Historical and Projected Changes in the Southern Hemisphere Surface Westerlies

Abstract

The Southern Hemisphere (SH) surface westerlies fundamentally control regional patterns of air temperature, storm tracks, and precipitation while also regulating ocean circulation, heat transport and carbon uptake. Wind-forced ocean perturbation experiments commonly apply idealized poleward wind shifts ranging between 0.5 and 10 degrees of latitude and wind intensification factors of between 10% and 300%. In addition, changes in winds are often prescribed ad hoc as a zonally uniform anomaly that neglects important regional and seasonal differences. Here we quantify historical and projected SH westerly wind changes based on examination of CMIP5, CMIP6, and reanalysis data. We find a significant reduction in the location bias of the CMIP6 ensemble and an associated reduction in the projected poleward shift compared to CMIP5. Under a high emission scenario, we find a projected end of 21st Century ensemble mean wind increase of ∼10% and a poleward shift of ∼0.8° latitude, although there are important seasonal and regional variations.