[MITgcm-support] Eta, ETAN and SIheff 2

[Elja Huibregtse]

Hi Martin,

In addition to my previous mail, I still have another question:

- You wrote that:
In the presence of sea ice it is the surface underneath sea ice. For a particular  
parameter configuration (#define ATMOSPHERIC_LOADING and  
useRealFreshWaterFlux=.true.,) the free surface is actually depressed  
by ice load (so that ice is not floating "on top" of the ocean but really in the ocean).

In my case, the global ocean is completely covered with ice. So, if the water is depressed by the ice load, where does the water go to? Or is it assumed that water is compressible?

Thanks, I really appreciate your help!
Elja

%----------------------------

Hi Martin,

Thank you for your reply.
'My' definitions of ETA and ETAN are:

* ETA is the output defined in write_state.f:
 CALL WRITE_FLD_XY_RL('Eta.',suff,etaN,myIter,myThid)
  Now, I see that the variable 'etaN' is written to ETA.

* ETAN follows from the diagnostics package (for example, in data.diagnostics)
  filename(1)  = 'ETAN'

Since, in my case, the output data for ETA and ETAN significantly differ from each other, I thought that one of them described the excitation of the ice layer and that the other one described the excitation of the ocean. This is probably incorrect...

Should ETA be equal to ETAN? If so, do you have some (general) suggestions what could be wrong in case they are not equal?
And secondly, does a parameter exist that describes the total deformation of the system, that is the deformation of the ocean and ice? Or is this (simply) ETAN+SIheff?

Thank you in advance,

Elja


-----Oorspronkelijk bericht-----
Van: mitgcm-support-bounces at mitgcm.org namens Martin Losch
Verzonden: di 9/2/2008 9:45
Aan: mitgcm-support at mitgcm.org
Onderwerp: Re: [MITgcm-support] Eta, ETAN and SIheff
 
Elja,

what do you mean by Eta and EtaN? From DYNVARS.h:
C     etaN  - free-surface r-anomaly (r unit) at current time level
so this is the name of the model variable for SSH. In the presence of  
sea ice it is the surface underneath sea ice. For a particular  
parameter configuration (#define ATMOSPHERIC_LOADING and  
useRealFreshWaterFlux=.true.,) the free surface is actually depressed  
by ice load (so that ice is not floating "on top" of the ocean but  
really in the ocean).

what is "Eta" in your question?

You can try to initialize SIheff (effective ice thickness = volume/ 
grid-cell are) from a file, and with useSEAICE=.true. set
usePW79thermodynamics = .false.,
       SEAICEadvHeff      = .false.,
       SEAICEadvArea      = .false.,
       SEAICEadvSnow      = .FALSE.,
       SEAICEadvSalt      = .FALSE.,
SEAICEuseDYNAMICS = .false., ! only to turn off the computation of  
unused drift velocities.

You'll still have some overhead from the ice model, but ice thickness  
should not change.

Martin

On 1 Sep 2008, at 13:12, Elja Huibregtse wrote:

> Hi Matt,
>
> Thanks for your reply!
>
> Actually, my results for Eta and Etan differ significantly from  
> each other. I modeled an ice layer on top of an ocean, and now I am  
> wondering whether Eta gives the displacement on top of the ocean  
> and Etan on top of the ice layer. Does this make sense?
>
> Regards,
> Elja
>
>
>
>
>
>
>
> -----Oorspronkelijk bericht-----
> Van: mitgcm-support-bounces at mitgcm.org namens Matthew Mazloff
> Verzonden: zo 8/31/2008 8:52
> Aan: mitgcm-support at mitgcm.org
> Onderwerp: Re: [MITgcm-support] Eta, ETAN and SIheff
>
> Hi Elja
>
> 1)  I think eta = etan ....not sure where discrepancies (if any)  
> come in
> SIheff is the effective ice thickness...the relationship would depend
> on surface boundary condition using...
>
> 2) sure you can fix SIheff, but i doubt there's a flag to do this.
> You'll have to hardcode a resetting of SIheff in the model...
>
> probably not to helpful...but thought id throw out a response
> -matt
>
> On Aug 29, 2008, at 11:35 AM, Elja Huibregtse wrote:
>
> > Dear all,
> >
> > I have two (trivial?) questions concerning modeling of ice:
> >
> > 1. What is the exact relation between Eta, ETAN and SIheff?
> > 2. Is it possible to fix the thickness of the ice, i.e. is it
> > possible to make the ice thickness independent of the ocean
> > temperature?
> >
> > Thank you very much in advance!
> >
> > Elja
> >
> >
> >
> > _______________________________________________
> > MITgcm-support mailing list
> > MITgcm-support at mitgcm.org
> > http://mitgcm.org/mailman/listinfo/mitgcm-support
>
>
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
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