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Lesson 9: Waves Physical Oceanography

Lesson 9: Waves Physical Oceanography. Last class we learned about currents. What two major types of currents are there? What is thermohaline circulation? Which current moves north along the U.S. East Coast (from Florida to North Carolina)?.

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Lesson 9: Waves Physical Oceanography

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  1. Lesson 9: Waves Physical Oceanography

  2. Last class we learned about currents • What two major types of currents are there? • What is thermohaline circulation? • Which current moves north along the U.S. East Coast (from Florida to North Carolina)?

  3. You may be familiar with another type of water movement in the ocean: waves This wave is breaking over the bow of a NOAA ship Today we will learn about the physical forces that cause waves to form and to break Photo: NOAA

  4. Understanding wave physics is important for human life (and not just for surfing) 1. A wave is the transmission of energy through matter – in this case through water • Two important types of waves are deepwater and shallow-water waves • Do you know what a tsunami is?

  5. A wave is transmission of energy through matter • When energy moves through matter, like water, matter moves and returns to its initial position • The energy is transmitted to its adjacent surroundings – in this case, adjacent water particles • Transmission of energy through the water moves the water particles in a circle motion known as orbital motion Wave Orbital motion

  6. H:L is the ratio of wave height to wavelength Period (T) refers to the time it takes for the same spot on two consecutive waves to pass the same point Speed = L/T Some important features of a wave Crest is the highest point of the wave Wavelength is the distance between identical points on two waves, from crest to crest Wave height is the distance from trough to crest Trough is the lowest point of the wave Photo: Navy

  7. There is more than one type of wave Note: D = water depth; L = wavelength • Deepwater waves occur when water depth is greater than 1/2 wavelength (D > 1/2 L) • Shallow-water waves occur when water depth is less than 1/20 wavelength (D < 1/20 L) • Shallow and deepwater waves can occur at the same time

  8. What is a tsunami? • A typical tsunami wavelength is several hundred miles long, as an example let’s say wavelength is 400 miles • The deepest part of the ocean is 7 miles deep • Based on this information, do you think a tsunami is a shallow or deep water wave?

  9. What is a tsunami? • L = 400 miles, D = 7 miles • D < 1/20 L • Tsunamis are shallow water waves! The ocean would have be deeper than 200 miles on average for a tsunami to be a deep water wave! • A tsunami is a shallow-water wave triggered by displacement of a large amount of water

  10. How does a wave break? The top part of the wave moves faster than the bottom The height of the wave increases As a deepwater wave moves toward shore, its wavelength decreases H:L ratio> 1:7 When the wave meets the ocean floor, the bottom of the wave slows The faster-moving top of the wave crashes over causing the wave to break. This happens as the wave depth gets closer to the wave height. (H:L ratio is greater than 1:7)

  11. Why is it important to know so many details about waves? • Waves can be very destructive • A tsunami is one type of destructive, shallow-water wave • Studying the causes and forces underlying waves can help scientists predict the timing and magnitude of these events and potentially save lives!

  12. Can you outrun a tsunami? • In today’s activity you will use wave information to calculate the speed of impending tsunamis • About how fast do you think tsunamis move? • Let’s find out…

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