Abstract
Abstract. High-quality volcanic ash forecasts are crucial to minimize the economic impact of volcanic hazards on air traffic. Decision-making is usually based on numerical dispersion modelling with only one model realization. Given the inherent uncertainty of such an approach, a multi-model multi-source term ensemble has been designed and evaluated for the Eyjafjallajökull eruption in May 2010. Its use for flight planning is discussed. Two multi-model ensembles were built: the first is based on the output of four dispersion models and their own implementation of ash ejection. All a priori model source terms were constrained by observational evidence of the volcanic ash cloud top as a function of time. The second ensemble is based on the same four dispersion models, which were run with three additional source terms: (i) a source term obtained from a model background constrained with satellite data (a posteriori source term), (ii) its lower-bound estimate and (iii) its upper-bound estimate. The a priori ensemble gives valuable information about the probability of ash dispersion during the early phase of the eruption, when observational evidence is limited. However, its evaluation with observational data reveals lower quality compared to the second ensemble. While the second ensemble ash column load and ash horizontal location compare well to satellite observations, 3D ash concentrations are negatively biased. This might be caused by the vertical distribution of ash, which is too much diluted in all model runs, probably due to defaults in the a posteriori source term and vertical transport and/or diffusion processes in all models. Relevant products for the air traffic management are horizontal maps of ash concentration quantiles (median, 75 %, 99 %) at a finely resolved flight level grid as well as cross sections. These maps enable cost-optimized consideration of volcanic hazards and could result in much fewer flight cancellations, reroutings and traffic flow congestions. In addition, they could be used for route optimization in the areas where ash does not pose a direct and urgent threat to aviation, including the aspect of aeroplane maintenance.
Highlights
Volcanic eruptions that spread out ash over large areas can have tremendous economic consequences, they are relatively rare compared to other high-impact natural hazards
In the EUNADICS-AV project, it has been argued that ash concentration maps at several flight levels are important as they can be used in the flight planning software
The whole flight track is not taken into account; rather, only some locations, which correspond to points where the highest values of ash load were measured, are considered
Summary
Volcanic eruptions that spread out ash over large areas can have tremendous economic consequences, they are relatively rare compared to other high-impact natural hazards (such as tropical cyclones, storms, etc). Following the consequences of the Eyjafjallajökull eruption in Europe, the London and Toulouse VAACs’ procedures have changed, and they provide concentration charts in the flight level (FL) bands FL000-200, FL200350, and FL350-550 for three contamination levels: 0.2 to 2 mg m−3 (low contamination), 2 to 4 mg m−3 (medium contamination), and > 4 mg m−3 (high contamination) (ICAO, 2016). These volcanic ash contamination charts (up to 18 h ahead) indicate hazardous zones and hazard levels, which can be used by authorities for flight safety
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