[MITgcm-devel] seaice

[chris hill]

Martin,

  These all sound good.
  Technically it should be possible to use gad to do the explicit part 
of ice advection. Jinlun may have comments on whether this makes sense 
algorithmically and on interactions with the implicit parts of the ice 
dynamics.

Chris
Martin Losch wrote:
> 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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> 
> 
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