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

[Dimitris Menemenlis]

I take back what I said earlier.  internal stress is probably
not sufficient to explain the behavior that you observe.
what’s the ocean doing under your sea ice?
to have such a steady speed for the ice,
there would have to be a large compensating
stress at bottom of ice, in addition to internal stress,
in other words the ice would have to move a lot of water underneath it

here is another experiment you can try.
reduce ice-ocean drag, e.g.,
SEAICE_waterDrag   = 1
to see if the ice will move more freely.

what exactly are you trying to study?
sea ice boundary conditions are tricky ...

> On Feb 23, 2016, at 12:58 AM, Jean Mensa <jean.mensa at yale.edu> wrote:
> 
> 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 <mailto: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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