The Eyjafjallajökull eruption: How well were the volcanic ash clouds predicted?

1. The Eyjafjallajökull eruption: How well were the volcanic ash clouds predicted? Helen Dacre and Alan Grant Robin Hogan, Dave Thomson, Ben Devenish, Jim Haywood, Franco Marenco, Ben Johnson, Albert Ansmann, Ina Mattis and Lieven Clarisse

2. Motivation

3. Motivation EUROCONTROL report from 14 - 20 April: • 75% of European airspace closed • 100,000 flights cancelled • 10 million passenger journeys affected • 7000 flights cancelled up to 18 May

4. Talk Outline • Operational volcanic ash transport and dispersion (VATD) models • Quantitative model predictions • Source parameter uncertainty • Meteorological input uncertainty • Future Work

5. Operational VATD Modelling MODEL OUTPUT INPUT

6. Eyjafjallajökull Source Parameters H

7. Column Integrated Mass Concentration 14-18th April

8. Fine-ash Fraction? Mastin et al. (2009)

9. Comparison with ground based lidar

10. IASI Volcanic Ash Product 12UTC 16th April 00UTC 16th April Leipzig Leipzig 22UTC 15th April 10UTC 16th April Leipzig Leipzig L. Clarisse

11. Scaling to Observed Concentration at Leipzig A. Ansmann I. Mattis 1.5%

12. MODIS Visible Image 12UTC 16th April Chilbolton 10:44UTC 16th April 12:24UTC 16th April (Hogan et al. 2011)

13. Scaling to Observed Concentration at Chilbolton (Hogan et al. 2011)

14. Eruption Plume Height Data 5-minute time series of plume height from the Icelandic radar (data from Petersen and Arason) Missing scan Cloud obscured Mountain obscured

15. Plume Height Reconstruction 4% 3%

16. Comparison with aircraft lidar

18. 5th May

19. 14th May

21. 5th 7.5% 14th 1.3 - 2.5% 17th 1.6%

22. Peak Concentration and Layer Width • Ash layer width = integrated column mass/max concentraton 5% 2%

23. Comparison with Airborne spectrometers

24. Fine Ash Particle Size Distribution 14th 2.1%

25. Fine Ash Particle Size Distribution 5th 10.6% 14th 2.1% 17th 3.1%

26. Fine Ash Fraction 3.5%

27. Summary • It is possible to identify the ash layers detected with the ground based and airborne lidars with layers in the NAME simulations • Observed ash layers are thinner than teh simulated layers and at lower altitude • Horizontal and vertical structure of the simulated ash clouds are sensitive to assumptions about the profile of the ash emissions – no best profile but for weak activity a uniform profile may be best but for greater activity a concentrated profile better • Quantitative comparison suggests that only about 3.5% of the erupted mass was in ash particles small enough to allow long-range transport • It is necessary to represent the large, short-term fluctuations in plume height accurately

28. Summary • NAME did a reasonable job of capturing the horizontal structure of the ash cloud subject to possible timing and positioning errors that occur due to meteorology • NAME underestimates maximum concentrations by a factor of about 2.5 • OR NAME overestimates layer with by a factor of 2.5 • Default particle size distribution in NAME contains too many 10-30µm diameter particles

29. Talk Outline • Operational volcanic ash dispersion modelling • Model input uncertainty • Eruption plume height, vertical distribution • Peak concentrations • Fine ash fraction • Particle size distribution • Model/observation comparisons • Satellites • Lidars (ground and aircraft based) • In-situ particle measurements • Will we do better next time? • Future work

30. Operational Volcanic Ash Modelling • NAME dispersion model • Input • Eruption location • Eruption start time and duration • Eruption height, vertical distribution • Eruption rate (fine ash fraction) • Particle size distribution, density • Sedimentation velocity • Meteorology • Output • Ash concentration • Mean travel time

31. Synoptic Analysis at 00UTC on 16th April

32. Modis AQUA visible image at 13:23 UTC 12UTC 16th April

33. IASI Measured Volcanic Ash 22UTC 14th April 10UTC 15th April 22UTC 15th April 10UTC 16th April