D visualization of gravity wave patterns within the airglow layer.

This work received funding from the Bavarian State Ministry of the Environment and Consumer Protection.