Ocean Tides The ocean surface rises and falls several feet on a predictable normal pattern – normally on a daily schedule. This is what is called the Tide.

High tide - the hightest level it gets to Low tide - the lowest level it gets to Tidal range - difference between high and low Ebb – when the tide is falling Flood – when the tide is rising

Nova Scotia Tides Wolfville, NS (16 m tidal range) Diurnal Tides (one high and one low every 12 hours and 25 minutes

Second highest tidal range at Ancorage Alaska ~ 12 m

Low tide in texas beach

Oops….don’t park at low tide!

To understand tides in the ocean 1.Moon – earth interaction 2.Sun’s influence 3.Edgs of ocean (continents)

Moon Gravity is the most influential force causing tides

The Earth-Moon System The Earth and Moon orbit their common center of gravity, the barycenter every days (lunar month)

Even that is simplified from the real situation! Enter: Apogee and Perigree

POINT? The earth is kind of slung around by all this… creating Centrifugal forces that sling the water away from the earth on the side opposite the moon!

2 high tide areas and 2 low tide areas

The earth rotates and the ocean is exposed to either the moon’s gravity or the centrifgal force in at it turns.

Earth rotates UNDER the the “BULDGES” – or “high tide areas”

BUT THE MOON IS NOT AT THE EQUATOR!!!! Now bulges are unequal in height P

Summary so far 1)The moon does not simply go around the earth, we and the moon swing around each other. 2)Moon’s gravity causes a “high tide” area on the side of the earth closest to it – pulling the water up a bit 3)The swing of the earth – centrifugal force – causes a second “high tide’ area away form the moon as the water is slung out a bit 4)The earth rotates under these forces causing daily changes in the higth of the ocean. 5)Since the moon & earth do not rotate in the plane of the equator, the “high tide” areas are off set. _tide.swf S

BUT THE MOON IS NOT AT THE EQUATOR!!!! Now bulges are unequal in height P

09_15 P

Summary so far 1)– Moon /earth interaction causes two areas of high tide 2)Earth rotates under it to create daily cycles of high tide/low tide 3)High tide can be 1)Diurnal – 1 high and 1 low each day 2)Semidiurnal – 2 high’s and 2 lows each day that are equal 3)Mixed – 2 high and 2 lows each day, but they are not equal

Sun’s Influence

Spring tides = highs are even higher – lows are even lower because the earth/moon/sun are all lined up Neap tides = Tides less extreme due to earth/moon/sun at right angles to each other

New Word: Syzygy Syzygy is when planetary things line up. Which tides happen during Syzygy of the earth sun and moon?

Tides are “standing waves” Fancy name = seiche This means they bounce back and forth in a particular ocean.

But the “standing wave” does bounce back and forth straight because of Coriolis! The ocean tides swirl!!!! In the same direction as the currents!

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Summary 1)Sun’s influence is not as much as the moon’s since it is so far away, but it does make a difference 1)Spring tide is when sun/moon work together 2)Neap tides are when their forces are not wokring together 2)Tides are “standing waves” that slosh back and forth- rotating because of Coriolis, this means there is very little tide effect in the middle of the oceans.

Tides can be used to generate electricty

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“RIP tides” Not a true “tides” Should be called “rip currents”, not tides They are often caused by the “falling tide”. But can also be caused by large waves.

Beaches have “sand bars” with breaks in them

Tidal Bores S

Tidal Bore Going Upriver in China S

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Waves can be used to generate power.