[MITgcm-support] Heat budget in MITGCM

[Ryan Abernathey]

Abhisek,

This is a very common question that unfortunately is not documented very
well. A couple of suggestions...

For the transport terms, (ADV* and DF*), keep in mind that these are FLUX
terms, defined on the cell boundaries. In order to calculate a heat budget,
you need to calculate the DIVERGENCE of those fluxes.
http://mitgcm.org/public/r2_manual/latest/online_documents/node71.html
Maybe this is obvious, but your email did not make it clear whether you
were doing this or not.

Likewise, TFLUX is the downward flux at the surface, in W/m^2. In order to
convert to temperature units, you need to divide by
HeatCapacity_Cp*rUnit2mass. For z coordinates, rUnit2mass is equal
to rhoConst.

There are some subtleties regarding tracer budgets under different free
surface treatments. Maybe someone else on the list understands this issue
better and is willing to explain. Anyway, those should be second-order
effects.

Good luck with your analysis.

-Ryan


On Sat, Nov 15, 2014 at 2:29 AM, Abhisek Chakraborty <abhisek.sac at gmail.com>
wrote:

> Dear Users,
>
> I am trying to analyze heat budget in MITGCM. From the diagnostic
> outputs I have the following terms
>
> TOTTTEND , ADVr_TH, ADVx_TH, ADVy_TH, DFrE_TH, DFxE_TH, DFyE_TH,
> DFrI_TH, KPPg_TH, TFLUX (i.e. all terms corresponding to tendency,
> advection, diffusion, KPP and total heat flux).
>
> Apart from these, I have other usual outputs like THETA, SALT etc.
>
> The tendency term is in degC/day, the other terms are in degC*m^3/s
> and TFLUX is in W/m^2. Thus I have converted the tendency term into
> degC/s by dividing by 86400.0 and the advection-diffusion terms are
> divided by cell volume (=RAC*RF*HFACC).
>
> I am using "linFSconserveTr=True".
>
> For the surface layer I have to consider TFLUX (watt/m^2), but how to
> convert it into degC/s unit?
>
> For subsurface levels, I am trying to equate tendency term with
> (advection + diffusion + KPP term). But there is a mismatch.
>
> Can somebody please guide me how to achieve the exact heat budget for
> both surface and subsurface levels ?
>
> Thanking in advance,
> Abhisek
>
> --
>
>
> *ABHISEK CHAKRABORTY*
>
> *Scientist - "SD"Oceanic Sciences Division (*AOSG/EPSA)*
>
> *Space Applications Centre*
>
> *Indian Space Research Organization*
>
> *Ahmedabad - 380 015*
>
> *Gujarat, INDIA*
> *Contact: +91-79-2691-6054 (O), +91-79-2686-1929(R)*
>
> _______________________________________________
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>
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