Transcript ppt - Department of Meteorology

Eyjafjallajokull eruption, 2010
The largest airspace shutdown since WWII:
Volcanic ash prediction and its challenges
Helen Dacre1, Alan Grant1, Natalie Harvey1,
Helen Webster2, Ben Johnson2, David Thomson2, Franco Marenco2
1University
of Reading 2UK Met Office
Helen Dacre
Department of Meteorology
University of Reading
1
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
2
Impact on the ground
Helen Dacre
Department of Meteorology
University of Reading
3
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
4
Volcanic Ash Advisory Centres
(VAAC)
Helen Dacre
Department of Meteorology
University of Reading
5
Volcanic Ash Graphics
Helen Dacre
Department of Meteorology
University of Reading
6
Volcanic Ash Transport and
Dispersion Models (VATD)
Helen Dacre
Department of Meteorology
University of Reading
7
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
8
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
9
Predicting Safe Ash Concentrations
Model simulation
14th April – 20th April 2010
Helen Dacre
Department of Meteorology
University of Reading
10
Comparison with ground-based lidar
Model column Integrated mass
00UTC 16th April
Leipzig
DFAF = 4%
(Dacre et al. 2011, JGR)
Helen Dacre
lidar
model
Department of Meteorology
University of Reading
11
Comparison with Airborne Lidar
Column Integrated Mass Loading
Vertical cross-section of ash
concentration,
Lidar (black), NAME (grey)
lidar
DFAF = 1.2%
model
(Grant et al. 2012, ACP)
Helen Dacre
Department of Meteorology
University of Reading
12
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)
Helen Dacre
Department of Meteorology
University of Reading
13
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
14
Why are volcanic ash layers so thin?
Location of EARLINET lidars
Observed Ash Layer Depth
Observations
NAME
NAME: narrow/wide
emission profile
Helen Dacre
Department of Meteorology
NAME: varying
turbulence scheme
University of Reading
15
Quantifying Uncertainty in Volcanic
Ash Forecasts
Helen Dacre
Department of Meteorology
University of Reading
16
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
17
EXTRA SLIDES
Helen Dacre
Department of Meteorology
University of Reading
18
Qualitative Evaluation
12 UTC 16th April
MODIS
visible
12:24UTC 16th April
Helen Dacre
IASI Volcanic Ash
10 UTC 16th April
Department of Meteorology
University of Reading
19