A method proposed by Salby for computing space-time Fourier transforms of asynoptic satellite data has been applied to stratospheric brightness temperature measurements from January and February 1979 in a search for two fast-moving low-wavenumber instabilities predicted in a numerical study by Lynch. The method is capable of producing spectra down to periods of approximately one day with no distortion due to the asynopticity of the data. No spectral peaks corresponding to the predicted modes were found; taking the noise level as the upper limit for their amplitudes at the altitudes observed, an upper limit of approximately 0.6 to 1.2 degrees Kelvin may be set for their peak amplitudes near the mesopause. ¿American Geophysical Union 1987