Ensemble data assimilation for an eddy-resolving ocean model of the Australian region

The Bluelink Ocean Data Assimilation System (BODAS) is an ensemble optimal interpolation system applied to a global ocean general-circulation model with 10 km resolution around Australia. BODAS derives estimates of forecast-error covariances (FECs) from a stationary 72-member ensemble of intraseasonal model anomalies. The FECs are localized around each observation to reduce the negative effects of sampling error and to increase the rank of the ensemble. The FECs have characteristics that reflect the length-scales and the anisotropy of the ocean circulation in different regions. BODAS assimilates in situ and satellite-derived observations of temperature, salinity and sea-level anomaly. Results from a 13-year ocean re-analysis demonstrate that the reanalysed fields are often in very good agreement with withheld observations, and provide a good synoptic representation of the eddy field around Australia.