Review of atmospheric turbulence over cities

TLDR

Urban turbulence shares key features with plant canopy flows, often describable as a plane mixing layer. The review recommends future field studies focus on turbulent exchange at the canopy top, within the canopy, and across the urban boundary layer. The authors critically review over fifty studies, focusing on 14 high‑quality experiments, and present observations as non‑dimensional statistics to enable comparison across urban and other rough surfaces. Wake production and uneven scalar sources create a roughness sub‑layer extending 2.5–3 times building height, casting doubt on conventional micrometeorological models within this region.

Abstract

Abstract This paper provides a comprehensive, critical review of turbulence observations over cities. More than fifty studies are analysed with their experimental conditions summarized in an appendix. The main results are based on 14 high‐quality experiments which met criteria based on stringent experimental requirements. The observations are presented as non‐dimensional statistics to facilitate comparison between urban studies and work conducted over other rough, inhomogeneous surfaces. Wake production associated with bluff bodies, and the inhomogeneous distribution of sources and sinks of scalars, result in a roughness sub‐layer which for the studies reviewed extends to about 2.5 to 3 times the height of the buildings. It is shown that within this region the basis of several traditional micrometeorological approaches to describe the turbulent exchange is in doubt. There are strong similarities to flow over plant canopies, and many of the turbulence characteristics can be interpreted in the framework of a plane mixing layer. Future field observations should concentrate on the turbulent exchange near the top and within the urban canopy as well as within the urban boundary layer.