- Slides: 30
Waves, Tides, and Currents
Waves • A wave is a rhythmic movement that carries energy through matter or space. • All waves have the same main parts.
• Still-Water Line - The level of the ocean if it were flat without any waves. Crest - The highest part of the wave above the stillwater line. Trough - The lowest part of the wave below the still -water line • Wave Height - The vertical distance between the crest and the trough. • Wavelength - The horizontal distance between each crest or each trough.
• Wave Period - The time it takes for two successive waves to pass a particular point. For example, it you are standing on a pier and start a stopwatch as the crest of a wave passes and then stop the stopwatch as the crest of the next wave passes, you have measured the wave period. Wave Frequency - The number of waves that pass a particular point in a given time period. Fetch – The distance the wind blows over open water. Amplitude - The amplitude is equal to one-half the wave height or the distance from either the crest or the trough to the still-water line.
Waves • The highest part of a wave is the • ________. The lowest part of a wave is the ______
Parts of Ocean Waves
Wavelength • The distance from the crest of one wave to the crest of the wave next to it is called wavelength.
Wave Height • Wave height is the vertical distance from the trough to the crest.
Waves • Most ocean waves are caused by wind that blows across the surface of the water. • Friction between the wind and water transfers energy from the wind to the water.
Waves • The longer and harder the wind blows and the greater the distance it travels, the higher the waves become…. .
Wave Movement • The wave travels • • forward…. But the water particles do not! The water particles move in a circular pattern as they are temporarily displaced by the energy of the wave.
Ocean Waves © 2002 Brooks/Cole, a division of Thomson Learning, Inc.
Transfer of Energy • A wave is really a transfer of energy from one water molecule to the next. • If all the water itself moved forward all the oceans would empty onto the shore!!!!!
Why Do Waves Break? • Water molecules do tend to travel forward as • they break on shore. Waves break when they approach shallow water.
Breakers • The bottom of the wave is slowed down by • • • friction with the ocean floor. The top of the wave is still moving forward, traveling faster than the bottom. Its momentum causes it to move past the bottom part of the wave. When this happens the wave topples over on itself, forming a breaker.
Wind Waves Approaching Shore What happens when wind waves break against the shore? © 2002 Brooks/Cole, a division of Thomson Learning, Inc.
What is a Current? A current is a continuous flow of water in a given direction A current is like a river in the ocean
Types of Ocean Currents There are two types of currents in the ocean: Surface Currents Density Currents
Causes of Surface Currents Three things cause surface currents: 1. Wind 2. Continents 3. Rotation of the Earth, also known as the Coriolis Effect
Heating of the Earth’s Surface • The sun’s rays strike the Earth at different angles • At the equator, the rays strike the Earth almost perpendicular to its surface, warming up a small area. • At high latitudes, the curve of the Earth causes the rays to strike a larger surface area-So the same amount of heat is distributed over a larger area. • The farther from the equator, the cooler the Earth
Surface Ocean Currents • Surface currents are caused by the • transfer of energy from winds. Surface currents occur in the top 100 – 300 m of water. – Example: Gulf Stream – 80 km wide, 5 km velocity (at fastest) • Gyre – circuit of currents around the periphery of an ocean basin (e. g. Gulf Stream is part of the North Atlantic Gyre)
Prevailing Winds Fig. 16. 14, p. 407
The water of the ocean surface moves in a regular pattern called surface ocean currents. The currents are named. In this map, warm currents are shown in red and cold currents are shown in blue.
Surface-Ocean Currents • Most are part of the gyres that • • • circulate in the ocean basins Gyres circulate clockwise in the northern hemisphere Gyres circulate counterclockwise in the southern hemisphere Why?
Observe direction of circulation of gyres Fig. 16 -12, p. 384