Transcript The Dynamic Ocean - Bakersfield High School

The Dynamic Ocean
Chapter 16
Section 2
Waves and Tides
Chapter 16-2 Overview
From where do ocean waves obtain their
energy?
 What three factors affect the characteristics
of a wave?
 How does energy move through a wave?
 What causes tides?

So what are waves????

They obtain their energy and motion from
wind.
Anatomy of a Wave


Crest
 The tops of the waves
Trough
 The bottom of the waves
Anatomy of a Wave Picture
Wave Characteristics
Wave height
 The vertical distance between the trough
and crest
 Wavelength
 The horizontal distance between two
successive crests OR two successive
troughs
 Wave period
 The time it takes one full wave
(wavelength) to pass a fixed position

Wave characteristics are
dependent on three factors:
Wind speed
 Length of time wind has blown
 Fetch
 Distance the wind traveled across open
water

Wave Motion
Waves travel great distances.
 The water does not travel the entire
distance, but the wave does.
 Consider the following: a floating object on
the water such as a rubber duck
 Disturb the water creating a wave
 What motion does the duck exhibit?
(Forward motion or up and down or both
– Explain)

Water particle movement diagram
So what is the true motion of water particles?

Circular orbital motion, see pictures on page
456 and 457
 It allows energy to travel forward yet the
individual water particles only move in a
circle
Breaking Waves continued

As the original wave advances toward shore:
 It begins to “feel bottom” at a water depth =
½ of its wavelength
Tides


Daily change in the elevation of the ocean surface.
Ocean tides result from the change in the
gravitational attraction exerted upon Earth by the
moon and the sun.
Ocean Tides
The moon is the primary body influencing
ocean tides
 It takes the moon 29 ½ days to make one
revolution around the Earth
 The sun is farther away and only has
about 46% of the moon’s effect
So how does this gravitational
force work?
Consider tug of war between two teams –
the Earth & the moon
 The moon is pulling on the Earth’s water
bodies that are closest to it --- this creates a
bulge on the side closest to the moon
 Therefore, the side farthest from the moon
has less pull

So what does it look like?



When the “bulge” is the greatest, we see a high
tide
When the pull is not great, we see a low tide
The moon makes a revolution around the Earth,
but the Earth is rotating which changes its position
of the pull from the moon
 Water moves toward the pull giving the high
tide where the pull is greatest and low tide
where the pull is the least strong
 Most coastal locations will see 2 high tides and
2 low tides each day
Tidal Cycle
The sun has some influence on tidal bulges
 Its influence is most noticed at full and new
moons as they sun and moon are aligned
 Alignment = combined forces pulling on
the Earth’s water
 Larger tidal bulges (higher hide tides)
are created as are larger tidal troughs
(lower low tides)

Tidal Cycle



Tidal range
 Difference in height between successive high and low
tides
Spring tides
 Tides having the greatest tidal range due to the
alignment of the Earth, moon & sun
 Experienced during full and new moons
 2 per month
Neap tides
 When the daily tidal range is the least
 Experienced at the first and third quarters of the moon
(when the moon and sun act on Earth at right angles)
 2 per month
 See figure 13, page 459
Tidal Patterns

Three main tidal patterns:
 Diurnal tides
 Semidiurnal tides
 Mixed tides



Diurnal tides
 A single high tide & a single low tide each day
 Typical near Gulf of Mexico
Semidiurnal tides each day
 Two high and two low tides
 Highs are similar in height as are the lows
 Common along the Atlantic coast of U. S.
Mixed tides
 Similar to semidiurnal pattern BUT
 Large inequality in high water heights and/or low
water heights
 Common along Pacific Coast of U. S. and other parts
of world