Localized injections of interactive volcanic aerosols and their climate impacts in a simple general circulation model

Abstract. A new set of standalone parameterizations is presented for simulating the injection, evolution, and radiative forcing by stratospheric volcanic aerosols against an idealized Held-Suarez-Williamson atmospheric background in the Energy Exascale Earth System Model version 2. Sulfur dioxide (SO₂) and ash are injected into the atmosphere with a specified profile in the vertical, and proceed to follow a simple exponential decay. The SO₂ decay is modeled as a perfect conversion to a long-living sulfate aerosol which persists in the stratosphere. All three species are implemented as tracers in the model framework, and transported by the dynamical core’s advection algorithm. The aerosols contribute simultaneously to a local heating of the stratosphere and cooling of the surface by a simple plane-parallel Beer-Lambert law applied on two zonally-symmetric radiation broadbands in the longwave and shortwave range. It is shown that the implementation parameters can be tuned to produce realistic temperature anomaly signatures of large volcanic events. In particular, results are shown for an ensemble of runs that mimic the volcanic eruption of Mt. Pinatubo in 1991. The design requires no coupling to microphysical subgrid-scale parameterizations, and thus approaches the computational affordability of prescribed-aerosol forcing strategies. The idealized simulations contain a single isolated volcanic event against a statistically uniform climate, where no background aerosols or other sources of externally-forced variability are present. This model configuration represents a simpler-to-understand tool for the development of climate source-to-impact attribution methods.