Simulations and parameterisation of shallow volcanic plumes of Piton de la Fournaise, Réunion Island, using Méso-NH version 4-9-3

摘要

In mesoscale models (resolution ~ 1 km) used for regional dispersion of pollution plumes thevolcanic heat sources and emissions of gases and aerosols, as well as the induced atmosphericconvective motions, are all sub-grid-scale processes (mostly true for weak effusive eruptions)which need to be parameterised. We propose a modified formulation of the EDMF scheme(eddy diffusivity/mass flux) proposed by Pergaud et al. (2009) which is based on a singlesub-grid updraft model. It is used to represent volcano induced updrafts tested for a case studyof the January 2010 summit eruption of Piton de la Fournaise (PdF) volcano. The validation of thismodified formulation using a reference large eddy simulation (LES) focuses on the ability of themodel to transport tracer concentrations up to 1–2 km above the ground in the lower troposphereas is the case of majority of PdF eruptions. The modelled volcanic plume agrees reasonably withthe profiles of SO₂ (sulfur dioxide) tracer concentrations and specific humidity found from thereference LES. Sensitivity tests performed for the modified formulation of the EDMF schemeemphasise the sensitivity of the parameterisation to ambient fresh air entrainment at the plumebase.