A LABORATORY INVESTIGATION OF CHARACTERISTICS OF TORNADO-LIKE VORTICES OVER VARIOUS ROUGH SURFACES

In this paper,the effects of surface roughness on tornado-like vortices are studied in the laboratory forsimulating tornado vortex at the Disaster Prevention Research Institute,Kyoto University,Japan.In the experiments,the distribution of the horizontal wind speed and direction at five different heightswere measured with a hot-wire anemometer and a mini-vane.The characteristics of wind speed and direc-tion distribution for the tornado vortex on the various rough surfaces were first revealed with the simulativemethod in laboratory.By changing the swirl ratio(S=tanθ/2a)of simulation device,it is found that,thesize of tornado-like vortex core will become almost identical,as the swirl ratio S exceeds a certain value(S>1.5).The experimental results can be used not only to explain the observed facts in the atmosphere but alsoto provide the experimental bases for some theoretical studies.