HR: 11:30h
AN: U51C-05    [PDF]
TI: Modeling Urban Surface-Atmosphere Sensible Heat Exchanges
AU: * Roberts, S M
EM: sroberts@geog.ubc.ca
AF: Department of Geography, University of British Columbia, 217 - 1984 West Mall, Vancouver, BC V6T 1Z2 Canada
AU: Oke, T
EM: toke@geog.ubc.ca
AF: Department of Geography, University of British Columbia, 217 - 1984 West Mall, Vancouver, BC V6T 1Z2 Canada
AU: Lemonsu, A
EM: aude.lemonsu@cnrm.meteo.fr
AF: Centre National de Recherches M\'{e}t\'{e}orologiques, M\'{e}t\'{e}o-France, 42 av Coriolis, Toulouse, 31057 France
AU: Grimmond, C
EM: grimmon@indiana.edu
AF: Atmospheric Science Program, Department of Geography, Indiana University, Student Building 120, Bloomington, IN 47405 United States
AU: Jackson, P
EM: pjackson@geog.ubc.ca
AF: Department of Geography, University of British Columbia, 217 - 1984 West Mall, Vancouver, BC V6T 1Z2 Canada
AB: Understanding the nature of energy partitioning at the surface of cities is prerequisite to gaining proper insight and ability to model their climatic environment and impacts. Of particular relevance in the urban setting is the surface-atmosphere exchange of sensible heat. The combined conductive-convective exchange of turbulent sensible heat flux ({\it Q$_{H}$}) and net storage heat flux ({\it $\Delta$Q$_{S}$}) has been shown to account for over 90% of the daytime net radiation at highly urbanized sites. This relation depends on surface structure, materials and the degree of surface-atmosphere coupling and its understanding is required in many applications; for example, to assess building climates, and to model evapo-transpiration, the urban heat island, and boundary layer growth. Observational studies, while allowing for general awareness of urban surface-atmosphere energetic interactions, are often limited in their applicability to other urban sites and/or processes. To overcome this, numerical models which aim to simulate urban climates have been developed. The Town Energy Balance (TEB) model of Masson (2000) couples the micro- and meso- scales and accurately represents the urban energy budget in meso-scale atmospheric models. TEB uses local canyon geometry together with surface and substrate radiative, thermal, moisture and roughness properties to simulate the effects produced by the presence of buildings. The urban system is simulated by calculating individual energy balances for walls, roads, and roofs, which are then integrated to resolve the local-scale surface energy balance. The model has been independently evaluated using measured fluxes from three dry sites - central Mexico City, a light industrial site in Vancouver (Masson {\it et al}., 2002) and the city center of Marseille, France (Lemonsu {\it et al}., 2003). At these sites, TEB simulated net radiation to within less than 10 W m$^{-2}$ and its partitioning into turbulent and storage heat fluxes to within a few tens of W $^{-2}$. TEB's good performance points towards its promise in conducting further analyses to better understand the primary criteria affecting local-scale urban surface-atmosphere energy exchanges. Such an analysis is performed for a site in Marseille and the results reveal that the wind regime plays the dominant role in energy partitioning in this environment. Varying urban geometry and surface radiative properties also result in appreciable changes whereas alterations to surface thermal parameters do little to impact the relative degree of surface-atmosphere sensible heat sharing.
DE: 3307 Boundary layer processes
DE: 3309 Climatology (1620)
DE: 3322 Land/atmosphere interactions
SC: U
MN: 2003 Fall Meeting