[MITgcm-devel] some idea for pkg/shelfice

[Martin Losch]

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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