Wave tank study of “cascade” modulation of bound capillary-gravity waves due to internal waves

A new mechanism of strong (“cascade”) modulation of capillary-gravity waves (CGW) under the action of internal waves was studied in wave tank experiments. The mechanism is connected with so-called bound CGW, which are nonlinear high-order harmonics of short gravity waves (SGW). The simple case of centimetre-millimetre-(cm-mm-) scale bound waves, generated by periodic decimetre-(dm-)scale SGW was investigated. The modulation coefficient of the bound harmonics including “parasitic” capillary ripples generated by SGW has been estimated. It is obtained that the modulation coefficient of bound CGW depends on the steepness of basic SGW and can be almost an order of magnitude larger than the modulation coefficient of SGW