1. Helen DacreDepartment of MeteorologyUniversity of Reading 1 Helen Dacre 1, Alan Grant 1, Natalie Harvey 1, Helen Webster 2, Ben Johnson 2, David Thomson 2, Franco Marenco 2 1 University of Reading 2 UK Met Office The largest airspace shutdown since WWII: Volcanic ash prediction and its challenges Eyjafjallajokull eruption, 2010

2. Helen DacreDepartment of MeteorologyUniversity of Reading 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. Helen DacreDepartment of MeteorologyUniversity of Reading 3 Impact on the ground

4. Helen DacreDepartment of MeteorologyUniversity of Reading 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. Helen DacreDepartment of MeteorologyUniversity of Reading 5 Volcanic Ash Advisory Centres (VAAC)

6. Helen DacreDepartment of MeteorologyUniversity of Reading 6 Volcanic Ash Graphics

7. Helen DacreDepartment of MeteorologyUniversity of Reading 7 Volcanic Ash Transport and Dispersion Models (VATD)

8. Helen DacreDepartment of MeteorologyUniversity of Reading 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. Helen DacreDepartment of MeteorologyUniversity of Reading 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/m 3 May 2010: -CAA revised the safe limit upwards to 4mg/m 3 – no fly zone -CAA created a Time Limited Zone between 2 and 4mg/m 3

10. Helen DacreDepartment of MeteorologyUniversity of Reading 10 Predicting Safe Ash Concentrations Model simulation 14 th April – 20 th April 2010

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

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

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

16. Helen DacreDepartment of MeteorologyUniversity of Reading 16 Quantifying Uncertainty in Volcanic Ash Forecasts

17. Helen DacreDepartment of MeteorologyUniversity of Reading 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. Helen DacreDepartment of MeteorologyUniversity of Reading 18 EXTRA SLIDES

19. Helen DacreDepartment of MeteorologyUniversity of Reading 19 Qualitative Evaluation 12 UTC 16 th April MODIS visible 10 UTC 16 th April IASI Volcanic Ash 12:24UTC 16 th April