Ocean Waves What is a Wave? A response to a generating force (in this case a pebble thrown into a pond) System returns to normal through restoring force (in this case, surface tension of the water) Ripple on Great Pond, Eastham, Massachusetts Laura Perkins Where re the waves?! No good waves in Louisiana Great waves in California Winter waves are best in some regions Waves are better at certain parts of the beach than at others Why? 1
Waves Large waves in certain regions http://www.youtube.com/watch?v=lhkftqxn6 qs Seasonal waves in other places http://www.youtube.com/watch?v=zfjrints7wi &feature=related Louisiana surfing: http://www.youtube.com/watch?v=yd3rlvrz YQg Wave Formation Anatomy of a Wave 2
Wind Waves Dimensions are astonishingly alike, no matter the size of the storm Wave Speed Speed is equal to wavelength divided by period C = L/T» C stands for celerity, another term for wave speed A wave s period always remains the same If wavelength becomes shorter, it slows down If it speeds up, the wavelength has to increase Wave Formation 3
Wave Travel Storm waves are generated by winds and pressure differences within the storm area Within the storm, waves are a jumbled mess of different wavelengths and heights Away from the storm, waves traveling at different speeds separate from the others This results in distinct groups of waves having similar size characteristics Wave Travel Group Speed Group speed is half of the individual wave speed V = C/2 Ripple on Great Pond, Eastham, Massachusetts Laura Perkins 4
Interference Constructive Destructive After point of interference, waves remain unchanged Interference Movement of Waves and Groups Carleton College Oceanography Course 5
Orbital Path No net movement Wave Motion Wave Motion Motion diminishes with depth Depth of wave is equal to half of the wave length D = L/2 Wind speed Wind duration Fetch distance Not enough fetch distance in Miami for big, consistent waves Wave Height 6
How big can Southern LA s waves get? Assume: A tropical storm force wind (58mph) 60 miles between here and the Bahamas Then: How big can Southern LA s waves get? Assume: A tropical storm force wind (58mph) 800 miles between here and the Bahamas Then: Shallow vs. Deep Waves Wave height, steepness, and speed change as a wave comes to shore Interaction with the bottom causes these changes 7
Deep Waves Depth of wave (D = L/2) is less than the depth of the water Speed (C) and period (P) are defined by the storm Wind Strength Wind Duration Fetch Distance Deep Wave does not feel bottom. Shallow vs. Deep Waves Depth of wave is equal to half of the wave length D = L/2 If the depth of the water < L/2 of the wave, it is no longer a deep wave. Shallow Waves Waves feel bottom. D < L/2 Wave slows down (C s < C d ) Wave height increases (h s > h d ) Wavelength decreases (L s < L d ) Speed solely dependent on water depth 8
Shallow Wave Group Movement Carleton College Oceanography Course Shallow Waves Wave Steepness Steepness is the wave s height divided by the wavelength S = H/L Steepness is what causes a wave to break 9
When does a wave break? When the height to wavelength ratio is greater than one to seven H/L > 1/7 Waves Coming to Shore Waves can approach coasts at an angle However, breaking waves almost always seem to be parallel with the coast Curving of Wave Trains The part of the wave that feels bottom first is slowed. The entire wave begins to curve around this slow point. 10
Curving of Wave Trains Energy is concentrated on land points Non-Wind Waves Tides Generated and restored by force of gravity Internal waves In case of ENSO, cause by relaxation of winddriven Ekman mixing of the surface layer (Kelvin waves) Tsunamis Generated by seismic events (earthquakes, landslides, etc.) and restored by gravity Tsunamis Carry huge amounts of energy As deep water waves, H is usually lower than waves generated by storms Hard to detect in the open ocean Large amounts of energy result in a tremendous increase in wave height (H) as the tsunami feels bottom 11
Chilean Landslide Chilean Landslide Chilean Landslide 12
Chilean Landslide Chilean Landslide Chilean Landslide 13
Chilean Landslide Chilean Landslide Chilean Landslide 14
Chilean Landslide Chilean Landslide Chilean Landslide 15
Chilean Landslide Chilean Landslide Chilean Landslide 16
Are tsunami s surfable? Japan Tsunami Japan Tsunami 17
Japan Tsunami Japan Tsunami Hawaiian Tsunami 18
Hawaiian Tsunami Hawaiian Tsunami Hawaiian Tsunami Hawaiian Tsunami 19
Hawaiian Tsunami Causes of Waves Wind Gravity Surface Tension Anatomy of Waves H, L, D, C, v, S Summary Summary Group Travel Interference Matter Transport or Energy Transport? Deep Waves vs. Shallow Waves Wave Height 20
Summary Different types of waves Storm (Wind) Internal Tides Tsunamis 21