[MITgcm-support] Hydrostatic pressure in LLC runs

[Jean-Michel Campin]

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/
> 

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