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Ocean Science An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 1 | Copyright
Ocean Sci., 12, 243-255, 2016
https://doi.org/10.5194/os-12-243-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Feb 2016

Research article | 12 Feb 2016

Effect of the North Equatorial Counter Current on the generation and propagation of internal solitary waves off the Amazon shelf (SAR observations)

J. M. Magalhaes1, J. C. B. da Silva1, M. C. Buijsman2, and C. A. E. Garcia3 J. M. Magalhaes et al.
  • 1CIMAR/CIIMAR – Interdisciplinary Centre of Marine and Environmental Research & Department of Geosciences, Environment and Spatial Planning, University of Porto, Rua dos Bragas 289, 4050-123 Porto, Portugal
  • 2University of Southern Mississippi, Department of Marine Science, 1020 Balch Blvd, Stennis Space Center, MS 39529, USA
  • 3Federal University of Rio Grande, Av. Itália, 96201-900, Caixa Postal 474, Rio Grande, Brazil

Abstract. Synthetic aperture radar (SAR) imagery from the Amazon shelf break region in the tropical west Atlantic reveals for the first time the two-dimensional horizontal structure of an intense Internal Solitary Wave (ISW) field, whose first surface manifestations are detected several hundred kilometres away from the nearest forcing bathymetry. Composite maps and an energy budget analysis (provided from the Hybrid Coordinate Ocean Model – HYCOM) help to identify two major ISW pathways emanating from the steep slopes of a small promontory (or headland) near 44° W and 0° N, which are seen to extend for over 500 km into the open ocean. Further analysis in the SAR reveals propagation speeds above 3 m s−1, which are amongst the fastest ever recorded. The main characteristics of the ISWs are further discussed based on a statistical analysis, and seasonal variability is found for one of the ISW sources. This seasonal variability is discussed in light of the North Equatorial Counter Current. The remote appearance of the ISW sea surface manifestations is explained by a late disintegration of the internal tide (IT), which is further investigated based on the SAR data and climatological monthly means (for stratification and currents). Acknowledging the possibility of a late disintegration of the IT may help explain the remote-sensing views of other ISWs in the world's oceans.

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Satellite imagery reveals intense internal solitary waves (ISWs) seen hundreds of kilometres from the Amazon shelf and extending for 500 km into the open ocean (propagating above 3 m/s, amongst the fastest ever recorded). Seasonality is discussed in light of the North Equatorial Counter Current, and a late disintegration of the internal tide (IT) is investigated based on climatological data. A late disintegration of the IT may explain other ISW observations in the world’s oceans.
Satellite imagery reveals intense internal solitary waves (ISWs) seen hundreds of kilometres...
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