Global grids have been constructed from high‐quality TIROS‐N microwave sounder unit measurements which closely approximate the 30‐ to 150‐mbar geopotential thickness. The grids compare favorably with conventional analyses. Grids for January 1979 are spectrally analyzed by Fourier transform for zonal wave numbers 1–10 over latitudes 80°N to 80°S. Both time mean and transient medium‐scale waves are discussed in some detail. In the time mean, wave 1 dominates all northern latitudes. In equatorial regions, wave 1 also is dominant, but a secondary spectral peak is noted at wave 4. The most remarkable feature seen is a strong medium‐scale structure with eastward movement in southern (summer) mid‐latitudes. Zonal wave numbers 5 and 6 have periods of about 10–15 days and 5 days, respectively. These results provide independent corroboration of such structures recently reported by several investigators. The mechanism by which the dominant medium‐scale waves are maintained is not understood.