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Lecture 20-23 Waves

# Depends on the speed of the wind and how long it

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Unformatted text preview: r’s surface l༆  ConHnual wind blowing will create an eddie upstream of the wave’s direcHon with a parHal vacuum…..meaning air pressure can push down on the wave front and increase it l༆  Greater than this wavelength the wave becomes a gravity wave 15 2. Wind Waves l༆  Gravity is the primary restoring force in a wind/gravity wave l༆  Wave will conHnue to grow if wind conHnues AND water depth > ½ the wavelength i.e. fricHon on the sea boMom does not rob the wave of energy l༆  Stability of gravity waves requires steepness raHo of < 1:7 AND angle at wave peak is >120° 16 Wave Trane 17 Wave Trane l༆  First wave has to DO WORK to liy the water ahead of it l༆  Its energy therefore dissipates and the wave disappears to be replaced by one behind it l༆  This therefore slows the overall speed of travel of the wave set or wave train l༆  Speed of movement of the wave train = 50% of speed of individual wave l༆  The waves themselves DO NOT travel forever but dissipate to be replaced by newly created waves behind them 18 l༆  Maximum height? Depends on the speed of the wind and how long it blows for. l༆  Greatest waves therefore in areas where water has travelled far with a prevailing wind: Portugal, BC, Hawaii, Southern Ocean…..prevailing winds! l༆  hMp://www.youtube.com/watch?v=OjPGCMRBwK0 l༆  “Fully developed sea” means waves reach maximum height aMainable given wind speed, direcHon and fetch l༆  Fetch is the length of water over which wind has blown l༆  Waves of 30m in height are possible 19 20 Rogue Waves l༆  Occur when diﬀerent wave sets are present in the same ocean basin 21 22 Wave Fetch l༆  Distance...
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