[MITgcm-support] 回复： Open boundary problem!

[Martin Losch]

Hi Ertyy (?),

from your files and figures, it looks like you have done everything correctly with respect to the obcs-package (I don't know about the OBCS_OPTIONS.h, but I assume that you allow N/E/W open boundaries there, too, otherise your velocities would not show up as they do).

The problem is that you will alway generate (unresolved) boundary layers along boundaries (open or not). These can mean total flow reversal as in your case, if, e.g., the surface forcing is such that the flow is different from what is prescribed along the boundaries. There is no real solution with the type of boundary conditions implemented, but you can try to introduce a sponge-layer like this in data.obcs (and ALLOW_OBCS_SPONGE in OBCS_OPTIONS.h):

 &OBCS_PARM01
[ your stuff as before ]
 useOBCSsponge = .true.,
 &
 &OBCS_PARM03
  Urelaxobcsinner = long relaxation time scale of your choice,
  Urelaxobcsbound = short relaxation time scale,
  Vrelaxobcsinner = long relaxation time scale,
  Vrelaxobcsbound = shore relaxation time scale,
   spongeThickness = # grid points,
 &

The model will then relax velocities near the boundaries to the prescribed ob-velocities according to the relaxation timescale (interpolated between the short and long time scale). This makes things smoother, but you might get another boundary layer where the sponge layer ends.

Good luck,

Martin


On May 27, 2010, at 9:40 AM, Ertyy wrote:

> Dear All:   
>   I have attached a snapshot of the modeled surface current at a corner, the north/west boundary is open and with prescribed velocity (regular northeastern direction), and I think the interior velocity is supposed to be almost the same direction, what's wrong with it?  
> 
> --- 10年5月27日，周四, Ertyy <antonypolar at yahoo.com.cn> 写道：
> 
> 发件人: Ertyy <antonypolar at yahoo.com.cn>
> 主题: [MITgcm-support] Open boundary problem!
> 收件人: mitgcm-support at mitgcm.org
> 日期: 2010年5月27日,周四,上午10:25
> 
> Dear MITgcm users:
>       I have configured an application for regioanl ocean circulation simulation based on the MITgcm, and got the lateral boundary data from SOAD reanalysis.
>      The prescribed open boundary conditions were turned on (u, v, S, T were prescribed), and the model can read in these data and put it on the right position.However, it seems that the interior can not feel the prescribed boundary value, especially for the velocity field, strong reflection happened at the bounday.
>      I have no idea what happens, and where the problem comes from, is anyone have experience with this?
> 
>  
> 
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