[MITgcm-support] Unwanted seiche caused by boundary condition on velocity

[Jody Klymak]

Hi Pär,

1) Did you lag one end relative to the other to account for the finite propagation time of th BT wave? 
2) Did you start with an initial condition for U,V, and Eta?  If you don't, you have nothing to accelerate the flow in the interior until the BT waves from the sides propagate in, and then it takes time for it all to come into balance, ie. you get a seiche

Even if you do these things, there will be a bit of a startup transient because your analytical solution won't be correct because of the form drag due to the sill. 

You can also force the model with a body force in exf_forcing.F.  Modify the gU and gV terms.

You may also want to check out my online energy diagnostics at https://github.com/jklymak/MITgcmcode if your non-linear terms will end up being large.

Cheers,  Jody








On Mar 9, 2014, at  8:23 AM, Pär Jansson <jansson.par at telia.com> wrote:

> Hi all!
> I'm modeling stratified (2-layer) flow over a fjord sill in MITgcm. Focusing on barotropic and baroclinic energy flux (u'p') etc.
> I get an unwanted surface seiche caused by the model boundary conditions, which complicates the analysis;
> The model (2dimensional x,z) velocity boundary condition u=A*sin(t*2*pi/T_tide) is applied in both western and eastern  boundary.
> Any ideas on how to remove or reduce the seiche?
> 
> Best regards!
> Pär
> 
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mitgcm.org/pipermail/mitgcm-support/attachments/20140309/ee00b372/attachment.htm>