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

Mon Dec 4 04:53:40 EST 2006

More on seaice/thsice.

I have put a few results of my 2deg experiment (to 80N), forced with  
CORE (modified NCAR/NCEP reanalysis) climatology:

http://mitgcm.org/~mlosch/run40
http://mitgcm.org/~mlosch/run41
http://mitgcm.org/~mlosch/run42
http://mitgcm.org/~mlosch/run43
http://mitgcm.org/~mlosch/run44
http://mitgcm.org/~mlosch/run45
http://mitgcm.org/~mlosch/run46

runs 40,41,42,45 are with seaice and growth-thermodynamics, runs  
43,44,46 with seaice+thsice. All netcdf files are 10day averages in  
the 101st year of integration, except for run43, which crashes at  
some time in the 6th decade, so that the netcdf files contains the  
51st year. I use asynchronous timestepping  
(deltaTtracer=12h,deltaTmom=20min) for all runs. there are also  
figures with appropriate files name (run40.png, etc) showing  
effective snow and ice thickness and ice concentration in march and  
august for the antarctic ocean. Details:
run40, not advection of snow, flooding (also included grid.* files).  
Here you see the strange snow patterns, where snow is as high as 160m  
(not included in colorscale), and depresses the sea surface by as  
much as 160m*0.33.
run41, advection of snow (scheme 2 for all variables): advection  
distributes the snow and thing look more physical
run42, advection of snow (scheme 2 for all variables), flooding=true:  
a lot less snow but much more ice, too much if you ask me.
run45, advection of snow and flooding, but advection scheme 1 for all  
variables: the different advection schemes makes the solution  
smoother, but not better, as expected.
run43, with thsice as is in the repository (crashed during the 6th  
decade, don't know why), this version of the code should probable  
vanish pretty soon? tiny concentrations/thicknesses at the ice margins
run44, with thsice and JMC's "new version" in seaice_advdiff.F: too  
be compared with run45. thsice leads to even more ice than the  
simpler thermodynamics of run45. Thickness is way too high (compare  
with www.seaice.de), and in summer the Eastern Weddell Sea should be  
almost ice free (only some ice along the Peninsula).
run46, like run44, but flooding turn off (commented out in  
thsice_calc_thickn.F): the flooding algorithm has less of an impact  
on the solution than for growth.

For a comparision with observations of concentrations see  
www.seaice.de, eg. March15, 2006 (from AMSR-E):
http://iup.physik.uni-bremen.de:8084/amsredata/asi_daygrid_swath/l1a/ 
s6250/2006/mar/asi-s6250-20060314-v5_nic.png
Aug15,2006
http://iup.physik.uni-bremen.de:8084/amsredata/asi_daygrid_swath/l1a/ 
s6250/2006/aug/asi-s6250-20060815-v5_nic.png

same dates in 1999 from SSMI
http://iup.physik.uni-bremen.de:8084/archive/south/1999/19990315.png
http://iup.physik.uni-bremen.de:8084/archive/south/1999/19990815.png

So, as far as I can see, the model produces first order distriubtions  
in all cases with too much extend in summer, too much ice in general  
and too much snow. Not too bad, but how much of this do we expect.  
I'll go and consult with my trusty ice specialists. But maybe someone  
on this list can comment too (Jinlun?)

Martin

On 30 Nov 2006, at 17:37, Martin Losch wrote:

> 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
>
> <snow4041.png>
>
> 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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>> MITgcm-devel at mitgcm.org
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>
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