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

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Abstract
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 image 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.