Tidal range

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Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun, by Earth's rotation and by centrifugal force caused by Earth's progression around the Earth-Moon barycenter. Tidal range depends on time and location.


Larger tidal range occur during spring tides (spring range), when the gravitational forces of both the Moon and Sun are aligned (at syzygy), reinforcing each other in the same direction (new moon) or in opposite directions (full moon). The largest annual tidal range can be expected around the time of the equinox if it coincides with a spring tide. Spring tides occur at the second and fourth (last) quarters of the lunar phases.

By contrast, during neap tides, when the Moon and Sun's gravitational force vectors act in quadrature (making a right angle to the Earth's orbit), the difference between high and low tides (neap range) is smallest. Neap tides occur at the first and third quarters of the lunar phases.

Tidal data for coastal areas is published by national hydrographic offices. [1] The data is based on astronomical phenomena and is predictable. Sustained storm-force winds blowing from one direction combined with low barometric pressure can increase the tidal range, particularly in narrow bays. Such weather-related effects on the tide can cause ranges in excess of predicted values and can cause localized flooding. These weather-related effects are not calculable in advance.

Mean tidal range is calculated as the difference between mean high water (i.e., the average high tide level) and mean low water (the average low tide level). [2]


The typical tidal range in the open ocean is about 1 metre (3 feet) (blue and green on the map on the right). Closer to the coast, this range is much greater. [ citation needed ] Coastal tidal ranges vary globally and can differ anywhere from near zero to over 11 m (36 ft). [3] [ failed verification ] The exact range depends on the volume of water adjacent to the coast, and the geography of the basin the water sits in. Larger bodies of water have higher ranges, and the geography can act as a funnel amplifying or dispersing the tide. [4] The world's largest tidal range of 11.7 metres (38.4 feet) occurs in Bay of Fundy, Canada, [3] [5] [ failed verification ] a similar range is experienced at Ungava Bay also in Canada [6] and the United Kingdom regularly experiences tidal ranges up to 15 metres (49 feet) between England and Wales in the Bristol Channel. [7]

The fifty coastal locations with the largest tidal ranges worldwide are listed by the National Oceanic and Atmospheric Administration of the United States. [3]

Some of the smallest tidal ranges occur in the Mediterranean, Baltic, and Caribbean Seas. A point within a tidal system where the tidal range is almost zero is called an amphidromic point.

The M2 tidal constituent, peak amplitude indicated by color. White lines are cotidal lines spaced at phase intervals of 30deg (a bit over 1 hr). Amphidromic points are the dark blue areas where the lines come together. M2 tidal constituent.jpg
The M2 tidal constituent, peak amplitude indicated by color. White lines are cotidal lines spaced at phase intervals of 30° (a bit over 1 hr). Amphidromic points are the dark blue areas where the lines come together.


The tidal range has been classified [9] as:

See also

Related Research Articles

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<span class="mw-page-title-main">Bay of Fundy</span> Bay on the east coast of North America

The Bay of Fundy is a bay between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine. It is an arm of the Gulf of Maine. Its tidal range is the highest in the world. The name is probably a corruption of the French word fendu, meaning 'split'.

<span class="mw-page-title-main">Lunar node</span> Where the orbit of the Moon intersects the Earths ecliptic

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<span class="mw-page-title-main">Amphidromic point</span> Location at which there is little or no tide

An amphidromic point, also called a tidal node, is a geographical location which has zero tidal amplitude for one harmonic constituent of the tide. The tidal range for that harmonic constituent increases with distance from this point, though not uniformly. As such, the concept of amphidromic points is crucial to understanding tidal behaviour. The term derives from the Greek words amphi ("around") and dromos ("running"), referring to the rotary tides which circulate around amphidromic points. It was first discovered by William Whewell, who extrapolated the cotidal lines from the coast of the North Sea and found that the lines must meet at some point.

<span class="mw-page-title-main">Physical oceanography</span> Study of physical conditions and processes within the ocean

Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.

<span class="mw-page-title-main">Atmospheric physics</span> The application of physics to the study of the atmosphere

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<span class="mw-page-title-main">Tidal marsh</span> Marsh subject to tidal change in water

A tidal marsh is a marsh found along rivers, coasts and estuaries which floods and drains by the tidal movement of the adjacent estuary, sea or ocean. Tidal marshes experience many overlapping persistent cycles, including diurnal and semi-diurnal tides, day-night temperature fluctuations, spring-neap tides, seasonal vegetation growth and decay, upland runoff, decadal climate variations, and centennial to millennial trends in sea level and climate.

<span class="mw-page-title-main">Chart datum</span> Level of water from which depths displayed on a nautical chart are measured

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Earth tide is the displacement of the solid earth's surface caused by the gravity of the Moon and Sun. Its main component has meter-level amplitude at periods of about 12 hours and longer. The largest body tide constituents are semi-diurnal, but there are also significant diurnal, semi-annual, and fortnightly contributions. Though the gravitational force causing earth tides and ocean tides is the same, the responses are quite different.

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<span class="mw-page-title-main">Vertical datum</span> Reference surface for vertical positions

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  1. "Hydrographic and Oceanographic Agencies". Archived from the original on 2010-03-25. Retrieved 2010-01-17.
  2. NOAA. "Tidal Datums" . Retrieved 26 Mar 2019.
  3. 1 2 3 NOAA. "FAQ Where are the highest tides?" . Retrieved 20 Aug 2021.
  4. NOAA. "It appears that the range of the tides gets larger the further the location from the equator. What causes this??" . Retrieved 23 Oct 2020.
  5. NOAA. "The highest tide in the world is in Canada" . Retrieved 23 Oct 2020.
  6. Charles T. O'Reilly, Ron Solvason, and Christian Solomon. "Resolving the World's largest tides", in J.A Percy, A.J. Evans, P.G. Wells, and S.J. Rolston (Editors) 2005: The Changing Bay of Fundy-Beyond 400 years, Proceedings of the 6th Bay of Fundy Workshop, Cornwallis, Nova ScotiSackville, NB.
  7. "Tidal range".
  8. Picture credit: R. Ray, TOPEX/Poseidon: Revealing Hidden Tidal Energy GSFC, NASA. Redistribute with credit to R. Ray, as well as NASA-GSFC, NASA-JPL, Scientific Visualization Studio, and Television Production NASA-TV/GSFC
  9. Masselink, G.; Short, A. D. (1993). "The effect of tidal range on beach morphodynamics and morphology: a conceptual beach model". Journal of Coastal Research. 9 (3): 785–800. ISSN   0749-0208.