eTheses Repository - University of Birmingham

Pino et al. 2004), convective activity and precipitation (e.g. Bornstein et al. 2000; Thielen et al.
2000), and air quality (e.g. Sarrat et al. 2006).
The correct representation of the thermal and dynamic effects of the urban surface on the
atmospheric boundary layer in mesoscale models has important implications for understanding
the urban effect, as well as studying pollutant dispersion and for simulating urban air quality. In
urban areas human activities are large sources of atmospheric pollutants, and their spatial
distribution, concentration and residence time in the atmosphere is driven largely by thermal and
dynamic processes over the city. In order to understand pollutant dispersion and assess urban air
quality and human exposure, dispersion models rely on atmospheric mesoscale models to
provide accurate meteorological fields representing the urban boundary layer (Seaman 2000;
Collier 2006; Sarrat et al. 2006).
At the microscale, the energy balance of the urban surface can be studied with building resolved
models, but due to computational costs and the need to provide highly detailed input data, these
are limited to analysing local urban meteorological and climatic conditions, or highly specific
studies such as the dispersion of pollutants from a specific source. In a mesoscale model with
typical spatial resolution of the order of a kilometre, it is impossible to resolve the effects of
single buildings due to computational cost, and it becomes more efficient, and indeed necessary,
to adopt a building averaged approach (Martilli et al. 2002).
In mesoscale models (i.e. models with a grid size that ranges from 100 m for research models to
10 km for operational mesoscale models) the interaction between the ground surface and the
atmosphere has typically been based on MOST, a first order approximation which assumes a
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