Keywords

urban modelling, surface schemes, roughness sublayer, parameterization, wind profile

Start Date

1-7-2002 12:00 AM

Description

Numerical Weather Prediction (NWP) models in connection with increasing capacities of computers in the last years have considerably increased the spatial (vertical and horizontal) resolution and practically become close to meso- and local-scale models. Nevertheless, in most NWP models, urban and non-urban areas are treated rather similarly, through similar sub-surface, surface and boundary layer formulations. No different/additional mechanisms or physics exist to account for specific urban dynamics and energetics and for their impact on atmospheric boundary layer. So, it is important to develop parameterizations of the urban effects in NWP models. The improvement of the urban meteorological forecast is also very important for the air pollution forecasting. The objective of this study is the modification of the Land Air Parameterization Scheme [Mihailovic, 1996] to include the parameterization of the urban effects. To this end, the original scheme was developed to take into account the complexity of urban surfaces through the new definition of wind profile over heterogeneous surface. The general equation for the wind speed profile depending on effective or aggregated values of roughness length and displacement height was used. To examine the model behavior, the numerical experiment for different parts of a hypothetical urban area has been performed. The results are in good agreement with the previous experimental observations. It was found that the most urbanized part of the city is the warmest, with a large sensible heat flux, large heat storage and weak latent heat flux. Simulated surface temperatures have shown the existence of urban heat island phenomenon.

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Jul 1st, 12:00 AM

Land air surface scheme (LAPS) for use in urban modelling

Numerical Weather Prediction (NWP) models in connection with increasing capacities of computers in the last years have considerably increased the spatial (vertical and horizontal) resolution and practically become close to meso- and local-scale models. Nevertheless, in most NWP models, urban and non-urban areas are treated rather similarly, through similar sub-surface, surface and boundary layer formulations. No different/additional mechanisms or physics exist to account for specific urban dynamics and energetics and for their impact on atmospheric boundary layer. So, it is important to develop parameterizations of the urban effects in NWP models. The improvement of the urban meteorological forecast is also very important for the air pollution forecasting. The objective of this study is the modification of the Land Air Parameterization Scheme [Mihailovic, 1996] to include the parameterization of the urban effects. To this end, the original scheme was developed to take into account the complexity of urban surfaces through the new definition of wind profile over heterogeneous surface. The general equation for the wind speed profile depending on effective or aggregated values of roughness length and displacement height was used. To examine the model behavior, the numerical experiment for different parts of a hypothetical urban area has been performed. The results are in good agreement with the previous experimental observations. It was found that the most urbanized part of the city is the warmest, with a large sensible heat flux, large heat storage and weak latent heat flux. Simulated surface temperatures have shown the existence of urban heat island phenomenon.