[MITgcm-devel] background diffKr in vertical mixing pkgs

[Martin Losch]

Hi Jean-Michel,

I don’t have any educated comments, but see below

Martin

On Nov 14, 2014, at 3:32 PM, Jean-Michel Campin <jmc at ocean.mit.edu> wrote:

> Hi,
> 
> Regarding the background value of vertical diffusivity in pkgs:
> ggl90, kl10, my82, pp81,
> we currently use the temperature diffusivity (diffKrNrT)
> but regarding ptracers default diffusivity (and default 3-D field diffKr), 
> we use the salinity one.
> 
> I am thinking of few changes:
> 1) It would be more consistent to change the background value in 
>   these vertical mixing schemes from diffKrNrT to diffKrNrS.
you mean for ptracers? I guess the idea behing using diffKrNrS was that passive tracers diffuse more like salinity (partical transport) than temperature (energy transport) on the microscopic/molecular level. Does not matter on macroscopic scales.
> 2) In addition, in the case where no vertical diffusivity for salinity is specified,
>   we could change the code to use the temperature diffusivity profile 
>   instead of diffKrSDefault. 
>   This way, if salinity is not stepped forward (only 1 tracer), the temp. 
>   diffusivity would be used as a default.
Sounds good to me
> 
> 3) Regarding the implemetation of ALLOW_3D_DIFFKR in pkgs kl10, my82 & pp81
>   I have the impression that the 3-D field (diffKr) is, at the end, not used
>   at all (added and then substracted). Will fix this part by using
>   the 3-D field diffKr as a minimum value in kl10_calc.F, my82_calc.F & pp81_calc.F
> 4) But in pkg ggl90 (where the background value can affect the vertical
>   diffusion of TKE), I am not sure what should be done with ALLOW_3D_DIFFKR:
>   continue to use diffKrNrT (or diffKrNrS) as the background ?
>   or decide to use the 3-D diffKr instead ?
> 
> Comments and advise are welcome.
> 
> Cheers,
> Jean-Michel
> 
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