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 tech-nique involves computing the (w, k, l) = (w, h, f) 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, f = tanÐ1(k/l), and w is the temporal frequency. The data are used to study the azimuthal distribution of wave energy propagation and the separability of the (h, f) spectrum. The h spectral indices, computed from power-law fits of the 2-D spectrum over the wave number range 2p/(200 km) < h < 2p/(20 km), vary between Ð1.6 and Ð3.6 as a function of f with a mean of Ð2.58. Consequently, the image spectrum is not separable in h and f. We show that nonseparability is most likely associated with distortion of the wave perturbations caused by the viewing geometry at large zenith angles.
Figure 1 Unambiguous 2-D horizontal wave number spectrum of the OH images acquired on 2 Feb 1995.
Figure 2 a) Horizontal wave number spectrum of OH intensity perturbations FOH(h) computed by integrating the 2-D spectrum plotted in Figure 1 over 0 < f < 2p. b) Azimuthal distribution of wave energy FOH(f) computed by integrating the 2-D spectrum plotted in Figure 1 over 2p/(200 km) < h < 2p/(20 km). c) The horizontal wind vector measured by the Na wind/temperature lidar during the observation period.
Figure 3 Variation of h spectral indices and FOH(f) with azimuth. The spectral indices were computed from least-squares power law fits to FOH(h, f) over the wave number range 2p/(200 km) < h < 2p/(20 km) at each 5û increment in f.
Figure 3 FOH(h, f) plotted versus h for f = 145û and 255û.
