The widespread disruption of European air trafﬁc in late April 2010, during the eruption of Eyjafjallajökull,showed the importance of early assessment of volcanic hazard from explosive eruptions. In this study, wefocus on the short-term hazard of airborne ash from a climatological perspective, focusing on eruptions onIceland. By studying eruptions of different intensity and frequency, we estimate the overall probability that ashconcentration levels considered hazardous to aviation are exceeded over different parts of Europe.
The method involves setting up a range of eruption scenarios based on the eruptive history of Icelandic volcanoes,and repeated simulation of these scenarios for 2 years' worth of meteorological data. Simulations are conducted using meteorological data from the ERA-Interim reanalysis set, which is downscaled using the Weather Researchand Forecasting (WRF) model. The weather data are then used to drive the Lagrangian particle dispersion model FLEXPART-WRF for each of the eruption scenarios. A set of threshold values, commonly used in Volcanic Ash Advisories, are used to analyze concentration data from the dispersion model.
We see that the dispersion of ash is highly dominated by the mid-latitude westerlies and mainly affect northern UK and the Scandinavian peninsula. The occurrence of high ash levels from Icelandic volcanoes is lower over con-tinental Europe but should not be neglected for eruptions when the release rate of ﬁne ash (<16 μm) is in theorder of 107 kg s−1 or higher.
There is a clear seasonal variation in the ash hazard. During the summer months, the dominating dispersiondirection is less distinct with some plumes extending to the northwest and Greenland. In contrast, during thewinter months, the strong westerly winds tend to transport most of the emissions eastwards. The affected area of a winter-time eruption is likely to be larger as high concentrations can be found at a further distance downwind from the volcano, effectively increasing the probability of hazardous levels of ash reaching the European continent.
The concentration thresholds for aviation, which were adopted after the Eyjafjallajökull eruption in 2010, havestrong inﬂuence on the hazard estimates for weaker eruptions but is less important for larger eruptions; thusash forecasts for weaker eruptions are likely more uncertain in comparison to larger eruptions.
2014. Vol. 286, 55-66 p.