Observations of the unambiguous 2-dimensional horizontal wave number spectrum of OH intensity perturbations

The unambiguous 2-D horizontal wave number spectrum of gravity wave perturbations in OH emission intensities is computed from imager observations acquired on 2 Feb 1995 at the Starfire Optical Range, NM. The technique involves computing the (ω, k, l) = (ω, h, φ) spectrum of OH images collected over a several hour period, where k is the zonal wave number, l is the meridional wave number, h = (k² + l²)1/2, φ = tan^-1 (k/l), and ω is the temporal frequency. The data are used to study the azimuthal distribution of wave energy propagation and the separability of the (h, φ) spectrum. The h spectral indices, computed from power-law fits of the 2-D spectrum over the wave number range 2π/(200 km) < h < 2π/(20 km), vary between -1.6 and -3.6 as a function of φ with a mean of -2.58. Consequently, the image spectrum is not separable in h and φ. We show that nonseparability is most likely associated with distortion of the wave perturbations caused by the viewing geometry at large zenith angles.