Reflection of a long-period gravity wave observed in the nightglow over Arecibo on May 8-9, 1989?

During the Arecibo Initiative for Dynamics of the Atmosphere (AIDA) campaig n in 1989 a characteristic of gravity wave perturbations observed in mesopa use region airglow emissions was that airglow brightness fluctuation's and airglow-derived temperature fluctuations often occurred either in phase or in antiphase. This stimulated the development of a theory suggesting that s uch in-phase fluctuations were most probably the result of strong reflectio ns occurring in the mesosphere and lower thermosphere region. Recent examin ation of a particular wave event and application of simple WKB-type theory has appeared to support this hypothesis. Here we bse a full-wave model and a WKB-type model, each coupled with a chemical-airglow fluctuation model de scribing O-2 atmospheric and OH Meinel airglow fluctuations, to assess the strength of wave reflection and also to explicitly calculate the phase diff erence between the airglow brightness and the temperature fluctuations. Our results suggest that reflection is not strong for the particular wave even t, and the model produces fairly large phase differences between the airglo w brightness and the temperature fluctuations (similar to 35 degrees and si milar to 134 degrees -165 degrees for the O-2 atmospheric and OH airglow em issions, respectively). These results are not particularly sensitive to the nominal mean winds used in the simulations. There is an instance when a re gion of minimum refractive index occurs directly above a region in which re flection is strongest, suggesting that the two are related. However, the re flection does not appear to be strong. Our results suggest that chemical ef fects can account for the inferred phases of the observed airglow fluctuati ons and that effects associated with wave reflection appear to play a relat ively minor role in the airglow fluctuations.