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Volume 14, issue 4 | Copyright

Special issue: Coastal marine infrastructure in support of monitoring, science,...

Ocean Sci., 14, 689-710, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Jul 2018

Research article | 25 Jul 2018

Wind-induced variability in the Northern Current (northwestern Mediterranean Sea) as depicted by a multi-platform observing system

Maristella Berta1, Lucio Bellomo2, Annalisa Griffa1,3, Marcello G. Magaldi1,4, Anne Molcard2, Carlo Mantovani1, Gian Pietro Gasparini1, Julien Marmain5, Anna Vetrano1, Laurent Béguery6, Mireno Borghini1, Yves Barbin2, Joel Gaggelli2, and Céline Quentin2 Maristella Berta et al.
  • 1CNR-ISMAR, Lerici, Italy
  • 2Université de Toulon, Aix-Marseille Université, CNRS, IRD, MIO, Toulon, France
  • 3RSMAS, University of Miami, Miami, FL, USA
  • 4Johns Hopkins University, Baltimore, MD, USA
  • 5Degreane Horizon, Cuers, France
  • 6ACSA, Meyreuil, France

Abstract. The variability and evolution of the Northern Current (NC) in the area off Toulon is studied for 2 weeks in December 2011 using data from a glider, a high-frequency (HF) radar network, vessel surveys, a weather station, and an atmospheric model. The NC variability is dominated by a synoptic response to wind events, even though the dataset also evidences early stages of transition from late summer to fall–winter conditions. With weak winds, the current is mostly zonal and in geostrophic balance even at the surface, with a zonal transport associated with the NC of  ≈ 1Sv. Strong westerly wind events (longer than 2–3 days) induce an interplay between the direct-wind-induced ageostrophic response and the geostrophic component: upwelling is observed, with offshore surface transport, surface cooling, flattening of the isopycnals, and reduced zonal geostrophic transport (0.5–0.7Sv). The sea surface response to wind events, as observed by the HF radar, shows total currents rotated at  ≈ −55 to −90° to the right of the wind. Performing a decomposition between geostrophic and ageostrophic components of the surface currents, the wind-driven ageostrophic component is found to rotate by  ≈ −25 to −30° to the right of the wind. The ageostrophic component magnitude corresponds to  ≈ 2% of the wind speed.

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The Northern Current (NC) in the NW Mediterranean Sea is studied by HF radar, glider, vessel survey, wind station, and model. NC variability is dominated by synoptic response to wind events, studied decomposing geostrophic and ageostrophic surface components. The combination of autonomous observing platforms with classical marine surveys provides high-resolution datasets for scientific purposes and practical applications such as the management of marine resources in the Mediterranean Sea.
The Northern Current (NC) in the NW Mediterranean Sea is studied by HF radar, glider, vessel...