[MITgcm-devel] depressed Eta and sIceLoad

Tue Oct 24 02:50:30 EDT 2006

Hi Patrick, Jean-Michel,
I agree, the depression of eta is caused by 104m of snow. I have no  
idea why the snow accumulates. I am afraid, this requires more  
digging into that awful growth.F routine, which I still don't quite  
understand.

The EVAP-bug doesn't have anything to do with this, but it is more  
fundamental as it caused my whole circulation and stratification to  
look terrible in the Southern Ocean. Now, things look much better!

Martin

On 23 Oct 2006, at 18:40, Patrick Heimbach wrote:

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