[MITgcm-devel] heff_max...more sea ice issues
Matthew Mazloff
mmazloff at MIT.EDU
Sun Dec 17 14:33:26 EST 2006
Hello,
My upper layer is 10m thick. When heff_max > 5m the model crashes.
(This only happens with dynamics on (LSR_ERROR = 1e-3 in my
calculations so not very accurate). With dynamics off the ice never
reaches this thickness.) I am modeling the Southern Ocean, I am sure
Arctic modelers must have this problem to an even greater degree.
What is other people's experiences with thick ice and stability?
Should an effective thickness capping be implemented?
Thanks
-Matt
fyi: I tried the free drift sea ice hack (i.e. setting uc ~ uvel in
seaice_advdiff.F) and the model crashed. The results were
odd....lots of numerical noise in AREA and, it appeared, no
significant advection.
On Dec 6, 2006, at 3:45 PM, Martin Losch wrote:
> Hi Jinlun,
>
> in the end, we want to be able to use a flux-limited 3rd order
> advection scheme, it's just not yet possible.
>
> Unfortunately my model stops at 80degN. I really need to set up a
> truly global ocean model. I do assume though, that there is
> something fishy with the precipitation in the CORE data set. Would
> be interesting to see if some-one else has a similar experience.
>
> In general, though, the ice extend is too large in winter (in
> particular in the Drake Passage, isn't it?). That 's the only thing
> that's still worrying me.
>
> XKI: I am only playing with this parameter to find out how the model
> (s) behave(s). In practice I will always use something around 2.
> XKI only appears in the denominator in budget.F, so I don't quite
> see what it does. I guess I have to dig up Hibler79/80 and have a
> look at the thermodynamics, right?
>
> M.
>
> On 6 Dec 2006, at 18:34, Jinlun Zhang wrote:
>
>>
>>
>> Martin Losch wrote:
>>
>>> Hi Jinlun,
>>> thanks for you input. I really enjoy this discussion!
>>>
>>> For clarification: I use the same advection for HEFF, HSNOW, and
>>> AREA. That is run47 has 1st order upwind for all three
>>> variables, while run41 has 2nd order central differences scheme
>>> (and not flooding algorithm). All runs use a little bit of
>>> diffusion (the default values of DIFF1=0.004), which is probably
>>> not good for run47.
>>
>> Hi Martin,
>>
>> Good the ice and snow advection is consistent. When you use 1st
>> order upwind, perhaps you do not have to use any diffusion (if you
>> have used any) since it is quite diffusive.
>>
>>>
>>>
>>> run48 uses only 10% of the snow precipitation, but uses flooding
>>> (it's just like 45). Are you saying that this should not reduce
>>> the ice amount? One source of the ice is flooded snow in the
>>> flooding algorithm in the current version of growth.F (http://
>>> dev.mitgcm.org/ cgi-bin/viewcvs.cgi/MITgcm/pkg/seaice/growth.F?
>>> rev=1.34&only_with_tag=MAIN&content-type=text/vnd.viewcvs-
>>> markup). One of my problems was, that the huge amounts of snow
>>> that you see in run40 (160m in some places, no flooding, no
>>> advection) are turned into ice by flooding and lead to ice
>>> thicknesses beyond my expectation. Either there is too much snow
>>> to begin with, or something is wrong in the handling of snow and
>>> not enough snow is melted.
>>
>> I was looking at wrong figure and had mistakenly thought that when
>> you reduced snow, ice was pretty much gone. But actually ice was
>> only slight reduced with run48, not really bad. Sorry for the
>> mistake.
>> I don't know what is wrong with run40, but I wonder if this huge
>> snow depth also occurs in the Arctic. If that is the case in
>> Arctic also, then definitely something is really wrong with the
>> model.
>>
>>>
>>> 1D tests: As far as I understand the physics of ice formation:
>>> Ice forms because the atmospheric heat flux cools the ocean
>>> surface below freezing. Ice continues to grow as long a the
>>> atmospheric surface flux continues to cool the ocean. In the
>>> presence of ice this atmospheric heat is "diffused" (conducted)
>>> through the ice according to the net conductivity. In the
>>> absense of snow this conductivity should be SEAICE_iceConduct
>>> (XKI in budget.F). If the ocean provides heat from below by
>>> upward transport of warmer waters (by vertical convection), then
>>> this heat flux can balance the atmospheric heat flux and stop
>>> the ice from growing. When you equate these fluxes roughly at
>>> equilibrium: Qocean = conductivity*(Tair-Tsurfocean)/hice you
>>> get the ice thickness that follows form this balance hice =
>>> conductivity*(Tair-Tsurfocean)/Qocean.
>>> Hypothetically I should be able to modify this "equilibrium
>>> thickness" by playing with the conductivity (or Qocean or the
>>> temperature difference). However I find that the model parameter
>>> XKI=SEAICE_iceConduct has no impact on hice (I use 1e-6 instead
>>> of 2!). That's puzzling, isn't? For the thsice package, the
>>> corresponding parameter does have an impact.
>>
>> Your reasoning sounds ok. But I am not sure why ice is so
>> insensitive to XKI in equilibrium. It does not make sense. Note
>> that XKI is a physical term that is likely determined by lad
>> experiments. Better not use a different number. Would be
>> interesting to see how sensitive ice thickness/extent is to XKI in
>> real simulations.
>> Jinlun
>>
>>>
>>> Martin
>>>
>>>
>>> On 5 Dec 2006, at 18:17, Jinlun Zhang wrote:
>>>
>>>>
>>>> Martin Losch wrote:
>>>>
>>>>> Jinlun,
>>>>> thanks for your opinion. The thsice thermodynamics are
>>>>> basically Winton's (2000) model, but we have not yet fully
>>>>> sorted out the advection part.
>>>>> I have now a run47 with SEAICEadvScheme = 1 (1st order upwind,
>>>>> too smooth) and no flooding, and and another one (run48) which
>>>>> is just like run45 but with only a 1/10th of the snow fall,
>>>>> just to see what happens, see
>>>>> http://mitgcm.org/~mlosch/run47.png
>>>>> http://mitgcm.org/~mlosch/run48.png
>>>>> As expected is run47 closest to what we expect. But run48 is
>>>>> not too bad either, too little snow (of course) and as a
>>>>> consequence too little ice. So either there is too much snow/
>>>>> precip in the atmospheric forcing, or there is something not
>>>>> kosher in the snow parameterizations. As the problems are
>>>>> similar with thsice I would agree that the forcing may be the
>>>>> problem ... I have to try and find different precipitation
>>>>> fields.
>>>>
>>>>
>>>> Marin,
>>>> Yeah run47.png looks pretty good. The advection works ok. But I
>>>> wonder what ice advction you are using, 2nd order or 1st order?
>>>> The one I installed is 2nd order. Ideally, the snow advection
>>>> should be exactly the same as the ice advection so ice and snow
>>>> won't devorce with each other.
>>>> It is not right with run48 that when the snow is turned off, ice
>>>> is gone. Some thing is wrong here.
>>>>
>>>>>
>>>>>
>>>>> I have also made another observation: I tried to run the
>>>>> different thermodynamics without any dynamics in a 1D case. I
>>>>> expect (and JMC agrees with me) that for constant air
>>>>> temperature (say -30degC), ice thickness should grow until
>>>>> there is some equilibrium thickness, when the remaining heat
>>>>> flux out of the ocean is balanced by the diffusive flux of
>>>>> heat through the ice. I assume that the diffusion is
>>>>> controlled by "SEAICE_iceConduct" for seaice and kice for
>>>>> thsice. The equilibrium thickness can roughly be estimated by
>>>>> hequil = conductivity*(Tair-Twater)/ heatflux.
>>>>> I have only succeded yet in reaching some equilibrium
>>>>> thickness with thsice (with an unrealistic value of kice=1e-6
>>>>> instead of 2). For growth, this only works if I turn on some
>>>>> precipitation (snow). Without snow HEFF is completely
>>>>> independent of SEAICE_iceConduct, which I don't think is right.
>>>>
>>>>
>>>> I don't understand this equil. ice thickness )-:. As said
>>>> above, without snow-without ice thing or ice not working right
>>>> without snow does not make sense to me.You might want to check
>>>> with Thorndike (199?) for a toy model of equil. ice thickness.
>>>> Jinlun
>>>>
>>>>>
>>>>> M.
>>>>>
>>>>> On 5 Dec 2006, at 03:39, Jinlun Zhang wrote:
>>>>>
>>>>>> Martin,
>>>>>>
>>>>>> I would vote run45.png for best performance except that the
>>>>>> summer ice is slightly overestimated. I would not vote
>>>>>> run41.png because of its weird snow distribution. The snow
>>>>>> pattern should generally follow the ice pattern (could mean
>>>>>> a problem with ice advection). I don't know why the snow
>>>>>> gets so thick with run40.png, the precip forcing could be
>>>>>> way off. But obviously snow advection helps a lot. Snow
>>>>>> flooding, if it overestimates ice, then turn it off, not big
>>>>>> deal (since what we do is to make the fields look like
>>>>>> observations). As for thsice, I don't know what is going on.
>>>>>> But for any ice thermodynamics that involves ice salinity
>>>>>> (if thsice uses ice salinity), there might be a singularity
>>>>>> in the formulation (I had such feeling before, but I could
>>>>>> be wrong).
>>>>>>
>>>>>> Jinlun
>>>>>
>>>
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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/pscweb2002/Staff/zhang/zhang.html
>>
>>
>>
>>
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