Transcript Slide 1

Met Office dust forecasting
Using the Met Office Unified Model™
David Walters: Manager Global Atmospheric Model Development, Met Office.
(with M.E. Brooks, B. Ingleby, B. Johnson, J. Mulcahy, Y. Pradhan)
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Dust forecasting with the MetUM
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Met Office Unified Model™
(MetUM)
A 'seamless' model used across all time and space scales.
MetUM framework includes:
OPS, VAR, VER …
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Met Office Unified Model™
Atmospheric model components
Dynamics:
Physics:
• Regular lat/lon grid.
• Spectral band radiation
• Non-hydrostatic dynamics with a
deep atmosphere.
• Diagnostic or prognostic cloud
• Semi-implicit time integration with
3D semi-Lagrangian advection.
• Mass flux convection
• Atmospheric tracer advection
• Mixed-phase ppn
• Boundary layer
• Gravity wave schemes
• JULES land-surface model
Aerosols/chemistry:
• CLASSIC: SO4, Soot, Biomass smoke, OCFF, xNO3, seasalt, dust
• United Kingdom Chemistry Aerosol (UKCA) community model
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Dust in the MetUM
Woodward (2001,2011)
Friction velocity scheme using explicit U* over bare soil only:
*
* 

U
U t   t
*3 
H  f bsU 1  * 1 
*

U
U

 

Horizontal flux:




2

 M rel

g


Kawamura (1951)
Dry Ut* prescribed for each bin
Iverson and White (1982)
Soil moisture contribution to Ut* from top soil layer
Fecan et al. (1999)
Horizontal flux calculated for 9 size divisions
Size division
1
2
3
4
5
6
7
8
9
Lower lim (mm)
0.0316
0.1
0.316
1.0
3.16
10
31.6
100
316
Upper lim (mm)
0.1
0.316
1.0
3.16
10
31.6
100
316
1000
Horizontal and vertical flux
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Saltation only
Dust in the MetUM
Crisis Area Model implementation
Mrel, sand/silt/clay & soil properties from HWSD
Nachtergaele et al (2008)
e.g. grid-box
clay fraction
Vertical flux:
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G  H 10(13.6 max(0.2, Fc )6)
Gillette (1979)
Dust in the MetUM
Mapping from horizontal to vertical flux
Using 6 size divisions:
• Dynamically diagnosed from horizontal flux distribution:
Gi 
9
Hi
H 

 H 
6
j
j 1
k
k 1
Currently used in
climate research
or
• Prescribed following a fixed size distribution:
Gi 
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
wi
6
j 1
wj
9
H 

1
k 1
k
Currently used in
limited area NWP
Dust in the MetUM
Mapping from horizontal to vertical flux
Using 2 size divisions:
Size division
1
2
3
4
5
6
7
8
9
Lower lim (mm)
0.0316
0.1
0.316
1.0
3.16
10
31.6
100
316
Upper lim (mm)
0.1
0.316
1.0
3.16
10
31.6
100
316
1000
Horizontal saltation flux
• Uses prescribed size distribution only
Size division
1
2
Lower lim (mm)
0.1
2
Upper lim (mm)
2
10
Vertical flux
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Gi 

9
wi
2
j 1
wj
H 

1
k 1
k
Currently used in
global NWP
Dust in the MetUM
Once dust is lifted:
• Transported by SL advection and
• Interacts with radiation scheme via direct
aerosol effect
Can use climatological
dust in radiation instead
• Removed via dry/wet deposition
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Balkanski et al. (2007)
Operational dust models
GlobalAfrica
Southern
North
Model
Asia
Model
Model
• N512
12km (~25km)
70L (80km
70L
lid)(80km lid)
• 4D-Var
3D-Var DA
•2
6 bin dust scheme since 2011
2008
• No dust DA
• Radiation
No dust inuses
LBCsclimatology
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Dust model validation
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Dust forecast validation
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Dust forecast validation
• Dust Aerosol Optical
Thickness (AOT)
compared to
AERONET
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Dust forecast performance
← →
DUST
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←
→
DUST
←…
DUST
Dust forecast validation
Equitable Threat Score (ETS):
fraction of observed events that were
Demanding
score
for small
correctly
predicted,
reduced
by the
numbers
you would
by chance.
scale features
asexpect
correct
prediction
0 – no skill means:
•1 exactly
- perfect right place
• right time (3 hour window)
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Other validation methods
• Subjective verification
(including from theatre)
• Verification of visibility against SYNOP/METAR
• Model inter-comparison
• Observational campaigns
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Global Model validation
Pre-operational testing (April 2011)
Met Office research news article on global dust forecasting:
http://www.metoffice.gov.uk/research/news/dust-forecasting
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Global Model results
Pre-operational testing
Skill scores over SAM region:
• beats the SAM for low severity events
• capturing inflow into domain
• misses high severity events
• high res models still required?
Model went operational
in July 2011
Provide forecasts to
SDS-WAS through
MACC-II project from
December 2011
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Future developments
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Dust model developments
• Validation show dust from areas with seasonal
vegetation is important: link dust emissions to
“radiative bare soil fraction”
• Dust DA currently being developed (to use
SEVERI and MODIS AOD products)
• Emissions sensitive to soil properties, soil
moisture etc: further improvements required in
these areas
• Continuing to develop satellite products
currently provided to WMO SDS-WAS
Feedback on these products appreciated
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Summary
Please take home the following points
• Met Office dust forecasts operational since 2008
• Model validation shows reasonable performance and has
identified areas of potential improvement
• Dust in 25km global NWP since summer 2011
• Global model data to SDS-WAS from December 2011
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Questions
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