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The largest airspace shutdown since WWII: Volcanic ash prediction and its challenges. Eyjafjallajokull eruption, 2010. 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 .

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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

impact on aircraft
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
talk outline
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
volcanic ash prediction challenges
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
defining safe ash concentrations
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
predicting safe ash concentrations
Predicting Safe Ash Concentrations

Model simulation

14th April – 20th April 2010

comparison with ground based lidar
Comparison with ground-based lidar

Model column Integrated mass

00UTC 16th April


DFAF = 4%



(Dacre et al. 2011, JGR)

comparison with airborne lidar
Comparison with Airborne Lidar

Column Integrated Mass Loading

Vertical cross-sectionof ash concentration,

Lidar (black), NAME (grey)

DFAF = 1.2%



(Grant et al. 2012, ACP)

comparison with in situ particle probes
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)

summary so far
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
why are volcanic ash layers so thin
Why are volcanic ash layers so thin?

Observed Ash Layer Depth

Location of EARLINET lidars



NAME: narrow/wide emission profile

NAME: varying turbulence scheme

outlook and future work
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
qualitative evaluation
Qualitative Evaluation

12 UTC 16th April

MODIS visible

IASI Volcanic Ash

12:24UTC 16th April

10 UTC 16th April