[MITgcm-support] seaice model

Thu Apr 29 10:14:44 EDT 2004

Martin,

didn't follow those lengthy conversions/mails in detail,
but were you saying the seaice only works on
the cubed grid?
That's not the case.

verification/natl_box_adjoint/

has configurations of the Lab Sea on lat-lon grid
with seaice model incorporated.
Read the README, in particular Experiment 6 and 12.
(note though, these are adjoint setups).

-p.

Quoting Martin Losch <mlosch at awi-bremerhaven.de>:

> Hey,
> I think I found the problem! Pointing at timestepping really helped, 
> Dimitris!
> 
> The pkg/seaice model uses consistently DELTAT for the timestep, except 
> when surfaceTendencyTice is computed, where it uses deltaTtracer (which 
> is correct, as far as I can see).
> BUT ... I would think, since we are dealing with the thermodynamic 
> properties, ALL DELTAT should be replaced by deltaTtracer, except for 
> the advective processes, where it should be deltaTmom (which sets 
> deltat) (I don't know about the dynamic solver, I guess you can control 
> the timestep by setting npseudo, but I don't understand yet, how that 
> relates to model time). I did this in growth.F, that is, replaced all 
> DELTAT with deltaTtracer and now the model is stable and gives 
> reasonable results!
> I can only guess that the reason why this has not been a problem, is 
> that asynchronous timestepping was not used so far? Or at least not 
> with such a big timestep as in global_ocean.cs32x15 or 
> global_ocean.90x40x15.
> 
> I cannot oversee, where exactly the deltaT should be replaced, but I am 
> almost positive, that it should be done everywhere in growth.F.
> 
> What do you think?
> 
> Martin
> 
> On Thursday, April 29, 2004, at 12:12 PM, Martin Losch wrote:
> 
> > 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
> >
> > _______________________________________________
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> > http://dev.mitgcm.org/mailman/listinfo/mitgcm-support
> 
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Patrick Heimbach     Massachusetts Institute of Technology
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