[MITgcm-support] On the vertical mixing parameterization

[Andrea Cimatoribus]

Hi,
from my experience with MITgcm and other models I can confirm your 
tests: background diffusivities are very important. In fact, in my 
experience, the results are much more sensitive to changes in background 
diffusivities than to changes in the turbulence model parameters (or, in 
fact, to using different turbulence models).
How much is the right amount of background diffusivity then depends on 
many details of your simulations. In general, I would say that higher 
resolution simulations need less background diffusivities (I get for 
instance very good results with molecular background values at ~200m 
resolution), but a final answer can only come from systematic comparison 
with observations. As far as I know, there can be no a priori answer.

Ciao,

Andrea Cimatoribus
postdoctoral researcher
EPFL ENAC IIE ECOL
https://people.epfl.ch/andrea.cimatoribus

On 16/01/17 22:39, whale wrote:
> Dear friends
>
>
>
> I am confused on the treatment of the vertical mixing parameterization
> in MITgcm.
>
> In my experiment, I have employed the KPP (Nonlocal K-Profile
> Parameterization for Vertical Mixing). As the manual explained, the KPP
> could control the vertical mixing by supplying vertical diffusivity and
> viscosity.
>
>
>
> The question is if I still need to set the other parameters of vertical
> mixing and viscosity in /date file/, such as diffKrT and diffKrS, when I
> have already employed the KPP.
>
>
>
> In my mind, these two parameters seem likely to be linked to the
> background vertical mixing, and I do not know if my understanding is
> right or not. Actually, I have already run two experiments with and
> without the diffKrT and diffKrS, respectively. The results of my two
> experiments are different from each other, and confirm that the diffKrT
> and diffKrS still have a great effect when the KPP is employed.
>
>
>
> Thank you for your consideration.
>
> Cheers
>
> Chengyan Liu
>
>
>
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