The Impact of 2022 Hunga Tonga-Hunga Ha’apai (Hunga) Eruption on Stratospheric Circulation and Climate

     The Hunga Tonga-Hunga Ha’apai (Hunga) volcanic eruption in January 2022 injected a substantial amount of water vapor and a moderate amount of SO₂ into the stratosphere. Both satellite observations in 2022 and subsequent chemistry-climate model simulations forced by realistic Hunga perturbations reveal large-scale cooling in the Southern Hemisphere (SH) tropical to subtropical stratosphere following the Hunga eruption. This study analyzes the drivers of this cooling, including the distinctive role of anomalies in water vapor, ozone, and sulfate aerosol concentration on the simulated climate response to the Hunga volcanic forcing, based on climate simulations with prescribed chemistry/aerosol. Simulated circulation and temperature anomalies based on specified-chemistry simulations show good agreement with previous coupled-chemistry simulations and indicate that each forcing of ozone, water vapor, and sulfate aerosol from the Hunga volcanic eruption contributed to the circulation and temperature anomalies in the Southern Hemisphere stratosphere. Our results also suggest that 1) the large-scale stratospheric cooling during the austral winter was mainly induced by changes in dynamical processes, not by radiative processes, and that 2) ozone’s radiative feedback contributed to the prolonged cold temperature anomalies in the lower stratosphere (~70 hPa level) and hence to long lasting cold conditions of the polar vortex.