Waves, Tides, and Currents Science 6

Currents Where are the Oceans? Identify the Oceans Tides Waves The Ocean Floor Ocean Storms

Where are the Oceans?

PREDICT: What percent of the earth is covered in water PREDICT: What percent of the earth is covered in water? What percent is land? Explain your prediction.

PREDICT:What percent of the earth’s water is salt PREDICT:What percent of the earth’s water is salt? What percent is fresh? Explain your prediction.

Waves

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 still-water 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, if 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 crest. The lowest part of a wave is the trough.

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

Waves The longer and harder the wind blows and the greater the distance over which it blows, 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.

Breaking Waves In general waves break when the depth of the water is a little greater than the height of the wave. Water depth 1.3 times the wave height A wave 30 cm high will break in 40 cm water.

What Makes A Wave? Let’s Make A Wave

Tides

What causes tides? The gravitational forces of the moon and sun on the water causes the tides.. The moon, being nearest, has the greatest effect even though the sun is the larger of the two. High tides are generated on the sides of the Earth nearest to and farthest from the moon

During new and full moon phases the moon, sun, and Earth are aligned causing a greater gravitational pull on the Earth. This results in higher high tides and lower low tides.

Spring Tides The Moon moves around Earth and Earth moves around the Sun. The Moon, Earth, and Sun line up twice a month-when the moon is full and then when it is new. The Moon and Sun pull together on Earth’s oceans. The result is high tides that are very high and low tides that are very low; Spring Tides Spring refers to the “springing up” of the water, not the spring season.

Neap Tides When the Sun and Moon are at a 90 degree angle with Earth, they no longer pull in the same direction. The pull of the Sun works against the pull of the Moon. High tides are not so high and low tides are not so low; Neap Tides Occur twice each month, when the Moon is in its first quarter and its third quarter phases.

Spring and Neap Tides http://home.hiwaay.net/~krcool/Astro/moon/moontides/ http://www.enchantedlearning.com/subjects/astronomy/moon/Tides.shtml

Currents

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: 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

What Causes the Wind? This difference in temperature between the equator and the poles causes our atmosphere and ocean to circulate. What does warm air do? What does cooler air do? This exchange of warm air and cool air causes the winds that prevail over the Earth.

Prevailing Winds FIGURE 16.14 The green arrows show major prevailing winds over the North and South Atlantic Oceans—the Trade Winds (easterlies) and the westerlies. The orange arrows show the surface oceanic currents in the same regions. Fig. 16.14, p.407

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 – 80km wide, 5km 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)

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 Figure 16.12 Major ocean currents of the world. Observe direction of circulation of gyres Fig. 16-12, p.384

The Coriolis Effect The Coriolis Effect is caused by the Earth’s rotation. Because the Earth is spinning objects do not move above it in a straight line. Objects are deflected in a curved path. This is what causes clouds in a hurricane to swirl. This is also why winds and currents move in circular paths

Why don’t we notice the Coriolis Effect? Something has to move a very long way before the Coriolis effect is noticeable - at least several hundred miles. For example, if you throw a football the path only curves a tiny bit due to the Coriolis effect - far too small for you to ever notice.

Coriolis Effect Animation Click below for animation http://www.classzone.com/books/earth_science/terc/content/visualizations/es1904/es1904page01.cfm http://www.kidsgeo.com/geography-for-kids/0089-coriolis-effect.php

Current: continuous flow of water in a given direction Surface currents – wind-driven flow in the top 400m of seas Example: Gulf Stream – 80km wide by 650m deep, 5km velocity (at fastest) Winds blow in particular directions due to differential heating of the earth’s surface Gyre – circuit of currents around the periphery of an ocean basin (e.g. Gulf Stream is part of the North Atlantic Gyre) Westerlies and trade winds produce gyres

Westerlies and trade winds produce gyres Trade winds blow from east to west toward the equator. As they move over the oceans, they push surface currents from east to west. Westerly winds (westerlies) blow from west to east, pushing surface currents along with them. http://www.weatherwizkids.com/wind1.htm http://www.kidsgeo.com/geography-for-kids/0095-westerlies.php http://www.kidsgeo.com/geography-for-kids/0094-trade-winds.php

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

Arctic Ocean Atlantic Ocean Pacific Ocean                                                                                                                       Indian Ocean On your map, color the warm currents red and the cold currents blue. Label the 4 oceans.                                                           

Ocean Weather, Temperature, and Tides Resources: Neptune’s Web Ocean Weather, Temperature, and Tides Ocean Planet Exhibit in the Smithsonian Museum of Natural History Secrets at Sea Game