[MITgcm-support] Problem with OBCS prescribe and Orlanski

[cimatori at libero.it]

Hi, we are trying to set up a model for the diffusion of sewage from a deep pipe in a gulf; for that 
reason we are using ptracers, obcs and exf.
We have an open western boundary with Orlanski, and an eastern open boundary with OBCS 
prescribe.
To make this work, we changed obcs_calc.F, as you could not use Orlanski and prescribe together 
before, and we split exf_get_obcs in west, south, for the same reason (see the attachments). We 
also changed the obcs_apply*.F as we want only a deep source on the east:

obcs_apply_uv.F
...
C     Set model variables to OB values on East/West Boundaries
#ifdef ALLOW_OBCS_EAST
CA-----------------------------------
       if (K.EQ.21) then
CA-----------------------------------
      DO J=1-Oly,sNy+Oly
C Eastern boundary
       IF (OB_Ie(J,bi,bj).NE.0) THEN
        uFld(OB_Ie(J,bi,bj),J,K,bi,bj)=OBEu(J,K,bi,bj)
     &                              *_maskW(OB_Ie(J,bi,bj),J,K,bi,bj)
        vFld(OB_Ie(J,bi,bj),J,K,bi,bj)=OBEv(J,K,bi,bj)
     &                              *_maskS(OB_Ie(J,bi,bj),J,K,bi,bj)
        uFld(OB_Ie(J,bi,bj)+1,J,K,bi,bj)=OBEu(J,K,bi,bj)
     &                              *_maskW(OB_Ie(J,bi,bj),J,K,bi,bj)
       ENDIF
      ENDDO
CA-------------------------
       endif
CA-------------------------
#endif

Now we get negative w velocities at the top of the columns interested by the eastern OBCS, and 
this has no physical reason (there's no heavy water above, and no negative w around). After 
24hours or so, model starts to put out NaNs.
Any idea?
Thanks,
Andrea Cimatoribus



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