QUANTITATIVE SKILL ASSESSMENT FOR COASTAL OCEAN MODELS
Coastal and Estuarine Studies, Vol. 47
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QUANTITATIVE SKILL ASSESSMENT FOR COASTAL OCEAN MODELS, COASTAL AND ESTUARINE STUDIES, VOL. 47, PAGES 31–48, 1995


Lagrangian Flows in Complex Eulerian Current Fields

Herman Ridderinkhof


Abstract

A framework which was developed originally to analyse nonlinear dynamical systems is used to obtain insight in the Lagrangian flows in complex 2D stationary and time-periodic current fields. The method involves the identification of hyperbolic fixed points in the Lagrangian displacement field and of the curves along which particles move from and to these points. In a stationary current field these curves are identical to the outermost streamline of the mass transport streamfunction surrounding an eddy and form the boundary between circulation cells and areas of throughflow. In a time-periodic current field these curves are either regular and similar to the flows in a stationary current field or, if chaotic advection occurs, show wild oscillations. These wild oscillations indicate a strong sensitivity of trajectories to their initial position and a quasi-random spreading of particles. An application of these methods to analyse the Lagrangian flows in tidal models of the Gulf of Maine and the Dutch Wadden Sea is discussed and compared. The stationary current fields in both models are qualitatively similar whereas the Lagrangian flows in the time-dependent current fields in both areas completely differ. In the Gulf of Maine no chaotic advection occurs and the displacement of particles is qualitatively similar to the displacement in the stationary current field. In the Wadden Sea chaotic advection occurs causing a quasi-random spreading of particles.

Citation: Ridderinkhof, H. (1995), Lagrangian Flows in Complex Eulerian Current Fields, in Quantitative Skill Assessment for Coastal Ocean Models, Coastal Estuarine Stud., vol. 47, edited by D. R. Lynch and C. N. K. Mooers, pp. 31-48, AGU, Washington, D. C.