[MITgcm-devel] description of seaice parameters

[Jinlun Zhang]

Hi Martin,

HO is a tunable para, which is used for calculating change in ice 
concentration, as shown in 
GAREA(I,J)=TWO*(ONE-AREA(I,J,2,bi,bj))*GAREA(I,J)/HO . In Hibler 
original original (1979), HO was set to 0.5, but later HO=2.0*HO was 
added in the coupled ice-ocean code, perhaps something was changed in 
GROWTH. So when I became his student and got the 'original' code from 
him in 1989, I saw this HO=2.0*HO in place and I dare not to take it out 
ever since.

I forgot to mention that using -1.96 degC or -1.86 would not make much 
difference since this is just a reference temperature that does not 
really change fluxes ( I did some experiments years back).

Jinlun

Martin Losch wrote:

> 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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>>