Investigation of a gravity wave ducting event in the upper mesosphere

Atmospheric gravity waves (GWs) play an important role in the transport of energy and momentum throughout the Earth’s atmosphere. GW effects couple the lower regions of the atmosphere with the middle and upper regions of the atmosphere and the neutral atmosphere with the ionosphere. The effects are particularly strong in the mesosphere and lower thermosphere (MLT), where upward-propagating GWs tend to deposit momentum and energy flux via breaking, viscous dissipation, or other processes. The resulting net drag, heating, and cooling impact the global circulation of the mean atmospheric flow. Consequently, the parameterization of GWs in global climate models is a key focus of contemporary research on the MLT region. The physical processes associated with GWs must be understood in addition to their statistical characteristics in order to better parameterize their effects on the atmosphere. Ducting is a process that can occur when a GW becomes trapped between two evanescent regions in the atmosphere. According to the linear GW theory, a fully ducted wave has zero vertical momentum flux, so the ducting process must also be understood in order to improve our parameterization of GWs in global climate models. In this thesis, correlative lidar and airglow observations of a highly resonant ducting event, which occurred on the night of January 18, 2015, above the Andes Lidar Observatory (ALO) on Cerro Pachón, Chile (30.0° S, 70.0° W), are presented and analyzed. A ducted quasi-monochromatic GW with large associated temperature (T’) and vertical wind (w’) perturbations was observed in the mesopause region. A coherent phase relationship, consistent with the linear GW theory, between the temperature and vertical wind perturbations associated with the GW was found. The results also appear to show the generation of a secondary upward-propagating wave above the primary duct