Explicit simulation of volcanic eruption plumes in atmospheric models: first results and implications

Explosive volcanic eruptions emit large amounts of solid and gaseous materials into the atmosphere, thereby affect weather and climate and pose hazards to human health and aviation. To constrain those impacts it is important to understand dynamical, microphysical and chemical evolution of the eruption plumes. Especially the density of a plume and atmospheric conditions control the dynamical development of an eruption plume. To simulate those plumes correctly the flow field has to be described as a multi-constituent multiphase flow system. This is realized in eruption plume models but not in the conventional atmospheric models. The latter neglect the partial density of ash particles in relation to total air mass and cannot treat for the effect of ash particles on dynamics during simulations. To overcome this limitation, we use a modified version of ICOsahedral Nonhydrostatic model with Aerosols and Reactive Trace gases (ICON-ART) in which we extended the existing equation set. This version of ICON-ART can consider a source of total mass during the eruption as well as a mass sink due to sedimentation of ash and other constituents. The mass source is accounted by an additional source term for total density, and the mass sink is accounted by implementing the lower boundary condition of the vertical velocity at the surface. This leads to a conserved dry air mass and changing total air mass, which affects dynamics and is crucial for handling multiphase flows correctly. Additionally, a momentum forcing as well as a temperature forcing cause the strong updraft within the plume region.

We simulated the real case of the Raikoke eruption in 2019 in a LES-mode for more detailed investigations of the plume. In this experiment, in addition to ash, we also emit water vapor which might lead to an additional upward motion in the convective plume region due to latent heat release when clouds develop. The results show that the model is able to reproduce the observed plume geometry vertically and horizontally. Moreover, we simulated gravity waves that developed during the eruption around the volcano. In combination with microphysics and aerosol dynamics, the new implementations in ICON-ART enable detailed investigations of volcanic plume development across scales.