Historical and projected changes in the Southern Hemisphere surface westerlies
Rishav Goyal, Alex Sen Gupta, Martin Jucker, Matthew H. England
Abstract
Changes to the Southern Hemisphere (SH) surface westerlies not only affect air temperature, storm tracks and precipitation; they are also pivotal in controlling global ocean circulation, ocean heat transport, and ocean carbon uptake. Wind-forced ocean perturbation experiments have commonly applied 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 without consistently accounting for physical constraints and can neglect important regional and seasonal differences. Here we quantify historical and future projected SH westerly wind changes based on examination of CMIP5, CMIP6 and reanalysis data. Under a high emission scenario, we find a projected end of 21 st Century annual mean westerly wind increase of ~10% and a poleward shift of ~0.8° latitude, although there are also significant seasonal and regional variations.