Freak waves: beyond the Nonlinear Schrodinger breathers

Nowadays, it is well known that one of the mechanisms of formation of rogue or freak waves is the modulational instability. Usually this instability is studied in the framework of exact solutions of the Nonlinear Schrodinger equation, known as breathers. In the present paper we present a new approach to the problem and use the Direct Numerical Simulation (DNS) of the Navier-Stokes equation for a two-phase flow (water-air) to study the dynamics of the modulational instability and its effect on air and water. If the wave steepness of the initial wave is large enough we observe wave breaking and the the formation of large scale dipole structures in the air. Because of multiple steepening and breaking of the waves under unstable wave packets, a train of dipoles is released in the atmosphere at a height comparable with the wave length. The amount of energy dissipated by the breakers in water and air is considered and, contrary to expectations, we observe that energy dissipation in air is larger than the one in the water. Possible consequences on the exchange of aerosols, gasses and wave modelling is discussed.