Abstract. Despite offsetting global mean surface temperature, various studies demonstrated that stratospheric aerosol injection (SAI) could influence the recovery of stratospheric ozone and have important impacts on stratospheric and tropospheric circulation, thereby potentially playing an important role in modulating regional and seasonal climate variability. However, so far, most of the assessments of such an approach have come from climate model simulations in which SO2 is injected only in a single location or a set of locations. Here we use CESM2-WACCM6 SAI simulations under a comprehensive set of SAI strategies achieving the same global mean surface temperature with different locations and/or timing of injections, namely an equatorial injection, an annual injection of equal amounts of SO2 at 15∘ N and 15∘ S, an annual injection of equal amounts of SO2 at 30∘ N and 30∘ S, and a polar strategy injecting SO2 at 60∘ N and 60∘ S only in spring in each hemisphere. We demonstrate that despite achieving the same global mean surface temperature, the different strategies result in contrastingly different magnitudes of the aerosol-induced lower stratospheric warming, stratospheric moistening, strengthening of stratospheric polar jets in both hemispheres, and changes in the speed of the residual circulation. These impacts tend to maximise under the equatorial injection strategy and become smaller as the aerosols are injected away from the Equator into the subtropics and higher latitudes. In conjunction with the differences in direct radiative impacts at the surface, these different stratospheric changes drive different impacts on the extratropical modes of variability (Northern and Southern Annular modes), including important consequences on the northern winter surface climate, and on the intensity of tropical tropospheric Walker and Hadley circulations, which drive tropical precipitation patterns. Finally, we demonstrate that the choice of injection strategy also plays a first-order role in the future evolution of stratospheric ozone under SAI throughout the globe. Overall, our results contribute to an increased understanding of the fine interplay of various radiative, dynamical, and chemical processes driving the atmospheric circulation and ozone response to SAI and lay the foundation for designing an optimal SAI strategy that could form a basis of future multi-model intercomparisons.
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 SO2injections 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.
more » « less- NSF-PAR ID:
- 10443895
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 19
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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