Dynamics of the South Java Current in the Indo-Australian Basin

A year-long deployment of a mooring in the South Java Current (SJC) of Indo nesia provides a fascinating insight into this poorly understood, semi-annu ally reversing boundary current. A striking three-week period of southeastw ard flow begins in mid-May 1997. An analytical model directly account for c hanges in velocity at this time due to the passage of a westerly wind-force d, downwelling Kelvin wave from the equatorial western Indian Ocean. The en tire water column is warmed, with a fresh cap overlying salty water, consis tent with the Indian Ocean source. Following the wave passage, the SJC is n orth-westward, and the prevailing southeasterly monsoon winds lead to upwel ling of cold, salty water. In early August, the SJC abruptly returns to sou th-eastward flow, and remains so until November 1997 in the face of steady south-easterly local winds. The anomalous flow direction and cooler water a re related to an upwelling Kelvin wave, forced by unseasonal prolonged east erly wind anomalies in the equatorial Indian Ocean. After a small reversal of flow in November 1997, the SJC is south-eastward, as expected during the north-east monsoon. A trend toward increasing salinities in the record is attributed to the increased input of salty Indian Ocean water, enhanced eva poration, and a lack of freshwater advection due to the regionally reduced precipitation during the 1997-98 El Nino.