Gravity wave momentum flux in the upper mesosphere derived from OH airglow imaging measurements

We report procedures to identify small-scale (20-100 km) atmospheric gravity waves from OH airglow images to estimate momentum fluxes carried by the waves. We also deduce contamination of background continuum emission in OH image, by comparing a simultaneous observation of OH lines measured by the Spectral Airglow Temperature Imager (SATI). We applied the procedures to a one-night dataset obtained at Shigaraki, Japan (34.9 degrees N, 136.1 degrees E) on November 19, 1999. The background wind, which is essential for deriving the intrinsic parameters of gravity waves, was measured by the Middle and Upper Atmosphere (MU) radar. Contamination of background continuum emission with the OH filter was deduced to be 30%. From these procedures, we found that the gravity waves identified in the OH images were mainly propagating southward or southeastward with horizontal wavelengths of 60-90 km and apparent phase speeds of 40-80 m/s. The estimated momentum fluxes on this night was 1-15 m(2) s(-2), with an average of 4.9 m(2) s(-2).