Extratropical Cyclone and Storm track Responses to Stratospheric Aerosol Injection in High-Resolution CESM Simulations

Abstract. Extratropical cyclones (ETCs) drive weather variability and dominate extreme wind and precipitation events in storm track regions. This study investigates ETC responses to stratospheric aerosol injection (SAI) compared to a high-emission (RCP8.5) and a reference scenario, using high-resolution CESM simulations with 0.25°/0.1° horizontal resolution in the atmosphere/ocean. Storm track activity is quantified using 2–6-day bandpass-filtered mean sea level pressure (MSLP), and individual cyclones are tracked using CyTRACK. SAI produces regionally asymmetric responses: the North Pacific storm track shifts equatorward, linked to SST changes, while the North Atlantic storm track shifts poleward, linked to an SAI-induced positive North Atlantic Oscillation (NAO) phase. The RCP8.5 scenario shows the fewest cyclones in both hemispheres, whereas cyclone frequency partially recovers toward reference levels under SAI. A risk analysis linking extreme events to ETCs through combined distance and vorticity masking shows that extreme precipitation events (>50 mm/day) increase by 18 % in both hemispheres under RCP8.5 but decrease by 11 % in the Northern Hemisphere and 6 % in the Southern Hemisphere under SAI. Near-surface wind extremes >25 m/s) decrease by 11 % under RCP8.5 and 5 % under SAI in the Northern Hemisphere, but with different spatial patterns. In the Southern Hemisphere, extreme wind events decrease by 4 % under RCP8.5 and 5 % under SAI. These findings demonstrate that SAI does not simply reverse warming-induced changes but produces new circulation patterns, highlighting the need for regional assessments of geoengineering impacts on midlatitude weather extremes.