Spring Tides Neap Tides | The Old Farmer's Almanac Rate this Article: Average: 3.4 (441 votes) The following is a explanation of spring and neap tides in relation to lunar and solar cycles. Since antiquity, people have noticed that oceans exhibit a much greater tidal range around the time of the full Moon and new Moon. This is when the Moon and Sun are either together in the sky or are on opposite sides of the heavens. Higher tides occur during these Moon phases because the Sun also exerts a gravitational pull on our oceans, although it is only 46 percent as strong as the Moon's. When the gravitational effects of the Sun and the Moon combine, we get spring tides, which have nothing to do with the season of spring. The term refers to the action of the seas springing out and then springing back. These are times of high high tides and low low tides. A week later, during either of the two quarter Moon phases , when the Sun and Moon are at right angles to each other and their tidal influences partially cancel each other out, neap tides occur, and the tidal range is minimal.

In fact, because the oceans take a bit of time to catch up to the geometry of the Moon, spring and neap tides usually occur about a day after the respective lunar cycles. Now morn has come, TY - JOUR AU - Iwasaki, Shinsuke AU - Isobe, Atsuhiko AU - Miyao, Yasuyuki TI - Fortnightly atmospheric tides forced by spring and neap tides in coastal waters JA - Scientific Reports PY - 2015/05/18/online VL - 5 SP - 10167 EP - PB - The Author(s) SN - UR - L3 - 10.1038/srep10167 M3 - Article L3 - #supplementary-information ER - What is the difference between spring tides and neap tides? | Reference.com What is the difference between spring tides and neap tides? A: Quick Answer The difference between spring and neap tides is that spring tides are much higher than normal and neap tides are lower than normal.

Spring tides occur because of the combined effects of the sun and moon, whereas neap tides happen when the sun and the moon are at right angles. Full Answer Spring tides are exceptionally high tides because the sun, moon and Earth are aligned, and this causes the gravitational pulls of the sun and moon on the Earth to be greatly multiplied. Earth experiences spring tides only during new and full moons. Because the sun and moon are at right angles together during a neap tide, the gravitational pulls partially cancel each other. The result is a very weak tide. Neap tides occur only during quarter moons. Difference Between Neap Tide and Spring Tide | Difference Between Difference Between Neap Tide and Spring Tide • Categorized under Nature | Difference Between Neap Tide and Spring Tide Neap Tide vs Spring Tide A tide is the rise and fall of the larger bodies of water. It occurs because of the gravitational forces between the Earth, the sun, and the moon. The varying circulations of the current of the sea water cause it to be brought up onto a landmass. Places in the ocean can experience two high and low tides in each day called a semidiurnal tide. Other locations experience only one high tide and low tide called a diurnal tide.

Characteristics of a tide change through different stages. When the sea level rises and covers the foreshore, known as a flood tide, and when the water reaches its highest point it is called a high tide or high water. After a period of time, the sea level recedes showing the intertidal zone again. This is called the ebb tide. And, finally, when the water stops falling back, the stage is called a low tide. One of the earliest explanations of tides comes from Galileo Galilei. In 1632, he wrote a book named “Dialogue Concerning the Two Chief World Systems.” However, the theory was heavily disputed. It said that the movement of the Earth around the sun caused the tides. Johannes Kepler tried to correct the mistake by suggesting that the moon is the one causing the tides based on the idea of observations in the past. However, this was rejected by Galileo. The idea was corrected when Isaac Newton explained that tides are caused by the gravitational attraction of masses. In a book he published in 1687, named “The Principia,” he used his theory of universal gravitation to prove the phenomenon is caused by the lunar and solar attractions.

There are different kinds of tides depending on the alignment of the sun and moon. These two kinds are the neap tide and the spring tide. Spring tides occur on the new moon and the full moon. In this case, the gravitational attraction of the moon and sun is combined making it stronger. The high tides become higher than usual, and the low tides become very low. The alignment also causes an increased speed in tidal currents which also contributes to changes in the characteristics. A neap tide occurs when the moon, the Earth, and the sun are at right angles. This causes the attraction to cancel each other and lessens the other affecting factors as well. The angles also cause the range high tide and the low tide to have minimal differences. Summary: 1.A tide is the variation in the surface levels of the larger bodies of water. It is caused by the gravitational attraction of the sun, the moon, and the Earth. There are different stages of tides: high tide, flood tide, ebb tide, and low tide. The earliest explanation of the phenomenon came from Galileo Galilei, and the idea was corrected throughout the course of history.

2.There are also different kinds of tides that exist depending on the position of the sun, moon, and Earth. One is the neap tide which occurs when the three are at right angles, canceling the effects of one another and causing the stages of the tide to have smaller differences. The other, called a spring tide, happens when the three bodies are aligned. The effects stack up and result in a greater difference in the stages of the tides. Related Posts The Moon And Tides Moon Tides How The Moon Affects Ocean Tides... The word "tides" is a generic term used to define the alternating rise and fall in sea level with respect to the land, produced by the gravitational attraction of the moon and the sun. To a much smaller extent, tides also occur in large lakes, the atmosphere, and within the solid crust of the earth, acted upon by these same gravitational forces of the moon and sun. What are Lunar Tides Tides are created because the Earth and the moon are attracted to each other, just like magnets are attracted to each other. The moon tries to pull at anything on the Earth to bring it closer. But, the Earth is able to hold onto everything except the water.

Since the water is always moving, the Earth cannot hold onto it, and the moon is able to pull at it. Each day, there are two high tides and two low tides. The ocean is constantly moving from high tide to low tide, and then back to high tide. There is about 12 hours and 25 minutes between the two high tides. Tides are the periodic rise and falling of large bodies of water. Winds and currents move the surface water causing waves. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side). Ocean levels fluctuate daily as the sun, moon and earth interact. As the moon travels around the earth and as they, together, travel around the sun, the combined gravitational forces cause the world's oceans to rise and fall. Since the earth is rotating while this is happening, two tides occur each day.

What are the different types of Tides When the sun and moon are aligned, there are exceptionally strong gravitational forces, causing very high and very low tides which are called spring tides, though they have nothing to do with the season. When the sun and moon are not aligned, the gravitational forces cancel each other out, and the tides are not as dramatically high and low. These are called neap tides. Spring Tides When the moon is full or new, the gravitational pull of the moon and sun are combined. At these times, the high tides are very high and the low tides are very low. This is known as a spring high tide. Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon. Neap Tides During the moon's quarter phases the sun and moon work at right angles, causing the bulges to cancel each other. The result is a smaller difference between high and low tides and is known as a neap tide.

Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons. The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years. High Tide / Low Tide Examples A view of the tides at Halls Harbour on Nova Scotia's Bay of Fundy. This is a time lapse of the tidal rise and fall over a period of six and a half hours. During the next six hours of ebb the fishermen unload their boats on the dock. That's a high tide every 12 and 1/2 hours! There are two high tides every 25 hours.

A Few Facts About Lunar Tides The gravitational force of the moon is one ten-millionth that of earth, but when you combine other forces such as the earth's centrifugal force created by its spin, you get tides. The sun's gravitational force on the earth is only 46 percent that of the moon. Making the moon the single most important factor for the creation of tides. The sun's gravity also produces tides. But since the forces are smaller, as compared to the moon, the effects are greatly decreased. Tides are not caused by the direct pull of the moon's gravity. The moon is pulling upwards on the water while the earth is pulling downward. Slight advantage to the moon and thus we have tides. Whenever the Moon, Earth and Sun are aligned, the gravitational pull of the sun adds to that of the moon causing maximum tides. Spring tides happen when the sun and moon are on the same side of the earth (New Moon) or when the sun and moon are on opposite sides of the earth (Full Moon).

When the Moon is at first quarter or last quarter phase (meaning that it is located at right angles to the Earth-Sun line), the Sun and Moon interfere with each other in producing tidal bulges and tides are generally weaker; these are called neap tides. Spring tides and neap tide levels are about 20% higher or lower than average. Offshore, in the deep ocean, the difference in tides is usually less than 1.6 feet The surf grows when it approaches a beach, and the tide increases. In bays and estuaries, this effect is amplified. (In the Bay of Fundy, tides have a range of 44.6 ft.) The highest tides in the world are at the Bay of Fundy in Nova Scotia, Canada. Because the earth rotates on its axis the moon completes one orbit in our sky every 25 hours (Not to be confused with moon's 27 day orbit around the earth), we get two tidal peaks as well as two tidal troughs. These events are separated by about 12 hours. Since the moon moves around the Earth, it is not always in the same place at the same time each day.

So, each day, the times for high and low tides change by 50 minutes. The type of gravitational force that causes tides is know as "Tractive" force. FAQs About Lunar Tides From - "The Astronomy Cafe" Why are there no ocean tides at the equator? "Tides are a very complex phenomenon. For any particular location, their height and fluctuation in time depends to varying degrees on the location of the Sun and the Moon, and to the details of the shape of the beach, coastline, coastline depth and prevailing ocean currents. The tidal bulge of the Moon follows along the path on the earth's surface which intersects with the orbital plane of the Moon. This plane is tilted about 23 degrees with respect to the equatorial plane of the earth. The result is that near the equator, the difference between high tide and low tide is actually rather small, compared to other latitudes. To see this, draw a circle inscribed in an ellipse, with the major axis of the ellipse rotated by 23 degrees with respect to the circle's horizontal diameter. Now measure the height of the elliptical contour just above the 'equator' of the circle.

You will see that it is quite small compared to other positions on earth, particularly at latitudes of 23 degrees or so. Even larger differences can occur depending on the shape of a bay or inlet or continental shelf." - Dr. Odenwald's ASK THE ASTRONOMER Why are ocean tides so different everywhere? "Because they depend on many factors including the geometry of your local coastline, and exactly where the Sun and Moon are located. Also, like the surface of a vibrating drum, the world oceans have vibratory modes that get stimulated in changing ways from minute to minute. Finally, there are storms at sea and elsewhere which move large quantities of water. Detailed forecasts are available for high and low tides in all sea ports." - Dr. Odenwald's ASK THE ASTRONOMER Why aren't the Atlantic and Pacific coast tides the same? "The nature of tides on the Earth's oceans is very complex. The oceans are, of course, being periodically 'forced' by a number of tidal sources including the Moon and the Sun, but this forcing has a number of different periods and harmonics.

The two dominant periods are sue to the Sun and Moon, these are referred to as the S1 and M2 'modes' which have roughly 12 hour periods because they raise TWO water tides on the ocean diametrically opposite each other. But, for a variety of reasons, any given port will not have two high and two low tides each day; also called 'semi-diurnal tides'. A careful monitoring of the tides at any port for several years will show that in addition to the major modes, there are as many as 300 minor or 'harmonic' modes as well. The World Ocean is a complex dynamical system. The natural velocity of a water disturbance depends on the depth and salinity of the water at each point it passes. When bodies of land circumscribe bodies of water, they produce a collection of resonating systems that favor water oscillations with certain frequencies over others. From among the 300+ harmonics that can be measured, every port and coastal location has its own unique signature depending on its latitude, longitude, water depth and salinity.

The result is that the 'two high two low' tide rule can be strongly modified so that the time between successive high tides can be greater than or less that 12 hours in many cases. The result is that for some locations, there can be days when only one high tide occurs. Looking at the Atlantic and Pacific Coast tide tables for 1995, the data for the various 'Standard Ports' showed that virtually all days had two high tides and two low tides in San Diego, San Francisco, New York and Charleston. There were, however a few days every few months when only a single high tide occurred." - Dr. Odenwald's ASK THE ASTRONOMER What is a Proxigean Spring Tide? "The Moon follows an elliptical path around the Earth which has a perigee distance of 356,400 kilometers, which is about 92.7 percent of its mean distance. Because tidal forces vary as the third power of distance, this little 8 percent change translates into 25 percent increase in the tide- producing ability of the Moon upon the Earth.

If the lunar perigee occurs when the Moon is between the Sun and the Earth, it produces unusually high Spring high tides. When it occurs on the opposite side from the Earth that where the Sun is located ( during full moon) it produces unusually low, Neap Tides. The High, High Tide is called the Proxigean Spring Tide and it occurs not more than once every 1.5 years. Some occurrences are more favorable that others. A very interesting book "Tidal Dynamics" by Fergus J. Wood, published in 1986 by Reidel Publishing Company, talks at great length about these tides, and their environmental consequences. Because of the gravitational nature of the interaction between the Earth, the Moon, and the water on the Earth, there is a curious amplification event called 'evection' that occurs when the Moon is at its closest 'perigee' distance called its 'proxigee'. The Moon draws even closer to the Earth than its ordinary perigee distance. Because of the complex dynamics of the Earth's oceans, their inertia, friction with the ocean floor, internal viscosity and the distribution of the continents, the maximum tides do not always coincide with the optimal times of proxigee.

Still, these tides can produce enormous damage when all factors come together optimally. There are many recorded instances of unusually high storm or coastal flooding during the proxigean times. On January 9, 1974 the Los Angeles Times reported 'Giant Waves Pound Southland Coast". During the last 400 years, there have been 39 instances or 'Extreme Proxigean Spring Tides' where the tide-producing severity has been near the theoretical maximum. The last one of these was on March 7 1995 at 22:00 hours Greenwich Civil Time during a lunar Full Moon. There were, in fact cases of extreme tidal flooding recorded during these particular spring tides which occur once every 31 years." - Dr. Odenwald's ASK THE ASTRONOMER If the Moon were to escape, what would happen to the Earth's oceans? "What happens is that the lunar water tides on the Earth go away, but the solar water tides still occur, but with about 1/3 or so the amplitude. There are still daily high and low tides, but they would be noticeably smaller.

There would be no 'Spring' or 'Neap' tides, however."- Dr. Odenwald's ASK THE ASTRONOMER Why does the Moon produce TWO water tides on the Earth and not just one? "It is intuitively easy to understand why the gravitational pull of the Moon should produce a water tide on the Earth in the part of the ocean closest to the moon along the line connecting the center of the Moon with the center of the Earth. But in fact not one but TWO water tides are produced under which the Earth rotates every day to produce about two high tides and two low tides every day. How come? It is not the gravitational force that is doing it, but the change in the gravitational force across the body of the Earth. If you were to plot the pattern of the Moon's 'tidal' gravitational force added to the Earth's own gravitational force, at the Earth's surface, you would be able to resolve the force vectors at different latitudes and longitudes into a radial component directed towards the Earth's center, and a component tangential to the Earth's surface.

On the side nearest the moon, the 'differential' gravitational force is directed toward the Moon showing that for particles on the Earth's surface, they are being tugged slightly towards the Moon because the force of the Moon is slightly stronger at the Earth's surface than at the Earth's center which is an additional 6300 kilometers from the Moon. On the far side of the Earth, the Moon is tugging on the center of the Earth slightly stronger than it is on the far surface, so the resultant force vector is directed away from the Earth's center. The net result of this is that the Earth gets deformed into a slightly squashed, ellipsoidal shape due to these tidal forces. This happens because if we resolve the tidal forces at each point on the Earth into a local vertical and horizontal component, the horizontal components are not zero, and are directed towards the two points along the line connecting the Earth and the Moon's centers. These horizontal forces cause rock and water to feel a gravitational force which results in the flow of rock and water into the 'tidal bulges'. There will be exactly two of these bulges.

At exactly the positions of the tidal bulges where the Moon is at the zenith and at the nadir positions, there are no horizontal tidal forces and the flow stops. The water gets piled up, and the only effect is to slightly lower the weight of the water along the vertical direction. Another way of thinking about this is that the gravitational force of the Moon causes the Earth to accelerate slightly towards the Moon causing the water to get pulled towards the Moon faster than the solid rock on the side nearest the Moon. On the far side, the solid Earth 'leaves behind' some of the water which is not as strongly accelerated towards the Moon as the Earth is. This produces the bulge on the 'back side' of the Earth."- Dr. Odenwald's ASK THE ASTRONOMER What Causes Tides? "There are several kinds of tides. The ones that break upon a beach every 10 seconds to a minute are caused by sea level disturbances out in the ocean produced by such things as storms. Also, the various circulation currents of sea water can have velocity components directed towards the land which will bring water up onto the beach.

As this water travels towards the beach from deep water to shallow water, its amplitude will increase until it finally 'breaks' as a full-fledged breaker, suitable for surfing etc. Now, underlying this minute to minute activity is a slower water wave which causes an alternating pattern of high-tide, low-tide, high-tide, low-tide in most places on the Earth that are directly on the ocean. This roughly 6 hour cycle is caused by the gravitational tugging of the Moon upon the Earth. This 'tidal' pull causes the shape of the solid Earth to be not perfectly round by something like a few dozen yards over its entire 27,000 mile circumference. The Earth gets distorted a small bit, but because it is solid rock its a small effect. The water in the oceans, however, gets distorted into a roughly ellipsoidal ( football-like) shape with a much larger amplitude. The orientation of this shape changes from minute to minute as the Moon orbits the Earth, which is why the high and low tide times change all the time. The Moon causes these tides by deforming the oceans, and as the Earth rotates under this ocean bulge, it causes a high tide to propagate onto beaches.

Because there are two bulges, we get two high tides, and also two low tides each day. The Sun also causes tides on the Earth because even though it is so far away, it is very massive. These solar tides are about half as strong as the ones produced by the Moon, and they cause the so-called Spring tides and the Neap Tides. When the bulge of ocean water raised by the Moon is added the a similar tidal bulge raised by the Sun, you get a higher, high tide called the Spring Tide. When the solar low tide is added to the lunar low tide, you get the Neap Tide. There may be even weaker tides caused by the gravitational influences of the planets Mars and Venus, but they are probably lost in the daily noise of individual tides."- Dr. Odenwald's ASK THE ASTRONOMER When the Earth, Moon and Sun are aligned for Spring Tides, are they highest at Full or New Moon? "Spring tides are about the same height whether at New or Full Moon, because the tidal bulge occurs on both sides of the Earth...the side toward the Moon ( or sun) and the side away from the Moon (or Sun).

They will not be equally high because the distance between the Earth and Sun, and the Earth and Moon both vary and so will their tide producing effectiveness. The highest Spring tides occur when the Moon is at its closest to the Earth...the so-called Perigee Tide."- Dr. Odenwald's ASK THE ASTRONOMER Tides Introduction Basic information on the tides may be found in How Deep is the Ocean, How High is the Sky? . This article describes what I have found in the excellent website UK Hydrographic Office , and is primarily an analysis of the tides actually observed at ports worldwide, with some attempt to explain the peculiarities, which are many. One thing I shall do is relate the tides to the position and phases of the moon. The phases of the moon are shown on many calendars. Spring tides are associtated with new and full moons, while neap tides are associated with the quarters. These principal phases are about a week apart. Indeed, this is the origin of the week. The UKHO site predicts from the current date plus six days, covering the period between spring and neap tides quite nicely, so one access shows the whole picture.

For the actual positions of the sun and moon, I use my planetarium program Sidera, but the reader may use a commercial equivalent. Theory of the Tides It will probably be good to give a brief account of the physical basis of ocean tides here. The reader is referred to Butikov (Reference 3) for details. The theory is rather subtle, and it is easy to form incorrect notions. A tidal theory must explain the following principal observations: (1) tides are in synchronism with the Moon's motion, with a period of 24h 50m; (2) a double, or semidiurnal, tide is typically observed; (3) high and low water occur when the Moon is near the horizon; (4) spring and neap tides alternate as the relation between Sun and Moon changes; and (5) tidal signatures are quite various, as is the range of the tide. The Chinese explained the tides as the breathing of the Earth. In classical times, the relation of the tides to the moon was clearly recognized and the reason assumed to have a physical cause, though this cause could not be explained.

Kepler and Galileo tried to understand the formation of the tides, but the key was Newton's gravitational theory. Newton and Bernoulli described the tidal forces and the ellipsoidal ocean surface they would produce. This static theory explained the connection with the moon, the semidiurnal tide, and the alternation of spring and neap tides as the superposition of the lunar and solar tides, and gave a reasonable estimate of the tidal range. However, it failed badly on the phase of the tide and its great complexity. The dynamical theory of Laplace and Airy considered the tides as the effect of the excitation of normal modes of oscillation of the ocean's surface. This explained the phase problem, as well as the extremely various nature of the tidal signatures. Although this was a complete and satisfactory explanation, it is very difficult to calculate tides a priori because of the complex nature of the oceans. Nevertheless, tides can be considered as the superposition of a large number of normal oscillations and quite reliably predicted from observations. We'll now sketch the dynamical theory of the tides. The tidal forces per unit mass are shown in the figure at the right.

They are symmetrical about the line joining the sun or moon and the earth, and have a quadrupole nature. They are due entirely to the differences in the gravitational attraction at different points of the body causing the tides. The gravitational acceleration due to the sun or moon at the centre of the earth is F = GM'/R2. The vertical component of the tidal force is Fv = (3/2)(r/R)F cos 2θ, and the horizontal component is Fh = (3/2)(r/R)F sin 2θ. These accelerations are very small (about 10-7 g). Constant terms have been omitted in these expressions, and only the terms that will vary as the earth rotates are included. The horizontal components will have the major effect, since they are perpendicular to the force of gravity. The forces due to these accelerations would produce an ellipsoidal shape r(θ) = r + a cos 2θ in a static fluid. The constant a is given by 2a = (3/2)(M'/M)(r/R)3r.

From this equation, the lunar tide should have an amplitude of 2a = 54 cm, and the solar tide 24 cm. These are quite reasonable values, but note that high and low tides come with the moon in the zenith or nadir, which is incorrect. Note especially the characteristic cubic dependence on r/R, which explains the predominance of the lunar tide, even though the forces due to the sun are greater on the earth. The phase velocity of a wave of a wavelength long compared to the depth of water is v = √(gh). If the ocean is assumed to be 3.5 km deep on the average, v = 185.2 m/s. The period of a wave with a wavelength of half the circumference of the earth, or about 20,000 km, will be about 30 h. Such a wave will represent the semidiurnal tides, and is a normal mode of "sloshing" of the oceans on the earth. While thinking about these things, remember that the oceans are a very thin layer of water compared to the size of the earth, and their movement will be predominantly lateral, of which the observed vertical tides are only a reflection.

The period of the lunar tidal forces as the earth rotates is half of 24h 50m, or 12h 25m. Similarly, the period of the solar tide is 12h. Both these periods are less than the natural period of about 30 h. When an oscillator is driven by a force of period less than its natural period, the steady-state motion is opposite in phase to the driving force. Therefore, high and low water will occur for θ about equal to 90°, which explains the observed relation between the tides and the position of the moon. The exact relation, and the amplitude of the tide, depends sensitively on the decay constant of the normal mode, which is very difficult to determine. If we consider further modes of oscillation of the ocean surface, we can appreciate the possiblility of very complex tidal motions that can, however, be expressed as the superposition of modes. It is interesting to note that the relation of the period of the natural motion and the period of the tidal forces is opposite for tides in the solid earth, so that earth tides are a maximum or minimum when the moon is at the zenith or nadir.

Tides at Plymouth The first thing I want to do is to pick a definite port, and see what the tides are like there over a period of time. We can find the lunitidal interval, and the establishment of the port by these observations. The port I chose is Plymouth (Devonport), Devon, England, at about 4.5°W and 50.3°N, on the Atlantic Ocean. A tidal plot for Plymouth is shown below. (From UKHO) This is a typical semidiurnal tide, but the small diurnal component is clearly visible in the alternating levels of the high tides. The tidal range for the tides of the 16th are 5.3 - 0.8 = 4.5 m and 5.5 - 0.7 = 4.8 m, taking what seem to be corresponding highs and lows. The average range is 4.65 m at the spring tide. On the 22nd, the ranges are 4.6 - 1.8 = 2.8 m and 4.3 - 2.0 = 2.3 m, with average 2.55 m.

In June 2003, 1st quarter was on the 7th, full moon on the 14th, last quarter on the 21st, and new moon on the 29th. The highest tides were on the 16th, and the lowest on the 23rd, in each case about 48 hours after the corresponding lunar phases. This is, then, roughly the "establishment of the port," which is the age of the tide at spring and neap. The moon was on the meridian at 1.15 on the 16th, and the next high tide was at 6.57, so the lunitidal interval was 5h 42m. On the 22nd, the moon was on the meridian at 6.15, and the next high tide was at 11.53, for an interval of 5h 38m. The high tide does seem to be predictable from the position of the moon. At Plymouth, when you see the moon on the meridian, the high tide will occur about 5h 40m later.

This semidiurnal tidal behavior is found all around Britain, except for a few places where there are disturbing features, such as at Portland Bill. It is also found on the Atlantic coast of the United States, but not on the Gulf or Pacific coasts, where diurnal tides predominate. Tides at Biloxi Biloxi, Mississippi, USA is on the northern shore of the Gulf of Mexico, at about 89°W and 30.4°N. The tidal plot is quite different than the one at Plymouth: (From UKHO) The tidal range is much smaller, less than 100 cm, and the tide is diurnal. There is little trace of any semidiurnal variation. The spring tide has a range of about 90 cm, but the neap range is only about 10 cm. The tidal plot looks very much like typical beats, except that the phase does not change at a node. It also looks like a diurnal wave amplitude modulated with a frequency of one month, which is probably closer to the truth.

Tides in the Bahamas Eleuthera Island is in the eastern part of the Bahamas, east of Nassau, facing the Atlantic Ocean at 76°W and 25°N. Its tidal plot is different from those of Plymouth and Biloxi: (From UKHO) The semidiurnal and diurnal tides are mixed, with the typical Atlantic semidiurnal tide predominating. The diurnal tide is prominent in the spring tides, but decreases to a small amount at the neap tides. The tidal range is also small, not exceeding 1 m, but is still larger than that in the Gulf. This tidal plot is typical of all the Atlantic Islands, such as Bermuda and St. Helena, which have a principally semidiurnal tide of amplitude less than 1m with a more or less prominent diurnal tide making tidal heights alternate. Midocean tides normally have a small range, not amplified by the presence of continents or resonant basins.

Tides in the Gulf of Mexico and the Caribbean Sea The Gulf of Mexico is a subcircular bay about 1000 miles from east to west, and 600-800 miles from north to south, with a surface area of about 715,000 mi2. Its centre is true sea floor, at a depth of 12,425 ft. in the Sigsbee Deep. Its formation began in the Mesozoic, when the shallow proto-Atlantic evaporated huge thicknesses of salt and anhydrite, mainly in the Jurassic. A constructive plate boundary then formed, opening the Gulf and separating the salt beds in the Cretaceous, while accreting terranes blocked of access to the Pacific. The structure and history of the Gulf are not yet well known, except sketchily. Water enters the Gulf through the Strait of Yucatan, about 140 miles wide, in the southeast, and leaves through the Straits of Florida, about 90 miles wide, in the northeast, to form the warm Gulf Stream.

The Caribbean Sea is wider than the Gulf, about 1900 miles from Central America to the Leeward Islands, but narrower, about 550 miles wide, and with a slightly larger area, 750,000 mi2. A tectonic plate occupies the area of the Sea, wedged between the subducting Pacific Plate on the west, and itself subducting beneath the Atlantic plate on the east. Its average depth probably does not exceed that of the Gulf by much, but on its northern side, in a line along the Sierra Maestra of Cuba and between the Caymans and Trinidad, is a subduction trench, the Bartlett Deep, that reaches 22,788 ft. in depth. The structure and history of the Caribbean are also not well known, but both the Gulf and the Caribbean are of great geological interest. I have compared the tides at Biloxi, Galveston, Tampico and Progreso, Yucatan, which are spaced around the Gulf. If the tidal plots are superimposed in front of a strong light, it is found that low water occurs almost precisely at the same time at these widely-separated points.

High water is almost as simultaneous, but there is some variation. It is clear that water is not sloshing from side to side of the Gulf, but the level at the centre is rising and falling with a period of one day. It would be impossible for all this water to enter and leave by the straits of Florida and Yucatan and distribute itself around the Gulf in the time available, so this simple drum-like oscillation is the only possibility. Furthermore, the period of oscillation must be quite close to 24 hours, so that the diurnal stimulus can resonate to give the observed tidal ranges. The semidiurnal stimulus would not excite a significant amplitude, as is observed. The favoring of diurnal oscillations and the discouragement of semidiurnal oscillations explains the observed tides quite well, at least qualitatively. Caribbean tides show more variations than Gulf tides, but are small in amplitude, less than 50 cm, and diurnal tides are prominent. In the eastern Caribbean, the tides at St. Croix, Virgin Islands, and at Willemstad, Nederlandse Antillen, are almost entirely diurnal, like Gulf tides.

The amplitude of the spring tide is about 40 cm, and of the neap tide, 15 to 20 cm at both locations. High spring tide at St. Croix occurs about 3 hours earlier than at Willemstad, but low tide about 2h 20m later. As the amplitude of the diurnal tide decreases and the small semidiurnal tide increases at neap tides, the time sequence may vary irregularly. The tides are not simultaneous, as in the Gulf. Further west, the tides at Colón, Panama and Port Royal, Jamaica have a similar pattern, the diurnal tide predominating, but with a significant semidiurnal component that is increasingly important towards neap tides. The phases at these two rather widely-separated ports are almost exactly the same, for both components. Most of the time, there is one high tide a day, with a small advance and recession between the low tide and the next high tide. The neap tide may, however be double, with two high tides about 10 hours apart. The Colón tide is about 2h later than the Port Royal tide.

At Belize City, in the far west of the Caribbean, the tide is mainly semidiurnal, but with a diurnal component that increases toward spring tides, as usual. Typically, there are two high tides with a shallow minimum between them, separated by deeper low tides once a day. The tidal range is small, from little more than 10 cm up to 25 cm. The phase of the semidiurnal tide is 180° out of phase with the semidiurnal component at Colón, so there seems to be some semidiurnal sloshing in this area. The diurnal resonance does not appear to be as strong in the Caribbean as it is in the Gulf, nor is it as simple. There is good evidence for semidiurnal sloshing from phase relations in the western Caribbean, from north to south. The small tidal ranges show that the tidal oscillations are not part of the Atlantic tides, which have much larger amplitudes. Tides in the Atmosphere The surface barometric pressure, averaging 1013.25 mb at sea level, fluctuates slowly by a maximum of about 50 mb because of weather conditions.

There is also a regular daily variation of up to a few mb showing diurnal and semidiurnal components, like the ocean tide. This atmospheric tide is completely solar, the lunar component being too small to observe. The effect is greatest at the equator and at continental locations, with a diurnal component of 0.3 to 0.5 mb, and a semidiurnal component of 1 - 2 mb, for a total range of 3 to 4 mb daily. This range is least at the solstices, and greatest at the equinoxes. In polar regions, the amplitude of the variation is only about 0.3 mb. At Washington, DC, the daily variation is 1.2 mb. The variation is similar at all stations, more similar than that of the ocean tides, but still with characteristic differences. The variation is a maximum at 10.00 hours and a minimum at 16.00 hours, with a second maximum at 22.00 hours and a second minimum at 04.00 hours, that is generally of lower amplituded.

At continental stations such as Kansas City and Grand Junction, the night-time maximum and minimum are largely suppressed, but at the equator the two amplitudes are about the same. The diurnal effect is attributed to the heating and cooling of the atmosphere, but the semidiurnal effect is a tidal variation. The diagram at right shows the relation of the tidal variation to the earth and sun. In this diagram, only the earth and atmosphere are rotating, while the sun and elliptical shape of the atmosphere (greatly accentuated) remain fixed. The pressure maximum is seen to lead the sun by about 30°. The atmospheric shape is very much like that usually drawn to illustrate the tides. While the ocean is confined in the ocean basins, and by inlets, estuaries and straits, the atmosphere is unconfined, and can move much more freely and regularly. Like the ocean, the atmosphere is a very thin sheet; half of its mass is below 6 km altitude. Tidal motions are, therefore, mainly in the horizontal with only small vertical velocities. The wavelengths of wave motions are much greater than the thickness of the atmosphere. In addition to the atmospheric pressure waves, normal modes of oscillation have been investigated.

The periods of these modes of oscillation are all less than about 24 hours. One of these oscillations was estimated to have a natural frequency of 11.94 hours, very close to half a day. The solar tide resonates with this mode, while the lunar tide does not. Since the losses are small, the resonance is sharp, and the amplitude of the oscillation excited by the regular stimulus of the sun's attraction can grow to the observed value. This is the reason for the predominance of the semidiurnal component, and the absence of the lunar tide. Without the resonance, atmospheric tides would be too small to observe. The atmospheric tide makes observations of 3-hour variations in atmospheric pressure at equatorial locations meaningless, since the variations sought are of the same magnitude. References The tidal plots used as illustrations are from the EasyTide service of UK Hydrographic Office . I presume that this educational, noncommercial use of a few examples is permissible, and I hestitate to pester authorities with such small matters, especially since the copyright notices specifically refer to commercial uses, and the plots used as examples in this page are of past tides, which are of no commercial value whatsoever.

I have, of course, given proper credit, and have maintained the copyright notices. F. A. Berry, E. Bollay and N. R. Beers, eds., Handbook of Meteorology (New York: McGraw-Hill, 1945). pp. 483-498 and 746-749. Atmospheric tides. E. I. Butikov, A dynamical picture of the oceanic tides, Am. J. Phys. 70, 1001-1011 (2002). R. de Levie, Tidal Analysis on a Spreadsheet, Am. J. Phys. 72, 644-651 (2004). A short history of tidal studies, and the use of Excel macros to analyze tidal data. The observed tides at Eastport, Maine from 1 June to 31 July 2001 are the example. This is a primarily semidiurnal tide with a small diurnal component.

The diurnal component shows up clearly in the power spectrum, but the author does not draw attention to it, instead looking for a solar semidiurnal tide (which is not evident) close to the strong lunar component. Long-period components are ignored. Composed by J. B. Calvert Created 17 June 2003 NOAA's National Ocean Service: Animation of spring and neap tides Back Together, the gravitational pull of the moon and the sun affect the Earths tides on a monthly basis. When the sun, moon, and Earth are in alignment (at the time of the new or full moon), the solar tide has an additive effect on the lunar tide, creating extra-high high tides, and very low, low tides  both commonly called spring tides. One week later, when the sun and moon are at right angles to each other, the solar tide partially cancels out the lunar tide and produces moderate tides known as neap tides. During each lunar month, two sets of spring and two sets of neap tides occur (Sumich, J.L., 1996). How often do spring tides occur? | Reference.com How often do spring tides occur?

A: Quick Answer Spring tides occur twice a month during the full and new moons. Spring tides are the result of the alignment of the Sun, Moon and Earth and the effects of their gravitational forces. Spring tides are also high tides. Full Answer A rare type of spring tide is a perigean spring tide: it occurs only a few times a year. The occurrence of this high tide type is due to the new or full moon being at its closest distance to the Earth. Another type of tide, the neap tide, occurs twice per month. However, this tide type occurs when the Moon's and Sun's gravitational forces form a 90-degree angle with respect to the Earth. Neap tides happen during the first and third quarter moons. Tides explained Yet More... Tides Most people grow up thinking that the tides are caused by the moon, and indeed that gravitational 'pull' of the moon is a major factor, as is the gravitational effect of the sun but there is another major factor, which is less often mentioned, and that is the force created by the rotation of the earth itself.

So the diagram on the left shows how the water on the earth gets pulled into a bulge one way by the moon's gravity and into a bulge on the opposite side by the rotational force of the earth. As the earth rotates on its axis once every 24 hours, if the moon stood still then the moon will be overhead and 'underfoot' once in every 24 hours giving (in most places) 2 high and 2 low tides a day, but as the moon is also orbiting in the same direction as the earth revolves it actually takes about 24 hours and 50 minutes for the moon to be in the same place overhead. So the period from one high tide to the next is about 12 hours 25 minutes. Spring Tides When the sun, moon and earth all line up at new (as in the picture) or full moon then we get the highest (and indeed lowest) tides which are called 'spring' tides (nothing to do with the time of year!).

In fact it takes a bit of time for the enormous mass of water to move, so the spring tide will actually occur a couple of days after the new (or full) moon, so the picture on the left is a simplification. You can find more on ( moon phases here ) Because of the tilt of the earth on its axis, at the equinox the sun appears to be over the equator and if there is a new or full moon at about the same time then all the forces contrive to create the highest of high tides and if the moon is also at perigee (closest to the earth in its orbit) then that will produce the biggest tides of all. Neap Tides When the moon is at first or third quarter (you can find more on moon phases here ) then the moon and sun are exerting forces from two different directions and the overall effect on the water is less, so the high tides are lower than average and the low tides are higher than the average and we call these low tides 'neap' tides. The word 'neap' is thought to have originated from the Middle English Word 'neep' meaning small.

Other Factors and Facts Although the sun, the moon and the rotation of the earth are the major forces involved in creating the tides the local conditions such as the shoreline and the contour of the ocean floor also have an effect. Because of this not everywhere has 2 tides a day - there are some places that experience what is known as a double-high water (e.g. Southampton) or double-low water (e.g. Portland). The highest tides of all (17m) occur in Canada and after a long running dispute between the famous tides of the Bay of Fundy and those of Ungava Bay on the northern coast of Quebec, the Canadian Hydrographic Service has declared a draw. Most people think of the Mediterranean area as being without tides and it is true that the tides there are very small, and can often go unnoticed as atmospheric conditions and headwinds can attenuate the effect of these tides making them difficult to see. The very smallest tidal ranges (actually 0) are found in the Adriatic and South of Sicily. "Everything has a natural explanation. The moon is not a god, but a great rock, and the sun a hot rock.

" Anaxagoras "I think that when NASA works on a moon shot, they know too well that all of the people working on it must do their job at 110 percent. Sometimes they probably put in 18 hour days, but they're aiming for the moon, and that's what counts. " Marvin Hamlisch

Question: In nature, what are Spring and Neap?
Answer: Tides