[MITgcm-devel] heff_max...more sea ice issues
Jinlun Zhang
zhang at apl.washington.edu
Thu Dec 21 14:22:31 EST 2006
Matt,
Sorry for the delayed response - somehow your email and Martin's
follow-up for this topic were all put in my junk email folder.
Your figure shows oscillation of heff_max. I have seen this before, the
ocean stress is not stable and the whole system (both ice and ocean) is
oscillating.
I am not sure if the C-grid itself is a problem. Martin, have you
include all the metrics terms in the C grid formulation in a generalized
curvilinear coor. system?
The ice dynamics solver is implicit, so you can use relatively longer
time step, but better use LSR_ERROR=1e-4. The solution of conservation
equations that I put in is constrained by time step, so you might want
to use smaller time step if you use the original solution.
Like Dimitris, I am also very much interested in the outcome if you
choose to use EVP.
Jinlun
Matthew Mazloff wrote:
> 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
>
> ------------------------------------------------------------------------
>
>
>
> 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
>>
>>
>>
>>
>> _______________________________________________
>> MITgcm-devel mailing list
>> MITgcm-devel at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-devel
>
>
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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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