Abstract
AbstractVolcanic activity is a major natural climate forcing and an accurate representation of volcanic aerosols in global climate models is essential. This is a complex task involving many uncertainties in the model design and setup and observations. We analyze the performance of the aerosol‐chemistry‐climate model SOCOL‐AERv2 for three medium‐sized volcanic eruptions. We focus on the impact of differences in volcanic plume height and SO2 estimates on the stratospheric aerosol burden. The influence of internal model variability and dynamics are addressed through an ensemble of free‐running and nudged simulations at different vertical resolutions. Comparing the modeled evolution of the stratospheric aerosol loading to satellite measurements reveals a good model performance. However, a conclusive validation is complicated by uncertainties in observations and emission estimates. The large spread in emitted sulfur amount and its vertical distribution consequently lead to differences in simulated aerosol burdens. Varying tropopause heights among free‐running simulations add to these differences, modulating the amount of sulfur injected into the stratosphere. In nudged mode, volcanic aerosol burden peaks are well reproduced, however changes in convection and clouds affect SO2 oxidation paths and cross‐tropopause transport, leading to increased background burdens compared to observations. This effect can be reduced by leaving temperatures unconstrained. A higher vertical resolution of 90 levels increases the stratospheric residence time of sulfate aerosol by reducing the diffusion out of the tropical reservoir. We conclude that the model set‐up (vertical resolution and free‐running vs. nudged) as well as forcing parameters (volcanic emission strength and plume height) contribute equally to the model uncertainties.
Highlights
Volcanic injections of sulfur dioxide SO2 into the stratosphere can have significant and sudden effects on the global climate
We focus on the impact of differences in volcanic plume height and SO2 estimates on the stratospheric aerosol burden
We evaluate the impact of the volcanic SO2 emission data on the simulated aerosol distribution by comparing a set of nudged model simulations using the four databases VolcBD1 to VolcBD4 to show the uncertainty related to the data retrieval after volcanic events
Summary
Volcanic injections of sulfur dioxide SO2 into the stratosphere can have significant and sudden effects on the global climate. SO2 can be injected into the stratosphere where it leads to the formation of sulfuric acid aerosol particles. These particles have a lifetime in the stratosphere of up to several years. Elevated aerosol levels in the stratosphere have various effects on the climate They prevent part of the solar radiation from reaching the Earth’s surface by scattering shortwave radiation back to space (e.g., Andersson et al, 2015). The cooling effect has inspired potential geoengineering schemes, where sulfur would artificially and continuously be injected into the stratosphere to achieve a counter effect to greenhouse gas-caused
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