Wind, temperature and stability conditions in an east-west oriented urban canyon

Nakamura, Yasuto; Oke, T. R.

doi:10.1016/0004-6981(88)90437-4

Cited by 381 publications

(231 citation statements)

References 15 publications

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“…For urban surfaces, the vertical extrapolation is performed down to the roof level, assuming that the resulting temperature is representative for the urban canyon as a whole, which is assumed homogeneously mixed. This homogeneous mixing assumption in the urban canopy layer is supported by several studies (e.g., [24,25]). …”

Section: The Urbclim Modelsupporting

confidence: 62%

Detailed Urban Heat Island Projections for Cities Worldwide: Dynamical Downscaling CMIP5 Global Climate Models

Lauwaet

Hooyberghs

Maiheu

et al. 2015

Climate

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Abstract:A new dynamical downscaling methodology to analyze the impact of global climate change on the local climate of cities worldwide is presented. The urban boundary layer climate model UrbClim is coupled to 11 global climate models contained in the Coupled Model Intercomparison Project 5 archive, conducting 20-year simulations for present (1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005) and future (2081-2100) climate conditions, considering the Representative Concentration Pathway 8.5 climate scenario. The evolution of the urban heat island of eight different cities, located on three continents, is quantified and assessed, with an unprecedented horizontal resolution of a few hundred meters. For all cities, urban and rural air temperatures are found to increase strongly, up to 7 °C. However, the urban heat island intensity in most cases increases only slightly, often even below the range of uncertainty. A potential explanation, focusing on the role of increased incoming longwave radiation, is put forth. Finally, an alternative method for generating urban climate projections is proposed, combining the ensemble temperature change statistics and the results of the present-day urban climate.

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Section: The Urbclim Modelsupporting

confidence: 62%

Detailed Urban Heat Island Projections for Cities Worldwide: Dynamical Downscaling CMIP5 Global Climate Models

Lauwaet

Hooyberghs

Maiheu

et al. 2015

Climate

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show abstract

“…When the thermal effects are substantial (due to solar radiation, the release of stored heat, and anthropogenic heat for example) they can have a profound impact on the thermal field itself, the flow field and therefore the pollutant dispersion in street canyons, as demonstrated by many previous studies [44][45][46][47][48]. The main parameter characterizing the stability is the bulk Richardson number…”

Section: Flow and Dispersion Under Unstable/stable Stratificationsmentioning

confidence: 99%

Transport processes in and above two-dimensional urban street canyons under different stratification conditions: results from numerical simulation

Britter

Norford

2014

Environ Fluid Mech

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Thermal stratification (neutral, unstable and stable) plays an important role in determining the transport processes in and above urban street canyons. This paper summarizes the recent findings of the effect of thermal stratification on the transport of momentum, heat, and pollutants in the two-dimensional (2D) urban street canyons in the skimming flow regime. Special attention is paid to the results from large-eddy simulations (LESs), while other experimental and numerical results are referred to when necessary. With increasing Richardson number, Ri, the drag coefficient of the 2D street canyon as felt by the overlying atmosphere decreases in a linear manner. Under neutral and stable stratification, a nearly constant drag coefficient of 0.02 is predicted by the LESs. Under unstable stratification, the turbulent pollutant transport is dominated by organized turbulent motions (ejections and sweeps), while under stable stratification, the unorganized turbulent motion (inward interactions) plays a more important role and the sweeps are inhibited. The unstable stratification condition also enhances the ejections of turbulent pollutant flux, especially at the leeward roof-level corner, where the ejections dominate the turbulent pollutant flux, outweighing the sweeps. With increasing Ri, both the heat (area active scalar source) and pollutant (line passive scalar source) transfer coefficients decrease towards a state where the transfer coefficients become zero at Ri ≈ 0.5. It should be noted that, due to the limit of the 2D street canyon configuration discussed in this paper, great caution should be taken when generalising the conclusions drawn here.

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“…In addition to surface temperature, the effect of street orientation on air temperature has also been investigated by researchers. Nakamura and Oke [63] observed the temporal development of the spatial distribution of air and surface temperature in an east-west oriented urban canyon (H/W = 1.06) in Japan. It was reported that air temperature differences in the daytime are largest on the north side since it is directly irradiated.…”

Section: Street Orientationmentioning

confidence: 99%

The Impact of Urban Design Descriptors on Outdoor Thermal Environment: A Literature Review

et al. 2017

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This paper presents a literature review on urban design indicators addressing the impact of urban geometry and vegetation on the outdoor thermal environment at the pedestrian level, as urban geometry and vegetation have been regarded as the most influential urban design factors that affect outdoor microclimate. The thermal balance concept is first introduced to elaborate how each component of energy fluxes is affected by the urban built environment, which helps to explore the underlying thermophysical mechanisms of how urban design modifies the outdoor thermal environment. The literature on numerous urban design descriptors addressing urban geometric characteristics is categorized into five groups in this paper according to the design features that the parameters entail, including land use intensity, building form, canyon geometry, space enclosure and descriptive characteristics. The literature on urban vegetation descriptors is reviewed together, followed by the combined effect of urban geometry and vegetation. This paper identifies a series of important urban design parameters and shows that the impact of design parameters on thermal environment varies with time, season, local climate and urban contexts. Contradictory impacts often occur between daytime and nighttime, or different seasons, which requests trade-offs to be achieved when proposing design strategies.

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Wind, temperature and stability conditions in an east-west oriented urban canyon

Cited by 381 publications

References 15 publications

Detailed Urban Heat Island Projections for Cities Worldwide: Dynamical Downscaling CMIP5 Global Climate Models

Detailed Urban Heat Island Projections for Cities Worldwide: Dynamical Downscaling CMIP5 Global Climate Models

Transport processes in and above two-dimensional urban street canyons under different stratification conditions: results from numerical simulation

The Impact of Urban Design Descriptors on Outdoor Thermal Environment: A Literature Review

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