How do volcanic eruptions effect cloud hydrometeor properties?A case study of the Raikoke eruption 2019

One of the major causes for uncertainties in atmospheric modelling are aerosol-cloud-interactions as stated in the IPCC report WG1 in 2021. The aerosols available in the atmosphere can act as cloud condensation nuclei (CCNs) or ice nucleating particles (INPs) and thereby have a direct effect on cloud formation and properties. The investigation of those effects is not easy since these properties also depend on other atmospheric conditions such as the synoptic state. In volcanic eruptions the emitted aerosols are a local perturbation in the atmospheric aerosol distribution independent of synoptic conditions. The volcanic aerosols such as SO₂ reacting to sulfuric acid or volcanic ash can act as CCNs and INPs respectively. Simulations with and without the eruption can be compared to directly quantify the effect of the volcanic aerosols on cloud properties. The simulations with an eruption can be compared to obervational data to verify the simulation results and improve the simulation setup.

In the presented work, the eruption of the Raikoke volcano in 2019 has been simulated using the ICOsahedral Nonhydrostatic model (ICON) and the module for Aerosols and Reactive Trace gases (ART) in limited area mode with up to 2.5 km horizontal resolution. The simulated area contains both the location of the eruption and a large cloud system consisting of liquid, mixed-phase and ice clouds. The eruption is modelled using the module fplume, a dynamics driven model predicting the vertical distribution of the emitted aerosols at the source. An ice nucleation parameterization specific for volcanic ash derived in laboratory experiments by Umo et al. (2021) for heterogeneous freezing has been implemented in the model.

First preliminary results will be shown with a focus on cloud hydrometeor properties of mixed-phase and ice clouds. Due to the location of the volcanic plume above the low liquid clouds it is found that ice crystal properties are more affected than liquid hydrometeors. The results using the ice nucleation parameterization by Umo et al. are compared to the commonly used parameterization for mineral dust particles by Ullrich et al. (2017). By specifically enabling aerosol-radiation and aerosol-cloud interactions seperately the direct and indirect impact of the eruption on the radiation balance will be quantified.