Statistical Characteristics of High‐Frequency Gravity Waves Observed by an Airglow Imager at Andes Lidar Observatory.

The long‐term statistical characteristics of high‐frequency quasi‐monochromatic gravity waves are presented using multi‐year airglow images observed at Andes Lidar Observatory (ALO, 30.3°S, 70.7°W) in northern Chile. The distribution of primary gravity wave parameters including horizontal wavelength, vertical wavelength, intrinsic wave speed, and intrinsic wave period are obtained and are in the ranges of 20–30 km, 15–25 km, 50–100 m s−1, and 5–10 min, respectively. The duration of persistent gravity wave events captured by the imager approximately follows an exponential distribution with an average duration of 7–9 min. The waves tend to propagate against the local background winds and show evidence of seasonal variations. In austral winter (May–August), the observed wave occurrence frequency is higher, and preferential wave propagation is equator‐ward. In austral summer (November–February), the wave occurrence frequency is lower, and the waves mostly propagate pole‐ward. Critical‐layer filtering plays a moderate role in determining the preferential propagation direction in certain months, especially for waves with a smaller observed phase speed (less than typical background winds). The observed wave occurrence and preferential propagation direction are related to the locations of convection activities nearby and their relative distance to ALO. However, direct wave generations are less likely due to the large distance between the ALO and convective sources. Other mechanisms such as secondary wave generation and possible ducted propagation should be considered. The estimated mean momentum fluxes have typical values of a few m2 s−2. Plain Language Summary: The area around the Andes contains hot spots of gravity waves due to surrounding geographical conditions, such as oceans, rainforests, and mountains. This study presents a statistical analysis of gravity waves with a shorter period based on 6‐year airglow emissions observations in the mesosphere over the Andes. Wave information of many gravity waves was extracted from the airglow emission images. The preferential wave propagation direction and wave occurrence frequency are found to be highly correlated with the convection activities nearby, especially during solstice seasons. In austral summer, waves might originate from the Amazon Basin through a long‐range ducted propagation, resulting in a southwestward propagation tendency. These waves would alter the atmospheric winds when they dissipate and deposit the momentum into the atmosphere. This study expands the understanding of gravity waves hot spots over the Andes to the upper atmosphere. Key Points: High‐frequency gravity waves were observed near the mesopause over the Andes with duration following an exponential distributionPreferential propagation direction of the waves shows seasonal dependence, southwestward in austral summer and equator‐ward in winterThe observed waves are likely associated with convections, playing an important role in shaping the observed wave directionality [ABSTRACT FROM AUTHOR]