Abstract/Summary

The Southern Hemisphere (SH) zonal circulation manifests a downward influence of the stratosphere on the troposphere from late spring to early summer. However, the strength and timescale of the connection, given the stratospheric state, has not been explicitly quantified. Here, SH zonal wind reanalysis time-series are analysed with a methodology designed to detect the minimal set of statistical predictors of multiple interacting variables via conditional independence tests. Our results confirm from data that the variability of the stratospheric polar vortex is a predictor of the tropospheric eddy-driven jet between September and January. The vortex variability explains about 40% of monthly mean jet variability at a lead time of one month, and can entirely account for the observed jet persistence. Our statistical model can quantitatively connect the multi-decadal trends observed in the vortex and jet during the satellite era. This shows how short-term variability can help understand statistical links in long-term changes.