Impact of the Latitude of Stratospheric Aerosol Injection on the Southern Annular Mode

The impacts of Stratospheric Aerosol Injection (SAI) strategies on the Southern Annular Mode (SAM) are analyzed with the Community Earth System Model. Using a set of simulations with fixed single-point SO₂ injections we demonstrate the first-order dependence of the SAM response on the latitude of injection, with the northern hemispheric and equatorial injections driving a response corresponding to a positive phase of SAM and the southern hemispheric injections driving a negative phase of SAM. We further demonstrate that the results can to first order explain the differences in the SAM responses diagnosed from the two recent large ensembles of geoengineering simulations utilizing more complex injection strategies – Geoengineering Large Ensemble and Assessing Responses and Impacts of Solar climate intervention on the Earth system with Stratospheric Aerosol Injection (GLENS and ARISE-SAI) – as driven by the differences in the simulated sulfate aerosol distributions. Our results point to the meridional extent of aerosol-induced lower stratospheric heating as an important driver of the sensitivity of the SAM response to the injection location.