Together a high pressure center and the Coriolis effect produce group of answer choices

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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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Longshore currents are generated when a "train" of waves reach the coastline and release bursts of energy.

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 drift can be very destructive to manmade structures. Click the image to view a slideshow and learn more.

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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These images of dangerous rip currents were taken at public swimming beaches. Click the image to view a slideshow and learn more.

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.

When waves travel from deep to shallow water, they break near the shoreline and generate currents. A rip current forms when a narrow, fast-moving section of water travels in an offshore direction. Rip current speeds as high as 8 feet per second have been measured--faster than an Olympic swimmer can sprint! This makes rip currents especially dangerous to beachgoers as these currents can sweep even the strongest swimmer out to sea.

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.

Major upwelling areas along the world's coasts are highlighted in red. Click the image for a larger view.

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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An oceanographer deploys a current meter in the 1920s while working in Alaska.

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.

Joseph Louis Lagrange (1736-1813) was the first mathematician to describe the path followed by fluids. To this day, all drifter buoy measurements are referred to as "Lagrangian measurements."

Leonhard Euler (1707-1783) was the first mathematician to describe the speed and direction of a liquid's flow as it passes a single point in space.

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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This animation shows the path of the global conveyer belt. The blue arrows indicate the path of deep, cold, dense water currents. The red arrows indicate the path of warmer, less dense surface waters. It is estimated that it can take 1,000 years for a "parcel" of water to complete the journey along the global conveyor belt.

Cold, salty, dense water sinks at the Earth's northern polar region and heads south along the western Atlantic basin.

The current is "recharged" as it travels along the coast of Antarctica and picks up more cold, salty, dense water.

The main current splits into two sections, one traveling northward into the Indian Ocean, while the other heads up into the western Pacific.

The two branches of the current warm and rise as they travel northward, then loop back around southward and westward.

The now-warmed surface waters continue circulating around the globe. They eventually return to the North Atlantic where the cycle begins again.

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.