Vortices

The first example of a dissipative structure is a vortex, such as that which forms when water drains through the plughole in a bathtub or sink. The smooth flow of water far away from the plughole changes to fast swirling motion that leads to the formation of a structured object, the vortex. Larger examples of vortices are tornadoes that are common in the USA (and recently starred in the movie Twister!): When cold air from Canada collides on the continent with warm air from the Gulf of Mexico, intense thunderstorms result. All air-masses have a certain amount of rotational motion to begin with. When such air converges into the updraft of an intense thunderstorm, the rotational motion speeds up because of the conservation of angular momentum. (Recall how a skater increases her rate of spin by drawing in her arms). The vortex is an example of a time-dependent complex system. It is difficult to characterize in terms of a few parameters as in equilibrium systems studied earlier. In fact notice that the formation of the vortex breaks the homogeneity, or symmetry, of the non-moving water/air-mass. Thus this is our first example of greater macroscopic structure or dynamical order, in a non-equilibrium system.