Chemistry Reference
In-Depth Information
wave height frequency spectra at two fetches are shown in Figure 3a, de-
monstrating that the frequencies of the dominant waves are different at the
large and small fetches, 4.7 Hz and 5.3 Hz, respectively.
The phase velocities of wind waves obtained from measurements using
the MOSA are presented as functions of the wave numbers in Figure 3b.
Note that in this set of experiments the parameter
L
of the MOSA was cho-
sen to be 10 cm. A theoretical dependence of the phase velocity of free
surface waves accounting for the wind drift are also presented in Figure 3b
at a drift velocity
V
dr
of 4 cm s
-1
. It follows from Figure 3b that the phase
velocities of cm-mm-scale wind waves do not obey the dispersion relation-
ship for free waves, being larger and increasing more slowly with wave
number in the range from about 2 rad cm
-1
to 10 rad cm
-1
than free waves.
The phase velocities in this wavelength range also increase with fetch (one
should remind that the phase velocities of the dominant waves, according
to the dispersion relationship of free surface waves, are larger at the large
fetch than at the small one). Both of these facts support the existence, in
the wind wave spectrum, of bound harmonics which propagate with the
phase velocity of the dominant waves. Note, that for better frequency reso-
lution in the spectrum of the MOSA signal we could discriminate between
peaks corresponding to free and bound waves at a given wave number.
However, in our experiments we determined only weighted mean of phase
velocities.
