[MITgcm-support] Hydrostatic pressure in LLC runs

[Dimitris Menemenlis]

Hi Xiaozhou, unfortunately Jean-Michel’s answer would require you to rerun the simulation.
Are you trying to do this study globally or in a small region.
If the later, I can point you to examples of running LLC4320 cutouts.
If the former, your best bet might be to use a small test domain to experiment
with best way to reproduce the diagnostics that Jean-Michel suggests,
based on the prognostic variables that have been saved for LLC4320.

Cheers, Dimitris


> On Oct 30, 2024, at 7:56 PM, Jean-Michel Campin <jmc at mit.edu> wrote:
> 
> Hi Xiaozhou,
> 
> Depending on your choice of parameters (mainly from main parameter file "data"), it might not be 
> completely straightforward to get back the pressure gradient tendency from just the T & S and EOS.
> This is the main reason why we have several diagnostics to help:
> 1) "PHIHYD " the kinematic Hydrostatic Pressure anomaly (or dynamic Hydrostatic Pressure anomaly  
>  divided by rhoConst); this could save you the effort of computing the density anomaly and to 
>  integrate vertically.
> 2) "Um_dPhiX" and "Vm_dPhiY" and directly the momentum tendency term from pressure gradient that 
>  can be used to close the momentum budget.
> 
> I would suggest that you start to use these last 2 and check how you momentum budget looks like.
> Then, specially if you are using z* (select_rStar > 0), we could give more details on how each
> diagnostics relates to the momentum equations, with or without z*.
> 
> Cheers,
> Jean-Michel
> 
> On Wed, Oct 30, 2024 at 11:36:49PM +0000, Xiaozhou Ruan wrote:
>> Dear MITgcm users,
>> 
>> I have been working on closing the momentum budget in LLC4320. Since I couldn???t locate the pressure output, I opted to calculate the hydrostatic pressure myself. I first used the densjmd95 routine to compute the in-situ density, then vertically integrated the density (multiplied by g) from the sea surface downward. However, the momentum budget doesn???t quite close. The pressure gradient field is very noisy, with many depth-invariant vertical stripes. Has anyone had experience closing the momentum budget with self-calculated hydrostatic pressure, or might be able to suggest any steps I may have missed in the pressure calculation? Thank you very much!
>> 
>> Best,
>> Xiaozhou
>> 
>> --
>> Xiaozhou Ruan
>> ???shaw-joe roo-ahn???
>> Assistant Professor
>> Department of Earth & Environment
>> Boston University
>> web:   https://xiaozhour.github.io/