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Evolution and Performance of the Urban Scheme in the Unified Model

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 Tile. No urbanization apart from manual increase in roughness over London.

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Evolution and Performance of the Urban Scheme in the Unified Model

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  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. Blending Height Surface 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. RN s  Ts4 E H g  Tg4 s  Ts4 G 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. Point 1: Upstream Point 2: Central London Point 3: Downstream Suburbs Point 4: Downstream Rural Point 1 Point 2 Point 3 Point 4 1 2 3 1.0 4 1.5 0.5 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. 2000 2001 2002 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 TEMPERATUREERRORS 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)

  11. 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. Troof Twall1 Twall2 Tstreet Troof Tcanyon Improvement of the Two-Tile Model:Geometry 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. r2 r1 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. Validation through idealized simulations Independent set of comparison: 4-tile and 2-tile models Difference in Heat Flux for H/W =0.1, 0.5, 1., 1.5, 2, 3 Surface Energy Balance H/W=3 H/W=0.1 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 * 70%*69.2%

  21. 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) Physical Parametrizations

  22. Canyon and Roof Tiles – M. Best

  23. Formation of the night timeurban heat island – urban canopy tile Unified Model – 1 km resolution 76 Layers Urban-No-Urban near surface temperature difference

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