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

A very high‐spatial resolution (∼21–23 m pixel at 85 km altitude) OH airglow imager at the Andes Lidar Observatory at Cerro Pachón, 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 ∼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. Images taken on the night of 29–30 October 2016 from a high‐spatial resolution OH airglow camera and simultaneous data from a Na wind‐temperature lidar, colocated at the Andes Lidar Observatory on Cerro Pachón, Chile, revealed the presence of a mesospheric bore. The bore was located in a ducted region formed by large temperature and wind gradients present in the 82–88 km altitude region. Such bores in the atmosphere, that appear as a moving wave, are analogous to bores that form in river channels. Many of the observed features of this atmospheric bore are consistent with previous observations and modeling. However, these new data also showed, at the very high‐spatial resolution that are unique to these images, that the bore dissipated, forming turbulent‐like features and causing a momentum flux divergence within a duct that accelerated the mean wind along the direction of the bore propagation. High‐spatial resolution observations captured a mesospheric bore with a distinct leading phase These observations also captured clear evidence of instabilities driving bore dissipat