Multi-model simulations of the evolution of aerosols and water vapor from the Hunga eruption.

The eruption of the Hunga volcano on January 15, 2022, was unprecedented in the satellite record because of the ~150 Tg of water injected in the stratosphere, paired to a relatively low (~0.5 Tg) sulfur dioxide injection. The uniqueness  of this eruption provides an opportunity to evaluate chemistry-climate models over a new range of conditions, different from the sulfur rich eruptions on which they have generally been tested. We  describe coordinated Hunga simulations from ten chemistry climate models with prognostic aerosol modules and show how the presence of the volcanic water vapor led to larger particles than would occur in a water-poor eruption. This has the effect of rapidly increasing the stratospheric aerosol optical depth in the first month and accelerating the settling of the volcanic aerosols in the following months. While the models are able to reproduce the observed evolution of the water vapor eruption plume and the distribution of volcanic aerosols. they fail to simulate the aerosol optical depth. Most of the difference between models and observations, and among models themselves, can be traced to the aerosol microphysics, which is highly dependent on the parameterizations made by each model.