[MITgcm-devel] seaice adjoint and EVP

Martin Losch Martin.Losch at awi.de
Tue May 29 13:40:00 EDT 2007 

Hi Jinlun, Dimitris,

I have followed Jinlun's suggestion and set dx = dx/2 in data, so  
that now we have an Arctic solution that is not really arctic  
anymore, everything is shrunk by a factor of 2. Except for the  
timestep which is still deltaT = seaice_deltaTdyn = 900sec,   
seaice_deltaTevp = 10sec, and with that the elastic parameter being  
1/3 the evp relaxation timescale is 300sec. The forcing is DAILY, the  
resolution about 13km, basically 1/8th of a degree.

Bottom line: I don't see any noise like Dimitris does, no stripes in  
the velocities.
I put the netcdf file (10 day snapshots of the first year) here:
http://mitgcm.org/~mlosch/aomip/runtst/diags2D.0000000000.glob.nc
in case you want to see for yourself.

Because of the really short relaxation time scale (compared to the  
forcing timescale) the evp solution is almost exactly VP, that is,  
almost all point fall onto the ellipse and there a very few points  
inside the ellipse, and certainly none outside.

Where does Dimitris noise come from? Could it be that is has to do  
with the stability in the ocean? Dimitris, could you do a run with  
deltaT = 900 or 600 instead of 1200, just to make sure that we are  
not chasing any ghosts?

Martin

On 26 May 2007, at 06:37, zhang at apl.washington.edu wrote:

> Martin,
>
> Are you using daily forcing? What is the time step? I wonder what  
> makes
> the problem go away. Maybe this thing is very resolution sensitive.  
> Do you
> want to try to artificially reduce the grid size, like adding lines  
> like
> DX*0.5 in the code?
>
> Jinlun
>
>> Hi there,
>> I am about to go home for an extended weekend, but I have give you
>> the latest news on EVP:
>>
>> I have tried to reproduce Dimitris' stripes in a configuration that
>> is similar to his: it's basically Ruediger Gerdes' Arctic grid:
>> rotated spherical grid with 1/4th degree resolution, so approximately
>> 25 to 27km resolution. This is a little coarser than Dimitris 18km,
>> but that's what I have. It's basically the grid of the AWI
>> contribution to AOMIP.
>>
>> The run is terrible because we don't have open boundaries, the
>> initial conditions are very noisy and the surface forcing has all
>> sorts of funny things in it, eg. a nice jump across the 0-meridian,
>> which is also impressed onto the surface fields in the run, oh well.
>>
>> But I do not see the stripines or noise that Dimitris sees in his evp
>> solution (I have 180 days by now). In fact with the default LSRerror
>> = 1e-4, the yield curves of the EVP solution are much better than
>> those of the LSR solution. I'll make some netcdf files available,
>> once these runs are finished (only one year runs, but still).
>>
>> Martin
>>
>> On 24 May 2007, at 18:20, Jinlun Zhang wrote:
>>
>>> Martin,
>>> I would think that the noisy log10(1-area) means velocities are not
>>> smooth in central arctic. We would likely see that if we make a log
>>> plot of velocity.
>>> Jinlun
>>>
>>> Martin Losch wrote:
>>>
>>>> Hi Jinlun,
>>>>
>>>> the velocities are quite smooth in the central Arctic, aren't
>>>> they,  just along the ice edge I see problems. However, where does
>>>> the noise  in the log10(1-area) plots come from? That seems to me
>>>> to be a  different issue. I am working on reproducing these
>>>> problems. Maybe  I'll find out something down that route.
>>>>
>>>> Martin
>>>> On 24 May 2007, at 17:58, Jinlun Zhang wrote:
>>>>
>>>>> It is not just over open water, but also in the central arctic.
>>>>> However, the noise is suppressed with 1s timestep over both open
>>>>> water and pack ice. So I start to think perhaps nothing is
>>>>> wrong,  just needing a small timestep.
>>>>> Jinlun
>>>>>
>>>>> Martin Losch wrote:
>>>>>
>>>>>> I have a new feeble theory for the noise in the evp solver over
>>>>>> open  ocean:
>>>>>>
>>>>>> heff = 0 over open ocean, therefore seaiceMassU/V = 0.
>>>>>> momentum equation in seaice_evp is discretized (in time) as
>>>>>> m*duice/dt = -m dphi/dx + tau_air + cd*(uice-uocean) + m*f*vice
>>>>>> +   \nabla\sigma
>>>>>> m*(uice(n+1)-uice(n))/dt = -m dphi(n)/dx + tau_air(n) - cd*(uice
>>>>>> (n +1)- uocean(n)) + m*f*vice(n) + \nabla\sigma(n),
>>>>>> so coriolis is explicit, ice-ocean stress is implicit. if the
>>>>>> mass  m  is zero (and zetaMin=0, so that zeta=eta=press = 0 over
>>>>>> open  ocen)  this reduces to
>>>>>> cd*uice(n+1) = tau_air(n) + cd*uocean(N)
>>>>>> so that uice ist a purely diagnostic quantity and not time
>>>>>> stepped.  cd is a function of uice-uocean at the nth time step,
>>>>>> averaged to  center points and the averaged back to velocity
>>>>>> points.
>>>>>>
>>>>>> Dimitris, could that be the problem, somehow I don't think so,
>>>>>> but  you can try by putting a minimum seaiceMassU/V in
>>>>>> seaice_dynsolver.F,  say seaiceMassU = max
>>>>>> (seaiceMassU,SEAICE_rhoIce*0.05)
>>>>>>
>>>>>> Martin
>>>>>>
>>>>>> On 22 May 2007, at 18:59, Jinlun Zhang wrote:
>>>>>>
>>>>>>> Hi Martin,
>>>>>>> Yeah, we are sort of stuck, but hey it is very interesting
>>>>>>> and   revealing.
>>>>>>> I would vote against masking ice velocities over open water
>>>>>>> because, as mentioned earlier, the ice velocities would be
>>>>>>> wrong  at  ice edge and the ice velocity discontinuity at ice
>>>>>>> edge will  get  into ocean. (o:. We don't do the masking with
>>>>>>> LSR solver,  perhaps  we can avoid doing that with EVP.
>>>>>>> Jinlun
>>>>>>>
>>>>>>> Martin Losch wrote:
>>>>>>>
>>>>>>>> Hi Jinlun,
>>>>>>>> the evp-solver is only in place for the C-grid. I don't have
>>>>>>>> the  time  to code the solver for the b-grid now. The b-grid
>>>>>>>> code (for  LSR) is  still working, but I have not kept it up
>>>>>>>> to  date, so  there may be a  few thing different other than
>>>>>>>> the  different grids.
>>>>>>>>
>>>>>>>> In general I though that the c-grid is perfect for evp as all
>>>>>>>> the   discretizations fall in place naturally. Only for this
>>>>>>>> \delta  term  one needs to average from center to corner
>>>>>>>> points  and vice  versa  (have a look at
>>>>>>>> seaice_calc_strainrates and  seaice_evp).  However,  there may
>>>>>>>> be issues with the coriolis  terms (commonly a  problem with
>>>>>>>> the c-grid).
>>>>>>>>
>>>>>>>> Actually, Elizabeth told us that she masks ice velocities
>>>>>>>> over   open  water in CICE.
>>>>>>>>
>>>>>>>> Now we are a little stuck, aren't we?
>>>>>>>>
>>>>>>>> Martin
>>>>>>>>
>>>>>>>> PS. I need to be able to reproduce these results myself (I
>>>>>>>> haven't  been able to, yet), maybe I can debug the stuff this
>>>>>>>> way.  Via email  etc. it's quite demanding (o:
>>>>>>>>
>>>>
>>>> _______________________________________________
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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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