Physical mechanisms for sporadic wind wave horse-shoe patterns

We consider three-dimensional crescent-shaped patterns often seen on water surface in natural basins and observed in wave tank experiments. The most c ommon of these 'horse-shoe-like' patterns appear to be sporadic, i.e., emer ging and disappearing spontaneously even under steady wind conditions. The paper suggests a qualitative model of these structures aimed at explaining their sporadic nature, physical mechanisms of their selection and their spe cific asymmetric form. (C) Elsevier, Paris.