PHYSICAL SIMULATIONS IN ROTATING TANK OF LEE CYCLOGENESIS

Some results of physical simulations of interactions between atmospher ic baroclinic flows and a tridimensional mountain, carried out in a ro tating tank, are presented and discussed. Complex dynamic and thermody namic processes occur when the so called lee, or secondary, cyclogenes is can develop; in this case, potential energy of the basic flow is co nverted into kinetic energy of its perturbation field, giving rise to strengthening and deepening of its pressure troughs. The presence of a n obstacle can exert a blocking on the colder lower layers of the impi nging stably stratified airflow, forcing it to deflect horizontally ro und its borders. In this way, these layers get the lee region with a d elay. These two effects, of blocking and delay, are the responsible fo r the initial pressure decrease downwind of the mountain and for the s ubsequent proper downstream baroclinic development. Following this rat her simple scheme, the lee cyclogenesis has been simulated in the rota ting tank of the IMG of GRENOBLE. The experiments were observed by thr ee TV cameras continuously recording the trajectories of dye tracers a t three levels of the stratified fluid. In order to measure the vertic al density profiles, a rectangular mesh of samplers was rapidly moved up and down in the tank.