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ment in case 1413 is considerably higher than that of the segment with
similar wind speed but in the absence of internal waves or surface slicks
(Fig. 3).
Fig. 3:
The ratio
B
III
(
k
)/
B
I
(
k
), as a representation of the modulation amplitude,
plotted as a function of
k
.
4 Discussion and conclusions
Using a free-drifting scanning slope sensor system, the wave number spec-
tra of surface roughness in the vicinity of an internal wave soliton were
measured. Associated with the internal wave event were two persistent lin-
ear slick bands. The surface roughness responded to the surface current
strain induced by the internal wave and displayed high roughness spikes at
the leading and trailing edges of the soliton. The response of the observed
roughness modulation has certain similarities with observations of internal
waves by synthetic aperture radars (Hughes and Gower 1983, Hughes and
Dawson 1988, Thompson and Gasparovic 1986). It is believed that the
primary mechanism is the modulation of short waves by straining of sur-
face current induced by the internal waves.
Interestingly, the amplitude of spectral modulation increased toward
higher wind speed and wave number (Fig. 3). This trend is opposite to the
prediction of the relaxation theory that assumes a monotonic increase in
