Tides

1. Tides Created by Michael Kramer

2. What is a Tide? • Tides are periodic, short term changes in height of the ocean surface at a particular place, caused by a combination of the gravitational force of the moon and un and the motion of Earth. • The wavelength of an average tide can be up to 17,500 km • They are the longest of all ocean waves • They are also called forced waves

3. Why are Tides Important? • They’re in the ocean, which means it’s in oceans bowl, and oceans bowl is very important! • Actually, tides play an important role in the life cycle of many organisms • Gives information necessary for underwater military engineer use • Helps the construction of bridges, docks, and breakwaters

4. Characteristics of Tides • Crest of the wave from is high tide and the trough is low tide • The vertical difference between high tide and low tide is the tidal range • The tidal period is the time between consecutive high/low tides

5. More Characteristics • There are three basic daily tides • 1. Semidiurnal tides- Two high tides and two low tides of nearly equal level each lunar day. • 2. Diurnal tides- One high and one low • 3. Mixed (also known as semidiurnal mixed)- successive high tides or low tides are of significantly different heights throughout the cycle. This is caused by blending diurnal and semidiurnal tides. • In the United States, Mixed tides are prevalent in the West Coast, Diurnal in the Gulf, and Semidiurnal in the East Coast

6. Diagrams of the Tides

7. Tides around the world

8. Gravitational pull Sun Moon Earth Ok that’s cool, but what makes tides? • Tides result from gravitational attraction and the centrifugal effect • What’s the centrifugal effect? • It’s when Gravity tends to pull Earth and the moon toward each other, but inertia keeps them apart. • Another way of saying what causes tides is that the gravitational pull of the sun and moon causes “bulges” on Earth that move as we rotate

9. More diagrams

10. Origin of Tides • The latitude of the tidal bulge is determined by the declination, the angle between Earth’s axis and the lunar and solar orbital plane. • A spring tide occurs when the sun, moon, and Earth are all in a straight line. During spring tides, high tides are very very high and low tides are very very low. These usually occur at two-week intervals corresponding to the new and full moons. Spring tides go with the Full and New Moon. • A neap tide occurs when the sun, moon, and Earth are aligned in a right angle. During neap tides, high tides aren’t that high and low tides aren’t that low. These also occur at two-week intervals. Neap tides go with the 1st and 3rd quarter of the moon.

11. Diagrams of Spring and Neap Tides

12. Equilibrium Theory of Tides • The equilibrium theory of tides is an idealized model of tides that considers Earth to be covered by an ocean of great and uniform depth capable of instantaneous response to the gravitational and inertial forces of the sun and moon. • This theory assumes that the seafloor does not influence the tides and that the ocean conforms instantly to the forces that affect the position of its surface. • It also treats tides as shallow-water waves. As Earth turns, landmasses divert, slow, and complicate movements of tidal crests.

13. Amphidromic Point • The node near the center of an ocean basin is called the amphidromic point. • This is a no-tide point in the ocean, around which the tidal crest rotates through one tidal cycle. • The crests sweep around aphidromic points like a wheel spokes from a rotating hub. • The Coriolis effect influence these tide waves because a large volume of water moves with waves. • The amphidromic point moves counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. • The height of tides increase with distance from an amphidromic point. • There are about a dozen of these points in the world, with five in the Pacific.

14. Tidal Datum • The tidal datum is the reference level to which tidal height is compared to, similar to an index fossil. • The tidal datum is the zero point seen in tide graphs. • This reference is not always set at mean sea level, which is the height of the ocean surface averaged over a few years’ time. • On coasts with mixed tides, the zero tide level is the average level of the lower of the two daily tides. On coasts with diurnal and semidiurnal tides, the zero tide level is the average level of all low tides.

15. Tidal Range • The tidal range is the high-water to low-water height difference that varies with basin configuration. In small areas such as lakes, the tidal range is small. • In larger areas, like the Baltic and Mediterranean seas, the tidal range is moderate. However, the tidal range is not the same over a whole ocean basin. • The largest tidal ranges are at the edges of largest ocean basins, like bays or inlets.

16. Tidal Currents • A tidal current is a mass flow of water induced by the raising or lowering of sea level owing to passage of tidal crests or troughs. • The rise or fall in sea level as a tide crest approaches and passes will cause a tidal current of water to flow into or out of bays and harbors. • Water rushing into an enclosed area because of the rise in sea level as a tide crest approaches is a flood current. Water rushing out due to the fall as the tide trough approaches is called an ebb current. • Slack water, a time of no currents, occurs at high and low tides when the current changes direction.

17. Solar and Lunar Tides • Solar tides are caused by the gravitational and inertial interaction of the sun and Earth. • The sun’s tractive forces develop in the same way as the moon’s, and the smaller solar bulges tend to follow the sun through the day. • Lunar tides are caused by gravitational and inertial interaction of the moon and Earth, and complete their cycle in a tidal day (known as a lunar day). • A complete tidal day is 24 hours and 50 minutes.

18. Ocean Bowl Quiz Time! Short Answer: The bulges are the troughs of the planet-sized waves that cause what type of tides?

19. Answer: Low Tides

20. Multiple Choice: • Semidiurnal Tides are most commonly found in what part of the United States? • W: West Coast • X: Gulf of Mexico • Y: East Coast • Z: Semidiurnal Tides are not found in the US

21. Multiple Choice: • Semidiurnal Tides are most commonly found in what part of the United States? • W: West Coast • X: Gulf of Mexico • Y: East Coast • Z: Semidiurnal Tides are not found in the US

22. Multiple Choice • Each time a tidal current changes directions there is a period of no current known as…? • W. Flood current • X. Ebb current • Y. Reversed current • Z. Slack current

23. Multiple Choice • Each time a tidal current changes directions there is a period of no current known as…? • W. Flood current • X. Ebb current • Y. Reversed current • Z. Slack current

24. Short Answer • What explains many characteristics of ocean tides by examining the balance and effects of the forces that allow a planet to stay in a stable orbit around the sun, or the moon to orbit the Earth? • Answer: Equilibrium Theory of Tides

25. Multiple Choice • The highest and lowest tides which occur when the moon and sun are lined up with the Earth are • W. Neap tides • X. Winter tides • Y. Spring tides • Z. Summer tides • ANSWER: Y

26. Multiple Choice • Which of the following best describes the impact of freshwater flow into an estuary? • W. The speed of flood tidal currents increases • X. Ebb tide is prolonged • Y. Flood tide is prolonged • Z. The tidal range is increased • ANSWER: X

27. GOOD JOB!!!