High-resolution stratospheric volcanic SO₂ injections in WACCM

Abstract. Aerosols from volcanic eruptions impact our climate by influencing the Earth’s radiative balance. The degree of their climate impact is determined by the location and injection altitude of the volcanic SO2. To investigate the importance of utilizing correct injection altitudes we ran climate simulations of the June 2009 Sarychev eruptions with three SO2 datasets, in the Community Earth System Model Version 2 (CESM2) Whole Atmosphere Community Climate Model Version 6 (WACCM6). We have compared simulations with WACCM’s default 1 km vertically resolved dataset M16 with our two 200 m vertically resolved datasets, S21-3D and S21-1D. The S21-3D is distributed over a large area (30 latitudes and 120 longitudes), whereas S21-1D releases all SO2 in one latitude and longitude grid-box, mimicking the default dataset M16. For S21-1D and S21-3D, 95 % of the SO2 was injected into the stratosphere, whereas M16 injected only 75 % to the stratosphere. This difference is due to the different vertical distribution and resolution of SO2 in the datasets. The larger portion of SO2 injected into the stratosphere for the S21 datasets leads to more than twice as high sulfate aerosol load in the stratosphere for the S21-3D simulation compared to the M16 simulation during more than 8 months. The temporal evolution in AOD from two of our simulations, S21-3D and S21-1D, follows the observations from the space-borne lidar instrument CALIOP closely, while the AOD in the M16 simulation is substantially lower. This indicates that the injection altitude and vertical resolution of the injected volcanic SO2 substantially impact the model’s ability to correctly simulate the climate impact from volcanic eruptions. The S21-3D dataset with the high vertical and horizontal resolution resulted in global volcanic forcing of -0.24 W/m2 during the first year after the eruptions, compared with only -0.11 W/m2 for M16. Hence, our study high-lights the importance of using high-vertically resolved SO2 data in simulations of volcanic climate impact, and calls for a re-evaluation of further volcanic eruptions.