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PARAMETERIZATION OF URBAN COVERS IN MESOSCALE MODELS

PARAMETERIZATION OF URBAN COVERS IN MESOSCALE MODELS. A. Lemonsu, S. Bélair, J. Mailhot, L. Tong, R. Pavlovic. Current meteorological models can be run at a resolution of a few hundreds of meters At such resolutions, the impact of cities on the surface exchanges must be taken into account

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PARAMETERIZATION OF URBAN COVERS IN MESOSCALE MODELS

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  1. PARAMETERIZATION OF URBAN COVERS IN MESOSCALE MODELS A. Lemonsu, S. Bélair, J. Mailhot, L. Tong, R. Pavlovic

  2. Current meteorological models can be run at a resolution of a few hundreds of meters • At such resolutions, the impact of cities on the surface exchanges must be taken into account • Town Energy Balance (TEB) urban canopy model (Masson 2000) now implemented in the official physics package of GEM and MC2 Direct impact on the surface energy exchanges Response of the atmospheric boundary layer Scientific context

  3. TEB urban surface scheme • Urban canopy model parameterizing water and energy exchanges between canopy and atmosphere • Model specifically dedicated to the built-up covers • Three-dimensionnal geometry • Radiative trapping and shadow effect • Heat storage • Wind, temperature and humidity inside the street • Water and snow • Idealized urban geometry • Mean urban canyon: 1 roof, 2 identical walls, 1 road • Isotropy of the street orientations • No crossing streets roof wall road

  4. Input data Prognostic variables Diagnostic variables Ua , Ta , qa Atmospheric level Rroof Rroof Snow Rtop QH industry QE industry QHroof QE roof QHtop QE top Water Snow Troof1 Troof2 Troof3 QHwall QE wall Rwall Tcanyon qcanyon Tibld QH traffic QE traffic QHroad QE road Rroad Rroad Snow Water Snow Twall1 Twall2 Twall3 Troad1 Troad2 Troad3

  5. Water Sea ice Urban Soil/Vegetation Glaciers Coupling with MC2 and GEM To couple TEB with MC2 and GEM requires : • To implement a new type of surface in the RPN’s physics package in order to take into account the urban areas • To develop urban land-cover databases to document the spatial distribution and spatial variability of urban areas (Leroux) • To define the heat and humidity releases due to human activities (Benbouta)

  6. Coupling with MC2 and GEM Implementation of urban classes in current land cover classification Dynamics package Calculation of cover fractions and averaged surface parameters Initialization of TEB Initial prognostic variables calculated from analysis/forecast Input parameters from land cover database Physics package Run of TEB on urban surface Extraction of aggregation fields Aggregation of fields according to fractions of each surface

  7. Modeling objectives Current studies : • Offline modeling over OKC to evaluate TEB over North American cities (Lemonsu, Tong) • 3D modeling with MC2 over OKC to study the impact of the urban parameterization on the boundary layer (Pelletier, Lemonsu) Future works : • Offline modeling over Montreal (MUSE period) to evaluate TEB under winter condition and to improve the snow package (Lemonsu, Tong, Bélair) • Objective evaluation of GEM 2.5 km including TEB (Tong, Bélair, Lemonsu)

  8. 300 299 100 298 80 297 60 296 40 20 3D modeling over Oklahoma City 2-m air temperature 2300 LST Fraction of built-up covers % K

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