Estimating the velocity and transport of Western Boundary Current Systems

Nathalie Zilberman (Scripps Institution of Oceanography, United States)


Dean Roemmich (Scripps Institution of Oceanography, USA); Sarah Gille (Scripps Institution of Oceanography, USA)

Event: 2014 Ocean Surface Topography Science Team Meeting

Session: Science Results from Satellite Altimetry: Regional and basin-scale processes and sea level rise

Presentation type: Type Poster

Calculating western boundary current (WBC) transport is a challenging task. Fine resolution is necessary to resolve the narrow path of WBCs. Analysis regions should extend far enough onshore to distinguish WBC from WBC recirculation. Deep measurements are required as WBCs often extend to depths greater than 1000 m. High-frequency sampling is needed to resolve the temporal variability of WBC systems. No single platform fits all criteria. For this reason, a preferred strategy is to combine multiple data sources. The high resolution expendable bathythermograph (HRX) network is a multi-national effort to study the thermal structure and volume transport of the 0-800 m upper ocean. Expendable bathythermograph (XBT) measurements have been collected every 3-4 months along specific routes in the Pacific, Indian, Atlantic, and Southern Oceans since the 1990s. The Argo dataset consists of temperature and salinity profiles collected in the 0-2000 m ocean since 1997. Argo float trajectories constitute a powerful tool for assessing absolute velocity from XBT and Argo shear and for providing Mean Dynamic Topography (MDT) estimates. In this study, XBT data are merged with Argo shear and trajectory-based velocities from the parking depth to infer the mean and the time-variability of the 0-2000 m volume transport in the East Australian Current (EAC) and the Kuroshio. The sampling of the HRX transects at 3-4-month intervals is not sufficient to capture the signature of the highly variable eddy-like features in the vicinity of WBCs. Sea surface height anomalies in the EAC and Kuroshio are highly correlated with subsurface temperature and salinity changes at interannual time scales. A method for combining altimetric data with HRX and Argo profiles to improve the resolution of small scale features and limit sampling errors in the HRX/Argo datasets is described. HRX/Argo/altimetry based estimates of the MDT and time-mean geostrophic velocities in the EAC and Kuroshio regions are presented. Geostrophic transport variability in the EAC and Kuroshio are studied at interannual time scales.
Nathalie Zilberman
Scripps Institution of Oceanography
United States