Observations and interpretation of gravity wave induced fluctuations in the OI (557.7 nm) airglow

Observations of fluctuations in the intensity and temperature of the O I (5 57.7 nm) airglow taken at Arecibo in 1989 are reported and interpreted on t he assumption that they are caused by gravity waves propagating through the emission layer. The data give the magnitude of Krassovsky's ratio as 3.5 /- 2.2, at periods between about 5 and 10 hours. Comparison with theory sho ws that the gravity waves responsible for the measured airglow variations m ust have long wavelengths of several thousand kilometers. The observed phas es of Krassovsky's ratio are in good agreement with theoretically predicted values at the long wavelengths and large periods for about half the cases. In the other cases, observed phases are near -180 degrees, suggesting that the waves responsible for the airglow fluctuations have experienced strong reflections in the emission layer. The observations emphasize the importan ce of knowing the full altitude profiles of temperature and winds for extra ction of wave information from the airglow fluctuations.