[MITgcm-support] funky ice dynamics in doubly periodic domain

[Jean Mensa]

>
> Hi Jean, how big is your domain, and which ECMWF wind product are you
> using?
>

domain is 200x400km and I use the era-interim product averaged in space at
each given time. This is to avoid discontinuity at the boundaries (does
that answer your second question?)


> And what does your effective sea ice thickness look like spatially as a
> function of time,
> especially at boundaries of your domain where you are bound to have some
> surface
> stress divergence or convergence?  Do you get any cracks?
>

ice thickness looks smooth. My impressions is that the lack of lateral
constrains prevents the ice from cracking.


> The reason I ask is because maybe what you are seeing is exactly what you
> should expect
> to see.  If there is not sufficient divergent or convergent wind stress on
> the ice


there is none!


> it could move as a monolithic slab as it thickens.  That is the sea ice
> cover is mostly driven by internal
> rather than surface stress, there is sufficient mass to smooth out wind
> speed fluctuations,
> and it integrates surface stress over space time.
>

glad to see that there might be a physical explanation... I am running a
simulation from thinner ice to see if it keeps better correlation with the
wind forcing,


> One way to test this hypothesis is to reduce ice strength, say:
>       SEAICE_strength    = 1  _d +04
> to see if the onset of the “steady ice speed” period happens a little
> later.
>

I will try that. Thank you for the suggestion!


> Another would be to close boundaries at edges of your domain then your ice
> should be immobilized (maybe?).
>

I would like the sea ice to be moving. I was thinking of prescribing ice
velocity at the boundaries as if ice was driven only by wind stresses
(mDu/Dt = tau_air) but I am afraid that the model will respond generating
artificial ice stresses...

thank you for your comments,
Jean


> Dimitris Menemenlis
>
> > On Feb 22, 2016, at 10:22 PM, Jean Mensa <jean.mensa at yale.edu> wrote:
> >
> > Hi all,
> > I have a doubly periodic high resolution simulation forced with ECMWF
> atmospheric forcing (forcings.png) running the seaice pkg with VP rheology.
> Thermodynamics variables look good (ice.png) but ice velocity does
> something funky and I am not sure why. During summer season ice thickness
> is minimum (H_I) and concentration low (A_I) and ice dynamics seems to be
> driven by wind stress. This is all good and fine except that during winter
> ice velocity (S_I) seems to converge to some constant value decoupling from
> wind stress. This does not seem right to me. Is that an artifact of the
> doubly periodic configuration? Notice that the simulation runs fine and
> gives no failed convergence warnings.
> > Thanks,
> > Jean
>
>
>
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