Evidence of reflection of a long-period gravity wave in observations of the nightglow over Arecibo on May 8-9, 1989

During the Arecibo Initiative in Dynamics of the Atmosphere (AIDA) campaign there were several unusual observations of the O-2 Atmospheric (0,1) and OH Meinel (6,2) brightness fluctuations being nearly 180 degrees out of phase. In this paper we discuss data from May 8-9, 1989, during which meteor radar and airglow instrumentations were operating and thus wind data were available. We show that the nearly out-of-phase result on this night is due to the fact that the OH Meinel brightness and temperature are out of phase while the O-2 atmospheric temperature and brightness are nearly in phase. The characteristics of the wave causing the out of phase fluctuations are derived and comparisons are made between results obtained by the Aerospace nightglow camera and those obtained by the York University airglow camera [Zhang ct al., 1993]. Although there are differences between them, both of the instrumental data sets are consistent with the presence of a wave with a horizontal wavelength greater than or equal to 600 km and a period of several hours. An analysis of these data shows that the out-of-phase: relationship is mast likely due to strong wave reflection in the lower thermosphere caused by thermal gradients and wind shears.