Effects of the quasi biennial oscillation in the tropics on interannual variations of atmosphere and chemistry in the extratropics

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Effects of the quasi biennial oscillation(QBO) in the tropics on interannual variations of atmosphere and chemistry in the extratropics were investigated with data of a chemistry-climate model(MRI-CCM) and the ERA-40 Reanalysis. It was found that the conventional Holton-Tan explanation that the equatorial winds in the lower stratosphere act as a waveguide for midlatitude planetary wave propagation cannot explain the winter circulation in either the ERA-40 data or the simulation. Although the composite differences in zonal wind and temperature show a slight yet statistically significant Holton-Tan effect, i. e., the stratospheric polar vortex is weaker and more disturbed under easterly QBO conditions, the EP-flux diagnostics do not show more poleward propagation in the midlatitude stratosphere. Rather, planetary waves propagate more equatorward as well as more upward during the easterly phase of the QBO. Further, future projection of the QBO and its effect on the extratropics was also investigated with the MRI-CCM.