1/26 APPLICATION OF THE URBAN VERSION OF MM5 FOR HOUSTON University Corporation for Atmospheric Research Sylvain Dupont Collaborators: Steve Burian, Jason Ching

2/26 Urbanized version of MM5 Drag-Force Approach DA-SM2-U èSimulation of meteorological fields within and above rural and urban canopies. èNeighborhood scale: 1-km horizontal grid spacing and few meter vertical grid spacing inside the canopy èCanopy elements are not explicitly defined but spatially averaged Soil Model for Sub-Meso scales - Urbanized version

3/26 General Objective Modeling air-quality for estimating human exposure to air pollution in urban areas by using CMAQ. Specific Objectives of this presentation èComputation of the Houston morphological parameters for DA-SM2-U. èInfluence of the Houston representation on the urban boundary layer structure èWhat degree of urban representation detail do we need at neighborhood scales ?

4/26 DA-SM2-U Introduced inside the Gayno-Seaman PBL scheme

5/26 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

6/26 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)

7/26 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

8/26 èParameterization of the turbulent length scale of Bougeault and Lacarrère (1989) inside the Gayno-Seaman PBL model. èAddition 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

9/26 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) èSM2-U(3D) is a multi-layers rural and urban canopy model derived from the one-layer canopy model SM2-U. èThe model estimates the sensible and latent heat fluxes at each level within the canopy.

10/26 Philadelphia case (July 14 th, 1995) èDA-SM2-U is capable of simulating the important features observed in the urban and rural roughness sub-layer. èComparison 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)

11/26 Meteorological fields inside the canopy at 2 m above the ground

12/26 Houston case èAugust 25 – September 1, 2000 (portion of the Texas 2000 Air Quality Study field program). èMM5 has been run by Nielsen-Gammon in a one-way nested configuration: 108-, 36-, 12-, and 4-km horizontal grid spacing. èDA-SM2-U is used for a 1-km horizontal grid spacing domain (141 x 133 x 48). èCanopy morphological parameters computed by Steve Burian

13/26 Morphological parameter domain MM5 1-km domain

14/26 Land Use / Land Cover USGS level II (38 categories)

15/26 Airborne LIDAR dataset from TerraPoint LLC èFor the all Harris county (compressed data is ~70 GB, uncompressed ~300+ GB) èGive the earth elevation and the elevation of the top of canopy elements. è1-m and 5-m horizontal grid spacing, èHorizontal accuracy of 15 to 20 cm RMSE, Vertical accuracy of 5 to 10 cm RMSE

16/26 Example of Airborne LIDAR

17/26 High-resolution aerial photos (Harris A) Land Use / Land Cover Airborne LIDAR data Building footprint dataset (Harris A) ArcView map calculator Morphological parameters for Harris A (1-km 2 horizontal resolution and 1-m vertical resolution) Correlation between the morphological parameter values and the Land Use Morphological parameters for the all computational domain +

18/26 Mean building and vegetation heightMean building and vegetation height Building plan area densityBuilding plan area density Vegetation plan area densityVegetation plan area density Building rooftop area densityBuilding rooftop area density Vegetation top area densityVegetation top area density Building frontal area density for 4 wind directionsBuilding frontal area density for 4 wind directions Vegetation frontal area densityVegetation frontal area density Wall-to-plan area ratioWall-to-plan area ratio Building height-to-width ratioBuilding height-to-width ratio Surface fraction of vegetation, roads, rooftops, and waterSurface fraction of vegetation, roads, rooftops, and water Sky view factor at ground level and as a function of heightSky view factor at ground level and as a function of height Aerodynamic roughness length and displacement height (Raupach, Macdonald, Bottema)Aerodynamic roughness length and displacement height (Raupach, Macdonald, Bottema) Mean orientation of streetsMean orientation of streets Approximations for impervious area, directly connected impervious area, and building materialApproximations for impervious area, directly connected impervious area, and building material For DA-SM2-U

19/26 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:

20/26 Detailed city Average city Roof fraction

21/26 Detailed city Average city Height-to- width ratio

22/26 Detailed city Average city

23/26 Surface temperature Detailed cityAverage city Detailed cityAverage city 4 p.m. 12 a.m.

24/26 4 p.m. Detailed cityAverage city Detailed cityAverage city TKE PBL height

25/26Conclusions èA neighborhood scale version of MM5 (DA-SM2-U) has been developed and tested successfully on Philadelphia. èA huge morphological database has been constructed on Houston for DA- SM2-U èThe 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.

26/26 Future plans èComparison 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. èCMAQ simulation on Houston by using meteorological fields from MM5- DA-SM2-U