Which of the following terms refers to the length of time that a wind blows over the ocean 2 points duration fetch speed surf?

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There is a lot of associated terminology when talking about waves. It's handy to know what it all means if you want to start forecasting your own surf. If you are looking to increase your own general surf vocabulary, then take a look at the surfing terminology section. OK, let's get cracking.

Glossary of Wave Terms

Amplitude

This is the vertical distance from still water level to wave peak. (Approximately half the height of the wave)

Barrel

The barrel is the hollow part of a breaking wave where there is a gap between the face of the wave and the lip of the wave as it curls over. One of the highlights for any surfer is catching a tube ride. See "Tube."

Bathymetry

This is the measurement of water depth at various places in a body of water

Capillary Waves

These are the first small waves created when the wind blows on the sea. (i.e. baby swell)

Chop

Moderate local winds form little waves known as chop which can kill a good surf session. It's also know as "wind chop."

Closeout

This is a wave that breaks along its entire length at the same time making it unsurfable. Closeouts can either be caused by a strong offshore wind or sea floor topography. It's also called "shutting down."

Corduroy

This is a swell line that looks like corduroy. See this corduroy swell picture that illustrates it perfectly.

Crest

The crest is the highest part of the wave above still water level. See also "Peak."

Crumble / Crumbly Waves

Waves affected by an onshore wind are said to crumble. The lip of the waves will "crumble" along the line and as a result spoil the waves for surfers.

Decay of Waves / Wave Decay

This is the decrease in wave height and increase in wavelength of a wave once it's outside the fetch.

Diffraction

When the wave comes into contact with an obstacle or barrier such as a breakwater, the energy of the wave is transmitted along a wave crest. Diffraction is the "spreading" of waves into the sheltered region within the barrier's geometric shadow.

Dumpy Shore Break

Waves that are breaking very close to shore in shallow water. They can be great fun to ride, but be careful not to break your board.

Fetch

Fetch is the area of sea surface where the wind generates the waves / swell. It's one of the key facets of the quality of a swell and the size of the waves.

Fully Developed Sea

Waves that have reached the maximum size possible for fetch, wind speed and wind duration are referred to as being fully developed.

Grinder / Grinding Wave

A powerful breaking wave. "The waves were grinding along the reef"

Glassy

Waves that have incredibly smooth faces due to the lack of local wind or a slight offshore wind. Have a look at this picture of a glassy Huntingdon Beach wave.

Ground Swell

This is when the waves are no longer being affected by the winds that generated them, typically outside the fetch.

Left

A "left" is a wave that breaks from left to right as you are looking from the beach.

Leftover

A wave that has passed through the lineup and not been caught by a surfer.

Lip

The lip is the upper-most part of the breaking wave where a surfer will do maneuvers such as a floater.

Neap Tide

Smaller than normal tides occurring when the gravitational pull of the sun and moon are at right angles to the earth.

Offshore Wave

In surfing terms this relates to the wind blowing from the shore. A ground swell mixed with offshore winds makes for cracking surf.

Onshore Waves

The opposite of offshore waves, these occur when the wind blows toward the beach, and as a result the waves lose their shape and crumble.

Peak

This is the highest part of the wave above still water level. See also "Crest."

Peak Direction

This is the wave direction at the frequency at which a wave spectrum reaches its maximum.

Peak Period / Wave Period

This represent the period of time it takes for consecutive wave crests or wave troughs to pass a given point. The greater the wave period is the better the swell.

Refraction

This represent the tendency of wave crests to become parallel to underwater contours as waves move into shallower waters. Waves moving in shallow waters move more slowly than waves moving in deeper water. Refraction can be seen where waves wrap round a point and their direction seems to change.

Right

A "right" is a wave that breaks from right to left when viewed from the beach

Significant Wave Height

How significant are your wave heights? You are likely to have seen significant wave height on surf reports. The significant wave height is the average height of the one-third highest waves of a given wave group.

Shoaling

Waves being forced to bunch together as they enter shallower water slow down and are said to be shoaling.

Shoredump

See dumpy shore break.

Spring Tide

These larger than normal tides occur when the gravitational pull of the sun and moon are combined in line. This is opposite to neap tides.

Surf

These are waves breaking near the shore. Tadaa!

Surf Zone

This represents the area from the shore out to where the waves start breaking

Tide

Tides are an increase and decrease in sea level resulting from the moon's and, to a lesser extent, sun's gravitational pull.

Trough

This is the lowest part between two successive waves. It can also be considered the part between two successive waves below still water level.

Tube

The hollow part of a breaking wave where there is a gap between the face of the wave and the lip of the wave as it curls over. See "Barrel."

Wall

The steep, unbroken section of a wave, out in front of a surfer. Reason: it looks like a wall made out of water. You'll probably hear surfers talking about a wave "walling up".

Wave Direction / Swell Direction

This is the direction from where the waves approach. (Not the direction in which they are heading) If a surf spot works on a northerly, this refers to a northerly swell direction.

Wavelength

This is the distance between two corresponding points on successive waves. (i.e. the distance between two peaks)

Whitewater

This is the foamy part of a wave that has broken

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The speed at which waves approach the shore depends on sea floor and shoreline features and the depth of the water. As a wave moves toward the beach, different segments of the wave encounter the beach before others, which slows these segments down. As a result, the wave tends to bend and conform to the general shape of the coastline. Also, waves do not typically reach the beach perfectly parallel to the shoreline. Rather, they arrive at a slight angle, called the “angle of wave approach.”

When a wave reaches a beach or coastline, it releases a burst of energy that generates a current, which runs parallel to the shoreline. This type of current is called a “longshore current.”

Discover: How does an island disappear?

Longshore currents are affected by the velocity and angle of a wave. When a wave breaks at a more acute (steep) angle on a beach, encounters a steeper beach slope, or is very high, longshore currents increase in velocity. Conversely, a wider breaking angle, gentler beach slope, and lower wave height slows a longshore current’s velocity. In either case, the water in a longshore current flows up onto the beach, and back into the ocean, as it moves in a “sheet” formation.

As this sheet of water moves on and off the beach, it can “capture” and transport beach sediment back out to sea. This process, known as “longshore drift,” can cause significant beach erosion.

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As longshore currents move on and off the beach, “rip currents” may form around low spots or breaks in sandbars, and also near structures such as jetties and piers. A rip current, sometimes incorrectly called a rip tide, is a localized current that flows away from the shoreline toward the ocean, perpendicular or at an acute angle to the shoreline. It usually breaks up not far from shore and is generally not more than 25 meters (80 feet) wide.

Rip currents typically reach speeds of 1 to 2 feet per second. However, some rip currents have been measured at 8 feet per second—faster than any Olympic swimmer ever recorded (NOAA, 2005b). If wave activity is slight, several low rip currents can form, in various sizes and velocities. But in heavier wave action, fewer, more concentrated rip currents can form.

Because rip currents move perpendicular to shore and can be very strong, beach swimmers need to be careful. A person caught in a rip can be swept away from shore very quickly. The best way to escape a rip current is by swimming parallel to the shore instead of towards it, since most rip currents are less than 80 feet wide. A swimmer can also let the current carry him or her out to sea until the force weakens, because rip currents stay close to shore and usually dissipate just beyond the line of breaking waves. Occasionally, however, a rip current can push someone hundreds of yards offshore. The most important thing to remember if you are ever caught in a rip current is not to panic. Continue to breathe, try to keep your head above water, and don’t exhaust yourself fighting against the force of the current.

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Winds blowing across the ocean surface often push water away from an area. When this occurs, water rises up from beneath the surface to replace the diverging surface water. This process is known as upwelling.

This graphic shows how displaced surface waters are replaced by cold, nutrient-rich water that “wells up” from below. Conditions are optimal for upwelling along the coast when winds blow along the shore.

Upwelling occurs in the open ocean and along coastlines. The reverse process, called downwelling, also occurs when wind causes surface water to build up along a coastline. The surface water eventually sinks toward the bottom.

Subsurface water that rises to the surface as a result of upwelling is typically colder, rich in nutrients, and biologically productive. Therefore, good fishing grounds typically are found where upwelling is common. For example, the rich fishing grounds along the west coasts of Africa and South America are supported by year-round coastal upwelling.

Seasonal upwelling and downwelling also occur along the West Coast of the United States. In winter, winds blow from the south to the north, resulting in downwelling. During the summer, winds blow from the north to the south, and water moves offshore, resulting in upwelling along the coast. This summer upwelling produces cold coastal waters in the San Francisco area, contributing to the frequent summer fogs. (Duxbury, et al, 2002.)

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Since the age of exploration, mariners have needed to know the speed and direction (velocity) of ocean currents to steer their ships within harbors and along trade and exploration routes. A mariner needs to be able to measure the velocity of currents by observing distance, time, and direction.

The simplest method of determining the velocity of a current involves an observer, a floating object or drifter, and a timing device. The observer stands on an anchored ship with a timer. He or she then places the drifter (such as a piece of wood) into the water and measures the amount of time the drifter takes to move along the length of the ship. He or she then stops the timer after the object has traveled some distance, and measures that distance, noting the direction in which the object moved.

The observer then divides the distance the object traveled by the time it took the object to travel that distance, which equals the speed of the current. By combining the speed of the object with the direction in which it moved, the observer can then determine the current’s velocity. Ocean currents typically are measured in knots.

Although they still follow the same essential concept to measure ocean currents, mariners today use more accurate and sophisticated instruments. Today, drifters are often elaborate buoys equipped with multiple oceanographic instruments. Some are equipped with global positioning system technology and satellite communications to relay their position in the ocean back to observers on land. Other drifters submerge for long periods of time to measure the ocean currents at depth. The drifter occasionally rises to the surface to send a signal that relays its position.

All drifter measurements are termed “Lagrangian measurements,” named after mathematician Joseph Louis Lagrange (1736-1813), who first described the path followed by fluids. But current velocities can be measured another way as well—using “Eulerian measurements.” Named after Swiss mathematician Leonhard Euler (1707-1783), Eulerian measurements involve describing fluid flow by measuring the speed and direction of the fluid at one point only. In this method, an instrument is anchored in the ocean at a given location, and the water movement is measured as it flows past the instrument.

Measuring currents by Eulerian methods is becoming increasingly more common. One reason is that it is easier to retrieve these expensive but stationary instruments than it is to locate floating drifters.

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Bowditch, N. 1995. American Practical Navigator. Bethesda, MD: Defense Mapping Agency Hydrographic/Topographic Center. pp. 873.

Duxbury, et al. 2002. Fundamentals of Oceanography, 4th edition. New York: McGraw Hill. pp. 344.

Lloyd, J.B. 1986. Eighteen Miles of History on Long Beach Island. Harvey Cedars, New Jersey. Down The Shore Publishing and the SandPaper, Inc. pp. 204.

National Oceanic and Atmospheric Administration (NOAA). 2005a. Ocean Explorer: Technology. Online at http://oceanexplorer.noaa.gov/technology/technology.html.

National Oceanic and Atmospheric Administration (NOAA). 2005b. Rip Current Safety. Online at http://www.ripcurrents.noaa.gov.

Pinet, P.R. 1998. Invitation to Oceanography. Sudbury, MA.: Jones and Bartlett Publishers. 596 pp.  Sudbury, MA.

Ross, D. 1995 Introduction to Oceanography. New York: HarperCollins College Publishers. pp. 199-226, 339-343.

Rutgers University. Geography Department. Cartography homepage. Historical Maps of New Jersey Online at: http://mapmaker.rutgers.edu/MAPS.html.

Thurman, H. 1994. Introductory Oceanography, 7th edition. New York: Macmillan Publishing Company. pp. 172-222.

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Thermohaline circulation drives a global-scale system of currents called the “global conveyor belt.” The conveyor belt begins on the surface of the ocean near the pole in the North Atlantic. Here, the water is chilled by arctic temperatures. It also gets saltier because when sea ice forms, the salt does not freeze and is left behind in the surrounding water. The cold water is now more dense, due to the added salts, and sinks toward the ocean bottom. Surface water moves in to replace the sinking water, thus creating a current.

This deep water moves south, between the continents, past the equator, and down to the ends of Africa and South America. The current travels around the edge of Antarctica, where the water cools and sinks again, as it does in the North Atlantic. Thus, the conveyor belt gets "recharged." As it moves around Antarctica, two sections split off the conveyor and turn northward. One section moves into the Indian Ocean, the other into the Pacific Ocean.

These two sections that split off warm up and become less dense as they travel northward toward the equator, so that they rise to the surface (upwelling). They then loop back southward and westward to the South Atlantic, eventually returning to the North Atlantic, where the cycle begins again.

The conveyor belt moves at much slower speeds (a few centimeters per second) than wind-driven or tidal currents (tens to hundreds of centimeters per second). It is estimated that any given cubic meter of water takes about 1,000 years to complete the journey along the global conveyor belt. In addition, the conveyor moves an immense volume of water—more than 100 times the flow of the Amazon River (Ross, 1995).

The conveyor belt is also a vital component of the global ocean nutrient and carbon dioxide cycles. Warm surface waters are depleted of nutrients and carbon dioxide, but they are enriched again as they travel through the conveyor belt as deep or bottom layers. The base of the world’s food chain depends on the cool, nutrient-rich waters that support the growth of algae and seaweed.

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