Validation of Martilli's urban boundary layer scheme with measurements from two mid-latitude European cities

Abstract

Abstract. Martilli's urban parameterization scheme is improved and implemented in a mesoscale model in order to take into account the typical effects of a real city on the air temperature near the ground and on the surface exchange fluxes. The mesoscale model is run on a single column using atmospheric data and radiation recorded above roof level as forcing. Here, the authors validate Martilli's urban boundary layer scheme using measurements from two mid-latitude European cities: Basel, Switzerland and Marseilles, France. For Basel, the model performance is evaluated with observations of canyon temperature, surface radiation, and energy balance fluxes obtained during the Basel urban boundary layer experiment (BUBBLE). The results show that the urban parameterization scheme represents correctly most of the behavior of the fluxes typical of the city center of Basel, including the large heat uptake by the urban fabric and the positive sensible heat flux at night. For Marseilles, the model performance is evaluated with observations of surface temperature, canyon temperature, surface radiation, and energy balance fluxes collected during the field experiments to constrain models of atmospheric pollution and transport of emissions (ESCOMPTE) and its urban boundary layer (UBL) campaign. At both urban sites, vegetation cover is less than 20%, therefore, particular attention was directed to the ability of Martilli's urban boundary layer scheme to reproduce the observations for the Marseilles city center, where the urban parameters and the synoptic forcing are totally different from Basel. Evaluation of the model with wall, road, and roof surface temperatures gave good results. The model correctly simulates the net radiation, canyon temperature, and the partitioning between the turbulent and storage heat fluxes.

Impact of urban parameterization on high resolution air quality forecast with the GEM – AQ model

“…Although results from a 1-D model of energy balance over a city show very good agreements with observations, implementations and applications of these processes in complex 3-D operational models are still challenging (e.g. Hamdi and Schayes, 2007;Baklanov et al, 2008;Oleson et al, 2008). In the case of simulations with grid resolution of a few kilometres, urban structures become grid-scale features, which leads to the need for more accurate description of these processes.…”

Modeling the energy balance in Marseille: Sensitivity to roughness length parameterizations and thermal admittance

“…Following Lemonsu et al [2004] and Hamdi and Schayes [2005] the plan area of vegetated surfaces per total plan area for this urban measurement site adds up to 14%. By multiplying 18.6 W m À2 by 0.86, an estimated daily mean of total Q F of 21.7 W m À2 for a 100% total urban area is obtained.…”

“…Measurements were taken using a pneumatic tower on the top of the CAAM. More detailed characteristics of this site are fully described in Lemonsu et al, 2004;Hamdi and Schayes, 2005;Mestayer et al, 2005], which also provides a detailed description of the micrometeorological measurements and instrumentation. The other stations are located in rural areas.…”

“…The weighting has a bell-shaped curve (weighting toward the middle of the path whereby first and last 15% of the path only play a minor role [Hartogensis et al, 2003]. Moreover, it has been shown that for the Marseille area, the spatial variability of the sensible heat fluxes measured by the LAS is small [Mestayer et al, 2005] and that this surface is rather homogeneous with a dense mixture of old buildings of four to six stories high and narrow streets in all directions [Lagouarde et al, 2002;Hamdi and Schayes, 2005]. Therefore two points in the middle of the pathline between Nedelec-Paradis (LAS1) and Timone-Nedelec (LAS2) are selected to be representative measurements sites to validate the modelled sensible heat flux for its respective model grid boxes covering the LAS' pathline ( Figure 2 and Table 3).…”

“…[12] The City Center of Marseille is a dense commercial and residential area, with 4 -6 storey buildings characterized by a variety of building materials and surfaces Lemonsu et al, 2004;Hamdi and Schayes, 2005;Mestayer et al, 2005] and a plan are of vegetated surfaces per total plan area of <14% Hamdi and Schayes, 2005], encompassing, trees, grass terrain and bare soil. Each land cover material has its own thermal properties, and therefore a wide range of volumetric heat capacity (C p ) and thermal conductivity values (k) for urban and natural surfaces has been chosen in order to test the sensitivity of the urban energy balance to the thermal characteristics of these surfaces.…”