Trends and anomalies in the coherence of the Southern Polar Vortex: A 26 year meta-study

The coherence and annual dissipation of the Southern Polar Vortex (SPV) are examined for anomalous behavior and trends, using data from the past 26 years, on four different levels in the Earth's atmosphere. In order to quantify the SPV's coherence in the sense of air masses moving collectively, a purely convection-based method which allows for the detection of spatial structures and their coherence is used. Having a quantitative method to define coherence allows for the detection of annual 'cessation dates' of the SPV. Trends in the cessation dates and coherence of the SPV at four levels in the atmosphere since 1999 are obtained. Hitherto unreported splitting events of the SPV-including in the most recent year 2024-are shown. Early cessation dates occur in known Sudden Stratospheric Warming years, but also in years in which spatial structures are seen to develop anomalously in the Southern Hemisphere or emanate from the tropics and impinge on the SPV. Consistently late cessation times in 2020-2022 are reported, and potential connections to weather events discussed.