[MITgcm-devel] Add mass VOLUME 2

[Jean-Michel Campin]

Hi Martin etal,

Moving to devel list. 

I think there was some cases (high res process study set-up, dx ~ dy ~ dz) where
pkg/icefront was used at the calving front but without any ice-shelf cavity.
But not sure if this is enough to justify 2 different pkgs; i can see
that icefront could take care of specific lateral melting processes, such as surface 
wave erosion.

The other thing that is not clear to me is that, the "lateral melting" we could 
estimate from pkg/icefront away from the calving front (i.e., within the ice cavity 
at a stair-case step) is dependent on model vertical coordinate (absent if using 
sigma-coords). Also with coarser horiz res (dx,dy >> dz), it is supposed to
be small compared to bottom melting (just because with dz << dx, dx ~ sqrt(dx^2+ dz^2)
= tilted bottom length). Or is it the aspect ratio of the ice-shelf away from
the calving front that matters ?

Cheers,
Jean-Michel

On Thu, Apr 27, 2017 at 03:50:41PM +0200, Martin Losch wrote:
> Hi Ian,
> 
> I agree with Jean-Michel, but wouldn???t that be chance to merge the two packages, sind they do essentially the same thing, once at the bottom of an ice shelf once along the edge(s)?
> 
> Martin
> 
> > On 26 Apr 2017, at 21:57, Jean-Michel Campin <jmc at mit.edu> wrote:
> > 
> > Hi Ian,
> > 
> > It looks like pkg/icefront does not have the "useRealFreshWaterFlux" implemented.
> > And since the melt is not (always) release at the surface, it would need to be
> > added to "addMass", with the corresponding CPP and run-time switch (selectAddFluid).
> > 
> > Cheers,
> > Jean-Michel
> > 
> > On Tue, Apr 25, 2017 at 11:18:42PM +0000, Fenty, Ian G (329C) wrote:
> >> Hi JM,
> >> 
> >> This email is almost identical in spirit to the one I wrote in March regarding a concern about the addition of freshwater volume following melting in an ice shelf cavity.  At the time you allayed concerns by telling us that melt in the cavity contributes to changes in sea-level the same way as surface real fresh-water fluxes (through EmPmR). To wit,
> >> 
> >> From shelfice_forcing_surf.F:
> >> 103		EmPmR(i,j,bi,bj) = EmPmR(i,j,bi,bj)
> >> 104 	     &         + shelfIceFreshWaterFlux(i,j,bi,bj)
> >> 
> >> Which is great.  We confirmed that global mean sea level increased when we turned on the shelfice package, as expected.
> >> 
> >> Now we are considering the ice front package and questions are again being raised about how the model adds mass following melt somewhere at depth along glacier face.  Presently, T and S tendencies calculated in ice front thermodynamics and are applied directly onto gS_arr and gT_arr in icefront_tendency_apply.F. To wit,
> >> 
> >> From icefront_tendency_apply.F:
> >> 104 	          gS_arr(i,j) = gS_arr(i,j)
> >> 105 	     &         + ICEFRONT_TendS(i,j,k,bi,bj)
> >> 
> >> Am I wrong in thinking that this approach will indeed change T and S but will not add mass associated with the meltwater volume?  
> >> 
> >> What is the proper way of treating the addition of meltwater at depth if the meltwater contribution is to increase ocean mass?  I know that one approach would be to dump the new meltwater volume into the surface level (through EmPmR) but that solution seems unsatisfactory because it would be inconsistent with implied heat fluxes.
> >> 
> >> Please help clarify this issue!
> >> 
> >> Thanks in advance,
> >> Ian
> >> 
> >> 
> >> On 3/1/17, 4:36 PM, "Jean-Michel Campin" <jmc at mit.edu> wrote:
> >> 
> >>    Hi Ian,
> >> 
> >>    I am going to cc to few others, since few things have been added for dynamical
> >>    coupling (project with Patrick & Dan Goldberg and others) that could be relevant to this.
> >> 
> >>    With pkg/shelfice: melt contribute to changes in sea-level the same way as surface
> >>    fresh-water flux, i.e., with useRealFreshWaterFlux=.TRUE.,
> >>    it's added to EmPmR in S/R SHELFICE_FORCING_SURF.
> >> 
> >>    However, it you are using: SHELFICEboundaryLayer=T (like in all 3 verification/isomip
> >>    experiments), it's not very consistent with where the temp & salt forcing are applied.
> >>    I have some pieces of code (not checked-in) that were intended to replace
> >>    this SHELFICEboundaryLayer=T treatment (for Dan's project) but I don't know if
> >>    he is using these pieces of code.
> >> 
> >>    There are also few run-time params in pkg/shelfice that might be relevant to this
> >>    fresh-water treatment:
> >>     SHELFICEadvDiffHeatFlux (tested in isomip.htd)
> >>     SHELFICEconserve
> >>    But I don't remember precisely what they do (Martin should know) and not very
> >>    clear about this "rFac" setting in shelfice_thermodynamics.F
> >> 
> >>    And before I forgot, what I said Tuesday on the phone regarding the ice-shelf 
> >>    geometry setting was not true, but there is indeed 2 ways to set-it up:
> >>     1) SHELFICEtopoFile= and SHELFICEmassFile=  (like in isomip/input.htd )
> >>    or
> >>     2) SHELFICEtopoFile= and SHELFICEloadAnomalyFile= (like in isomip/input)
> >> 
> >>    Cheers,
> >>    Jean-Michel
> >> 
> >> 
> >> 
>