[MITgcm-devel] real-fresh-water-flux with pkg/shelfice

[Jean-Michel Campin]

Hi Martin and others,

Looking at how to make shelfice to work with useRealFreshWaterFlux=T :

1) I think there will be few things to change in solve_for_pressure.F
  (+ integr_continuity.F, integrate_for_w.F, cg3d.F & pre_/post_cg3d.F)
  for z* and/or for Non-Hydrostatic,
  but if we leave these 2 options on the side for now, should work
  as long as EmPmR has been updated to include ice-shelf melting.

2) Regarding where/when to modify EmPmR (to add melting):
a) one option would be fill-up EmPmR (and may be also Qnet)
  in shelfice_thermodynamics.F and rely on usual way surface forcing
  is apply to T,S time-stepping.
  The problem here is that external_forcing_surf.F is not ready yet 
  to deal with ks > 1.
b) a simpler alternative (involving less changes) would be to continue
  to rely on shelfice_forcing_surf.F (called from external_forcing_surf.F)
  to copy shelficeForcingT/S into surfaceForcingT,S
  and to add a piece of code there to update/modify EmPmR.
  This would make a difference if using balanceEmPmR (that would
  balance EmPmR over ocean surface - excluding shelfice melting -
  but this might even be better.

3) The other things involve changes in shelfice_thermodynamics.F:
  I would propose that:
  a) we keep unchanged the "SHELFICEBoundaryLayer" part together with
  the 2 S/R within shelfice_forcing.F but
  b) for the case SHELFICEBoundaryLayer=F, we could just compute the melting
  rate (shelfIceFreshWaterFlux ?) in shelfice_thermodynamics.F
  and push shelficeForcingT/S calculation to shelfice_forcing_surf.F
  I am not sure about the current setting of cFac/rFac according to
  SHELFICEconserve/useRealFreshWaterFlux, and there might be some simpler
  (and more consistent with main model options such as useRealFreshWaterFlux
  & nonlinFreeSurf with temp,salt_EvPrRn settings) ways to change this.

I might have missed something there (did not check too carefully);
and any comment is appreciated.

Cheers,
Jean-Michel