Discovering a current in the 21st century with altimetry

Image of the month - April 2007

Ocean currents can be discovered in the 21st century: oceanographers found a current, the South Indian Counter Current, looking closely at altimetry data. This surface current, which goes eastwards from Madagascar at about 25°S is the counterpart of a westward current closer to Equator. If it can't be seen at every time, averaging current velocities in the region shows it clearly.

Altimetry measurements represent a huge quantity of information on the ocean (a Topex/Poseidon 10-day cycle gathered more measurements than the previous 100 years of in situ measurements). Continuity of these measurement over long period will bring to light new phenomena, not very proeminent on instantaneous views, but that show up over longer periods.

Geostrophic surface currents (deduced from Absolute dynamic topography) averaged over 5 years (August 2001 - May 2006) East of Madagascar. A narrow current is visible at about 25°S from Madagascar to about 100°E, with an attenuation from 80°E. Pink lines are in situ observations (Woce program data), that confirm this current. (Credits University of Cape Town).

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Reference :

  • Siedler, G., M. Rouault, and J.R.E. Lutjeharms, 2006: Structure and origin of the subtropical South Indian Ocean Countercurrent, Geophys. Res. Lett, 33, L24609, doi:10.1029/2006GL027399