APPLICATION OF THE URBAN VERSION OF MM5 FOR HOUSTONUniversity Corporation for Atmospheric ResearchSylvain DupontCollaborators: Steve Burian, Jason Ching

E-mail: dupont@hpcc.epa.gov

Urbanized version of MM5Drag-Force ApproachDA-SM2-USimulation of meteorological fields within and above rural and urban canopies.Neighborhood scale: 1-km horizontal grid spacing and few meter vertical grid spacing inside the canopyCanopy elements are not explicitly defined but spatially averagedSoil Model for Sub-Meso scales - Urbanized version

General ObjectiveModeling air-quality for estimating human exposure to air pollution in urban areas by using CMAQ.Specific Objectives of this presentationComputation of the Houston morphological parameters for DA-SM2-U.Influence of the Houston representation on the urban boundary layer structureWhat degree of urban representation detail do we need at neighborhood scales ?

DA-SM2-UIntroduced inside the Gayno-Seaman PBL scheme

Latent heat flux

Sensible heat flux

roof

LEpav

natural soil

water

Ts pav

Root zone layer

Diffusion

Drainage network

Drainage outside the system

Infiltration

Deep soil layer

Paved surface

Surface layer

Drainage

Precipitation

Anthropogenic

heat flux

Storage heat flux

Net radiation

Hsens pav

Gs pav

Roughness approach

Drag-Force approach

Ts roof

wall

Q

int

T

bare soil

Rn pav

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Rn can

Tint

Qwall

Ts roof

Ts can

Hsens can

LEcan

Gs can

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Rn can

Tint

Qwall

Ts roof

Ts can

Hsens can

LEcan

Gs can

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Rn can

Tint

Qwall

Ts roof

Ts can

Hsens can

LEcan

Gs can

_1029856457.unknown

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Momentum equation = forcing terms(modification of vertical turbulent transport term)+ momentum sources due to building horizontal surfaces (friction force)+ momentum sources due to the pressure and viscous drag forces induced by the vegetation and the building vertical surfaces

Heat equation = forcing terms (modification of vertical turbulent transport term)+ sensible heat sources from surfaces+ anthropogenic heat sources (Taha, 1999)Humidity equation= forcing terms(modification of vertical turbulent transport term)+ humidity sources from surfaces + anthropogenic humidity sources (not considered)

TKE equation= forcing terms(modification of vertical turbulent transport) + shear production by building horizontal surfaces + buoyant production from the surface sensible heat fluxes + wake production due to the presence of vegetation and buildings

+ dissipation due to the accelerated cascade of TKE from large to small scales due to the canopy elements

Parameterization of the turbulent length scale of Bougeault and Lacarrre (1989) inside the Gayno-Seaman PBL model.

Addition of a turbulent length scale in the dissipation rate of TKE to consider the size of the wake eddies inside the canopy (following Martilli et al. (2002) for building canopy).Turbulent Length Scale

SM2-U(3D)Dupont et al.: 2003a, Parameterisation of the Urban Water Budget by Using SM2-U model. (Submitted to Journal of the Applied Meteorology)Dupont et al.: 2003b, Parameterisation of the Urban Energy Budget with the SM2-U model for the Urban Boundary Layer Simulation.(Submitted to Boundary-Layer Meteorology)SM2-U(3D) is a multi-layers rural and urban canopy model derived from the one-layer canopy model SM2-U.The model estimates the sensible and latent heat fluxes at each level within the canopy.

Philadelphia case (July 14th, 1995)DA-SM2-U is capable of simulating the important features observed in the urban and rural roughness sub-layer.

Comparison with measurements showed that the surface air temperature simulation above rural and urban areas is improved with DA-SM2-U compared to the standard version of MM5.Dupont et al.: 2003c, Simulation of Meteorological Fields within and above Urban and Rural Canopies with a Mesoscale Model (MM5).(Submitted to Boundary-Layer Meteorology)

Meteorological fields inside the canopy at 2 m above the ground

Houston caseAugust 25 September 1, 2000 (portion of the Texas 2000 Air Quality Study field program).

MM5 has been run by Nielsen-Gammon in a one-way nested configuration: 108-, 36-, 12-, and 4-km horizontal grid spacing.

DA-SM2-U is used for a 1-km horizontal grid spacing domain (141 x 133 x 48).

Canopy morphological parameters computed by Steve Burian

Morphological parameter domainMM5 1-km domain

Land Use / Land Cover USGS level II (38 categories)

Airborne LIDAR dataset from TerraPoint LLCFor the all Harris county (compressed data is ~70 GB, uncompressed ~300+ GB)

Give the earth elevation and the elevation of the top of canopy elements.

1-m and 5-m horizontal grid spacing,

Horizontal accuracy of 15 to 20 cm RMSE, Vertical accuracy of 5 to 10 cm RMSE

Example of Airborne LIDAR

High-resolution aerial photos (Harris A) Land Use / Land CoverAirborne LIDAR dataBuilding footprint dataset (Harris A)ArcView map calculator Morphological parameters for Harris A(1-km2 horizontal resolution and 1-m vertical resolution)Correlation between the morphological parameter values and the Land Use Morphological parameters for the all computational domain +

Mean building and vegetation height Building plan area densityVegetation plan area densityBuilding rooftop area densityVegetation top area densityBuilding frontal area density for 4 wind directionsVegetation frontal area densityWall-to-plan area ratioBuilding height-to-width ratioSurface fraction of vegetation, roads, rooftops, and waterSky view factor at ground level and as a function of heightAerodynamic roughness length and displacement height (Raupach, Macdonald, Bottema)Mean orientation of streetsApproximations for impervious area, directly connected impervious area, and building materialForDA-SM2-U

Detailed city: specific morphological parameters are deduced for each grid cell of Harris A, outside they are deduced following the Land Use from their correlations in Harris A.Average city: morphological parameters are deduced following the Land Use for the entire domain.Influence of the city representation:

Detailed cityAverage cityRoof fraction

Detailed cityAverage cityHeight-to-width ratio

Detailed cityAverage city

Detailed cityAverage cityDetailed cityAverage city4 p.m.12 a.m.

Surface temperature

Detailed cityAverage cityDetailed cityAverage cityTKEPBL height

4 p.m.

ConclusionsA neighborhood scale version of MM5 (DA-SM2-U) has been developed and tested successfully on Philadelphia.A huge morphological database has been constructed on Houston for DA-SM2-UThe choice of the representation of the city of Houston (detailed or average city) seems to have an impact on the UBL structure, especially during unstable conditions.This study needs to be continued with different average representations of the city.

Future plansComparison of simulated and observed surface meteorological fields (25 surface observation stations).The first results seem to indicate an improvement of the wind speed at 10 m by comparison to the results of the standard version of MM5. However, the see breeze seems to be too weak toward the city.CMAQ simulation on Houston by using meteorological fields from MM5-DA-SM2-U

IntroductionIntroduction