[MITgcm-support] How to diagnose the diapycnal diffusivity?

Mon Jul 16 08:39:16 EDT 2018

Hi Yang,

So far as I know, GM parameterization is an adiabatic scheme, which means that this parameterization do not change water properties (e.g., density).  You can read their paper in 1995 which showed that GM scheme is effectively an advection rather than diffuion.  So neither GM90 nor GM_VisbK (Visbeck et al. 1997) is diapycnal.

In MITgcm, diagnosing diapycnal diffusion is not straightforward as it is a z-coordinate model.  But you can use the resorting method by Griffies et al. (2000) to diagnose the 'effective' diapycnal diffusivity.  Effective means those processes act to homogenize water density, such as the explicit diapycnal diffusivity you set in the model (diffKr), spurious numerical diffusivity associated with advection scheme, those caused by other parameterizations (e.g., KPP, tidal mixing) etc.

You can refer to Griffies's paper for details.  Hope this helps.

References:
Griffies, S. M., R. C. Pacanowski, and R. W. Hallberg, 2000: Spurious Diapycnal Mixing Associated with Advection in a z-Coordinate Ocean Model. Mon. Wea. Rev., 128, 538-564.
Visbeck, M., J. Marshall, and T. Haine, 1997: Specification of Eddy Transfer Coefficients in Coarse-Resolution Ocean Circulation Models. J. Phys. Oceanogr., 27, 381-402.

------------------
 Best regards 

Yu-Kun Qian (钱钰坤) 
Center for Monsoon and Environment Research 
 Department of Atmospheric Sciences
School of Environmental Science and Engineering 
 Sun Yat-sen University 
No. 135 Xingang West Road, Haizhu District 
Guangzhou, 510275, P.R. China 
Tel; 020-84115227 
Email: qianyk at mail3.sysu.edu.cn      

------------------ 原始邮件 ------------------
发件人: "yzb"<853245241 at qq.com>;
发送时间: 2018年7月16日(星期一) 晚上8:23
收件人: "mitgcm-support"<mitgcm-support at mitgcm.org>; 

主题: Re: [MITgcm-support] How to diagnose the diapycnal diffusivity?

Thank you. It really helps me. I will read the document carefully.

------------------ Original ------------------
From:  "Martin Losch"<Martin.Losch at awi.de>;
Date:  Mon, Jul 16, 2018 08:20 PM
To:  "MITgcm Support"<mitgcm-support at mitgcm.org>;

Subject:  Re: [MITgcm-support] How to diagnose the diapycnal diffusivity?

As far as I know, the parameters \kappa_{\rho} and \kappa_{GM} are constant parameters that you specify in data.gmredi (from GMREDI.h:
C     GM_isopycK       :: Isopycnal diffusivity [m^2/s] (Redi-tensor)
C     GM_background_K  :: Thickness diffusivity [m^2/s] (GM bolus transport)
). You  can have variable \kappa_{GM} (documentation: <https://mitgcm.readthedocs.io/en/latest/phys_pkgs/gmredi.html#variable> ), but you need to turn it on explicitly with the appropriate CPP- and runtime-flags, and then GM_VisbK is the approriate diagnostics for this particular version of variable \kappa_{GM}.
In recent code, there are all sorts of other options that I am not familiar with, but they maybe worth exploring.

Martin

> On 16. Jul 2018, at 13:57, yzb <853245241 at qq.com> wrote:
> 
> 
> Thanks for you reply. Sorry for the confusion of my question. This is something I should have written more about the diapycnal diffusivity. The diffusivity I want to calculate is the diapycnal mixing ( ,unit is m^2/s), maybe can be regarded as eddy coefficient. I am not sure the  which is in the Gmredi pkg can be represented for it. There is a diagnostics option in Gmredi pkg which is called 'GM_VisbK' and this may be relate to my question.
> 
> ------------------ Original ------------------
> From:  "Martin Losch"<Martin.Losch at awi.de>;
> Date:  Mon, Jul 16, 2018 07:35 PM
> To:  "MITgcm Support"<mitgcm-support at mitgcm.org>;
> Subject:  Re: [MITgcm-support] How to diagnose the diapycnal diffusivity?
> 
> Yang,
> 
> when you run your model with a default debugLevel (=1), then you’ll a file called “available_diagnostics.log”, that will show you all diagnostics for your particular configuration. If you have turned on GM (useGMredi=.TRUE. in data.pkg), then you the GM-diagnostics should be part of that list. I am not sure if there is a diagnostic for diapycnal diffusivity (do you mean diffusive flux?) …
> 
> Martin
> 
> > On 16. Jul 2018, at 11:12, yzb <853245241 at qq.com> wrote:
> > 
> > Hello,
> > 
> >      I want to diagnose the diapycnal diffusivity directly from model. But I don't know the diagnostic name of it. Could anyone tell me the diagnostic name? Meanwhile, I found the package of Gmredi may contain this diagnosis. If so, what's the diagnostic name in that package? 
> > 
> >     Thanks,
> >     Yang
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support
> 
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