Evolution and Performance of the Urban Scheme

1
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
2
History of the Urban Tile

• No urbanization apart from manual increase in
  roughness over London.
• 1996 Tile scheme in SSFM (SCM relaxation
  forcing from operational 12 km UK Mes) with urban
  tile.
• 1998 Operational SSFM with urban canopy tile.
• 2000 Operational 12 km Mesoscale model with urban
  canopy tile
• 2004 Surface-only model research implementation
  of two-tile model with modified surface
  parameters
• 2004 SCM research implementation of two-tile
  model depending on canyon geometry
• April 2005 Operational 4 km with urban canopy
  tile.
• March 2006 Operational 4 km adds change to
  anthropogenic heat source.
• April 2007 3D model research implementation of
  two-tile model depending on canyon geometry

3
UM Tile Surface Exchange

• Treats heterogeneous surfaces using blending
  height techniques.
• Nine surface types,
• Broad Leaf Trees
• Needle Leaf Trees
• C3 Grass
• C4 Grass
• Shrub
• Urban
• Water
• Soil
• Ice
• Each tile has a full surface energy balance.
• 4 layer soil temperature and moisture.

Schematic of potential temperature profile at
nighttimes
4
The Urban Canopy Model M. Best

• This includes a radiatively coupled canopy
• high thermal inertia to simulate wall
  effects,
• weak coupling with the soil,
• strong coupling with the atmosphere.
• The urban tile also has
• Enhanced roughness.
• Enhanced drainage.
• Modified albedo.

5
Formation of the night timeurban heat island
urban canopy tile
Unified Model 1 km resolution 76 Layers
Height above ground (m)
Temperature (K)
Urban fraction is derived from 25 m resolution
data, based LANDSAT and generated by CEH
6
Operational Implementation

• WMO Block 3 stations
• London
• 5 cities index

7
Impact of the Urban Canopy in Met Office
Operational Mesoscale Model
RMS ERROR
MONTHLY TEMPERATURE ERRORS
BIAS
8
Impact of Anthropogenic Heat Fluxes P. Clark
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)
ALTNAHARRA
LONDON
MONTHLY TEMPERATURE ERRORS
Data averaged over 21 cases, representative of
typical weather conditions
9

• Surface-only tests against Mexico City and
  Vancouver data show that the model performance
  increases if
• The ratio between roughness length for heat and
  momentum is reduced.
• The urban tile is split into one canyon and one
  roof.
• Development of a two-tile model with reduced
• roughness length for
  heat

Sensible Heat Flux for Mexico City (Best,
Grimmond and Villani, 2006)
10
(Best, Grimmond and Villani, 2006)
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Improvement of two-tile model dependence on
canyon geometry
The new two-tile model Simplification of a
four-tile model

• Averaging over Canyon Orientations
• Identical Walls
• One Surface Energy Balance for the Canyon
  (Mixing, Exchange of Radiation) and One for the
  Roof
• Identical Walls and
  Street
• Geometry Effects on
• Radiation Effective Albedo and Emissivity
• Transfer of Heat Surface Resistance Network
• Increase in Thermal Inertia

12
Improvement of the two-tile model Radiation

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

13
Improvement of the Two-Tile ModelGeometry
Dependent Transfer Coefficients
The way the canyon transfers scalars differs
significantly from a flat surface (J. Barlow et
al., 2004, I. Harman et al., 2004)
From a 4-tile model towards a 2-tile model
14
Formulation of Facet Resistance
Formulation of Total Resistance
U(1)
U(?)
Formulation of Heat Roughness Length
15
Improvement of the two-tile model Storage of
Heat

• Surface heat flux to the soil G is defined as

W
H
H
W
Independent testing showed that this technique is
more efficient than multiplying the heat capacity
16

• Independent set of comparison
• 4-tile and 2-tile models

Validation through idealized simulations
Difference in Heat Flux for H/W 0.1, 0.5, 1.,
1.5, 2, 3
Surface Energy Balance
H/W3
H/W0.1
Both models are forced with averaging over canyon
orientations for solar radiation and equal
surface parameters in the canyon
17

• Independent set of comparison
• 4-tile and 2-tile models

Validation against Mexico City observations
Observations 4-tile
2-tile
18
Future Work

• TESTS
• Full comparison between the urban canopy and the
  canyon geometry dependent two-tile model
• Further improvement of the resistance network to
  include recirculation and ventilated areas
• Implementation of drag bulk approach
• 3D CASE STUDIES
• Mapping canyon geometry for urban land use.
  Creation of new ancillaries
• One-year simulation over London
• PERSPECTVES
• Design of building scenarios for adaptation to
  climate change

19

• Thank you for your attention !

20
Anthropogenic Heat

• Energy Consumption for UK in million of tonnes of
  oil equivalent
• Conversion to W / m2 for urban areas, being 2.9
  UK area
• 70 is assumed to be produced in urban areas
  (the rest being for net inputs conversion and
  lost in generation)
• Out of the 70 , estimates of energy dissipation
  per sector
• 28.5 domestic with 80 of dissipation
• 32.5 transport with 67 of dissipation
• 20.5 industry with 75 dissipation
• 18.5 with 50 dissipation,
• giving 69.2 of dissipation
• Anthropogenic Heat Conversion Factor to W / m2
  7069.2

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Physical Parametrizations

• Edwards-Slingo Radiation
• (Edwards Slingo 1996)
• Mixed phase precipitation
• (Wilson Ballard 1999)
• Extending to prognostic cloud fraction (Wilson,
  Bushell)
• Extending to prognostic cloud water, rain water,
  ice, snow, graupel (Forbes)
• Met Office Surface Exchange Scheme (MOSES I and
  II)
• (Cox, Essery, Betts)
• Non-local Boundary Layer
• (Lock et al 2000)
• New GWD scheme GLOBE orography, smoothed
  (Raymond filter)
• Mass flux convection scheme with CAPE closure,
  downdraft and momentum transport, separate
  shallow cumulus
• (Gregory and Rowntree, Kershaw, Grant)

22
Canyon and Roof Tiles M. Best
23
Effect of Thermal Capacity M. Best
24
Formation of the night timeurban heat island
urban canopy tile
Unified Model 1 km resolution 76 Layers
Urban-No-Urban near surface temperature difference