The role of southern high latitude wind stress in global climate

Abstract

In this paper, the role of westerly winds at southern high latitudes in global climate is investigated in a fully coupled ocean-atmosphere general circulation model. In the model, the wind stress south of 40°S is turned off with ocean and atmosphere fully coupled both locally and elsewhere. The coupled model explicitly demonstrates that a shutdown of southern high latitude wind stress induces a general cooling over the Antarctic Circumpolar Current (ACC) region, with surface Ekman flow and vertical mixing playing competitive roles. This cooling leads to an equatorward expansion of sea ice and triggers an equivalent barotropic response in the atmosphere to accelerate westerly anomalies. The shutdown of southern high latitude wind stress also significantly reduces global meridional overturning circulation (MOC). The Antarctic MOC (AnMOC) nearly disappears while the Atlantic MOC (AMOC) is weakened by 50%, suggesting a strong control of the southern high latitude winds over the thermohaline circulation (THC). In spite of a substantial weakening of the AMOC, the interhemispheric SST seesaw appears to be not significant due to an equatorward extension of the southern extratropical cooling through coupled wind-evaporation-SST (WES) feedback. In addition, it is found that the weakening of Atlantic MOC by as much as 50% is capable of cooling the time mean subpolar Atlantic temperature by only about 1°C.