Editing Surfing (section)

==Surf waves==
<!-- [[Surf wave]] redirects here -->{{See also|Ocean surface wave}}
[[File:Pipeline Barrel (51633882).jpeg|thumb|Pipeline barrel at [[Pūpūkea, Hawaii]]]]
[[File:A surfer surfing on the ocean (Unsplash).jpg|thumb|Surfer getting tubed at [[Sunset Beach (Oahu)|Sunset]] on the [[North Shore (Oahu)|North Shore]] of [[Oahu]]]]
[[File:Surfers at Mavericks.jpg|thumb|right|A large wave breaking at [[Mavericks, California|Mavericks]]]]

[[Swell (ocean)|Swell]] is generated when the wind blows consistently over a large space of open water, called the wind's [[fetch (geography)|fetch]]. The size of a swell is determined by the strength of the wind, and the length of its fetch and duration. Because of these factors, the surf tends to be larger and more prevalent on coastlines exposed to large expanses of ocean traversed by intense [[low-pressure area|low pressure systems]].

Local wind conditions affect wave quality since the surface of a wave can become choppy in blustery conditions. Ideal conditions include a light to moderate "offshore" wind, because it blows into the front of the wave, making it a "[[Barreling wave|barrel]]" or "tube" wave. Waves are left-handed and right-handed depending upon the breaking formation of the wave.

Waves are generally recognized by the surfaces over which they break.<ref>The Bluffer's Guides, The Bluffer's Guide to Surfing, Oval Books, 2008.</ref> For example, there are beach breaks, reef breaks and point breaks.

The most important influence on wave shape is the [[bathymetry|topography of the seabed]] directly behind and immediately beneath the breaking wave. Each break is different since each location's underwater topography is unique. At beach breaks, sandbanks change shape from week to week. [[Surf forecasting]] is aided by advances in information technology. Mathematical modeling graphically depicts the size and direction of swells around the globe.

Swell regularity varies across the globe and throughout the year. During winter, heavy swells are generated in the mid-latitudes, when the North and South [[polar front]]s shift toward the [[Equator]]. The predominantly Westerly winds generate swells that advance Eastward, so waves tend to be largest on West coasts during winter months. However, an endless train of [[mid-latitude cyclone]]s cause the [[isobar (meteorology)|isobar]]s to become undulated, redirecting swells at regular intervals toward the tropics.<!-- what is an undulated isobar? -->

East coasts also receive heavy winter swells when low-pressure cells form in the sub-tropics, where slow moving [[Anticyclone|highs]] inhibit their movement. These lows produce a shorter fetch than polar fronts, however, they can still generate heavy swells since their slower movement increases the duration of a particular wind direction. The variables of fetch and duration both influence how long wind acts over a wave as it travels since a wave reaching the end of a fetch behaves as if the wind died.

During summer, heavy swells are generated when cyclones form in the tropics. [[Tropical cyclone]]s form over warm seas, so their occurrence is influenced by [[El Niño-Southern Oscillation|El Niño and La Niña]] cycles. Their movements are unpredictable.

Surf travel and some surf camps offer surfers access to remote, tropical locations, where [[tradewinds]] ensure offshore conditions. Since winter swells are generated by [[mid-latitude cyclone]]s, their regularity coincides with the passage of these lows. Swells arrive in pulses, each lasting for a couple of days, with a few days between each swell.

The availability of free [[Numerical weather prediction|model data]] from the [[NOAA]] has allowed the creation of several [[surf forecasting]] websites.

===Tube shape and speed===
[[File:Wave-shape-intensity.svg|thumb|upright=1.35|The [[geometry]] of tube shape can be represented as a ratio between length and width.]]

Tube shape is defined by length to width ratio. A perfectly cylindrical [[vortex]] has a ratio of 1:1. Other forms include:
* Square: <1:1
* Round: 1–2:1
* Almond: >2:1

''Peel'' or ''peeling off'' as a descriptive term for the quality of a break has been defined as "a fast, clean, evenly falling curl line, perfect for surfing, and usually found at pointbreaks."<ref>{{Cite book|last=Warshaw|first=Matthew|title=The Encyclopedia of Surfing|publisher=Harvest Book Harcourt Inc|year=2005|isbn=978-0151--00579-6|location=Orlando|pages=e.g. 452}}</ref>

Tube speed is the rate of advance of the break along the length of the wave, and is the speed at which the surfer must move along the wave to keep up with the advance of the tube.<ref name="Lewis et al 2015" /> 
Tube speed can be described using the peel angle and wave celerity. Peel angle is the angle between the wave front and the horizontal projection of the point of break over time, which in a regular break is most easily represented by the line of white water left after the break. A break that closes out, or breaks all at once along its length, leaves white water parallel to the wave front, and has a peel angle of 0°. This is unsurfable as it would require infinite speed to progress along the face fast enough to keep up with the break. A break which advances along the wave face more slowly will leave a line of new white water at an angle to the line of the wave face.<ref name="Lewis et al 2015" /><ref name="Mendonca et al 2012" />

:<math>V_s = \frac {c}{sin \alpha}</math><ref name="Lewis et al 2015" />

Where:
:<math>V_s = </math>velocity of surfer along the wave face
:<math>c = </math>wave celerity (velocity in direction of propagation)
:<math>\alpha =</math>peel angle

In most cases a peel angle less than 25° is too fast to surf.<ref name="Lewis et al 2015" />

* Fast: 30°
* Medium: 45°
* Slow: 60°

{| class="wikitable" style="text-align:center"
|+Wave intensity table
|-
! !! Fast !! Medium !! Slow
|-
! Square
| [[G-Land|The Cobra]] || [[Teahupoo]] || [[Shark Island, Cronulla Beach|Shark Island]]
|-
! Round
| [[G-Land|Speedies]], [[Gnaraloo]] || [[Banzai Pipeline]] ||
|-
! Almond
| [[Lagundri Bay]], [[Snapper Rocks|Superbank]] || [[Jeffreys Bay]], [[Bells Beach, Victoria|Bells Beach]] || [[Angourie Point]]
|}

===Wave intensity===
The type of break depends on shoaling rate. Breaking waves can be classified as four basic types: spilling (ξ<sub>b</sub><0.4), plunging (0.4<ξ<sub>b</sub><2), collapsing (ξ<sub>b</sub>>2) and surging (ξ<sub>b</sub>>2), and which type occurs depends on the slope of the bottom.<ref name="Lewis et al 2015" />

Waves suitable for surfing break as spilling or plunging types, and when they also have a suitable peel angle, their value for surfing is enhanced. Other factors such as wave height and period, and wind strength and direction can also influence steepness and intensity of the break, but the major influence on the type and shape of breaking waves is determined by the slope of the seabed before the break. The breaker type index and [[Iribarren number]] allow classification of breaker type as a function of wave steepness and seabed slope.<ref name="Lewis et al 2015" />

===Artificial reefs===
The value of good surf in attracting surf tourism has prompted the construction of [[artificial reef]]s and sand bars. Artificial surfing reefs can be built with durable sandbags or concrete, and resemble a submerged breakwater. These artificial reefs not only provide a surfing location, but also dissipate wave energy and shelter the coastline from erosion. Ships such as [[Seli 1]] that have accidentally stranded on sandy bottoms, can create sandbanks that give rise to good waves.<ref>{{cite web|title=Seli 1: One Year On|url=http://www.zigzag.co.za/news/enviro/6709/Seli-1|work=ZigZag|publisher=Online Publishers Association South Africa|access-date=25 May 2012|author=Clayton Truscott|date=23 September 2009}}</ref>

An artificial reef known as [[Chevron Reef]] was constructed in [[El Segundo, California]] in hopes of creating a new surfing area. However, the reef failed to produce any quality waves and was removed in 2008. In [[Kovalam]], South West India, an artificial reef has successfully provided the local community with a quality lefthander, stabilized coastal soil erosion, and provided good habitat for [[marine life]].<ref>{{cite news |title=India's first artificial reef to protect Kovalam |url=http://timesofindia.indiatimes.com/india/Indias-first-artificial-reef-to-protect-Kovalam/articleshow/5951403.cms |access-date=25 May 2012 |newspaper=[[The Times of India]] |date=20 May 2010 }}</ref> ASR Ltd., a New Zealand-based company, constructed the Kovalam reef and is working on [[Boscombe Surf Reef|another reef]] in Boscombe, England.

===Artificial waves===
[[File:Surf IMG 0949 (3120282731).jpg|thumb|upright=0.8|Surfing a stationary, artificial wave in Southern California]]

Even with artificial reefs in place, a tourist's vacation time may coincide with a "flat spell", when no waves are available. Completely artificial [[wave pool]]s aim to solve that problem by controlling all the elements that go into creating perfect surf, however there are only a handful of wave pools that can [[simulate]] good surfing waves, owing primarily to construction and operation costs and potential liability. Most wave pools generate waves that are too small and lack the power necessary to surf. The [[Seagaia Ocean Dome]], located in Miyazaki, Japan, was an example of a surfable wave pool. Able to generate waves with up to {{convert|3|m|ft||abbr=on|sigfig=1}} faces, the specialized pump held water in 20 vertical tanks positioned along the back edge of the pool. This allowed the waves to be directed as they approach the artificial sea floor. Lefts, Rights, and A-frames could be directed from this pump design providing for rippable surf and barrel rides. The Ocean Dome cost about $2&nbsp;billion to build and was expensive to maintain.<ref>{{cite web|url=http://www.surfline.com/mag/pulse/2000/nov/11_8_japan.cfm|title=MADE IN JAPAN Unlike its counterparts, Miyazaki's Ocean Dome wavepool is for real|author=Duncan Scott|date=8 November 2000|work=Surfline|publisher=Surfline/Wavetrak, Inc|access-date=25 May 2012}}</ref> The Ocean Dome was closed in 2007. In England, construction is nearing completion on the Wave,<ref name="the-wave">{{cite web |title=Sustainable inland surfing destinations |website=The Wave Bristol |url=http://thewave.com/Bristol/ |access-date=11 December 2017 }}</ref> situated near [[Bristol]], which will enable people unable to get to the coast to enjoy the waves in a controlled environment, set in the heart of nature.

There are two main types of artificial waves that exist today. One being artificial or stationary waves which simulate a moving, breaking wave by pumping a layer of water against a smooth structure mimicking the shape of a breaking wave. Because of the velocity of the rushing water, the wave and the surfer can remain stationary while the water rushes by under the surfboard. Artificial waves of this kind provide the opportunity to try surfing and learn its basics in a moderately small and controlled environment near or far from locations with natural surf.