Evolution of a narrow-band spectrum of random surface gravity waves

Numerical simulations of the evolution of gravity wave spectra of fairly narrow bandwidth have been performed both for two and three dimensions. Simulations using the nonlinear Schrodinger (NLS) equation approximately verify the stability criteria of Alber (1978) in the two-dimensional but not in the three-dimensional case. Using a modified NLS equation (Trulsen et al. 2000) the spectra 'relax' towards a quasi-stationary state on a timescale (epsilon(2)omega(0))(-1). In this state the low-frequency face is steepened and the spectral peak is downshifted. The three-dimensional simulations show a power-law behaviour omega(-4) on the high-frequency side of the (angularly integrated) spectrum.