ENERGY AND MOMENTUM GROWTH-RATES IN BREAKING WATER-WAVES

Finding a parameter whose threshold controls the onset of breaking in nonlinear modulating surface gravity wave trains has been an elusive p roblem. Our numerical study of the fully nonlinear two-dimensional inv iscid problem on a periodic spatial domain for a range of wave group s tructures examined the behavior of dimensionless relative growth rates of the local mean wave energy and momentum-densities. We found that t hese growth rates at the envelope maxima of the wave group oscillate o n a fast time scale with a significant dynamic range and that a univer sal threshold exists for the maximum of either of these growth rates t hat determines whether breaking will occur.