Tidal range is the difference in height between high tide and low tide.

Tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...

s are the rise and fall of

sea level Mean sea level (MSL, often shortened to sea level) is an mean, average surface level of one or more among Earth's coastal Body of water, bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical ...

s caused by gravitational forces exerted by the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

and Sun, by

Earth's rotation Earth's rotation or Earth's spin is the rotation of planet Earth around its own Rotation around a fixed axis, axis, as well as changes in the orientation (geometry), orientation of the rotation axis in space. Earth rotates eastward, in progra ...

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 In geometry and trigonometry, a right angle is an angle of exactly 90 Degree (angle), degrees or radians corresponding to a quarter turn (geometry), turn. If a Line (mathematics)#Ray, ray is placed so that its endpoint is on a line and the ad ...

to the

Earth's orbit Earth orbits the Sun at an astronomical unit, average distance of , or 8.317 light-second, light-minutes, in a retrograde and prograde motion, counterclockwise direction as viewed from above the Northern Hemisphere. One complete orbit takes & ...

), 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. 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).

Geography

The typical tidal range in the open ocean is about – mapped in blue and green at right. Mean ranges near coasts vary from near zero to , with the range depending 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. The world's largest mean tidal range of occurs in the

Bay of Fundy 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 bay was ...

, Canada (more specifically, at Burntcoat Head, Nova Scotia). The next highest, of , is at Ungava Bay, also in Canada,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 Scotia.'' Sackville, NB. and the next, of , in the Bristol Channel, between England and Wales. The highest predicted extreme (not mean) range is , in the Bay of Fundy. The maximum range in the Bristol Channel is . The fifty coastal locations with the largest ranges worldwide are listed by the

National Oceanic and Atmospheric Administration The National Oceanic and Atmospheric Administration (NOAA ) is an American scientific and regulatory agency charged with Weather forecasting, forecasting weather, monitoring oceanic and atmospheric conditions, Hydrography, charting the seas, ...

of the United States. Some of the smallest tidal ranges occur in the

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

, Baltic, and

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

s. A point within a tidal system where the tidal range is almost zero is called an amphidromic point.

Classification

The tidal range has been classified as: * Micro-tidal – when the tidal range is lower than 2 metres (6'6¾"). * Meso-tidal – when the tidal range is between 2 metres and 4 metres (6'6¾" and 13'1½"). * Macro-tidal – when the tidal range is higher than 4 metres (13'1½").

References

{{physical oceanography Tides Oceanography

Geography

Classification

See also

References