[MITgcm-devel] some idea for pkg/shelfice

[Jean-Michel Campin]

Hi Martin,

I have started to do (A), and have 2 issues:
1) it does change results, because of machine truncation
 (conversion shelficeLoadAnomaly --> shelficeMass --> shelficeLoadAnomaly)
  can always put a test " IF ( SHELFICEloadAnomalyFile .EQ. ' ' ) THEN"
  but I would prefer not to, and update the isomip results.
2) I am getting many "TAF recomputation warnings" (10 more than before)
 and not sure how to fix this.

Regarding the other things, need to look into the details of realFreshWater
code, to see if it has a good chance to works when kSurf <> 1.
And will check also the CD-code with NonLin-FreeSurf (should not be too
difficult since it happens at the 1rst iteration), but will be easier once
I am able to specify the ice-shelf mass.

Cheers,
Jean-Michel

On Thu, Apr 04, 2013 at 04:24:33PM +0200, Martin Losch wrote:
> Hi Jean-Michel,
> 
> some useful suggestions! 
> 
> I totally agree with A. Do you want to do that?
> 
> B: I found this
> > C     with "real fresh water flux" (affecting ETAN), 
> > C     there is more to modify
> >       rFac = 1. _d 0
> >       IF ( SHELFICEconserve .AND. useRealFreshWaterFlux ) rFac = 0. _d 0
> in the code, but rFac is never used. Not sure what happened here. I think we postponed the real freshwater flux business here. If you know how to do that, I am all for it.
> 
> C: I use the CD scheme, because I needed to get all the smoothing I needed (have a look at section 3 of Losch (2008)). I am sure the CD-scheme can be replaced by biharmonic viscosity. I never got the shelfice package to work with the non-linear free surface. even without r*, but I cannot remember if I tried it only with CD turned on. It's probably better to try without.
> 
> The noise that "called for" the CD scheme is due to the step-wise topography (and partial cells). I always planned to try r* to get a (numerically) "smooth" surface, by depressing the surface layer according the SHELFICEloadAnomaly (or better your SHELFICE_Mass). That might solve many numerical problems, e.g. noise, dynamic coupling, and introduce new ones (e.g., layers that get too thin, pressure gradient errors). I just never got around to trying that out.
> 
> Martin
> 
> On Apr 3, 2013, at 3:47 AM, Jean-Michel Campin <jmc at ocean.mit.edu> wrote:
> 
> > Hi Martin,
> > 
> > Some here have been using pkg/shelfice and, in order to make
> > more progress, there are few things that could be changed:
> > 
> > A) add a new variable for the mass of ice (per unit area):
> > I propose to do this, and to allow to specify (through a file)
> > the ice-shelf mass. 
> > To start with, fully backward compatible with no result changes,
> > will allow either to specify:
> >   a) R_shelfice & SHELFICEloadAnomaly (same as now)
> > or b) R_shelfice & SHELFICE_Mass
> > and with the relation between the 2:
> >  SHELFICE_Mass = SHELFICEloadAnomaly/gravity - Ro_surf*rhoConst
> > (since Ro_surf is negative).
> > At the end of shelfice_thermodynamics.F, will compute SHELFICEloadAnomaly,
> > and in case of (a), SHELFICEloadAnomaly from the file will be converted 
> > (in shelfice_init_varia.F) to SHELFICE_Mass using the same relation.
> > Advantages:
> > 1) mass of ice is (much) more natural than SHELFICEloadAnomaly;
> >  + it does not dependent on hFacMin truncation.
> > 2) should allow in the future to step forward SHELFICE_Mass.
> > 3) they are few places where SHELFICE_Mass can be used
> > (e.g., pressure @ the base of the ice-shelf = SHELFICE_Mass*gravity, 
> >  instead of R_shelfice as it is now, 
> >  also total thickness of the ice = SHELFICE_Mass/rho_ice ...)
> > but will let you decide what should be modified or not.
> > 
> > B) implement real-fresh-water flux with pkg/shelfice:
> > I think it would not be too hard to allow the surface forcing
> > to be applied at the surface level (kSurf) even if kSurf <> 1
> > This way, if we put the SHELFICE melting into PmE, we will get
> > the real-fresh-water formulation with little more modif.
> > 
> > C) current isomip experiment: found a problem when turning on
> > the non-lin free-surf (without z*), got some strange (and wrong)
> > currents because of the CD-scheme. Would need confirmation,
> > Likely due to a Pb in CD-scheme with non-lin free-surf and
> > large variations of hFac (+ kSurf <> 1 ?), will need to be confirmed.
> > Can you remember us why CD-scheme is used (since the resolution 
> > is high enough, ~10.km, to run without) ?
> > 
> > Cheers,
> > Jean-Michel
> > 
> > 
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> 
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