Observation and modeling of gravity wave propagation through reflection and critical layers above Andes Lidar Observatory at Cerro Pachón, Chile

Abstract

AbstractA complex gravity wave event was observed from 04:30 to 08:10 UTC on 16 January 2015 by a narrow‐band sodium lidar and an all‐sky airglow imager located at Andes Lidar Observatory (ALO) in Cerro Pachón (30.25°S, 70.73°W), Chile. The gravity wave packet had a period of 18–35 min and a horizontal wavelength of about 40–50 km. Strong enhancements of the vertical wind perturbation, exceeding 10 m s−1, were found at ∼90 km and ∼103 km, consistent with nearly evanescent wave behavior near a reflection layer. A reduction in vertical wavelength was found as the phase speed approached the background wind speed near ∼93 km. A distinct three‐layered structure was observed in the lidar data due to refraction of the wave packet. A fully nonlinear model was used to simulate this event, which successfully reproduced the amplitudes and layered structure seen in observations. The model results provide dynamical insight, suggesting that a double reflection occurring at two separate heights caused the large vertical wind amplitudes, while the three‐layered structure in the temperature perturbation was a result of relatively stable regions at those altitudes. The event provides a clear perspective on the filtering processes to which short‐period, small‐scale gravity waves are subject in mesosphere and lower thermosphere.