TOPAZ

Towards an Operational Prediction system for

the North Atlantic European coastal Zones

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2nd July 2007: TOPAZ is upgraded to its third version, with double horizontal resolution (11 to 16 km from the Arctic to the Equator) and assimilation of ice drift data from Ifremer. This upgraded system constitutes the Arctic system of the MERSEA v2 integrated system.

Following the encouraging results of the DIADEM MAST-III project, TOPAZ aims at providing real-time forecasts for both the physics and ecology of the North Atlantic ocean.

As its predecessor, TOPAZ develops advanced data assimilation systems for a coupled primitive equation ocean circulation and marine ecosystem model for the North Atlantic and the Nordic Seas with enhanced resolution in the European coastal zones, assimilating satellite data available for real time operational use.

TOPAZ keeps improving the results obtained in DIADEM, partly thanks to the increased computer resources recently available. Our strategy is to take advantage of the newly available CPU and memory space for upgrading both the circulation and the ecological models and for increasing their resolution. Besides, the efficiency of the various data assimilation schemes is improved.

Features of the new model system are the following :

• The Miami Isopycnic Coordinate Ocean Model (MICOM) is replaced by the Hybrid Coordinate Ocean Model (HYCOM). It adds a fixed vertical coordinate to the original isopycnic coordinate and allows for a better description of the vertical movements of water masses.
• The original ecological model by Fasham, Ducklow and Mc Kelvie (FDM model) is improved so that the phytoplankton can adapt to changes in the physical and biogeochemical environment. In particular, the new model allows variable carbon to nitrogen (C:N) and carbon to chlorphyll ratios (C:N-REcoM= C:N Regulated Ecosystem Model).
• An ice model is coupled to the physical model HYCOM, and measurements of ice concentration and ice thickness are assimilated.
• The model grid resolution is increased (18 to 35 km), and a common discretization for both the physics and biology is now possible, which simplifies their coupling.

The data assimilation schemes used in the TOPAZ project are:

• The Ensemble Kalman Filter (EnKF, used in the real-time experiment).
• The Singular Evolutive Extended Kalman Filter (SEEK).
• The Ensemble Optimal Interpolation (EnOI) scheme.

The observations used are satellite observed Sea Level Anomaly (SLA), Sea Surface Temperature (SST), Sea-ice concentrations from SSMI and - soon - Coriolis in-situ data.

The major outcomes in terms of products are short term forecasts issued weekly, open for public access and end users.