[MITgcm-support] obcs with staggered grid

[Jean-Michel Campin]

Hi Gordon,

I did not see any answer to your message; below are some (late) comments.

On Mon, Aug 10, 2015 at 10:12:24PM -0400, Weifeng (Gordon) Zhang wrote:
> Hi,
> 
> I am a little puzzled by the way mitgcm handles the open boundary
> conditions.
> 
> In obcs_cal.F, OBWu, OBWv, OBWw, OBWt, and OBWs are specified. Are
> these variables at the same grid locations (the model does the
> interpolation/extroplation internally), or they are at their own
> staggered grid locations with half-grid offsets?
The model does not interpolate OBCS values: They are supposed to be
at the right location, i.e. on the staggered grid, at the OB location.
You could find some information in the manual, section 6.3.1.4

> If the variables are at the staggered grid locations, how come they
> have the same size in all directions? Shouldn't there be a size
> offset of 1 in some of the variables, for instance, OBWv's size in y
> being greater than the y-size of the other variables by 1, and
> OBWw's vertical size being greater than the other variables by 1?
All input binary files (e.g., initial Temp,Salt U,V ...) have the
same size, no difference between U,V and T,S, as well as all output (*.data)
binary files. And this is also the case for OBC input fields.

> For OBWw, because it is 0 on the bottom interface, the bottom OBWw
> is neglected? What about OBWv then, how is it handled on the north
> and south boundaries?
May be getting familiar with MITgcm plain binary output in a simple
set-up (one of the tutorials) might help to figure out how OBCS input
files work ?

Cheers,
Jean-Michel

> 
> Thanks,
> 
> Gordon
> 
> 
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