5
Flow Over Modified Surfaces
Abstract
In this chapter, an assessment of airflow over modified surfaces was made,
mainly corresponding to urban areas, hills, or of transition between surfaces with
different roughness, different land uses, and ambient temperatures. This surface
heterogeneity that leads to a development of an internal boundary layer,
including sublayers, with a determined height and influence length or fetches
were analyzed. In the same way, the variation of surface temperatures leads to
internal thermal boundary layers with estimable heights. Airflow patterns over
isolated arrayed building elements were assessed with turbulent changes in
vertical velocity profiles, typical wakes or cavities, or horizontal wrapping
horseshoe vortices, in the context of urban heat island or stratification effects,
with implications in items as distinct as atmospheric thermal regimes or pollutant
dispersion. The main patterns of airflow over isolated or grouped hills were
discussed, with an analysis of air circulation around and over hills under
different stability conditions, characterized through Froude number variation.
Finally, a discussion was carried out of the dynamics of specific atmospheric
case studies, such as katabatic winds or Foehn and Bora-type descending flow in
hills under inversion conditions, with potential relevant theoretical
extrapolations.
5.1 Introduction
In the previous chapters, atmospheric fluxes in the surface layer over relatively
homogeneous and flat surfaces were described. Such idealized surfaces occur in
seas, plains, ice, and forests. However, in many real situations, surface characteristics vary over distances as short as 100 m. Among examples of surface heterogeneity are coastlines, valleys, hills, and transition areas between rural and urban
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. Rodrigues et al., Fundamental Principles of Environmental Physics,
https://doi.org/10.1007/978-3-030-69025-0_5
133
Flow Over Modified Surfaces
Abstract
In this chapter, an assessment of airflow over modified surfaces was made,
mainly corresponding to urban areas, hills, or of transition between surfaces with
different roughness, different land uses, and ambient temperatures. This surface
heterogeneity that leads to a development of an internal boundary layer,
including sublayers, with a determined height and influence length or fetches
were analyzed. In the same way, the variation of surface temperatures leads to
internal thermal boundary layers with estimable heights. Airflow patterns over
isolated arrayed building elements were assessed with turbulent changes in
vertical velocity profiles, typical wakes or cavities, or horizontal wrapping
horseshoe vortices, in the context of urban heat island or stratification effects,
with implications in items as distinct as atmospheric thermal regimes or pollutant
dispersion. The main patterns of airflow over isolated or grouped hills were
discussed, with an analysis of air circulation around and over hills under
different stability conditions, characterized through Froude number variation.
Finally, a discussion was carried out of the dynamics of specific atmospheric
case studies, such as katabatic winds or Foehn and Bora-type descending flow in
hills under inversion conditions, with potential relevant theoretical
extrapolations.
5.1 Introduction
In the previous chapters, atmospheric fluxes in the surface layer over relatively
homogeneous and flat surfaces were described. Such idealized surfaces occur in
seas, plains, ice, and forests. However, in many real situations, surface characteristics vary over distances as short as 100 m. Among examples of surface heterogeneity are coastlines, valleys, hills, and transition areas between rural and urban
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
A. Rodrigues et al., Fundamental Principles of Environmental Physics,
https://doi.org/10.1007/978-3-030-69025-0_5
133