The Influence of the Quasi-Biennial Oscillation on the Troposphere in Wintertime in a Hierarchy of Models, Part 2-Perpetual Winter WACCM runs

Experiments with the Whole Atmosphere Community Climate Model (WACCM) are used to understand the influence of the stratospheric tropical Quasi-Biennial Oscillation(QBO) in the troposphere. The zonally symmetric circulation in thermal wind balance with the QBO affects high frequency eddies throughout the extratropical troposphere. The influence of the QBO is strongest and most robust in the North Pacific near the jet exit region, in agreement with observations. Variability of the stratospheric polar vortex does not appear to explain the effect that the QBO has in the troposphere in the model, though it does contribute to the response in the North Atlantic. Anomalies in tropical deep convection associated with the QBO appear to damp, rather than drive, the effect of the QBO in the extratropical troposphere. The thermal wind response to QBO momentum anomalies interacting with tropospheric transient waves appears to be the crucial mechanism through which the QBO produces significant anomalies in the extratropical troposphere. The response to QBO winds of realistic amplitude is stronger for perpetual February radiative conditions and sea surface temperatures than perpetual January conditions, consistent with the observed response in reanalysis data, in a coupled seasonal WACCM integration, and in dry model experiments described in part 1.