The Eyjafjallaj

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The Eyjafjallajökull eruption How well were the
volcanic ash clouds predicted?

• Helen Dacre and Alan Grant
• Robin Hogan, Dave Thomson, Ben Devenish, Jim
  Haywood, Franco Marenco, Ben Johnson, Albert
  Ansmann, Ina Mattis and Lieven Clarisse

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Motivation
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Motivation

• EUROCONTROL report from 14 - 20 April
• 75 of European airspace closed
• 100,000 flights cancelled
• 10 million passenger journeys affected
• 7000 flights cancelled up to 18 May

Level Concentration (mg/m3)
High gt 4
Medium 0.2 - 2
Low lt 0.2
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Talk Outline

• Operational volcanic ash transport and dispersion
  (VATD) models
• Quantitative model predictions
• Source parameter uncertainty
• Meteorological input uncertainty
• Future Work

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Operational VATD Modelling
MODEL
OUTPUT
INPUT
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Eyjafjallajökull Source Parameters
H
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Column Integrated Mass Concentration 14-18th
April
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Fine-ash Fraction?
Mastin et al. (2009)
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Comparison with ground based lidar
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IASI Volcanic Ash Product
12UTC 16th April
00UTC 16th April
Leipzig
Leipzig
10UTC 16th April
22UTC 15th April
Leipzig
Leipzig
L. Clarisse
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Scaling to Observed Concentration at Leipzig
A. Ansmann I. Mattis
1.5
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MODIS Visible Image
12UTC 16th April
Chilbolton
1224UTC 16th April
1044UTC 16th April
(Hogan et al. 2011)
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Scaling to Observed Concentration at Chilbolton
(Hogan et al. 2011)
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Eruption Plume Height Data
Missing scan
Cloud obscured
Mountain obscured

• 5-minute time series of plume height from the
  Icelandic radar (data from Petersen and Arason)

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Plume Height Reconstruction
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3
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Comparison with aircraft lidar
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5th May
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14th May
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14th 1.3 - 2.5
5th 7.5
17th 1.6
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Peak Concentration and Layer Width
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2

• Ash layer width integrated column mass/max
  concentraton

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Comparison with Airborne spectrometers
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Fine Ash Particle Size Distribution
14th 2.1
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Fine Ash Particle Size Distribution
5th 10.6
14th 2.1
17th 3.1
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Fine Ash Fraction
3.5
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Summary

• It is possible to identify the ash layers
  detected with the ground based and airborne
  lidars with layers in the NAME simulations
• Observed ash layers are thinner than teh
  simulated layers and at lower altitude
• Horizontal and vertical structure of the
  simulated ash clouds are sensitive to assumptions
  about the profile of the ash emissions no best
  profile but for weak activity a uniform profile
  may be best but for greater activity a
  concentrated profile better
• Quantitative comparison suggests that only about
  3.5 of the erupted mass was in ash particles
  small enough to allow long-range transport
• It is necessary to represent the large,
  short-term fluctuations in plume height
  accurately

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Summary

• NAME did a reasonable job of capturing the
  horizontal structure of the ash cloud subject to
  possible timing and positioning errors that occur
  due to meteorology
• NAME underestimates maximum concentrations by a
  factor of about 2.5
• OR NAME overestimates layer with by a factor of
  2.5
• Default particle size distribution in NAME
  contains too many 10-30µm diameter particles

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Talk Outline

• Operational volcanic ash dispersion modelling
• Model input uncertainty
• Eruption plume height, vertical distribution
• Peak concentrations
• Fine ash fraction
• Particle size distribution
• Model/observation comparisons
• Satellites
• Lidars (ground and aircraft based)
• In-situ particle measurements
• Will we do better next time?
• Future work

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Operational Volcanic Ash Modelling

• NAME dispersion model
• Input
• Eruption location
• Eruption start time and duration
• Eruption height, vertical distribution
• Eruption rate (fine ash fraction)
• Particle size distribution, density
• Sedimentation velocity
• Meteorology
• Output
• Ash concentration
• Mean travel time

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Synoptic Analysis at 00UTC on 16th April
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Modis AQUA visible image at 1323 UTC
12UTC 16th April
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IASI Measured Volcanic Ash
22UTC 14th April
10UTC 15th April
22UTC 15th April
10UTC 16th April
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