MEDIUM-SCALE GRAVITY WAVE OBSERVATIONS USING AIRGLOW KEOGRAMS OVER THE BRAZILIAN COMANDANTE FERRAZ ANTARCTIC STATION

Despite the many observations of gravity waves over the Antarctic Peninsula and the Drake Passage, revealing the wave's characteristics and parameterizing their activity over the stratosphere and mesosphere, much of the wave spectra still need to be investigated as the instruments and data processing have their limitations. This study examines the characteristics of medium-scale gravity waves (MSGW) observed during the 2022 winter over the Antarctic Peninsula using keograms of all-sky airglow images. The OH-NIR (700-900 nm) and OI557,7 nm all-sky airglow images were acquired by an imager installed at the Brazilian Comandante Ferraz Antarctic Station (EACF, 62°S), which is about 200 km from the tip of the Antarctic Peninsula. The original images were pre-processed to obtain unwarped and flat fielded images, after which keograms were constructed. A Butterworth band-pass filter was then applied to the keograms to reduce noise. The keogram technique allows a better characterization of the MSGWs spectra. Waves were identified by applying wavelet analysis over the keograms lines (times series), and the wavelet properties and reconstruction were used to obtain their observed and horizontal characteristics. MSGWs with horizontal wavelengths from 100 to 450 km, periods between 20 and 90 min, and phase speeds between 50 and 200 m/s were measured. These waves' intrinsic parameters and vertical propagation characteristics were further estimated using wind data from a nearby meteor radar and temperature data from satellite soundings in close proximity. The values of the estimated vertical wavelength are distributed uniformly between 10 and 60 km, and the intrinsic parameters were found to be similar to those of the observed parameters. This quasi-similarity is due to the fast phase speed of the observed waves, which is much greater than the typical background wind speed at the observation altitude (about 88 km). Finally, momentum fluxes of the MSGW were estimated, with the majority presenting values below 10 m2s-2.