[MITgcm-devel] seaice

Tue Feb 14 10:26:44 EST 2006

Martin,

The code below doesn't look right - the divergence of fluxes should be 
split into separate loops and applied consecutively otherwise the scheme 
will not be monotonic. Also, be sure to use "forward" time-stepping with 
dst2/3. I'm not sure what code you based this on but I hope it wasn't 
from gad...

A.

Martin Losch wrote:

> GAD:
>
> I have tried using dst3fl (withoug any explicit diffusion). It runs  
> stably for 20 years now, but now my ice (instead of being too little)  
> is growing endlessly (37 m in the western Weddell Sea), so I have the  
> suspicion that I am make severe mistakes: Could someone who  
> understand gad_calc_rhs have a look at the attached routine and tell  
> me, if I have done things right? In particular in the update of HEFF,  
> is it correct to have advFac=1?:
>
>>         DO j=1-Oly,sNy+Oly-1
>>          DO i=1-Olx,sNx+Olx-1
>>           HEFF(i,j,1,bi,bj)=HEFF(i,j,3,bi,bj) + DELTT *
>>      &         maskC(i,j,kSurface,bi,bj)*recip_rA(i,j,bi,bj)
>>      &       *( (fZon(i+1,j)-fZon(i,j))
>>      &         +(fMer(i,j+1)-fMer(i,j))
>>      &         -localT(i,j)*( (uTrans(i+1,j)-uTrans(i,j))
>>      &                       +(vTrans(i,j+1)-vTrans(i,j))
>>      &                       )*advFac
>>      &         )
>
>
> Martin
>
>
>
> On Feb 14, 2006, at 3:57 PM, chris hill wrote:
>
>> 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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