On the formation of the bulge in a spilling breaking water wave (Q1128087)

We investigate the early stages of a spilling breaking water wave leading to the formation of a bulge on the forward face of the wave. Simultaneous space-time measurements of the free-surface elevation of a spilling breaking water wave are analyzed. The analysis, carried out in the frame of reference moving with the wave crest, reveals that the formation of the bulge is due to the presence of a shock-like mode. Following this observation, we present a two-dimensional quantitative model which reproduces both the formation of the bulge and the sudden increase in the wave steepness.