OBSERVATIONS OF GRAVITY-WAVES FROM MULTISPECTRAL MESOSPHERIC NIGHTGLOW EMISSIONS OBSERVED AT 23-DEGREES-S

Simultaneous measurements of the OI 557.7 nm, O-2 atmospheric (0,1) band, NaD and OH (9,4) band emissions obtained during the period October-November 1989 at Cachoeira Paulista (23 degrees S, 45 degrees W), Brazil, have been analysed to study gravity waves in the mesospheric region at a low-latitude station in the southern hemisphere. It was found that, when these emissions showed large temporal intensity variations, there were also short period quasi-coherent temporal variations superposed on them, suggesting a possible passage of internal gravity waves in the emission layers. Cross-correlation analysis indicates that the time lag between the different emissions is smaller for short period variations compared with the long period variations. The wave parameters, namely a vertical wavelength of 12 km, a horizontal derived wavelength of 200 km with a period of 80 min, estimated from one of the observed short-period coherent oscillations, are typical of the internal gravity waves at the airglow emission height.