A LABORATORY STUDY OF THE URBAN HEAT-ISLAND IN A CALM AND STABLY STRATIFIED ENVIRONMENT .2. VELOCITY-FIELD

A fully turbulent, low-aspect-ratio buoyant plume with no initial mome ntum under calm and stably stratified conditions is produced in a conv ection tank. The plume is generated by a circular heat island at the b ottom of the tank. Two analytical models, a bulk convection model and a hydrostatic model, are developed to formulate similarity relations f or the low-aspect-ratio plume. The convective velocity scale W-D, sugg ested by the analytical models, is used as the similarity parameter fo r both the mean velocity and standard deviations of velocity fluctuati ons. The normalized standard deviations of horizontal and vertical vel ocities agree with each other for two heating rates, as well as with f ield observations in the center of Sapporo, Japan. The suggested scali ng and empirical relations based on our experimental results may be ap plied to the velocity fields of other low-aspect-ratio plumes in calm and stably stratified environments. Further investigations are recomme nded to confirm the results of the current study.