Variations in the East Auckland Current from satellite radar altimeter data

Abstract

We analysed satellite radar altimeter data for the New Zealand area during the period November 1992 to June 1994. Sea‐surface height anomalies from the Topex‐Poseidon and ERS—1 radar altimeter data were consistent in locating and identifying variability within most of the recognised major features in the area. Near the New Zealand coast, the tidal models used in the analysis did not perform well. A considerable error in the modelled M2 tidal component was apparent as an aliased signal with a period of about 62 days (sampled at a 10 day orbital repeat period). A correction was made to remove the error. Profiles of cross‐track current anomalies were deduced for the East Auckland Current system and there was good general agreement between Topex‐Poseidon and ERS‐1 products. Using surface measurements along one subsatellite track, the height data were calibrated and a history of absolute cross‐track currents to the north‐east of North Cape was produced. This showed a strong east‐southeastward flow between 33.5°S and 34°S, with a return flow meandering between 32°S and 33°S. The strength of the current at a fixed location varied considerably, with a possible seasonal influence. The histories of cross‐track current‐anomaly profiles, along with current‐anomaly vectors constructed for the track cross‐over points, give a coherent picture of features in the area. In particular, an anticyclonic eddy to the north‐east of New Zealand is identified moving south‐eastward during the spring of 1993.

Keywords:

• satellite altimetry
• East Auckland Current
• dynamic topography
• Topex‐Poseidon
• ERS‐1