Jin Wu 
long gravity waves. Later, slow moving short waves are considered 
(Longuet-Higgins 1969) to be swept through by fast-moving long waves 
and to lose their energy to the long waves ata rate proportional to the 
orbital velocity in the long waves. More recently, Hasselmann (1972) 
found that the work done on the long waves through the sweeping is 
balanced by the loss of potential energy due to taking mass of high 
potential energy from the crests of long waves and returning it ata 
lower potential level in the troughs. The dynamics of nonlinear inter- 
action of oceanic waves is therefore rather confused. However, all 
of these models are based on one common phenomenon : long waves 
sweeping through short waves and causing short waves to break on 
the forward faces of the longwave crests. Some physical evidence 
substantiating this basic phenomenon has been obtained through photo- 
graphs of glitter patterns (Wu 197Ib). 
Figure 13 shows that the minimum radius of curvature is 
observed at a positive angle for all of the wind velocities. The mini- 
mum radius of curvature is undoubtedly produced by crests and 
troughs of the shortest waves. The present results therefore seem 
to confirm earlier observations and conclusions that waves with the 
smallest radii of curvature, very likely produced by nonlinear wave- 
wave interaction, ride on the forward faces of long carrier waves 
having positive slopes. In other words, the skewed shape of the angu- 
lar distribution of average radius of curvature is probably due to the 
nonlinear wave-wave interaction. 
V.5 Low and high grazing angles for back scattering. 
The reflection and back scattering of electromagnetic waves 
impinging on the air-sea.interface depend on the sizes of the specu- 
lar areas, The latter can be described statistically by the average 
radius of curvature. The distribution of the size of the specular areas 
was considered by Schooley (1955) to be substantially the same for 
all slopes. The results, obtained here and shown in figures 13 and 14 
suggest that this earlier consideration may be approximately true for 
the ocean surface and at limited angles near the normal to the hori- 
zon. As discussed in the previous section, the skewed angular distri- 
bution of surface curvature seems to be as expected as a result of 
parasitic capillaries at medium wind velocities and of nonlinear wave - 
wave interaction at high wind velocities. 
The measurements for the three highest wind velocities are 
most interesting for practical application, because the surface struc- 
tures for these three cases are believed to be very similar to the air- 
sea interface. As shown in figures 13 and 14, and stated in the pre- 
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