[MITgcm-devel] another bug in growth.F ?

[Martin Losch]

Hi Dimitris and others,

I have no 100year of running my 2deg configuration with isotropic  
grid in the southern hemisphere for 41 different parameter  
combinations/code versions. Here is my superficial summary:
1. The crucial fix for the sea ice distribution (AREA+HEFF) is the  
evap*(1-area) fix. I think we can agree on that
2. If snow is not advected or turned into ice by submersion (flooding  
algorithm), it accumulates at rates of more than 1m/y consistent with  
the surface forcing (precipitation) provided by the CORE climatology.  
This happens only in areas with perennial ice cover and only in the  
southern hemisphere (my domain stops at 80N). The pattern of snow  
accumulation is a little strange, which is the straw that I cling to  
in thinking that there is still a bug in the handling of snow in  
growth (see attached figure for a typical pattern, run40).
3. If I use flooding but no advection of snow, the snow look OK, but  
there is far too much ice (thickness), especially in summer (area),  
run38 in a previous figure.
4. If I use advection of snow but no flooding, the snow is  
distributed and can melt (I guess), run41 in attached figure. There  
is still a litte too much snow after 100 year (3.6m in a few areas  
west of the Antarctic peninsula, but I could live with that). Be  
aware that the advection I use is the 2nd order (default) advection,  
and I am afraid, that the advection of snow is not properly done in  
this case, but that should be a minor issue. Ice looks reasonable in  
this case maybe a little thin in a few areas in summer, but appears  
to be problem of the 0-layer thermodynamics, I guess.
5. What will happen with flooding and advection of snow I don't know  
yet (not part of my 41 different combinations), but tomorrow (will  
this be run42?).

So my preliminary conclusions are:
1. The snow is still not handled properly in growth/seaice_advdiff
2. with advection of snow the problems are smallest (may be even  
smaller with additional flooding)

Martin

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On 30 Nov 2006, at 16:49, Dimitris Menemenlis wrote:

> Jinlun, the beer/crap comment was in jest.  Everyone who has used  
> pkg/seaice appreciates your effort in making this package available  
> to MITgcm and also your subsequent help with bug fixes and with  
> other modifications.
>
> Martin, I also find that
>
>> cdm       IF(FICE(I,J,bi,bj).GT.ZERO) THEN
>>           IF(atemp(i,j,bi,bj).LE.273.15 _d 0 ) THEN
>
> has very little impact on growth.F both for the forward solution as  
> well as for the high forward sensitivity of the model that you and  
> Patrick reported.  What does remove the high forward sensitivity is  
> commenting out the snow-melt addition.
>
>> C Now melt snow if there is residual heat left in surface  
>> level                 C Note that units of YNEG and SEAICE_SALT  
>> are m of ice                          cdm       IF(RESID_HEAT 
>> (I,J,bi,bj).GT.ZERO.AND.                                 cdm   
>> &         HSNOW(I,J,bi,bj).GT.ZERO)  
>> THEN                                   cdm        GHEFF(I,J)=MIN 
>> (HSNOW(I,J,bi,bj)/SDF/ICE_DENS,                        cdm   
>> &         RESID_HEAT 
>> (I,J,bi,bj))                                           cdm         
>> YNEG(I,J,bi,bj)=YNEG(I,J,bi,bj)+GHEFF 
>> (I,J)                           cdm        HSNOW(I,J,bi,bj)=HSNOW 
>> (I,J,bi,bj)-GHEFF(I,J)*SDF*ICE_DENS            cdm         
>> SEAICE_SALT(I,J,bi,bj)=SEAICE_SALT(I,J,bi,bj)-GHEFF 
>> (I,J)             cdm       ENDIF
>
> So back to where we were before latest exchange.
>
> Dimitris
>
> -- 
> Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
> Jet Propulsion Lab, California Institute of Technology
> MS 300-323, 4800 Oak Grove Dr, Pasadena CA 91109-8099
> tel: 818-354-1656;  fax: 818-393-6720
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