TIDES

Paddle Surfing in France Construct an explanation for the phenomena you observed

Tides The periodic short term changes in the height (rise or fall) of the ocean surface at a particular place Caused by a combination of Distance between the Earth, moon and sun Gravitational force of the moon and the sun and the motion of Earth Moon’s influence 2x’s the sun’s (it is closer to Earth)

Tides The longest of all waves Wavelength = ½ Earth’s circumference They are always in shallow water And the fastest Speed is proportional to wavelength Tides move quickly ~1600 kilometers per hour (1000 mph)

1. shape and depth of the ocean floor TIDES Tides are extremely long waves caused by the gravitational attraction of the Moon and the Sun on Earth. They are also affected by the: 1. shape and depth of the ocean floor 2. latitude (greater pull at equator) 3. volume of water NOAA NASA

What Causes Tides? Tides are caused by the interaction of Earth, the Moon, and the Sun. Gravity is the reason for tides. Gravity is the force exerted by an object that pulls other objects toward it.

Moon’s Gravity and Tides The Moon’s gravity affects the water on Earth’s surface. Since the Moon is close to the Earth, it has a strong gravitational pull on it (closer objects have stronger gravitational pull).

Moon’s Gravity – Tidal Bulges The Moon pulls on the water on the side nearest to it more strongly than it pulls on the center of the Earth. This pull creates a bulge of water, called a tide bulge, on the side of Earth facing the the Moon.

Moon’s Gravity – Tidal Bulges The water on the side of Earth facing away from the Moon has a less strong pull. This water is “left behind” and forms a second bulge. As Earth rotates, different places on the planet’s surface pass through the areas of the tidal bulges and have the change in water levels.

Tidal Bulges – High Tide In places where there are tidal bulges, high tide is occurring along the coastlines. High Tide High Tide

Tidal Bulges – Low Tide In places between the bulges, low tide is occurring. LOW TIDE LOW TIDE

Tides occur when Earth rotates beneath the bulge A tidal day is 24 hours 50 minutes long because the moon rises 50 minutes later each day

The Earth and Moon revolve around each other and rotate on their axes. Earth’s rotation = 24 hours (one day) Moon’s rotation = 24 hours and 50 minutes (lunar day) Tides occur 50 minutes later every day because of the rotation time difference. Moon As the Earth turns, locations move out of the bulge and low tides (ebb) result. high tide low tide

Variations in Tides The moon can also move 28 ½ degrees above or below the equator each month Tidal bulges are offset relative to this change

Tidal range is the difference between high and low tide.

The Bay of Fundy, Nova Scotia has the greatest range in the world ~53 feet.

Sun-Earth-Moon System Ocean responds to inertial and gravitational forces of the sun too

Sun’s Gravity and Tides The Sun is so large that its gravity also affects tides. At times, the Sun and Moon pull together on Earth’s waters in the same direction. At other times they pull in different directions.

Spring Tides When the sun, Earth and moon are aligned, solar and lunar tides are additive Results in higher high tides and lower low tides Occur at two week intervals during new moons and full moons

Neap Tides When the sun, Earth and moon are at right angles, the solar will reduce the lunar tide Results in lower high tides and higher low tides Occur at two week intervals, arriving one week after the spring tide (during first quarter and last quarter moons)

Tides are greater in North America in the winter because the Earth is slightly closer to the Sun in winter.

Tides are also greater at times during the month when the moon and earth are closer together.

Daily Tide Cycle Most seashores have four tides every day – two high tides and two low tides. A change of from low to high tide or vice versa takes about 6 hours and 12 minutes. Changes in tides can be drastic (can notice) or or less dramatic (can’t notice).

Monthly Tide Cycle Changes in the positions of Earth, the Moon, and Sun affect the height of tides during a month.

Frequency is how often tides occur Frequency is how often tides occur. There are some exceptions but basically there are 3 types: Semi-diurnal = 2 equal high and low tides per day each 6 hours - 12 ½ minutes apart ex: east coast of U.S. 2. Diurnal = 1 high and 1 low tide per day each 12 hours - 25 minutes apart ex: Gulf of Mexico, S.E. Asia 3. Mixed = 2 high tides and 2 low tides of unequal range each 6 hours - 12 ½ minutes apart ex: west coast of U.S.

Importance of Tides Greatly influences coastal marine life Different organisms have adapted to areas within the intertidal zone Ships use the tides to exit and enter port Tidal power is the only marine energy source that has been successfully exploited on a large scale