The Dynamic Ocean

Chapter 16Chapter 16

Section 2Section 2

Waves and TidesWaves and Tides

Chapter 16-2 Overview

From where do ocean waves obtain their From where do ocean waves obtain their energy?energy?

What three factors affect the characteristics What three factors affect the characteristics of a wave?of a wave?

How does energy move through a wave?How does energy move through a wave? What causes tides?What causes tides?

So what are waves????

They obtain their energy and motion from They obtain their energy and motion from wind. wind.

Anatomy of a Wave

CrestCrest The The topstops of the waves of the waves

TroughTrough The The bottombottom of the waves of the waves

Anatomy of a Wave Picture

Wave Characteristics Wave Wave heightheight

The The verticalvertical distance between the distance between the troughtrough and and crestcrest

WavelengthWavelength The The horizontalhorizontal distance between two distance between two

successive crests OR successive crests OR twotwo successive successive troughstroughs

Wave Wave periodperiod The time it takes one full wave The time it takes one full wave

(wavelength) to (wavelength) to passpass a fixed position a fixed position

Wave characteristics are dependent on three factors:

Wind speedWind speed Length of Length of timetime wind has blown wind has blown FetchFetch

DistanceDistance the wind traveled across open the wind traveled across open waterwater

Wave Motion

Waves travel great distances. Waves travel great distances. The water does not travel the entire The water does not travel the entire

distance, but the wave does. distance, but the wave does. Consider the following: a floating object on Consider the following: a floating object on

the water such as a rubber duckthe water such as a rubber duck Disturb the water creating a waveDisturb the water creating a wave What motion does the duck exhibit? What motion does the duck exhibit?

(Forward motion or up and down or both (Forward motion or up and down or both – Explain)– Explain)

Water particle movement diagram

So what is the true motion of water particles?

Circular orbitalCircular orbital motion, see pictures on motion, see pictures on page 456 and 457page 456 and 457 It allows energy to travel It allows energy to travel forwardforward yet the yet the

individual water particles only move in a individual water particles only move in a circlecircle

Breaking Waves continued As the original wave advances toward shore:As the original wave advances toward shore:

It begins to “feel bottom” at a water depth = It begins to “feel bottom” at a water depth = ½ ½ of its wavelengthof its wavelength

Tides Daily change in the elevation of the ocean surface.Daily change in the elevation of the ocean surface. Ocean tides result from the change in the Ocean tides result from the change in the

gravitational attraction exerted upon Earth by the gravitational attraction exerted upon Earth by the moon and the sun.moon and the sun.

Ocean Tides

The The moomoon is the primary body influencing n is the primary body influencing ocean tidesocean tidesIt takes the moon It takes the moon 29 ½29 ½ days to make one days to make one revolution around the Earthrevolution around the EarthThe sun is farther away and only has The sun is farther away and only has about about 46%46% of the moon’s effect of the moon’s effect

So how does this gravitational force work? Consider tug of war between two teams – Consider tug of war between two teams –

the Earth & the moonthe Earth & the moon The moon is pulling on the Earth’s water The moon is pulling on the Earth’s water

bodies that are closest to it --- this creates a bodies that are closest to it --- this creates a bulgebulge on the side closest to the moon on the side closest to the moon

Therefore, the side farthest from the moon Therefore, the side farthest from the moon has has lessless pull pull

So what does it look like?

When the “bulge” is the greatest, we see a When the “bulge” is the greatest, we see a high high tidetide

When the pull is not great, we see a When the pull is not great, we see a lowlow tide tide The moon makes a revolution around the Earth, The moon makes a revolution around the Earth,

but the Earth is but the Earth is rotatingrotating which changes its which changes its positionposition of the pull from the moon of the pull from the moon Water moves Water moves towardtoward the pull giving the high the pull giving the high

tide where the pull is greatest and low tide tide where the pull is greatest and low tide where the pull is the least strongwhere the pull is the least strong

Most coastal locations will seeMost coastal locations will see 2 2 high tides and high tides and 22 low tides each day low tides each day

Tidal Cycle

The sun has some influence on tidal bulgesThe sun has some influence on tidal bulges Its influence is most noticed at Its influence is most noticed at fullfull and and newnew

moons as they sun and moon are alignedmoons as they sun and moon are aligned AlignmentAlignment = combined forces pulling on = combined forces pulling on

the Earth’s waterthe Earth’s waterLargerLarger tidal bulges (higher hide tides) tidal bulges (higher hide tides)

are created as are are created as are largerlarger tidal troughs tidal troughs (lower low tides)(lower low tides)

Tidal Cycle

Tidal rangeTidal range Difference in Difference in heightheight between successive high and low between successive high and low

tidestides Spring tidesSpring tides

Tides having the greatest tidal range due to the Tides having the greatest tidal range due to the alignment of the Earth, moon & sunalignment of the Earth, moon & sun

Experienced during Experienced during fullfull and and newnew moons moons 22 per month per month

Neap tidesNeap tides When the daily tidal range is the leastWhen the daily tidal range is the least Experienced at the Experienced at the firstfirst and and thirdthird quarters of the moon quarters of the moon

(when the moon and sun act on Earth at right angles)(when the moon and sun act on Earth at right angles) 2 2 per monthper month See figure 13, page 459See figure 13, page 459

Tidal Patterns

Three main tidal patterns:Three main tidal patterns: DiurnalDiurnal tides tides Semidiurnal Semidiurnal tidestides MixedMixed tides tides

Diurnal tidesDiurnal tides A A singlesingle high tide & a high tide & a singlesingle low tide each day low tide each day Typical near Gulf of MexicoTypical near Gulf of Mexico

Semidiurnal tides each daySemidiurnal tides each day TwoTwo high and high and twotwo low tides low tides Highs are similar in height as are the lowsHighs are similar in height as are the lows Common along the Common along the AtlanticAtlantic coast of U. S. coast of U. S.

Mixed tidesMixed tides Similar to semidiurnal pattern BUTSimilar to semidiurnal pattern BUT Large Large inequalityinequality in high water heights and/or low in high water heights and/or low

water heightswater heights Common along Common along PacificPacific Coast of U. S. and other parts Coast of U. S. and other parts

of worldof world