The International Urban Energy Balance Comparison Project: Initial Results from Phase 2.

Many urban land surface schemes have been developed, incorporating different assumptions about the features of, and processes occurring at, the surface. Here, the first results from Phase 2 of an international comparison are presented. Evaluation is based on analysis of the last 12 months of a 15 month dataset. In general, the schemes have best overall capability to model net all-wave radiation. The models that perform well for one flux do not necessarily perform well for other fluxes. Generally there is better performance for net all wave radiation than sensible heat flux. The degree of complexity included in the models is outlined, and impacts on model performance are discussed in terms of the data made available to modellers at four successive stages

Initial results from Phase 2 of the international urban energy balance model comparison

Urban land surface schemes have been developed to model the distinct features of the urban surface and the associated energy exchange processes. These models have been developed for a range of purposes and make different assumptions related to the inclusion and representation of the relevant processes. Here, the first results of Phase 2 from an international comparison project to evaluate 32 urban land surface schemes are presented. This is the first large-scale systematic evaluation of these models. In four stages, participants were given increasingly detailed information about an urban site for which urban fluxes were directly observed. At each stage, each group returned their models' calculated surface energy balance fluxes. Wide variations are evident in the performance of the models for individual fluxes. No individual model performs best for all fluxes. Providing additional information about the surface generally results in better performance. However, there is clear evidence that poor choice of parameter values can cause a large drop in performance for models that otherwise perform well. As many models do not perform well across all fluxes, there is need for caution in their application, and users should be aware of the implications for applications and decision making

A large-eddy simulation study of thermal effects on turbulent flow and dispersion in and above a street canyon

Thermal effects on turbulent flow and dispersion in and above an idealized street canyon with a street aspect ratio of 1 are numerically investigated using the parallelized large-eddy simulation model (“PALM”). Each of upwind building wall, street bottom, and downwind building wall is heated, and passive scalars are emitted from the street bottom. When compared with the neutral (no heating) case, the heating of the upwind building wall or street bottom strengthens a primary vortex in the street canyon and the heating of the downwind building wall induces a shrunken primary vortex and a winding flow between the vortex and the downwind building wall. Heating also induces higher turbulent kinetic energy and stronger turbulent fluxes at the rooftop height. In the neutral case, turbulent eddies generated by shear instability dominate mixing at the rooftop height and appear as band-shaped perturbations in the time–space plots of turbulent momentum and scalar fluxes. In all of the heating cases, buoyancy-generated turbulent eddies as well as shear-generated turbulent eddies contribute to turbulent momentum and scalar fluxes and band-shaped or lump-shaped perturbations appear at the rooftop height. A quadrant analysis shows that at the rooftop height, in the neutral case and in the case with upwind building-wall heating, sweep events are less frequent but contribute more to turbulent momentum flux than do ejection events. By contrast, in the case with street-bottom and downwind building-wall heating, the frequency of sweep events is similar to that of ejection events and the contribution of ejection events to turbulent momentum flux is comparable to that of sweep events

Phase 2 of the International urban energy balance comparison project - Forcing Data

Phase 2 - known as Alpha during project - data from Melbourne, Australia Grimmond C, M Blackett, M Best, J Baik, S Belcher, J Beringer, S Bohnenstengel, I Calmet, F Chen, A Coutts, A Dandou, K Fortuniak, M Gouvea, R Hamdi, M Hendry, M Kanda, T Kawai, Y Kawamoto, H Kondo, E Krayenhoff, S Lee, T Loridan, A Martilli, V Masson, S Miao, K Oleson, R Ooka, G Pigeon, A Porson, Y Ryu, F Salamanca, G Steeneveld, M Tombrou, J Voogt, D Young, N Zhang 2011: Initial Results from Phase 2 of the International urban energy balance comparison project, Intern. J Climatology 31, 244-272 https://doi.org/10.1002/joc.2227 Forcing data in two formats *.dat - ascii text file *.nc - netCD

Phase 2 of the International urban energy balance comparison project - Forcing Data

Phase 2 - known as Alpha during project - data from Melbourne, Australia Grimmond C, M Blackett, M Best, J Baik, S Belcher, J Beringer, S Bohnenstengel, I Calmet, F Chen, A Coutts, A Dandou, K Fortuniak, M Gouvea, R Hamdi, M Hendry, M Kanda, T Kawai, Y Kawamoto, H Kondo, E Krayenhoff, S Lee, T Loridan, A Martilli, V Masson, S Miao, K Oleson, R Ooka, G Pigeon, A Porson, Y Ryu, F Salamanca, G Steeneveld, M Tombrou, J Voogt, D Young, N Zhang 2011: Initial Results from Phase 2 of the International urban energy balance comparison project, Intern. J Climatology 31, 244-272 https://doi.org/10.1002/joc.2227 Forcing data in two formats *.dat - ascii text file *.nc - netCD