Eyjafjallajokull eruption 2010 The largest airspace shutdown since

Eyjafjallajokull eruption, 2010 The largest airspace shutdown since WWII: Volcanic ash prediction and its challenges 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 Helen Dacre Department of Meteorology University of Reading 1

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 Helen Dacre Department of Meteorology University of Reading 2

Impact on the ground Helen Dacre Department of Meteorology University of Reading 3

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 Helen Dacre Department of Meteorology University of Reading 4

Volcanic Ash Advisory Centres (VAAC) Helen Dacre Department of Meteorology University of Reading 5

Volcanic Ash Graphics Helen Dacre Department of Meteorology University of Reading 6

Volcanic Ash Transport and Dispersion Models (VATD) Helen Dacre Department of Meteorology University of Reading 7

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 Helen Dacre Department of Meteorology University of Reading 8

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 2 mg/m 3 • May 2010: - CAA revised the safe limit upwards to 4 mg/m 3 – no fly zone - CAA created a Time Limited Zone between 2 and 4 mg/m 3 Helen Dacre Department of Meteorology University of Reading 9

Predicting Safe Ash Concentrations Model simulation 14 th April – 20 th April 2010 Helen Dacre Department of Meteorology University of Reading 10

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

Comparison with Airborne Lidar Column Integrated Mass Loading Vertical cross-section of ash concentration, Lidar (black), NAME (grey) lidar DFAF = 1. 2% model (Grant et al. 2012, ACP) Helen Dacre Department of Meteorology University of Reading 12

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) Helen Dacre Department of Meteorology University of Reading 13

Summary so far … Q. Can VATD models predict the structure of volcanic ash clouds? - Horizontally to within ~100 km - Vertically peak to within ~ 1 km 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 Helen Dacre Department of Meteorology University of Reading 14

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

Quantifying Uncertainty in Volcanic Ash Forecasts Helen Dacre Department of Meteorology University of Reading 16

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 Helen Dacre Department of Meteorology University of Reading 17

EXTRA SLIDES Helen Dacre Department of Meteorology University of Reading 18

Qualitative Evaluation 12 UTC 16 th April MODIS visible 12: 24 UTC 16 th April Helen Dacre IASI Volcanic Ash 10 UTC 16 th April Department of Meteorology University of Reading 19