[MITgcm-support] difference between PH and PHL

[Jody Klymak]

On Aug 5, 2013, at  16:27 PM, Jean-Michel Campin <jmc at ocean.mit.edu> wrote:

> 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)

OK, well, I guess the confusion is in find_rho.F, in which different equations of state appear to use different conventions?

calc_phi_hyd.F uses "rhoInSitu" which so far as I can tell is calculated in do_oceanic_phys.F L520 or so by a call to find_rho_2d.  For that function, for a linear equation of state the code is:

       refTemp=tRef(kRef)
       refSalt=sRef(kRef)

       dRho = rhoNil-rhoConst

       DO j=jMin,jMax
        DO i=iMin,iMax
         rhoLoc(i,j)=rhoNil*(
     &     sBeta*(sFld(i,j)-refSalt)
     &   -tAlpha*(tFld(i,j)-refTemp) )
     &        + dRho
        ENDDO
       ENDDO

So perhaps an inconsistency has crept in between the meaning for Linear Equation of state (which use, a lot), and the non-linear ones?  I note that "POLY3" at least has a different coding and indeed appears to add in rho_ref.  

Thanks,   Jody




> 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
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>>> 
>>> 
>>> -- 
>>> 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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--
Jody Klymak    
http://web.uvic.ca/~jklymak/