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Long-wave radiative flux divergence and nocturnal cooling of the urban atmosphere

II: Within an urban canyon


Results from measurements of long-wave radiative flux divergence on calm, cloudless nights from within an urban canyon are presented. Results show the existence of three-dimensional (volume) radiative divergence in the canyon-air system. The results are compared with air temperature cooling rates (energy storage change) in the canyon. With calm, cloudless conditions, radiative divergence is the dominant mechanism controlling air temperature changes. In the early part of the night this results in air cooling, but radiative warming was commonly observed after midnight. Canyon-air volume radiative divergence is found to be considerably less than that observed previously above roof-level, and in rural areas. Measured cooling rates in the canyon are poorly predicted by a surface-oriented cooling approach. This again points to the importance of the atmospheric radiation balance.

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Nunez, M., Oke, T.R. Long-wave radiative flux divergence and nocturnal cooling of the urban atmosphere. Boundary-Layer Meteorol 10, 121–135 (1976). https://doi.org/10.1007/BF00229280

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  • Cool Rate
  • Temperature Cool
  • Radiative Warming
  • Radiation Balance
  • Urban Atmosphere