Evidence for a solar cycle signal in tropospheric winds

Amplitudes and phases of the 11-year solar cycle in wind speed and temperature at radiosonde levels have been determined. These results are based on 174 stations over the northern hemisphere for the 25-year data period 1949–1973. Amplitudes and phases were estimated by the method of time-lagged correlation with the quasi-periodic 10.7-cm solar radio flux. The largest atmospheric amplitudes are near the tropopause level during winter, where in several regions over 40% of the interannual variance of the wind speeds is explained by the solar cycle. The hemispheric patterns of amplitude and phase suggest that the year-to-year latitudinal oscillations of the jet stream and the amplitude of the major standing long waves both appear to vary with the solar cycle. It is suggested that these results are due to changes in ultraviolet radiation, causing changes in ozone, and thus in stratospheric temperature, height, and wind fields. These changes may influence long-wave vertical propagation characteristics and the direct radiation exchange between the stratosphere and troposphere. Possible problems with this hypothesis are discussed. To verify this hypothesis, the morphology of the solar cycle changes in stratospheric wind and temperature and the associated effect on tropospheric standing waves must be estimated. These results show that atmospheric responses to the solar cycle vary with longitude as well as with latitude. Hence studies of the atmospheric solar cycle must avoid arbitrarily combining stations over broad geographical areas or as zonal means.