Dynamics of Southern Hemisphere Atmospheric Circulation Response to Anthropogenic Aerosol Forcing

Anthropogenic aerosols, concentrated largely in the Northern Hemisphere, not only affect the local climate but also induce pronounced changes in atmospheric circulation that extend into the Southern Hemisphere (SH). In coupled historical single-forcing simulations, aerosol forcing induces a deceleration of both the subpolar jet (SPJ) and the subtropical jet (STJ) in SH in austral winter. Atmospheric general circulation model experiments indicate that the STJ is weakened by an interhemisphere gradient in the zonal mean sea surface temperature (SST) and an anomalous cross-equatorial Hadley circulation, while the SPJ response shares similar feedbacks with the greenhouse gas forcing. Specifically, atmospheric eddy adjustments are important for the SPJ change. The atmospheric response unique to anthropogenic aerosol forcing (e.g., cross-equatorial Hadley cell and the weakened SH STJ) can be exploited for climate change attribution.