Abstract
Urban heat dome flow, which is also referred to as urban heat island circulation, is important for urban ventilation and pollutant transport between adjacent cities when the background wind is weak or absent. A “dome-shaped” profile can form at the upper boundary of the urban heat island circulation. The horizontal extent of the heat dome is an important parameter for estimating the size of the area it influences. This study reviews the existing data on the horizontal extent of the urban heat dome flow, as determined by using either field measurements or numerical simulations. A simple energy balance model is applied to obtain the maximum horizontal extent of a single heat dome over the urban area, which is found to be approximately 1.5 to 3.5 times the diameter of the city’s urban area at night. A linearized model is also re-analysed to calculate the horizontal extent of the urban heat dome flow. This analysis supports the results from the energy balance model. During daytime, the horizontal extent of the urban heat dome flow is found to be about 2.0 to 3.3 times the urban area’s diameter, as influenced by the convective turbulent plumes in the rural area.
Highlights
Urban heat dome flow, which is referred to as urban heat island circulation, is important for urban ventilation and pollutant transport between adjacent cities when the background wind is weak or absent
The energy for maintaining the urban heat dome flow is fed by the positive heat flux in the urban area, i.e., the left side of Equation [1]
Where the urban heat dome extends over the rural area, its heat is transported to the rural surface
Summary
Urban heat dome flow, which is referred to as urban heat island circulation, is important for urban ventilation and pollutant transport between adjacent cities when the background wind is weak or absent. A linearized model is re-analysed to calculate the horizontal extent of the urban heat dome flow. The horizontal extent of the urban heat dome flow is found to be about 2.0 to 3.3 times the urban area’s diameter, as influenced by the convective turbulent plumes in the rural area. Urban heat domes are characterized by convergent inflows at the atmosphere’s lower level, upward flows in the form of turbulent plumes over the urban area, divergent outflow in the atmosphere’s upper level, and a “dome-shaped” upper boundary (See Fig. 1) at the interface between the inversion layer and the divergent outflow region. The mechanisms and characteristics of the urban heat dome flows are important to consider for understanding pollutant dispersion, urban heat removal, and the transport of regional pollutants between adjacent cities under calm, stably stratified background environments. In this study, the daytime refers to the time slot between the time about 4 hours after sunrise and the time before the sunset, when the daytime urban heat dome flow is in
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