[MITgcm-devel] description of seaice parameters

[Martin Losch]

Hi Jinlun,

while we were comparing codes, I found that the parameter HO 
(demarcation thickness between thin and thick ice, here at AWI they 
call it "lead closing parameter") is half the size of what people use 
here, and then it is doubled:
>       HO         = 0.5       _d 0
> C DOUBLE HO BECAUSE OF MOD IN GROWTH
>       HO=2.0*HO
in growth.F (the only place it is used), the factor two is taken out 
again:
>           GAREA(I,J)=TWO*(ONE-AREA(I,J,2,bi,bj))*GAREA(I,J)/HO + ...
Why is that so?

Martin

PS. I forwarded your question about AWI ice dynamics and expect an 
answer by this afternoon.


On Sep 13, 2005, at 12:51 AM, Jinlun Zhang wrote:

> Hi Martin,
>
> Good observations. When I wrote the seaice model for MITgcm, I tried 
> to keep Hibler original as much as possible. For example, -1.96 degC 
> and SEAICE_strength=2.75e4 are  Hibler original. The thermodynamics is 
> also from Hibler original. However, ice dynamics is from Zhang and 
> Hibler (1997), although all the names of the variables are 
> deliberately kept the same. The Zhang and Hibler dynamics method is 
> fast, and has been adapted for parallel computing, as in MITgcm. This 
> dynamics code has been sent out to some European researchers, but who 
> knows how many groups, if any, are using it. Would be interested to 
> know what ice dynamics AWI is using.
>
> Jinlun
>
> Martin Losch wrote:
>
>> Hi Dimitry,
>>
>> I have talked to one of our sea-ice specialists about the default 
>> parameter values in seaice_readparms.F. There are a few small 
>> differences in what he uses. The biggest difference is in 
>> SEAICE_freeze, which is -1.96degC in seaice_readparms.F, but 
>> -1.86degC in his code. Maybe still another reason for the thin ice 
>> around Antarctica and the large erroneous polynyas in the high-res 
>> cubed sphere experiments. Also he uses a smaller value of 
>> pstart=1.5e4 (instead of SEAICE_strength=2.75e4 in 
>> seaice_readparms.F). Only FYI.
>>
>> However, we found that the parameters 
>> SEAICE_sensHeat/latentWater/latentIce are not really the coefficients 
>> as described in SEAICE_READPARMS.h but
>> (density of air)*(heat capacity of air/latent heat of water/latent 
>> heat of ice)*(transfer coefficient)
>>
>> At least, that's what we found by comparing the code and default 
>> values. If you want me to do it I'll change the description in 
>> SEAICE_READPARAMS.h to reflect this, so that future seaice-novices do 
>> not stumble over this?
>>
>> Martin
>>
>> PS. It is funny that the seaice code and the code that is used at AWI 
>> are very similar (variable names etc.). It is obvious that both codes 
>> are derivatives from the same (original Hibler?) code.
>>
>> _______________________________________________
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>
>
> -- 
>
> Jinlun Zhang
> Polar Science Center, Applied Physics Laboratory
> University of Washington, 1013 NE 40th St, Seattle, WA 98105-6698
>
> Phone: (206)-543-5569    Fax:    (206)-616-3142
>
> zhang at apl.washington.edu
> http://psc.apl.washington.edu/IDAO
>
>
>
>
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