from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A tendency to diffuse
- n. a coefficient of diffusion; especially the amount of heat that passes through a given area in unit time
from the GNU version of the Collaborative International Dictionary of English
- n. Tendency to become diffused; tendency, as of heat, to become equalized by spreading through a conducting medium.
from The Century Dictionary and Cyclopedia
- n. The power or rate of diffusion.
- n. Specifically, in physical, a physical constant expressing the rate of diffusion of a dissolved substance in the solvent.
Sorry, no etymologies found.
WHAT'S GOING ON: "Fick's first law of diffusivity" is at work.
I'm pretty sure he actually got it wrong, because his implementation used calculations at a point for diffusivity, but the algorithm he was using varied considerably over the bottom grid cell.
Climate for a nice modern treatment of this problem, which attempts to use ocean heat uptake data to constrain the vertical diffusivity.
In one of the GISS models, the happen to introduce a false diffusivity to deal with type of numerical instability at the poles.
You really need to jointly estimate climate sensitivity and vertical diffusivity of the ocean, and the uncertainty in the latter makes a big difference to estimates of the former.
Sometimes those writing code will decide to just introduce a false diffusivity thermal or viscous depending on the specifics to solve the problem.
Molecular diffusivity tends to provide a cutoff frequency at small scales.
Also, I do want to be careful to note that computations being what they are, sometimes, some approximations — including unphysical artificial diffusivity– may be ok.
Water has a different thermal diffusivity than rock, fractured rock is going to be different still,… Plus heat comes up from the interior of the earth as anyone who has gone down in a deep mine knows.
The verdict on this possibility awaits reconciliation of a suite of discordant field and modeling estimates of diffusivity in the real ocean Archer et al., 2000.
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