The Role of Southern High Latitude Wind Stress in Global Climate

In this paper, the role of westerly winds at southern highlatitudes in global climate is investigated in a fully coupledocean-atmosphere general circulation model. In the model, the windstress south of 40^oS is turned off with ocean andatmosphere fully coupled both locally and elsewhere. The coupledmodel explicitly demonstrates that a shutdown of southern highlatitude wind stress induces a general cooling over the AntarcticCircumpolar Current (ACC) region, with surface Ekman flow andvertical mixing playing competitive roles. This cooling leads to anequatorward expansion of sea ice and triggers an equivalentbarotropic response in the atmosphere to accelerate westerlyanomalies.The shutdown of southern high latitude wind stress alsosignificantly reduces global meridional overturning circulation(MOC). The Antarctic MOC (AnMOC) nearly disappears while theAtlantic MOC (AMOC) is weakened by 50%, suggesting a strongcontrol of the southern high latitude winds over the thermohalinecirculation (THC). In spite of a substantial weakening of the AMOC,the interhemispheric SST seesaw appears to be not significant due toan equatorward extension of the southern extratropical coolingthrough coupled wind-evaporation-SST (WES) feedback. In addition, itis found that the weakening of Atlantic MOC by as much as 50% iscapable of cooling the time mean subpolar Atlantic temperature byonly about 1^oC.