Influence of the mean wind field on the separability of atmospheric perturbation spectra

The effects of Doppler shifting caused by the mean wind field on the separability of gravity wave spectra are analyzed using the gravity wave models developed recently by Gardner et al. (1993). If the intrinsic joint vertical wave number (m) and temporal frequency (ω) spectrum is separable, Doppler effects associated with even small mean winds will destroy separability of the observed joint (m, ω0) spectrum, particularly at high vertical wave numbers. The effect can have a substantial impact on the measured m-spectrum especially when the observations are not sensitive to the lowest or highest observed frequencies. Data averaging or low-pass temporal filtering can result in substantial reduction of the spectrum magnitude at high m values while data prewhitening or high-pass temporal filtering can result in significant distortion of the spectrum at low m values. These results have important implications for observational tests of the various gravity wave spectral models.