Classification of Stratosphere Winter Evolutions Into Four Different Scenarios in the Northern Hemisphere

International audienceAmong the 70 northern hemisphere winters from 1950 to 2020, 61 have been classified intofour independent scenarios with a new technique based on analyzing empirical orthogonal functions ofstratospheric zonal wind fluctuation patterns at the edge of the polar vortex. These four scenarios represent atypical zonal wind evolution in the stratosphere modulated by timings of stratospheric warmings occurring inwinter. First, there are three scenarios (January mode, February mode, and Double mode) for which the polarvortex generally breaks down with a reversing of zonal winds in midwinter, known as sudden stratosphericwarmings (SSWs) events, at different times. The last one is a non-perturbed scenario with two under-modes forwhich only the timing of the polar vortex transition to its summer state differs, either radiative or dynamical.Consistently with these wind patterns, the wave-1 and wave-2 anomaly evolutions confirm that these scenariosare associated with independent dynamics behaviors and significant differences between wave-1 and wave-2activities. We found that the wave-1 anomaly evolutions drop systematically for each scenario when thestratospheric winds weaken, while this correlation with the wave-2 anomaly evolutions is not observed for allscenarios. These different dynamical behaviors confirm that the scenarios are either mainly dynamically drivenby wave-1 or both driven by wave-1 and wave-2. Until early December, the modes possess similar increasingevolutions of the wave-1 activity due to the seasonal cycle. After, the scenarios separate, suggesting that themechanisms responsible for the winter unfolding act in the previous months