WAVE PERIODS

(Oceanography) Wind generates waves that have a wide range of periods; it is responsible for pure capillary waves (ripples), which have periods less than 0.1 second, and for most gravity waves, which have periods from 0.1 second to approximately 30 seconds. Wind-driven gravity waves contain, on the average, more energy than waves of any other period. Seas (waves being actively generated by the wind during a storm) have periods of 4-10 seconds, and swells (waves that have radiated from the wind storm) have periods of 10-30 seconds. Wind storms are also responsible for waves with periods longer than 30 seconds; these storms excite Seiches (standing waves that do not move forward but instead move up and down) whose typical periods range from 5-10 minutes, and storm surges (large waves having periods from 1-100 hours).