The OCCAM global ocean model

The OCCAM project has developed several high resolution models of the World Ocean - including the Arctic Ocean and marginal seas such as the Mediterranean. Some early results from our highest resolution (1/12th degree) global model are available in poster form. The information on this page refers chiefly to our earlier, 1/4 and 1/8th degree global models. The project is being carried out by researchers at the National Oceanography Centre, Southampton in collaboration with colleagues from the Universities of East Anglia and Edinburgh.

A selection of animation sequences from the model are available for viewing (using quicktime and mpeg formats). Two 4 Mb Quicktime movies which show the global ocean surface temperature field can be downloaded. More detailed mpeg sequences, each covering a smaller area, may be selected via the OCCAM area selector. Features of special interest are :

Data from the OCCAM model can be requested using the OCCAM data selector. This service replaces our older JAVA-based system which we have been forced to retire due to hardware failure. The new service is superior in many aspects, not least in the quality of the simulation that the data comes from. Full details of this simulation are available in an internal report (PDF):

SOC Internal Report No. 99 "The OCCAM 66 Level Model: physics, initial conditions and external forcing" .

However, if you have had data from the old server/simulation and are returning for essential additions then please email your requirements to the contact point given on the new server. We shall do our best to support such ongoing work but all new projects are advised to use the new service.

More details are given below but please note these details refer to the older integrations that we are in the process of replacing. Other information, including figures, is available from the OCCAM posters and papers pages.

Model details

Geographic Coverage: Full Globe, 1/4 lat x 1/4 long
Depths: 36 levels, 20m thick near surface, 255m at 5500m. (A table of exact values is available)
Topography: DBDB5
Time: 14 year simulation
A technical report containing details of the first main run of the OCCAM model is now available via anonymous ftp in either PostScript or PDF files.

Archive datasets

Parameters: Sea level, potential temperature, salinity and velocity.
600 Mbytes - all parameters, every 15 days.
Formats: Include 32 bit 'IEEE floating point', 'hdf' and 'netcdf' formats.

We are starting to move towards publication of the contents of our model data archive, the metadata, using XML. If you have a good XML reader and do not mind downloading 3MB files, the current version of the metadata file is given here: occam.xml. Note however that because it is so large your browser is likely to hang if you don't save it straight to a file.

PI: Dr. David J. Webb, National Oceanography Centre, Southampton.
Project manager: Beverly A. de Cuevas, NOCS, Southampton SO14 3ZH, U.K.

Model Description

OCCAM is a primitive equation numerical model of the global ocean. It is based on the GFDL MOM version of the Bryan-Cox-Semtner ocean model but includes a free surface and improved advection schemes. A regular longitude-latitude grid is used for the Pacific, Indian and South Atlantic Oceans. A rotated longitude-latitude grid is used for the Artic and North Atlantic Oceans, which has its poles on the equator in the Indian and Pacific Oceans. This overcomes the singularity that otherwise arises at the North Pole. A simple channel model is used to connect the two grids through the Bering Strait.

The model depths are based on the DBDB5 data set, with sill depths checked against against original surveys.

The model was started from the Levitus annual mean temperature and salinityfields. The surface forcing uses ECMWF monthly mean winds and relaxation to the Levitus seasonal surface temperature and salinity fields.

The model is run on the UK Research Councils' multi-processor Cray-T3D operated by the University of Edinburgh. The initial model run for 12 model years will be completed by September 1996. The results are being used to understand the heat flows and movements of different water types in the ocean. They are also being used to help analyse the data from WOCE, the World Ocean Circulation Experiment.

Publications and Other Information

Some of our published manuscripts and postscript versions of documentation are available via our publications page. Adobe PDF versions of conference posters are available via our posters page.

OCCAM has participated in several European (EC) projects. For more information, please see the following, local and remote, pages:

Data Assimilation

The OCCAM model has been run with high resolution forcing using the six-hourly ECMWF re-analysis data from 1992 onwards. In collaboration with the Department of Meteorology at the University of Edinburgh, this configuration has been used in a series of data assimilation experiments as part of two EU Environment and Climate Projects. More information on these projects can be found on the following web pages:

Output, in the form of snapshots of two dimensional fields from the simulation and assimilation runs with high frequency forcing may be requested from the following web page:

Other projects

OCCAM is also involved with the following NERC funded projects:

Links to other large-scale modelling efforts, world-wide, can now be found on a separate list of related topics

The latest versions of OCCAM software available via anonymous ftp are:

Moma is a modified version of the GFDL MOM model, designed for use with array processor computers. Moma.mpi is a message passing version of moma, which uses the mpi library. Moma.pvm is similar and uses the pvm library. The OCCAM global model is very similar in structure to moma.pvm. Mplot is an x-windows plotting program for displaying the hdf files generated by OCCAM, moma, moma.mpi and moma.pvm.

A release of mplot98v1.3 can now be accessed via the mplot98 home page. This page contains information on downloading and installing the software (which has now been changed from previous releases). mplot98v1.3 now comes with an on-line user-manual ( , which is also provided in PostScript format, when downloaded. The user-manual can be downloaded separately via the mplot home page as a compressed tar file.

Related to OCCAM amd moma is SEA, the Southampton - East Anglia Parallel Ocean Circulation Model. This contains more physics options than moma and also comes with detailed documentation.

The OCCAM team at NOCS are:

Previous members of the group include

OCCAM is partly funded as a core activity of the James Rennell Division for Ocean Circulation and Climate. The James Rennell Division is one of the NOCS Divisions funded by the Natural Environment Research Council and managed by the University of Southampton.

For further information contact Beverly de Cuevas.

Last Updated: David Webb, 23th January 2009