A Regime Perspective on the North Atlantic Eddy-Driven Jet Response to Sudden Stratospheric Warmings

The winter North Atlantic eddy-driven jet (NAJ) has been shown to exhibit three preferred latitudinal positions. Here we examine, for the first time, the influence of major Sudden Stratospheric Warmings (SSWs) on the regime behaviour of the NAJ using an ensemble of climate model experiments with stratospheric conditions nudged towards a major SSW, but with each ensemble member having freely evolving tropospheric conditions. The SSW experiment is compared to a control ensemble in which stratospheric variability is absent. The experiments show that the SSW leads to an increased daily occurrence of the southerly NAJ state by around 20% and a reduced occurrence of the northerly state. The NAJ autocorrelation function shows increased persistence on timescales up to 2 weeks, which is connected to the increased occurrence of the southerly jet regime. This suggests changes to the characteristics of NAJ variability as a result of SSWs. In contrast, the North Atlantic Oscillation shows a shift towards more negative values with little change in variance. These results aid in understanding the mechanisms by which SSWs impact on Euro-Atlantic climate.