[MITgcm-support] Problem with OBCs (bug ?)

[Nicolas Grisouard]

Ok thank you both for the clarification, I'll keep that in mind.

Nicolas

Martin Losch wrote:
> Nicolas, David,
>
> just to clarify: the obcs-package can read time-dependent (and 
> time-independent) boundary values from input files with and without 
> the exf package. For "simple" idealized experiments the non-exf 
> variant is usually sufficient (and I actually recommend that here, but 
> with exf you can get the same results). The limitation is that all 
> forcing fields (surface forcing and open boundary forcing) must be 
> specificed at the same time intervals, e.g. there parameters in data 
> (from exp4):
> # periodicExternalForcing=.TRUE.,
> # externForcingPeriod=600.,
> # externForcingCycle=1200.,
> lead to the behavior that new forcing and boundary condition files are 
> read every 600 (model-)sec, and that after 1200sec, the model takes 
> the first record of the forcing files again (so in this case there 
> need to be 2 records in the files).
> With exf you can do the same thing, but you can specify the "period" 
> and "cycle" for each field individually, and you have the full 
> calendar functionality. The downside is that you have to spend more 
> time configuring the namelists (and consequently there are more traps 
> along the way).
>
> Nicolas, what you are doing is perfectly OK in terms of time 
> dependence. With the exf ("external forcing", not just surface 
> forcing) pkg or the above method, you'll just have a little more 
> flexibility, e.g., you don't need to recompile the model, you can use 
> the same exectuable with different input fields, which can be handy.
>
> Martin
>
>
> On 25 Jun 2008, at 16:53, David Hebert wrote:
>
>> Nicolas,
>>
>> I believe you need to use exf (and cal) to set time periods for 
>> forcing with OBCS. So say you wish to start from 0 and after n 
>> timesteps you want to have U and V on the boundary. Then you need exf 
>> to set the period to n * dt.
>>
>> Now as a quick pointer, exf will read from OBCS file every n 
>> timesteps, so you will need a value for U and V for each "snapshot" 
>> in time time that it reads. Also, exf interpolates between 
>> "snapshots", so be sure to add and extra two snapshots. Otherwise at 
>> last timestep simulation will crash because it can't read last OBCS 
>> value.
>>
>> David

-- 
Nicolas GRISOUARD
PhD Student - ERES division
Laboratoire des Ecoulements Geophysiques et Industriels
BP 53
38041 Grenoble cedex 9 France
tel : +33 (0)476 825 037 - fax : +33 (0)476 825 271