Modes of the southern extension of the East Madagascar Current

• Published in: Journal of Geophysical Research - Oceans Vol. 114; no. C1; pp. C01005 - n/a
• Main Authors: Siedler, Gerold, Rouault, Mathieu, Biastoch, Arne, Backeberg, Bjorn, Reason, Chris J. C., Lutjeharms, Johann R. E.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 01.01.2009; Blackwell Publishing Ltd
• Subjects: Currents; Earth sciences; Earth, ocean, space; Eddies and mesoscale processes; Exact sciences and technology; General circulation; Marine; Oceanography; Physical; Topographic/bathymetric interactions; Western boundary currents; Indian Ocean Islands; Madagascar; Indian Ocean; East Madagascar Current; Mozambique Basin; Agulhas current; ISW, Indian Ocean, Madagascar; ISW, West Indian Ocean, Madagascar Current; ISW, Mozambique; ISW, Indian Ocean; ISW, West Indian Ocean, Agulhas Current; currents; models; extension; cross-correlation; Space remote sensing; Surface current; Satellite observation; transport; slopes; subtropical zone; Long term; BASIC; Persistence; propagation; Countercurrent; Dynamic height; flow field; Vortex; direction; high resolution
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2008JC004921

Data sets from satellite observations and a nested high‐resolution model are used to study a source region of the Agulhas Current. Altimeter‐derived geostrophic surface currents are averaged over varying periods, providing evidence of the persistence of flow patterns in the extension of the southern branch of the East Madagascar Current (SEMC). South of Madagascar, the SEMC separates into one branch toward the Agulhas Current and into a second branch retroflecting and connecting to the Subtropical Indian Ocean Countercurrent (SICC). Good agreement is found between long‐term mean patterns of observational and model dynamic heights. Two basic modes are identified in the SEMC extension, with anticyclonic motion favoring retroflection in the northern Mozambique Basin when the extension is in a southwestward direction and cyclonic motion occurring in the case of the SEMC flowing westward along the southern Madagascar slope. A cross‐correlation sequence between model SEMC transports and the modal changes in the extension region displays a correlation at about 1‐month lag which agrees with eddy propagation time from the SEMC to the outflow region. Mean model SEMC transports are determined using floats released at 21°S, and the contribution of the SEMC to the SICC is obtained using floats injected at 55°E with the model running backward. Almost half of the SEMC volume transport contributes to the Agulhas system, and about 40% of SICC water originates from the SEMC.