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Abstract:
The injection of sulfate aerosol precursors into the lower stratosphere (SAI) has been proposed to mitigate some of the negative impacts of rising greenhouse gas levels. Despite offsetting global mean surface temperature, various studies demonstrated that SAI will also increase lower stratospheric temperatures, which can impact on stratospheric and tropospheric circulation and thus potentially play an important role in modulating regional and seasonal climate variability, as well as influence the recovery of stratospheric ozone. However, so far most of the assessments of such an approach has come from climate model simulations in which SO2 is injected in the lower stratosphere in the equatorial region. While the choice of injection location could lead to different climate impacts, a systematic assessment of this has so far been missing.Here we address this using the CESM2-WACCM6 model, a comprehensive Earth System Model with interactive aerosol and stratospheric chemistry. We perform a set of five sensitivity experiments with constant point injections of 12 Tg-SO2/yr at 22 km at 30°S, 15°S, 0°, 15°N and 30°N. We demonstrate the strong dependence of the simulated changes in tropospheric circulation, including changes in the Hadley Circulation and tropospheric jets, and in the associated precipitation patterns on the latitude of SAI. We then examine the latitude dependence of stratospheric responses, focusing on the impacts on stratospheric ozone and the modes of high latitude variability (SAM and NAM). Overall, the results contribute to an increased understanding of the underlying physical processes that drive the atmospheric and climate response to SAI.
