Ash Cloud Forecasts: Decide on the location of the outbreak

Why the spread of volcanic ash clouds is difficult to predict

Eruption cloud of Eyjafjallajökull on April 17, 2010 © Árni Friðriksson / CC-by-sa 3.0
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How far does the ash cloud of a volcanic eruption? And how much does it threaten flight safety? These issues and the associated uncertainties led to a Europe-wide air traffic chaos in April 2010 following the eruption of the Eyjafjallajökull volcano. Now researchers have compared propagation simulations with a variety of readings and pinpointed the source of the problem: too little information from the outbreak. Because the knowledge of the height of the eruption cloud and the exact particle sizes and concentrations at the point of outbreak are decisive for the quality of the propagation prognosis.

After the Eyjafjallajökull eruption in April / May 2010, the authorities had closed large parts of European airspace for safety reasons, resulting in more than 100, 000 canceled flights in the first week. The resulting traffic chaos had sparked fierce criticism of airlines and passengers, as the authorities had relied only on propagation models. The outbreak of Icelandic volcano Grimsvötn in May 2011 also resulted in short-term blockages of airspace based on the models of the Volcanic Ash Advisory Center (VAAC) in London. The quality of such propagation models is therefore of great importance

Importance for air traffic.

Simulation and measured values ​​in comparison

Unlike sand dust, volcanic ash can melt in the engines of modern aircraft, severely damaging them. For safety reasons, therefore, limits have been set for the concentration of ash: at concentrations below 200 micrograms per cubic meter of air, it is assumed that there is no risk to air traffic. At concentrations of 2000 micrograms per cubic meter, however, air traffic is prohibited. Propagation models therefore need not only predict the route and speed of the ash cloud, but also the concentration of ash particles.

Researchers from the Leibniz Institute for Tropospheric Research (IfT), the University of Leeds and the German Aerospace Center (DLR) have now simulated the ash spread for the days between April 14 and 18, 2010. The input data used included satellite data for determining the height of the volcanic ash cloud as well as results of DLR aircraft measurements on the size distribution of the ash particles. The model results were compared with a variety of measurements from Europe. Among them were measurements of the Leipzig Lidar at the IfT, which was able to investigate the ash cloud over Leipzig with the help of a laser beam. display

Concentration forecasts too inaccurate

"It showed that the temporal and spatial spread in the models works well, but the predictions about the concentration of the ash particles are still inaccurate, " explains Ina Tegen from

Institute for Tropophosphate Research. From the scientists' point of view, this is mainly due to the input data. If the statements about the height of the volcanic eruption or the particle concentrations at the outbreak site are not sufficiently known, then these errors continue in the prognosis and can lead to inaccurate assessments about the safety of the aircraft in the air f lead.

Since the ashes in different layers of the air can spread differently depending on the altitude, information is needed in which heights of the volcano hurls which amounts of ash. For the troposphere researchers, the eruption of the Eyjafjallaj kull was an opportunity to improve knowledge about the spread of dust particles in the atmosphere, because these tiny particles are not only important the climate, but can also have a variety of effects on human health. The findings could improve the models in the future and thus the accuracy of the prediction of the ash concentration in future outbreaks. (Atmospheric Environment, 2011; DOI: 10.1016 / j.atmosenv.2011.05.021)

(Leibniz Institute of Tropospheric Research, 31.05.2011 - NPO)