Abstract
The mean velocity field of south Indian Ocean has been derived by combining high resolution maps of sea level anomalies and the surface drifter data from the Global Drifter program from 1993 to 2012 with a resolution of 1/3 × 1/3 degrees in latitude and longitude. The estimated mean velocity field exhibits strong western boundary currents, zonal currents and eastern boundary currents. The Agulhas Current shows a velocity of above 1.5 m s-1 at around 35°S. The distribution of energy associated with the fluctuating motion and the mean flow illustrates that mesoscale variability are particularly relevant in the Mozambique Channel, south of Java and around 40°S. Advection of mesoscale features along the western boundary is evident in the distribution of eddy fluxes. The long-term average monthly surface velocity field exhibits large variations in surface currents. The most change is observed in the South Equatorial Current which shows spatial and temporal variations.
Highlights
South Indian Ocean plays a major role in the global ocean circulation by mediating inter-oceanic exchanges between Pacific and Atlantic oceans
The Eulerian mean velocity field obtained by combining the satellite altimeter and drifter data reveals the near surface flow pattern of the south Indian Ocean (Fig. 4a, the gaps in the Indonesian Passage are due to lack of enough drifter observations)
The anticyclonic gyral circulation is characterized by the zonal broad South Equatorial Current, strong western boundary currents and weak eastern boundary currents
Summary
South Indian Ocean plays a major role in the global ocean circulation by mediating inter-oceanic exchanges between Pacific and Atlantic oceans. The Agulhas Current is primarily driven by the large scale pattern of wind stress curl between the southeast trade winds and the westerlies (Lutjeharms 2006) It flows along the east coast of Africa as a narrow fast boundary current until it is separated from the continent, looping anticlockwise south of Africa and feeding back into the Indian Ocean as the eastward Agulhas Return Current. In the present study, efforts have been made to present a high resolution (1/3 × 1/3 degrees latitude and longitude) quantitative description of the mean circulation and seasonal variability of the south Indian Ocean currents by combining satellite altimeter and the satellite tracked drifter observations. The Eddy Kinetic Energy (EKE), which is a measure of the degree of mesoscale variability, the Mean Kinetic Energy (MKE), ratio of EKE to MKE as well as the eddy fluxes have been presented to infer the mesoscale variability occurring in south Indian Ocean
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