A Laboratory Study of the Urban Heat Island in a Calm and Stably Stratified Environment. Part I: Temperature Field

摘要

An extensive and systematic water-tank study was performed to simulate the urban heat island under a calm and stably stratified environment. The objective was to examine the mean-temperature field, mixing height, and heat-island intensity as functionsof surface heating rates, heat-island sizes, and ambient temperature gradients. The scaling parameters for the temperature field associated with the heat-island plume are the diameter D, surface heating rate H_0, and Brunt-Vaisala frequency N of the ambient stratification. The induced plume was turbulent, and the Froude number was found to be the most important similarity parameter. The differences between low-and high-aspect-ratio plumes are discussed, and simple theoretical models are proposed for low aspect-ratio plumes. The experimental results generally confirm the theoretical predictions and agree reasonably well with field observations, in spite of several limitations of the laboratory simulation. The mean-temperature distributions are found tohave a universal shape that is a function of location only. The results are described in two papers. In this paper, the temperature fields are described. Part II describes the velocity fields and develops analytical models that apply to low-aspect-ratio plumes.