The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations

This study provides a long-term description of the poleward East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport, and variability based on both ;2.5 yr of continuous in situ measurements and ;21 yr of satellite altimeter data. An array of five moorings was deployed at 238S off eastern Madagascar as part of the Indian–Atlantic Exchange in present and past climate (INATEX) observational program. On average, the EMC has a horizontal scale of about 60–100 km and is found from the surface to about 1000-m depth. Its time-averaged core is positioned at the surface, at approximately 20 km from the coast, with velocity of 79 (621) cm s-1. TheEMCmean volume transport is estimated to be 18.3 (68.4) Sverdrups (Sv; 1 Sv [ 106m3 s-1). During the strongest events, maximum velocities and transport reach up to 170 cms-1 and 50 Sv, respectively. A good agreement is found between the in situ transport estimated over the first 8m of water column [0.32(60.13) Sv] with the altimetry-derived volume transport [0.28 (60.09) Sv]. Results from wavelet analysis display a dominant nearly bimonthly (45–85 days) frequency band of transport variability, which explains about 41% of the transport variance. Altimeter data suggest that this band of variability is induced by the arrival of westward-propagating sea level anomalies, which in turn are likely represented by mesoscale cyclonic and anticyclonic eddies. Annual averages of the altimeter-derived surface transport suggest that interannual variabilities also play a role in the EMC system