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Abstract:
The accurate modelling of the emission of ash into the atmosphere during explosive volcanic eruption is a fundamental step for reliable ash dispersal simulations outputs. Particularly for operational applications (e.g., ash dispersion forecasts issued by the Volcanic Ash Advisory Centres), fast and reliable plume simulation tools are necessary, which is why several simplified plume models have been developed. Some of these models take into account the effect of wind, which is crucial for the estimation of the emission rate of ash in case of bent-over plumes. These models accounts for the enhanced entrainment by means of an entrainment coefficient, whose value is still a matter of debate in the community. Concerning the distortion effect, it has been often suggested that in case of bent-over plumes it is better to correct H by decreasing it by subtracting the plume radius, if available.
By comparing observations with measured data and using REFIR, a tool that allows obtaining time series of mass eruption rate by using a combination of simplified plume models, we suggested a new estimate of the wind entrainment coefficient and a new plume centreline correction for the Eyjafjallajökull 2010 eruption. In this presentation we introduce the results of these corrections and their application to atmospheric dispersion simulations carried out by using the simulation tool FALL3D. We show how the simulation outputs, in particular the extent of the volcanic ash cloud and the ash concentration, are significantly affected by the chosen parametrization of entrainment and centreline correction.
