Index: branches/2015/dev_r5087_NOC2_JATTR/DOC/TexFiles/Chapters/Chap_MISC.tex
===================================================================
--- branches/2015/dev_r5087_NOC2_JATTR/DOC/TexFiles/Chapters/Chap_MISC.tex	(revision 5116)
+++ branches/2015/dev_r5087_NOC2_JATTR/DOC/TexFiles/Chapters/Chap_MISC.tex	(revision 5117)
@@ -141,4 +141,60 @@
 computational domain is laid out on local processor memories following a 2D 
 horizontal splitting. % (see {\S}IV.2-c) ref to the section to be updated
+
+\subsection{Simple subsetting of input files via netCDF attributes}
+
+The extended grids for use with the under-shelf ice cavities will result in redundant rows
+around Antarctica if the ice cavities are not active. A simple mechanism for subsetting
+input files associated with the extended domains has been implemented to avoid the need to
+maintain different sets of input fields for use with or without active ice cavities. The
+existing 'zoom' options are overly complex for this task and marked for deletion anyway.
+This alternative subsetting operates for the j-direction only and works by optionally
+looking for and using a global file attribute (named: \np{open\_ocean\_jstart}) to
+determine the starting j-row for input. The use of this option is best explained with an
+example: Consider an ORCA1 configuration using the extended grid bathymetry and coordinate
+files:
+\vspace{-10pt}
+\begin{alltt}
+\tiny
+\begin{verbatim}
+eORCA1_bathymetry_v2.nc
+eORCA1_coordinates.nc
+\end{verbatim}
+\end{alltt}
+\noindent These files define a horizontal domain of 362x332. Assuming the first row with
+open ocean wet points in the non-isf bathymetry for this set is row 42 (Fortran indexing)
+then the formally correct setting for \np{open\_ocean\_jstart} is 41. Using this value as the
+first row to be read will result in a 362x292 domain which is the same size as the original
+ORCA1 domain. Thus the extended coordinates and bathymetry files can be used with all the
+original input files for ORCA1 if the ice cavities are not active (\np{ln\_isfcav =
+.false.}). Full instructions for achieving this are:
+
+\noindent Add the new attribute to any input files requiring a j-row offset, i.e:
+\vspace{-10pt}
+\begin{alltt}
+\tiny
+\begin{verbatim}
+ncatted  -a open_ocean_jstart,global,a,d,41 eORCA1_coordinates.nc 
+ncatted  -a open_ocean_jstart,global,a,d,41 eORCA1_bathymetry_v2.nc
+\end{verbatim}
+\end{alltt}
+ 
+\noindent Add the logical switch to \ngn{namcfg} in the configuration namelist and set true:
+%--------------------------------------------namcfg--------------------------------------------------------
+\namdisplay{namcfg_orca1}
+%--------------------------------------------------------------------------------------------------------------
+
+\noindent Note the j-size of the global domain is the (extended j-size minus
+\np{open\_ocean\_jstart} + 1 ) and this must match the size of all datasets other than
+bathymetry and coordinates currently. However the option can be extended to any global, 2D
+and 3D, netcdf, input field by adding the:
+\vspace{-10pt}
+\begin{alltt}
+\tiny
+\begin{verbatim}
+lrowattr=ln_use_jattr
+\end{verbatim}
+\end{alltt}
+optional argument to the appropriate \np{iom\_get} call and the \np{open\_ocean\_jstart} attribute to the corresponding input files. It remains the users responsibility to set \np{jpjdta} and \np{jpjglo} values in the \np{namelist\_cfg} file according to their needs.
 
 %>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Index: branches/2015/dev_r5087_NOC2_JATTR/DOC/TexFiles/Namelist/namcfg_orca1
===================================================================
--- branches/2015/dev_r5087_NOC2_JATTR/DOC/TexFiles/Namelist/namcfg_orca1	(revision 5117)
+++ branches/2015/dev_r5087_NOC2_JATTR/DOC/TexFiles/Namelist/namcfg_orca1	(revision 5117)
@@ -0,0 +1,12 @@
+!-----------------------------------------------------------------------
+&namcfg        !   parameters of the configuration
+!-----------------------------------------------------------------------
+   cp_cfg      =  "orca"               !  name of the configuration
+   jp_cfg      =       1               !  resolution of the configuration
+   jpidta      =     362               !  1st lateral dimension ( >= jpi )
+   jpjdta      =     292               !  2nd    "         "    ( >= jpj )
+   jpkdta      =      75               !  number of levels      ( >= jpk )
+   jpiglo      =     362               !  1st dimension of global domain --> i =jpidta
+   jpjglo      =     292               !  2nd    -                  -    --> j  =jpjdta
+   jperio      =       6               !  lateral cond. type (between 0 and 6)
+   ln_use_jattr = .true.               !  use (T) the file attribute: open_ocean_jstart if present
