[MITgcm-support] changes related to pkg/shelfice (Jean-Michel Campin)

[Martin Losch]

Hi Madeline,

the ice shelf floats on the ocean, and when the dynamics of the ocean requires ETA to change, it changes (for implicit free surface and realFreshWaterFlux=.true.). This requires the (virtual) ice shelf to move up and down with the ocean sea surface. This "feature" has not changed. It was there from the very beginning of the shelfice pkg. The recent change just shifts a (small) stationary contribution of the hydrostatic pressure by the ice shelf from ETA into phi0surf, so it's really a cosmetic change that will probably be useful for the non-linear free surface working with the shelfice-pkg.

I image that a truly "flexing ice shelf" requires, from a dynamical point of view, that there is some resistance due to the stiffness of the ice shelf. The ocean probably "feels" this resistance as an extra surface pressure that changes as a function of ETAN (amplitude of excursion) and distance from the grounding line according to the stiffness of the ice shelf. This flexing ice shelf was never implemented, as it is part of a fully coupled ice-shelf-ocean interaction. As Dimitris pointed out to me, this could maybe be accomplished adding this pressure to the atmospheric pressure, but you'd have to do that at very short intervals.

Does that make sense?

Martin

On Apr 29, 2012, at 8:02 PM, Madeline Miller wrote:

> Hi Martin,
> 
> So, now the ice shelf can locally flex or bend a small amount?
> 
> Madeline
> 
> Madeline,
> 
> the cells at the ice-ocean interface are filled with ice above the ice interface and ocean/water below.
> I don't understand the second question, but I think the answer is "no". (o:
> 
> Martin
> 
> On Apr 27, 2012, at 8:16 PM, Madeline Miller wrote:
> 
> > Hi Jean-Michel and Martin,
> >
> > Can you clarify what the other parts of the partial cell are filled with (air or ice)? Is this to account for the ice shelf losing contact with the water or to allow the ice shelf to have higher resolution bumps?
> >
> > Madeline
> >
> >
> > Today's Topics:
> >
> >   1. changes related to pkg/shelfice (Jean-Michel Campin)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Thu, 26 Apr 2012 12:05:21 -0400
> > From: Jean-Michel Campin <jmc at ocean.mit.edu>
> > To: mitgcm-support at mitgcm.org
> > Subject: [MITgcm-support] changes related to pkg/shelfice
> > Message-ID: <20120426160521.GA29910 at ocean.mit.edu>
> > Content-Type: text/plain; charset=us-ascii
> >
> > Hi pkg/shelfice users,
> >
> > The hydrostatic pressure calculation under ice-shelf has been changed today
> > ( model/src/set_parms.F, cvs version 1.14 :
> > > account for partial cells in surface level below ice-shelf for hydrostatic
> > > pressure calculation (set uniformFreeSurfLev to F if using shelfice pkg)
> > )
> > in order to account for partial-cell in the surface-level in contact
> > with the ice-shelf (just below the ice-shelf).
> >
> > pkg/shelfice allows to have partially filled grid-cell (a sea-water fraction
> > given by hFacC below an ice fraction (dry) above) below ice-shelf.
> > In the previous and original version, the hydrostatic pressure was calculated
> > assuming a 100% sea-water fraction in the surface grid cell below ice-shelf.
> > This is no longer the case and the partial-cell fraction is now taken
> > into account. This is more consistent with the remaining part of the model
> > which knows about partial cell filling.
> >
> > Making the transition to the new version:
> > You might need to update the input file SHELFICEloadAnomalyFile
> > (specified in data.shelfice) if the previous loading anomaly file was
> > accounting for only fully ice (dry) grid-cell, consistent with the
> > original pressure calculation.
> > See changes in MITgcm/verification/isomip/input/gendata.m, cvs version 1.2.
> > Note that the changes do not affect the way partial-cell are defined,
> > so that restarting with the new version but from a pickup file that was
> > produced with the original version should not be a problem.
> >
> > If for some reasons, after updating your code, you want to revert back
> > to the original version (to reproduce the old results), you will need
> > to edit the file "model/src/set_parms.F":
> >  66       uniformFreeSurfLev = usingZCoords
> >  67 C- Note: comment line below to revert to full-cell hydrostatic-pressure
> >  68 C        calculation in surface grid-cell below ice-shelf
> >  69       uniformFreeSurfLev = usingZCoords .AND. .NOT.useShelfIce
> >  70       IF ( selectNHfreeSurf.NE.0 .AND.
> > and comment out the line 69:
> >  69 c     uniformFreeSurfLev = usingZCoords .AND. .NOT.useShelfIce
> >
> > And if you have questions, you can contact the support list.
> >
> > Thanks,
> > Jean-Michel
> >
> >
> >
> >
> >
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-support
> 
> Martin Losch
> Martin.Losch at awi.de
> 
> 
> 
> 
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support

Martin Losch
Martin.Losch at awi.de