Annual sea level amphidromes in the South China Sea revealed by merged altimeter data

Annual phase-amplitude characteristics of sea level anomaly (SLA) in the South China Sea (SCS) are investigated by a merged SLA data set derived from simultaneous measurements of Envisat, Geosat-Follow-on (GFO), Jason-1, and TOPEX/Poseidon (T/P) from January 2004 to December 2005. Four annual amphidromes instead of two are revealed and their locations, surrounding the Vietnam eddy, distinguish two distinctive regimes of annual variations in the SCS, a basin scale monsoon regime and a local Vietnam eddy regime. Their existence suggests that the annual amphidrome is not only a common feature on global scale, but also a phenomenon in regional seas. However, the locations of these amphidromes in the SCS vary considerably from year to year, in contrast to the annual amphidomes found in the tropical ocean basins, which are much more stable.