1 / 39

Tides

Tides. http://www.montereyinstitute.org/noaa/lesson10.html. Essential Points. Tides occur because the Sun and Moon pull stronger on one side of the earth than the other There are two tidal bulges on opposite sides of the Earth Solar and Lunar tidal effects can reinforce or weaken each other

aliza
Download Presentation

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. Tides

  2. http://www.montereyinstitute.org/noaa/lesson10.html

  3. Essential Points • Tides occur because the Sun and Moon pull stronger on one side of the earth than the other • There are two tidal bulges on opposite sides of the Earth • Solar and Lunar tidal effects can reinforce or weaken each other • Actual tide motions in the oceans are very complex and are affected by landforms and the Coriolis effect, among other things.

  4. https://www.uwgb.edu/dutchs/EarthSC102Notes/102TheOceans.HTM

  5. Why are there tides? Because of the uneven gravitational pull of the Sun and the Moon

  6. The Earth and Moon’s orbits are not complete circles but elliptical. Aphelion is when the Earth is furthest away from the Sun. Perihelon is when it is closest. Apogee is when the Moon is furthest away from the Sun, perigee is when it is closest. These affect the height of the tides.

  7. Both Moon and Sun Cause Tides High tide occurs when the Moon is overhead. Low tide is when the Moon is 90° from overhead. There are two high and low tides every day. The Sun also causes tides but the Sun's effect on Earth is half the Moon's because of its distance. The highest tides occur when the Earth, Sun, and Moon are in a line (new and full Moon). The smallest tides occur when the Moon is in either quarter phase.

  8. Animation: http://www.wiley.com/college/strahler/0471480533/animations/ch19_animations/animation3.html

  9. Spring Tides • New or Full Moon • Sun and Moon Pulling in Parallel Directions • Lunar and Solar Tides Add Up • Unusually Large Tidal Range • Neap Tides • First or Last Quarter • Sun and Moon Pulling At Right Angles • Lunar and Solar Tides Partially Cancel • Unusually Small Tidal Range

  10. Why there are 2 bulges: Moon's gravity pulls the ocean. The Moon and Earth actually orbit around the Earth-Moon centre of mass (about 1500 km beneath the surface of the Earth) Motion of Earth around centre of mass creates a bulge on the far side of the Earth

  11. Both Moon and Sun Cause Tides

  12. The Earth takes 24 hours to rotate so an observer at point A would see the tide go from high tide to low tide twice and back to high tide. The interval between one high tide and the next is about 12 hours 25 minutes. The extra 25 minutes is due to the movement of the moon.

  13. Waves

  14. Essential Points • Waves are created by the wind • Water in waves oscillates but does not move with the wave • Waves move energy, so ocean waves move energy across the ocean. • What happens when waves hit the shore • Storm surges can be catastrophic

  15. Waves move energy, so ocean waves move energy across the ocean. Energy is moving at the speed of a wave but the water is not moving with the wave. A seagull bobbing on the waves moves in circles, each circle equal in diameter to the wave’s height.

  16. Energy is transferred in these circular “orbits”. Orbital ocean waves occur at the boundary between 2 different media such as air and water or layers of water of different densities. Wind waves have relatively small wavelengths.

  17. Note: water in a wave oscillates but does not move with the wave.

  18. The circular motion of water particles continues under water. The diameters of the orbits reduce in size. At half a wavelength deep the motion has almost stopped.

  19. Waves travel in groups called wave trains. The leading wave continuously disappears, while a new wave is continuously formed at the back of the train. The wave train travels at half the speed of any individual wave. Follow wave number 5.

  20. Wind waves are formed by the transfer of wind energy into water. Wind waves grow from the friction of wind on the surface forming ripples, or capillary waves. The capillary waves deflect and slow the surface wind causing some of the wind’s energy to be transferred into the water, driving the wave forwards (a). More energy is added at (b)

  21. The larger waves are mature, regular wind waves and the tiny ripples are capillary waves.

  22. The most common waves are caused by wind. • Three factors affect the growth of wind waves. • Wind strength – the wind must be moving faster than the wave crests for energy to transfer from air to sea • Wind duration – the length of time a wind blows; high winds that blow only a short time don’t generate large waves • Fetch - the uninterrupted distance over which the wind blows.

  23. A strong wind must blow continuously in one direction for nearly 3 days for the largest waves to develop fully. • A fully developed sea has the maximum wave size possible for a wind of specific strength, duration and fetch. • Longer exposure to wind at that speed doesn’t increase the waves because energy is lost due to the breaking of wave tops.

  24. The largest waves occur in the Southern Ocean because there is virtually nothing to stop the winds. Waves can get over 11 metres in height. Waves don’t get high in cyclones because the circular motion of air means that there is not much fetch.

  25. This map shows global wave height showing that the largest waves occur in the Southern Ocean. The wind is least in tropical and subtropical oceans.

  26. This shows an internal wave that forms between water of different densities, especially at the base of a pycnocline. These usually have different wavelengths from the surface waves.

  27. Wind wave height is related to wavelength. Moderate sized wind waves in the open ocean have a maximum ratio of 1:7 wave height to wavelength. This ratio is the wave steepness. Waves 7 metres long will not be more than 1 metre high. If a wave gets any higher than 1:7 it will break. Excess energy will become whitecaps and turbulence.

  28. Waves and wave trains can interfere with each other when they meet. 2 overlapping waves of different wavelengths are shown here. At 1 the crests and troughs will be larger. At 2 the crests and troughs will be small.

  29. http://www.kettering.edu/~drussell/Demos/superposition/superposition.htmlhttp://www.kettering.edu/~drussell/Demos/superposition/superposition.html

  30. A wave train breaks against the shore. The swell “feels” bottom when the water is shallower than half the wavelength. The wave crests become peaked because the wave’s energy is packed into less water depth. The circular wave motion interacts with the ocean floor and slows down the wave. The waves behind stay at their original speed. Wavelength shortens but period stays the same. The wave height increases until it nearly reaches 1:7. Wave breaks when ratio of wave height to water depth is about 3:4.

More Related