ON THE ASSOCIATION BETWEEN THE QBO AND THE EXTRATROPICAL STRATOSPHERE

Although diagnostic studies and mechanistic model experiments have found that, on average, the polar vortex in northern winter is stronger and colder in the west than in the east years of the equatorial Quasi-Biennial Oscillation (QBO), we show with an expanded data base that the results are not statistically significant. The reason for the insignificance is that in 36% of the winters (13 out of 36) the vortex was warm and weak in the west, and cold and strong in the east years. Only at low activity in the 11-yr solar cycle did the difference between the west (cold) and the east (warm) years become statistically significant. At high solar activity the west years had a warm and the east years a cold polar vortex in the mean. We show this association with the 11-yr solar cycle also in terms of the geostrophic wind.