Structure and variability of the Norwegian Atlantic Current and associated eddy field from surface drifters
Maria Andersson, Inga Koszalka, Joe LaCasce, Cecilie Mauritzen, Kjell-Arild Orvik
University of Bergen, Norway
(Abstract received 08/13/2009 for session A)
ABSTRACT
The Norwegian Atlantic current (NwAC) transports warm and saline Atlantic water northward toward the Arctic Ocean, being an important part of the global thermohaline circulation and affecting the distribution of the ice cover in the Arctic. Therefore it is crucial to monitor spatio-temporal variability of the current and the associated heat transport as it passes through the Nordic Seas towards the Arctic. In this study we use information extracted from Lagrangian instruments to build a more complete picture of the surface circulation in the Nordic Seas with NwAC as its key component. In the POLEWARD project, SVP drifters have been deployed to track fluid parcels in the NwAC as it traverses the Nordic Seas. In the period June 2007 to October 2008, 118 ARGOS-tracked drifters, drogued at 15 meters depth, were deployed in the NwAC. We combine this data with historical data from SVP drifters in the same region available through Global Drifter Program database. By augmenting the historical data set, the POLEWARD deployments allow a Lagrangian study of the seasonal variability of the circulation, which was insofar limited because of the paucity of the Lagrangian data set in the area. The interpolated, quality controlled and low-pass filtered position data have been used to construct maps of the mean velocity field, the eddy kinetic energy and the principal axes of variance for both summer and winter seasons. Also estimations of Lagrangian time and space scales have been performed. The drifters reveal strong, localized current systems along the Norwegian coast, the continental margins and their extensions to the Barents Sea and Spitsbergen. The eddy kinetic energy reveals stronger variability in the Lofoten Basin area, particularly in the wintertime. The variance axes show significant variations, both spatially and seasonally.
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