Impacts of stratospheric aerosol injection on precipitation and winds associated with extratropical cyclones in the Southern Hemisphere

Abstract This study seeks to describe the impact of Stratospheric Aerosol Injection (SAI) under climate change scenarios on precipitation and 10 m winds caused by extratropical cyclones in the Southern Hemisphere, using data from three international initiatives: the Earth system with SAI, the stratospheric aerosol geoengineering large ensemble, and the Geoengineering Model Intercomparison Project (GeoMIP/G6Sulfur). Cyclone-related variables were examined across three time periods—the reference period (2015–2024), the near future (2040–2059), and the far future (2080–2099)—with a focus on four key subdomains: the Southeast Pacific Ocean, Southwest Atlantic Ocean, Southern Africa, and Australia. In the first part of the study, we assessed precipitation and wind intensity associated with cyclones under both SAI and no-SAI scenarios. Results show that the SAI scenario generally leads to cyclones with reduced precipitation and weaker winds compared to the no-SAI scenario, though exceptions were noted in the GeoMIP/G6Sulfur simulations. In the second part, we analyzed the contribution of extratropical cyclones to total precipitation and wind intensity within each subdomain. The findings reveal that this contribution decreases under the SAI scenario from the near to the far future. This trend is consistent across both precipitation and wind intensity. In the final part of the study, we examined the synoptic characteristics of extratropical cyclones in each subdomain using composite analysis. During the reference period, the three initiatives successfully reproduced the typical structure of extratropical cyclones as observed in reanalysis data, albeit with differences in the magnitude of precipitation. In contrast, there is no spatial homogeneity in the composite differences between SAI and no-SAI during the future periods. For example, one project may show reduced precipitation in a specific quadrant of the cyclone in one domain, but display a different pattern in others. This variability is also observed across different projects and time periods analyzed. The main conclusion is that SAI appears to mitigate some of the effects of global warming by weakening extratropical cyclones, and contributing to decreasing regionally precipitation and wind intensity associated with these systems.