[MITgcm-support] difference between PH and PHL

[Jean-Michel Campin]

Hi Jody,

I will try to clarify:
1) for atmospheric setup (buoyancyRelation='ATMOSPHERIC', fluidIsAir=T),
 you are right, phiRef contains the geopotential height computed from
 tRef (sRef dependence is ignored, assuming dry air).
2) with oceanic set up in z type coordinate (z or z*, but not pressure)
 the reference state is homogenous rhoConst, and phiRef is
 just -gravity*rC or rF, so that Nicolas was right in this case.
  P(i,j,k)/rhoConst = -g*rC(k) + PH(i,j,k) + PNH(i,j,k)
 or:
  P(i,j,k)/rhoConst = PHrefC(k) + PH(i,j,k) + PNH(i,j,k)
3) with oceanic set up in pressure coordinate, it would be more logical
 to use tRef,sRef (similar to atmosphere in pressure coords) 
 but instead we continue to use rhoConst to define the reference state.
see in model/src/set_ref_state.F, lines 255-272.

And the way the hydrostatic pressure anomaly is computed is consistent with
the definition of PhiRef (i.e., uses tRef only if atmosphere in p,
otherwise based on rhoConst).

I hope I did not make too much confusion.

Cheers,
Jean-Michel

On Mon, Aug 05, 2013 at 01:42:42PM -0700, Jody Klymak wrote:
> Hi All,
> 
> On Aug 5, 2013, at  13:24 PM, Nicolas Grisouard <nicolas.grisouard at stanford.edu> wrote:
> 
> > I'm going to quote Jean-Michel, who answered this question when I asked it a couple of years ago (Jan. 7 2012 to be specific):
> > 
> > "From those output files, the pressure P can be obtained as:
> > P(i,j,k)/rhoConst = -g*rC(k) + PH(i,j,k) + PNH(i,j,k) 
> 
> Except this isn't quite correct.  
> > P(i,j,k)/rhoConst = -g*rC(k) + PH(i,j,k) + PNH(i,j,k) + PHref(k)
> where PHref(k) is the hydrostatic pressure due to Tref and Sref.
> see calc_phi_hyd.F and find_rho.F.  Unless I am grossly misunderstanding the code.
> Thanks,   Jody
> 
> 
> 
> > 
> > And PHL would be the equivalent of PH (hydrostatic pressure potential anomaly)
> > but at the bottom, so that the hydrostatic pressure at the bottom Pb
> > would be: Pb(i,j)/rhoConst = g*Depth(i,j) + PHL(i,j)
> > 
> > Cheers,
> > Jean-Michel"
> > 
> > It's pretty useful, because you don't have to interpolate the hydrostatic pressure on the topography.
> > Cheers,
> > Nico.
> > 
> > On 05/08/13 06:12, Robert Nazarian wrote:
> >> Hi,
> >> 
> >> I'm using the MITgcm internal wave code and analyzing the pressure perturbations. I noticed in the output directory that         there are PH and PHL files, which are both hydrostatic pressure files. Can someone elaborate on the difference between the two?
> >> 
> >> Thanks so much,
> >> Rob
> >> 
> >> Robert Nazarian
> >> Department of Atmospheric and Oceanic Sciences
> >> Princeton University
> >> rn2 at princeton.edu
> >> 
> >> 
> >> _______________________________________________
> >> MITgcm-support mailing list
> >> MITgcm-support at mitgcm.org
> >> http://mitgcm.org/mailman/listinfo/mitgcm-support
> > 
> > 
> > -- 
> > Nicolas Grisouard - Postdoctoral Scholar
> > Stanford School of Earth Sciences
> > 473 via Ortega - room M11
> > Stanford, CA 94305-4216
> > Dept. fax: (+1) 650-498-5099 
> > Office Skype ID: nicolas.grisouard
> > http://nicolas.grisouard.free.fr
> > http://www.mendeley.com/profiles/nicolas-grisouard/
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> 
> --
> Jody Klymak    
> http://web.uvic.ca/~jklymak/
> 
> 
> 
> 

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