Articles | Volume 8, issue 5
Development and technical paper
13 May 2015
Development and technical paper |  | 13 May 2015

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

S. G. Sivia, F. Gheusi, C. Mari, and A. Di Muro

Abstract. In mesoscale models (resolution ~ 1 km) used for regional dispersion of pollution plumes the volcanic heat sources and emissions of gases and aerosols, as well as the induced atmospheric convective 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 single sub-grid updraft model. It is used to represent volcano induced updrafts tested for a case study of the January 2010 summit eruption of Piton de la Fournaise (PdF) volcano. The validation of this modified formulation using a reference large eddy simulation (LES) focuses on the ability of the model to transport tracer concentrations up to 1–2 km above the ground in the lower troposphere as is the case of majority of PdF eruptions. The modelled volcanic plume agrees reasonably with the profiles of SO2 (sulfur dioxide) tracer concentrations and specific humidity found from the reference LES. Sensitivity tests performed for the modified formulation of the EDMF scheme emphasise the sensitivity of the parameterisation to ambient fresh air entrainment at the plume base.

Short summary
A sub-grid shallow convection scheme is adapted such that the size and intensity of the ground heat source provided by an eruption is initialised for modelling the sub-grid updraft. This parameterisation is tested on a 1-D single column model with a 1km resolution for an eruption observed at PdF in January 2010. The modelled plume agrees well with the SO2 concentrations found with LES and the adapted scheme emphasizes the sensitivity of the parameterisation to entrainment at the plume base.