SIMULATION OF THE ENERGY BUDGET OF AN URBAN CANYON .1. MODEL STRUCTURE AND SENSITIVITY TEST

This paper presents the formulation and results of a simple numerical model designed to simulate the climate of an urban canyon. The model i s two-dimensional in nature and is based on the observation that ambie nt airflow which traverses the long-axis of a symmetrical canyon drive s a circulating vortex within the canyon air space which results in th e exchange of heat, mass and momentum at the canyon top. A simple mode l is described which consists of two components: a semi-empirical mode l to relate within-canyon airflow to ambient wind velocity, and an ene rgy budget model for canyon surfaces. The model in capable of simulati ng many aspects of the canyon climate, including the canyon surface an d top energy budget and surface and air temperatures. Sensitivity test s with the model indicate that the canyon top energy budget is remarka bly stable for many changes in canyon parameters. Canyon geometry (exp ressed as a height/width ratio) caused the greatest changes with incre ased narrowness being associated with less heat exchange across the ca nyon top. The model's predictions appear intuitively reasonable and co mpare well with existing measurement data. The results suggest that th e coupling between the urban boundary and canopy layers in terms of be at exchange may be a function of canyon geometry.