GFI/BCCR Seminar: Assessment of the TOPAZ4 Arctic ice-ocean reanalysis (1991-2013)

Laurent Bertino (NERSC, Bergen, Norway):

Assessment of the TOPAZ4 Arctic ice-ocean reanalysis (1991-2013)

Abstract
We will present a synthesis of the ice-ocean TOPAZ4 reanalysis for the period 1991-2013. TOPAZ4 is a modeling and data assimilation system based on the Nansen Center's version of the HYCOM model at horizontal resolution of about 12 km and an Ensemble Kalman Filter (EnKF), integrating a dynamical ensemble of 100 members, similarly to the assimilation system NorCPM. The multivariate properties of the EnKF allow the TOPAZ system to assimilate several ocean and sea ice data types simultaneously, both in real-time forecasts applications (exploited operationally at MET Norway) and in reanalysis mode. The TOPAZ system constitutes the Arctic component of the Copernicus Marine Services (http://marine.copernicus.eu).

The results from a 23-years reanalysis show realistic circulation features, a good stability of the assimilation efficiency and its ability to provide physically consistent error estimates for most of the assimilated variables. Rather minor degradations are found compared to independent observations. The application of data assimilation also reveals limitations of the model, notably in terms of sea ice drift and motivates further developments of new sea ice rheology models.