[MITgcm-support] Heat budget in MITGCM

Jean-Michel Campin jmc at ocean.mit.edu
Tue Nov 18 12:12:17 EST 2014


Hi Abhisek,

I would recommand to concentrate first on any level except the surface (k=1),
and try to close the budget ; then, once you get a clean closed budget
for levels at depth, you can revisit the surface level problem.

at depth (k>1):
the way you estimate the tendency is not what is done in the model,
see e.g.:
http://mitgcm.org/public/r2_manual/latest/online_documents/node73.html

The diagnostics for the KPP non-local term is like a vertical flux 
(added to fVerT), so it can be treated (for budget purpose) the same way 
as DIFrI_TH.

at the surface, you can search the mitgcm-support archive and find some
information there, e.g.:
http://mitgcm.org/pipermail/mitgcm-support/2014-April/009093.html
but it's likely that you would need additional diagnostics output,i
e.g. WTHMASS & WSLTMASS at k=1.

Cheers,
Jean-Michel

On Tue, Nov 18, 2014 at 09:49:34PM +0530, Abhisek Chakraborty wrote:
> Many thanks Ryan, Dimitris, John and Gael for your suggestions.
> 
> 
> I am not much familiar with MATLAB, so for me it was too much difficult to
> understand the code shared by Gael, though I tried to look into it.
> 
> 
> As a matter of fact is that I am using is the ECCO1 version (1 deg global,
> 50 levels, excluding poles; i=1:360; j=1:160; k=1:50) of MITGCM with linear
> free surface and linFSConserveTR=True. The diagnostic parameters are
> written in every day with diagnostic timephase=0. Model parameterizations
> are KPP and GM-Redi.
> 
> 
> I’d like to analyze the heat budget at a particular location, say, (i,j,k).
> So, from the suggestions by Ryan, Dimitris and looking into the Gael’s
> code, I am trying the following:
> 
> 
> !!Cell volumes (center difference)
> 
> Cvx = (RAC(i+1,j) - RAC(i-1,j)) * RF(k) * hFacC(i,j,k)
> 
> Cvy = (RAC(i,j+1) - RAC(i,j-1)) * RF(k) * hFacC(i,j,k)
> 
> Cvz = RAC(i,j) * (RF(k+1) – RF(k)) * hFacC(i,j,k)
> 
> 
> 
> !!Divergence of advection & diffusion by center difference
> 
> 
> if (k>1) then
> 
>          adc_dif_vert_k = (ADVr_TH(i,j,k+1) – ADVr_TH(I,j,k-1))/cvz +
> 
>                               (DIFrE_TH(I,j,k+1) – DIFrE_TH(I,j,k-1))/cvz +
> 
>                               (DIFrI_TH(I,j,k+1) – DIFrI_TH(I,j,k-1))/cvz
> 
> else
> 
>          adc_dif_vert_k = 0.0
> 
> endif
> 
> 
> 
> adc_dif_hori_k = (ADVx_TH(i+1,j,k) – ADVx_TH(i-1,j,k))/cvx +
> 
>                          (ADVy_TH(i,j+1,k) – ADVy_TH(i,j-1,k))/cvy +
> 
>                          (DIFxE_TH(i+1,j,k) – DIFxE_TH(i-1,j,k))/cvx +
> 
>                          (DIFyE_TH(i,j+1,k) – DIFyE_TH(i,j-1,k))/cvy
> 
> 
> !!To account for the  shortwave heating
> 
> depth=RF(k)
> 
> swfrac=0.62*exp(depth/0.6) + (1.0-0.62) * exp(depth/20)
> 
> if(depth < -200.0) then
> 
> swfrac=0.0
> 
> endif
> 
> if (k=1)then
> 
>                swfrac=1.0
> 
> endif
> 
> 
> !!Finally balance
> 
> 
> TOTTTEND/86400.0 = - adc_dif_vert_k -  adc_dif_hori_k +
> (oceQsw/(rhoConst*Cp)) * swfrac * hFacC(I,j,k) + KPPg_TH(i,j,k)
> 
> 
> Please let me know whether I am doing properly or not.
> 
> 
> 
> 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)*
> 
> On Tue, Nov 18, 2014 at 5:06 AM, gael forget <gforget at mit.edu> wrote:
> 
> > 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
> > <http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/gael/matlab_class/gcmfaces_diags/diags_set_D.m> match
> > those used in pkg/diagnostics
> >
> > I should also mention that diags_set_D.m
> > <http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/gael/matlab_class/gcmfaces_diags/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.pd
> > <http://mitgcm.org/viewvc/MITgcm/MITgcm_contrib/gael/matlab_class/gcmfaces.pd>
> > f
> > … 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)*
> >>
> >
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-support
> >
> >
> >
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> > http://mitgcm.org/mailman/listinfo/mitgcm-support
> >
> >

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