[MITgcm-support] PH and PHRefC

[Jody Klymak]

Hi all,

OK, about once a year I get re-confused about the meaning of the data contained in `PH`, `PHL`, and `PHRefC`.  I use a linear equation of state in z-coordinates with an oceanic buoyancy relation, so it should be pretty simple.

One would think that to get the total pressure one would just add P = PH + PHRefC, but that is indeed not the case if tRef and/or sRef vary with depth (k).  PHRefC is simply g*Z (where Z is the z at the center of the cells).  PH is the dynamic pressure: (1/rho_0) \int (rho-rho_{Ref}(z)) g dz.  Nowhere, that I can tell, is the cumulative integral of rho_{Ref} stored (nor indeed tRef or sRef).  

My sleuthing, mainly so I don’t do this again (ha), but perhaps is useful to others, is at 

https://gist.github.com/jklymak/156c30b5344a9cf63e8aebc429fee1c6

I do wonder why PHRefC doesn’t include the full reference pressure using tRef and sRef to calculate rhoRef: i.e. (1/rho_0) \int g rho_{Ref}(z) dz. I don’t need g*zc saved for any reason.  But maybe other co-ordinate systems or EOSs make sense of this variable?

Thanks,   Jody