Large-Eddy Simulation of Mesoscale Circulations Forced by Inhomogeneous Urban Heat Island

Zhang, Ning; Wang, Xueyuan; Peng, Zhen

doi:10.1007/s10546-013-9879-x

Cited by 40 publications

(25 citation statements)

References 54 publications

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“…Kang and Lenschow (), Zhang et al . () and Zhu et al . ()), which facilitate cloud formation and moist convection.…”

Section: Resultsmentioning

confidence: 99%

“…The higher sensible heat flux over urban areas can result in urban-rural circulations and stronger vertical motions over urban areas (not shown here but see e.g. Kang and Lenschow (2014), Zhang et al (2014a) and Zhu et al (2016)), which facilitate cloud formation and moist convection. Figure 6 shows the vertical profiles of potential temperature, relative humidity, and cloud water mixing ratio of case CTL and case URB.…”

Section: Impacts Of the Existence Of An Urban Islandmentioning

confidence: 93%

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An idealized LES study of urban modification of moist convection

Zhu

Zhou

et al. 2017

Quart J Royal Meteoro Soc

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To understand the impacts of urbanization on moist convection, we explore how an idealized circular urban island affects the diurnal cycle and spatial distribution of rainfall over urban and surrounding rural areas at the diurnal equilibrium state using large‐eddy simulations (LES) performed with the Weather Research and Forecasting (WRF) model. Compared to the control case where the whole domain is covered by grassland, the existence of an urban island significantly enhances the rainfall rate over the urban area as the stronger surface heating creates convergence zones and stronger vertical motions over the urban area. A suite of experiments is then conducted to investigate the effects of soil moisture of the surrounding rural land and the urban size on precipitation. Results show that as the rural soil moisture increases, both urban and rural precipitation rates increase almost linearly. This increase is not attributed to the urban heat island (UHI) effect but rather a stronger moisture deficit effect in the urban area creating a stronger moisture inflow. When the urban area becomes larger but the initial available water remains the same in the domain, the UHI effect and moisture deficit effect increase but the total water supply decreases. As a result, the urban rainfall rate increases first and then decreases as the urban size increases. This suggests that there is an ‘optimal’ scale at which the urban rainfall rate is maximized, at least in our modelling framework. Our simulations further suggest that this optimal scale occurs when the urban fraction lies between 1 and 10%.

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“…Kang and Lenschow (), Zhang et al . () and Zhu et al . ()), which facilitate cloud formation and moist convection.…”

Section: Resultsmentioning

confidence: 99%

Section: Impacts Of the Existence Of An Urban Islandmentioning

confidence: 93%

An idealized LES study of urban modification of moist convection

Zhu

Zhou

et al. 2017

Quart J Royal Meteoro Soc

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“…Due to the above listed modifications, the surface temperatures and near-surface air temperatures over urban patches are generally higher than those over rural areas, thus resulting in an urban heat island (UHI) [13][14][15]. Some factors at the meso-scale contribute to the development of an UHI, whereas other UHIs are related to natural factors, such as weather and location.…”

Section: Introductionmentioning

confidence: 99%

Radiation Balance of Urban Materials and Their Thermal Impact in Semi-Desert Region: Mexicali, México Study Case

et al. 2015

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Net radiation is an essential forcing of climate in the lower layers of Earth's atmosphere. In this paper, radiation balance is measured in clay soil and green grass, and is compared with three urban materials. These materials: asphalt, concrete and white painted elastomeric polystyrene roofing sheet are widely used in Mexicali, Baja California, México. This study was carried out during August of 2011, the hottest time of the year. The 24-hour average values of net radiation found were: 137.2 W·m −2 for asphalt, 119.1 for concrete, 104.6 for clay soil, 152 for green grass and 29.2 for the polystyrene insulation. The latter two types of materials are likely to be the most effective in reducing urban heat island effects. This variation in the radiation balance has widespread implications for human living conditions, as land cover change tends to be towards surfaces that have higher levels of net radiation.

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“…Zhang et al . [] studied the turbulent characteristics and mesoscale circulations caused by different urban and rural heating rates and found that the UHI intensity has an obvious impact on the spatial distribution of the wind field.…”

Section: Introductionmentioning

confidence: 99%

“…Wang [2009] investigated the influence of UHI circulations induced by urban-rural contrasts in terms of surface sensible heat flux and roughness on flow statistics using LES and found that an isolated UHI could enhance the horizontal velocity variance in the central urban area through the low-level flow convergence. Zhang et al [2014] studied the turbulent characteristics and mesoscale circulations caused by different urban and rural heating rates and found that the UHI intensity has an obvious impact on the spatial distribution of the wind field.…”

Section: Introductionmentioning

confidence: 99%

Impacts of surface heterogeneity on dry planetary boundary layers in an urban‐rural setting

Zhu

Cong

et al. 2016

JGR Atmospheres

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Understanding the impacts of land use and land‐cover change such as urbanization is essential in many disciplines. This study investigates the impacts of urban‐rural contrasts in terms of momentum roughness length (z0) and aerodynamic surface temperature (TSK) on dry planetary boundary layers (PBLs) using large‐eddy simulations (LES) with the Weather Research and Forecasting (WRF) model. In addition, the impacts of small‐scale heterogeneities within urban areas are also examined. The original WRF‐LES is modified in order to use prescribed TSK as surface boundary conditions. Numerical simulations are then conducted to examine turbulence characteristics and mesoscale circulations resulting from large‐scale urban‐rural contrasts as well as small‐scale heterogeneities in urban areas. The results indicate that (1) the urban‐rural contrasts in z0 and TSK have significant but different impacts on surface heat fluxes, mesoscale circulations, and the wind and potential temperature profiles. Compared to the case where the whole domain is homogeneous, increases in z0 and/or TSK in urban areas in the center of domain induce stronger sensible heat fluxes, stronger urban circulations, and weaker inversions at the top of the PBL. (2) When the patch size that characterizes the urban heterogeneity scale is comparable to the size of the whole urban area, the simulated results are strongly dependent on both the heterogeneity scale and the specified surface temperature values. As the patch size decreases, the simulated results become more similar to those over a homogeneous urban surface.

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Large-Eddy Simulation of Mesoscale Circulations Forced by Inhomogeneous Urban Heat Island

Cited by 40 publications

References 54 publications

An idealized LES study of urban modification of moist convection

An idealized LES study of urban modification of moist convection

Radiation Balance of Urban Materials and Their Thermal Impact in Semi-Desert Region: Mexicali, México Study Case

Impacts of surface heterogeneity on dry planetary boundary layers in an urban‐rural setting

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