A 45-Year Climatological Study of Arctic Stratospheric Polar Vortex Dynamics and Morphology using ERA5 Data (1979-2023)

Abstract The Arctic Stratospheric Polar Vortex (SPV) is known for its high interannual variability, with major Sudden Stratospheric Warmings (SSWs) occurring approximately every second year and with three Exceptionally Strong Vortex (ESV) events in the past decades, which are associated with springtime ozone depletion. Understanding the dynamical and morphological properties of the SPV is crucial for predicting these extreme events, and SPV variability in general. This study utilizes data from 45 Northern Hemisphere (NH) extended winter seasons, covering the period from September to May, at lower, middle and upper stratosphere heights. We explore the influence of different climate variability modes — El Nino-Southern Oscillation, Quasi-Biennial Oscillation, Arctic Oscillation, and Indian Ocean Dipole — on the vortex's dynamical properties. In February, March and April of the 2019 NH winter, the climatological anomaly reached an all-time high of SPV strength, with record-low ozone due to an exceptionally strong vortex, though its intensity did not extend to the upper stratosphere. Other ESV winters were 1996 and 2010. The EPV gradient increases more sharply with altitude than the area, indicating a stronger upper stratospheric vortex boundary that resists tropospheric wave disturbances. During some SSW events, the vortex area may recover, but the EPV gradient remains weak. During the period from 1989 to 1995, no extreme events were recorded, and the SPV strength remained close to the climatological average during the extended winter. The SPV center shows a significant latitudinal shift move away from the pole by the 14.31 km/year. In stable vortex years without SSWs, the center shifts poleward, typically positioned in the western hemisphere. We quantify climatic variability and its role in extreme SPV events, highlighting the significant influence of the Quasi-Biennial Oscillation and Arctic Oscillation. Breakup timing, influenced by tropospheric waves, shows minor variations across levels. The vortex begins forming in the upper levels and dissipates progressively from the lower stratosphere. Notably, a statistically significant decreasing trend towards earlier vortex formation is seen in the upper stratosphere. We quantify the variability in the formation and deformation of the vortex across different levels and analyze the interannual variability of Polar Stratospheric Clouds and their relationship with SPV dynamics and associated ozone loss during late winter and early spring. We hypothesized that both SSWs and ESVs could potentially occur in a single NH winter in future.