Testing the stratospheric radiative heating and surface cooling caused by volcanic aerosols in models with prescribed and interactive volcanic plumes

Abstract:

The radiative forcing of the volcanic plume that comprises atmospheric heating and surface cooling defines the volcanic climate impact. The top-of-the-atmosphere forcing combines these two effects and characterizes the change of the energy balance of climate system as a whole.

In order to account for volcanic effect, the up-to-date climate models either use pre-calculated volcanic aerosol optical characteristics or interactively simulate the chemical and microphysical processes in the volcanic plume. However, they demonstrate a wide range of climate responses that are not always consistent with available observations. For example, the models tend to show that the stratosphere is overheated or underestimate the total cooling at the top of the atmosphere.

In this study, we evaluate the radiative forcing and climate responses in the models with prescribed volcanic aerosol datasets (CCMI, CMIP6, and SATO) and in those, where volcanic aerosols are interactively calculated. We show that the shortwave forcing is mostly sensitive to the total optical depth and single scattering albedo, and lesser extent to the vertical structure of the volcanic aerosols. The longwave forcing defines the most of the stratospheric heating. The different radiative schemes might produce different radiative forcing for the same datasets, and different datasets might cause different forcing in the same model. Together with inherent uncertainties of volcanic aerosol observations, those result in large uncertainties in forcing and a wide spread of climatic responses in the employed models.