Improving volcanic ash forecasts with ensemble-based data assimilation

• Main Author: Fu, Guangliang (author)
• Other Authors: Lin, H.X. (promotor), Heemink, A.W. (promotor), Delft University of Technology (degree granting institution)
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: Data assimilation; volcanic ash forecast; aircraft data; satellite data; high performance computing; spurious correlations; Eyjafjallajökull
• Online Access: http://resolver.tudelft.nl/uuid:97d82967-998a-413d-b1f8-8c46f3e064cc; https://doi.org/10.4233/uuid:97d82967-998a-413d-b1f8-8c46f3e064cc

The 2010 Eyjafjallajökull volcano eruption had serious consequences to civil aviation. This has initiated a lot of research on volcanic ash forecasting in recent years. For forecasting the volcanic ash transport after eruption onset, a volcanic ash transport and diffusion model (VATDM) needs to be run with Eruption Source Parameters (ESPs) such as plume height and mass eruption rate as input, and with data assimilation techniques to continuously improve the forecast. Reliable and accurate ash measurements are crucial for providing successful ash clouds advices. In the first phase of this research work, simulated aircraft-based volcanic ash measurements, will be assimilated into a transport model to identify the potential benefit of this kind of observations in an assimilation system. The results show that assimilating aircraft-based measurements can improve the state of ash clouds, and can provide an improved forecast. We also show that for an advice on the aeroplane flying level, aircraft-based measurements should preferably be taken at this level. Furthermore it is shown that in order to make an acceptable advice for aviation decision makers, accurate knowledge about uncertainties of ESPs and measurements is of great importance. The forecast accuracy of distal volcanic ash clouds is important for providing valid aviation advice during volcanic ash eruptions. However, because the distal part of a volcanic ash plume is far from the volcano, the influence of eruption information on this part becomes rather indirect and uncertain, resulting in inaccurate volcanic ash forecasts in these distal areas. In this thesis, we use real-life aircraft in situ observations, measured in the North-West part of Germany during the 2010 Eyjafjallajökull eruption, in an ensemble-based data assimilation system to investigate the potential improvement on the forecast accuracy with regard to the distal volcanic ash plume. We show that the error of the analyzed volcanic ash state can be significantly reduced by assimilating real-life ...