cold advection

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 (see pigpen problem). Another commonly advected substance is heat, and here the fluid may be water, air, or any other heat-containing fluid material. Any substance, or conserved property (such as heat) can be advected, in a similar way, in any fluid.
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Transport of cold air into a region by horizontal winds.