Scalar turbulence

The advection of a passive substance by a turbulent flow is important in ma ny natural and engineering settings. The concentration of such a substance can exhibit complex dynamic behaviour that shows many phenomenological para llels with the behaviour of the turbulent velocity field. Yet the statistic al properties of this so-called 'passive scalar' turbulence are decoupled f rom those of the underlying velocity field. Passive scalar turbulence has r ecently yielded to mathematical analysis, and such progress may ultimately lead to a better understanding of the still intractable problem of fluid tu rbulence itself.