High-resolution volcanic SO2 emissions in WACCM produce more realistic AODs

Volcanic climate impact is strongly correlated with how high its effluents reach in the atmosphere. Volcanic SO2 injected into the stratosphere can have a residence time of several years, whereas injections in the troposphere only have a residence time of weeks.We have performed simulations of the 2009 Sarychev eruption with the Community Earth System Model version 2 (CESM2), Whole Atmosphere Community Climate Model version 6 (WACCM6). We have compared the standard model dataset with two high-resolution datasets developed in our group to investigate the importance of utilizing highly vertically and horizontally resolved SO2 datasets. The default dataset M16 1 used in WACCM has a vertical resolution of 1 km and is released in one latitude longitude gridbox. Our two high-vertical resolution datasets, S21-3D, and S21-1D, were created from the dataset of Sandvik et al. 2. These datasets have a vertical resolution of 200 m, spanning from 7.6 to 18.6 km. S21-3D is distributed over several latitudes and longitudes, whereas S21-1D releases all SO2 in one latitude longitude gridbox to mimic the default dataset in WACCM. The SO2 from S21-3D, and S21-1D is injected at a higher altitude than the M16, leading to a longer residence time for both the SO2 and the formed stratospheric aerosol. The S21-3D dataset has the highest stratospheric SO2 and SO4 concentrations of the three simulations and the concentrations peak later than the other two simulations. The results from the S21-1D dataset are similar to those from the S21-3D simulation but with slightly lower concentrations. The simulated S21-3D AOD agrees with AOD from the space-borne lidar instrument CALIOP. In the simulation with the M16 dataset, the AOD is underestimated by >50%. The volcanic radiative forcing from the Sarychev eruption was 31% lower at the end of 2009 in the simulation with M16 compared to the simulation with S21-3D. Our results show that the vertical resolution of SO2 injections substantially impacts the models ability to correctly simulate the climate effects of volcanic eruptions, especially if the SO2 is injected in the vicinity of the tropopause. Future work will involve simulating a high vertically resolved dataset of SO2 of other volcanic eruptions since 2006. References 1 Mills,M. J.,A. Schmidt,R. Easter,S. Solomon,D. E. Kinnison,S. J. Ghan,R. R. III Neely,D. R. Marsh,A. Conley,C. G. Bardeen, et al. (2016),Global volcanic aerosol properties derived from emissions, 19902014, using CESM1(WACCM),J. Geophys. Res. Atmos., 121,23322348, doi:10.1002/2015JD024290. 2 Sandvik, O. S., Friberg, J., Sporre, M. K., and Martinsson, B. G.: Methodology to obtain highly resolved SO2 vertical profiles for representation of volcanic emissions in climate models, Atmos. Meas. Tech., 14, 71537165, https://doi.org/10.5194/amt-14-7153-2021, 2021.