[MITgcm-support] Comparison of advection schemes

[Ed Hill]

On Thu, 2004-07-22 at 14:15, Sergio Jaramillo wrote:
> Hi all,
> 
> I am trying to understand the effects of the choice of advection scheme 
> on the tracer field evolution in a laboratory tank. I see that if I use 
> some advection schemes (e.g. centered fourth order) I need some finite 
> amount of diffusion, but I don't know how to introduce it in the model 
> (let alone how to pick the right value), as in the laboratory I don't 
> have turbulence, and  I am somewhat apprehensive about using bi-harmonic 
> diffusion. Perhaps someone could give me a hint on this? Or recommend me 
> some references I should read to understand better the current advection 
> schemes available in MITgcm?

Hi Sergio,

If you're modeling diffusion of passive aqueous chemicals in laboratory
tanks, then the following may be helpful:

  1) aqueous molecular diffusion of the chemicals you are using 
     (which is typically in the range of 10^-5--10^-7 cm^2/s and 
     well-known for many chemicals) gives you a good lower bound

  2) mechanical mixing (or "dispersion") is often modeled as a 
     Fickian diffusion process with an order of magnitude (or 
     orders of magnitude depending on the strength) larger 
     diffusion coefficient

And if you're running actual experiments and have a camera handy then
there are ways to estimate the rates of observed dispersion/diffusion.

Ed

-- 
Edward H. Hill III, PhD
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