[MITgcm-devel] exf wind-stress masking

[Jean-Michel Campin]

Hi Martin and others,

I think the masking is not "strictly necessary" so that
not masking fields in exf when using seaice is OK.
Was conscerned about wind-stress computation (which depends
on air temp & SST in exf), but it is masked in exf_mapfields.F
when put on C-grid. And in pkg/seaice wind-stress does not depend on 
air temperature.

However, I think it would be better to always masks the air-temp
(and may be also the air humidity & lwflux) to avoid computing
fluxes (sensible, latent, net-LW) using SST from a land point.

And regarding seaice_ocean_stress (in relation with useHB87stressCoupling),
might be cleaner to make the changes you propose to remove the exf-masking
dependency; or could leave it as it is (little odd, but more accurate ?).

Cheers,
Jean-Michel

On Tue, Jan 10, 2012 at 02:14:23PM -0500, Jean-Michel Campin wrote:
> 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
> > >>> 
> > >>> _______________________________________________
> > >>> MITgcm-devel mailing list
> > >>> MITgcm-devel at mitgcm.org
> > >>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
> > >> 
> > >> 
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