[MITgcm-devel] seaice

[Martin Losch]

Hi Dimitris,
I am probably playing too much with the seaice model right now, but  
here are a few points that I'd like to make (and maybe check them in,  
even if they break lab_sea):

1. I am now sure that there is a bug in advect.F that does NOT affect  
lat-lon-grid simulations, but WILL affect cubed-sphere simulations  
and all other irregular grid simulations. It's basically an idexing  
error (see my previous email). I think I will just fix that.

2. I would like to replace all DXTICE DYTICE SINEICE CSTICE etc with  
the proper combination of variables dxF,dxG, etc. from GRID.h. This  
will --- at least as far as I can see --- make sure that the grid  
information is correct and the same grid parameters that are used for  
the ocean are used for seacie.
Since I want to use the seaice model on a cubed sphere grid, I do  
care about this. However, this will change the lab_sea and very like  
(more dramatically) any cubed sphere set-up that you may have (I am  
currently currently playing with global_ocean.cs32x15 + seaice). Will  
I get your OK?

3. Advection schemes: for properties such as volume and fractional  
area, the advection scheme should not produce negative (or positve)  
overshoots. A 2nd order central difference scheme does that (eg., can  
produce negative thicknesses). The scheme in advect.F is 2nd order  
central difference, but I don't understand the time stepping scheme,  
so it may be OK. Nevertheless, I naively think, a positive scheme may  
be better, but it is no longer conservative, eg. 2n-order with flux  
limiter (e.g, Hunke's CSIM5 uses MPDATA) or DST3FL that I use  
routinely for geochemical tracers. The nice thing is, that all of  
these schemes are there (in generic_advdiff), one just needs to pick  
one. I have tried dst3fl, but again, I do not understand the time  
stepping in advect.F (nor do I understand fully how gad_calc_rhs  
works): I have tried dst3fl and I even got it to work, but only  
halfway. If I am not mistaken, the DST schemes look as if they are  
explicit in time, that is, h(n+1) = h(n) + gh(n)*deltaT. I can  
compute gh(n), but for that I need to know what the different time  
levels are, eg.,
HEFF(:,:,1,:,:) = current time level?
HEFF(:,:,2,:,:) = do I need these?
HEFF(:,:,3,:,:) = ?
Or do I just update HEFF(:,:,1,:,:) in advect.F?

Martin

On Feb 14, 2006, at 2:07 PM, Dimitris Menemenlis wrote:

> Martin and Jinlun, I am out of my depth when it comes to advection  
> schemes.  Is there a reason for changing the scheme that is there  
> already in pkg/seaice?
>
> For cubed-sphere grid right now, I assumed that grid is rectangular  
> near the Poles (CS*ICE=1, TNG*ICE=0).  This was a quick fix to get  
> going but it is not exact.  So maybe that explains why you get  
> different numerical values?
>
> Regarding coastal sflux from seaice.  One does expect coastal  
> regions around Antarctica to be ice/salt factories, but maybe too  
> much salt is being rejected.  Carl recently send me some slides and  
> Ph.D. thesis from Dirk Notz:
> http://ecco.jpl.nasa.gov/~dimitri/Notz/talk_MPI16112005.pdf
> http://ecco.jpl.nasa.gov/~dimitri/Notz/PhD_thesis_Dirk.pdf
> suggesting there is considerable uncertainty regarding how much  
> salt is rejected during sea ice creation.
>
> Dimitris
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