[MITgcm-support] Heat budget in MITGCM

[gael forget]

Hi Abhisek, et al,

the following matlab code may provide some guidance :
http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/gael/matlab_class/gcmfaces_diags/diags_set_D.m

It does not cover every possible combination of model options
(e.g., no kpp or thsice) of course, but treats a few. In that code, 
it is assumed that 
1) the setting for the diagnostics package was according to
     http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/gael/verification/global_oce_llc90/input/data.diagnostics
     which includes vertical integration. The relevant diagnostics
     for budget are those with filename like 'diags/budg2d_snap_set1',
2) tendencies have been pre-computed by differencing between 
    consecutive (monthly) snap shots — so that ETAN 
    really means dETAN/dt in this context, and similarly for
    THETA, SALT, etc. The other variable names used in
    diags_set_D.m match those used in pkg/diagnostics

I should also mention that diags_set_D.m is part of a 
broader framework (gcmfaces) which is documented in
http://mitgcm.org/viewvc/*checkout*/MITgcm/MITgcm_contrib/gael/matlab_class/gcmfaces.pdf
… although I am afraid this documentation is also 
lacking wrt the budget diagnostic codes.

Cheers,
Gael

On Nov 17, 2014, at 5:53 PM, Dimitris Menemenlis <dmenemenlis at gmail.com> wrote:

> … and you probably already know this, but not clear from your email:
> shortwave is not dumped in surface level only, but rather is distributed with exponentially
> decaying profile in top 200-m, with subtle modifications if this heating is occurring within
> the KPP mixing layer depth.
> 
>> On Nov 17, 2014, at 2:44 PM, Ryan Abernathey <ryan.abernathey at gmail.com> wrote:
>> 
>> 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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