“The Vortex Ain’t Alright”: Diagnosing the Features of a Preconditioned Polar Vortex Prior to Sudden Stratospheric Warmings with Time Series Motifs

Sudden stratospheric warmings (SSWs) are dramatic events that strongly disrupt the stratospheric polar vortex (hereinafter, the polar vortex) during winter. SSWs in northern hemisphere winters have historically occurred at a rate of about 6 events per decade, and it is well-known that these events can influence weather and climate in the troposphere, often leading to enhanced forecast skill at longer lead times. While the triggering mechanisms behind SSWs are still not fully understood, most research has either focused on the role of anomalous planetary wave fluxes from the troposphere in forcing SSWs, or on the stratosphere's control over dynamical evolution. One concept that is thought to be a common puzzle piece in either case is vortex preconditioning, which is underlain by the idea that there exist certain preconditioned states of the polar vortex that make later large stratospheric disturbances favorable, or possibly even inevitable. In this presentation, I will present work that uses time series motif discovery techniques to help diagnose specific features of vortex preconditioning in reanalysis data.