advection: one construct, many systems

In hydrogeology, advection is the transport of a dissolved substance by the flowing groundwater itself, as the water moves through the pores of an aquifer at its average linear, or seepage, velocity. It is the primary spreading mechanism for a contaminant plume, acting together with, but distinct from, hydrodynamic dispersion and molecular diffusion. Bear's Dynamics of fluids in porous media sets out advective transport in porous flow. It is the same construct as advection in the atmosphere and ocean (a property carried along by the bulk motion of the fluid), realised here in groundwater and quantified from the seepage velocity.[1]

Unit

The solute flux carried by groundwater moving at the average linear (seepage) velocity

Recovery means

Not applicable

Measured by

Computed from the seepage velocity (the Darcy flux divided by porosity) times the solute concentration

In physical oceanography, advection is the transport of heat, salt, nutrients, or any dissolved or suspended property by the bulk movement of seawater, the currents. The great ocean currents advect warmth from the tropics poleward, shaping climate, and the advective terms sit alongside diffusion in every tracer budget. Pond and Pickard's Introductory dynamical oceanography presents advection in the conservation equations for the sea. It is the identical construct as atmospheric advection (a property carried by the mean flow), here realised in the ocean and measured by current-weighted fluxes of heat and salt.[2]

Unit

The flux of a property carried by ocean currents (e.g. heat or salt transport)

Recovery means

Not applicable

Measured by

Estimated from the current velocity multiplied by the transported property's concentration, integrated across a section

In atmospheric science, advection is the transport of a property of the air (heat, moisture, momentum) by the horizontal bulk motion of the wind, as distinct from vertical convection. Warm advection occurs where the wind blows from warmer toward colder regions, and the advection of temperature and vorticity drives much of the day-to-day evolution of weather systems. Holton's An introduction to dynamic meteorology formulates advection in the governing equations. The referent is the carrying of a quantity by the mean flow, the same transport process that moves heat and salt in the ocean and solutes through the ground.[3]

Unit

The rate a conserved property is carried past a point by the bulk flow (flux per unit area)

Recovery means

Not applicable

Measured by

Computed as the dot product of the velocity field with the gradient of the transported property