The topology of the flow induced by two and three satellite vortices in a bucket.

Many tornadoes include smaller, rapidly spinning subvortices or suction vortices. When such vortices are present, narrow traces of extreme destruction can be observed alongside the path of the tornado's center, where a weaker level of destruction is found. We will present a laboratory experiment mimicking such multiple-vortex tornadoes. The investigation involves a shallow layer of water driven into rotation by a rotating disc at the bottom of an open stationary cylindrical tank. This fluid layer exhibits a system of two and three satellite vortices equally distributed on a circle, located at the vertices of a polygon. The distribution of vorticity along the diameter of these satellite vortices is quasi-parabolic. We will report on the flow topology and the advection of passive particles using a dynamical systems approach. Poincare\'{e} maps and the finite-time Lyapunov exponent (FTLE) fields reveal the fluid exchanged between different flow regions surrounding elliptic and hyperbolic points. (edited)