[MITgcm-devel] seaice

Alistair Adcroft adcroft at mit.edu
Tue Feb 14 10:49:53 EST 2006 

Yes - use the gad_advection routine which calculates the tendancy due to 
advection alone (no other parameterizations) and does the 
multi-dimensional stuff. I just had a look at it and it looks 
complicated because of the cube stuff but it should be callable almost 
as a black-box.

A.

Martin Losch wrote:

> Alistair, Chris,
> thanks for the quick feedback.
>
> I adopted the code from gad_calc_rhs.F and NOT from gad_advection.F.
> But this is exactly my problem: I never know what is really used.
> So, Alistair, are you saying I should use gad_advection instead of  
> gad_calc_rhs as a template?
> Isn't forward time stepping h(n+1) = h(n) + gh(n)*deltaT ?
>
> Martin
> On Feb 14, 2006, at 4:26 PM, Alistair Adcroft wrote:
>
>> 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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>>>>>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
>>>>>
>>>>>
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