CH 3 Waves and Tides

Waves

The wind not only drives surface currents, it also causes waves

Fundamental Features of Water Waves

Wave Crest: is the highest portion of the wave.Wave Trough: is the lowest portion of the wave.Wavelength: is the linear distance separating wave crestsWave Height: is the distance from crest to trough

from An Introduction to the World's Oceans, 8th edition by K.A. Sverdrup, A.C. Duxbury, and A.B. Duxbury (2004)

•Crest move up and forward

•trough moves down and back

•The water molecules don’t move anywhere they just move in circles transferring energy.

•The faster and longer the wind blows, the larger the waves get.

•The size of the wave also depends on how much open water wind affects

•wave crests up into sharp peaks (seas)

•waves begin to spread out (swells)

• waves begin move into the shallows

•the bottom forces the water molecules to drag

•waves behind the front wave catch up

•they begin to pile up getting taller and steeper until they fall forward and break creating a surf

•Surface at any location can be affected by wind and therefore cause waves.

•Waves coming from different directions, strengths, and distances can result in these waves interacting and wave cancellation.

•If the crest of the two waves collides they can result in a larger wave (Rogue Wave)

•The sea surface has been rising and falling in the rhythmic patterns known as tides

•Tides alternately expose and submerge organisms

•Tides are caused by the gravitational pull of the moon and sun

Tide

•The moon’s gravity pulls the water in the ocean toward the moon

•On the opposite side of the earth, furthest from the moon

•the pull is weaker so the water actually bulges away from the moon because of centrifugal force

•Pull towards the moon and pull toward the other side (bulging)

•Deep water under the bulge and shallow away from the bulge

•As the earth rotates the planet’s surface will alternately lie under the bulge and then away from it

•High tide occurs with the point is under the bulge.

•Earth takes 24 hours to complete a rotation, the pt will have two high tides and two low tides every day

•The moon advances a little during the earth’s rotation

•it takes earth an additional 50 minutes to line up with the moon again

Fig. 3.32

•Sun produces tidal bulges, but not as strong

•When the sun and moon are in line with each other (full and new moon) called spring tides.

•When the sun and moon are at right angles called neap tides (moon is at the first and third quarter)

•Most places are semidiurnal, two high tides and two low tides a day

•Diurnal tides, only one high tide and one low tide every day. (Antarctica, Gulf of Mexico, Caribbean, and Pacific)

Fig. 3.33