the university of reading helen dacre the prediction and observation of volcanic ash clouds during...
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The University of Reading Helen Dacre Qualitative Spatial Verification 12 UTC 16 th April MODIS visible 10 UTC 16 th April IASI Volcanic Ash Lieven Clarisse 12:24UTC 16 th AprilTRANSCRIPT
The University of Reading Helen Dacre
The Prediction And Observation Of Volcanic Ash Clouds During TheEyjafjallajökull Eruption
Helen Dacre and Alan GrantR. Hogan, D. Thomson, F. Marenco, B. Johnson, A. Ansmann, I. Mattis, L. Clarisse
The University of Reading Helen Dacre
AIM: to compare NAME simulations of ash clouds with observations of ash clouds with a view to
estimating the distal fine ash fraction (DFAF)
Qualitative model evaluation
Quantitative model evaluation Plume height Vertical distribution of ash Ash size distribution
Future volcanic ash predictions
Talk Outline
The University of Reading Helen Dacre
Qualitative Spatial Verification 12 UTC 16th April
MODIS visible
10 UTC 16th April
IASI Volcanic Ash Lieven Clarisse
12:24UTC 16th April
The University of Reading Helen Dacre
Quantitative Verification
DFAF is defined as the % of the total emitted mass that is carried by small particles (<100μm diameter) and transported long distances (> 1000km) from the volcano
observed column massDistal fine ash fraction NAME column mass
225.0/1
0.365height PlumerateEruption
50 km from volcano (Thor Thordarson)
1. SENSITIVITY OF DFAF TO PLUME HEIGHT FLUCTUATIONS
Comparison with ground-based lidars
(Petersen and Arason, 2011)
Mountain Missing
Cloud
The University of Reading Helen Dacre
DFAF at Leipzig and Chilbolton on 16th April
DFAF = 4% DFAF = 3%
Robin Hogan
Albert Ansmann, Ina Mattis
2. SENSITIVITY OF DFAF TO VERTICAL DISTRIBUTION OF ASH
Comparison with airborne lidars
Uniform Concentrated
The University of Reading Helen Dacre
DFAF on 17th May
uniform
concentrateduniform
concentrated
Alan Grant, Franco Marenco
Observed ash layers
concentrated DFAF =1.6%
uniform DFAF = 2.7%
The University of Reading Helen Dacre
Comparison for all flights
DFAF = 2%
Alan Grant
3. SENSITIVITY OF DFAF TO EFFECTIVE ASH SIZE DISTRIBUTION
Comparison with in-situ aerosol measurements
0.1 0.55
20
70
4.4
0
20
40
60
80
% o
f tot
al m
ass
Particle Diameter (µm)
0.1-0.30.3-11-33-1010-3030-100
The University of Reading Helen Dacre
Distal FAF from in-situ measurements
Average concentration on 14th May
14th May
Size distribution on flight Effective ash size distribution
14th MayoriginalDFAF = 2.8%
newDFAF = 2.2%Ben
Johnson
The University of Reading Helen Dacre
DFAF Summary
3.5%
The University of Reading Helen Dacre
GENERAL NAME identifies observed ash layers subject to possible timing
and positioning errors due to meteorology Observed ash layers are thinner and lower than simulated layers
SOURCE PARAMETER UNCERTAINTY Plume height - necessary to represent short-term fluctuations Vertical distribution - no best profile but related to activity Ash size distribution - Large percentage of < 10µm particles
DFAF ~ 3.5% of the erupted mass was in ash particles small enough to allow long-range transport
Future Volcanic Eruptions