Advection.

Here in Hampshire County we got a weather advisory about “cold air advection”; the last word was new to me, and of course I dashed off to look it up: according to the Glossary of Meteorology, it’s “The process of transport of an atmospheric property solely by the mass motion (velocity field) of the atmosphere.” The OED, updated December 2011, has a somewhat more comprehensible definition, “The transfer of heat, energy, etc., by the (esp. horizontal) movement of air in the atmosphere; such movement itself.” The etymology:

< classical Latin advectiōn-, advectiō (of goods) transportation, carriage < advect-, past participial stem of advehere to bring (see advehent adj.) + -iō -ion suffix¹. In sense 2 after German Advektion (1896 or earlier in meteorological, 1898 or earlier in oceanographical use; 1871 (as †Advection) or earlier in general sense ‘transportation, carriage’).

Note that “sense 2” is the one I quoted, first attested in 1910; sense 1, which was not in the earlier editions of the OED, is:

1. Medicine. Growth (of new blood vessels) towards a stimulus; (also) transport (by blood vessels) towards a part of the body. rare. Now disused.

1896 Trans. Pathol. Soc. Philadelphia 17 49 It is possible, according to the views of Metchnikoff and of Leber, that the advection, if not the primary formation of new bloodvessels in the healing of wounds, is entirely under the influence of the chemotactic or a similar force.
1900 D. H. Goodsall & W. E. Miles Dis. Anus & Rectum I. iii. 59 In the interval between the receipt of the injury and the appearance of the abscess, some depressed condition of the constitution occurred, which permitted the advection, through the blood stream, of the infective agent to the damaged tissue.

Lexicography marches on!

Comments

  1. jack morava says:

    Then there’s TRANSvection, eg `Levitation or transvection in the paranormal context is the rising of a human body and other objects into the air by mystical means or meditation’

    https://en.wikipedia.org/wiki/Levitation_(paranormal)

    also used in mathematics in symplectic geometry, cf OED:

    Anatomy and Zoology. Epithet of a bone of the suspensorium in the skull of fishes, between the hyomandibular and the quadrate bones.

    1839–47 Todd’s Cycl. Anat. & Physiol. III. 833/1 The symplectic bones seem to be peculiar to Fishes.

  2. There are actually two technical senses of advection, one used primarily in practical meteorology or climatology and the other in more abstract fluid mechanics. Both could, I suppose, fall under the broad definition, “The transfer of heat, energy, etc., by the (esp. horizontal) movement of air in the atmosphere; such movement itself.” However, if you start writing down equations describing heat transfer, the two terms look very different.

    In meteorology, advective heat transfer between the atmosphere and the land (or sea) surface is the rate of energy transfer that is dependent on the wind speed at the surface. When the air is still, there is heat transfer that follows Newton’s Law of cooling—proportional to the temperature difference between the ground and the air. When the air is moving, there is also another contribution to the heat transfer—the advective transfer term—which is proportional to the temperature difference and to the wind speed v.* This is actually the origin of the familiar phenomenon of wind chill; when cold air is moving over your skin, you lose heat more quickly than if the air were still, although wind chill is not usually described as “advective.”

    The other sense of advection is related to a different velocity-dependent term, which arises in the equations of hydrodynamics. This involves the temporal derivative of a function of the state of a fluid in motion. (The function of the state can be the temperature, or the velocity of motion itself, or any other intrinsic property of the fluid, like its chemical makeup if reactions are going on.) The equations are most naturally expressed in terms of what is known as a convective time derivative D/Dt = ∂/∂t + u ⋅ ∇, where u is the local velocity of the fluid motion. The second term is the advection term. When writing down the equations of motion for the fluid mass itself (the Euler equations or, when viscosity is included, the Navier-Stokes equations), the advective term is what makes the equations nonlinear, giving rise to all kinds of fascinating phenomena.

    * For high wind speeds, the dependence on v could be more general, but a linear approximation is usually good enough.

  3. although wind chill is not usually described as “advective.”

    Well, I’m going to start doing so, dammit. It’s an impressive word.

  4. Jen in Edinburgh says:

    Whereas convection is the same kind of transfer by horizontal movement? Or is something much more complicated going on which will make my brain hurt?

  5. Advection is heat transfer by moving hot material to a cold place. Convection is where the movement of that material is caused by hot fluids rising and cold ones sinking, like water circulating in a pot (or more generally by other “internal” causes, like salinity differences.) Forced convection… I think that is like advection in the general sense, but where the material movement is caused by man-made devices, like fans.

    I’m probably wrong about all that, and will be corrected.

  6. @Y: Convection is heat transfer from location x to y due to hotter material from x replacing colder material from y (or vice versa, obviously). However, the typical way that convection works is quite inhomogeneous, with “bubbles” of hot material relocating from one site to another, then mixing with the fluid mass located around their new locations. Of course, even this description is a huge idealization—whereas realistic convective processes involve ill-defined blobs of fluid moving around, mixing with their immediate environments, and interacting with the omnipresent turbulence.

    Thus we have the primary difference between a “conventional” oven and a convection oven. The regular oven heats the air (and the food) inside by a combination of conduction and radiative (infrared) heat transfer. A convection oven, by contrast, heats a quantity of air in a separate smaller space, then blows it into the main oven chamber. The superheated air passes over the food and transfers more heat, advectively, to the food than the ambient air wood at the same temperature.

  7. John Emerson says:

    Didn’t “advection” use to be described as”warm winds”?

  8. Brett: I don’t understand how your “convection” in the general sense differs from advection. I stand by my advictions.

  9. John Cowan says:

    Hampshire County

    Ha, a redundancy! I shall report you to the Squad Squad.

  10. Stu Clayton says:

    A heated argument advects invective.

  11. @Brett
    You can get into a big argument over the question of how a conventional oven works. For me, the crucial fact is that the temperature of an oven doesn’t change when you open the oven door and let the hot air out. So, it’s principally transferring heat via radiation from the oven walls to the things being cooked. The alternative explanation is that Big Oven is lying to us about what’s going on in our cooking fixtures.

  12. John Cowan says:

    I don’t know about Big Oven, but when I open the door of my gas oven, the temperature in the room immediately rises, which means that the temperature in the oven cools. What is more, if I leave the oven open, the air inside and outside the oven reach equilibrium very quickly at a temperature much lower than the oven thermometer setting (otherwise I’d be baked).

  13. My toaster oven is advertised as having a convection oven baking mode. All it means is that it has a fan that blows the hot air around, rather than letting spontaneous convection do its job.

    *note to self* Invent minor variant on this mode of operation and call it an advection oven.

  14. General Electric sold a “trivection oven,” which became a recurring joke on 30 Rock, starting with the pilot episode. A later episode had Alec Baldwin’s character (who was, in universe, the creator of the trivection oven) ask a group of G. E. engineers “how many vections” the company’s newest oven design had.

  15. In case if anyone is wondering, Dis. Anus & Rectum stands for “Diseases of the rectum and anus” by D. H. Goodsall and W. E. Miles published in two editions in 1900 and 1905.

    It was described as “the classic masterpiece of rectal surgery”.

  16. Lars Mathiesen says:

    The thermostat of a conventional oven (or rather its thermocouple) is usually located very close to the metal walls, and on mine its held by metal clamps — so it probably only reacts to the oven door being open if the metal starts cooling down. If you have a full 16A phase to the heating elements it might be able to maintain wall temperature even with the door open, you’d have to try and see.

    But even if the food is mainly heated by radiation when the door is closed (which learnèd opinion differs on innit), I’m pretty sure room temperature air will cool it down though the walls are still hot.

    (The ‘convection’ mode of a multi-function tabletop thing is so-called in opposition to microwaves and grill element — though I’m pretty sure that the one I used to have had resistive heating only where the fan was and didn’t heat the walls).

    This reminds me on the physics of pumping a swing while seated (alternately leaning back with feet forward, and the opposite) — it seems that it is usually modelled as a rotating dumbbell or wheel on a rigid pendulum arm, and that works, but the treatments I have found freely admit that they don’t know how a chain would even transfer angular forces like the model does, or if the kinks in the chains are actually more important by changing the direction of the force relative to the line between fulcrum and user center of gravity.

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