Evaluation of Urban Surface Energy Fluxes Using an Open-Air Scale Model

Abstract

The thermal behavior of an urban surface is crucial to understand, but it is difficult to predict using conventional measurement or modeling approaches. In this study, an integrated method is proposed for evaluating urban energy exchanges with an open-air scale model of a building–street canyon surface array. The technique, which potentially combines the flexibility of modeling with the reliability of empirical observation under natural turbulence and radiative loading, is tested in hot, arid summer conditions to gauge its ability for reproducing surface–atmosphere energy fluxes that are representative of diurnal patterns in actual urban settings. After identifying the inertial sublayer, which is created above the scaled roughness array at a point near its downwind edge, roughness parameters utilized in the calculation of turbulent sensible heat flux are determined for two different array configurations of varying frontal area density and compared with existing data from field studies and morphometric models. For each geometric configuration, the relative sharing of radiant energy between storage and turbulent fluxes is compared with published findings obtained by conventional methods, as is the diurnal pattern of each component flux. Roughness parameters that are obtained conform to the expected ranges, as do daytime and overall daily fluxes and flux ratios. Overall, radiation absorption and heat storage are higher in the array with deeper canyons, and in both arrays the share of sensible heat channeled into the atmosphere is both higher in magnitude and later in reaching its peak intensity than that which is stored within the scaled urban fabric. This thermal time lag, when evaluated by fitting data to a published model for parameterizing heat storage from net radiation, shows a high correlation with hysteresis behavior in actual cities.

Review of urban climate research in (sub)tropical regions

“…Using an outdoor scale model Pearlmutter et al (2005Pearlmutter et al ( , 2006 investigated the microclimate and energy balance of an urban canopy in an arid environment. Turbulent transfer has been studied by Yadav et al (1996) at a semi-urban site in Delhi and by Tsai and Tsuang (2005) in urbanized Dunhe (Taiwan).…”

Progress in Urban Meteorology :A Review

“…In contrast to this obvious influence of vegetation cover on Q G /Q Ã , a direct influence of urban surface geometry on Q G /Q Ã is not evident in observed data. However, numerical work (Arnfield and Grimmond 1998) and outdoor experiment using scale models (Pearlmutter et al 2005) suggest that surface geometry does influence Q G /Q Ã ; radiation absorption and heat storage are higher in building arrays with deeper canyons.…”

“…Pioneering outdoor experiments using large-scale obstacles (e.g., @1 m) such as MUST and Kit FOX (Hanna and Chang 2001) focused on dispersion processes and did not consider energy balance. Pearlmutter et al (2005) …”

Recent development of assessment tools for urban climate and heat‐island investigation especially based on experiences in Japan

“…The results of the following references - Uehara et al (2000), Christen et al (2003), Moriwaki et al (2003), Offerle et al (2003), Rotach et al (2003), and Mutoh and Narita (2005) -are expected to be very useful. The scaled model experiments are also important, such as Yee and Biltoft (2004), Pearlmutter et al (2005), and Narita et al (2006). The results of the detailed simulation in the urban canyon space such as Kanda et al (2004) are useful to develop the urban canopy model.…”