Urban parameterization

The parameterisation has been tested on the city of Basel (Switzerland), Mexico City (Mexico), Copenhagen (Denmark), and verified versus the BUBBLE experiment (Basel Urban Boundary Layer Experiment Rotach et al., 2005 [549]). The verification results (Figure 9.11) show that the urban parameterization scheme is able to catch most of the typical processes induced by an urban surface Inside the canopy layer, the wind speed, the friction velocity and the atmospheric stability are reduced. In the other hand, even if the main effects of the urban canopy are reproduced, the comparison with the measurement seems indicates that some physical processes are still missing in the parameterization. In most of the cases, the model still overestimates the wind speed inside the canopy layer and it can have difficulties to simulate the maximum of the friction velocity which appears above the building roofs. 

Figure 9.11 Vertical profiles of wind velocity (left), friction velocity (middle), and potential temperature (right) measured (points), simulated with MOST (dashed line) and with the urban parameterization of Martilli et al. 2002 [393] (solid line) (Clappier, Ch. 3.4 in Baklanov and Joffre, [30]).

Figure 9.12 Temperature measured and simulated with and without the BEP urban parameterization over Mexico City. The simulation without the urban parameterization underestimates the temperature (Clappier, Ch. 2.16 in Baklanov, 2003 [29]).

Some attempts have been made to use reactive hydrocarbons in conjunction with inert chemical tracers to deduce HO concentrations in urban plumes (139,140,141). Difficulties in deducing [HO ] from these experiments have been studied by McKeen et al (142), who conclude that such experiments can underpredict HO concentrations by a factor of 2 when more reactive hydrocarbons are used and parameterization of transport processes is not properly accounted for. 

An integrated AQ modelling system similar to those previously sketched has been applied in two different urban environments with the intent to highlight its sensitivity to dispersion process parameterizations and AQ model initialization... 

The vertical structure of PBL and SL is very important for ACTMs, so increasing the vertical resolution and improved parameterizations of BL are necessary. The meteorological improvements are already worked out for some aspects (stable PBL) and the urban characteristics should be included in the new surface scheme. In the meso-scale model the urban parametrization is already available (TEB Town Energy Budget in SURFEX and BEP Building Effect Parameter-isation in Enviro-HIRLAM). 

As has been mentioned above, the StA size distribution depends both on specific inflaming material and on the way of its pyrolysis, and on the properties of the environment, into which the StA particles are injected [42]. The size distribution of StA from urban and forest fires has been suggested to be parameterized by log-normal distribution [38]... 

The second module option of Figure 9.5 was realised with the Building Effect Parameterization (BEP) model, developed by the Swiss partner EPFL. It includes the urban sub-layer parameterisation suggested by Martilli et al 2002 [393] with modifications for implementation into NWP models and several further improvements (e.g., Hamdi and Shayes, 2005 [250] Clappier, Ch. 3.4 in Baklanov and Mestayer, 2004 [33]). 

UDM (Urban Dispersion Model) (Hall et al., 2002 [248]) is a widely-used model developed by the UK Defence Science and Technology Laboratory (DSTL) based on assumptions of a Gaussian shape and empirical parameterizations developed from special field and laboratory experiments involving obstacle arrays. 

Baklanov, A., Mestayer, P, Clappier, A., Zilitinkevich, S., Joffre, S., Mahura, A., and Nielsen, N.W. (2005) On parameterizations of urban atmosphere sublayer in meteorological models, Atmospheric Chemistry and Physics Discuss. 5, 12119— 12176. 

Brown, M.J., and Williams, M.D. (1998) An Urban Canopy Parameterization for Mesoscale Meteorological Models. Los Alamos National Laboratory, Report LA-UR-98-3831. 

Roulet, Y.-A., Martilli, A., Rotach, M W and Clappier, A.(2005) Validation of an Urban Surface Exchange Parameterization for Mesoscale Models - ID Case in a Street Canyon, Journal of Applied Meteorology Vol. 44, No. 9,1484-1498. 

Li Xiaoh, He Jinhai, et al. 2003. The design of urban canopy parameterization of MM5 and its numerical simulations. Acta Meteor Sinica (in Chinese), 61(5) 526-538. 

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