A circulation description of a rip current neck

Abstract

This paper considers wave-driven rip currents from a circulation–vorticity point of view. A highly simplified description of rip currents using continuous generation of point vortices at fixed locations is found to have a wide range of applicability around the rip neck. Rip scaling becomes straightforward, and is seen to collapse to a single form. Numerical experiments with this simplified system have the ability to predict well startup transients including previously unexplained peaks, and frequency-dependent effects of wave groups on rip currents. Quantitative mean currents in the rip neck are represented moderately well by this theory.