The study has found that the influence of climate change and the depletion in stratospheric ozone are the major drivers over the Atlantic Oceans that shift the westerly winds further south. However, over the Pacific and Indian oceans, natural variations induced by sea surface temperature changes in the tropical Pacific also play an important role in the southward shift and can intensify these winds in the southwest Pacific Ocean.

A major component of this natural variation is the Interdecadal Pacific Oscillation (IPO). This is a shift in the state of sea surface temperatures, air pressure and wind direction over decadal timescales. The study found that the state of the IPO in the early-21st Century led to warming in the subtropics and mid-latitudes, which increased the generation of transient eddies at around 55°S, acting to strengthen and shift the winds south. Changes in the Southern Hemisphere westerly winds have profound impacts on Southern Hemisphere rainfall patterns, the Southern Ocean and Antarctica. Understanding the mechanisms that create these wind shifts has significant implications for prediction of Southern Hemisphere climate over the coming decades.

Paper: Yang, D., Arblaster, J. M., Meehl, G. A., England, M. H., Lim, E. P., Bates, S., & Rosenbloom, N. (2020). Role of tropical variability in driving decadal shifts in the Southern Hemisphere summertime eddy-driven jet. Journal of Climate, (2020). https://doi.org/10.1175/JCLI-D-19-0604.1