Abstract
Abstract. Numerical dispersion models are used operationally worldwide to mitigate the effect of volcanic ash on aviation. In order to improve the representation of the horizontal dispersion of ash plumes and of the 3D concentration of ash, a study was conducted using the MOCAGE model during the European Natural Airborne Disaster Information and Coordination System for Aviation (EUNADICS-AV) project. Source term modelling and assimilation of different data were investigated. A sensitivity study of source term formulation showed that a resolved source term, using the FPLUME plume rise model in MOCAGE, instead of a parameterised source term, induces a more realistic representation of the horizontal dispersion of the ash plume. The FPLUME simulation provides more concentrated and focused ash concentrations in the horizontal and the vertical dimensions than the other source term. The assimilation of Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol optical depth has an impact on the horizontal dispersion of the plume, but this effect is rather low and local compared to source term improvement. More promising results are obtained with the continuous assimilation of ground-based lidar profiles, which improves the vertical distribution of ash and helps in reaching realistic values of ash concentrations. Using this configuration, the effect of assimilation may last for several hours and it may propagate several hundred kilometres downstream of the lidar profiles.
Highlights
Volcanic ash is a potential threat to aircraft engines (Clarkson et al, 2016), and the atmospheric transport of ash clouds can cause severe perturbations and even disruptions to air traffic and large economic losses (IATA, 2010)
In order to evaluate the benefit of assimilation of lidar profiles, comparisons of ash concentrations at the MOCAGE levels that correspond to the altitude of the aircraft measurements are provided
The flight is quite close to the Cabauw lidar, and as shown in Fig. 8, the result of assimilation still leads to underestimation of ash concentrations
Summary
Volcanic ash is a potential threat to aircraft engines (Clarkson et al, 2016), and the atmospheric transport of ash clouds can cause severe perturbations and even disruptions to air traffic and large economic losses (IATA, 2010). Continuous monitoring of ash clouds worldwide has been the duty of Volcanic Ash Advisory Centres (VAACs), which issue warnings and information in their respective domain of responsibility (ICAO, 2021). They provide at least qualitative information (i.e. presence of ash in different vertical layers, at different forecast lead times), and some VAACs issue quantitative estimates of ash concentration. In Europe, the London and Toulouse VAACs issue messages when volcanoes erupt in their domain of duty to warn of the presence of ash in different layers, defined as flight level (FL) bands: FL000–FL200, FL200–FL350 and FL350–FL550. The concentration forecasts are given in the same FL bands as stated above, up to 18 h ahead
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