Inter-comparing five forecast operational systems in the North Atlantic and Mediterranean basins: The MERSEA-strand1 methodology

The methodology to achieve a real time inter-comparison of five state-of-the-art operational forecast systems for the North Atlantic and Mediterranean basins is presented. All systems provide analysis and near real-time prediction of the three-dimensional ocean through Opendap servers. A standard set of diagnostics called metrics, is described. Definition and examples of metrics are given. An inter-comparison of the five systems is conducted over a 1 year period using those metrics. It is shown that the methodology developed allows a successful inter-comparison. It has been adopted by the GODAE community. It is also shown that the systems are consistent with the current knowledge of the ocean circulation and climatologies. Systems are deficient in the representation of specific water masses characteristics as Mode waters. Data assimilation of vertical profiles of temperature and salinity solve such deficiencies. Metrics also allow a monitoring of the system's North Atlantic overturning stream function and will allow detecting any changes in the coming year system's thermohaline circulation.