Difference between revisions of "Tide"

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{{Definition|title=Tide
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|definition= The periodic rise and fall in the level of the water in oceans and seas as a result of gravitational attraction of the sun and moon and the rotation of the earth.<ref> CIRIA (1996). ''Beach management manual'', CIRIA Report 153.</ref>.}}
  
Tides are the longest of oceanic waves. So long in fact, that often, we only observe them as a rise and fall of sea level over a period of several hours. However, a good understanding of tides and tide-generated currents is important for all areas of [[ICZM]]. Together with wind-generated waves, tides play an extremely important part in coastal processes, geomorphology, flood risk, species zonation and water quality.
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A more general definition from a geophysical viewpoint is
  
The aim of this article is to present a broad overview of tides, with links to more specific articles for those who are interested.
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{{Definition|title=Tide (more general)
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|definition= A tide is a distortion in the shape of a body induced by the gravitational pull of another nearby object.<ref> Morrison & Owen (1996). "The Planetary System", Addison-Wesley. </ref>.}}
  
== Introduction ==
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The term 'tide' in the Coastal Wiki refers to the first definition.
  
It is worth considering two definitions of tides. Within coastal science and engineering, tides are often taken to mean:
 
  
{{
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==Notes==
Definition|title=Tide
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The tide (more precisely, the '''astronomical tide''') is the large-scale water motion generated by the rotation of the earth in combination with the varying gravitational influence on the ocean of celestial bodies, especially the moon and the sun. These phenomena cause predictable and regular oscillations in the water level, which are referred to as the tide. The astronomical tide at a specific location can be predicted and is published in Tidal Tables.  
|definition= The periodic rise and fall in the level of the water in oceans and seas; the result of gravitational attraction of the sun and moon.<ref> CIRIA (1996). ''Beach management manual''. CIRIA Report 153.</ref>.}}
 
  
However, we should never lose sight of the astronomical perspective:
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The term 'tide' is sometimes used for the combined effect of astronomical tide and wind-driven set-up or set-down of the sea level (including [[#Storm surge|storm surges]]). 
  
{{
 
Definition|title=Tide (more general)
 
|definition= A tide is a distortion in the shape of one body induced by the gravitational pull of another nearby object.<ref> Morrison & Owen (1996). "The Planetary System".</ref>.}}
 
  
  
The tides of our planet display extremely complex behaviour. For example, in the Mediterranean, the [[tidal range]] is very small (<1m), whereas in the Bay of Fundy, Canada, the shape of the bay augments the [[tidal range]] to over 15m. In Europe, the biggest tides can be found in the Severn estuary (12m) in the UK and near Mont Saint Michel, in France, where the tide goes out 9km and reputedly comes in faster than a person can run.
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==Related articles==
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:[[Ocean and shelf tides]]
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:[[Tidal motion in shelf seas]]
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:[[Coriolis acceleration]]
  
The importance of tides around our coasts is often in the currents they generate, which can reach speeds of up to 5 m/s<ref>Brown et al. (1989). Waves, tides and shallow-water processes. Ed. G. Bearman. Open University. Pergamon Press.</ref> (Bay of Fundy). The rising tide is usually referred to as the flood, whereas the falling tide is called the ebb. The [[tidal currents]] of the ebb and flood play a major part in shaping our coasts, transporting large volumes of [[sediment]] and moulding [[estuary]] environments.
 
 
[[Tidal resonance]] can produce strange behaviour, for example, on the south coast of the UK, Southampton Water famously exhibits two high waters, approximately thirty minutes apart.
 
 
In contrast to the majority of coastal processes, the tides can be predicted with very good accuracy, for as many as two hundred years into the future. However, there is sometimes a difference between the observed and predicted tide, due to weather induced effects such as the [[storm surge]].
 
 
== Theory of tides ==
 
 
Sir Isaac Newton (1642-1727) was the first to suggest that the planets produced the tides on earth, through their mutual gravitational pull. Astronomical tides are those tidal movements which are governed by the planets. The tide-generating forces can be precisely calculated through the motion of the planets ([[the equilibrium theory of tides]]), and the response of the oceans to these forces is modified by the effects of topography ([[the dynamical theory of tides]]) and by the transient effect of passing weather patterns ([[storm surge]]s).
 
 
==Introduction to the equilibrium theory==
 
 
The Earth and the Moon revolve around each other (around a common centre of mass) with a [[period]] of 27.3 days.
 
 
The tidal range is largest just after a full or new moon.
 
 
 
The magnitude of the Sun’s tide producing force is about 0.46 that of the Moon, because, although enormously greater in mass than the Moon, the Sun is some 360 times further from the Earth. <ref???>  The solar tide has a semi-diurnal period of 12 hours.
 
 
 
==Introduction to the dynamical theory of tides==
 
Kelvin wave
 
Cotidal and corange lines. Figure
 
Amphidromic point
 
 
==Terminology==
 
 
Admiralty charts provide useful information on the bathymetry of a coastal area, as well as tidal range and frequency.
 
ODN / Ordnance Datum Newlyn
 
Admiralty Chart
 
CD / Chart Datum
 
HAT
 
LAT
 
MHWS
 
MHWN
 
MLWS
 
MLWN
 
 
 
==The frequency of tides==
 
 
Tides in many parts of the world (eg. English Channel) can be described as semi-diurnal (occurring twice a day), while some tides show purely diurnal behaviour (once a day) as evident in parts of the Mediterranean.
 
 
- Spring neap cycle
 
- Nodal? cycle
 
semi-diurnal
 
diurnal
 
 
 
==Tidal measurement==
 
 
Tide gauge
 
Data sets
 
 
==Tidal prediction==
 
 
Since we can predict the movement of the planets to extremely good accuracy, we can use this to predict the tides.
 
 
-harmonic analysis
 
Tidal constituents
 
 
 
 
==Tidal currents==
 
 
Tidally generated bedforms
 
tide dominated coasts
 
 
 
==Tides in estuaries==
 
 
estuary evolution
 
estuary hydrodynamics
 
stratified estuaries
 
partially-mixed estuaries
 
well-mixed estuaries
 
halocline
 
salt-wedge estuaries
 
coriolis force
 
flood-dominant estuaries
 
ebb-dominant estuaries
 
bar-built estuaries
 
drowned river valleys
 
rias
 
fjiords
 
Tidally generated bedforms
 
intertidal
 
 
==Related topics==
 
 
Tidal power
 
Internal tides
 
Navigation
 
Intertidal and biology
 
tidal bore
 
 
 
 
The equilibrium theory of tides
 
 
Tide producing forces vary directly with the mass of the attracting body, but are inversely propoertional to the cube of its distance from Earth.
 
 
 
The dynamical theory of tides
 
 
 
 
 
==See also==
 
Definitions related to tides are: [[tidal current]], [[tidal flat]], [[tidal wave]], [[astronomical tide]], [[highest astronomical tide]] (HAT), [[lowest astronomical tide]] (LAT), [[mean high water springs]] (MHWS), [[mean high water neaps]] (MHWN), [[mean high water]] (MHW), [[mean low water]] (MLW).
 
 
For more definitions of coastal terms and a sketch, see [[Definitions of coastal terms]].
 
 
An article related to tides is: [[waves]].
 
  
 
==References==
 
==References==
 
<references/>
 
<references/>
 
Article by
 
{{author
 
|AuthorID=18394
 
|AuthorFullName=Somerville, Tracy
 
|AuthorName=Tracy}}
 
 
[[Category:Help]]
 

Latest revision as of 20:37, 1 April 2021

Definition of Tide:
The periodic rise and fall in the level of the water in oceans and seas as a result of gravitational attraction of the sun and moon and the rotation of the earth.[1].
This is the common definition for Tide, other definitions can be discussed in the article

A more general definition from a geophysical viewpoint is

Definition of Tide (more general):
A tide is a distortion in the shape of a body induced by the gravitational pull of another nearby object.[2].
This is the common definition for Tide (more general), other definitions can be discussed in the article

The term 'tide' in the Coastal Wiki refers to the first definition.


Notes

The tide (more precisely, the astronomical tide) is the large-scale water motion generated by the rotation of the earth in combination with the varying gravitational influence on the ocean of celestial bodies, especially the moon and the sun. These phenomena cause predictable and regular oscillations in the water level, which are referred to as the tide. The astronomical tide at a specific location can be predicted and is published in Tidal Tables.

The term 'tide' is sometimes used for the combined effect of astronomical tide and wind-driven set-up or set-down of the sea level (including storm surges).


Related articles

Ocean and shelf tides
Tidal motion in shelf seas
Coriolis acceleration


References

  1. CIRIA (1996). Beach management manual, CIRIA Report 153.
  2. Morrison & Owen (1996). "The Planetary System", Addison-Wesley.