© Crown copyright Met Office Experiences with a 100m version of the Unified Model over an Urban...

© 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


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).


COPE IOP2 5/07/2013w at 325m

1.5km 500m

200m 100m

Kirsty Hanley

Below 500m in “turbulence permitting” regime


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).


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)


100m – Several Buildings per gridbox


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!)


30th Sept 2011 Case

Shortwave at WCC

Data courtesy ACTUAL project


14UTC 30/09/11

1.5m T


14UTC 30/09/11

W at 293m

Southerly wind

N.B.spin up at inflow boundary


30th Sept 2011 vertical velocity

100mModel

Lidar

Data courtesy of ACTUAL project.


Heat Fluxes 14 UTC 30/09/11

1.5km 500m 100m

ParameterisedExplicitTotal


Domain size very important

Small domain (30x30km) Subset of std domain

Spin up of turbulence gives rolls initially (also seen in convection Work)



100mModel

Lidar



Small100mModel

Lidar


4km 2.2km 1.5km 500m

200m 100m Radar

Often see similar effect in convection models..


Boundary layer rolls are often a valid meteorological phenomenon….

….but not if spin up aritifact as air enters domain.

Cloud in London 333m model


293m w 14UTC 30/09/11

100m 55m


Heat Fluxes 14 UTC 30/09/11

55m100m

ParameterisedExplicitTotal


Wind directions

Barlow et al


Wind directions

Barlow et al

Reversal at low levels at night.


Model wind direction

5UTC01/10/11

0

300

BT Tower


Model wind direction and orographic height (100m)

WCC


25th July 2012

Vertical velocity at293m


25th July 2012 aerosolBackscatterObsGrimmond andKotthaus

1.5km model


25th July 2012 aerosolBackscatterObsGrimmond andKotthaus

100m model


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.


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.


Thank you for listening.Any questions?

© Crown copyright Met Office Experiences with a 100m version of the Unified Model over an Urban...

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