[MITgcm-support] obcs

[Thomas Haine]

I'm trying to understand how obcs are applied but I'm confused by OBCS.h
and obcs_apply_uv.F

OBCS.h says:

 These are input arrays (of integers) that contain the *absolute*
C computational index of an open-boundary (OB) point.
C A zero (0) element means there is no corresponding OB in that column/row.
C The computational coordinate refers to "tracer" cells.
C For a northern/southern OB, the OB V point is to the south/north.
C For an eastern/western OB, the OB U point is to the west/east.
C eg.
C     OB_Jnorth(3)=34  means that:
C          T( 3 ,34) is a an OB point
C          U(3:4,34) is a an OB point
C          V( 4 ,34) is a an OB point
C while
C     OB_Jsouth(3)=1  means that:
C          T( 3 ,1) is a an OB point
C          U(3:4,1) is a an OB point
C          V( 4 ,2) is a an OB point

and in obcs_apply_uv.F:

      DO I=1-Olx,sNx+Olx
C Northern boundary
       IF (OB_Jn(I,bi,bj).NE.0) THEN
        vFld(I,OB_Jn(I,bi,bj),K,bi,bj)=OBNv(I,K,bi,bj)
     &                              *_maskS(I,OB_Jn(I,bi,bj),K,bi,bj)
        uFld(I,OB_Jn(I,bi,bj),K,bi,bj)=OBNu(I,K,bi,bj)
     &                              *_maskW(I,OB_Jn(I,bi,bj),K,bi,bj)
        vFld(I,OB_Jn(I,bi,bj)+1,K,bi,bj)=OBNv(I,K,bi,bj)
     &                              *_maskS(I,OB_Jn(I,bi,bj),K,bi,bj)
       ENDIF
      ENDDO

There seem to be some inconsistencies here:

i) Why are both U(3,34) and U(4,34) OB points in the first example?
(similarly 2nd example)

ii) Why is V(4,34) an OB point, not V(3,33) in the first example?
(similarly 2nd example)

iii) The code doesn't seem to implement either the rules illustrated in
the examples, or the rule about a northern/southern OB having the OB V
point to the south/north.

I'm confused!  Can anyone clarify please?

Thanks, Tom.
-- 
--------------------------------------------
 Thomas W. N. Haine
                                                                                                                                                              
 Associate Professor of Physical Oceanography,
 Department of Earth & Planetary Sciences,
 329 Olin Hall, The Johns Hopkins University,
 Baltimore, MD 21218, USA.
 Tel : 410 516 7048,   Fax : 410 516 7933
 Thomas.Haine at jhu.edu
 http://www.jhu.edu/~eps/faculty/haine
--------------------------------------------