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© Crown copyright Met Office
Experiences with a 100m version of the Unified Model over an Urban AreaHumphrey Lean
MetOffice@Reading, Reading, UK
WWOSC Montreal, Aug 2014
Thanks to P Clark, J Barlow, S Lane, S Grimmond, S Kotthaus
© Crown copyright Met Office
100m Unified Model versions
• Cold pooling in valleys COLPEX (Clark, Vosper, Carter)
• Convection (Carter, Halliwell, Hanley)
• StCu (Bootle)
• London (Lean)
• (Also 300m Weymouth model for Olympic sailing) and 300m London model (fog).
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COPE IOP2 5/07/2013w at 325m
1.5km 500m
200m 100m
Kirsty Hanley
Below 500m in “turbulence permitting” regime
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Why 100m London Model ?• Ask question “what might a 100m model of London do for us” (What can it do and not do).
• Potential to better represent effects due to small scale surface features (e.g. river, small scale orography, urban surfaces etc).
• Potential to better represent small scale meteorological features e.g. convection, boundary layer etc.
• Would hope to eventually couple to hydrology, air quality etc.
• Potential uses in short range forecasting and climatological applications.
• Don’t talk about precipitation today (see other talk but may be problematic).
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100m London Model Configuration
• Taken from from 100m models (COLPEX, Convection):
• 140 levels (doubled 70 level set).
• No convection scheme
• 3d Smagorinsky mixing (as oposed to 2d + BL in UKV)
• 3s timestep
• Best urban scheme (as UKV operational)
• Nested in 500m which is nested in UKV (1.5km UK model)
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100m – Several Buildings per gridbox
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Current domain
80x80kmNested in UKVAnd 500m
Urban fraction
Chelmsford
Guildford
Luton
Tunbridge Wells
Goes out to quite rural places (not Cardington, Detling or Chilbolton though!)
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30th Sept 2011 Case
Shortwave at WCC
Data courtesy ACTUAL project
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14UTC 30/09/11
1.5m T
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14UTC 30/09/11
W at 293m
Southerly wind
N.B.spin up at inflow boundary
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30th Sept 2011 vertical velocity
100mModel
Lidar
Data courtesy of ACTUAL project.
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Heat Fluxes 14 UTC 30/09/11
1.5km 500m 100m
ParameterisedExplicitTotal
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Domain size very important
Small domain (30x30km) Subset of std domain
Spin up of turbulence gives rolls initially (also seen in convection Work)
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30th Sept 2011 vertical velocity
100mModel
Lidar
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30th Sept 2011 vertical velocity
Small100mModel
Lidar
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4km 2.2km 1.5km 500m
200m 100m Radar
Often see similar effect in convection models..
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Boundary layer rolls are often a valid meteorological phenomenon….
….but not if spin up aritifact as air enters domain.
Cloud in London 333m model
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293m w 14UTC 30/09/11
100m 55m
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Heat Fluxes 14 UTC 30/09/11
55m100m
ParameterisedExplicitTotal
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Wind directions
Barlow et al
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Wind directions
Barlow et al
Reversal at low levels at night.
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Model wind direction
5UTC01/10/11
0
300
BT Tower
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Model wind direction and orographic height (100m)
WCC
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25th July 2012
Vertical velocity at293m
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25th July 2012 aerosolBackscatterObsGrimmond andKotthaus
1.5km model
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25th July 2012 aerosolBackscatterObsGrimmond andKotthaus
100m model
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Conclusions
• We are experimenting with a 100m version of Unified Model over London with similar configuration to other high resolution versions
•Reasonable attempt to capture convective boundary layer in a couple of cases.
• Represents orographic flows and sea breezes in agreement with observations.
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Future Work
• Quantify behaviour of convective BL at different resolutions compared to observations.
• Understand in more detail behaviour of model.
• Urban/rural comparisons.
• Look for small scale features that might be better resolved (e.g. due to river, parks etc).
• Address deficiencies of representation of surface.
© Crown copyright Met Office
Thank you for listening.Any questions?