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 die s eparability of gravity wave spectra are analyzed using the gravity wav e models developed recently by Gardner et al. (1993). If the intrinsic joint vertical wave number (m) and temporal frequency (omega) spectru m is separable. Doppler effects associated with even small mean winds will destroy separability of the observed joint (m,omega(o)) spectrum, particularly at high vertical wave numbers. The effect can have a sub stantial impact on the measured m-spectrum especially when the observa tions are not sensitive to the lowest or highest observed frequencies. Data averaging or low-pass temporal filtering can result in substanti al reduction of the spectrum magnitude at high m values while data pre whitening or high-pass temporal filtering can result in significant di stortion of the spectrum at low m values. These results have important implications for observational tests of the various gravity wave spec tral models.