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In several papers, the solar cycle (SC) effect in thelower atmosphere has been linked observationally to the Quasi-biennialOscillation (QBO) of the zonal circulation. Salby and Callaghan (2000) inparticular analyzed the QBO wind measurements, covering more than 40 years,and discovered that they contain a large SC signature at 20 km. We presenthere the results from a study with our 3-D Numerical Spectral Model (NSM),which relies primarily on parameterized gravity waves (GW) to describe theQBO. In our model, the period of the SC is taken to be 10 years, and the relativeamplitude of radiative forcing varies exponentially with height, i.e., 0.2%at the surface, 2% at 50 km, and 20% at 100 km and above. Applying spectralanalysis to identify the SC signature, the model generates a relativelylarge modulation of the QBO, which reproduces the observationsqualitatively. The numerical results demonstrate that the QBO modulation,closely tracking the phase of the SC, is robust and persists at least for 70years. The question is what causes the SC effect, and our analysis showsthat four interlocking processes are involved: (1) In the mesosphere ataround 60 km, the solar UV variations generate in the zonal winds a SCmodulation of the 12-month annual oscillation, which is hemisphericallysymmetric and confined to equatorial latitudes like the QBO. (2) Althoughthe amplitude of this equatorial annual oscillation (EAO) is relativelysmall, its SC modulation is large and extends into the lower stratosphereunder the influence of, and amplified by, wave forcing. (3) The amplitudemodulations of both EAO and QBO are essentially in phase with the imposed SCheating for the entire time span of the model simulation. This indicatesthat, due to positive feedback in the wave mechanism, the EAO apparentlyprovides the pathway and pacemaker for the SC modulation of the QBO. (4) Ouranalysis demonstrates that the SC modulations of the QBO and EAO areamplified by tapping the momentum from the upward propagating gravity waves.Influenced and amplified by wave processes, the QBO thus acts as conduit totransfer to lower altitudes the larger SC variations in the UV absorbed inthe mesosphere. Our model produces in the temperature variations of the QBOand EAO measurable SC modulations at polar latitudes near the tropopause.The effects are apparently generated by the meridional circulation, andplanetary waves presumably, which redistribute the energy from theequatorial region where the waves are very effective in amplifying the SCinfluence

The QBO as potential amplifier and conduit to lower altitudes of solar cycle influence