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Ocean waves lecture
Ocean waves are characterized by their amplitude, wavelength, frequency, and period. Amplitude refers to the height of the wave from still water level to the crest. Wavelength is the distance between two identical points on successive waves. Frequency is the number of waves passing a fixed point per second, while period is the time for one full wave cycle. Wave height depends on factors like fetch (distance over water the wind blows) and breaking occurs when the wave steepness exceeds about 1/7. Breaking waves can be spilling, plunging, or surging.
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Ocean waves lecture
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- 2. Wave characteristics Average level 1cycle 1 cycle Cycle = one unit of a wave 1 cycle = one complete wave Crest Trough
- 3. Wave characteristics Amplitude andHeight Amplitude 1 cycle Height Significant Wave Height (Hs) = average height of the one-third highest waves Height
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- 5. Wave characteristics Frequency =how often the wave repeats itself (cycles) in one second. Frequency = cycles per second = Hertz (Hz) e.g., 4 Hz = 4 cycles /second 1st 1 sec. 4th
- 6. Wave characteristics Period =the time it takes for a wave to complete one cycle. period .01 Time (sec.) e.g., Period = 10 sec Frequency = 1 = .10 Hz 10 Formula: f = 1 p p = 1 f High frequency = small period Low frequency = large period 10 20
- 7. Wave formation Fetch =distance traveled by wind across open water.
- 8. Wave formation Fetch =distance traveled by wind across open water.
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- 10. Particle displacement – Waveorbitals
- 11. Particle displacement – Waveorbitals
- 12. Particle displacement – Waveorbitals Stokes Drift
- 13. Wave particle displacement- Longitudinal
- 14. A wave movingonto the shore
- 15. A wave movingonto the shore
- 16. A wave movingonto the shore
- 17. A wave movingonto the shore
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- 21. Wave refraction • Waverefraction • Bending of a wave • Causes waves to arrive nearly parallel to the shore • Consequences of wave refraction – Wave energy is concentrated against the sides and ends of headlands – Wave energy is spread out in bays and wave attack is weakened – Over time, wave erosion straightens an irregular shoreline
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- 24. When do wavesbreak? – Limited by ratio between wave height and wave length (H/L) – Limiting steepness 1/7 How are they predicted? – wave forecasting (or hindcasting) depends on wind velocity, duration, and fetch (WaveWatch III) – Linear wave theory predicts wave heights Breaking Waves http://polar.ncep.noaa.gov/waves/wavewatch/
- 25. Breaking Waves • Spilling •Plunging • Surging
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- 33. Wave erosion • Breakingwaves exert a great force • Wave erosion is caused by ‒ Wave impact and pressure ‒ Abrasion by rock fragments
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- 37. Wave periods • Largerwave period = higher energy = higher wave • Wave height is limited by ratio between wave height and wave length (H/L) • Limiting steepness 1/7
- 38. Garret McNamara on100 ft wave in Portugal 2014
- 39. Rogue Waves Rogue wavescan form from merging waves or strong wind and waves plus opposing currents
- 40. 100 ft+ roguewave in Southern Ocean Rogue Waves
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