Evolution and Performance of the Urban Scheme in the Unified Model

Aurore Porson, Ian Harman, Pete Clark, Martin Best, Stephen Belcher

University of Reading

JCMM- Met Office

History of the Urban TileHistory of the Urban Tile No urbanization apart from manual increase in roughness over London.No urbanization apart from manual increase in roughness over London.

1996 Tile scheme in SSFM (SCM + relaxation forcing from operational 12 km UK Mes) 1996 Tile scheme in SSFM (SCM + relaxation forcing from operational 12 km UK Mes) with urban tile.with urban tile.

1998 Operational SSFM with urban canopy tile.1998 Operational SSFM with urban canopy tile.

2000 Operational 12 km Mesoscale model with urban canopy tile2000 Operational 12 km Mesoscale model with urban canopy tile

2004 Surface-only model research implementation of two-tile model with modified 2004 Surface-only model research implementation of two-tile model with modified surface parameterssurface parameters

2004 SCM research implementation of two-tile model depending on canyon geometry2004 SCM research implementation of two-tile model depending on canyon geometry

April 2005 Operational 4 km with urban canopy tile.April 2005 Operational 4 km with urban canopy tile.

March 2006 Operational 4 km adds change to anthropogenic heat source. March 2006 Operational 4 km adds change to anthropogenic heat source.

April 2007 3D model research implementation of two-tile model depending on canyon April 2007 3D model research implementation of two-tile model depending on canyon geometrygeometry

Blending Height

Surface

UM Tile Surface ExchangeUM Tile Surface Exchange Treats heterogeneous Treats heterogeneous

surfaces using ‘blending surfaces using ‘blending height’ techniques.height’ techniques.

Nine surface types, Nine surface types, – Broad Leaf Trees Broad Leaf Trees – Needle Leaf TreesNeedle Leaf Trees– C3 GrassC3 Grass– C4 GrassC4 Grass– ShrubShrub– UrbanUrban– WaterWater– SoilSoil– IceIce

Each tile has a full surface Each tile has a full surface energy balance.energy balance.

4 layer soil temperature and 4 layer soil temperature and moisture.moisture.

Schematic of potential temperature profile at nighttimes

s Ts4g Tg

4

H E s Ts4

G

RN

The Urban Canopy Model – The Urban Canopy Model – M. BestM. Best

This includes a This includes a radiatively coupled ‘canopyradiatively coupled ‘canopy’: ’: – high thermal inertia to simulate wall effects, high thermal inertia to simulate wall effects, – weak coupling with the soil, weak coupling with the soil, – strong coupling with the atmosphere.strong coupling with the atmosphere.

The urban tile also has:The urban tile also has:– Enhanced roughness.Enhanced roughness.– Enhanced drainage.Enhanced drainage.– Modified albedo.Modified albedo.

Formation of the night timeFormation of the night timeurban heat island – urban canopy tileurban heat island – urban canopy tile

Unified Model – 1 km resolution 76 Layers

1

23

4

0.5

1.0

1.5

Point 2

Point 3

Point 1

Point 4

Point 1: Upstream

Point 2: Central London

Point 3: Downstream Suburbs

Point 4: Downstream Rural

Urban fraction is derived from 25 m resolution data, based LANDSAT and generated by CEH

Temperature (K)

Hei

ght

abov

e gr

ound

(m

)

Operational ImplementationOperational Implementation

WMO Block 3 WMO Block 3 stationsstations

LondonLondon

5 cities index5 cities index

Impact of the Urban Canopy in Met Office Impact of the Urban Canopy in Met Office Operational Mesoscale ModelOperational Mesoscale Model

2000 2001 2002

BIA

SR

MS

ER

RO

R

MO

NT

HLY

TE

MP

ER

AT

UR

E E

RR

OR

S

Impact of Anthropogenic Heat Fluxes – P. ClarkImpact of Anthropogenic Heat Fluxes – P. Clark

LONDON ALTNAHARRA

MO

NT

HL

Y T

EM

PE

RA

TU

RE

ER

RO

RS

From statistics on full energy consumption over the UK from 1995 through to 2003 Monthly heat flux values vary from 17 W/m2 (August) to 26 W/m2 (December)

Data averaged over 21 cases, representative of ‘typical’ weather conditions

Surface-only tests against Mexico City and Vancouver data Surface-only tests against Mexico City and Vancouver data show that the model performance increases if: show that the model performance increases if:

The ratio between roughness length for heat and The ratio between roughness length for heat and momentum is reduced.momentum is reduced.

The urban tile is split into one canyon and one roof. The urban tile is split into one canyon and one roof.

Development of a two-tile model with Development of a two-tile model with reduced reduced

roughness length for heatroughness length for heatSensible Heat Flux for Mexico City (Best, Grimmond and Villani, 2006)

(Best, Grimmond and Villani, 2006)

Improvement of two-tile model: Improvement of two-tile model: dependence on canyon geometrydependence on canyon geometry

Averaging over Canyon OrientationsAveraging over Canyon Orientations Identical WallsIdentical Walls One Surface Energy Balance for the Canyon (Mixing, Exchange of Radiation) and One for the RoofOne Surface Energy Balance for the Canyon (Mixing, Exchange of Radiation) and One for the Roof Identical Walls and StreetIdentical Walls and Street Geometry Effects on:Geometry Effects on:

– Radiation: Effective Albedo and EmissivityRadiation: Effective Albedo and Emissivity– Transfer of Heat: Surface Resistance NetworkTransfer of Heat: Surface Resistance Network– Increase in Thermal InertiaIncrease in Thermal Inertia

The new two-tile model = Simplification of a four-tile model

Improvement of the two-tile model: RadiationImprovement of the two-tile model: Radiation

Albedo and Emissivity to depend on canyon geometry andAlbedo and Emissivity to depend on canyon geometry and to include exchange of radiation in the canyon (I. Harman, 2004)to include exchange of radiation in the canyon (I. Harman, 2004)

Troof

Twall1 Twall2

Tstreet

From a 4-tile model towards a 2-tile model

The way the canyon The way the canyon transfers scalars differs transfers scalars differs significantly from a flat significantly from a flat surface (J. Barlow et al., surface (J. Barlow et al., 2004, I. Harman et al., 2004, I. Harman et al., 2004)2004)

Improvement of the Two-Tile Model:Improvement of the Two-Tile Model:Geometry Dependent Transfer CoefficientsGeometry Dependent Transfer Coefficients

Troof

Tcanyon

r1

r2

Formulation of Total Resistance

Formulation of Facet Resistance

Formulation of Heat Roughness Length

U()

U(1)

Improvement of the two-tile model: Improvement of the two-tile model: Storage of HeatStorage of Heat

Surface heat flux to the soil G is defined as:Surface heat flux to the soil G is defined as:

Independent testing showed that this technique is more efficient than multiplying the heat capacity

W

W

HH

Independent set of comparison:Independent set of comparison:

4-tile and 2-tile models4-tile and 2-tile models

Surface Energy BalanceDifference in Heat Flux for H/W =0.1, 0.5, 1., 1.5, 2, 3

Both models are forced with averaging over canyon orientations for solar radiation and equal surface parameters in the canyon

H/W=0.1

H/W=3

Validation through idealized simulations

Independent set of comparison:Independent set of comparison:

4-tile and 2-tile models4-tile and 2-tile models

Validation against Mexico City observations

Observations

4-tile

2-tile

Future WorkFuture Work

TESTS: TESTS: – Full comparison between the urban canopy and the canyon geometry dependent two-tile Full comparison between the urban canopy and the canyon geometry dependent two-tile

modelmodel– Further improvement of the resistance network to include recirculation and ventilated Further improvement of the resistance network to include recirculation and ventilated

areasareas

Implementation of drag bulk approachImplementation of drag bulk approach

3D CASE STUDIES:3D CASE STUDIES:– Mapping canyon geometry for urban land use. Creation of new ancillariesMapping canyon geometry for urban land use. Creation of new ancillaries– One-year simulation over LondonOne-year simulation over London

PERSPECTVESPERSPECTVES– Design of building scenarios for adaptation to climate changeDesign of building scenarios for adaptation to climate change

Thank you for your attention !Thank you for your attention !

Anthropogenic HeatAnthropogenic Heat

Energy Consumption for UK in million of tonnes of oil equivalentEnergy Consumption for UK in million of tonnes of oil equivalent Conversion to W / mConversion to W / m2 2 for urban areas, being ~ 2.9 % UK areafor urban areas, being ~ 2.9 % UK area 70 % is assumed to be produced in urban areas (the rest being 70 % is assumed to be produced in urban areas (the rest being

for net inputs conversion and lost in generation)for net inputs conversion and lost in generation) Out of the 70 %, estimates of energy dissipation per sector:Out of the 70 %, estimates of energy dissipation per sector:

– 28.5 % domestic with 80% of dissipation28.5 % domestic with 80% of dissipation– 32.5 % transport with 67% of dissipation32.5 % transport with 67% of dissipation– 20.5% industry with 75% dissipation20.5% industry with 75% dissipation– 18.5 % with 50 % dissipation,18.5 % with 50 % dissipation,– giving 69.2% of dissipationgiving 69.2% of dissipation

Anthropogenic Heat = Conversion Factor to W / mAnthropogenic Heat = Conversion Factor to W / m2 * 2 * 70%*69.2%70%*69.2%

Physical ParametrizationsPhysical Parametrizations Edwards-Slingo Radiation Edwards-Slingo Radiation

– (Edwards & Slingo 1996)(Edwards & Slingo 1996) Mixed phase precipitation Mixed phase precipitation

– (Wilson & Ballard 1999)(Wilson & Ballard 1999)– Extending to prognostic cloud fraction (Wilson, Bushell)Extending to prognostic cloud fraction (Wilson, Bushell)– Extending to prognostic cloud water, rain water, ice, snow, graupel Extending to prognostic cloud water, rain water, ice, snow, graupel

(Forbes)(Forbes) Met Office Surface Exchange Scheme (MOSES I and II)Met Office Surface Exchange Scheme (MOSES I and II)

– (Cox, Essery, Betts)(Cox, Essery, Betts) Non-local Boundary Layer Non-local Boundary Layer

– (Lock et al 2000)(Lock et al 2000) New GWD scheme + GLOBE orography, smoothed (Raymond filter)New GWD scheme + GLOBE orography, smoothed (Raymond filter) Mass flux convection scheme with CAPE closure, downdraft and Mass flux convection scheme with CAPE closure, downdraft and

momentum transport, separate shallow cumulusmomentum transport, separate shallow cumulus– (Gregory and Rowntree, Kershaw, Grant)(Gregory and Rowntree, Kershaw, Grant)

Canyon and Roof Tiles – M. BestCanyon and Roof Tiles – M. Best

Formation of the night timeFormation of the night timeurban heat island – urban canopy tileurban heat island – urban canopy tile

Urban-No-Urban near surface temperature differenceUnified Model – 1 km resolution 76 Layers