[MITgcm-support] phihydlow formula

[Benny Cheng]

That's good news. Based on what you said, it's just as good as using 
hFacC. Danke!

- Benny

On Tue, 2004-08-17 at 23:46, Martin Losch wrote:
> Benny,
> 
> in an older version of the code (somewhere around checkpoint46m), I 
> coded the computation of phiHydLow using the hFacC's, but (I think) 
> Jean-Michel moved this part out of calc_phi_hyd to diag_phi_rlow. The 
> "problem" (maybe JMC can confirm) is that phiHyd is integrated  in two 
> steps from the kth cell face (phiHydF, only an intermediate value) to 
> the kth cell center  (phiHydC) (where it's value is needed for 
> dynamics) and in second step to the k+1th cell  face, for the next 
> cycle in the k-loop, this way only values from the k-th level are used 
> and no reference to k+1,k-1 is necessary. diag_phi_rlow uses the 
> dynamically relevant value phiHydC at the cell center and integrates 
> further to the bottom, which is deltaZ=ddRloc=rC-R_low "meters" away. 
> If the bottom is ABOVE the cell center (hFacC<0.5), then ddRloc<0 and 
> we are integrating backwards a little. With hFacC's you'd need to 
> integrate from phiHydF at level k which at this point no longer exists. 
> I guess that's the whole secret (true, Jean-Michel?).
> 
> so the answer is: the same informations that's used to compute the 
> hFacC's (rC-R_low, see ini_masks_etc.F) is used here, therefore the 
> masks are properly applied.
> 
> Martin
> 
> On Aug 17, 2004, at 6:37 PM, Benny Cheng wrote:
> 
> > Thanks Martin. I'm more interested in whether some land masking is
> > applied to the integral or not, since Ichiro thinks it's a "bug" 
> > without
> > it. Dimitri already replied that it was masked. The way it's done in 
> > the
> > code is rather complicated (min ,max , ddrloc ,rec_drm, drlocm), and if
> > it is equivalent to hfacc, why not just use it? perhaps not...
> > - Benny
> >
> > On Tue, 2004-08-17 at 00:01, Martin Losch wrote:
> >> Benny,
> >> the formulae are all in the documentation, so equation 1.32 on that
> >> page is it. As I wrote in my previous email to the other thread, for
> >> height coordinates, b in 1.32 is the scaled density g\rho/\rho_{0}. In
> >> the code it's actually the scale density anomaly, as Dimitris pointed
> >> out: g(\rho-\rho_{0})/\rho_{0}, so the phiHyd and phiHydLow is the
> >> corresponding pressure anomaly scaled by \rho_{0}. If you compute the
> >> full bottom pressure (including the g\rho_{0}H contribution), then you
> >> won't see much except topography. Because topography (=depth) 
> >> dominates
> >> the bottom pressure, it really only makes sense to look at 
> >> fluctuations
> >> of bottom pressure. and for those the choice of \rho_{0} (=rhoConst in
> >> data) is irrelevant.
> >>
> >> There is a paper by John Marshall which also should have all the
> >> formulae:
> >> Marshall, J. A. Adcroft, J-M Campin and  C. Hill (2004)
> >>   Atmosphere-ocean modeling exploiting fluid isomorphisms. submitted 
> >> to
> >> Monthly Weather Review. You can download a preprint from
> >> http://paoc.mit.edu/paoc/marshall/latest_papers.htm
> >> Also in Losch etal 2004 JPO 34(1), pp 306-319, we describe the
> >> ismorphism and all equations in detail in the appendix (in particulare
> >> Eq A23 and the following text). Appendix C describes the 
> >> discretization
> >> issue I was alluding to earlier. If you don't have access to JPO, you
> >> can download a preprint from
> >> http://mitgcm.org/~mlosch/nonbouss_pp.pdf
> >>
> >> Good luck,
> >> Martin
> >>
> >> On Aug 16, 2004, at 11:54 PM, Benny Cheng wrote:
> >>
> >>> Could someone show me or email me the exact phihydlow computation ( 
> >>> in
> >>> mathematical notation , not code) used in the MITgcm. It looks rather
> >>> murky to tread through the code... is it close to what is described 
> >>> in
> >>> http://mitgcm.org/sealion/online_documents/node20.html ? thanks.
> >>>
> >>> - Benny
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> MITgcm-support mailing list
> >>> MITgcm-support at mitgcm.org
> >>> http://dev.mitgcm.org/mailman/listinfo/mitgcm-support
> >>>
> >> Martin Losch // mailto:mlosch at awi-bremerhaven.de
> >> Alfred-Wegener-Institut für Polar- und Meeresforschung
> >> Postfach 120161, 27515 Bremerhaven, Germany
> >> Tel./Fax: ++49(471)4831-1872/1797
> >> http://www.awi-bremerhaven.de/People/show?mlosch
> >>
> >>
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> >
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> 
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