[MITgcm-support] Heat Budget in tutorial (Global Ocean Simulation at 4 deg)

[Krishnakumar Rajagopalan]

Hi Martin,

Thanks a lot for your suggestions.

I did make some errors in the calculation of the mass_cell. Earlier I considered 
the thickness of the cell as rf(i,j,k), but now I multiply  rf(i,j,k) with 
hFacC(i,j,k)  to find the thicknes of the cells. The volume of the  cell is now 
calculated as rAc(i,k)*rf(i,j,k)*hFac(i,j,k), where rAc(i,j) is the area of 
tracer cell.  As the temperature and salinity fields in the cells change with 
time, there are some changes in the  potential density of the cells. I 
have averaged the densities at time=0 and time = 800 yrs to find the mean 
density. Now mass of the cell is calculated as volume_cell*mean_density_cell.  I 
have also changed the value of  Cp from 4000 to 3994 J/kg/k , which is the value 
the solver is using. These changes have reduced del H by a small amount. Please 
take a look at attached figure 1. I have also revised the calculation of the 
surface heat flux. It is now calculated as surfFacT.*rAc and integrated over 
the ocean surface as sum(sum(surfFacT.*rAc )), at any time, which is then 
integrated over time, to find Q. ( Q is practically unchanged). Figure 2 shows 
the ratio of Q/del_H and the ratio increases linearly.

The attached config.tar file contains CPP_OPTIONS.h (this tutorial uses the 
default CPP_OPTIONS.h  and is located only in /build) ,all files in /code 
directory and the data* files. 


It would be great if you could give us some comments.

Best regards

Krishnakumar
( Sorry about the delay in replying, I was carefully checking my post 
processing)




________________________________
From: Martin Losch <Martin.Losch at awi.de>
To: mitgcm-support at mitgcm.org
Sent: Mon, May 16, 2011 10:12:00 PM
Subject: Re: [MITgcm-support] Heat Budget in tutorial (Global Ocean Simulation 
at 4 deg)

Krishnakumar,

what would be interesting in this context are details of your configuration, 
e.g. the content of your "code" directory (main the cpp-flags that you use), and 
your namelists (data* files).

Wild guess:
Did you ever plot the ratio of the two curves? From the figure it looks like 
this ratio might be constant, which would then point to an inconsistency in your 
analysis (e.g. Cp is no the same as in the model, or there is a 
problem/systematic inaccuracy with the computation of the "mass_cell", etc.)

Martin

On May 16, 2011, at 9:25 PM, Krishnakumar Rajagopalan wrote:

> Hi All,
> 
>  
> It seems that the heat globally added at the ocean surface does not match the 
>heat absorbed by the ocean.
> 
>  
> Let Ho and Ht denote the initial  enthalpy and enthalpy at time, t,  of the 
>ocean.  Then (Ht – Ho) represents the change in enthalpy , del H, of the ocean 
>which is calculated from  summing  over all the cells, mass_cell*Cp*( T(t) - 
>T_initial  ),  where T_initial  and T(t) represent the initial temperature and 
>temperature at time, t, of the cell.  The quantity, del H,  at any time , must  
>equal the heat supplied to the ocean till that time,  which in the case of this 
>tutorial comes from the restoring term { -lamba*(theta-SST) }  and Qnet.  I have 
>integrated the diagnostic,  surfForcT (model surface forcing for Temperature), 
>over the area of the ocean and with time to calculate the heat, Q entering the 
>ocean. (The surfForcT is output every month). In (attached) figure, the red line 
>shows del  H as a function of time and the blue line shows Q supplied to the 
>ocean  upto that time, t .  Ideally the two lines must coincide.  What could be 
>the reason for this apparent discrepency which actually increases with time ?
> 
> Thanks in advance
> 
> Krishnakumar
> 
> 
>  
> <dH_and_Q.jpg>_______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
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