Key People:
Lewis Fry Richardson

Richardson number, parameter that can be used to predict the occurrence of fluid turbulence and, hence, the destruction of density currents in water or air. It was defined by the British meteorologist Lewis Fry Richardson, a pioneer in mathematical weather forecasting. Essentially the ratio of the density gradient (the change in density with depth) to the velocity gradient, the Richardson number is defined asEquation.in which g is gravity, ρ is density, u is velocity, and z is depth. The Richardson number, or one of several variants, is of practical importance in weather forecasting and in investigating density and turbidity currents in oceans, lakes, and reservoirs.

Related Topics:
fluid flow

turbulence, In fluid mechanics, a flow condition (see turbulent flow) in which local speed and pressure change unpredictably as an average flow is maintained. Common examples are wind and water swirling around obstructions, or fast flow (Reynolds number greater than 2,100) of any sort. Eddies, vortices, and a reduction in drag are characteristics of turbulence. Lowered drag enables golf balls to travel farther than they would do otherwise, and the dimpled surface of golf balls is meant to encourage turbulence in the boundary layer. If swimsuits with rough surfaces help swimmers to move faster, as has been claimed, the same explanation may apply.

This article was most recently revised and updated by Robert Curley.