Indices, which reflect variations of the zonal geostrophic wind at the 10-mb-surface of the northern hemisphere, are compared with solar activity fluctuations applying methods of statistical frequency analysis. At a frequency corresponding to half the synodic rotation period of the sun, a significant response of the stratospheric circulation to solar activity is found for nearly all latitudes between 10 and 80° N. Considering the detailed coherency spectra it is suggested that a stratospheric “system”, e.g. a high or low pressure belt with an average position near 50° N, oscillates with the synodic period of the solar rotation. The periodic variations are probably modulated by annual, semiannual and 4-monthly oscillations of the solar radiation or of stratospheric quantities. Satellite measurements of the stratospheric radiance (temperature) indicate that the response to solar activity fluctuations resulting in quasiperiodic changes of stratospheric properties with half the rotation period of the sun, is a global phenomenon.