The velocity and vorticity fields beneath gravity-capillary waves exhibiting parasitic ripples

An experimental investigation of near-surface flow beneath gravity-capillar y waves (4.21-6.70 Hz) is presented. In this frequency regime, there exist visible parasitic capillary ripples. especially along the forward face of t he underlying waves, if the steepness exceeds some moderate value. Relative ly strong vortices are generated by these progressive waves, and for the fi rst time their velocity fields are measured, their vorticity fields are cal culated, and the results reported. A relevant theoretical model, first intr oduced by Longuet-Higgins, is also discussed and wherever possible compared to the experiments. Numerical simulations by Mui and Dommermuth are examin ed as they relate to these experiments, and it is shown that qualitative ag reement exists between the experiments and the analytic-numerical predictio ns. (C) 2001 Elsevier Science B.V. All rights reserved.