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This 6 page Class Notes was uploaded by Erica on Wednesday September 23, 2015. The Class Notes belongs to BIOEE 1540 at Cornell University taught by Bruce C. Monger in Fall 2015. Since its upload, it has received 77 views.
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Date Created: 09/23/15
Week 3 Wednesday Sept 7th Friday Sept 11TH Ocean Waves Fundamental Principles Wave Parameters Wavelength crest to crest distance Wave Speed distance a wave crest travels per unit time Wave Period time it takes a wave crest to travel one wavelength Wave Frequency number of crests passing a fixed location per unit time rPSNNtquot Waves propagate energy but NOT mass What Determines Wave Speed Deep Water Waves v Shallow Water Waves 1 Wave speed propagation is a function of wavelength and bottom depth Longer wavelength faster travel Deeper water faster travel Under certain circumstances only one dominates the impact on wave speed 0 Very deep water 9 wavelength alone determines speed 0 Very shallow water 9 bottom depth alone determines speed 2 Wave Speeds Deep Water Waves bottom depth is deeper than 12 the wavelength 0 Speed is a function of wavelength only 0 Longer wavelength 9 waves move faster Shallow Water Waves bottom depth is shallower than 1 20 the wavelength 0 Speed is a function of depth only 0 All waves in shallower water move slower 0 Intermediate Waves L 20 lt Depth lt LZ 0 Wave speed is a function of both wavelength and depth Week 3 Wave Dispersion Selfsorting of deep water waves based on wavelength 0 Occurs because longer wavelength waves travel faster Fetch gti Dispersion 7 ll ml ll lllll ll VP Jig J 3 l WU w w H l Seas Ocean swell Wave Pro le Wave Refraction the bending of shallow water wave fronts TOP View wave ray 0 Occurs because of a change in Wm crest A bottom depth 939 s s d o Consequence focusing and defocus1ng of wave energy on 92 bottom 8 headlands and bays W d2 I J Week 3 Breaking Waves Longshore Sediment Transport 0 Occurs when the wave strikes the beach at an angle wave wave height surf zone l crowding moreases ll aquot f wave energr density the top of the wave increases with moves faster than crowding waves and the bottom of the waves slow down Shallowel39 Water wave and the wave as water gets depths push waves eventually spills over shallower upward and breaks Winter and Summer Beach Profiles Summer 0 Gentle waves push offshore sandbar shoreward 9 Creates wide and gently sloping sandy summer beach Winter 0 Storm waves drag sand off the beach to be stored in offshore sandbar 9 Results in a rocky winter beach Ripe Currents 1 Initiated when large waves push water onto an elevated beach face 2 Beached water is funneled back off the beach through narrow breaks in underwater sand bars 9 forms accelerated jets of water rip currents 3 Rip currents can pull a person hundreds of meters offshore 4 Rip currents are seldom wider than about 10 meters Week 3 What Determines Wave Height Determined by Wind s speed duration and fetch Wind Speed 0 Sets the upper possible limit on wave height for a fully developed sea Duration of Wind Event 0 Modulates the upper possible limit on wave height The distance over which wind can blow without obstruction Modulates the upper possible limit on wave height Limited by the size of the storm system in the open ocean Larger fetch effectively gives the storm more time to increase in size of a given wave before the wave propagates out from under the storm center Fetch O O O O 20 U a 15 E E 3 10 cu I cu is 5 i Tsunami Waves 3 45 feet 20 I I I 5 10 15 Wind Speed meters secquot 25 3 60 mph Tsunami wave generation at a convergent plate boundary Indonesian Earthquake December26 2004 japanese Tsunami March 11 2011 Week 3 Internal Waves Travel along density discontinuities in the ocean interior Ocean Tides Equilibrium Theory of Tides Highly idealized but very instructive Equilibrium Tide Theory Daily Patterns diurnal semidiurnal and mixed semidiurnal tidal patterns Monthly Patterns springneap tidal pattern 1 Tide wave is treaded as a deepwater wave in equilibrium with lunar solar forcing 2 No interference of the tide wave s propagation by continents 3 Daily Tidal Patterns 0 Diurnal 1 high amp 1 low tide per day 0 Semidiurnal 2 equal high tides amp 2 equal low tides per day 0 Mixed Semidiurnal 2 unequal high tides amp 2 unequal low tides per day quotTidal Buldges on opposite sides of earth cause the normal risefall of tides over a 1 day period Monthly Tidal Patterns 0 The tidal force that the sun exerts on the earth is about 46 of the tital force that the moon exerts on the earth 0 Spring Tides occur when the moon and sun pull along the same line New and full moon 0 Neap Tides occur when the moon pulls at 90 degrees to the sun First and last quarter moon Dynamic Theory of Tides 1 Tide wave treated as a forced shallowwater wave 0 Not in equilibrium with lunar solar forcing Week 3 0 Tide waves are shallowwater waves Considered a shallowwater wave for depths ltL 20 or bottom depths lt 1000 km 0 Under ideal conditions the tide wave speed would be determined only by ocean bottom depth but this would only be the case if it were a freely propagating wave which it is not 0 Frictional drag slows the tide wave down so the earth spins out from directly under the moon before the tide crest can catch up 0 Result of this the high tide occurs at a time after the moon appears to pass overhead 2 Affected by the Coriolis Force 0 Since tidal waves have the same length scale as the earth and motions are on the order of a day the Coriolis Force has significant effect on the direction of wave propagation Acts exactly to the right of the direction of motion in the northern hemisphere Acts exactly to the left of the direction of motion in the southern hemisphere 3 Coriolis Force causes a rotary motion of a tide wave in a closed ocean basin Rotary tides depicted with cotidal lines Special Cases Tidal ranges can be exaggerated by 0 Forcing ocean water into a narrow embayment o Tidal forcing that is in resonance with the tide wave
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