[MITgcm-devel] Re: [MITgcm-support] icebergs

[Martin Losch]

Hi Dimitris,
as far as I understand z*, it makes excursions of the freesurface below 
the top layer possible; it is needed if |eta| > delz(surface). I view 
z* as a surface terrain-following coordinate. Why not extend it to more 
than one level? It's a question of how thin the layers are allowed to 
get.
Since I hadnt' got the answer from the experts yet, I went ahead and 
tried it out. My observations:
1. you need to balance the initial state between the pressure load and 
the initial surface elevation. If you don't do that the system blows up 
immediately during the adjustment process unless you specify a very 
small time step (CFL). This problem is similar to the oceanic pressure 
coordinate initialization, so it seems do-able.
2. I have not yet understood, how the different parameters should be 
set. What's the difference between select_rStar=1,2, 
nonlinFreesurf=1,2,3,4? hFacInf/Sup, how small big can they get?

So if for a stationionary iceberg it could work, it could also work for 
continental ice shelves and caverns. But since the model is still 
z-coordinate and not bottom terrain-following, the slope processes 
(bottom water sliding down the slopes) are still going to be 
misrepesented, and you don't gain so much. What do you think?

Martin

On Sep 29, 2004, at 4:13 PM, Dimitris Menemenlis wrote:

> Alistair and Jean-Michel, can this really be done?
> I was under impression that z* required delZ>>200m?
> For Antarctic Bottom Water formation, a really crucial
> piece of missing physics is shelf processes.  If we can
> model 200m-deep icebergs, we should be able to
> model 1000m-ice shelves?
>
> D.
>
> On Wednesday 29 September 2004 06:24 am, Martin Losch wrote:
>> In a sigma model this would be simple, with the toplayer always being
>> beneath the iceberg. What about the z*-coordinate? From the
>> Adcroft+Campin2004 paper I don't see any real limitations on the size
>> of the depression of the free surface. Am I right? Could I place an
>> iceberg with a draught of, say, 200m (with delZ<<200m) into a basin by
>> specifying the pressure load p=2000000Pa? What parameter setting would
>> I need?
>> nonlinFreeSurf=4,
>> exactConserv=.true.,
>> select_rstar=2,
>> ?
>
> -- 
> Dimitris Menemenlis <menemenlis at jpl.nasa.gov>
> Jet Propulsion Lab, California Institute of Technology
> MS 300-323, 4800 Oak Grove Dr, Pasadena CA 91109-8099
> tel: 818-354-1656;  fax: 818-393-6720
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