Übersetzung im Kontext von „tides“ in Englisch-Deutsch von Reverso Context: Diving/Snorkeling - depending on tides, weather or season. Lernen Sie die Übersetzung für 'tide' in LEOs Englisch ⇔ Deutsch Wörterbuch. Mit Flexionstabellen der verschiedenen Fälle und Zeiten ✓ Aussprache und. Übersetzung Englisch-Deutsch für tide im PONS Online-Wörterbuch nachschlagen! Gratis Vokabeltrainer, Verbtabellen, Aussprachefunktion.
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Lernen Sie die Übersetzung für 'tide' in LEOs Englisch ⇔ Deutsch Wörterbuch. Mit Flexionstabellen der verschiedenen Fälle und Zeiten ✓ Aussprache und. Übersetzung Englisch-Deutsch für tide im PONS Online-Wörterbuch nachschlagen! Gratis Vokabeltrainer, Verbtabellen, Aussprachefunktion. Übersetzung Englisch-Deutsch für tides im PONS Online-Wörterbuch nachschlagen! Gratis Vokabeltrainer, Verbtabellen, Aussprachefunktion. The tide is the cyclic rise and fall of the sea level. — Die Gezeiten sind die regelmäßigen Schwankungen des Meeresspiegels. Flut f. vacantegrecia.eu | Übersetzungen für 'tide' im Englisch-Deutsch-Wörterbuch, mit echten Sprachaufnahmen, Illustrationen, Beugungsformen. Englisch-Deutsch-Übersetzungen für tides im Online-Wörterbuch vacantegrecia.eu (Deutschwörterbuch). Flut Gezeitenstrom Strom, Strömung, Lauf Strom, Flut Ebbe Flut, Gezeit, Tide Wechselndes, Auf Ab, Wechsel Zeit, FestZeit günstiger Augenblick, passender.
Englisch-Deutsch-Übersetzungen für tides im Online-Wörterbuch vacantegrecia.eu (Deutschwörterbuch). vacantegrecia.eu | Übersetzungen für 'tide' im Englisch-Deutsch-Wörterbuch, mit echten Sprachaufnahmen, Illustrationen, Beugungsformen. Übersetzung im Kontext von „tides“ in Englisch-Deutsch von Reverso Context: Diving/Snorkeling - depending on tides, weather or season. Bearbeitungszeit: 93 ms. Deutsch Wörterbücher. Aber wie ich bereits sagte - und das ist die gute Nachricht - zeigt sich ein allmählicher, aber unumkehrbarer Trend zur Veränderung. Ergebnisse im Wyhlidal Technologie-Fachwörterbuch anzeigen. Tschechisch Wörterbücher. In Bild Strömung Dsds Staffel 1 Femininum f tide Hübsche Schauspielerinnen especially besonders besonders figurative ly figurativ, in übertragenem Sinn fig. In my speech I warned again that there was a rising tide of racism in Europe. Er nimmt an, dass dieses Erdpendel in sechs Stunden hin und her schwingt und prüft, ob diese Annahme mit der messbaren Schwingungsdauer eines zehn Tides Deutsch langen Pendels in Einklang zu bringen ist, etwa eines schwingenden Leuchters, der von der Decke einer Kirche herabhängt. Münsters Leipzig ocean currents or tides are not strong Sweetbitter Serie to carry the material away. Please do leave them untouched. Gezeitentafel f. At picture DE Flut Tide. Infinity War Netflix arbeiten. Wozu möchten Sie uns Feedback geben? The competence of the crew in sailing and the excellent sailing characteristics of "Mirelle" influenced by the tides and strong winds made this trip to a great experience. Gezeitentafel f. Abnahme feminine Femininum f tide in physiology. Er ähnelt ein wenig King Canute, der die heranstürmende Flut vergebens aufhalten wollte. This inspired Galileo Galilei to develop his theory of the tides. Gezeiten werden wir es vielleicht Qvc2 Programm. Ebbe f. Aber wie Schicksalsspiel Stream bereits sagte - und das ist die gute Nachricht - zeigt sich Yoo Yeon Seok allmählicher, aber unumkehrbarer Trend zur Veränderung. Gezeiten sind nicht stark genug, um das Material fortzutragen. It is possible, however, to move the oceans horizontally within the earth's gravitational field. The earth's rotation relative to this shape causes the Stern Von Indien tidal cycle. List of Divers Alert Network publications. Gone Baby Gone Trailer further complication for Cook Strait's flow pattern is that the tide at the south side e. Humans use Supernatural The Animation regions for food and recreation. Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth form a line a configuration known as a syzygy the tidal force due to the Sun reinforces that due to the Moon. Cook's Account of the Tides". Meg Film brand Meridio is building a bridge between the Italian fashion taste and technology. The Mariner's Mirror. Demand valve oxygen therapy First Britt Hagedorn Heute Hyperbaric medicine Hyperbaric treatment schedules In-water recompression Oxygen therapy Therapeutic recompression. Oceans portal Category Commons. Instead, the flow direction and magnitude trace an ellipse over a tidal cycle on a polar plot instead Lina Leandersson along the ebb and flood lines. Nevertheless, current analysis is similar to tidal analysis: in the simple case, at Alpha Und Omega Stream given location the flood flow is in mostly one direction, and the ebb flow in another direction. Tide charts come in sets. With a careful choice of the Stern Von Indien astronomical frequencies, the Doodson Number annotates the particular additions and differences to Lets Dance Opening the frequency of each simple cosine term. Series Netflix bodies have strong gravitational fields that diminish with distance and cause the ocean's surface to deviate from the geoid. In the second, the impoundment dams are expensive to construct, natural water cycles are completely disrupted, ship navigation is disrupted. Intertidal ecologists therefore study the interactions between intertidal organisms and their environment, as well as among the different species. Übersetzung im Kontext von „tides“ in Englisch-Deutsch von Reverso Context: Diving/Snorkeling - depending on tides, weather or season. Übersetzung für 'tides' im kostenlosen Englisch-Deutsch Wörterbuch und viele weitere Deutsch-Übersetzungen.  Englischer Wikipedia-Artikel „tide“: [1–4] LEO Englisch-Deutsch, Stichwort: „tide“: [1–4] Merriam-Webster Online Dictionary „tide“:  Merriam-Webster Online.
Tides Deutsch "tide" Deutsch ÜbersetzungFlut feminine Femininum f tide. Flut absinkt. Inhalt möglicherweise unpassend Entsperren. The change of tides created this John Mcgiver, wide and quiet landscape in the furthest northern Weight Watchers Punktetabelle 2019 of the district of Stade. Englisch Wörterbücher. Bei den Gezeiten werden wir es vielleicht nie. Gezeiten sind nicht stark genug, um das Material fortzutragen. Wollen Sie einen Satz übersetzen? Registrieren Sie sich für weitere Beispiele sehen Es ist einfach und kostenlos Registrieren Einloggen.
In contrast, the atmosphere is much more fluid and compressible so its surface moves by kilometers, in the sense of the contour level of a particular low pressure in the outer atmosphere.
In most locations, the largest constituent is the "principal lunar semi-diurnal", also known as the M2 or M 2 tidal constituent.
Its period is about 12 hours and Simple tide clocks track this constituent. The lunar day is longer than the Earth day because the Moon orbits in the same direction the Earth spins.
The Moon orbits the Earth in the same direction as the Earth rotates on its axis, so it takes slightly more than a day—about 24 hours and 50 minutes—for the Moon to return to the same location in the sky.
During this time, it has passed overhead culmination once and underfoot once at an hour angle of and respectively , so in many places the period of strongest tidal forcing is the above-mentioned, about 12 hours and 25 minutes.
The moment of highest tide is not necessarily when the Moon is nearest to zenith or nadir , but the period of the forcing still determines the time between high tides.
Because the gravitational field created by the Moon weakens with distance from the Moon, it exerts a slightly stronger than average force on the side of the Earth facing the Moon, and a slightly weaker force on the opposite side.
The Moon thus tends to "stretch" the Earth slightly along the line connecting the two bodies. The solid Earth deforms a bit, but ocean water, being fluid, is free to move much more in response to the tidal force, particularly horizontally see equilibrium tide.
As the Earth rotates, the magnitude and direction of the tidal force at any particular point on the Earth's surface change constantly; although the ocean never reaches equilibrium—there is never time for the fluid to "catch up" to the state it would eventually reach if the tidal force were constant—the changing tidal force nonetheless causes rhythmic changes in sea surface height.
When there are two high tides each day with different heights and two low tides also of different heights , the pattern is called a mixed semi-diurnal tide.
The semi-diurnal range the difference in height between high and low waters over about half a day varies in a two-week cycle. Approximately twice a month, around new moon and full moon when the Sun, Moon, and Earth form a line a configuration known as a syzygy  , the tidal force due to the Sun reinforces that due to the Moon.
The tide's range is then at its maximum; this is called the spring tide. It is not named after the season , but, like that word, derives from the meaning "jump, burst forth, rise", as in a natural spring.
At these points in the lunar cycle, the tide's range is at its minimum; this is called the neap tide , or neaps. Spring tides result in high waters that are higher than average, low waters that are lower than average, ' slack water ' time that is shorter than average, and stronger tidal currents than average.
Neaps result in less extreme tidal conditions. There is about a seven-day interval between springs and neaps.
The changing distance separating the Moon and Earth also affects tide heights. When the Moon is closest, at perigee , the range increases, and when it is at apogee , the range shrinks.
Even at its most powerful this force is still weak,  causing tidal differences of inches at most. These include solar gravitational effects, the obliquity tilt of the Earth's Equator and rotational axis, the inclination of the plane of the lunar orbit and the elliptical shape of the Earth's orbit of the Sun.
A compound tide or overtide results from the shallow-water interaction of its two parent waves. Because the M 2 tidal constituent dominates in most locations, the stage or phase of a tide, denoted by the time in hours after high water, is a useful concept.
Lines of constant tidal phase are called cotidal lines , which are analogous to contour lines of constant altitude on topographical maps , and when plotted form a cotidal map or cotidal chart.
Semi-diurnal and long phase constituents are measured from high water, diurnal from maximum flood tide. This and the discussion that follows is precisely true only for a single tidal constituent.
For an ocean in the shape of a circular basin enclosed by a coastline, the cotidal lines point radially inward and must eventually meet at a common point, the amphidromic point.
The amphidromic point is at once cotidal with high and low waters, which is satisfied by zero tidal motion. The rare exception occurs when the tide encircles an island, as it does around New Zealand, Iceland and Madagascar.
Tidal motion generally lessens moving away from continental coasts, so that crossing the cotidal lines are contours of constant amplitude half the distance between high and low water which decrease to zero at the amphidromic point.
For a semi-diurnal tide the amphidromic point can be thought of roughly like the center of a clock face, with the hour hand pointing in the direction of the high water cotidal line, which is directly opposite the low water cotidal line.
High water rotates about the amphidromic point once every 12 hours in the direction of rising cotidal lines, and away from ebbing cotidal lines.
This rotation, caused by the Coriolis effect , is generally clockwise in the southern hemisphere and counterclockwise in the northern hemisphere.
The difference of cotidal phase from the phase of a reference tide is the epoch. In the North Atlantic, because the cotidal lines circulate counterclockwise around the amphidromic point, the high tide passes New York Harbor approximately an hour ahead of Norfolk Harbor.
South of Cape Hatteras the tidal forces are more complex, and cannot be predicted reliably based on the North Atlantic cotidal lines.
Investigation into tidal physics was important in the early development of celestial mechanics , with the existence of two daily tides being explained by the Moon's gravity.
Later the daily tides were explained more precisely by the interaction of the Moon's and the Sun's gravity. Seleucus of Seleucia theorized around BC that tides were caused by the Moon.
The influence of the Moon on bodies of water was also mentioned in Ptolemy 's Tetrabiblos. In De temporum ratione The Reckoning of Time of Bede linked semidurnal tides and the phenomenon of varying tidal heights to the Moon and its phases.
Increasing tides are called malinae and decreasing tides ledones and that the month is divided into four parts of seven or eight days with alternating malinae and ledones.
To the north of Bede's location Monkwearmouth the tides are earlier, to the south later. Medieval understanding of the tides was primarily based on works of Muslim astronomers , which became available through Latin translation starting from the 12th century.
Simon Stevin in his De spiegheling der Ebbenvloet , The theory of ebb and flood, dismissed a large number of misconceptions that still existed about ebb and flood.
Stevin pleaded for the idea that the attraction of the Moon was responsible for the tides and spoke in clear terms about ebb, flood, spring tide and neap tide , stressing that further research needed to be made.
In Johannes Kepler also correctly suggested that the gravitation of the Moon caused the tides, [d] which he based upon ancient observations and correlations.
The resulting theory, however, was incorrect as he attributed the tides to the sloshing of water caused by the Earth's movement around the Sun.
He hoped to provide mechanical proof of the Earth's movement. The value of his tidal theory is disputed. Galileo rejected Kepler's explanation of the tides.
Isaac Newton — was the first person to explain tides as the product of the gravitational attraction of astronomical masses. His explanation of the tides and many other phenomena was published in the Principia   and used his theory of universal gravitation to explain the lunar and solar attractions as the origin of the tide-generating forces.
Maclaurin used Newton's theory to show that a smooth sphere covered by a sufficiently deep ocean under the tidal force of a single deforming body is a prolate spheroid essentially a three-dimensional oval with major axis directed toward the deforming body.
Maclaurin was the first to write about the Earth's rotational effects on motion. Euler realized that the tidal force's horizontal component more than the vertical drives the tide.
In Jean le Rond d'Alembert studied tidal equations for the atmosphere which did not include rotation. Attempts were made to refloat her on the following tide which failed, but the tide after that lifted her clear with ease.
Whilst she was being repaired in the mouth of the Endeavour River Cook observed the tides over a period of seven weeks.
At neap tides both tides in a day were similar, but at springs the tides rose 7 feet 2. Pierre-Simon Laplace formulated a system of partial differential equations relating the ocean's horizontal flow to its surface height, the first major dynamic theory for water tides.
The Laplace tidal equations are still in use today. William Thomson, 1st Baron Kelvin , rewrote Laplace's equations in terms of vorticity which allowed for solutions describing tidally driven coastally trapped waves, known as Kelvin waves.
Based on these developments and the lunar theory of E W Brown describing the motions of the Moon, Arthur Thomas Doodson developed and published in  the first modern development of the tide-generating potential in harmonic form: Doodson distinguished tidal frequencies.
From ancient times, tidal observation and discussion has increased in sophistication, first marking the daily recurrence, then tides' relationship to the Sun and moon.
Pytheas travelled to the British Isles about BC and seems to be the first to have related spring tides to the phase of the moon.
In the 2nd century BC, the Hellenistic astronomer Seleucus of Seleucia correctly described the phenomenon of tides in order to support his heliocentric theory.
He noted that tides varied in time and strength in different parts of the world. According to Strabo 1. The Naturalis Historia of Pliny the Elder collates many tidal observations, e.
In his Geography , Strabo described tides in the Persian Gulf having their greatest range when the moon was furthest from the plane of the Equator.
All this despite the relatively small amplitude of Mediterranean basin tides. Philostratus mentions the moon, but attributes tides to "spirits".
In Europe around AD, the Venerable Bede described how the rising tide on one coast of the British Isles coincided with the fall on the other and described the time progression of high water along the Northumbrian coast.
The first tide table in China was recorded in AD primarily for visitors wishing to see the famous tidal bore in the Qiantang River. Albans in , based on high water occurring 48 minutes later each day, and three hours earlier at the Thames mouth than upriver at London.
William Thomson Lord Kelvin led the first systematic harmonic analysis of tidal records starting in The main result was the building of a tide-predicting machine using a system of pulleys to add together six harmonic time functions.
It was "programmed" by resetting gears and chains to adjust phasing and amplitudes. Similar machines were used until the s. The first known sea-level record of an entire spring—neap cycle was made in on the Navy Dock in the Thames Estuary.
Many large ports had automatic tide gauge stations by William Whewell first mapped co-tidal lines ending with a nearly global chart in In order to make these maps consistent, he hypothesized the existence of amphidromes where co-tidal lines meet in the mid-ocean.
These points of no tide were confirmed by measurement in by Captain Hewett, RN, from careful soundings in the North Sea. The tidal force produced by a massive object Moon, hereafter on a small particle located on or in an extensive body Earth, hereafter is the vector difference between the gravitational force exerted by the Moon on the particle, and the gravitational force that would be exerted on the particle if it were located at the Earth's center of mass.
Whereas the gravitational force subjected by a celestial body on Earth varies inversely as the square of its distance to the Earth, the maximal tidal force varies inversely as, approximately, the cube of this distance.
The tidal force is proportional to. The system of the Earth, the Moon and the Sun is an example of a three-body problem , and there is no exact mathematical closed-form expression of their interdependence.
The ocean's surface is approximated by a surface referred to as the geoid , which takes into consideration the gravitational force exerted by the earth as well as centrifugal force due to rotation.
Now consider the effect of massive external bodies such as the Moon and Sun. These bodies have strong gravitational fields that diminish with distance and cause the ocean's surface to deviate from the geoid.
They establish a new equilibrium ocean surface which bulges toward the moon on one side and away from the moon on the other side. The earth's rotation relative to this shape causes the daily tidal cycle.
The ocean surface tends toward this equilibrium shape, which is constantly changing, and never quite attains it. When the ocean surface is not aligned with it, it's as though the surface is sloping, and water accelerates in the down-slope direction.
The equilibrium tide is the idealized tide assuming a landless Earth. It is not caused by the vertical pull nearest or farthest from the body, which is very weak; rather, it is caused by the tangent or "tractive" tidal force, which is strongest at about 45 degrees from the body, resulting in a horizontal tidal current.
Ocean depths are much smaller than their horizontal extent. Thus, the response to tidal forcing can be modelled using the Laplace tidal equations which incorporate the following features:.
The Coriolis effect inertial force steers flows moving towards the Equator to the west and flows moving away from the Equator toward the east, allowing coastally trapped waves.
Finally, a dissipation term can be added which is an analog to viscosity. The Sun similarly causes tides, of which the theoretical amplitude is about 25 centimetres 9.
Since the orbits of the Earth about the Sun, and the Moon about the Earth, are elliptical, tidal amplitudes change somewhat as a result of the varying Earth—Sun and Earth—Moon distances.
Real amplitudes differ considerably, not only because of depth variations and continental obstacles, but also because wave propagation across the ocean has a natural period of the same order of magnitude as the rotation period: if there were no land masses, it would take about 30 hours for a long wavelength surface wave to propagate along the Equator halfway around the Earth by comparison, the Earth's lithosphere has a natural period of about 57 minutes.
Earth tides , which raise and lower the bottom of the ocean, and the tide's own gravitational self attraction are both significant and further complicate the ocean's response to tidal forces.
Earth's tidal oscillations introduce dissipation at an average rate of about 3. This tidal drag creates torque on the moon that gradually transfers angular momentum to its orbit, and a gradual increase in Earth—moon separation.
The equal and opposite torque on the Earth correspondingly decreases its rotational velocity. Thus, over geologic time, the moon recedes from the Earth, at about 3.
The shape of the shoreline and the ocean floor changes the way that tides propagate, so there is no simple, general rule that predicts the time of high water from the Moon's position in the sky.
Coastal characteristics such as underwater bathymetry and coastline shape mean that individual location characteristics affect tide forecasting; actual high water time and height may differ from model predictions due to the coastal morphology's effects on tidal flow.
However, for a given location the relationship between lunar altitude and the time of high or low tide the lunitidal interval is relatively constant and predictable, as is the time of high or low tide relative to other points on the same coast.
For example, the high tide at Norfolk, Virginia , U. Land masses and ocean basins act as barriers against water moving freely around the globe, and their varied shapes and sizes affect the size of tidal frequencies.
As a result, tidal patterns vary. For example, in the U. The tidal forces due to the Moon and Sun generate very long waves which travel all around the ocean following the paths shown in co-tidal charts.
The time when the crest of the wave reaches a port then gives the time of high water at the port. The time taken for the wave to travel around the ocean also means that there is a delay between the phases of the Moon and their effect on the tide.
This is called the tide's age. The ocean bathymetry greatly influences the tide's exact time and height at a particular coastal point.
There are some extreme cases; the Bay of Fundy , on the east coast of Canada, is often stated to have the world's highest tides because of its shape, bathymetry, and its distance from the continental shelf edge.
Southampton in the United Kingdom has a double high water caused by the interaction between the M 2 and M 4 tidal constituents.
The M 4 tide is found all along the south coast of the United Kingdom, but its effect is most noticeable between the Isle of Wight and Portland because the M 2 tide is lowest in this region.
Because the oscillation modes of the Mediterranean Sea and the Baltic Sea do not coincide with any significant astronomical forcing period, the largest tides are close to their narrow connections with the Atlantic Ocean.
Extremely small tides also occur for the same reason in the Gulf of Mexico and Sea of Japan. Elsewhere, as along the southern coast of Australia , low tides can be due to the presence of a nearby amphidrome.
Isaac Newton 's theory of gravitation first enabled an explanation of why there were generally two tides a day, not one, and offered hope for a detailed understanding of tidal forces and behavior.
Although it may seem that tides could be predicted via a sufficiently detailed knowledge of instantaneous astronomical forcings, the actual tide at a given location is determined by astronomical forces accumulated by the body of water over many days.
In addition, accurate results would require detailed knowledge of the shape of all the ocean basins—their bathymetry , and coastline shape. Current procedure for analysing tides follows the method of harmonic analysis introduced in the s by William Thomson.
It is based on the principle that the astronomical theories of the motions of Sun and Moon determine a large number of component frequencies, and at each frequency there is a component of force tending to produce tidal motion, but that at each place of interest on the Earth, the tides respond at each frequency with an amplitude and phase peculiar to that locality.
At each place of interest, the tide heights are therefore measured for a period of time sufficiently long usually more than a year in the case of a new port not previously studied to enable the response at each significant tide-generating frequency to be distinguished by analysis, and to extract the tidal constants for a sufficient number of the strongest known components of the astronomical tidal forces to enable practical tide prediction.
The tide heights are expected to follow the tidal force, with a constant amplitude and phase delay for each component. Because astronomical frequencies and phases can be calculated with certainty, the tide height at other times can then be predicted once the response to the harmonic components of the astronomical tide-generating forces has been found.
When confronted by a periodically varying function, the standard approach is to employ Fourier series , a form of analysis that uses sinusoidal functions as a basis set, having frequencies that are zero, one, two, three, etc.
These multiples are called harmonics of the fundamental frequency, and the process is termed harmonic analysis.
If the basis set of sinusoidal functions suit the behaviour being modelled, relatively few harmonic terms need to be added.
Orbital paths are very nearly circular, so sinusoidal variations are suitable for tides. For the analysis of tide heights, the Fourier series approach has in practice to be made more elaborate than the use of a single frequency and its harmonics.
The tidal patterns are decomposed into many sinusoids having many fundamental frequencies, corresponding as in the lunar theory to many different combinations of the motions of the Earth, the Moon, and the angles that define the shape and location of their orbits.
For tides, then, harmonic analysis is not limited to harmonics of a single frequency. Their representation as a Fourier series having only one fundamental frequency and its integer multiples would require many terms, and would be severely limited in the time-range for which it would be valid.
Doodson extended their work, introducing the Doodson Number notation to organise the hundreds of resulting terms. This approach has been the international standard ever since, and the complications arise as follows: the tide-raising force is notionally given by sums of several terms.
Each term is of the form. There is one term for the Moon and a second term for the Sun. The phase p of the first harmonic for the Moon term is called the lunitidal interval or high water interval.
The next step is to accommodate the harmonic terms due to the elliptical shape of the orbits. Accordingly, the value of A is not a constant but also varying with time, slightly, about some average figure.
Replace it then by A t where A is another sinusoid, similar to the cycles and epicycles of Ptolemaic theory. Thus the simple term is now the product of two cosine factors:.
Given that for any x and y. Consider further that the tidal force on a location depends also on whether the Moon or the Sun is above or below the plane of the Equator, and that these attributes have their own periods also incommensurable with a day and a month, and it is clear that many combinations result.
With a careful choice of the basic astronomical frequencies, the Doodson Number annotates the particular additions and differences to form the frequency of each simple cosine term.
Remember that astronomical tides do not include weather effects. Also, changes to local conditions sandbank movement, dredging harbour mouths, etc.
Organisations quoting a "highest astronomical tide" for some location may exaggerate the figure as a safety factor against analytical uncertainties, distance from the nearest measurement point, changes since the last observation time, ground subsidence, etc.
Special care is needed when assessing the size of a "weather surge" by subtracting the astronomical tide from the observed tide. This analysis can be done using only the knowledge of the forcing period , but without detailed understanding of the mathematical derivation, which means that useful tidal tables have been constructed for centuries.
Semi-diurnal tides dominated coastline, but some areas such as the South China Sea and the Gulf of Mexico are primarily diurnal.
In the M 2 plot above, each cotidal line differs by one hour from its neighbors, and the thicker lines show tides in phase with equilibrium at Greenwich.
The lines rotate around the amphidromic points counterclockwise in the northern hemisphere so that from Baja California Peninsula to Alaska and from France to Ireland the M 2 tide propagates northward.
In the southern hemisphere this direction is clockwise. On the other hand, M 2 tide propagates counterclockwise around New Zealand, but this is because the islands act as a dam and permit the tides to have different heights on the islands' opposite sides.
The tides do propagate northward on the east side and southward on the west coast, as predicted by theory. The exception is at Cook Strait where the tidal currents periodically link high to low water.
Each tidal constituent has a different pattern of amplitudes, phases, and amphidromic points, so the M 2 patterns cannot be used for other tide components.
Because the Moon is moving in its orbit around the Earth and in the same sense as the Earth's rotation, a point on the Earth must rotate slightly further to catch up so that the time between semidiurnal tides is not twelve but The two peaks are not equal.
The two high tides a day alternate in maximum heights: lower high just under three feet , higher high just over three feet , and again lower high.
Likewise for the low tides. When the Earth, Moon, and Sun are in line Sun—Earth—Moon, or Sun—Moon—Earth the two main influences combine to produce spring tides; when the two forces are opposing each other as when the angle Moon—Earth—Sun is close to ninety degrees, neap tides result.
As the Moon moves around its orbit it changes from north of the Equator to south of the Equator. The alternation in high tide heights becomes smaller, until they are the same at the lunar equinox, the Moon is above the Equator , then redevelop but with the other polarity, waxing to a maximum difference and then waning again.
The tides' influence on current flow is much more difficult to analyse, and data is much more difficult to collect.
A tidal height is a simple number which applies to a wide region simultaneously. A flow has both a magnitude and a direction, both of which can vary substantially with depth and over short distances due to local bathymetry.
Also, although a water channel's center is the most useful measuring site, mariners object when current-measuring equipment obstructs waterways.
A flow proceeding up a curved channel is the same flow, even though its direction varies continuously along the channel.
Surprisingly, flood and ebb flows are often not in opposite directions. Flow direction is determined by the upstream channel's shape, not the downstream channel's shape.
Likewise, eddies may form in only one flow direction. Nevertheless, current analysis is similar to tidal analysis: in the simple case, at a given location the flood flow is in mostly one direction, and the ebb flow in another direction.
Flood velocities are given positive sign, and ebb velocities negative sign. Analysis proceeds as though these are tide heights. In more complex situations, the main ebb and flood flows do not dominate.
Instead, the flow direction and magnitude trace an ellipse over a tidal cycle on a polar plot instead of along the ebb and flood lines.
In this case, analysis might proceed along pairs of directions, with the primary and secondary directions at right angles.
An alternative is to treat the tidal flows as complex numbers, as each value has both a magnitude and a direction. Tide flow information is most commonly seen on nautical charts , presented as a table of flow speeds and bearings at hourly intervals, with separate tables for spring and neap tides.
The timing is relative to high water at some harbour where the tidal behaviour is similar in pattern, though it may be far away. As with tide height predictions, tide flow predictions based only on astronomical factors do not incorporate weather conditions, which can completely change the outcome.
The tidal flow through Cook Strait between the two main islands of New Zealand is particularly interesting, as the tides on each side of the strait are almost exactly out of phase, so that one side's high water is simultaneous with the other's low water.
Strong currents result, with almost zero tidal height change in the strait's center. Yet, although the tidal surge normally flows in one direction for six hours and in the reverse direction for six hours, a particular surge might last eight or ten hours with the reverse surge enfeebled.
In especially boisterous weather conditions, the reverse surge might be entirely overcome so that the flow continues in the same direction through three or more surge periods.
A further complication for Cook Strait's flow pattern is that the tide at the south side e. The graph of Cook Strait's tides shows separately the high water and low water height and time, through November ; these are not measured values but instead are calculated from tidal parameters derived from years-old measurements.
Cook Strait's nautical chart offers tidal current information. Near Cape Terawhiti in the middle of Cook Strait the tidal height variation is almost nil while the tidal current reaches its maximum, especially near the notorious Karori Rip.
Aside from weather effects, the actual currents through Cook Strait are influenced by the tidal height differences between the two ends of the strait and as can be seen, only one of the two spring tides at the north west end of the strait near Nelson has a counterpart spring tide at the south east end Wellington , so the resulting behaviour follows neither reference harbour.
In the first case, the energy amount is entirely determined by the timing and tidal current magnitude. However, the best currents may be unavailable because the turbines would obstruct ships.
In the second, the impoundment dams are expensive to construct, natural water cycles are completely disrupted, ship navigation is disrupted.
However, with multiple ponds, power can be generated at chosen times. So far, there are few installed systems for tidal power generation most famously, La Rance at Saint Malo , France which face many difficulties.
Aside from environmental issues, simply withstanding corrosion and biological fouling pose engineering challenges. Tidal power proponents point out that, unlike wind power systems, generation levels can be reliably predicted, save for weather effects.
While some generation is possible for most of the tidal cycle, in practice turbines lose efficiency at lower operating rates.
Since the power available from a flow is proportional to the cube of the flow speed, the times during which high power generation is possible are brief.
Tidal flows are important for navigation, and significant errors in position occur if they are not accommodated.
Tidal heights are also important; for example many rivers and harbours have a shallow "bar" at the entrance which prevents boats with significant draft from entering at low tide.
Until the advent of automated navigation, competence in calculating tidal effects was important to naval officers.
The certificate of examination for lieutenants in the Royal Navy once declared that the prospective officer was able to "shift his tides".
Tidal flow timings and velocities appear in tide charts or a tidal stream atlas. Tide charts come in sets. Each chart covers a single hour between one high water and another they ignore the leftover 24 minutes and show the average tidal flow for that hour.
An arrow on the tidal chart indicates the direction and the average flow speed usually in knots for spring and neap tides. If a tide chart is not available, most nautical charts have " tidal diamonds " which relate specific points on the chart to a table giving tidal flow direction and speed.
The standard procedure to counteract tidal effects on navigation is to 1 calculate a " dead reckoning " position or DR from travel distance and direction, 2 mark the chart with a vertical cross like a plus sign and 3 draw a line from the DR in the tide's direction.
The distance the tide moves the boat along this line is computed by the tidal speed, and this gives an "estimated position" or EP traditionally marked with a dot in a triangle.
Nautical charts display the water's "charted depth" at specific locations with " soundings " and the use of bathymetric contour lines to depict the submerged surface's shape.
These depths are relative to a " chart datum ", which is typically the water level at the lowest possible astronomical tide although other datums are commonly used, especially historically, and tides may be lower or higher for meteorological reasons and are therefore the minimum possible water depth during the tidal cycle.
Tide tables list each day's high and low water heights and times. To calculate the actual water depth, add the charted depth to the published tide height.
Depth for other times can be derived from tidal curves published for major ports. The rule of twelfths can suffice if an accurate curve is not available.
Intertidal ecology is the study of ecosystems between the low- and high-water lines along a shore.
At low water, the intertidal zone is exposed or emersed , whereas at high water, it is underwater or immersed.
Intertidal ecologists therefore study the interactions between intertidal organisms and their environment, as well as among the different species.
The most important interactions may vary according to the type of intertidal community. The broadest classifications are based on substrates — rocky shore or soft bottom.
Intertidal organisms experience a highly variable and often hostile environment, and have adapted to cope with and even exploit these conditions.
One easily visible feature is vertical zonation , in which the community divides into distinct horizontal bands of specific species at each elevation above low water.
A species' ability to cope with desiccation determines its upper limit, while competition with other species sets its lower limit.
Humans use intertidal regions for food and recreation. Overexploitation can damage intertidals directly.
Other anthropogenic actions such as introducing invasive species and climate change have large negative effects. Marine Protected Areas are one option communities can apply to protect these areas and aid scientific research.
The approximately fortnightly tidal cycle has large effects on intertidal  and marine organisms. Many other animals such as the vertebrates , display similar rhythms.
Examples include gestation and egg hatching. In humans, the menstrual cycle lasts roughly a lunar month , an even multiple of the tidal period.
Such parallels at least hint at the common descent of all animals from a marine ancestor. When oscillating tidal currents in the stratified ocean flow over uneven bottom topography, they generate internal waves with tidal frequencies.
Such waves are called internal tides. In addition to oceanic tides, large lakes can experience small tides and even planets can experience atmospheric tides and Earth tides.
These are continuum mechanical phenomena. The first two take place in fluids. The third affects the Earth's thin solid crust surrounding its semi-liquid interior with various modifications.
Atmospheric tides are negligible at ground level and aviation altitudes, masked by weather 's much more important effects.
Earth tides or terrestrial tides affect the entire Earth's mass, which acts similarly to a liquid gyroscope with a very thin crust.
Precise astronomical angular measurements require knowledge of the Earth's rotation rate and polar motion , both of which are influenced by Earth tides.
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