Subpolar Southern Ocean Seasonal Variability of the Geostrophic Circulation From Multi‐Mission Satellite Altimetry

Abstract

AbstractA novel multi‐satellite product is used to shed light on the sea surface height seasonal cycle and associated geostrophic circulation in the subpolar Southern Ocean. We find three main modes of variability governing the Sea Level Anomaly seasonal cycle, all of them primarily governed by wind forcing. The main mode of seasonal variability is associated with the seasonality of the main subpolar gyres governed by large‐scale wind stress curl, qualitatively consistent with Sverdrup dynamics. The second seasonal mode is related to the Antarctic Slope Current (ASC), governed by the coastal easterlies, with a rapid circumpolar propagation of anomalous sea‐level along the continental slope that is dynamically consistent with the so‐called Southern Mode. The first two modes induce an acceleration of the gyres and the ASC in winter. The third seasonal mode appears to be driven by sea ice‐modulated surface stress and induces an offshore extension of the ASC from autumn to winter.