A "Boreing" Night of Observations of the Upper Mesosphere and Lower Thermosphere Over the Andes Lidar Observatory

A very high-spatial resolution (similar to 21-23 m pixel at 85 km altitude) OH airglow imager at the Andes Lidar Observatory at Cerro Pachon, Chile observed considerable ducted wave activity on the night of 29-30 October 2016. This instrument was collocated with a Na wind-temperature lidar that provided data revealing the occurrence of strong ducts. A large field of view OH and greenline airglow imager showed waves present over a vertical extent consistent with the altitudes of the ducting features identified in the lidar profiles. While waves that appeared to be ducted were seen in all imagers throughout the observation interval, the wave train seen in the OH images at earlier times had a distinct leading nonsinusoidal phase followed by several, lower-amplitude, more sinusoidal phases, suggesting a likely bore. The leading phase exhibited significant dissipation via small-scale secondary instabilities suggesting vortex rings that progressed rapidly to smaller scales and turbulence (the latter not fully resolved) thereafter. The motions of these small-scale features were consistent with their location in the duct at or below similar to 83-84 km. Bore dissipation caused a momentum flux divergence and a local acceleration of the mean flow within the duct along the direction of the initial bore propagation. A number of these features are consistent with mesospheric bores observed or modeled in previous studies.