A small-scale oceanic eddy off the coast of West Africa studied by multi-sensor satellite and surface drifter data.

Alpers, W., Brandt, Peter , Lazar, A., Dagorne, D., Sow, B., Faye, S., Hansen, M., Rubino, A., Poulain, P.-M. and Brehmer, P. (2013) A small-scale oceanic eddy off the coast of West Africa studied by multi-sensor satellite and surface drifter data. Remote Sensing of Environment, 129 . pp. 132-143. DOI 10.1016/j.rse.2012.doi:10.032.

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Abstract

A small-scale oceanic eddy, which was generated in autumn 2011 at the headland of Cap-Vert off the coast of Senegal, West Africa, and then propagated westward into the open North Atlantic Ocean, is studied by multi-sensor satellite and surface drifter data. The eddy was generated after a sudden increase of the trade winds causing an enhanced southward flow and upwelling at the coast of Senegal. After this wind burst event, an extremely nonlinear cyclonic eddy with a radius of about 10 to 20 km evolved downstream of Cap-Vert with Rossby number larger than one. Our analysis suggests that the eddy was generated by flow separation at the headland of Cap-Vert. The eddy was tracked on its way into the open North Atlantic Ocean from satellites over 31 days via its sea surface temperature and chlorophyll-a (CHL) signature and by a satellite-tracked surface drifter. The satellite images show that this small-scale eddy transported nutrients from the upwelling region westward into the oligotrophic North Atlantic thus giving rise to enhanced CHL concentration there. Maximum CHL concentration was encountered few days after vortex generation, which is consistent with a delayed plankton growth following nutrient supply into the euphotic zone within the eddy. Furthermore, the eddy was imaged by the synthetic aperture radar (SAR) onboard the Envisat satellite. It is shown that the radar signatures of cold eddies result from damping of short surface waves by biogenic surface films which arise from surface-active material secreted by the biota in the cold eddy as well as by the change of the stability of the air–sea interface.
Highlights:
► Processes during the onset of coastal upwelling off West Africa ► Multi-sensor remote sensing and in-situ observations ► Highly-nonlinear, small scale eddy generation at Cap-Vert ► NRCS reduction in parts of the eddy due to biogenic surface films

Document Type: Article
Additional Information: WOS:000315308300012
Keywords: Small-scale eddy; Trade winds; Coastal upwelling; SST; Chlorophyll-a; MODIS; SAR; Surface drifter; West Africa; Cap-Vert; SYNTHETIC-APERTURE RADAR; SOUTHERN CALIFORNIA BIGHT; MESOSCALE EDDIES; SPIRAL EDDIES; WIND-SPEED; LABORATORY EXPERIMENTS; BIOLOGICAL PRODUCTION; REDUCED-GRAVITY; SEA; PHYTOPLANKTON
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.rse.2012.doi:10.032
ISSN: 0034-4257
Projects: SOPRAN, Future Ocean
Date Deposited: 23 Nov 2012 12:11
Last Modified: 23 Jan 2019 14:05
URI: http://oceanrep.geomar.de/id/eprint/19278

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