Fronts and strong currents of the upper southeast Indian Ocean

Hydrographic data, ADCP velocity and sea level anomaly derived from the satellite altimeter have been jointly analyzed in the southeast Indian Ocean.Results show the locations and orientations of the major oceanic fronts as well as the characteristics of the currents within these fronts in the area.Double subtropical fronts are observed in the section along 120°E, which conflicts with the frontal structure frequently observed before-the North Subtropical Front (NSTF) and South Subtropical Front (SSTF) merge into a single STF between 110°~115°E.The Subantarctic Front (SAF), influenced by the out-of-phase double eddies, runs across 48°S three times between 120° and 127°E.The surface current within the SAF is strengthened up to 105.4 cm/s by the geostrophic effect of these eddies.Furthermore eddies may cause the strong current to split up into two branches within the SAF.The SAF and the primary polar front (PF1) can be identified individually in the ADCP data with a separation distance of about 0.3° at latitude between 140° and 145°E, although they cannot be identified separately in the low-resolution hydrographic data.The different thermohaline characteristics of Circumpolar Deep Water (CDW) and Modified Circumpolar Deep Water (MCDW) result in the formation of Southern Antarctic Circumpolar Current Front (SACCF) in the southeast Indian Ocean.It consistently turns northward along the east flank of the Kerguelen Plateau after it runs through the Princess Elizabeth Trough and turns southward sharply north of 60°S with a little seasonal variations.It is shown that the locations and orientations of the SAF, the primary PF and SACCF in the ACC of the southeast Indian Ocean can be identified more precisely by the current distribution derived from ADCP data than by hydrographic data, because these fronts are usually accompanied by strong currents.However, the locations and orientations of the STF and the secondary PF are more difficult to be identified through current data, since these two fronts are usually not accompanied by any jet.The STF the and the secondary PF are usually confined in the first few hundred meters of the upper ocean and the latter is often determined by the northern terminus of 2℃ isothermal.