Significant contributions of volcanic aerosols to decadal changes in the stratospheric circulation

Abstract:

The stratospheric circulation is an important element of climate as it determines the concentration of radiatively active species like water vapour and aerosol above the tropopause. Climate models predict that increasing green-house gas levels speed up the stratospheric circulation. However, these results have been challenged by observational estimates of the circulation strength,constituting an uncertainty in current climate simulations. Here, we quantify the effect of volcanic aerosol on the stratospheric circulation focussing on the Mt. Pinatubo eruption and discussing further the minor extratropical volcanic eruptions after 2008. We show that the observed pattern of decadal circulation change over the past decades is substantially driven by volcanic aerosol injections, consistent with numerical global atmosphere-chemistry model EMAC (ECHAM/MESSy Atmospheric Chemistry) in the lower stratosphere. Thus,climate model simulations need to realistically take into account the effect of volcanic eruptions, including the minor eruptions after 2008, for a reliable re-production of observed stratospheric circulation changes.