[MITgcm-support] Orlanski vs sponge obcs in ocean modelling

[Jody Klymak]

Orlanski chooses a *single* wave speed based on the data it gets.  So if you send a mode-1 internal wave at the bdy then it’ll do a decent job of passing that through.  But if you have more than one wave speed it doesn’t work.  I don’t know what happens w/ the barotropic wave, but if there are strong BT waves in the simulation I imagine that could cause problems.

As I said before, a sponge is the only realistic way to absorb outgoing IW energy. 

Cheers   Jody


> On 15 Nov 2017, at  8:40 AM, Dimitris Menemenlis <menemenlis at jpl.nasa.gov> wrote:
> 
> I think that Orlanski is for barotropic waves only, not internal waves.
> 
> Sponge boundary condition could help with internal waves but in some circumstances it could make sense to let them internal waves bounce around at edge of your your domain.  In real world you will have internal waves entering your domain as well as exiting.  So the bouncing waves at boundary could compensate in part for you lack of internal wave forcing at your boundary.
> 
> On 11/15/2017 08:10 AM, Yangxin He wrote:
>> Hey there,
>> I am forcing internal waves from the west boundary, and I want no reflection from the east boundary.
>> 1) Which boundary condition will be better for me? Orlanski or sponge?
>> 2) About the Orlanski BC, the original Orlanski bc, which he proposed in 1976, have problems when waves approach the boundary with an angle. Later in 1984, Raymond and Kuo improved the original Orlanski BC so that the improved bc can account for waves from all directions.  The question is, which one does MITgcm implement? the original or the improved Orlanski BC?
>> Thanks
>> Yangxin
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--
Jody Klymak    
http://web.uvic.ca/~jklymak/