The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations
Ponsoni, L.; Aguiar-González, B.; Ridderinkhof, H.; Maas, L. (2016).
The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations. J. Phys. Oceanogr. 46: 1045-1065. dx.doi.org/10.1175/JPO-D-15-0154.1
In: Journal of Physical Oceanography. American Meteorological Society: Boston, etc.,. ISSN 0022-3670; e-ISSN 1520-0485, meer
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| Author keywords |
Geographic location/entity; Indian Ocean; Circulation/ Dynamics; Boundary currents; Eddies; Mesoscale processes |
| Abstract |
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 23°S 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 (±21) cm s-1. The EMC mean volume transport is estimated to be 18.3 (±8.4) Sverdrups (Sv; 1 Sv = 106 m3 s-1). During the strongest events, maximum velocities and transport reach up to 170 cm s-1 and 50 Sv, respectively. A good agreement is found between the in situ transport estimated over the first 8 m of water column [0.32 (±0.13) Sv] with the altimetry-derived volume transport [0.28 (±0.09) 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. |
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