The effects of solar activity on the geopotential height and temperature fields of the 50-, 30- and 10-mbar surface, resolved into zonal harmonic components, were investigated. This was done by means of cross-spectral analysis between the 10.7-cm radiation of the sun and plantary waves up to zonal wave number 3. Frequent significant responses of various harmonic components in a broad range of oscillation frequencies give evidence that solar activity plays a significant role for the dynamics of the middle and lower stratosphere. Oscillations of the amplitudes of the zonal harmonics that are coherent with solar activity fluctuations were extracted from the spectra and recomposed into coherent (planetary) waves. Three waves with periods of 25 days (near to the sun's rotation period), 13.6 days (first harmonic of solar rotation), and 15.1 days (corresponding to the well-known 15- to 16-day wave in the atmosphere) are examined in detail. They show the properties of free planetary modes (13.6 and 15.1 days) and possibly of internal waves (25 days) at higher latitudes. Vacillation cycles of the mean atmospheric state (including stationary waves) seem to be important for the generation of the studied wave phenomena.