A Study of the Atmospheric Response Due to a Diurnal Heating Function Characteristic Of an Urban Complex

FRED M. VUKOVICH Research Triangle Institute, Research Triangle Park, N.C.

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Abstract

The variation of the differential heating required to depict the diurnal behavior of the urban heat island is established from temperature data obtained in the literature and from other sources. A simple, linear, three-layer model was developed to study the response of the urban atmosphere to the differential heating in the no-mean-wind case. The only driving force in the model was differential heating. The solutions suggest that the urban atmosphere experiences a short period of upward vertical motion in the early evening (the urban heat island circulation) in response to the positive differential heating at this time and a short period of downward vertical motion in the late morning in response to the negative differential heating at that time. The latter response would prevent diffusion of pollutants in the vertical and would bring an elevated pollution layer over the city to the surface. Therefore, the dynamic response could be responsible for the production of a “critical episode” in the city.

Abstract

The variation of the differential heating required to depict the diurnal behavior of the urban heat island is established from temperature data obtained in the literature and from other sources. A simple, linear, three-layer model was developed to study the response of the urban atmosphere to the differential heating in the no-mean-wind case. The only driving force in the model was differential heating. The solutions suggest that the urban atmosphere experiences a short period of upward vertical motion in the early evening (the urban heat island circulation) in response to the positive differential heating at this time and a short period of downward vertical motion in the late morning in response to the negative differential heating at that time. The latter response would prevent diffusion of pollutants in the vertical and would bring an elevated pollution layer over the city to the surface. Therefore, the dynamic response could be responsible for the production of a “critical episode” in the city.

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