Measuring gravity wave momentum fluxes with airglow imagers

We describe a new technique for estimating the vertical fluxes of horizonta l momentum in the mesopause region using airglow imager data. The azimuthal distribution of the relative airglow intensity or rotational temperature v ariance associated with both monochromatic and quasi-random waves is comput ed from the unambiguous two-dimensional horizontal wave number spectrum. Th e variance distribution is used in a gravity wave model to predict the cros s-correlation coefficient between the vertical and horizontal wind perturba tions (and hence the momentum flux) as a function of azimuth angle. The tec hnique is applied to OH imager data collected during five nights in Februar y and April 1995 at the Starfire Optical Range, New Mexico. To validate the technique, the cross-correlation coefficients and momentum fluxes derived from the imager data are compared with the zonal and meridional fluxes meas ured by a co-located Na wind/temperature lidar employing the standard dual- beam Doppler technique. The mean zonal and meridional cross-correlation coe fficients and momentum fluxes inferred from the OH imager data are -0.27 +/ - 0.011 (-11.9 +/- 0.49 m(2)/s(2)) and 0.009 +/- 0.011 (0.44 +/- 0.53 m(2)/ s(2)), respectively. The corresponding zonal and meridional coefficients an d fluxes measured by the lidar are -0.26 +/- 0.04 (-11.9 +/- 3.9 m(2)/s(2)) and -0.081 +/- 0.10 (-3.76 +/- 4.7 m(2)/s(2)), respectively. These results demonstrate that creditable estimates of momentum fluxes at mesopause heig hts can be derived from OH image data.