[MITgcm-devel] upcoming changes in seaice_growth.F

[Gael Forget]

Hi Dimitris,

we are not going to remove areaMin because it is needed in the LEGACY branch.

rev.87 is when I added the merged branch (which I refer to as EVOLUTION) including
the set of pathological cases that I thought required some treatment. The one you are referring 
to (area=max(area,areaMin) if ice is present) I included based on Martin's comment
C     The default of A22 = 0.15 is a common threshold for defining
C     the ice edge. This ice concentration usually does not occur
C     due to thermodynamics but due to advection.

After I completed this phase of the merging in October, I sent a detailed email to the devel list, entitled
	[MITgcm-devel] wrapping up seaice_growth.F  october 2010 revision
where I was referring to this pathological cases part specifically, and suggesting comparison runs. 
I don't recall getting much feedback. So, to be on the safe side, SEAICE_GROWTH_LEGACY has 
remained the default since then. I am still hoping to get more feedback...

Have you ever tried the EVOLUTION branch? Did you notice any big difference compared 
with LEGACY branch results? (I didn't at the time)

Cheers,
Gael

On May 27, 2011, at 4:30 AM, Menemenlis, Dimitris (3248) wrote:

> Gael and Ian, I am also a little worried about suggested removal of areaMin, mainly because I don't remember why areamin is there in the first place.
> 
> Digging back in CVS tree, areaMin (formerly under more informative name of A22) has been around since beginning of time, i.e., since first check-in of pkg/seaice on branch release1 some 8.5 years ago.  That is, it originates from the original Jinlun/Hibler code.
> 
> First a clarification, areamin (or A22) was never supposed to be used as an actual minimum on AREA.  Up to seaice_growth version 1.86 areamin was only used to regularize thickness for seaice_solve4temp computations.  Attached figure shows histogram of AREA for the cube92 integration carried out with checkpoint 62h (revision 1.64 of seaice_growth).  There is no 0.15 threshold.  Starting in seaice_growth version 1.87, areamin is used to modify AREA directly.
> 
> Gael can you explain the 1.86 to 1.87 modification.  Did you actually mean to establish a lower threshold of .15 for AREA or is this threshold somehow removed later in routine?
> 
> Second, Patrick noted that the areamin regularization causes trouble with adjoint back in revision 1.2 of seaice_growth:
> "cph
> (all
> these
> initialisations
> involving
> AREA
> are
> nasty
> "non-linear")"
> and I added a cryptic comment in revision 1.6 that says:
> "transfering all regularization of local ice thickness to seaice_growth
> as a first step towards possibly getting rid of A22 altogether".
> 
> 
> So it seems that removing the areamin regularization was something we meant to do for a long time but I forget why it never got done.
> 
> Ian do you know what is impact of removing the areamin regularization on seaice_solve4temp?
> 
> Thanks
> 
> Dimitris Menemenlis
> 
> On May 25, 2011, at 2:04 PM, Pierre Rampal wrote:
> 
>>> With regard to 1.1) Ian argued at the time that we don't need
>>> areaMin (old A22) to be a run time parameter. Opinions?
>> If I understand well, if areaMin is no longer a run time parameter, it will be impossible to change his value from data.seaice, is it right? If it is, I'm not sure that it is a good idea as it would be better to look first at the sensitivity of models results to a change in this value. To do that with convenience, it seems to me important to be able to change its value from data.seaice. Indeed, I would expect some important changes in air-sea fluxes in coarse resolution setup by changing this value. As you mention below, areaMin is currently set to 0.15, which is somehow very large. So, before having tested the effect of changing it from 0.15 to 10^-5  or any other value, I would keep it as a run time variable.
> 
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