Chemistry Reference
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when the water surface was agitated by rain (
Figure 4
f). The (non-ori-
ented) ring waves, which are generated by the rain, cause a strong reduc-
tion of the NOR in the frequency range between 3 and 12 Hz (which is the
characteristic frequency range of the ring-wave spectrum, see Bliven et al.
(1997)).
Fig. 2.
Frequency dependence of the normalised orientation ratio, NOR (see (1)),
measured with the two-dimensional laser slope gauge at different wind speeds
(columns) without rain (upper row) and with rain at a rain rate of R = 160 mm h
-1
(lower row). The water surface was covered with oleyl alcohol
At 7 m s
-1
(Figures 4c and g) we measured a rain-induced decrease in
the NOR also at higher frequencies (i.e., up to 25 Hz, compare Figure 4g).
On the one hand, the high-frequency part of the wave-slope spectrum is
strongly damped by the slick, particularly, those waves which are travel-
ling in crosswind direction (and which are not directly generated by the
wind). On the other hand, the high-frequency part of the ring-wave spec-
trum causes an additional reduction of the NOR at higher frequencies.
Thus, the observed effect is caused by the two counteracting effects de-
