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Abstract. Analysis of the variability of the last 18 yr (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) of a 32 yr run of a new near-global, eddy-resolving ocean general circulation model coupled with biogeochemistry is presented. Comparisons between modelled and observed mean sea level (MSL), mixed layer depth (MLD), sea level anomaly (SLA), sea surface temperature (SST), and chlorophyll a indicate that the model variability is realistic. We find some systematic errors in the modelled MLD, with the model generally deeper than observations, which results in errors in the chlorophyll a, owing to the strong biophysical coupling. We evaluate several other metrics in the model, including the zonally averaged seasonal cycle of SST, meridional overturning, volume transports through key straits and passages, zonally averaged temperature and salinity, and El Niño-related SST indices. We find that the modelled seasonal cycle in SST is 0.5-1.5 • C weaker than observed; volume transports of the Antarctic Circumpolar Current, the East Australian Current, and Indonesian Throughflow are in good agreement with observational estimates; and the correlation between the modelled and observed NINO SST indices exceeds 0.91. Most aspects of the model circulation are realistic. We conclude that the model output is suitable for broader analysis to better understand upper ocean dynamics and ocean variability at mid-and low latitudes. The new model is intended to underpin a future version of Australia's operational short-range ocean forecasting system.

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The generation and evolution of eddies in the ocean are largely due to instabilities that are unpredictable, even on short time-scales. As a result, eddyresolving ocean reanalyses typically use data assimilation to regularly adjust the model state. In this study, we present results from a second-generation eddy-resolving ocean reanalysis that is shown to match both assimilated and with-held observations more closely than its predecessor; but involves much smaller adjustments to the model state at each assimilation. We compare version 2 and 3 of the Bluelink ReANalysis (BRAN) in the Australian region.Overall, the misfits between the model fields in BRAN3 and observations are 5-28% smaller than the misfits for BRAN2. Specifically, we show that for BRAN3 (BRAN2) the sea-level, upper ocean temperature, upper-ocean salinity, and near-surface velocity match observations to within 7.7 cm (9.7 cm), 0.68 tively. We also show that the increments applied to BRAN3 -the artificial adjustments applied at each assimilation step -are typically 20-50% smaller than the equivalent adjustments in BRAN2. This leads us to conclude that the performance of BRAN3 is more dynamically consistent than BRAN2, rendering it more suitable for a range of applications, including analysis of ocean variability, extreme events, and process studies.

SUMMARYThe 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.