[MITgcm-devel] heff_max...more sea ice issues
Matthew Mazloff
mmazloff at MIT.EDU
Mon Dec 18 15:30:55 EST 2006
Hi Martin,
In SEAICE_OPTIONS.h I set #define SEAICE_CGRID
I am using seaice model version checkpoint58s_post.
So unless I have missed something, I am using the C-grid seaice model.
Matt
On Dec 18, 2006, at 3:25 PM, Martin Losch wrote:
> Hi Matt,
>
> are you using the original B-grid dynamics code? If so, do you have
> some sort ice-ocean stress turned on? Apparently ice-ocean stress
> can be a problem with the B-grid model. If it is not too much
> effort, try to run with the C-grid dynamics (#define
> SEAICE_USE_CGRID or so) and see what happens. With the C-grid the
> ice-ocean coupling seems to be less of a problem (at least thats's
> what Dimitris sees in his runs).
>
> Martin
>
> On 18 Dec 2006, at 20:57, 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
>> <heff_max.jpg>
>>
>>
>> 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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>>
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