scholarly journals Numerical Study of the Daytime Planetary Boundary Layer over an Idealized Urban Area: Influence of Surface Properties, Anthropogenic Heat Flux, and Geostrophic Wind Intensity

2016 ◽  
Vol 55 (4) ◽  
pp. 1021-1039 ◽  
Author(s):  
Serena Falasca ◽  
Franco Catalano ◽  
Monica Moroni
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Numerical Study ◽  
Geostrophic Wind ◽  
Anthropogenic Heat ◽  
Heat Island ◽  
Control Parameters ◽  
Reference Case ◽  
Anthropogenic Heat Flux ◽  
Wind Intensity

AbstractLarge-eddy simulations of an idealized diurnal urban heat island are performed using the Weather Research and Forecasting Model. The surface energy balance over an inhomogeneous terrain is solved considering the anthropogenic heat contribution and the differences of thermal and mechanical properties between urban and rural surfaces. Several cases are simulated together with a reference case, considering different values of the control parameters: albedo, thermal inertia, roughness length, anthropogenic heat emission, and geostrophic wind intensity. Spatial distributions of second-moment statistics, including the turbulent kinetic energy (TKE) budget, are analyzed to characterize the structure of the planetary boundary layer (PBL). The effect of each control parameter value on the turbulent properties of the PBL is investigated with respect to the reference case. For all of the analyzed cases, the primary source of TKE is the buoyancy in the lower half of the PBL, the shear in the upper half, and the turbulent transport term at the top. The vertical advection of TKE is significant in the upper half of the PBL. The control parameters significantly influence the shape of the profiles of the transport and shear terms in the TKE budget. Bulk properties of the PBL via proper scaling are compared with literature data. A log-linear relationship between the aspect ratio of the heat island and the Froude number is confirmed. For the first time, the effect of relevant surface control parameters and the geostrophic wind intensity on the bulk and turbulent properties of the PBL is systematically investigated at high resolution.

scholarly journals Integrating Urban Form, Function, and Energy Fluxes in a Heat Exposure Indicator in View of Intra-Urban Heat Island Assessment and Climate Change Adaptation

Climate ◽  
2019 ◽  
Vol 7 (6) ◽  
pp. 75 ◽  
Author(s):  
Ilias Agathangelidis ◽  
Constantinos Cartalis ◽  
Mat Santamouris
Keyword(s):  
Climate Change ◽  
Heat Flux ◽  
Urban Heat Island ◽  
Urban Form ◽  
Heat Exposure ◽  
Geographical Information ◽  
Anthropogenic Heat ◽  
Heat Island ◽  
Anthropogenic Heat Flux ◽  
Urban Heat

Cities worldwide are getting warmer due to the combined effects of urban heat and climate change. To this end, local policy makers need to identify the most thermally vulnerable areas within cities. The Local Climate Zone (LCZ) scheme highlights local-scale variations; however, its classes, although highly valuable, are to a certain extent generalized in order to be universally applicable. High spatial resolution indicators have the potential to better reflect city-specific challenges; in this paper, the Urban Heat Exposure (UHeatEx) indicator is developed, integrating the physical processes that drive the urban heat island (UHI). In particular, the urban form is modeled using remote sensing and geographical information system (GIS) techniques, and used to estimate the canyon aspect ratio and the storage heat flux. The Bowen ratio is calculated using the aerodynamic resistance methodology and downscaled remotely sensed surface temperatures. The anthropogenic heat flux is estimated via a synergy of top–down and bottom–up inventory approaches. UHeatEx is applied to the city of Athens, Greece; it is correlated to air temperature measurements and compared to the LCZs classification. The results reveal that UHeatEx has the capacity to better reflect the strong intra-urban variability of the thermal environment in Athens, and thus can be supportive for adaptation responses. High-resolution climate projections from the EURO-CORDEX ensemble for the region show that the adverse effects of the existing thermal inequity are expected to worsen in the coming decades.

scholarly journals Opposite Effects of Aerosols on Daytime Urban Heat Island Intensity between Summer and Winter

2020 ◽  
Author(s):  
Wenchao Han ◽  
Zhanqing Li ◽  
Fang Wu ◽  
Yuwei Zhang ◽  
Jianping Guo ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Pollution ◽  
Urban Heat Island ◽  
Planetary Boundary Layer ◽  
Urban Areas ◽  
Urban Heat Island Intensity ◽  
Heat Island ◽  
Different Seasons ◽  
Urban Heat ◽  
The Impact

Abstract. The urban heat island intensity (UHII) is the temperature difference between urban areas and their rural surroundings. It is commonly attributed to changes in the underlying surface structure caused by urbanization. Air pollution caused by aerosol particles can affect the UHII by changing the surface energy balance and atmospheric thermodynamic structure. By analyzing satellite data and ground-based observations collected from 2001 to 2010 at 35 cities in China and using the WRF-Chem model, we found that aerosols have very different effects on daytime UHII in different seasons: reducing the UHII in summer, but increasing the UHII in winter. The seasonal contrast in the spatial distribution of aerosols between the urban centers and the suburbs lead to a spatial discrepancy in aerosol radiative effect (SD-ARE). Additionally, different stability of the planetary boundary layer induced by aerosol is closely associated with a dynamic effect (DE) on the UHII. SD-ARE reduces the amount of radiation reaching the ground and changes the vertical temperature gradient, whereas DE increases the stability of the planetary boundary layer and weakens heat release and exchange between the surface and the PBL. Both effects exist under polluted conditions, but their relative roles are opposite between the two seasons. It is the joint effects of the SD-ARE and the DE that drive the UHII to behave differently in different seasons, which is confirmed by model simulations. In summer, the UHII is mainly affected by the SD-ARE, and the DE is weak, and the opposite is the case in winter. This finding sheds a new light on the impact of the interaction between urbanization-induced surface changes and air pollution on urban climate.

scholarly journals Assessment of Planetary Boundary Layer Parameterizations and Urban Heat Island Comparison: Impacts and Implications for Tracer Transport

2020 ◽  
Vol 59 (10) ◽  
pp. 1637-1653
Author(s):  
Israel Lopez-Coto ◽  
Micheal Hicks ◽  
Anna Karion ◽  
Ricardo K. Sakai ◽  
Belay Demoz ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Urban Heat Island ◽  
Planetary Boundary Layer ◽  
Urban Areas ◽  
Greenhouse Gas Emission ◽  
Sensible Heat Flux ◽  
Heat Island ◽  
Tracer Transport ◽  
Urban Heat ◽  
The Impact

AbstractAccurate simulation of planetary boundary layer height (PBLH) is key to greenhouse gas emission estimation, air quality prediction, and weather forecasting. This paper describes an extensive performance assessment of several Weather Research and Forecasting (WRF) Model configurations in which novel observations from ceilometers, surface stations, and a flux tower were used to study their ability to reproduce the PBLH and the impact that the urban heat island (UHI) has on the modeled PBLHs in the greater Washington, D.C., area. In addition, CO2 measurements at two urban towers were compared with tracer transport simulations. The ensemble of models used four PBL parameterizations, two sources of initial and boundary conditions, and one configuration including the building energy parameterization urban canopy model. Results have shown low biases over the whole domain and period for wind speed, wind direction, and temperature, with no drastic differences between meteorological drivers. We find that PBLH errors are mostly positively correlated with sensible heat flux errors and that modeled positive UHI intensities are associated with deeper modeled PBLs over the urban areas. In addition, we find that modeled PBLHs are typically biased low during nighttime for most of the configurations with the exception of those using the MYNN parameterization, and these biases directly translate to tracer biases. Overall, the configurations using the MYNN scheme performed the best, reproducing the PBLH and CO2 molar fractions reasonably well during all hours and thus opening the door to future nighttime inverse modeling.

Numerical study of a mesoscale vortex in the planetary boundary layer of the meiyu front

2012 ◽  
Vol 26 (6) ◽  
pp. 788-802 ◽  
Author(s):  
Hangfeng Shen ◽  
Guoqing Zhai ◽  
Ye Zhu ◽  
Yaqin Xu
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Numerical Study ◽  
Mesoscale Vortex ◽  
Meiyu Front
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