Characteristics of Antarctic Stratospheric Variability During Winter: A Case Study of the 2024 Sudden Stratospheric Warming and Its Surface Impacts

Abstract

In mid-winter 2024, extraordinary stratospheric warming occurred over the sub-Antarctic region with two distinctive warming maxima in mid-July to early August, followed by record negative anomalies in the southern annular mode (SAM) during late July to early August. However, the causality between these stratospheric and tropospheric extreme events remains unclear due to the rarity of such downward coupling during Southern Hemisphere (SH) winter—previous Antarctic stratospheric warmings and their associated downward coupling have largely occurred during SH spring. Here we provide insights into the dynamics and climate impacts of wintertime Antarctic vortex variability during 1979–2023 and compare the climatological behavior of wintertime SH stratosphere-troposphere coupling with that observed during mid-winter 2024. During 1979–2023, compared to the springtime stratospheric polar vortex variability in the SH, which is characterized by variations in vortex strength and breakdown timing and its robust signature in surface climate, wintertime variability in the SH stratospheric circulation is marked by expansion and contraction of the vortex with generally weak linkages to surface circulation. The 2024 mid-winter event mirrored many historical features of wintertime variability at stratospheric levels but had a much stronger signature in surface climate. It was unique with a record contraction of the vortex accompanied by record increases in polar stratospheric temperatures for July. These unusual stratospheric conditions atypically led to substantially higher-than-normal Antarctic ozone concentrations in July and August, delaying the development of the ozone hole, and record negative values in the SAM and extraordinary warmth over the Antarctic continent in early August 2024.