[MITgcm-devel] depressed Eta and sIceLoad

[Patrick Heimbach]

Need to look more closely, but you might be right
(Dimitris should confirm).
Essentially, we're evaporating too much where
it's ice-covered. 

Still, J.M. and I think that your main problem
is tons of snow.

-p.



On Mon, 2006-10-23 at 11:40, Martin Losch wrote:
> Thanks! Now I do not have any excuses any more to not learn the  
> diagnostics package (o: I am still using taveFreq for everything ...
> 
> Another thing about the seaice model:
> While looking for possible causes for this depression in eta, I found  
> the following part in growth.F, where the freshwater flux is computed:
>            EmPmR(I,J,bi,bj)= maskC(I,J,kSurface,bi,bj)*(
>       &         EVAP(I,J,bi,bj)-RUNOFF(I,J,bi,bj)
> CML     &         EVAP(I,J,bi,bj)*(ONE-AREA(I,J,2,bi,bj))
> CML     &         -RUNOFF(I,J,bi,bj)
>       &         +SEAICE_SALT(I,J,bi,bj)*0.92 _d 0/SEAICE_deltaTtherm
>       &         )
> I added the commented lines to test whether it makes a difference to  
> suppress evaporation underneath sea-ice, and it does seem to make a  
> big difference in my Weddell Sea (part of my global 2x2 model  
> config): The WDW of the Weddell Sea is eroded much more slowly (which  
> is good) by (erroneous) deep convection. I get the impression that  
> with the original code one extracts too much water (adds too much  
> salt) to the surface of the ocean underneath ice (evaporation + sea  
> ice formation), so that I get too saline surface waters and  
> consequently too much convection!
> 
> I think that's a bug!
> Martin
> 
> 
> On 23 Oct 2006, at 17:05, Patrick Heimbach wrote:
> 
> >
> > Hi Martin,
> >
> > I implemented some initial diagnostics
> > (i.e. using pkg/diagnostics)
> > for the seaice package over the weekend.
> > It does include HSNOW.
> >
> > So you could have a look at it.
> > As template for the use of diagnostics
> > check out labsea/input/
> > which has two seaice variables as part
> > of the diagnostics list
> > (you need to add 'SIhsnow ').
> >
> > You need code updates in pkg/seaice, pkg/diagnostics
> > and model/src.
> >
> > Hope it works.
> >
> > -p.
> >
> >
> >
> > On Mon, 2006-10-23 at 10:50, Jean-Michel Campin wrote:
> >> Hi Martin,
> >>
> >> My first guess would be the snow-thickness (unfortunately, there was
> >> not many diagnostic for this field in pkg/seaice, may be Patrick
> >> add one), since in the run I did, there was quiet a lot of snow.
> >> Cheers,
> >> Jean-Michel
> >>
> >>
> >> On Mon, Oct 23, 2006 at 10:26:09AM +0200, Martin Losch wrote:
> >>> Hi Jean-Michel,
> >>>
> >>> unfortunately I cannot say when, but at sometime the sIceLoad fields
> >>> started to cause problems in the height field Eta. With useSeaice
> >>> = .true., useRealFreshWaterFlux=.true., exactConserv=.true., and
> >>> LINEAR free surface (#undef NONLIN_FRSURF) I get local  
> >>> depressions of
> >>> ETA underneath seaice  along the coast of -40m and more in 100years.
> >>> They go away, when I set useRealFreshWaterFlux = .false. I need to
> >>> mention, that I have a global EmPmR imbalance of approximately 10cm
> >>> per year, so that my mean Eta is approximately -11m after 100years,
> >>> but that wasn't a problem earlier. I attach a figure which shows Eta
> >>> and surface velocities averaged over the years 91 to 100 of a 100
> >>> year integration. What I find strange is that the strong depression
> >>> in Eta does not have any corresponding signal in the surface
> >>> velocities. T/S do not have any striking anomalies in these regions
> >>> around Antartica, either, that could compensate Eta-gradients of  
> >>> more
> >>> 10m per 100km. The model does not explode, the mean effective ice
> >>> thickness is way below 2m in the areas of Eta-depression.
> >>>
> >>> Do you have any idea what's going on?
> >>>
> >>> Martin
> >>
> >>
> >>> _______________________________________________
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> >>
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> > -- 
> > Dr Patrick Heimbach | heimbach at mit.edu | http://www.mit.edu/~heimbach
> > MIT | EAPS, 54-1518 | 77 Massachusetts Ave | Cambridge, MA 02139, USA
> > FON: +1-617-253-5259 | FAX: +1-617-253-4464 | SKYPE: patrick.heimbach
> >
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-- 
Dr Patrick Heimbach | heimbach at mit.edu | http://www.mit.edu/~heimbach
MIT | EAPS, 54-1518 | 77 Massachusetts Ave | Cambridge, MA 02139, USA
FON: +1-617-253-5259 | FAX: +1-617-253-4464 | SKYPE: patrick.heimbach