[MITgcm-devel] Add sea ice surface forcing to pkg/seaice

[Jean-Michel Campin]

Hi Dimitris,

In reverse order:
let's separate the real modifications related to snowPrecip 
and the cleaning issue (adding DIAGNOSTICS_IS_ON or constant setting), 
since mixing both is going to be painful to trace back changes.

My question 2.b is not stupid, because snowPrecip (when specified
from a file) can fall over open ocean (whereas with empty snowPrecipFile,
it only snows when some ice is present).

And regarding 2.a: I think we know how snow accumulates:
If snow is falling at a rate of 1.cm per hour, I expect afer 1 hour
to have the actual snow thickness to have increased by 1.cm
(and not by 1000 time more in the case where the area is 10^-3).

Cheers,
Jean-Michel

On Mon, Apr 23, 2012 at 06:32:05PM +0000, Menemenlis, Dimitris (3248) wrote:
> Jean-Michel, thank you for looking at this.
> 
> I don't want to waste too much of your, Gael's, or Martin's time with this
> so I will check in a version of seaice_growth.F that does the same thing
> but does not change the verification results.  The code is slightly
> longer (and uglier?) than Revision 1.166, but I think OK until more
> folks start using snowPrecip as input for pkg/seaice.
> 
> Answers to your comments below:
> 
> 1) lab_sea.hb87 seems very sensitive to truncation errors.
> Even before latest changes to seaice_growth, it fails on my laptop.
> 
> I am interested in those two conditions:
> >  a) if the seaice-fraction is small (e.g., 10^-3), and a snow storm
> >  pass by, will all the snow pile up over this little ice fraction ?
> >  b) snow over fully open ocean grid-cell ?
> so I made sure that they give reasonable-loking results.
> Snow over fully open ocean grid does what we expect it to do, i.e.,
> cool the ocean surface through negative latent heat release and then,
> when SST reaches the freezing point, it starts growing "fresh" ice, provided
> SEAICE_VARIABLE_SALINITY and SEAICEuseFlooding are defined.
> The sea ice fraction (AREA) is initially small, but it very quickly grows
> to reasonable-looking values.  Since we don't know how the ice
> concentration should grow in open ocean during a snow storm,
> I think that default behavior is OK for now.  The most important
> feature is the negative latent heat release, which is modeled
> with sufficient accuracy irrespective of sea ice fraction.
> 
> I tried to do this:
> > c) less urgent: heat conservation and heat budget diagnostics ?
> > Would be good to clarify point 2.a before updating the results
> > (in case seaice_growth.F needs to be changed again).
> correctly, but a second pair of eyes on this would not hurt.
> With version 1.167 of seaice_growth.F, all the stuff pertaining
> to snowPrecip will be contained within
> "IF ( snowPrecipFile .NE. ' ' ) THEN, ..., ENDIF"
> so if there is issues with heat conservation,
> they will be restricted to the specific case of snowPrecip.
> 
> Finally, I notice that:
> 1) seaice_growth.F does a lot of diagnostic computations, whether they are needed or not.
> Shouldn't these computations be contained within
> IF ( DIAGNOSTICS_IS_ON('????????',myThid) ) THEN, ..., ENDIF
> statements?
> 2) seaice_growth.F contains lots of constants, e.g., "0.0 _d 0", etc., which could be
> replaced with parameters "ZERO", etc., from SEAICE_PARAMS.h
> Happy to take care of either of these two changes, if requested to do so.
> 
> Dimitris Menemenlis
> 
> On Apr 23, 2012, at 6:12 AM, Jean-Michel Campin wrote:
> 
> > Hi Dimitris and others,
> > 
> > few things:
> > 1) my impression (after a quick look at your changes) is that 
> > with empty snowprecipFile, it's only truncation error changes.
> > But still 2 fwd exp are failing (global_ocean.cs32x15.seaice & lab_sea.hb87
> > since the criteria on baudelaire with gfortran is 13 digits) 
> > which would require to update the output.
> > Regarding AD tests, seems OK, don't see any new "fail".
> > 
> > 2) I don't have time now to check the case where snowprecip is specified
> > (+ little time I have is spent checking which testreport output changes)
> > and I don't know much about seaice_growth.F ; Can someone (Gael, Dimitris, 
> > Martin, ...) check what does snowprecip do in the current seaice_growth.F ?
> > In particular:
> >  a) if the seaice-fraction is small (e.g., 10^-3), and a snow storm
> >  pass by, will all the snow pile up over this little ice fraction ?
> >  b) snow over fully open ocean grid-cell ?
> >  c) less urgent: heat conservation and heat budget diagnostics ?
> > Would be good to clarify point 2.a before updating the results
> > (in case seaice_growth.F needs to be changed again).
> > 
> > Cheers,
> > Jean-Michel
> 
> 
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