[MITgcm-support] doubt regarding OBCs

[Nicolas Grisouard]

Hi,

(1) The default behavior for the boundaries is periodic. If you set useOBCS as false, then what you get on one side is the extension of what happens on the opposite side.

(2) Now if you just set useOBCS as true without specifying anything (like orlanski), then the default value prescribed at the "open" boundaries is zero for all perturbation variables, and the reference profiles for the stratification agents. The obcs package does not choose values for you, unless you ask for a semi-automatic package, like orlanski, to be activated.

Does that make sense with what you see?

Cheers,
Nicolas.

On Jul 22, 2012, at 1:07 AM, Himansu Pradhan <oceancalling at gmail.com> wrote:

> Hi MITgcm users,
> 
> i have a doubt regarding Open Boundary Conditions. 
> I have 3 experiments configured as :
> In
> expA
>  
> data.pkg
> useOBCS = .FALSE.
> 
> here i get values at boundary. 
> 
> expB 
> 
> data.pkg
> useOBCS = .TRUE.
> 
> data.obcs
> # Open-boundaries
> &OBCS_PARM01
> OBCSfixTopo=.FALSE.,
> OB_Jnorth=190*-1,
> OB_Jsouth=190*1,
> OB_Ieast=170*-1,
> OB_Iwest=170*1,
> 
> useOrlanskiN/S/E/W=.FALSE.,
> 
> here i get "ZERO" values at boundary.  
> 
> expC
> data.pkg
> useOBCS = .TRUE.
> 
> data.obcs
> # Open-boundaries
> &OBCS_PARM01
> OBCSfixTopo=.FALSE.,
> OB_Jnorth=190*-1,
> OB_Jsouth=190*1,
> OB_Ieast=170*-1,
> OB_Iwest=170*1,
> 
> useOrlanskiN/S/E/W=.TRUE.,
> 
> here at the boundary, values are according to orlanski boundary conditions. this is OK.
> 
> My query is (1), in expA, what is happening at the boundary ? where do i get those values / what values are they ????? 
> 
> (2) In expB , pls explain me what is happening here................... 
> 
> thanking all in advance,
> 
> himansu
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