Circumpolar response of Southern Ocean eddy activity to a change in the Southern Annular Mode

Abstract

Analysis of satellite altimeter data reveals anomalously high Eddy Kinetic Energy (EKE) in the Antarctic Circumpolar Current (ACC) during the period 2000-2002. Around 2-3 years earlier (1998), the circumpolar eastward wind stress (as quantified by the Southern Annular Mode; SAM) showed a significant positive peak, and we have shown previously that the ACC peaked around 1998 in response. An eddy-resolving ocean model is used to investigate the delay between wind forcing and the eddy response, and demonstrates that the lag is due to the time taken to influence the deep circulation of the ACC. Winds over the Southern Ocean have shown a strong climatic increase over the past few decades. If this increase in winds is also reflected as an increase in eddy activity (as our analysis suggests it might), then the increased poleward heat flux may have played a significant role in the observed warming of the Southern Ocean.