Calculating the Self-Consistent Vertical Structure of a Multicomponent Stratospheric Volcanic Plume in a Fine-Resolution Regional Model

Abstract:

It is well known that the vertical distribution of optically-active aerosols and gases in a volcanic stratospheric plume affects the life-time and transport of volcanic cloud. Here we focus on the intermediate range evolution that follows the initial release of volcanic materials and is governed by the complex dynamical/physical/chemical/microphysical processes that eventually define the vertical structure and altitude of the volcanic cloud. This intermediate stage was never completely simulated because of insufficient spatial resolution and lack of required physics in the large-scale models. We modified the regional WRF-Chem v3.7.1 model to calculate the evolution of stratospheric volcanic emissions with potentially cloud-resolving grid spacing. The simulation for the Pinatubo-size eruption are conducted for 6 months in a tropical belt of 45S – 45N and is driven by the boundary conditions from ERA-Interim reanalysis. The right phase of QBO is imposed by the spectral nudging of stratospheric zonal wind. We have simultaneously injected water vapor, ash, SO2 and have calculated vertical lifting and horizontal transport of volcanic plume accounting for the radiative effect of all of the ingredients: SO2, ash, water vapor, and sulfate. We consider interactively the sulfur cycle, differential self-lofting, gravitational deposition of ash and sulfate particles, calculate OH, but keep ozone prescribed from observations. Differential radiative heating and gravitational deposition lead to a separation of ash, SO2 and sulfate plumes with the SO2 tending to penetrate into the Mesosphere. The plume evolution, especially effect of water, depends drastically on the initial height of the emission. The sulfate plume rises 5-7 km above the level of initial injection and its equilibrium height is sensitive to the injection level and strongly affects the horizontal dispersion of a volcanic cloud.