Advection

Advection is the transport of a property (heat, salt, momentum, a tracer) by the bulk motion of a fluid, written as the term v dot grad(C) in the conservation equation for property C. In the ocean it dominates lateral redistribution: currents carry heat poleward and salt across basins, distinct from diffusion, which acts down the gradient by molecular or turbulent stirring. The advective heat flux of the Gulf Stream reaches order 1 petawatt. The Peclet number, the ratio of advective to diffusive transport, measures which process controls a given balance.