# What exactly is the difference between advection and convection?

After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms.

Sometimes, the term convection seems to include advection and diffusion, sometimes not. After all, equations exhibit two different terms for advection and diffusion, and we don't call the sum of them a convective term. When we talk about a convective term, it is indeed the advective term!

It seems:

• transport of pollutants in a river by bulk water flow downstream relates to advection

• boiling water for pasta relates to convection

Maybe, a conserved property such as energy can be advected, but we only use convection for transport of "ensembles of molecules".

So, is there a difference? Could we figure it out with examples?

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– Qmechanic Apr 27 '12 at 15:40

Convection is the movement of a fluid, typically in response to heat.

Advection is the movement of some material dissolved or suspended in the fluid.

So if you have pure water and you heat it you will get convection of the water. You can't have advection because there is nothing dissolved or suspended in the fluid to advect.

If you have silt suspended in the water and heat it then you will get convection of the water and advection of the silt.

If you have silt suspended in the water and the water is just flowing in a river you will get advection of the silt, but you would not normally describe the water movement as convection.

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It can be pointed out that the mechanism of convection is the advection of the velocity field along with the fluid. This is proper usage of the term, even when there isn't a different material solute, just a velocity field. – Ron Maimon Apr 27 '12 at 18:25

Advection is the horizontal movement of air Convection is the vertical movement of air

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Interesting approach. But what happens if we do not consider air but cells for instance? – Wok Jun 11 '14 at 12:40
Need to add that: There are also vertical advection phenomenon of air too. IMHO that in this paper written in 1981, the author developed the physical model to depict the vertical advection and it continued to use in today's model. – Han Zhengzu Mar 27 at 14:43

## protected by Qmechanic♦Jun 11 '14 at 4:28

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