Rajesh Bhaskaran

Eulerian and Lagrangian Langmuir circulation patterns

An idealized Langmuir circulation pattern in the oceanic surface layer consists of parallel rolls with a fixed spatial periodicity. Observed surface manifestations of the circulation patterns, formed as collections of floating material and known as windrows, are roughly parallel to the surface wind direction, but form a network of intersecting lines. Field observations of the windrow intersections, referred to as “Y-junctions,” indicate a preferred orientation in which the two forks of the “Y” coalesce when viewed from upwind (the Y-junctions are said to point downwind). Weakly nonlinear theory yields patterns in the instantaneous Eulerian fields, for example contours of surface convergence, that show joinings and bifurcations at locations that may be termed pattern defects. These take the form of downwind-pointing Y-junctions occurring at negative defects and their obverse at positive defects with no preference for either type. We show that the preferential orientation of the Y-junctions can be explained...