Helen Dacre Department of Meteorology University of Reading 1

Helen Dacre1, Alan Grant1, Natalie Harvey1, Helen Webster2, Ben Johnson2, David Thomson2, Franco Marenco2

1University of Reading 2UK Met Office

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

Eyjafjallajokull eruption, 2010

Helen Dacre Department of Meteorology University 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

Helen Dacre Department of Meteorology University of Reading 3

Impact on the ground

Helen Dacre Department of Meteorology University 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

Helen Dacre Department of Meteorology University of Reading 5

Volcanic Ash Advisory Centres (VAAC)

Helen Dacre Department of Meteorology University of Reading 6

Volcanic Ash Graphics

Helen Dacre Department of Meteorology University of Reading 7

Volcanic Ash Transport and Dispersion Models (VATD)

Helen Dacre Department of Meteorology University 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

Helen Dacre Department of Meteorology University 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/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

Helen Dacre Department of Meteorology University of Reading 10

Predicting Safe Ash Concentrations

Model simulation 14th April – 20th April 2010

Helen Dacre Department of Meteorology University of Reading 11

00UTC 16th April

Model column Integrated mass

Leipzig

lidar

model

Comparison with ground-based lidar

DFAF = 4%

(Dacre et al. 2011, JGR)

Helen Dacre Department of Meteorology University 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)

Helen Dacre Department of Meteorology University of Reading 13

Comparison with In-situ Particle Probes Location of FAAM aircraft profiles

Profile of ash concentrationMeasured (black), model (red)

DFAF = 2.6%

(Dacre et al. 2013, ACP)

Helen Dacre Department of Meteorology University 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

Helen Dacre Department of Meteorology University of Reading 15

Why are volcanic ash layers so thin?

Location of EARLINET lidars Observed Ash Layer Depth

ObservationsNAME

NAME: varying turbulence scheme

NAME: narrow/wide emission profile

Helen Dacre Department of Meteorology University of Reading 16

Quantifying Uncertainty in Volcanic Ash Forecasts

Helen Dacre Department of Meteorology University 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

Helen Dacre Department of Meteorology University of Reading 18

EXTRA SLIDES

Helen Dacre Department of Meteorology University of Reading 19

Qualitative Evaluation12 UTC 16th April

MODIS visible 10 UTC 16th April

IASI Volcanic Ash12:24UTC 16th April