Climatology of High-frequency Gravity Waves Observed by an Airglow
Imager at Andes Lidar Observatory
Abstract
The long-term climatology of high-frequency quasi-monochromatic gravity
waves is presented using multi-year airglow images observed at Andes
Lidar Observatory (ALO, 30.3ºS, 70.7ºW) in northern Chile. A large
number of high-frequency gravity waves were retrieved from OH airglow
images. The distribution of primary 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 ms-1, and 5–10 min, respectively. The waves
tend to propagate against the local background winds and show clear
seasonal variations. In austral winter (Ma–Aug), the observed wave
occurrence frequency is higher and preferential wave propagation is
equator-ward. In austral summer (Nov–Feb), the wave occurrence
frequency is lower and the waves mostly propagate pole-ward.
Critical-layer filtering plays an important role in determining the
preferential propagation direction in certain months, especially for
waves with a small observed phase speed (less than typical background
winds). The wave occurrence and preferential propagation direction are
shown to be related to the locations of convection activities nearby and
their relative distance to ALO. However, other possible wave sources
such as secondary wave generation and possible ducted propagation cannot
be ruled out. The estimated momentum fluxes have typical values of a few
to 10 m2s-2 and show seasonal
variations with a clear anti-correlation with local background wind
directions.