[MITgcm-support] How to calculate the phiHyd (hydrostatic pressure potential anomaly) with model output ?

[Martin Losch]

Hi,

there are couple of constant “rho”s in the code, e.g. rhoConst, rhoNil, rhoConstFresh, which all have a default, which can be changed. I usually check, which value the model actually uses (because I always forget, how the defaults are determined), in the stanard output (or in an MPI run in STDOUT.0000).

For the EOS calculation, checkout how “find_rho_2d” (in find_rho.F) does it: it uses “rhoNil” to scale the density (this should be “\rho_c”, while rhoConst = “\rho_0”). I am not sure if the 1D field rhoRef is used in this context.

Hope this helps,

Martin

> On 7. Oct 2022, at 08:39, Mike Fan <ifanliming at outlook.com> wrote:
> 
> Hello all,
>  
> I want to use the model output (temp & salt & eta) to calculate the phiHyd, Through reading the guidebook, I learned that phiHyd is called hydrostatic pressure potential anomaly, using the equation like 4.2. Baroclinic Ocean Gyre ― MITgcm checkpoint68k-6-g80404458a documentation <https://mitgcm.readthedocs.io/en/latest/examples/baroclinic_gyre/baroclinic_gyre.html#output-files>.
>  
> In my model, setting a linaer EOS, implicitFreeSurface=’true’, and rhoConst=999.8. Here is my question, there is a rho_0, how the model calculates it? 
>  
> What I have done. I set rho_0=rhoref (got from RhoRef.data & RhoRef.meta), but the result is not the same as the phiHyd (got from phiHyd.00000******.t0**.nc).
>  
>  
> Leming
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