[MITgcm-support] changes related to pkg/shelfice

[Jean-Michel Campin]

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