MLT gravity wave climatology in the South America equatorial region observed by airglow imager

An all-sky CCD imager for OH, O sub(2) and OI (557.7 nm) airglow emission measurements was operated at Sao Joao do Cariri (Cariri), Brazil (7 degree S, 36 degree W), from October 2000 to December 2004. A large amount of image data, more than 3000 h of observation and around 1000 wave events, makes it possible to classify the gravity wave characteristics, which are statistically significant. The observed waves show a typically short horizontal wavelength (5-45 km) and a short period (5-35 min), and horizontal phase speeds of 1 to 80 m/s. In most cases band-type waves (horizontal wavelength between 10 and 60 km) showed a clear preference for the horizontal propagation direction from the South American continent to the Atlantic Ocean. Ripples also have similar features but with different anisotropy. In this paper we focus our discussion on the wave characteristics of the bands and ripples and a comparison between them.