Laser-like wave amplification in straits

Abstract

We present the research of ocean surface wind waves excitation in non-homogeneous situations, on the example of deep water strait in presence of the constant wind, blowing perpendicular to the coastal line. The used statistical wave model is based on Hasselmann equation with high-wavenumbers wave-breaking dissipation, exact nonlinear four-waves interaction and ZRP wind input term. At the first stage, the waves propagate in the wind direction in a step-like moving front manner, which is the combination of self-similar fetch-limited and duration-limited solutions of Hasselmann equation. The second stage begins further, when sufficient amount of wave energy is concentrated at the incoming waves shore line. Beginning with that time, the nonlinear wave interactions start formation of the wave groups, propagating across and against the wind. Despite the absence of long-wave dissipation, the system asymptotically evolves into complicated quasi-stationary state, comprising of the self-similar ``wind sea'' in the wind direction, and quasi-monochromatic waves, radiated close to orthogonally with respect to the wind, while slightly tilting counter the wind direction with the angle increasing toward the wave turbulence origination shore line, and reaching $15^{\circ}$ close to it. The total wave energy in the asymptotic state surpasses the wave sea energy propagating along the wind by two times due to the presence of quasi-orthogonal and counter the wind wave fields. The very similar turbulence structure was previously observed experimentally, this paper presents theoretical explanation of these results. It is suggested to name this laser-like radiation phenomenon by Nonlinear Ocean Waves Amplifier, simplified to the abbreviation NOWA.