NOCS ORCA1 home page

The NOCS ORCA1 home page

ORCA1 configurations page

Links to downloadable versions of the configuration and input files for active versions of ORCA1 are provided at the bottom of this page but please browse the following paragraphs to ensure that you collect the correct configuration files to match your needs.

The source files files are independent of the vertical grid. The ORCA1 configuration can be enabled using the new key: key_orca_r1. Prior to v3.3, a 42 level grid, with depths closely matching those used in the Hadley Centre's HadGOM1 model, was the default choice and this was configured by adding the following preprocessor key to the P_P setting in the Makefile prior to compilation:


However, other vertical grids were defined and these could be accommodated within the ORCA1 configuration by assigning a particular integer value to the key.

For example, following discussions with Anne-Marie Treguier in August 2006, we agreed a 64 level vertical grid which matched requirements for projects at IFREMER and is very similar to the OCCAM vertical resolution. This configuration was supported without the introduction of new keys or modules with some preprocessing directives in par_ORCA_R1.h90. The relevant code snippets can be viewed here. This alternative vertical grid was enabled by setting the preprocessor key to 64 with the following setting in the Makefile.:


A 46 level configuration was also introduced which is compatible with the DRAKKAR projects ORCA025 and ORCA05 configurations. This was enabled by:


Any other value would default to the 42-level grid but more alternatives could be supported by using the #elif preprocessor construct.

The following graph compares the level thicknesses for the 42 and other configurations. The standard ORCA2 vertical grid (31 levels) is also shown for comparison. Click on the image to obtain a larger version.

reproduced courtesy of Ian Culverwell, UKMO

To avoid confusion the ftp links for files particular to any one vertical grid are listed on separate pages. The following links list the files which are independent of the vertical grid:

FTP links:

Source code:

From v3.3 onwards, basic support for the ORCA1 configuration is included in the tagged release. Please note however, the ORCA1 is not a reference configuration which means that newly introduced features and parameterisations will not necessarily have been tested with the ORCA1 configuration. Any problems should be reported to the NEMO system team but a rapid response can not be guaranteed. For simplicity, from v3.3 onwards only two vertical grids are supported in the tagged release. These are the 46-level Drakkar configuration (default) and the new 75-level configuration which uses a double-tanh function to obtain a 1m vertical resolution at the surface (key_orca_r1=75). See the code snippets page for the parameter settings required if you wish to reintroduce either the 64-level or 42-level cases. Both these grids used the single tanh function so changes should be made by copying and altering the default (46-level) case.

The following are the modified source code modules required to configure and run the ORCA1 configuration with earlier versions of NEMO. The versions provided are compatible with the v3.2 release of NEMO (Paris revision 1780 to be precise). The modules are available in complete form in a tar file or as a UNIX patch file:


A tar file containing modified source modules (not required from v3.3 onwards). These are:
Source modules for earlier releases are still available but the use of older versions is not encouraged:
A tar file containing modified source files compatible with the v3.2_beta release of NEMO (Paris revision 1634)
A tar file containing modified source modules for the v3.1 tagged release.
A tar file containing modified source modules for the v3_beta tagged release.
Additional modified source modules that fix or enhance code in v3_beta modules which is not strictly part of ORCA1 base code. These fixes were always expected to be temporary.
sbcfwb.F90 - Reported bug fix to emp correction (not currently used)
sbcssr.F90 - Fixed support for nn_ssr=2 option and added enhanced relaxation under ice
trazdf.F90 - Added check to prevent negative salinities that can occur (rarely) near
             Arctic river mouths.
A UNIX patch file which can be applied to old v3_beta code

Surface input fields:
The complete grid definition for ORCA1
The full-depth bathymetry suitable for use with the partial-cells option. Needs to be renamed or symbolically linked as
Contains three separate mask fields (tmaskatl, tmaskpac, tmaskind) with values of 1 only at wet points in the respective ocean basins. This file is the input file needed by some of the CDFTOOLS utilities.
Monthly river and coast runoff values derived from the DRAKKAR ORCA025 fields
Monthly SST fields derived from PHC3 climatology.
Monthly SSS fields derived from PHC3 climatology.
Monthly SST fields derived from Levitus 2005 climatology.
Monthly SSS fields derived from Levitus 2005 climatology.
Monthly surface chlorophyll climatology derived from ORCA2 file (originally SEAWIFS)
Monthly dust input climatology derived from ORCA2_PISCES fields
2D input field to control spatial variations in viscosity.
2D input field of dissipation associated with the internal wave energy; M2 tidal component (key_zdftmx) [untested]. Needs to be renamed or symbolically linked as
2D input field of dissipation associated with the internal wave energy; K1 tidal component (key_zdftmx) [untested]. Needs to be renamed or symbolically linked as
2D input field mask to control enhanced tidal mixing in the Indonesion throughflow region (key_zdftmx and ln_tmx_itf=.true.) [untested]. Needs to be renamed or symbolically linked as

Atmospheric forcing:
For atmospheric forcing fields we use the Drakkar Forcing Set 4 (DFS4) composite of NCEP and ECMWF fields. These are available for 1958 onwards. See the Surface Forcing page for details of how to obtain the fields and the required ORCA1 weights files for use with the interpolation on the fly option.

Initial conditions and namelists:

Finally, to obtain a complete configuration, please select files from one of the following sets:

Note only the first two configurations are supported "out of the box" with the tagged releases from v3.3 onwards. The 64 and 42 level versions are provided as legacy versions but their use will require code additions to par_ORCA_R1.h90 in order to obtain the correct vertical grid.