Editing Tide (section)

== Characteristics ==
Four stages{{dubious |Not really, right? Just two active stages. The other 2 are just names for static levels. |date= February 2025}} in the tidal cycle are named:
* {{anchor|Low|Low tide}}The water stops falling, reaching a [[local minimum]] called '''low tide'''.
* {{anchor|Flood|Flood tide}}Sea level rises over several hours, covering the [[intertidal zone]]; '''flood tide'''.
* {{anchor|High|High tide}}The water stops rising, reaching a [[local maximum]] called '''high tide'''.
* {{anchor|Ebb|Ebb tide}}Sea level falls over several hours, revealing the intertidal zone; '''ebb tide'''.

Oscillating [[Current (fluid)|currents]] produced by tides are known as '''tidal streams''' or '''[[tidal currents]]'''. The moment that the tidal current ceases is called ''[[slack water]]'' or ''slack tide''. The tide then reverses direction and is said to be turning. Slack water usually occurs near high water and low water, but there are locations where the moments of slack tide differ significantly from those of high and low water.<ref>{{Cite book |first=George L. |last=Mellor |title=Introduction to physical oceanography |publisher=Springer |date=1996 |isbn=1-56396-210-1 |page=169}}</ref>

Tides are commonly ''semi-diurnal'' (two high waters and two low waters each day), or ''diurnal'' (one tidal cycle per day). The two high waters on a given day are typically not the same height (the daily inequality); these are the ''higher high water'' and the ''lower high water'' in [[tide table]]s. Similarly, the two low waters each day are the ''higher low water'' and the ''lower low water''. The daily inequality is not consistent and is generally small when the Moon is over the [[Equator]].{{efn|Tide tables usually list ''mean lower low water'' (mllw, the 19 year average of mean lower low waters), ''mean higher low water'' (mhlw), ''mean lower high water'' (mlhw), ''mean higher high water'' (mhhw), as well as ''perigean tides''. These are ''mean'' values in the sense that they derive from mean data.<ref>{{cite web |url=http://www.ecy.wa.gov/programs/sea/swces/products/publications/glossary/words/H_M.htm |title=Glossary of Coastal Terminology: H–M |publisher=[[Washington Department of Ecology]], State of Washington |access-date=5 April 2007 |archive-date=21 November 2017 |archive-url=https://web.archive.org/web/20171121042259/http://www.ecy.wa.gov/programs/sea/swces/products/publications/glossary/words/H_M.htm |url-status=live }}</ref>}}

=== Reference levels ===
{{see also|Chart datum#Definitions}}
[[File:Tide terms.png|thumb|upright=3.65|center|Illustration by the course of half a month]]

The following reference tide levels can be defined, from the highest level to the lowest:
* ''[[Highest astronomical tide]]'' (HAT) – The highest tide which can be predicted to occur. Note that meteorological conditions may add extra height to the HAT.
* ''[[Mean high water springs]]'' (MHWS) – The average of the two high tides on the days of spring tides.
* ''Mean high water neaps'' (MHWN) – The average of the two high tides on the days of neap tides.
* ''[[Mean sea level]]'' (MSL) – This is the average sea level. The MSL is constant for any location over a long period.
* ''Mean low water neaps'' (MLWN) – The average of the two low tides on the days of neap tides.
* ''[[Mean low water springs]]'' (MLWS) – The average of the two low tides on the days of spring tides.
* ''[[Lowest astronomical tide]]'' (LAT) – The lowest tide which can be predicted to occur.<ref>{{cite web |title=Definitions of tidal terms |url=http://www.linz.govt.nz/hydro/tidal-info/tidal-intro/definitions |website=Land Information New Zealand |access-date=20 February 2017 |archive-date=30 August 2014 |archive-url=https://web.archive.org/web/20140830114240/http://www.linz.govt.nz/hydro/tidal-info/tidal-intro/definitions |url-status=live }}</ref>

=== Range variation: springs and neaps ===
{{further|Tidal range}}
[[File:Tide schematic.svg|thumb|left|alt=Spring tide: the Sun, moon, and earth form a straight line. Neap tide: the Sun, moon, and earth form a right angle.|The types of tides]]

{{anchor|springtide|Spring}}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 (astronomy)|syzygy]]<ref>{{Cite book |title=Mathematical astronomy in Copernicus's De revolutionibus |volume=1 |first1=Noel M. |last1=Swerdlow |first2=Otto |last2=Neugebauer |publisher=Springer-Verlag |date=1984 |isbn=0-387-90939-7 |page=76 |url=https://books.google.com/books?id=4YDvAAAAMAAJ&q=Syzygy |via=[[Google Books]] |access-date=2020-11-22 |archive-date=2023-09-16 |archive-url=https://web.archive.org/web/20230916153030/https://books.google.com/books?id=4YDvAAAAMAAJ&q=Syzygy |url-status=live }}</ref>), 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 [[Spring (season)|the season]], but, like that word, derives from the meaning "jump, burst forth, rise", as in a natural [[Spring (hydrosphere)|spring]]. 
Spring tides are sometimes referred to as ''syzygy tides''.<ref name="Harris1981">{{cite book |last=Harris |first=D.L. |title=Tides and Tidal Datums in the United States |publisher=[[United States Army Corps of Engineers]], Coastal Engineering Research Center |series=Special report (Coastal Engineering Research Center (U.S.))) |year=1981 |url=https://books.google.com/books?id=kbIse3HQ74wC&pg=PA32 |access-date=2021-08-24 |page=32 |via=[[Google Books]] |archive-date=2023-09-16 |archive-url=https://web.archive.org/web/20230916153028/https://books.google.com/books?id=kbIse3HQ74wC&pg=PA32 |url-status=live }}</ref>

{{anchor|Neap}}When the Moon is at [[Gibbous|first quarter]] or third quarter, the Sun and Moon are separated by 90° when viewed from the Earth (in [[quadrature (astronomy)|quadrature]]), and the solar tidal force partially cancels the Moon's tidal force. At these points in the lunar cycle, the tide's range is at its minimum; this is called the '''neap tide''', or '''neaps'''. "Neap" is an Anglo-Saxon word meaning "without the power", as in ''forðganges nip'' (forth-going without-the-power).<ref>{{cite OED2|neap²}} Old English (example given from AD 469: ''forðganges nip'' – without the power of advancing). The Danish ''niptid'' is probably from the English. The English term neap-flood (from which neap tide comes) seems to have been in common use by AD 725.</ref>
Neap tides are sometimes referred to as ''quadrature tides''.<ref name="Harris1981"/>

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.

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<gallery class="center">
File:High tide sun moon same side beginning.png|''Spring tide:'' Sun and Moon on the same side (0°)
File:Low tide sun moon 90 degrees.png|''Neap tide:'' Sun and Moon at 90°
File:High tide sun moon opposite side.png|''Spring tide:'' Sun and Moon at opposite sides (180°)
File:Low tide sun moon 270 degrees.png|''Neap tide:'' Sun and Moon at 270°
File:High tide sun moon same side end.png|''Spring tide:'' Sun and Moon at the same side (cycle restarts)
</gallery>
{{clear}}