The University of Reading Helen Dacre
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
The University of Reading Helen Dacre
Motivation
The University of Reading Helen Dacre
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
Motivation
Level Concentration (mg/m3)
High > 4
Medium 0.2 - 2
Low < 0.2
The University of Reading Helen Dacre
Operational volcanic ash transport and dispersion (VATD) models
Quantitative model predictions
Source parameter uncertainty
Meteorological input uncertainty
Future Work
Talk Outline
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Operational VATD Modelling
INPUT MODEL OUTPUT
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0.1 0.55
20
70
4.4
0
20
40
60
80
% o
f tot
al m
ass
Particle Diameter (µm)
0.1-0.3
0.3-1
1-3
3-10
10-30
30-100
Eyjafjallajökull Source Parameters
0.225H=0.365M
H
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Column Integrated Mass Concentration 14-18th April
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Fine-ash Fraction?
Mastin et al. (2009)
COMPARISON WITH GROUND BASED LIDAR
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IASI Volcanic Ash Product
12UTC 16th April00UTC 16th April
Leipzig
10UTC 16th April22UTC 15th April
L. Clarisse
Leipzig Leipzig
Leipzig
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1.5%
Scaling to Observed Concentration at Leipzig
A. AnsmannI. Mattis
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MODIS Visible Image
12UTC 16th April
12:24UTC 16th April10:44UTC 16th April
Chilbolton
(Hogan et al. 2011)
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Scaling to Observed Concentration at Chilbolton
(Hogan et al. 2011)
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5-minute time series of plume height from the Icelandic radar (data from Petersen and Arason)
Eruption Plume Height Data
Missing scanCloud obscuredMountain obscured
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Plume Height Reconstruction
4% 3%
COMPARISON WITH AIRCRAFT LIDAR
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5th May
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14th May
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17th 1.6%
14th 1.3 - 2.5%5th 7.5%
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Peak Concentration and Layer Width
2%
5%
Ash layer width = integrated column mass/max concentraton
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%
0
20
40
60
80
% o
f tot
al m
ass
Particle Diameter (µm)
0.3-1
1-3
3-10
10-30
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Fine Ash Fraction
3.5%
The University of Reading Helen Dacre
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
Summary
The University of Reading Helen Dacre
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
Summary
The University of Reading Helen Dacre
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
Talk Outline
The University of Reading Helen Dacre
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
Operational Volcanic Ash Modelling
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Synoptic Analysis at 00UTC on 16th April
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Modis AQUA visible image at 13:23 UTC
12UTC 16th April
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IASI Measured Volcanic Ash
22UTC 14th April
10UTC 16th April
10UTC 15th April
22UTC 15th April
The University of Reading Helen Dacre
The University of Reading Helen Dacre