[MITgcm-support] nonhydrostatic w boundary condition

[David Hebert]

Thanks Martin for your response. So it looks like whenever 
INTEGR_CONTINUITY is called, w is computed via INTEGRATE_FOR_W, then 
OBCS_APPLY_W applies boundary values for W.

I have been trying to use sponge layer to relax interior solutions to 
the boundary without much success. I am wondering the following: I have 
been running model in nonhydrostatic mode WITHOUT specifying W open 
boundary values. If I am not mistaken, in this configuration all OB?w 
will be set to zero in OBCS_INIT_VARIABLES. Then when OBCS_APPLY_W is 
called the boundary value for W obtained via continuity is replaced by 
zero. Then zero would always be used for boundary values when w is 
timestepped, would it not? And since there is no sponge code for W as of 
yet, would this be conducive to reflections/boundary noise?

Thanks,

David


Thanks

On 04/19/10 02:15, Martin Losch wrote:
> In nonhydrostatic mode, vertical velocities are still computed from "div U = 0". If the 3D pressure solver has converged perfectly, this wVel is the same as the one obtained from stepping the w-equation. If not (in practice you have only finite accuracy), the differences are small, and you have to make a decision which equation you want to satisfy, dw/dt = Gw, or delU=0. In the MITgcm, delU=0, as far as I know. However, W at the open boundary is reset to the prescribed value (see integr_continuity).
>
> If (div U) is not zero, you'll generally get extra sources in the tracer equations. I bet that this will also happen along the open boundaries.
>
> Martin
>
> On Apr 16, 2010, at 7:42 PM, David Hebert wrote:
>
>    
>> In nonhydrostatic mode it looks like it is possible to prescribe all components (u,v,w) of velocity at the boundaries. Is that right? Are there consequences if continuity ("del dot U") is not strictly matched?
>>
>> Thanks,
>>
>> David
>>
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>
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-- 
David A. Hebert
Naval Research Lab
Stennis Space Center, MS 39529
david.hebert at nrlssc.navy.mil
Phone: (228) 688-5846
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