FUMAPEX Experience of Model Urbanisation - Meteorological and Air Quality Models for Urban Areas - page 61

8.2 Methodology for Urbanization of City-Scale
Meteorological Models
8.2.1 FUMAPEX Strategy to Improve NWP and Meso-Scale
Meteorological Models for Urban Areas
The FUMAPEX (FUMAPEX, 2005; Baklanov et al., 2005) strategy to improve
NWP and meso-scale meteorological models includes the following aspects for the
urbanisation of relevant submodels or processes:
(i) Model down-scaling, including increasing vertical and horizontal resolution
and nesting techniques (one- and two-way nesting);
(ii) Modification of high-resolution urban land-use classifications, parameteriza-
tions and algorithms for roughness parameters in urban areas, based on the
morphometric method;
(iii) Specific parameterization of the urban fluxes in meso-scale models;
(iv) Modelling/parameterization of meteorological fields in the urban sublayer;
(v) Calculation of the urban mixing height based on prognostic approaches.
The following meso-meteorological and NWP models were used for urban
conditions or for different variants of the “urbanisation” scheme (user/developer
teams are in brackets, cf. www.fumapex.dmi.dk): 1. DMI-HIRLAM (DMI); 2.
Local Model LM (DWD, MeteoSwiss, EPA Emilia-Romagna); 3. MM5 (CORIA,
met.no, UH); 4. RAMS (CEAM, Arianet); 5. Topographic Vorticity-Mode (TVM)
Mesoscale Model (UCL); 6. Finite Volume Model FVM (EPFL); 7. SUBMESO
model (ECN).
8.2.2 Urban Fluxes and Sublayer Parameterisation
Two main approaches to simulate urban canopy effects are considered :
1. Modifying existing non-urban approaches (e.g., the Monin-Obukhov similarity
theory,) for urban areas by finding appropriate values for the effective roughness
lengths, displacement height, and heat fluxes (adding anthropogenic heat flux,
heat storage capacity and albedo change). In this case, the lowest model level is
close to the top of the urban canopy (displacement height), and a new analytical
model is suggested for the urban roughness sublayer which is the critical region
where pollutants are emitted and where people live (Zilitinkevich and Baklanov,
2004).
2. Alternatively, source and sink terms are added in the momentum, energy and
turbulent kinetic energy equations to represent the effects of buildings. Different
parameterizations (Masson, 2000; Martilli et al., 2002) have been developed to
estimate the radiation balance (shading and trapping effect of the buildings), the