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A pilot reanalysis of TOPAZ system (2003-2008)

Francois Counillon, Pavel Sakov, Laurent Bertino
Mohn Sverdrup Center/NERSC
(Abstract received 12/17/2010 for session X)

The TOPAZ system constitutes the Arctic forecasting system of the MyOcean project. Monitoring the dynamics in the Arctic is complex because the ocean mesoscale is small and the ice behaves non-linearly and quickly. This justifies the use of advanced ensemble-based data assimilation methods like the Ensemble Kalman Filter. In 2010, a new version of the TOPAZ system has been developed with improvements of the HYCOM model parameterization, dynamics, and resolution as well as in the data assimilation setup. A pilot reanalysis of 5 years is proceeding. The system assimilates observations of SST, along-track SLA, ice concentrations, icedrift and Argo, ITP, and Nansen database T/S profiles. The along track SLA and ice drift data are assimilated in asynchronous mode. The system shows satisfactory skill, and some limitations that lead to modification of our data assimilative system. First, the model shows a bias in SST and mean Sea Surface Height that were estimated with the EnKF. Second, unrealistic updates were obtained in areas where the error was larger than ensemble spread. This issue was handle using a moderation technique.

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2011 LOM Workshop, Miami, Florida February 7 - 9, 2011