Influence of the Southern Annular Mode on the sea ice–ocean system

Abstract

The global sea ice–ocean model ORCA2‐LIM, driven by the NCEP/NCAR (National Centers for Environmental Prediction‐National Center for Atmospheric Research) reanalysis daily 2‐m air temperatures and 10‐m winds and by monthly climatologies for precipitation, cloud cover, and relative humidity, is used to investigate the impact of the Southern Annular Mode (SAM) on the Antarctic sea ice‐ocean system. Our results suggest that the response of the circumpolar Southern Ocean consists of an annular and a non‐annular component. For the sea ice cover, the non‐annular component seems to be the most important. The annular component strongly affects the overall patterns of the upper ocean circulation. When the SAM is in its positive phase, a northward surface Ekman drift, a downwelling at about 45°S, and an upwelling in the vicinity of the Antarctic continent are simulated. The non‐annular component has a significant impact at the regional scale, especially in the Weddell, Ross, Amundsen, and Bellingshausen Seas. In those regions, the pressure pattern associated with the SAM induces meridional winds which advect warmer air in the Weddell Sea and around the Antarctic Peninsula and colder air in the Amundsen and Ross Seas. This implies a dipole response of sea ice to the SAM, with on average a decrease in ice area in the Weddell Sea and around the Antarctic Peninsula and an increase in the Ross and Amundsen Seas during years with a high SAM index. The long‐term trend in the observed sea ice area does not appear to be related to the trend in the SAM index.