[MITgcm-support] Zonal and vertically averaged diagnostics

[Ryan Abernathey]

Hi Andrea,

I think what you want to do is fairly standard. The MITgcm has  
extensive diagnostics built in. But it doesn't take spatial integrals  
for you--it just does time averages. To do zonal and depth integrals,  
you have to process the diagnostic output offline. Most people do this  
using MATLAB or python. Make sure you check out the  
available_diagnostics.log output by the diagnostics package to see  
which diagnostics are available in your configuration.

Computing a mass (volume) budget is fairly trivial. You simply  
integrate the transports (UVEL, VVEL, WVEL) across whatever surface  
you want using the proper grid geometry. (The output grid files can be  
very useful for this.) Correct me if I'm wrong, but the zonal- and  
depth-integrated volume transport across any latitude in the basin you  
described should be zero, no?

Budgets for salt or any other tracer should be fairly straightforward  
to compute as well. The diagnostics package automatically makes the  
necessary fluxes available through variables like ADVx_SLT, DFxE_SLT,  
surForcS, etc. It provides these values averaged at every grid point.  
If you want to compute a budget for a different volume, you have to  
integrate the fluxes yourself off-line.

Conservation of volume is very good in MITgcm, up to numerical  
precision. Budgets for other tracers (heat, salt, etc.) can be more  
difficult do close exactly if you have many different packages enabled  
(gmredi, kpp, etc.), but for a simple setup you should be able to do it.

Hope this helps.

Cheers,
Ryan


On Nov 10, 2011, at 5:44 AM, cimatori wrote:

> Dear MITgcm users,
>
> I have a question on diagnostic output, hope it's not too trivial...
>
> I am interested in computing a mass budget (both total mass and salt
> mass) for a basin with simple geometry (box+periodic channel), and I
> would like to output some transport terms integrated both zonally and
> vertically. In other words, I want to compute the budget at each
> different latitude from south to north (keeping the northern boundary
> fixed). This means that I would have to output a vector with the  
> size of
> the number of grid points along y.
> As fas as I could understand, this doesn't seem to be a standard  
> choice
> for the diagnostics package. Did anybody try something like this? Is
> there some tutorial case including an example?
>
> Apart from this, is there any reference on how good or bad the mass
> budget in MITgcm might be?
>
> Any suggestion would be of great help, thanks!
> Andrea
>
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