Phase modulation of short wind waves by long waves

Laboratory Experiments were conducted in a water-wave tank to explore the phase modulation of short wind waves in particular in their high-frequency spectrum by monochromatic,mechanically generated long waves (LW).Using the intrinsic mode decomposition (IMD) method,the observed surfacee levation tmie series is decomposed into a set of intrinsic mode functions (MIFs) that can be related to short wind waves with different oscillation scales,and the squared amplitudes of MIFs are phase averaged along the profile of LWR esults show that the energy distributions of short wind waves with different oscillation scales present different characteristics.The dominant wind wave energy decreases with the increase in the LW steepness,which is distributed in-phase with the LW and symmetric with respect to the LW trough.In contrast,the mesoscale wind wave energy increases with the increase in the LW steepness.The energy of the upwind quadrant of the LW is slightly higher than that of the downwind one.Finally,the energy of high frequency wind waves also increases with the increase in the LW steepness,but decreases with the increase in the fetch length.The energy of the upwind quadrant of the LW is significantly higher than that of the down wind one.