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TIDE Tides are huge shallow-water waves - the largest waves in the ocean. They are caused by a combination of the gravitational force of the moon and sun and the motion of Earth. The moon''s influence on tides is about twice that of the sun''s THE EQUALIBRIUM THEORY OF TIDES The Moon and Tidal Bulges The Sun''s role Sun and Moon together THE DYNAMIC THEORY OF TIDES Tidal Patterns and Amphidromic Points Tidal Datum Tidas in Confined Basins Tidal Currents Tidal Friction PREDICTING TIDES TIDES AND MARINE ORGANISMS POWER FROM THE TIDES Tides=astronomical tides Water Encyclopedia :: St-Ts Tides -------------------------------------------------------------------------------- Ads by Google SW Design Optimization - Free Design Optimization Demos Design Better Products: SolidWorks - SolidWorks.com/Free_Demos Tides - Looking for Tides? Find exactly what you want today. - Yahoo.com Tide® Official Site - Get Your Clothes Beyond Clean w/ Tide. Great Stain Removal Power. - www.Tide.com Leadership Course - Leadership Certificates From Notre Dame U. 100% Online. Enroll Now! - www.NotreDameOnline.com -------------------------------------------------------------------------------- Ocean tides are periodic rises and falls in the level of the sea, and are formed by the gravitational attraction of the Moon and Sun on the water in the ocean. Although the Moon is much smaller than the Sun, it has a greater gravitational attraction for the Earth because the Moon is much closer to Earth. This causes the oceans to bulge out in the direction of the Moon. Equilibrium Theory centrifugal force Lunar Tides Solar Tides Water Encyclopedia :: St-Ts Tides -------------------------------------------------------------------------------- Ads by Google SW Design Optimization - Free Design Optimization Demos Design Better Products: SolidWorks - SolidWorks.com/Free_Demos Tides - Looking for Tides? Find exactly what you want today. - Yahoo.com Tide® Official Site - Get Your Clothes Beyond Clean w/ Tide. Great Stain Removal Power. - www.Tide.com Leadership Course - Leadership Certificates From Notre Dame U. 100% Online. Enroll Now! - www.NotreDameOnline.com -------------------------------------------------------------------------------- Ocean tides are periodic rises and falls in the level of the sea, and are formed by the gravitational attraction of the Moon and Sun on the water in the ocean. Although the Moon is much smaller than the Sun, it has a greater gravitational attraction for the Earth because the Moon is much closer to Earth. This causes the oceans to bulge out in the direction of the Moon. Equilibrium Theory of Tides Two theories help explain tides. The equilibrium theory of tides uses the universal laws of physics, as applied to a water-covered Earth. The dynamic theory of tides studies tides as they occur in the real world, modified by landmasses, geometry of the ocean basins, and Earth''s rotation. The equilibrium tidal theory begins with a hypothetical, water-covered planet and its satellite moon orbiting the Sun. The Moon is held in orbit with Earth by Earth''s gravitational force. There is also a centrifugal force pulling the Moon away from Earth and trying to send it spinning out into space. Earth and the Moon rotate around the common center of mass of the Earth-Moon system; this system is held in orbit by the Sun''s gravitational attraction while centrifugal force pulls the center of the mass away from the Sun. Both forces, gravitational and centrifugal, must reach and maintain equilibrium to hold the Earth-Moon system in orbit. Most ocean shorelines experience a high tide and a low tide (shown here) every day. Certain locations have two high and two low tides per day. Still other locations have mixed or unequal tide cycles. In the Earth-Moon-Sun system, the mass of the Sun is greatest, but its extreme distance renders its gravitational pull nominal. The tidegenerating force of the Moon and Sun vary as the inverse cube of their distances from Earth. The mass of the Moon is very small by comparison, but it is considerably closer, and therefore has a greater attractive effect on water particles than does the Sun. Lunar Tides. Water responds to the Moon''s gravitational force by flowing toward it, making a bulge on the surface of the ocean. On the side of Earth facing the Moon, gravitational force is applied to water particles toward the Moon. This force produces a lunar bulge in the layer of ocean water. At the same time, the centrifugal force of the Earth-Moon system acting on the water particles at Earth''s surface opposite the Moon creates a second bulge. Two lunar bulges on opposite sides of Earth are created on a planet covered by a uniformly deep ocean. The bulges represent the crests of the two tidal waves (high tide), directly opposite each other, and the low water areas are the two troughs (low tide). The equilibrium tidal theory predicts tides that are semidiurnal, which means two high and two low tides each day. Earth and the Moon are moving in the same direction along their orbit with the Sun. Earth rotates once during a 24-hour period but Earth must turn an extra 12 degrees, or 50 minutes, for the Moon to be directly over the same place as the day before because of the Moon''s rotation. Therefore a tidal day is not 24 hours long but rather 24 hours and 50 minutes, and the tidal period between high tides is 12 hours and 25 minutes. This explains why tides arrive at the same location about an hour later each day. The wavelength of the two tidal waves is one-half the circumference of Earth. Solar Tides. The Moon plays the greatest role in tide-building, but the Sun also produces its own tidal bulge. Though of much greater mass, the Sun''s distance reduces its tide-raising force to only 46 percent that of the Moon, and the tide period is 24 hours, not 24 hours and 50 minutes. The lunar Tidal maxima are greatest during spring tides (part [a]), which arise during each phase of a new moon or a full moon when Earth, Sun, and Moon are aligned. Conversely, twice each month when the Sun and Moon are at right angles to the Earth and hence are opposing one another, the tidal ranges are slighter and are called neap tides (part [b]). bulge created by the Moon has greater influence on the ocean and continually moves eastward relative to the solar bulge produced by the Sun. On land, the tides appear to flood in during a high tide, earning the name flood tide, and then flow back out to sea as an ebb tide. Earth''s rotation is responsible for carrying the landmasses into and out of the tidal bulges. It is as if Earth were constantly rotating inside a fluid envelope of ocean whose tidal bulges are supported by both the Moon and Sun. Spring and Neap Tides Dynamic Theory of Tides Tide Patterns Declination Tides Coriolis Effect Landforms and Tides Tides in Bays and Estuaries Tide Prediction and Tide Tables grafics Water Encyclopedia http://www.waterencyclopedia.com/Ce-Cr/Coastal-Ocean.html - coastal ocean http://www.waterencyclopedia.com/Da-En/Energy-from-the-Ocean.html -energy from the ocean http://www.waterencyclopedia.com/En-Ge/Estuaries.html -estuaries http://www.waterencyclopedia.com/Mi-Oc/Ocean-Currents.html -ocean currents http://www.waterencyclopedia.com/Tw-Z/Waves.html - waves Equilibrium Theory of Tides The equilibrum theory of tides deals primarily with the position and attraction of Earth, the moon, and the sun.It assumes that the ocean conforms instantly to the forces affecting the position of its surface and only approximately predicts the behavior of the tides. Lunar tides Gravity and inertia cause the ocean surface to bulge.Tides occur as Earth rotates beneath the bulges. Gravity bulge - the bulge toward the moon, and the opposite inertia bulge. The bulges follow the moon. One Lunar day =24H +50min (Earth -Moon movement) Tidal locking tidal bulge -- a bulge on one body created by the gravitational attraction on it by another. Two tidal bulges form, one on the side near the attracting body and one on the opposite side. Little bit Astronomy GRAVITATIONAL DEFORMATION A descriptive explanation of ocean tides Tidal records Theory of tides The dynamic theory takes into account the speed of the long-wavelength tide wave in water of varying depth, the presence of interfering continents, and the circular movement or rhythmic back-and-forth roking of water in ocean basins. It more accurately predicts the behavior of the tides than the equilibrium theory does. Tides Amphidromic point Amphidromic points occur because of the coriolis effect and interference within oceanic basins, seas and bays creating a wave pattern — called an amphidromic system — which rotates around the amphidromic point. At the amphidromic point, there is almost no vertical movement. There can be tidal currents as the water levels on either side of the amphidromic point are not the same. An amphidromic point is a point within a tidal system where the tidal range is almost zero. ENCYCLO semidiurnal (twice daily) tides diarnal tides Mixed tides Mixed tide like in LA When heights of two successive high tides or two low tides are markedly different, we have a mixed tide Identify higher high water tide (HHW), lower high water tide (LHW), higher low water tide (HLW), & lower low water tide (LLW) Times of high stands & low stands are not simply related to passage of moon overhead Semidiurnal And Diurnal Tides In most places, tides are semidiurnal (twice-daily), meaning that there are two tidal cycles (with one high tide and one low apiece) each day. In other words, during a typical day the tides reach their highest point along the shore and their lowest point twice each day. The high-water level reached during one of the high tide stages is usually higher than the other high point, and the low water level reached during one of the low tide stages is usually lower than the other low tide point. This difference is called the diurnal inequality of the tides. In a few locations, tides occur only once a day, with a single high tide and a single low tide. Such tidal cycles are known as diurnal (daily) tides. In both diurnal and semidiurnal settings, a rising tide is termed a flood tide and a falling tide is termed an ebb tide. The moment when the water reaches its highest point at high tide (or its lowest point at low tide) is called the slack tide, since the water level is then static, neither rising nor falling, at least for a short time. The Cause & Nature of Tides Tide Classification Tidal Datums Tidal Datums Mean Higher High Water, Mean High Water, Diurnal Tide Level, Mean Tide Level, Mean Sea Level, Mean Low Water, Mean Lower Low Water, Great Diurnal Range, Mean Range of Tide, Mean Diurnal High Water Inequality, Mean Diurnal Low Water Inequality, Greenwich High Water Interval, Greenwich Low Water Interval, Station Datum, National Tidal Datum Epoch Tidal range Tides in broad confined basins Tides in narrow restricted basins tidal bore tidal wave tidal current flood current ebb current slack water tidal friction meteorogical tides predicting tides power from the tides slack water Water livel Tidal range Video Video Do tides affect volcanoes? Tides in broad confined basins/Tides in narrow restricted basins Glossary of geology By Julia A. Jackson, James P. Mehl, Klaus K. E. Neuendorf, American Geological Institute Sedimentology and Sedimentary Basins By Mike R. Leeder WHAT IS A LAGOON? Microfacies of carbonate rocks By Erik Flügel Tidal Wave -Tidal bore Video: tidal wave in thailand Frozen "Tidal Wave" Images in Antarctica The photographs were taken by scientist Tony Travouillon in Antarctica. Many of the images can be seen in a gallery on Travouillon''s website. The pictures do not show a giant wave somehow snap-frozen in the very act of breaking. The formation contains blue ice, and this is compelling evidence that it was not created instantly from a wave of water. Blue ice is created as the ice is compressed and trapped air bubbles are squeezed out. The ice looks blue because, when light passes through thick ice, blue light is transmitted back out but red light is absorbed Tidal Wave -Rogue wave Tidal Currents Tidal Currents There are several different kinds of currents including oceanic, river, and wind-driven; all with their own driving force. This page addresses only the tidal currents. As mentioned before, tidal currents (a horizontal motion) are a result of the rise and fall of the water level due to tides (a vertical motion). The effects of tidal currents on the movement of water in and out of bays and harbors can be substantial. Some Terminology Set The set of a current is the direction that it flows toward. Note that this is the opposite of the way winds are reported. Drift This is the speed of a current. On ocean waters it is usuallly stated in knots; in rivers, mph. Velocity As the typical term in physics infers, this is an indication of both speed and direction (set and drift). Speed How fast the water is moving in relation to a stationary object (e.g. shore, light house). Flood Flow The tidal current is in flood when it is coming from the sea to the shore (tide is coming in, or high tide is ensuing). Ebb Flow The tidal current is in ebb when it is coming from shore and returning to the sea (low tide ensuing). Slack Water The point between flood and ebb (or ebb and flood) currents when there is no horizontal movement. Stand The point where vertical changes stop as the tide reverses. This is not the same as slack water; this is a tidal (vertical) occurence, not a tidal current (horizontal) occurence. Maximum Current The normal maximum speeds of the ebb and flood currents. This does not include effects of weather or run off from rain or melting snow, which can significantly effect tidal currents. Imagine a large, long, narrow bay on the coast. We position one person on the ship anchored at the opening to the sea (lower right) and another at the distant white light, a point on the bay as far from the sea as he can get. We assume the tide is low and there are no tidal currents in the bay. The tide comes in and reaches high tide at 11 am so the person at the mouth of the bay reports high tide at 11 am. Meanwhile the person inland is still watching the water level rise until, at 1 pm, he announces high tide where he is. That''s a difference of two hours between high tide in the two locations. Let''s look at what actually happens throughout the cycle. As the tide comes in, the water entering the bay has to overcome slow water to move forward into the bay (viscosity) so this change is not seen at the other end of the bay immediately. The tidal currents in the bay are now in flood flow. When the tide is highest at the entrance of the bay, the tide is at high stand in that location, but there is still a flood flow into the bay because the high stand has not been reached further into the bay yet. A while later, half way into the bay (the red light), the water also reaches its high stand, but there''s still a flood flow because the high stand has not yet been reached further in. Finally the high stand is reached all the way inside the bay at the white light and the current stops. It doesn''t reverse; it stops. This is called slack water. Even though the tide may have started going out at the bay''s entrance, the current in the bay stops, like a ball that has been thrown up in the air stops at the apex of its flight before falling back to earth. As the tide starts going out, the same thing happens in reverse. The water level once again changes first at the bay''s entrance while the water further in the bay may still be at high stand. The current in the bay, though, is now in ebb flow. When the ocean is at low tide at the entrance of the bay, the water is at its low stand. Further into the bay, low stand has not yet been reached so the ebb flow continues. Finally low stand is reached all the way inside the bay and once again slack water occurs in the bay. To summarize, we can list the sequence of events at any point in the bay, but the time at which these events occur will be different between any two points at different distances from the sea. The sequence is as follows (starting at low tide): Flood flow, when the tide starts to rise. High stand, when highest water level is reached and flood flow continues. High slack water, when high stand is reached throughout the bay and flood flow stops. Ebb flow, when the tide starts to receed. Low stand, when the lowest water level is reached and ebb flow continues. Low slack water, when low stand is reached throughout the bay and ebb flow stops. The same applies to rivers flowing into the sea, but with some important differences. The water flowing from the river will tend to hinder the movement of water into the river, hence causing the flood current to be less swift. On the other hand, the ebb flow currents can be extremely swift because water leaving the river at low tide is augmented by water flowing from the river. Add to that the possibility of rain and/or snow runoff inland that has caused the river to swell, and ebb currents can be even faster. In some waters, even the maximum current is so swift that less powerful boats must wait for slack water to navigate them. Tidal acceleration Glossary of Meteorological Terms Tide Prediction Turbine technology is turning the tides into power of the future SeaGen Tidal System Lewis Smith, Environment Reporter Energy resources: Tidal power Rennewable energy: Tidal power Slack water |
