Warm Up 2/25/08 What is true about an ocean current that is moving toward the equator? a. It is cold. c. It is warm. b. It is slow. d. It is fast. The energy that drives surface ocean currents comes from ____. a. salinity variations c. temperature differences b. wave action d. wind Because of the Coriolis effect, ocean currents in the Northern Hemisphere are deflected to the ____. a. left c. south b. right d. north Answers: 1) a. 2) c. 3) b.

Waves and Tides Chapter 16, Section 2

Waves Ocean waves are energy traveling along the boundary between ocean and atmosphere Waves transfer energy through the ocean, that’s why even on a calm day in the middle of the ocean there may still be waves from a far off storm

Waves

Wave Characteristics Most ocean waves obtain their energy and motion from the wind Crests – the tops of the waves Troughs – the bottoms of the waves Wave Height – the vertical displacement between crest and trough Wavelength – the horizontal distance between two successive crests or two successive troughs Wave Period – the time it takes one wavelength to pass a fixed position The height, length, and period that are eventually achieved by a wave depend on three factors: (1) wind speed; (2) length of time the wind has blown; and (3) fetch Fetch – distance that the wind has traveled across open water

Concept Check From where do ocean waves obtain their energy? Wind

Wave Motion Waves can travel great distances across ocean basins As a wave travels, the water particles pass the energy along by moving in a circle; so the water doesn’t move, only the energy Circular orbital motion allows energy to move forward through the water while the individual water particles that transmit the wave move around in a circle The wind energy is not only transmitted along the surface, but also downward

Anatomy of a Wave

Concept Check How does energy move by means of a wave? Circular orbital motion allows energy to move forward through a wave, while the individual water particles that transmit the wave move around in a circle.

Breaking Waves As long as a wave is in deep water, it is unaffected by water depth When a wave approaches shore, the water becomes shallower and influences wave behavior As a wave advances on the shore, the slightly faster waves further out will catch-up and decrease the wavelength, making the wave grow steadily higher When a critical point is reached, the wave is too steep to support itself and the wave front collapses, or breaks, and the water advances up the shore

Breaking Waves

Tides Tides are regular changes in the elevation of the ocean surface Other than waves, they are the easiest ocean movements to observe Newton showed that there is a mutually attractive force between any two bodies, Earth and the moon Ocean tides result from differences in the gravitational attraction exerted upon different parts of Earth’s surface by the moon and, to a lesser extent, by the sun

The Cause of Tides The primary body that influences the tides is the moon The gravitational pull is greatest on the side of Earth closest to the moon, causing Earth to be stretched slightly On the side of Earth closest to the moon, the pull of the moon’s gravity on the oceans is greater than it is on solid Earth Water will flow towards this tidal “bulge”, creating a high tide As Earth rotates, it will go “through” the tidal bulges, resulting in alternating high and low tides

Cause of Tides

Concept Check What force produces tides? Gravity

Tidal Cycle The sun also produces tidal bulges, slightly smaller than those produced by the moon The influence is most noticeable during new and full moon phases (Earth-moon-sun are aligned), causing larger tidal bulges Tidal Range – the difference in height between successive high and low tides Spring Tides – have the greatest tidal range due to the alignment of the Earth-moon-sun system (new and full moons) Neap Tides – daily tidal range is less due to the sun and moon acting against each other

Spring Tides

Neap Tides

Tidal Patterns Tides at various locations respond differently to the tide-producing forces Three main tidal patterns exist worldwide: diurnal tides, semidiurnal tides, and mixed tides Diurnal Tidal Pattern – characterized by a single high tide and a single low tide each tidal day Semidiurnal Tidal Pattern – characterized by two high tides and two low tides each tidal day Mixed Tidal Pattern – characterized by a large inequality in high water heights, low water heights, or both

Tidal Patterns

Concept Check What are the three types of tidal patterns? Diurnal, semidiurnal, and mixed

Assignment (Due 2/28/08) Read Chapter 16 (pg. 448-467) Do Chapter 16 Assessment #1-30 (pg. 471-472) Print out “Investigation 16 – Shoreline Features” for Wednesday

Cool Down What celestial bodies influence Earth’s tides? The moon and the sun Explain how the forces of gravity and inertia lead to tides in Earth’s oceans. On the side of Earth closest to the moon, the force of gravity is larger than that of inertia, which creates a tidal bulge. On the side of Earth opposite the moon, the force of inertia is greater than that of gravity, creating a similar tidal bulge. What is one new thing you learned today? Explain.