Numerical estimation of the effective albedo of an urban canyon

SummaryThe paper focuses on the absorption of shortwave radiation in an urban street canyon. To test the effective albedo of the canyon an analytic solution of the multiple reflection problem is applied. The infinitesimally long canyon is divided into slices and a matrix of view factors for the slices is defined. Incoming shortwave radiation includes direct and diffuse parts and shadowing effects are included in the analysis. The model is validated against Aida’s (1982) scale model data and measurements in a real canyon. The results demonstrate a rapid decrease of the effective albedo as the canyon aspect ratio (its height to width, H/W) are increased. It is also shown that diurnal changes of the effective albedo can be very complex depending on the particular combination of H/W ratio, surface reflectivity and canyon orientation.

[1]  I. D. Watson,et al.  The determination of view-factors in urban canyons , 1984 .

[2]  Valéry Masson,et al.  A Physically-Based Scheme For The Urban Energy Budget In Atmospheric Models , 2000 .

[3]  C. L. Brest.  Seasonal albedo of an urban/rural landscape from satellite observations , 1987 .

[4]  Douw G. Steyn,et al.  The calculation of view factors from fisheye‐lens photographs: Research note , 1980 .

[5]  C. Willmott.  ON THE VALIDATION OF MODELS , 1981 .

[6]  Katsuhito Yamaguchi,et al.  The Influence Of Urban Canopy Configuration On Urban Albedo , 2001 .

[7]  Timothy R. Oke,et al.  Parameterization of Net All-Wave Radiation for Urban Areas , 2003 .

[8]  Aya Hagishima,et al.  A computer system to support Albedo Calculation in urban areas , 2004 .

[9]  C. S. B. Grimmond,et al.  Rapid methods to estimate sky‐view factors applied to urban areas , 2001 .

[10]  Manabu Kanda,et al.  A Simple Theoretical Radiation Scheme for Regular Building Arrays , 2005 .

[11]  T. Lyons,et al.  Comments on “The Determination of View-Factors in Urban Canyons” , 1985 .

[12]  U. Sievers,et al.  A numerical simulation scheme for the albedo of city street canyons , 1985 .

[13]  M. Nunez,et al.  Estimating global solar radiation , 1975 .

[14]  E. Sparrow,et al.  Radiation Heat Transfer , 1978 .

[15]  David J. Sailor,et al.  Modeling the diurnal variability of effective albedo for cities , 2002 .

[16]  A. Arnfield.  VALIDATION OF AN ESTIMATION MODEL FOR URBAN SURFACE ALBEDO , 1988 .

[17]  F. Eaton,et al.  The Net Radiation Budget of the St. Louis Metropolitan Area , 1978 .

[18]  Werner H. Terjung,et al.  SOLAR RADIATION AND URBAN HEAT ISLANDS , 1973 .

[19]  Aris Tsangrassoulis,et al.  Numerical estimation of street canyon albedo consisting of vertical coated glazed facades , 2003 .

[20]  T. Oke.  The energetic basis of the urban heat island , 1982 .

[21]  Joël Noilhan.  A model for the net total radiation flux at the surfaces of a building , 1981 .

[22]  T. Oke,et al.  Long-wave radiative flux divergence and nocturnal cooling of the urban atmosphere , 1976 .

[23]  M. Aida,et al.  Urban albedo as a function of the urban structure — A model experiment , 1982 .

[24]  R. Belarbi,et al.  Modelling solar effects on the heat and mass transfer in a street canyon, a simplified approach , 2005 .

[25]  Ian N. Harman,et al.  Radiative Exchange in an Urban Street Canyon , 2004 .

[26]  D. S. Munro,et al.  Sensitivity studies on the calculation of the radiation balance of urban surfaces: II. Longwave radiation , 1989 .

[27]  A. Arnfield.  AN APPROACH TO THE ESTIMATION OF THE SURFACE RADIATIVE PROPERTIES AND RADIATION BUDGETS OF CITIES , 1982 .

[28]  M. Aida,et al.  Urban albedo as a function of the urban structure — A two-dimensional numerical simulation , 1982 .