[MITgcm-support] eta at OBCS

[Jean-Michel Campin]

Hi,

Thanks Stefano for your message.
I just want to add 1 little thing about obcs_apply_eta.f :
This routine is only used with non-linear free-surface, to
get the volume flux at the open boundaries (product of velocity
by length by height); it has no effect on the pressure 
gradient at the OB.

Jean-Michel

On Wed, Oct 19, 2005 at 05:15:22PM +0200, Stefano Querin wrote:
> Hi Ming,
> just some hints (I'm a bit busy in these days, sorry...).
> There are many mails about eta and OBCs: try to find them on the mitgcm 
> website, you will find lots of informations.
> Anyway, if you need to impose eta on the OB (i.e. external tidal 
> forcing...), I suggest you to convert the sea surface elevation (eta) into 
> barotropic velocity (Vbaro) "offline":
> 
> Vbaro=c*eta/H
> 
> c=(gH)**1/2
> 
> g: gravity acc.;
> H: water column heigth;
> c: celerity of small (compared to the water column heigth: eta<<H) 
> amplitude perturbations.
> 
> It is also possible to impose u, v, w, T, S and eta as well: you have to 
> customize some routines (I modified obcs_prescribe_read.F , exf_set_obcs.F 
> , obcs_readparms.F , OBCS.h , OBCS_OPTIONS.h  in such a way to be able to 
> read OBeta values from files). Remember to set  #define NONLIN_FRSURF in 
> CPP_OPTIONS.h and nonLinFreeSurf~=0 in data (if I remeber correctly...): in 
> this case you must run only in hydrostatic mode.
> 
> If you need a radiation condition on the OB: Orlanski OBC does not control 
> the inflow/outflow in the domain so you could obtain a very anomalous 
> increase/decrease in the sea surface level (for example, try to run the 
> plume on slope verification experiment for a longer period)!
> 
> If there is something wrong, please someone correct me!
> Good luck!
> 
> Stefano
> 
> 
> ----- Original Message ----- 
> From: "Ming Guo" <gming at karluk.physics.mun.ca>
> To: <mitgcm-support at mitgcm.org>
> Sent: Wednesday, October 19, 2005 4:09 PM
> Subject: Re: [MITgcm-support] eta at OBCS
> 
> 
> >Is obcs_apply_eta.f the file should be included?
> >But I am not sure how to do it.
> >
> >
> >On Wed, 19 Oct 2005, Ming Guo wrote:
> >
> >>Hi,
> >>anyone can give me some hints or examples of dealing with eta on open 
> >>boundary?
> >>
> >>It seems that obcs only calculates u,v,w,s and t.
> >>
> >>thanks,
> >>
> >>Ming
> >>
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