Strengthened SPV‐Annular Mode Coupling in the Southern Hemisphere Contrasts With Northern Hemisphere Trends

Abstract While the decadal weakening in the coupling between the Northern Hemisphere (NH) stratospheric polar vortex (SPV) and the Arctic Oscillation (AO) has been well documented, a critical gap remains in our understanding of the corresponding decadal dynamics involving the Antarctic Oscillation (AAO) in the Southern Hemisphere (SH). Using reanalysis data sets spanning 1960 to 2025, we identify a contrasting weak‐to‐strong decadal transition in the SH winter SPV‐AAO coupling. This transition is characterized by a strengthened phase‐locking relationship, in which weak and strong SPV states become increasingly aligned with negative and positive AAO phases, respectively. Vertically, stratospheric anomalies become progressively more connected to the troposphere. Horizontally, the associated circulation pattern evolves from a weak wavenumber‐3‐like structure to a Pacific‐dominated configuration, ultimately forming a more balanced multi‐basin configuration across the Pacific, Atlantic, and Indian Ocean sectors. Conversely, the NH exhibits a contrasting decadal weakening in both the SPV‐AO coupling and the phase‐locking relationship. Vertically, the initially coherent stratosphere‐troposphere connection becomes progressively weaker. Horizontally, the NH SPV‐AO link is associated with a progressive disruption of the AO action center over the North Pacific basin, evolving from a robust positive center into structures with meridional and then zonal sign reversals. These findings highlight the contrasting reconfigurations of single‐ and multi‐basin patterns that shape the hemispheric asymmetry in stratosphere‐troposphere coupling.