[MITgcm-devel] heff_max...more sea ice issues
Matthew Mazloff
mmazloff at MIT.EDU
Mon Dec 18 14:57:07 EST 2006
Hi Jinlun,
I am not 100% sure what is happening. The info I have comes from the
monitor output.
with: SEAICEuseDYNAMICS = .TRUE. the model crashes after 6
months. Heff_max is not a smooth function but jumps quite a bit with
time
with: SEAICEuseDYNAMICS = .FALSE. the model runs successfully
for one year. Heff_max is smooth in time and the values are at the
low side of the oscillations I see with the dynamics on: I've
attached a picture below
The advcfl_W_hf_max is similar in both models...perhaps it is the
seaice model that is crashing. Without ice dynamics, however, the
ocean velocity fields have larger maxima. But the cfl numbs
associated with these maxima are still OK.
So maybe it is the ice model that is unstable. I do not know what
stability criteria I should consider with the ice model. My setup:
1/6 degree resolution, 900 second timesteps, using C-grid ice model
configuration, LSR_ERROR = 1e-3.
I know this really isn't too much info....sorry about that. Any ideas?
Thanks for the help,
Matt
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On Dec 18, 2006, at 1:53 PM, Jinlun Zhang wrote:
> Hi Matt,
>
> When the model crashes, is it the ice that crashes, or the ocean
> crashes? Generally, thick ice won't cause crashes (or make the
> ocean more stable) because it moves slower and it does not create
> big buoyancy change. So change heff_max generally won't help much
> if the model would eventually blow up. And it is not a good idea to
> set heff_max low because if would create lots of side effect
> (buoyancy). One sensitivity study is to turn off ice dynamics and
> run the model for sufficiently long to see what happens. Another
> thing is to make sure the calculation of ocean surface stress is
> robust?
>
> Jinlun
>
> Matthew Mazloff wrote:
>
>> 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
>>>>>>>
>>>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> MITgcm-devel mailing list
>>>>> MITgcm-devel at mitgcm.org
>>>>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
>>>>
>>
>
> --
>
> 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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