Airglow imaging of gravity waves 1. Results from a small network of OH nightglow scanning imagers

Images of the variations of OH nightglow intensities have been recorded by a three-station network of scanning radiometers in southwestern Ontario dur ing the period from May until September 1998. Each radiometer performs a 16 by 16 point raster scan of the night sky every minute, turning itself on a nd off when the solar depression angle is < 6 degrees. The horizontal phase velocity, horizontal wavelength, and frequency of the internal gravity wav es are derived from the OH intensity measurements using joint time-frequenc y analysis techniques, including the S transform, localized cross-spectral analysis, and generalized instantaneous frequency. The ensemble of gravity waves seen in all three instruments are analyzed and observed to have a str ong dependence in their propagation direction with the majority of waves se en at each of the three sites having a horizontal wave vector in the northe ast direction. The most common parameters observed for horizontal phase spe ed is 45 m/s, horizontal wavelength is 25 km, and period is 10 min.