Anomalous current structure in the eastern equatorial Indian Ocean during the south-west monsoon of 1994

Abstract

Analysis of hydrographic data collected along 80°, 84° and 88°E between 5 °N and 3 °S during peak south-west monsoon (July–August) of 1994 in the eastern equatorial Indian Ocean (EEIO) reveals thermohaline variability and anomalous current structure in the upper ocean. A warm (28.4–28.8°C) and less-saline (33 to 34.8) deep (60-75m) homogeneous layer characterizes the surface mixed layer. The south-west monsoon current, advecting the Arabian Sea High Salinity Water eastwards,appears as an eastward undercurrent (˜50 cm s^–1) below 125 m at 80 °E between 1 °and 1.5 °N and in the upper 100 m in the vicinity of the equator with an eastward increase of core velocity between 75 and 100 m. This undercurrent has a transport of 4 Sv at 80 °E. The westward flow in the upper layers north of the equator is anomalous, as the surface winds have an eastward zonal component. The associated westward transport is 44 Sv between 84 °and 88 °E. This equatorial westward flow appears to be influenced by the anomalously strong north-westward coastal current off Sumatra and westward propagating Rossby waves.