[MITgcm-support] Orlanski radiation condition parameters

[Jody Klymak]

Hi Paul,

Others should correct me if I am mistaken, but I don’t think Orlanski will work particularly well for this case because you do not have one dominant wave speed in your problem.  Rather, you might try a gentle sponge. 

Cheers,   Jody


> On Apr 12, 2022, at 11:58 AM, Burns, Paul <P.Burns2 at exeter.ac.uk> wrote:
> 
> Hi,
> 
> This is a bit basic, but I would like to check my implementation of my lateral boundary conditions.  I am running a 2D simulation and prescribe (Dirichlet conditions) a Garrett-Munk spectrum of waves on my left boundary, which then propagate into my domain.  I would like to allow the motions in the interior solution to radiate away through my right boundary, so I've asked the model to use the Orlanski condition on the right boundary. 
> 
> In Orlanski (1976) it states that the (variable) phase velocity C must be less than the maximum numerical velocity, which for my setup is dx/dt = 25/1 = 25 m/s.  So in data.obcs I've set Cmax = 20 m/s.  This is quite different to the value used in the 'Gravity Plume On a Continental Slope' tutorial, which has a similar domain size to mine, but this is because of my much smaller timestep due to my fine vertical grid required for my features of interest.  I realise I am using large aspect ratio cells, but this is to keep the simulation feasible with the compute resources I have.  I will try and test sensitivity of my results to horizontal resolution.
> 
> Can someone confirm how you fix the remaining parameter of the Orlanski scheme? That is, 
>  cVelTimeScale
> 
> 
> 
> Many thanks,
> Paul
> 
> 
> 
>                                                                                       
> Dr Paul Burns MInstP FRMetS
> Research Fellow
> Geophysical and Astrophysical Fluid Dynamics Group
> Department of Mathematics
> Harrison Building
> University of Exeter
> 
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