The lunitidal interval measures the time lag from lunar culmination to the next high

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravity, 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 t ...

at a given location. It is also called the high water interval (HWI). Sometimes a term is not used for the time lag, but instead the terms ''age'' or ''establishment'' of the tide are used for the entry that is in

tide table Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. Tide heights at intermediate times (between high and low water) can be approxim ...

s. Tides are known to be mainly caused by the

Moon's gravity image:MoonLP150Q grav 150.jpg, 300px, Radial gravity anomaly at the surface of the Moon in Gal (acceleration), mGal The gravitational acceleration, acceleration due to gravity on the surface of the Moon is approximately 1.625 m/s2, about 16. ...

. Theoretically, peak tidal forces at a given location would concur when the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

reaches the

meridian Meridian or a meridian line (from Latin ''meridies'' via Old French ''meridiane'', meaning “midday”) may refer to Science * Meridian (astronomy), imaginary circle in a plane perpendicular to the planes of the celestial equator and horizon * ...

, but a delay usually precedes high tide, depending largely on the shape of the coastline and the sea floor. Therefore, the lunitidal interval varies from place to place – from 3 hours over deep oceans to eight hours at

New York Harbor New York Harbor is at the mouth of the Hudson River where it empties into New York Bay near the East River tidal estuary, and then into the Atlantic Ocean on the east coast of the United States. It is one of the largest natural harbors in t ...

. The lunitidal interval further varies within about +/-30 minutes according to the lunar phase. (This is caused by the time interval associated with the solar tides.) Hundreds of factors are involved in the lunitidal interval, especially near the shoreline. However, for those far away enough from the coast, the dominating consideration is the speed of

gravity waves In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two media when the force of gravity or buoyancy tries to restore equilibrium. An example of such an interface is that between the atmosphere ...

, which increases with the water's depth. (It is proportional to the square root of the depth, for the extremely long gravity waves that transport the water that is following the Moon around the Earth. The oceans are about 4 km deep and would have to be at least 22 km deep for these waves to keep up with the Moon. As mentioned above, a similar time lag accompanies the solar tides, a complicating factor that varies with the

lunar phase Concerning the lunar month of ~29.53 days as viewed from Earth, the lunar phase or Moon phase is the shape of the Moon's directly sunlit portion, which can be expressed quantitatively using areas or angles, or described qualitatively using the t ...

s.) By observing the age of leap tides, it becomes clear that the delay can actually exceed 24 hours in some locations. The approximate lunitidal interval can be calculated if the moonrise, moonset, and high tide times are known for a location. In the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

, the Moon reaches its

highest point A list of highest points typically contains the name, elevation, and location of the highest point in each of a set of geographical regions. Such a list is important in the sport of highpointing. A partial list of highpoint lists is below: World ...

when it is southernmost in the sky. Lunar data are available from printed or online

tables Table may refer to: * Table (furniture), a piece of furniture with a flat surface and one or more legs * Table (landform), a flat area of land * Table (information), a data arrangement with rows and columns * Table (database), how the table data ...

. Tide tables forecast the time of the next high water.NOAA Tides & Currents
/ref> The difference between these two times is the lunitidal interval. This value can be used to calibrate certain clocks and wristwatches to allow for simple but crude tidal predictions.

References

{{DEFAULTSORT:Lunitidal Interval Physical oceanography Tides

See also

References