[MITgcm-devel] exf wind-stress masking

[Jean-Michel Campin]

Hi Martin,

I would like to do more tests, since I realized there are some 
combinations that are not tested (but not so exotic that
they can be used), such as exf-interp + seaice.

I think we agree that we don't want ocean surface temperature on land
to have an effect on the solution. And this is what I would like to 
check first.

Cheers,
Jean-Michel

On Tue, Jan 10, 2012 at 10:56:01AM +0100, Martin Losch wrote:
> Hi Jean-Michel,
> 
> the reason appears to be the unmasked taux/tauy.
> 
> The are added to FORCEX/Y0 which in turn is added to FORCEX/Y, and these are then added to the rhs, but with masking (seaiceMaskU/V). In seaice_ocean_stress taux/tauy are used, but without masking (and as far as I can see that's also the case in seaice_freedrift).
> 
> I can fix that by masking taux/y with maskW/S or seaiceMaskU/V if you like and then the dependence on the exf-masking goes away.
> 
> Martin
> 
> 
> 
> On Jan 9, 2012, at 9:20 PM, Jean-Michel Campin wrote:
> 
> > Hi Martin,
> > 
> > I did some quick tests, comparing with/without masking of exf variables
> > (In the 1rst case, I've just commented out the block:      
> >      IF ( useSEAICE ) THEN
> > C     Do not filter with pkg/seaice because of B/C-grid interpolation
> >       ....
> > in pkg/exf/exf_init_fixed.F)
> > 
> > And I only get different results in 2 exp.:
> > a) lab_sea/input.fd   (SEAICEuseFREEDRIFT=.true.)
> > b) lab_sea/input.hb87 (EVP & useHB87stressCoupling)
> >   (but diff goes away with useHB87stressCoupling=F)
> > 
> > Regarding SEAICEuseFREEDRIFT, the differences comes from 
> > seaice_freedrift.F (I don't get any difference with my free-drift         
> > computation within seaice_lsr.F).
> > 
> > To conclude:
> > 1) it's worth to know that these 2 options (SEAICEuseFREEDRIFT
> >   and useHB87stressCoupling) are sensitive to masking within EXF.
> > 2) I think it might be better to always (whether we use SEAICE or
> >  not) mask heat-flux & fresh water flux related fields, 
> >  and to leave only wind & windstress not masked when using SEAICE.
> > 
> > Cheers,
> > Jean-Michel
> > 
> > On Wed, Jan 04, 2012 at 09:32:35AM +0100, Martin Losch wrote:
> >> Hi Jean-Michel,
> >> 
> >> I am not sure, but I think that for B-grid seaice, the wind (stress) needs to be available a Z-points and this interpolation is done in pkg/seaice/dynsolver.F, so that when masking in exf removes wind values over land, you underestimate the wind over boundary values of seaice.
> >> Having said that, the boundary points of B-grid seaice have (uice,vice)=0 as a boundary conditions, so that this masking does not make any difference, so on second thought you are probably right, and this differentiation can be removed safely.
> >> 
> >> M.
> >> 
> >> On Jan 3, 2012, at 5:49 PM, Jean-Michel Campin wrote:
> >> 
> >>> Hi, 
> >>> 
> >>> I am going to check-in some unfinished changes in exf:
> >>> I realized that the masking of the wind-stress is wrong (when not on 
> >>> C-grid, which happen when interpolated or read from A-grid file).
> >>> I fixed this problem and will check-in this (involves also EXF_PARAMS.h
> >>> & exf_init_fixed.F) and update output of global_with_exf exp.
> >>> 
> >>> I also started to add some params in EXF_PARAMS.h + exf_init_fixed.F
> >>> for 2-components vector interpolation (I did this before the stress
> >>> mask fix), will be part of the changes but they are not yet used.
> >>> 
> >>> Regarding masking, I don't see a clear reason why it's only
> >>> applied when not using SEAICE. If exf works fine without
> >>> masking (when using SEAICE), then why do we care about applying
> >>> masks ?
> >>> 
> >>> Also, noticed that exf_init_fixed.F does not compile with default 
> >>> pkg/icefront settings (might have been better to put all this
> >>> icefront - exf code in pkg/icefront and still call some utility 
> >>> exf & cal S/R).
> >>> 
> >>> Cheers,
> >>> Jean-Michel
> >>> 
> >>> _______________________________________________
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> >>> MITgcm-devel at mitgcm.org
> >>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
> >> 
> >> 
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