The Influence of Zonally Asymmetric Stratospheric Ozone Changes on the Arctic Polar Vortex Shift

Recent studies have found a shift of the Arctic stratospheric polar vortex toward Siberia during late winter since 1980, intensifying the zonally asymmetric ozone (ZAO) depletion in the northern middle and high latitudes with a stronger total column ozone decline over Siberia compared with that above other regions at the same latitudes. Using observations and a climate model, this study shows that zonally asymmetric stratospheric ozone depletion gives a significant feedback on the position of the polar vortex and further favors the stratospheric polar vortex shift toward Siberia in February for the period 1980-99. The polar vortex shift is not significant in the experiment forced by zonal mean ozone fields. The February ZAO trend with a stronger ozone decline over Siberia causes a lower temperature over this region than over the other regions at the same latitudes, due to shortwave radiative cooling and dynamical cooling. The combined cooling effects induce an anomalous cyclonic flow over Siberia, corresponding to the polar vortex shift toward Siberia. In addition, the ZAO depletion also increases the meridional gradient of potential vorticity over Siberia, which is favorable for the upward propagation of planetary wave fluxes from the troposphere over this region. Increased horizontal divergence of planetary waves fluxes over the region 60 degrees-75 degrees N, 60 degrees-90 degrees E associated with ZAO changes accelerates the high-latitude zonal westerlies in the middle stratosphere, further enhancing the shift of the stratospheric polar vortex toward Siberia. After 2000, the ZAO trend in February is weaker and induces a smaller polar vortex shift than that in the period 1980-99.