Keywords. Currents, Unidirectional; Spectra; Theory; Waves, Wind. 



Discussion . Interactions between steady nonuniform currents and gravity 

 waves are generalized to include the case of a random gravity wave 

 field. The Kitaigorodskii-Pierson-Moskowitz frequency spectrum is used 

 as the basic spectral form for zero current condition. Modified spec- 

 tral functions in both wave number and frequency spaces under the 

 influence of current are found by using energy conservation and kine- 

 matic wave conservation laws. The relative importance of the current- 

 wave interaction was measured by the nondimensional parameter U/C , with 

 U as the current speed and Cq the phase speed of a wave under no 

 current. As a result of the current-wave interaction, the magnitude and 

 the location of the energy peak in the spectrum are altered. 



Since the phase speed of gravity waves is a monotonically 

 decreasing function of wave number and frequency, the influence of 

 current will be predominant at the higher wave number range. Further- 

 more, the contribution from the higher wave number range dominates the 

 surface slope spectrum; the current conditions change the surface slope 

 pattern drastically. This phenomenon is studied by use of Phillips' 

 equilibrium range spectrum in wave number space. It was found that the 

 root-mean-square (rms) surface slope is extremely sensitive to the 

 change of current conditions especially for the case of adverse current, 

 but eventually becomes saturated at a high positive value. The surface 

 slope data together with a generalized dispersion relation offer a 

 possible current measurement technique which appears ideally suited for 

 remote -sens ing devices such as stereoscopic photography and radar 

 scattering. (author's abstract) 



Coastal Engineering Significance. This is one of the few investigations 

 of the effect of current on the generation of wave spectra (see also 

 GADZHIYEV, KITAYGORODSKIY, and KRASITSKIY, 1978). The findings that 

 opposing currents produce a high surface slope and that this slope 

 approaches an equilibrium value are in agreement with intuitive expec- 

 tations. The authors suggested that slope and dispersion relations can 

 be used in satellite observation of waves. This suggestion has been the 

 object of many subsequent studies. 



21. HUGHES, B.A., and GRANT, H.L., "The Effect of Internal Waves on 

 Surface Wind Waves 1. Experimental Measurements," Journal of 

 Geophysical Research, Vol. 83, No. CI, Jan. 1978, pp. 443-454. 



Keywords. Currents, Wave-Induced; Experiment; Observation; Waves, Wind. 



Discussion. The paper describes a combination of experiment and field 

 observation. Initially a research vessel generated internal waves by 

 proceeding slowly through an area with a layer of relatively freshwater 

 at the sea surface. Then, after about 5 minutes, the ship traveled 

 through the group of internal waves with measuring instruments in 

 position. 



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