Alexander Baklanov - Böcker

Most of practically-used turbulence closure models are based on the concept of downgra- ent transport. Accordingly the models express turbulent uxes of momentum and scalars as products of the mean gradient of the transported property and the corresponding turbulent transport coef cient (eddy viscosity, K , heat conductivity, K , or diffusivity, K ). Fol- M H D lowing Kolmogorov (1941), turbulent transport coef cients are taken to be proportional to the turbulent velocity scale, u , and length scale, l : T T K ? K ? K ? u l . (1) M H D T T 2 Usually u is identi ed with the turbulent kinetic energy (TKE) per unit mass, E ,and K T is calculated from the TKE budget equation using the Kolmogorov closure for the TKE dissipation rate: ? ? E /t , (2) K K T where t ? l /u is the turbulent dissipation time scale. This approach is justi ed when it T T T is applied to neutral stability ows, where l can be taken to be proportional to the distance T from the nearest wall. However, this method encounters dif culties in strati ed ows (both stable and uns- ble). The turbulent Prandtl number Pr = K /K exhibits essential dependence on the T M H strati cation and cannot be considered as constant.

Most of practically-used turbulence closure models are based on the concept of downgra- ent transport. Accordingly the models express turbulent uxes of momentum and scalars as products of the mean gradient of the transported property and the corresponding turbulent transport coef cient (eddy viscosity, K , heat conductivity, K , or diffusivity, K ). Fol- M H D lowing Kolmogorov (1941), turbulent transport coef cients are taken to be proportional to the turbulent velocity scale, u , and length scale, l : T T K ? K ? K ? u l . (1) M H D T T 2 Usually u is identi ed with the turbulent kinetic energy (TKE) per unit mass, E ,and K T is calculated from the TKE budget equation using the Kolmogorov closure for the TKE dissipation rate: ? ? E /t , (2) K K T where t ? l /u is the turbulent dissipation time scale. This approach is justi ed when it T T T is applied to neutral stability ows, where l can be taken to be proportional to the distance T from the nearest wall. However, this method encounters dif culties in strati ed ows (both stable and uns- ble). The turbulent Prandtl number Pr = K /K exhibits essential dependence on the T M H strati cation and cannot be considered as constant.

‘Mesoscale Modelling for Meteorological and Air Pollution Applications’ combines the fundamental and practical aspects of mesoscale air pollution and meteorological modelling. Providing an overview of the fundamental concepts of air pollution and meteorological modelling, including parameterization of key atmospheric processes, the book also considers equally important aspects such as model integration, evaluation concepts, performance evaluation, policy relevance and user training.

This book for the first time gives an overall view of the current situation in urbanization of meteorological and air quality models around the world. It discusses and makes recommendations on the best practice and strategy for urbanization of different types of meteorological and air quality models.Based on the selected presentations given at the COST728 workshop, the contributions are arranged in four parts: urban morphology and databases; parameterizations of urban canopy; strategy for urbanization of different types of models; and evaluation and city case studies / field studies. The chapters treat either dynamic (on wind and turbulent) and thermal effects (on temperature and energy in general). The final chapter of this volume summarizes the discussion and conclusions from the four main topics and provides recommendations and future requirements. This monograph is oriented towards numerical weather prediction and air quality modelling communities.