30.01.2017: FB1-Seminar

11:00 h, Hörsaal, Düsternbrooker Weg 20

Abstract:

In the thermocline of the midlatitude North Atlantic the Gulf Stream dominates the Meridional Overturning Circulation (MOC), marking a distinct boundary between the material properties of the subtropical and subpolar gyres.  The present, broad understanding is that meridional transfer of heat and freshwater between gyres and within the MOC depends on Gulf Stream processes involving the mesoscale and sub-mesoscale.  The involvement of these smaller scales in the detailed processes presents observational and modelling challenges.  Over the last few decades, Lagrangian pathways of water parcels in the Gulf Stream region and from deep convection sites in the Labrador Sea have been sampled sparsely by floats and drifters, leading to characterisation of the Gulf Stream as either a 'barrier' and a 'blender' to material transport and mixing.  Simplifying models such as that by Bower (1991) have been developed to make sense of the complex nature of transport across the Gulf Stream.  This talk will examine Lagrangian coherent structures (LCS) diagnosed from over 20 years of AVISO satellite altimetry, testing the relevance of the Bower model and exploring other processes that may explain the flow structure.  To explain the LCS perspective of Gulf Stream transport and mixing requires kinematics, dynamical instability and subsequent changes to flow topology.  The implications of these findings for climate modelling are also discussed.

Bower, A. S. (1991), A simple kinematic mechanism for mixing fluid parcels across a meandering jet, Journal of Physical Oceanography, 21(1), 173–180.

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