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Quantifying the impact of surface heterogeneities on the radiative response of a simplified urban surface

Authors Simone Kotthuas
Atsushi Inagaki
Fredrik Lindberg
CSB Grimmond
Manabu Kanda
Published in ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment. 20-24 July 2015, Toulouse, France
Publication year 2015
Published at Department of Earth Sciences
Language en
Subject categories Climate Research, Meteorology and Atmospheric Sciences, Physical Geography


Radiation exchanges at the urban surface strongly influence climate conditions within cities. Therefore they directly impact outdoor human thermal comfort, have implications to building energy use and partly determine the energy available to turbulent surface fluxes. The radiative response of the urban surface is a function of both material composition and geometric arrangement of the surface objects. Hence it is crucial to understand how both aspects integrate to the bulk surface characteristics of albedo and emissivity to successfully interpret observed energy exchanges and provide realistic values for model parameterisations. Radiation fluxes are often observed with radiometers installed above the urban canopy. Given the latter is spatially complex and its interaction with the incoming solar radiation may change over time, dynamic modelling approaches are required to relate the fluxes observed to the surface source area. In this study the relative importance of material properties and the three-dimensional surface structure on radiation fluxes at different locations above the urban canopy are considered. Both long- and shortwave radiation fluxes were observed atvarious locations above a simplified urban setting, the Comprehensive Outdoor Scale Model experiment for urban climate (COSMO; Tokyo Institute of Technology, Japan) and high-reflectance materials were installed in the source areas of the radiometers for certain periods. Surface temperatures of all facets were measured by thermal imagery to provide further insight into radiative heating and cooling of the various surfaces. The simplified canopy allows for the spatio-temporal variations observed to be directly associated with certain source area characteristics (e.g. fraction of roof surface). Observations are compared to results from the dynamic radiation model SOLWEIG (Lindberg et al. 2008), characterising the spatial variations of radiation fluxes across the whole canopy. Given SOLWEIG can also be applied in complex, real city settings, conclusions drawn help to advance source area calculations of radiometers operated in many urban climate studies.

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