The largest airspace shutdown since WWII: Volcanic ash prediction and its challenges

1. The largest airspace shutdown since WWII: Volcanic ash prediction and its challenges Eyjafjallajokull eruption, 2010 Helen Dacre1, Alan Grant1, Natalie Harvey1, Helen Webster2, Ben Johnson2, David Thomson2, Franco Marenco21University of Reading 2UK Met Office

2. Impact on aircraft • Volcanic ash is hard and abrasive • Volcanic ash can cause engine failure • >126 incidents of encounters with ash clouds since 1935 • Ash-encounter (AE) severity index ranging from 0 (no notable damage) to 5 (engine failure leading to crash) • Difficult to predict what a safe level of ash concentration is for aircraft to fly through

3. Impact on the ground

4. Talk Outline • Volcanic ash impacts • Volcanic ash advisory centres (VAAC’s) • Volcanic ash transport and dispersion models • Safe volcanic ash concentrations • Model evaluation • Summary • Current and future work

5. Volcanic Ash Advisory Centres (VAAC)

6. Volcanic Ash Graphics

7. Volcanic Ash Transport and Dispersion Models (VATD)

8. Volcanic Ash Prediction Challenges • Plume height and vertical profile may be unknown at onset of eruption and/or time varying • MER is not obtainable by direct observation • Mass fraction of fine ash (< 100μm) is not obtainable by direct observation • The possibility of aggregation of particles exists, but little detailed information is known

9. Defining Safe Ash Concentrations • April 2010 • Closure of European airspace caused huge economic difficulties • Aircraft manufacturers pressed to define limits on how much ash a jet engine can ingest without damage • CAA set the safe upper limit of ash density to be 2mg/m3 • May 2010: • CAA revised the safe limit upwards to 4mg/m3 – no fly zone • CAA created a Time Limited Zone between 2 and 4mg/m3

10. Predicting Safe Ash Concentrations Model simulation 14th April – 20th April 2010

11. Comparison with ground-based lidar Model column Integrated mass 00UTC 16th April Leipzig DFAF = 4% lidar model (Dacre et al. 2011, JGR)

12. Comparison with Airborne Lidar Column Integrated Mass Loading Vertical cross-sectionof ash concentration, Lidar (black), NAME (grey) DFAF = 1.2% lidar model (Grant et al. 2012, ACP)

13. Comparison with In-situ Particle Probes Location of FAAM aircraft profiles Profile of ash concentration Measured (black), model (red) DFAF = 2.6% (Dacre et al. 2013, ACP)

14. Summary so far … Q. Can VATD models predict the structure of volcanic ash clouds? • Horizontally to within ~100km • Vertically peak to within ~ 1km but ash layers too thick • Elevated source gives the best simulated ash clouds if information on the plume height is available Q. Can VATD models predict the concentration of volcanic ash clouds? • Reasonably when combined with an appropriate distal fine ash fraction of ~ 2-6% • Peak concentrations underestimated by a factor ~2

15. Why are volcanic ash layers so thin? Observed Ash Layer Depth Location of EARLINET lidars Observations NAME NAME: narrow/wide emission profile NAME: varying turbulence scheme

16. Quantifying Uncertainty in Volcanic Ash Forecasts

17. Outlook and Future Work • Icelandic volcanic activity is very likely to occur in the next 10-20 years so we need to develop a system that minimises disruption • Existing VATD can be used to provide reasonable guidance for aviation but there are still large uncertainties • We need to effectively communicate the uncertainty in ash forecasts so they can be used in risk based decisions • Assimilation of satellite observations • Ensemble forecasting

18. Extra slides

19. Qualitative Evaluation 12 UTC 16th April MODIS visible IASI Volcanic Ash 12:24UTC 16th April 10 UTC 16th April