[MITgcm-support] noise in high resolution run

Nicolas Wienders wienders at ocean.fsu.edu
Wed Apr 5 10:02:20 EDT 2006

> Hi there,
> my final comment about the noise in my 1/6th degree run:
> It's gone! With a very high friction parameter of 1e12 for both  
> viscosity and diffusivity (which is almost the maximum allowed) and  
> cosPower=4., I have now a 1year run which looks good to me (at  
> first sight), see http://mitgcm.org/~mlosch/noise6.png
> My time step is 600s. When I reduce the friction, which I think I  
> should be able to do, then I run into stability problems after some  
> integration time (e.g. 5e11 allows me to run for 98 days before  
> blowing u

Dear martin

With the values you mention the stability parameter

Sl=4. (Ah.dt)/(dx^2) is now equal to about 7.10^6
and this parameter is usually to be left < 0.6 !
I am surprised you can get any solution.

On our side, very simple configuration, 1/4 or 1/8 degree,
25 vertical levels, NATL gyre, gmredi, and cheapaml, i still
can't get read of the same kind of noise whatever i do with
the viscosities and diffusivities.

The last try was Ah = viscAh = 3000.
                              Az = viscAz=10^{-4}

See picture attached.
The noise is visible for U and V, and W for layers > 1.

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