[MITgcm-devel] seaice

Martin Losch mlosch at awi-bremerhaven.de
Tue Feb 14 10:10:52 EST 2006 

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

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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
>>> _______________________________________________
>>> MITgcm-devel mailing list
>>> MITgcm-devel at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
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