1 / 70

07 Waves & Tides

07 Waves & Tides. I. Nautical terms and definitions A. NAUTICAL MILE 1. Unit of measurement used by all nations for air and sea travel 2. Based on the circumference of the Earth.

eldon
Download Presentation

07 Waves & Tides

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 07 Waves & Tides

  2. I. Nautical terms and definitions A. NAUTICAL MILE 1. Unit of measurement used by all nations for air and sea travel 2. Based on the circumference of the Earth. a. The equator is a circle going around center of the Earth such that it cuts the planet into 2 equal halves b. That circle is divided into 360 arcs or “degrees” c. Each degree is subdivided into 60 arcs or “minutes”

  3. A. NAUTICAL MILE (continued) • A minute of the Earth’s equator is 1 nautical mile. • A nautical mile is 1.85 kilometers or 1.15 miles

  4. I. Nautical terms and definitions (continued) B. KNOT 1. Unit of measurement of speed 2. One knot = 1 nautical mile per hour 3. The term “knots per hour” is incorrect as it would literally mean “nautical miles per hour per hour”

  5. I. Nautical terms and definitions (continued) C. CURRENT 1. A body of water moving in a definite direction 2. Currents can be generated by… a. …breaking waves b. …wind c. …Coriolis effect d. …temperature and salinity differences e. …tides

  6. C. CURRENT (continued) 3. A current’s direction can be affected by… a. …depth contours b. …shoreline configurations c. …interactions with other currents

  7. I. Nautical terms and definitions (continued) D. WAVE 1. A disturbance or oscillation that travels through a medium accompanied by a transfer of energy. 2. The transfer of energy from one point to another, often occurs with NO permanent displacement (= movement) of the medium’s particles

  8. Diagram of a floating seagull demonstrating how a wave will travel, but the molecules of water or structures floating in the water do not. Garrison, T. 2007, Oceanography, Fig. 10.1, p. 266

  9. Garrison, T. 2007, Oceanography, Fig. 10.3, p. 267

  10. D. WAVE (continued) 3. Anatomy of a wave a. CREST: Highest part b. TROUGH: Lowest part c. HEIGHT: Vertical distance between the top of a crest and the bottom of an adjacent trough d. WAVELENGTH: Horizontal distance between 2 adjacent crests or 2 adjacent troughs e. FREQUENCY: Number of crests passing a stationary point per second f. PERIODICITY: Time required for a crest to move one wavelength

  11. Garrison, T. 2007, Oceanography, Fig. 10.2, p. 266

  12. D. WAVE (continued) 4. What causes waves to “break”? a. As wave approaches shore, friction with the bottom slows movement of deeper portion of wave. b. Consequently, the wave’s crest now moves faster than the lower portion of wave c. Lower portion can no longer support the crest d. Instability occurs when depth is about 1/20 of wavelength

  13. Garrison, T. 2007, Oceanography, Fig. 106, p. 269

  14. D. WAVE (continued) 5. What is the energy source for waves? a. Wind generates ocean waves b. Sudden, significant displacements of the earth’s crust (= earthquakes) generate tsunami waves (misnamed “tidal waves”)

  15. D. Wave (continued) 6. ROGUE WAVES a. Occasionally waves much larger than average will “suddenly” appear and sweep the beaches

  16. Many beaches along the US west coast such as this one in Central California are bordered by steep cliffs. Beachwalkers are in danger of being swept away during a sudden appearance of a rogue wave series Photo Jack O’Brien, July, 2013

  17. 6. Rogue Waves (continued) • b. Example: Mavericks Surf Contest, Half-Moon Bay, CA (February, 2010) • The Mavericks Surf Contest offers a $150,000 purse…even though it is held only when conditions are prime…Tim West estimated the waves were 20 to 25 feet measured from the back, with 40-foot faces…

  18. b. Example: Mavericks Surf Contest, (continued) • …Despite big wave warnings, two walls of water caught dozens of spectators off-guard and knocked them to a rocky beach…Thirteen people swept from a seawall had significant injuries, including broken legs and hands.

  19. 6. Rogue Waves (continued) • c. Occur when beach waves originate from more than one oceanic storm source. • (1) Arrival of waves is not synchronous • (2) When the crest from a wave from Storm #1 arrives at same time as the trough of a wave from Storm #2, their effects on wave heights are cancelled. • (3) When the crest from a wave from Storm #1 arrives at same time as the crest of a wave from Storm #2, their effects on wave height are doubled.

  20. 6. Rouge Waves (continued) Trough 1 + Trough 2 Trough 1 + Crest 2 Crest 1 + Crest 2 Storm #2 Storm #1

  21. diurnal semidiurnal Tide types & vertical ranges in North America

  22. II. Tides are generated by gravitational pull exerted by 2 bodies in earth’s solar system A. Gravitational force is… 1. …directly proportional to mass 2. …inversely proportional to square of distance B. Moon’s effect on earth’s tides is much greater than the effect of the sun C. Sun’s effect is less because of its greater distance from earth

  23. III. Tidal height determined by the relative position of the sun & moon to earth A. Water bulges toward sun and moon B. Secondary bulges 1. Side away from moon & sun 2. Maintained by centrifugal force C. Low tides occur between bulges

  24. III. Relative Position (continued) D. Moon rotates around earth in 24 hours & 50 minutes (= not exactly 24 hours) 1. Ideally, there are 2 highs & 2 lows every tidal cycle 2. Tidal heights and timing are affected by… a. …barriers to water movement caused by topographical & geographical features b. …angle of moon’s orbit around earth relative to the sun’s position

  25. IV. Types of tides A. Monthly cycle 1. SPRING TIDES a. Sun aligned with moon b. Greatest highs and lows during full & new moons c. Crests and troughs of tidal bulges overlap with one another

  26. Greatest tidal highs & lows occur when sun & moon are aligned

  27. A. Monthly cycle (continued) 2. NEAP TIDES a. Sun is positioned 90° to moon during quarter moons b. Minimum vertical range c. Tidal bulges cancel each other

  28. Least differences in tidal heights occur when sun & moon are at a right angle to one another

  29. IV. Types of tides (continued) B. Daily cycles 1. DIURNAL TIDE [DIURNAL = day] a. One complete cycle in a day b. One high tide and one low tide per day c. Common in the Gulf of Mexico

  30. B. Daily tide cycles (continued) 2. SEMI-DIURNAL TIDE [SEMI = ½] a. Two complete cycles in a day b. Two approximately equal high tides c. Two approximately equal low tides d. Typical of tides on Eastern Coast of U.S.

  31. B. Daily tide cycles (continued) 3. MIXED SEMI-DIURNAL TIDE a. Two complete tidal cycles in a day, but… b. The 2 highs and 2 lows are NOT equal c. There is a “high high”, a “low high”, a “high low, and a “low low” c. Typical of tides on West Coast of U.S.

  32. V. Local topography/geography can significantly influence water height A. Water oscillates in semi-enclosed basins (“sloshes” back and forth as it does in a bathtub)

  33. Topography can significantly influence water height (continued) • TIDAL BORE • 1. Occurs when the leading edge of the incoming tide forms a standing wave of water that travels upstream

  34. http://www.google.com/imgres?imgurl=http://bayoffundy.com/assets/tidal-bore-wave1.jpg&imgrefurl=http://bayoffundy.com/about/tidal-bore/&h=200&w=300&sz=50&tbnid=qVSGExgqeepPhM:&tbnh=93&tbnw=140&prev=/search%3Fq%3Dtidal%2Bbore%2Bpictures%26tbm%3Disch%26tbo%3Du&zoom=1&q=tidal+bore+pictures&usg=__Ia3gEaqvv39MViFrCJ7P0Nt2Jb4=&docid=trW9daoDsvYSNM&sa=X&ei=hPDFUfq7O5HC9gTqioGIBw&ved=0CDwQ9QEwBQ&dur=2112#imgdii=qVSGExgqeepPhM%3A%3Buk7oHrfPTBGojM%3BqVSGExgqeepPhM%3Ahttp://www.google.com/imgres?imgurl=http://bayoffundy.com/assets/tidal-bore-wave1.jpg&imgrefurl=http://bayoffundy.com/about/tidal-bore/&h=200&w=300&sz=50&tbnid=qVSGExgqeepPhM:&tbnh=93&tbnw=140&prev=/search%3Fq%3Dtidal%2Bbore%2Bpictures%26tbm%3Disch%26tbo%3Du&zoom=1&q=tidal+bore+pictures&usg=__Ia3gEaqvv39MViFrCJ7P0Nt2Jb4=&docid=trW9daoDsvYSNM&sa=X&ei=hPDFUfq7O5HC9gTqioGIBw&ved=0CDwQ9QEwBQ&dur=2112#imgdii=qVSGExgqeepPhM%3A%3Buk7oHrfPTBGojM%3BqVSGExgqeepPhM%3A

  35. B. TIDAL BORE (continued) 2. Water is pushed up when it… a. …encounters a current from a river b. …enters into the narrow upper portion of a funnel-shaped bay

  36. http://bayoffundy.com/about/tidal-bore/

  37. B. TIDAL BORE (continued) 3. Tidal bores occur during FLOOD (= rising) tides, never during EBB (= lowering) tides. 4. Bay of Fundy is a classical example

  38. 46 ft 51 ft 25 ft 9.5 ft Spring tidal heights at localities in the Bay of Fundy

  39. V. Topography can significantly influence water height (continued) C. Most of the damage in Mobile Bay from Hurricane Katrina occurred in the Dog River watershed 1. Height of storm surge increased as water was pushed up into the bay. 2. Strong winds from the east drove water up into Dog River destroying boats and water front property 3. Impact of Katrina was not as great in areas north, south and east of Dog River (Causeway did flood)

  40. Causeway Dog River Mobile Bay

  41. V. Topography can significantly influence water height (continued) D. Hilo, Hawaii 1. Faces the earthquake-prone western coasts of North and South America

More Related