The response of mixed-phase and ice clouds to volcanic eruptions- A model case study of the Raikoke eruption 2019

Aerosol-cloud-interactions are one of the major causes of uncertainty in the radiative forcing as presented in the IPCC report WG1 (2021). The aerosols in the atmosphere can act as cloud condensation nuclei (CCNs) or ice nucleating particles (INPs) and affect cloud properties. A quantification of the impact of aerosols on these properties is difficult since clouds are also strongly affected by synoptic conditions.

Volcanic eruptions are an ideal testbed as they cause a local perturbance of aerosol concentrations in the atmosphere. The emitted aerosols such as SO2 reacting to sulfuric acid or ash can act as CCNs or INPs respectively. By comparing a simulation with and without the volcanic eruption the impact can be quantified directly. The simulation with an eruption can be validated by comparison to observations, e.g. satellite data.

In the presented work, the eruption of the Raikoke volcano in 2019 is simulated using the ICOsahedral Nonhydrostatic model (ICON) and the module for Aerosols and Reactive Trace gases (ART). The model is run in limited area mode on a R2B10 grid with about 2.5 km horizontal resolution for a time span of 3 days. The volcanic plume is simulated using a setup provided by J. Bruckert. During this time, the plume overlaps with cloud systems associated with a low-pressure system east of the volcano. The simulations with and without the eruption are compared to observational data to improve the implemented interaction mechanisms between cloud particles and volcanic aerosols with a focus on ice nucleation due to volcanic ash particles. Additionally, a new parameterization for volcanic ash formulated by Umo et al. (2021) based on laboratory experiments is implemented and compared to the commonly used ice nucleation parameterizations for mineral dust by e.g. Ullrich et al. (2017). First results of an offline calculation of the ice nucleation active site show a decrease in the ice nucleating efficiency for the parameterization for volcanic ash.

These first results on the interactions between the volcanic ash plume and mixed-phase and ice clouds will be presented.