[MITgcm-devel] seaice adjoint and EVP

Sat May 26 00:37:45 EDT 2007

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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>>> 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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