[MITgcm-support] Question about closing heat budget

[Martha Buckley]

The TOTTEND term only works with a linear free surface.  Otherwise, you
should output snapshots of ETAN and THETA and use these to calculate the
tendency term yourself.
Martha


On Wed, May 4, 2016 at 10:45 PM, Jacob Wenegrat <jwenegrat at stanford.edu>
wrote:

> Hello All,
>
> First off let me thank everyone who has contributed to the MITgcm and the
> mailing list. It's a great tool, and I've gotten quite a bit of help
> already digging through the mailing list archive.
>
> I am currently running a simple reentrant channel model of a front, and
> finding that while the momentum budget closes nicely following previous
> advice found in the archive, closing the heat budget is proving more
> challenging.
>
> To date I've followed the instructions posted here for closing the heat
> budget:
> http://mitgcm.org/download/daily_snapshot/MITgcm/doc/Heat_Salt_Budget_MITgcm.pdf
> .
>
> Specifically, considering only subsurface grid cells (and with no
> shortwave fluxes):
>
> TOTTTEND/86400 = ADV_Tend + KPP_Tend + DIFF_Tend
>
> Where ADV_tend = d/dx ADVx_TH + d/dy ADVy_TH + d/dz ADVr_TH (accounting
> for cell volume in calculating this).
> KPP_Tend = d/dz KPPg_TH (accounting for cell vol).
> DIFF_Tend = d/dx DFxE_TH + d/dy DFyE_TH + d/dz DFrE_TH+ d/dz DFrI_TH
> (accounting for cell volume)
>
> I find that this balance works well at the beginning of my simulation,
> works quite poorly in the middle (when the flow goes baroclinically
> unstable), and then works reasonably well again towards the end as the
> front spins down, although it is not completely closed.
>
> Specific questions are:
> 1) I am using tempAdvScheme: 33, which I gather from the documentation has
> associated diffusion which can be difficult to diagnose. Does the
> associated diffusive flux from this end up within any of the above
> diagnostics? Might this be the cause of the large residuals after the
> formation of sharp frontal regions?
>
> 2) The tendency term appears to be a small residual between the
> across-channel (y) and vertical flux divergences. As the features sharpen
> to near grid-scale, might the finite differencing (and later interpolation
> back to the tracer grid points) be causing problems?
>
> More generally any suggestions of avenues to pursue would be greatly
> appreciated. I'm not sure how the mailing list deals with attachments, so I
> haven't included my data file, but can easily do so if useful.
>
> Thanks,
> Jacob
>
> --
> Jacob Wenegrat
> Postdoctoral Fellow
> Dept. of Earth System Science
> Stanford University
>
> Email: jwenegrat at stanford.edu
> Web: http://web.stanford.edu/~jacob13
>
>
>
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>



-- 
Martha W. Buckley
marthabuckley at gmail.com
http://sites.google.com/site/marthabuckley/home
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