[MITgcm-support] Open Boundary Conditions in MITgcm

[Klymak Jody]

>  I suggest that you hope that someone else will provide and answer, or you'll have to go and read the original papers. In orlanski_east.F there is some text about the parameters and suggestions about setting them.
> 
> Your configuration looks OK to me, but what happens when you do not use the balancing code (useOBCSbalance = .false.)? Maybe this velocity correction causes some of the reflection?

I think that the problem with Orlanski or its elaborations is that the assume one wave speed (Orlanski is worse in that it assumes one wave propagation direction).  So, for a stratified internal wave problem it might do fine at getting rid of mode 1, but can't help you for higher modes.  So, I bet if you do a Hovmoller diagram you see that it is mode 2 that reflects.   Dale Durran has some papers on the subject - a google of "Durran Orlanski" turns them up.  

I looked into all this for a few days a couple of years ago and decided the sponge was a fine way to do things for my applications.  It comes at the expense of some computational domain, but again I take care of this by telescoping the sponges so that the forcing reservoir is very large and far from the regions of interest.  You can usually get pretty clean waves this way.  

Hopefully someone who is an expert in this can say something more definitive.  

Cheers,   Jody

PS, Serge, you are correct, that the forcing is done in obcs_calc.F.  My mistake.


> Martin
> 
> On Feb 28, 2011, at 9:59 PM, fancer fancer wrote:
> 
>> Hi Martin. Sorry for belated answer and thanks for replies.
>> 
>> There are small changes then I use Orlanski conditions, reflected waves have smaller amplitudes, but they are still reflected.
>> I use default values CMAX and cVelTimeScale. I have not found some information about Orlanski radiation boundary condition in free access. Could You please tell me some formula or rule for these parameters selection (for waves reflection minimizing)? Not trivial task to get it from code.
>> 
>> P.S. My project in attachment, if it needed.
>> 
>> -Serge
>> 
>> On Thu, Feb 24, 2011 at 10:31 AM, Martin Losch <Martin.Losch at awi.de> wrote:
>> Serge,
>> claim
>> you might have noticed that the documentation of the obcs-pkg is incomplete:
>> <http://mitgcm.org/public/r2_manual/latest/online_documents/node236.html>
>> but can find all the information about the OB_Ieast etc. indices and other run-time parameters. For more you'll have to consult the code in pkg/obcs and the corresponding experiments in verification I am afraid.
>> 
>> There is a orlanski-radiation conditions. To turn it on you need to re-compile with
>> #define ALLOW_ORLANSKI
>> in OBCS_OPTIONS.h and useOrlanskiNorth/South/East/West=.true. for the boundary of intererst. There are some experiments that use this option (e.g. tutorial_plume_on_slope, dome). If you are not happy with that, you'll need to implement something on your own.
>> 
>> I hope this helps,
>> Martin
>> 
>> On Feb 20, 2011, at 5:12 PM, fancer fancer wrote:
>> 
>>> Hello, MIT gcm support.
>>> I am novic at modeling with MIT gcm, thus I have several questions about this model and about obcs package, especially.
>>>      • My first application describe itnternal waves propagation, generated by temperature and salinity stratification, in 2D area. This is the trivial task, because MIT gcm has internal waves verification example. It is necessary, what waves go through boundaries, but not reflect of that boundaries. How made it with obcs package or with other way? I made many experiments, but whitout positive results.
>>>      • Is there more detailed information about open boundies setting in MIT gcm, it is desirable with picture, where OB_Ieast, OB_Iwest, OB_Jsouth, OB_Jnorth represented in a modeling area?
>>> In advance, thanks for help.
>>> Yours sincerely, Serge Semin.
>>> P.S, Sorry for my emglish, I'm still learning.
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>> 
>> 
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