Oscillating crescent-shaped water wave patterns

A new type of persistent three-dimensional crescent-shaped water wave patterns was found experimentally in the laboratory. The particular features of the patterns are their oscillating character and the regular orthogonal grid the crescent crests form in the plane view. They emerge from a steep initially two-dimensional paddle-generated wave amplified by wind. The patterns are composed of the basic wave and two nonsymmetric oblique satellites with longitudinal components of wavevector equal to that of the basic wave and twice this wave number. The main mechanism of their formation was identified to be a five-wave resonant interaction process. However, the mechanism of the sharp selection of these particular harmonics was found not to be explained within the framework of existing theories. (C) 1999 American Institute of Physics. [S1070- 6631(99)02411-3].