What term describes the separation of wind waves by wavelength as they move away from the fetch?

• A. Dispersion
• B. Refraction
• C. Diffraction
• D. Interference

Answer: (A)

Dispersion is the process by which waves of different wavelengths travel at different speeds, causing a wave train to spread out and separate as it moves away from the wind fetch. For gravity waves in deep water, longer wavelengths travel faster than shorter ones because phase speed increases with wavelength. As the fetch-origin waves propagate, the longer components pull ahead while the shorter ones lag, so the spectrum becomes sorted by wavelength. This is different from refraction, which is a change in direction due to varying depth; diffraction, which is bending around obstacles; and interference, which is the combination of waves that can reinforce or cancel each other. So the separation by wavelength described here is dispersion.