1. The University of Reading Helen Dacre The Prediction And Observation Of Volcanic Ash Clouds During The Eyjafjallajökull Eruption Helen Dacre and Alan Grant R. Hogan, D. Thomson, F. Marenco, B. Johnson, A. Ansmann, I. Mattis, L. Clarisse

2. The University of Reading Helen Dacre AIM: to compare NAME simulations of ash clouds with observations of ash clouds with a view to estimating the distal fine ash fraction (DFAF) Qualitative model evaluation Quantitative model evaluation  Plume height  Vertical distribution of ash  Ash size distribution Future volcanic ash predictions Talk Outline

3. The University of Reading Helen Dacre Qualitative Spatial Verification 12 UTC 16 th April MODIS visible 10 UTC 16 th April IASI Volcanic Ash Lieven Clarisse 12:24UTC 16 th April

4. The University of Reading Helen Dacre Quantitative Verification DFAF is defined as the % of the total emitted mass that is carried by small particles ( 1000km) from the volcano 50 km from volcano (Thor Thordarson)

5. 1. SENSITIVITY OF DFAF TO PLUME HEIGHT FLUCTUATIONS Comparison with ground-based lidars (Petersen and Arason, 2011) Mountain Missing Cloud

6. The University of Reading Helen Dacre DFAF at Leipzig and Chilbolton on 16 th April DFAF = 4%DFAF = 3% Robin Hogan Albert Ansmann, Ina Mattis

7. 2. SENSITIVITY OF DFAF TO VERTICAL DISTRIBUTION OF ASH Comparison with airborne lidars Uniform Concentrated

8. The University of Reading Helen Dacre DFAF on 17 th May uniform concentrated uniform concentrated Alan Grant, Franco Marenco Observed ash layers concentrated DFAF =1.6% uniform DFAF = 2.7%

9. The University of Reading Helen Dacre Comparison for all flights DFAF = 2% Alan Grant

10. 3. SENSITIVITY OF DFAF TO EFFECTIVE ASH SIZE DISTRIBUTION Comparison with in-situ aerosol measurements

11. The University of Reading Helen Dacre Distal FAF from in-situ measurements Average concentration on 14 th May 14 th May Size distribution on flightEffective ash size distribution 14 th May original DFAF = 2.8% new DFAF = 2.2% Ben Johnson

12. The University of Reading Helen Dacre DFAF Summary 3.5%

13. The University of Reading Helen Dacre GENERAL NAME identifies observed ash layers subject to possible timing and positioning errors due to meteorology Observed ash layers are thinner and lower than simulated layers SOURCE PARAMETER UNCERTAINTY Plume height - necessary to represent short-term fluctuations Vertical distribution - no best profile but related to activity Ash size distribution - Large percentage of < 10µm particles DFAF ~ 3.5% of the erupted mass was in ash particles small enough to allow long-range transport Future Volcanic Eruptions