On the interaction between surface and internal waves

General modulation equations describing the effect of subsurface currents induced by internal waves on nonlinear surface waves are derived by using the method of multiscale asymptotic expansions. The numerical solution to the problem of a one-dimensional wave interaction is found under conditions close to the group velocity resonance. Smoothing of the down current surface waves at a current induced by internal waves is shown to be accompanied by a high-frequency envelope modulation while the profile of the opposing current is reproduced by the wave envelope. Long surface waves can form the wave modulation forerunner going ahead of the internal wave, while relatively short surface waves create the trace of the internal wave.