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
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 – 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)
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