Boundary-Layer Meteorology

, Volume 104, Issue 2, pp 261–304

An Urban Surface Exchange Parameterisation for Mesoscale Models

  • Alberto Martilli
  • Alain Clappier
  • Mathias W. Rotach
Article

DOI: 10.1023/A:1016099921195

Cite this article as:
Martilli, A., Clappier, A. & Rotach, M.W. Boundary-Layer Meteorology (2002) 104: 261. doi:10.1023/A:1016099921195

Abstract

A scheme to represent the impact of urban buildings on airflow in mesoscale atmospheric models is presented. In the scheme, the buildings are not explicitly resolved, but their effects on the grid-averaged variables are parameterised. An urban quarter is characterised by a horizontal building size, a street canyon width and a building density as a function of height. The module computes the impact of the horizontal (roof and canyon floor) and vertical (walls) surfaces on the wind speed, temperature and turbulent kinetic energy. The computation of the shortwave and longwave radiation, needed to compute the temperature of the urban surfaces, takes into account the shadowing and radiation trapping effects induced by the urban canyons. The computation of the turbulent length scales in the TKE equation is also modified to take into account the presence of the buildings.

The parameterisation is introduced into a mesoscale model and tested in a bidimensional case of a city over flat terrain. The new parameterisation is shown to be able to reproduce the most important features observed in urban areas better than the traditional approach which is based only on the modification of the roughness length, thereby retaining the Monin–Obukhov similarity theory. The new surface exchange parameterisation is furthermore shown to have a strong impact on the dispersion characteristics of air pollutants in urban areas.

Air pollution Mesoscale models Street canyon Urban boundary layer Urban climatology Urban energy balance 

Copyright information

© Kluwer Academic Publishers 2002

Authors and Affiliations

  • Alberto Martilli
    • 1
  • Alain Clappier
    • 1
  • Mathias W. Rotach
    • 2
  1. 1.Lausanne (EPFL), Air and Soil Pollution LaboratorySwiss Federal Institute of TechnologyLausanne
  2. 2.Institute for Climate ResearchSwiss Federal Institute of Technology, Zurich (ETHZ)ZurichSwitzerland

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