Canyon geometry and the nocturnal urban heat island: Comparison of scale model and field observations
01 Jul 1981-International Journal of Climatology (John Wiley & Sons, Ltd.)-Vol. 1, Iss: 3, pp 237-254
TL;DR: In this paper, a simple hardware scale model is used to simulate nocturnal cooling rates for rural and urban environments under calm and cloudless conditions, and the results of the experiments show that canyon geometry in the central portion of a city (as measured by the sky view factor) is a relevant variable in producing nocturnurnal urban heat islands due to its role in regulating long-wave radiative heat loss.
Abstract: A simple hardware scale model is used to simulate nocturnal cooling rates for rural and urban environments under calm and cloudless conditions. Comparison with field observations gathered under similar conditions shows the model capable of reproducing many of the features of the temporal development of urban heat islands and the long-wave radiative exchange in urban canyons. The model is used to investigate the roles played by rural/urban differences in geometry and thermal admittance. The results of the experiments show that canyon geometry in the central portion of a city (as measured by the sky view factor) is a relevant variable in producing nocturnal urban heat islands due to its role in regulating long-wave radiative heat loss. It is also demonstrated that this measure is central to the relationship between city size and heat island intensity. The importance of canyon geometry as a feature of urban design is discussed. Thermal admittance differences can also produce realistic heat island features but their magnitude requires quantification in the field.
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TL;DR: In this article, the authors reviewed progress in urban climatology over the two decades since the first publication of the International Journal of Climatology (IJC) and highlighted the role of scale, heterogeneity, dynamic source areas for turbulent fluxes and the complexity introduced by the roughness sublayer over the tall, rigid roughness elements of cities.
Abstract: Progress in urban climatology over the two decades since the first publication of the International Journal of Climatology is reviewed. It is emphasized that urban climatology during this period has benefited from conceptual advances made in microclimatology and boundary-layer climatology in general. The role of scale, heterogeneity, dynamic source areas for turbulent fluxes and the complexity introduced by the roughness sublayer over the tall, rigid roughness elements of cities is described. The diversity of urban heat islands, depending on the medium sensed and the sensing technique, is explained. The review focuses on two areas within urban climatology. First, it assesses advances in the study of selected urban climatic processes relating to urban atmospheric turbulence (including surface roughness) and exchange processes for energy and water, at scales of consideration ranging from individual facets of the urban environment, through streets and city blocks to neighbourhoods. Second, it explores the literature on the urban temperature field. The state of knowledge about urban heat islands around 1980 is described and work since then is assessed in terms of similarities to and contrasts with that situation. Finally, the main advances are summarized and recommendations for urban climate work in the future are made. Copyright © 2003 Royal Meteorological Society.
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Cites background or methods from "Canyon geometry and the nocturnal u..."
...…and numerical simulation modelling of the street surface UHI under calm, night-time conditions, when solar shading is absent and turbulent interactions between street and air and advective fluxes are minimal (Oke, 1981; Arnfield, 1990b; Johnson et al., 1991; Oke et al., 1991; Swaid, 1993a)....
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...The hardware scale model simulation of UC cooling of Oke (1981) presents the hypothesis that, for clear skies, calm air and an absence of significant anthropogenic heating, maximum UHI intensity can be related to the ‘openness’ of the urban structure, represented by canyon AR or sky view factor,…...
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TL;DR: In this article, the authors investigated the results of recent urban canyon field studies and of scale and mathematical modelling to find a range of canyon geometries that are compatible with the apparently conflicting design objectives of mid-latitude cities.
1,493 citations
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01 Jan 2002TL;DR: The third edition of Gordon Bonan's comprehensive textbook introduces an interdisciplinary framework to understand the interaction between terrestrial ecosystems and climate change as discussed by the authors, which is suitable for advanced undergraduate and graduate students studying ecology, environmental science, atmospheric science, and geography.
Abstract: The third edition of Gordon Bonan's comprehensive textbook introduces an interdisciplinary framework to understand the interaction between terrestrial ecosystems and climate change. Ideal for advanced undergraduate and graduate students studying ecology, environmental science, atmospheric science, and geography, it reviews basic meteorological, hydrological, and ecological concepts to examine the physical, chemical, and biological processes by which terrestrial ecosystems affect and are affected by climate. This new edition has been thoroughly updated with new science and references. The scope has been expanded beyond its initial focus on energy, water, and carbon to include reactive gases and aerosols in the atmosphere. The new edition emphasizes the Earth as a system, recognizing interconnections among the planet's physical, chemical, biological, and socioeconomic components, and emphasizing global environmental sustainability. Each chapter contains chapter summaries and review questions, and with over 400 illustrations, including many in color, this textbook will once again be an essential student guide.
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TL;DR: In this paper, the surface radiant temperature heat islands of Vancouver, British Columbia, Seattle, Washington, and Los Angeles, California were used to display the surface temperature heat island data.
Abstract: NOAA AVHRR satellite infra-red data are used to display the surface radiant temperature heat islands of Vancouver, British Columbia, Seattle, Washington, and Los Angeles, California. Heat island intensities are largest in the day-time and in the warm season. Day-time intra-urban thermal patterns are strongly correlated with land-use; industrial areas are warmest and vegetated, riverine or coastal areas are coolest. Nocturnal heat island intensities and the correlation of the surface radiant temperature distribution with land use are less. This is the reverse of the known characteristics of near-surface air temperature heat islands. Several questions relating to the interpretation and limitations of satellite data in heat island analysis and urban climate modelling are addressed.
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TL;DR: In this article, the authors demonstrate the relationship existing between the size of a village, town or city and the magnitude of the urban heat island it produces by analyzing data gathered by automobile traverses in 10 settlements on the St. Lawrence Lowland, whose populations range from 1000 to 2 million inhabitants.
1,938 citations
TL;DR: In this paper, air temperature measurements from car traverses in and near Vancouver, BC are used to test two urban heat island models: one an empirical model, the other a theoretical advective model.
Abstract: Air temperature measurements from car traverses in and near Vancouver, BC are used to test two urban heat island models: one an empirical model, the other a theoretical advective model The empirical model describes the Vancouver observations well, whereas the advective one performs rather poorly This discrepancy may be attributed to a failure to distinguish between meteorological conditions in the urban canopy, and those in the overlying urban boundary layer This leads to a reassessment of the explanation of the relationship between city size (as measured by population) and the heat island intensity (as measured in the urban canopy)
505 citations
TL;DR: In this article, a method for inferring the distribution of surface heat and evaporative fluxes and the ground moisture availability and thermal inertia (ground conductive capacity) was used to analyze two urbanized areas, Los Angeles and St. Louis.
Abstract: A method for inferring the distribution of surface heat and evaporative fluxes and the ground moisture availability and thermal inertia (ground conductive capacity) is used to analyze two urbanized areas, Los Angeles and St. Louis. The technique employs infrared satellite temperature measurements in conjunction with a one-dimensional boundary-layer model. Results show that there is a marked reduction of evaporation and moisture availability and a corresponding elevation of sensible heat flux over urbanized areas and over cropped areas with low vegetative cover. Conversely, low heat flux and high evaporation characterize vegetated and, especially, forested areas. Warm urban centers appear directly related to a reduction in vegetation, which normally allows for a greater fraction of available radiant energy to be converted into latent heat flux. The distribution of thermal inertia was surprisingly ill-defined and its variation between urban and rural areas was quite small. Thus, the increased heat storage within the urban fabric, which has been proposed as the underlying cause of the nocturnal heat island, may be caused mainly by enhanced daytime surface heating which occurs because of surface dryness, rather than by large spatial variations in the conductivity of the surface.
308 citations
TL;DR: In this paper, the role of urban and rural surfaces in the growth and decay of the urban heat island was investigated and the results suggest that nocturnal energy exchange in the city is complex.
259 citations