[MITgcm-devel] seaice revisited

[Martin Losch]

Hi there,
(mainly for Dimitris and Jean-Michel, but I don't know how much this  
will affect the ECCO runs)

after all my problems with the seaice package, I have recoded the lsr  
solver. I finally realized how much easier it is to discretize  
everything in finite volumes (after being involve with the MITgcm for  
how many years?). I attached the discretization FYI (and maybe for  
checking). I also found that I made a mistake with the metric terms in  
the EVP solver.

Unfortunately my new code breaks all verification experiments with  
seaice:  lab_sea and the like because, I changed (fixed) the treatment  
of the metric terms, fixed the EVP code, etc. global_ocean.cs32x15  
because I switched from some finite differences somehow copied and  
adapted from the B-grid code to finite volumes. Even without metric  
terms the code is different.

But now the best: I have finally added the full metric terms (also for  
curvilinear grids) because it is so easy to do with finite volumes  
(see the attached PDF). I hope I understood how metric terms are  
computed on a curvilinear grid. So Dimitris can rerun all his cubed  
sphere experiments with metric terms (not that it will matter too much  
in the end at high resolution), and I am anxious to see if it works.

How should I check in the fixes? The old seaice_lsr is not quite  
correct (bugs in the metric terms) and the evp code needs to be fixed,  
it is clearly wrong in the metric terms, too. We can have new routine  
seaice_lsr_fv.F or so, or we can replace the old seaice_lsr.F with a  
new finite volume version, thereby loosing all backward compatibility.  
Because the old seaice_lsr.F is not very nice and contains erros,  
which I would need to fix anyway (but only concerning the metric  
terms), old results will be lost for spherical grids anyway (but maybe  
not for cubed sphere). I will include a new flag that allows you to  
switch of the metric terms (mainly for testing).

If I make all these changes, I would also in a second step change a  
few defaults that are senseless (e.g. that now is not advected by  
default is really annoying, also the flooding algorithm, no_slip is  
not turned on, cliped ice velocities is turned on, etc. etc.)

What do you think?
Martin

PS. We shouldn't worry about the ceaice-manuscripts, because there we  
do not use metric terms, the conclusions will not be affected.

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