Tides ‪commons.wikipedia.org

What Are Tides? Tides are the daily rise and fall of Earth’s waters on its coastlines As the tide comes in, the level of water on the beach rises, and as the tide goes out, the level of water on the beach goes down Tides occur in all bodies of water But most noticeable along the shore of large lakes and the ocean It rises for a period of hours until it reaches its highest level, and then it begins to fall, or recede, to its lowest level. This rise and fall of the ocean is known as the tide. Its highest and lowest levels are, of course called high and low tides

High Tides High tides are when the water reaches its highest point.

Low Tides Low tides are when the water reaches its lowest point

Tidal range: the difference between high and low tide Intertidal zone High tide Low tide

Alma at High Tide Alma at Low Tide

Tides are generated by: Gravitational pull of the moon and sun Centripetal force of the rotating Earth TIDES: Tides are the slow, periodic vertical rise and fall of the sea surface. They are usually described as being either diurnal or semi-diurnal. Diurnal tides have one high water and one low water in each lunar day (about 24.8 hours), while semi-diurnal tides have two high and two low waters in the same time period. While these tidal changes are easier to observe where land and water meet, they exist everywhere -- even in the middle of the ocean. Tidal ranges along the shoreline vary by location. For example, the tides in Canada's Bay of Fundy, an Atlantic Ocean inlet west of Nova Scotia, rise and fall as much as 50 feet, while the tidal range in Lake Superior is measured in inches. High and low tides are the result of the attractive forces (gravitational pull) of the moon and sun on a rotating Earth.

The Cause of Tides Gravitational and centripetal forces pull ocean water into a huge wave with a wavelength the size of an ocean basin. In principle, the sun and moon create two bulges on opposite sides of the Earth. The relative positions of the sun and moon change slowly, so the bulge changes position Tidal bulges follow Moon as it rotates around Earth The earth is also rotating, so as a coastline rotates into the bulge, the tide rises. As it rotates out, the tide falls.

Centripetal force vs Centrifugal force Centrifugal force (Latin for "center fleeing") describes the tendency of an object following a curved path to fly outwards, away from the center of the curve. It's not really a force; it results from inertia i.e. the tendency of an object to resist any change in its state of rest or motion. Centripetal force is a "real" force that counteracts the centrifugal force and prevents the object from "flying out", keeping it moving instead with a uniform speed along a circular path

Why the Moon is Stronger than the Sun Which has a bigger effect on the earth and its tides? Gravity- pull or attraction between objects; varies with mass of object. The gravitational attraction between the moon and the Earth is very small compared to gravity felt by an object at the Earth’s surface due to the Earth itself. Centrifugal force- because the earth and moon are rotating simultaneously around a common center of mass, the water of the oceans shifts from the center of rotation, creating a 2nd tidal bulge on the side of the earth that faces away from the moon. The influence of the moon on the tides is about twice the influence of the sun. The sun has much more gravity but affects the tides less than the moon because it’s so much farther away. the gravitational pull of the moon and sun - moon has 2x greater gravitational pull than the sun - sun is 10 million x more massive than the moon and is 390 times farther away

The Sun, Moon, and Types of Tides Neap Tides

The Sun, Moon, and Types of Tides When the moon is in a quarter phase, the lines from it and the sun to the Earth form a right angle. The sun’s gravitation pulls to the side of the moon’s tidal bulge. This tends to raise the low tide and lower the high tide. These weaker tides are called neap tides.

The Sun, Moon, and Types of Tides Spring Tides

Spring tides When there’s a new moon (no moon visible), both the sun and the moon are aligned on the same side of Earth, and during a full moon, the sun and moon are aligned on opposite sides of Earth. When the sun, the moon, and the Earth are aligned on a 180° plane, their gravity works together, raising the height of the tidal water bulges

GRAVITATIONAL & CENTRIPETAL GRAVITATIONAL FORCE CENTRIPETAL The closeness of the moon to Earth (238,857 miles), and the distance to the sun (92,955,770 miles), accounts for the moon having a tide-raising force nearly 2.5 times greater than the sun. The position of these celestial bodies results in significant variations in pulling forces causing above or below normal tidal ranges. The range between a high and a low tide is greatest when the sun, moon and Earth are in alignment. These are spring tides. When the sun and moon are at right angles to the Earth, their gravitational forces significantly reduce each other. This causes the neap tide, a period of decreased tidal range. The term neap is an acronym for near even as possible. Bulges are about the same size Tide-generating forces are a result of the gravitational attraction between the Earth, sun, and moon. It was not until Sir Isaac Newton (who lived from 1642-1727) discovered the law of gravity that the effect of the sun and the moon on the tides was fully understood. All surfaces of the Earth are pulled toward the moon and sun. This force has little effect on land masses, but it does have a very great and obvious effect on the water of the Earth's oceans. Twice each month the tidal range reaches a maximum and these large tides are called the spring tides. Halfway through the monthly cycle the range is much smaller, and these weak tides are called neap tides. As the moon rotates around the Earth, it pulls the water on the nearest side of the Earth outward into a bulge. A similar bulge on the opposite side of the Earth is caused by the water being thrown outward by the planet's spin. These two bulges travel around the globe, producing two high tides each day. During time of the new moon and full moon, when the sun and moon are in a straight line, their gravitational pull combine and produce spring tides; at this time the high tides are very high and the low tides are very low. When sun and moon are at right angles from the Earth, during the quarter phases of the moon, the gravitational pull on the oceans is less producing a smaller difference between high and low tide known as a neap tide. Some locations have much bigger tides than others. Tidal ranges are usually small in the middle of the ocean but can be very large where tidal waters are funneled into a bay or river estuary. Hawaii has hardly any tidal range at all while the water in the Bay of Fundy, in Canada, has a range of about 40 feet. GRAVITATIONAL & CENTRIPETAL

The Cause of Tides Isaac Newton proposed a simplistic explanation of tides equilibrium theory, which assumes that the Earth is perfectly uniform His Universal Gravitation theory helped to explain how the gravity of the moon (and the sun) were related to tides

Universal Gravitation Law Newton’s law states that all particles of mass have a gravitational attraction for all other particles Gravitational force is: proportional to the sum of the two masses inversely proportional to the square of the distance between their centers of mass

The moon’s gravitational pull on liquids is much more noticeable than on solids. Because liquids move more easily than solids

The Cause of Tides Pierre-Simon Laplace modified Newton’s model to account for tidal variations His model is called dynamic theory of tides lunar and solar gravity imperfect sphere of the Earth the season time of the month shape of the ocean basin Obstacles, reefs, islands Coriolis effect all influence the tides

Amphidromic points Tides rotate around more than a dozen amphidromic points where the water doesn’t rise and fall with the tides tides occur in a pinwheel-shaped, standing-wave pattern There is no vertical tidal movement at an amphidromic point, but away from that point there may be magnified tidal motion as the tides change throughout the day

Tidal flow around an amphidromic point. tidal magnitude is shown on the dotted lines and the pinwheel represents the progression of the tide around the basin.

Tidal Patterns diurnal tide - a single high and low tide daily The Gulf of Mexico has diurnal tides. semidiurnal tides - two roughly equal high and low tides daily, as predicted by Newton’s model. The east coast of US has semidiurnal tides, Cape Cod mixed tides – two unequal high and low tides daily Hawaii, Pacific coast of the US have mixed tides Lunar day has 24.8 hr or 24 hr 50 min Lunar day is 50 minutes longer than a solar day because the Moon is moving in its orbit around Earth Diurnal tides have one high water and one low water in each lunar day (about 24.8 hours), while semi-diurnal tides have two high and two low waters in the same time period. 24 hr 50 min or 12 hr 25 min if semidiurnal from another source

They are usually described as being either diurnal or semi-diurnal They are usually described as being either diurnal or semi-diurnal. Diurnal tides have one high water and one low water in each lunar day (about 24.8 hours), while semi-diurnal tides have two high and two low waters in the same time period. While these tidal changes are easier to observe where land and water meet, they exist everywhere -- even in the middle of the ocean. Tidal ranges along the shoreline vary by location.

Flood currents move toward the coast - landward. TIDAL CURRENTS: The rise and fall of the tide is accompanied by the horizontal flow of water called a tidal current. The usual terms used to describe the direction of this horizontal movement are ebb and flood. Ebb currents occur when tidal currents are moving away from the coast - seaward. Flood currents move toward the coast - landward. Under certain conditions, tidal currents can move more than 10 knots. In a purely semi-diurnal current, the flood and ebb each last about 6 hours. Speed of tidal currents depends upon the shape and dimensions of the harbor, coastal areas and ocean bottom. The configuration also influences vertical range of the tide itself.

The Bay of Fundy: Site of the world’s largest tidal range Tidal energy is focused by shape and shallowness of bay or ocean basin Maximum spring tidal range in Minas Basin = 17 meters (56 feet) Tides in Canada's Bay of Fundy, an Atlantic Ocean inlet west of Nova Scotia, rise and fall 50 feet

http://www. youtube. com/watch http://www.youtube.com/watch?v=u3LtEF9WPt430 sec bay of fundy time lapse tides good http://www.youtube.com/watch?v=dmcMQU5AAg4best 2 min  http://www.youtube.com/watch?v=LWumonz87rA1.5 min nova scotia fast but wind noise

Highest Tides One of the world's largest tides occurs in Turnagain Arm south of Anchorage Alaska – 42 feet http://margymuses.blogspot.com/2010/03/tidal-flats-anchorage.html mud flats near anchorage in cook inlet Tides in Lake Superior are measured in inches

Tidal Patterns and Currents daily tides create a current that flows into and out of bays, rivers, harbors, and other restricted spaces The inflow is called a flood current the outflow is called a slack current The midpoint between high and low tides creates slack tide, when there is little water moving Large ships may only be able to enter or exit a harbor during high tide to ensure sufficient water depth for travel

Tidal bore The incoming high tide produces a wave that flows into a river, bay, or other relatively narrow area is a true tidal wave and can be several meters high On the Amazon River in South America and the Severn River in England, surfers can take long rides on the tidal bore

Tidal bore http://www.youtube.com/watch?v=xiKoWAiqufE quintang river 1 min news report 90 ft http://www.youtube.com/watch?v=J8Q1ecIr-NM3 min in Chinese good http://www.youtube.com/watch?v=SNjVlUBmtGo50 http://www.youtube.com/watch?v=4DlqVuNMydk national geographic 1 min

Sites with high potential for tidal power generation

Grunion Grunion are the only fish that come completely out of the water to spawn Spawning cycles are timed precisely with the tides

Grunion, Coral spawning – Lunar Effects on life…

Palolo worm The Pacific palolo worm (Eunice viridis) and its West Indian relative (E. fucata) incredible reproductive behavior linked to the lunar cycle the rear half of each worm transforms dramatically, developing fast-growing reproductive organs. The worm itself reverses its position within its tube, so that it is now pointing head-down, the posterior body half breaks off from the rest of the worm and swims up toward the sea's surface - it has developed a pair of eyes to assist it At the surface, the bag bursts, releasing its contents – millions of palolo worms have all undergone this radical metamorphosis at precisely the same time, the sea is soon awash with a mass of sperm and eggs, It occurs twice a year on the neap tides of the last quarter moon in October and November for the Pacific species, and the third quarter moon in June and July for the West Indian species of palolo worm "The Pacific palolo worm (Eunice viridis) and its West Indian relative (E. fucata) exhibit one of the most incredible examples of reproductive behavior on record, which is intimately linked to the lunar cycle. These two annelid species are polychaete worms, and normally remain secure within tubes excavated by them in coral or under rocks, with their heads at the open end of their tubes - until the breeding season, that is."When this period approaches, the rear half of each worm transforms dramatically, developing fast-growing reproductive organs. The worm itself reverses its position within its tube, so that it is now pointing head-down, with its highly modified posterior half-projecting out of the tube. Once the reproductive organs are fully developed, the posterior body half breaks off from the rest of the worm (which remains inside its tube but realigns itself so that its head is at the tube's open end again), and swims up toward the sea's surface - almost as if it were a separate animal in its own right. Indeed, it has even developed a pair of eyes to assist it in locating the surface."As it swims, the worm's posterior body half undergoes a further transformation, its internal structures and segmentation breaking down, so that when it reaches the surface it is nothing more than a writhing bag of either sperm or eggs (the sexes are separate in these species). At the surface, the bag bursts, releasing its contents - and, bearing in mind that millions of palolo worms have all undergone this radical metamorphosis at precisely the same time, the sea is soon awash with a mass of sperm and eggs, yielding a vast bout of communal, random fertilization. What makes these worms' reproductive behavior even more extraordinary is the exact nature of this event's timing. It occurs twice a year on the neap tides of the last quarter moon in October and November for the Pacific species, and the third quarter moon in June and July for the West Indian species of palolo worm." (Shuker 2001:94-95) http://www.asknature.org/strategy/33851607f85736798b23846be4547453

Palolo worm spawning palolo_smitsonian2_lge

Atmospheric Tides Lunar gravitational affects earth’s atmosphere Cause slight periodic fluctuations in weather patterns Theory predicts stronger lunar pressure oscillations in the tropics but their amplitude rarely exceeds 100 microbars or 0.01 percent of the average surface pressure. Detection of such a tiny signal masked by much larger pressure variations associated with weather phenomena required the development of special statistical techniques and the accumulation of a long series of regular observations.Surprisingly, such observations show that the sun also causes semidiurnal tides in the atmosphere, which are more than 20 times stronger, although the solar gravitational forcing is less than half that of the moon. After all, it is the moon that causes the dominant tides in the ocean, not the sun. (The average lunar day is about 51 minutes longer than the solar day because of the moon¿s rotation around Earth and this allows scientists to reliably separate the two tides in long observational records.) Apparently, Laplace had suspected this, suggesting that the strong solar tide was primarily generated by solar heating and not by solar gravity. Scientists finally confirmed this hypothesis in the 1960s when it became possible to develop adequate models of solar atmospheric heating. As with the gravitational pull of a celestial body, the uneven solar heating on Earth's dayside distorts the spherical symmetry of the atmosphere, but in a more complex way. The thermal solar tide therefore consists of several dominant waves, the most prominent being the diurnal and semidiurnal ones.Pressure variations cause tidal oscillations in other atmospheric characteristics as well. It is common for atmospheric waves to grow in amplitude with height as the air becomes thinner. The lunar tide, however, remains weak compared to the solar tide in the upper atmosphere. Still, at altitudes above roughly 80 kilometers (50 miles) lunar tides have been detected in winds, temperature, airglow emissions and a number of ionospheric parameters. Almost two centuries after atmospheric lunar tides were predicted and first observed, they are still studied. http://www.scientificamerican.com/article.cfm?id=does-the-moon-have-a-tida