Advection is transport in a fluid. The fluid is described mathematically for such processes as a vector field, and the material transported is described as a scalar concentration of substance, which is present in the fluid. A good example of advection is the transport of pollutants or silt in a river: the motion of the water carries these impurities downstream. Another commonly advected substance is heat, and here the fluid may be water, air, or any other heat-containing fluid material. Any subs… (More on Advection)