Observational and numerical studies of wintertime urban boundary layer

Observational analyses and numerical simulations were carried out to study the characteristics of the winter urban boundary layer of a large city. The observations showed that with light winds the ground inversion at nighttime in urban areas was about 200 m deep. The heat island circulation, caused mainly by anthropogenic hearing, induced reverse flow at the downwind part of the city. A shallow internal boundary layer with a depth of 50-80 m developed from the fringe of the city. In the daytime heavy smoke attenuated the solar radiation, and caused a cold island in the urban area, and retarded the development of a convective boundary layer. The features described above were well simulated by the numerical model. (C) 2000 Elsevier Science Ltd. All rights reserved.