A comparison of namemodel predictions and observations from the 2010 Eyjafjallajökull eruption

During the 2010 eruption of the Icelandic volcano Eyjafjallajökull, improvements were made to the modelling procedure at the UK Met Office, enabling peak ash concentrations within the volcanic cloud to be estimated. In this paper we describe the ash concentration forecasting method and its rationale. To validate the ash concentration modelling procedure, predicted ash concentrations are compared against peak ash observations obtained from both ground based and research aircraft instrumentation. This comparison highlights the many sources of error and the uncertainties involved. Despite the challenges of predicting ash concentrations, the ash forecasting method employed here is found to give useful guidance on likely ash concentrations. Predicted peak ash concentrations are found to lie within about one and a half orders of magnitude of the observed peak concentrations. Significant improvements in the agreement between modelled and observed values are seen if a buffer zone accounting for positional errors in the predicted ash cloud is used. Sensitivity of the predicted ash concentrations to the source properties (e.g. the eruption height and the vertical distribution of ash at the source) is assessed and, in some cases, seemingly minor uncertainties in the source properties are found to have a large effect on predicted ash concentrations.