[MITgcm-support] seaice model

[Martin Losch]

Dimitris,

BTW, I think I have been CC-ing all of my emails to Jinlun, haven't I?

On Wednesday, April 28, 2004, at 03:49 PM, Dimitris Menemenlis wrote:

The CS-grid is fine, but I cannot think of any reason, why the 
seaice-pkg shouldn't work on the global_ocean.90x40x15 grid. I mean, I 
don't expect any realism (without an Artic basin nor Ross nor Wedell 
Sea), but it should be stable; I would like to understand these extreme 
growth rates (which lead to the high salinities), and why they occur. 
Maybe I should start sending plot. These extreme ice thicknesses occur 
only in singular grid cells (admittedly 4x4 degrees wide).

>> But the problems I have there are the same, plus, with the cubed 
>> sphere
>> grid I no longer know what I am doing (o: But essentially, the same
>
> There's a bunch of matlab and other diagnostics for looking at stuff.
> I think it's worth the effort getting used to this grid ... eventually
> you will get hooked and become an addict like the rest of us, except
> for Alistair who leaves us to swallow his dust and is always moving to
> newer and greener pastures.
As you saw from my last email to support, I already demonstrated my 
greenhornishness.

>> thing happens as with lat-lon grid. Ice thicknesses become very large,
>> huge freshwater flux out of the ocean, strong horizontal divergences 
>> in
>> the ocean, large vertical velocities and violation of the vertical
>> cfl-criterion. If I reduce the timestep even further, the model runs
>> longer but eventually it blows up, too (all after less than a year of
>> integration).
>
> I was looking back at some preliminary comparisons that I did
> of pkg/thsice and of pkg/seaice, with and without dynamics
> in the 32x32x6x15 config.  All three integrations ran fine
> for five years and there does not seem to be any anomalous
> behavior.  But I am integrating all three with 1 hour time
> steps.   So maybe it's just a time step issue?

This may very well be that case: Certainly, with a 
tracerTimeStep=3600s, you won't run into the CFL problems, that I have. 
But I only have these problems with useSeaIce=.TRUE., with out seaice I 
can use a long tracer timestep of 86400s (172800s in the 
global_ocean.90x40x15 experiment) so which part of the seaice-pkg needs 
the small timestep?
I am now refering to the global_ocean.cs32x15 configuration:
Sea ice dynamics:
- with SEAICEuseDynamics=.false. I have the same problems as before,
- with npseudo = 24 which for tracerTimeStep=86400 effectively means 
SEAICE_DT=3600s, I have the same problems
- I also turned off the advection (not turned of the the flag 
SEAICEuseDYNAMCICS, which BTW uses the same timestep as the 
thermodynamics. In the context of asynchronous time stepping this 
should maybe be the momentum timestep deltaTmom? I don't know. Anyway, 
turning off advection does no help either (doesn't surprise me because 
U/VICE should be zero if SEAICEuseDYNAMICS=.false.)

This leaves me to believe it has to do with the thermodynamic part. I 
also ran the model with the thsice-pkg, and that does not appear to 
need the short time step.

Martin