Abstract: We study experimentally the
dynamics and statistics of capillary waves forced by random
steep gravity waves mechanically generated in laboratory.
Capillary waves are produced here by gravity waves from
nonlinear wave interactions. Using a spatio-temporal measurement
of the free-surface, we characterize statistically the random
regimes of capillary waves in the spatial and temporal Fourier
spaces. For a significant wave steepness (0.2 - 0.3), power-law
spectra are observed both in space and time, defining a
turbulent regime of capillary waves transferring energy from
large scale to small scale. Analysis of temporal fluctuations of
spatial spectrum demonstrates that the capillary power-law
spectra result from the temporal averaging over intermittent and
strong nonlinear events transferring energy to small scale in a
fast time scale, when capillary wave trains are generated in a
way similar to the parasitic capillary wave generation
mechanism. The frequency and wavenumber power-law exponents of
wave spectrum are found to be in agreement with those of the
weakly nonlinear wave turbulence theory. However, the energy
flux is not constant through the scales and the wave spectrum
scaling with this flux is not in good agreement with wave
turbulence theory. These results suggest that theoretical
developments beyond the classic wave turbulence
theory are necessary to describe the dynamics and
statistics of capillary waves in natural environment. In
particular, in presence of broad scale viscous dissipation and
strong nonlinearity, the role of non-local and non-resonant
interactions could be reconsidered.