Sanae Unoki, Ichiro Isozaki


Indentations of a shoreline or ups and downs of sea bottom form a small oscillating system of water. When the period of natural oscillation in it is near that of advancing sea waves a forced standing oscillation develops there, accompanied by an uneven mean surface level of second order. If the height of the sea waves varies slowly with time, the mean surface fluctuates with the period same as that of the envelope of the sea waves, and such fluctuation will be sent back offshore as a surf beat when it is released by breaking of the original sea waves. The generated long wave seems to be correlated positively or negatively with the envelope of the sea waves, depending on the topography of the basin and the period of the incident sea waves. A possibility of generation of similar long wave in front of a breakwater or a steep beach is also suggested.


surf beats; surf beat generation

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