[MITgcm-support] OBCS forcing

[Martin Losch]

Hi Gianmaria,
ok, I misunderstood your problem. To be honest, I have never prescribed 
Eta at the OBs, but I think it is only possible if you use a non-linear 
free surface (#define NONLIN_FRSURF in CPP_OPTIONS, and some run time 
flag, that I'd have to look up myself in data). Have you tried that?

Martin

On Jan 31, 2006, at 10:50 AM, Gianmaria Sannino wrote:

> Hi Martin,
>
> I'm a little bit confusing because exp4 seems to be balanced in terms 
> of volume flux through the four boundaries. This is also clear from 
> the OBC files:
>  OBNuFile = 'OBmeridU.bin',
>  OBSuFile = 'OBmeridU.bin',
>  OBWuFile = 'OBzonalU.bin',
>  OBEuFile = 'OBzonalU.bin',
>  OBWsFile = 'OBzonalS.bin',
>
> The U components both at east and west are the same, while the V 
> component at north and south are zero (for default).
> Actually my problem is different. I need to simulate a channel that is 
> always unbalanced in term of volume flux. I guess this is possible to 
> simulate only if you impose also the surface elevation at the two 
> boundaries. This is what I did, but what happens in the model domain 
> is that the free surface does not 'feel' the imposed eta OBC.
> Is this behaviour related to the fact that the model is using the 
> implicit free surface?
>
> gianmaria
>
> On Tue, 31 Jan 2006 09:05:43 +0100
>  Martin Losch <mlosch at awi-bremerhaven.de> wrote:
>> Hi Gianmaria,
>>
>> this should be possible. Have a look at verification/exp4, where 
>> there are 4 open boundaries and a net flux.
>> I am only guessing, but you may have a problem with an initial shock. 
>> Either ramp up your net flux or start from a circulation that is a 
>> little more consistent with your boundary conditions,eg. uVel = const 
>> = uVel(on open boundary).
>>
>> Martin
>> On Jan 30, 2006, at 6:32 PM, Gianmaria Sannino wrote:
>>
>>> Hello
>>>  
>>> I have a query about OBCS.
>>>  
>>> I'm simulating an east-west channel with a strait in the middle.
>>> This channel is forced through the specification of U,V and eta at 
>>> the two edges in order to simulate a two-layer system with a net 
>>> eastward volume flux. The problem is that  cg2d: Sum(rhs) does not 
>>> converge and the model crash after some time step.
>>> This problem does not exist if the net flux is zero.
>>> Is the model able to simulate this kind of experiment?
>>>  
>>>  
>>> thanks
>>> gianmaria
>>>  
>>>  
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>>
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> ******************************************************
> Gianmaria Sannino   ENEA (Italian Agency for Energy and Environment)
> Climate Project - Ocean Modelling Unit SP 91 - via Anguillarese 301
> S.M. di Galeria, 00060 ROMA, ITALY
> Voice: (+39) 06 3048 6799   Fax: (+39) 06 3048 4264
> e-mail: gianmaria.sannino at casaccia.enea.it
> URL: http://clima.casaccia.enea.it/staff/sannino/
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