[MITgcm-devel] exf wind-stress masking

[Jean-Michel Campin]

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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> 
> 
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