Ocean Currents: Forces, Concepts, Types, Maps | Sea Life, Islands and Oceania

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OCEAN CURRENTS

Gulf Stream map from 1943
The term "current" describes the motion of something. Ocean.currents describe the movement of water from one location to another in the sea. Currents are vital for: 1) moving nutrients and food sources in the sea; 2) cooling, heating and providing water to terrestrial areas, and 3) transferring heat from the Equator to the Poles.

Currents are generally measured in meters per second or in knots (1 knot = 1.85 kilometers per hour or 1.15 miles per hour). Currents affect the Earth's climate by driving warm water from the Equator and cold water from the poles around the Earth. The warm Gulf Stream, for instance, brings milder winter weather to Bergen, Norway, than to New York, much further south.

Ocean currents are driven mainly by prevailing winds and differences in water density, which changes with temperature and salinity of the seawater. The overall pattern of ocean circulation appears to driven by thermohaline circulation (“thermo” for heat and “haline” for salinity”) — a conveyor belt driven by the sinking of dense cold water in North Atlantic. This draws warm surface water (the Gulf Stream) from the south and sets in motion currents that affect all the world’s oceans.

Currents can also be influenced by salt and and influxed of fresh water. Salt water is heavier than fresh water, As fresh water enters the systems it rides over ocean water and pulls some of the salt water into it, creating a sort of vacuum that draws in more deep ocean water. Saline water that flows from warm areas to cold areas loses heat and becomes more saline as water evaporates. The coldness and high salinity makes the water more dense. It sinks into the oceans. As it does surface water moves in to displace it.

Websites and Resources: National Oceanic and Atmospheric Administration (NOAA) noaa.gov; “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 uv.es/hegigui/Kasper ; Woods Hole Oceanographic Institute whoi.edu ; Cousteau Society cousteau.org ; Monterey Bay Aquarium montereybayaquarium.org

Important Terms for Ocean Currents and Circulation

Ocean currents off Panama

According to the “Introduction to Physical Oceanography”: 1) General Circulation is the permanent, time-averaged circulation. 2) Abyssal also called the Deep Circulation is the circulation of mass, in the meridional plane, in the deep ocean, driven by mixing. 3) Wind-Driven Circulation is the circulation in the upper kilometer of the ocean forced by the wind. The circulation can be caused by local winds or by winds in other regions. 4) Gyres are wind-driven cyclonic or anticyclonic currents with dimensions nearly that of ocean basins. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

5) Boundary Currents are currents flowing parallel to coasts. Two types of boundary currents are important: A) Western boundary currents on the western edge of the ocean tend to be fast, narrow jets such as the Gulf Stream and Kuroshio Current off Japan; B) • Eastern boundary currents are weak, e.g. the California Current. 6) Squirts or Jets are long narrow currents, with dimensions of a few hundred kilometers, that are nearly perpendicular to west coasts. 7) Mesoscale Eddies are turbulent or spinning flows on scales of a few hundred kilometers.

In addition to flow due to currents, there are many types of oscillatory flows due to waves. Normally, when we think of waves in the ocean, we visualize waves breaking on the beach or the surface waves influencing ships at sea. But many other types of waves occur in the ocean. A) Planetary Waves depend on the rotation of the earth for a restoring force, and they including Rossby, Kelvin, Equatorial, and Yanai waves. B) Surface Waves sometimes called gravity waves, are the waves that eventually break on the beach. The restoring force is due to the large density contrast between air and water at the sea surface. C) Internal Waves are sub-sea wave similar in some respects to surface waves. The restoring force is due to change in density with depth. D) Tsunamis are surface waves with periods near 15 minutes generated by earthquakes. E) Tidal Currents are horizontal currents and currents associated with internal waves driven by the tidal potential. F) Edge Waves are surface waves with periods of a few minutes confined to shallow regions near shore. The amplitude of the waves drops off exponentially with distance from shore.

Forces Behind Ocean Currents

Oceanic currents are driven by three main factors: 1) Winds drive currents that are at or near the ocean's surface. Near coastal areas winds tend to drive currents on a localized scale and can result in phenomena like coastal upwelling. On a more global scale, in the open ocean, winds drive currents that circulate water for thousands of miles throughout the ocean basins. [Source: NOAA]

2) Thermohaline circulation. This is a process driven by density differences in water due to temperature (thermo) and salinity (haline) variations in different parts of the ocean. Currents driven by thermohaline circulation occur at both deep and shallow ocean levels and move much slower than tidal or surface currents.

3) The rise and fall of the tides. Tides create a current in the oceans, which are strongest near the shore, and in bays and estuaries along the coast. These are called "tidal currents." Tidal currents change in a very regular pattern and can be predicted for future dates. In some locations, strong tidal currents can travel at speeds of eight knots or more.

Prevailing winds both push water and create circulation by displacing water at the surface that allows upwelling — the upward flow of cold water from deep in the ocean to the surface of the sea. The cold oxygen-poor water is often rich in nutrients such as nitrates, phosphate and silicate that are consumed by creatures on the bottom of the food chain beginning with phytoplankton that in turn feed marine life further up the food chain.

Important Concepts in the Study of Ocean Currents

According to the “Introduction to Physical Oceanography”: To begin our study of currents near the sea surface, let’s consider first the response of the ocean to an impulse that sets the water in motion. For example, the impulse can be a strong wind blowing for a few hours. The water then moves only under the influence of Coriolis force (force resulting from the earth's rotation that deflects movement to the right in the northern hemisphere and to the left in the southern hemisphere). Such motions are said to be inertial. The mass of water continues to move due to its inertia. If the water were in space, it would move in a straight line according to Newton’s second law. But on a rotating earth, the motion is much different. The following are some important things to consider when discussing currents. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

Ocean Currents

1) Changes in wind stress produce transient oscillations in the ocean called inertial currents : A) Inertial currents are very common in the ocean. B) The period of the current is (2π)/f. 2) Because of the Coriolis Affect, movement can be 90 degrees to the right of the wind in the northern hemisphere and 90 degrees to the left of the wind in the southern hemisphere.

3) Steady winds produce a thin boundary layer, the Ekman layer, at the top of the ocean. Ekman boundary layers also exist at the bottom of the ocean and the atmosphere. The Ekman layer in the atmosphere above the sea surface is called the planetary boundary layer. 4) The Ekman layer at the sea surface has the following characteristics: A ) Direction: 45 degrees to the right of the wind looking downwind in the Northern Hemisphere. B) Surface Speed: 1–2.5 percent of wind speed depending on latitude. C) Depth: approximately 40–300 meters depending on latitude and wind velocity.

4) Careful measurements of currents near the sea surface show that: A) Inertial oscillations are the largest component of the current in the mixed layer. B) The flow is nearly independent of depth within the mixed layer for periods near the inertial period. Thus the mixed layer moves like a slab at the inertial period. C) An Ekman layer exists in the atmosphere just above the sea (and land) surface. Surface drifters tend to drift parallel to lines of constant atmospheric pressure at the sea surface. This is consistent with Ekman’s theory. E) The flow averaged over many inertial periods is almost exactly that calculated from Ekman’s theory.

5) Spatial variability of Ekman transport, due to spatial variability of winds over distances of hundreds of kilometers and days, leads to convergence and divergence of the transport such as producing upwelling far away from where the winds that generate them. 6) Ekman pumping, which is driven by spatial variability of winds, drives a vertical current, which drives the interior geostrophic circulation of the ocean.

Tides and Currents

Tides go up and down; currents move left and right. Tides create a current in the oceans, near the shore, and in bays and estuaries along the coast but currents in the open ocean are generally influenced more other factors. [Source: NOAA]

Tides are driven by the gravitational force of the moon and sun. Tides are characterized by water moving up and down over a long period of time. Oceanic currents are driven by several factors. One is the rise and fall of the tides. Tides create a current in the oceans, near the shore, and in bays and estuaries along the coast. These are called "tidal currents." Tidal currents are the only type of currents that change in a very regular pattern and can be predicted for future dates. Currents are generally influenced more by winds and thermohaline circulation.

Ocean current map from 1943, made in World War II

Currents in coastal areas can be caused the ebb and flow of tides. In bays and straits where the water narrows the tides and currents can be quite strong. In some places such as the Bay of Fundy water levels can range 50 feet between low and high tide. In places where there are narrow straight currents can reach 15 knots when the tide ebbs and then lie still for 15 minutes or so and then start flowing with equal velocity in the other direction.

Wind Driven Circulation

You would think that currents on the surface of the ocean follow the prevailing winds. While this often true it isn’t always the case. Robert Stewart wrote in the “Introduction to Physical Oceanography”: Sometimes “strong currents, such as the North Equatorial Countercurrents in the Atlantic and Pacific Ocean go upwind. Spanish navigators in the 16th century noticed strong northward currents along the Florida coast that seemed to be unrelated to the wind. How can this happen? And, why are strong currents found offshore of east coasts but not offshore of west coasts? Answers to the questions can be found in a series of three remarkable papers published from 1947 to 1951. In the first, Harald Sverdrup (1947) showed that the circulation in the upper kilometer or so of the ocean is directly related to the curl of the wind stress if the Coriolis force varies with latitude. Henry Stommel (1948) showed that the circulation in oceanic gyres is asymmetric also because the Coriolis force varies with latitude. Finally, Walter Munk (1950) added eddy viscosity and calculated the circulation of the upper layers of the Pacific. Together the three oceanographers laid the foundations for a modern theory of ocean circulation. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

Sverdrup’s Theory of the Oceanic Circulation: While Sverdrup was analyzing observations of equatorial currents, he came upon the equation below relating the curl of the wind stress to mass transport within the upper ocean. To derive the relationship, Sverdrup assumed that the flow is stationary, that lateral friction and molecular viscosity are small, that non-linear terms such as u ∂u/∂x are small, and that turbulence near the sea surface can be described using a vertical eddy viscosity. He also assumed that the wind-driven circulation vanishes at some depth of no motion.

Eddies and Whirlpools

An eddy is a circular current of water. The ocean is a huge body of water that is constantly in motion. General patterns of ocean flow are called currents. Sometimes theses currents can pinch off sections and create circular currents of water called an eddy. NASA satellite images show eddies and small currents responsible for the swirling pattern of phytoplankton blooms. [Source: NOAA]

You may have seen an eddy if you've ever gone canoeing and you see a small whirlpool of water while you paddle through the water. The swirling motion of eddies in the ocean cause nutrients that are normally found in colder, deeper waters to come to the surface. Significant eddies are assigned names similar to hurricanes. In the U.S., an oceanographic company called Horizon Marine assigns names to each eddy as they occur. The names follow chronologically along with the alphabet and are decided upon by staff at Horizon Marine. The staff try to think of creative ways to assign names. For example, an eddy that formed in the Gulf of Mexico in June 2010 is named Eddy Franklin after Ben Franklin, as he was known to have done research on the Gulf Stream.

Ocean bottom currents

Old Sow is the name of the Western Hemisphere's largest whirlpool. While the turbulent water of Old Sow can be dangerous to small-craft mariners, its swirling motion has a positive environmental effect. It causes nutrients and tiny sea creatures normally found in the bay’s colder, deeper waters to rise to the surface. This process, called upwelling, ensures good eating for the resident fish and seabirds.

When the tide comes in from the Bay of Fundy, located off the Atlantic Coast between the State of Maine and the Province of New Brunswick, a tremendous amount of ocean water, called a current, flows swiftly into a confined area called the Western Passage before emptying upriver into Passamaquoddy Bay. After making a sharp right turn to the north and traversing a deep trench, flowing past an underwater mountain, and encountering several countercurrents, a portion of the current "pinches off" to form the huge circular current called Old Sow, and, often, several smaller ones, nicknamed “piglets.” Circular currents of all sizes are commonly known as whirlpools, vortexes, eddies, and gyres.

Old Sow varies in size but has been measured at more than 250 feet in diameter, about the length of a soccer field. While the turbulent water can be dangerous to small-craft mariners — some of whom have barely escaped a 12-foot drop into the Sow’s gaping maw — its swirling motion has a positive environmental effect. It causes nutrients and tiny sea creatures normally found in the bay’s colder, deeper waters to rise to the surface. This process, called upwelling, ensures good eating for the resident fish and seabirds. So why is the whirlpool called "Old Sow?" According to folklore, the name refers to the "grunting" noise — which sounds like hungry pigs slurping up their slop — made by the giant churning gyre. "Sow" may also be a mispronunciation of the word "sough" (pronounced suff), which means "sucking noise" or "drain."

Turbidity Currents

A turbidity current is a rapid, downhill flow of water caused by increased density due to high amounts of sediment. Turbidity currents can be caused by earthquakes, collapsing slopes, and other geological disturbances. Once set in motion, the turbid water rushes downward and can change the physical shape of the seafloor. [Source: NOAA]

Turbidity is a measure of the level of particles such as sediment, plankton, or organic by-products, in a body of water. As the turbidity of water increases, it becomes denser and less clear due to a higher concentration of these light-blocking particles.

Turbidity currents can be set into motion when mud and sand on the continental shelf are loosened by earthquakes, collapsing slopes, and other geological disturbances. The turbid water then rushes downward like an avalanche, picking up sediment and increasing in speed as it flows.

Global Ocean Conveyor Belt

Turbidity currents can change the physical shape of the seafloor by eroding large areas and creating underwater canyons. These currents also deposit huge amounts of sediment wherever they flow, usually in a gradient or fan pattern, with the largest particles at the bottom and the smallest ones on top.

NOAA scientists use current meters attached with turbidity sensors to gather data near underwater volcanoes and other highly active geological sites. Also, satellite imagery is used to observe turbidity by measuring the amount of light that is reflected by a section of water.

Geostrophic Currents and the Rubber Duckie Spill

A geostrophic current is an oceanic current in which the pressure gradient force is balanced by the Coriolis effect. The direction of geostrophic flow is parallel to the isobars, with the high pressure to the right of the flow in the Northern Hemisphere, and the high pressure to the left in the Southern Hemisphere. [Source: Wikipedia]

According to the “Introduction to Physical Oceanography”: Within the ocean’s interior away from the top and bottom Ekman layers, for horizontal distances exceeding a few tens of kilometers, and for times exceeding a few days, horizontal pressure gradients in the ocean almost exactly balance the Coriolis force resulting from horizontal currents. This balance is known as the geostrophic balance. The dominant forces acting in the vertical are the vertical pressure gradient and the weight of the water. The two balance within a few parts per million. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

Thus pressure at any point in the water column is due almost entirely to the weight of the water in the column above the point. The dominant forces in the horizontal are the pressure gradient and the Coriolis force. They balance within a few parts per thousand over large dist Barotropic and Baroclinic Flow: If the ocean were homogeneous with constant density, then constant-pressure surfaces would always be parallel to the sea surface, and the geostrophic velocity would be independent of depth. In this case the relative velocity is zero, and hydrographic data cannot be used to measure the geostrophic current. If density varies with depth, but not with horizontal distance, the constant-pressure surfaces are always parallel to the sea surface and the levels of constant density, the isopycnal surfaces. In this case, the relative flow is also zero. Both cases are examples of barotropic flow. Flow is primarily parallel to temperature fronts, and strong currents can exist along fronts even though the front may not move. It is therefore essential to track the motion of small eddies embedded in the flow near the front and not the position of the front.

The Rubber Duckie Spill illustrates some of these concepts. On January 10, 1992 a 12.2-m container with 29,000 bathtub toys, including rubber ducks washed overboard from a container ship at 44.7 degrees N, 178.1 degrees E . Where these rubber duckies floated and where they ended up, sometimes months and years later, gave scientists good data on currents and circulation in the sea.

click once and the click the Wikicommons image

Oceanic Transport of Heat and the Global Ocean Conveyor Belt

According to the “Introduction to Physical Oceanography”: The ocean carry about half the heat out of the tropics needed to maintain earth’s temperature. Heat carried by the Gulf Stream and the north Atlantic drift keeps the far north Atlantic ice free, and it helps warm Europe. Norway, at 60 degrees N is far warmer than southern Greenland or northern Labrador at the same latitude. Palm trees grow on the west coast of Ireland, but not in Newfoundland which is further south.[Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

Wally Broecker (1987), working at Lamont-Doherty Geophysical Observatory of Columbia University, calls the oceanic component of the heat-transport system the Global Conveyor Belt. The basic idea is that surface currents carry heat to the far north Atlantic. There the surface water releases heat and water to the atmosphere, and it becomes sufficiently cold, salty, and dense that it sinks to the bottom in the Norwegian and Greenland Seas. It then flows southward in cold, bottom currents. Some of the water remains on the surface and returns to the south in cool surface currents such as the Labrador Current and Portugal Current. Richardson (2008) has written a very useful paper surveying our understanding of the global conveyor belt.

The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity. The ocean is not a still body of water. There is constant motion in the ocean in the form of a global ocean conveyor belt. This motion is caused by a combination of thermohaline currents in the deep ocean and wind-driven currents on the surface. Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface. [Source: NOAA]

The ocean conveyor gets its “start” in the Norwegian Sea, where warm water from the Gulf Stream heats the atmosphere in the cold northern latitudes. This loss of heat to the atmosphere makes the water cooler and denser, causing it to sink to the bottom of the ocean. As more warm water is transported north, the cooler water sinks and moves south to make room for the incoming warm water. This cold bottom water flows south of the equator all the way down to Antarctica. Eventually, the cold bottom waters returns to the surface through mixing and wind-driven upwelling, continuing the conveyor belt that encircles the globe.

The deep bottom water from the north Atlantic is mixed upward in other regions and ocean, and eventually it makes its way back to the Gulf Stream and the North Atlantic. Thus most of the water that sinks in the north Atlantic must be replaced by water from the far south Atlantic. As this surface water moves northward across the equator and eventually into the Gulf Stream, it carries heat out of the south Atlantic. So much heat is pulled northward by the formation of north Atlantic bottom water in winter that heat transport in the Atlantic is entirely northward, even in the southern hemisphere. Much of the solar heat absorbed by the tropical Atlantic is shipped north to warm Europe and the northern hemisphere.

Gyres

A gyre is a large system of rotating ocean currents. There are five major gyres, which are large systems of rotating ocean currents. The ocean churns up various types of currents. Together, these larger and more permanent currents make up the systems of currents known as gyres. [Source: NOAA]

Wind, tides, and differences in temperature and salinity drive ocean currents. The ocean churns up different types of currents, such as eddies, whirlpools, or deep ocean currents. Larger, sustained currents — the Gulf Stream, for example — go by proper names. Taken together, these larger and more permanent currents make up the systems of currents known as gyres.

The five major gyres are: 1) the North Pacific Subtropical Gyre; 2) the South Pacific Subtropical Gyre; 3) the North Atlantic Subtropical Gyre, 4) the South Atlantic Subtropical Gyre, and 5) the Indian Ocean Subtropical Gyre. In some instances, the term “gyre” is used to refer to the collections of plastic waste and other debris found in higher concentrations in certain parts of the ocean. While this use of "gyre" is increasingly common, the term traditionally refers simply to large, rotating ocean currents.

Upwelling

Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away. This process is known as “upwelling.” 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 and the surface water eventually sinks toward the bottom.

Upwelling brings deep, cold, often nutrient-rich water to the surface that “wells up” from below. There are five major coastal currents affiliated with strong upwelling zones, the California Current, the Humboldt Current off Peru, the Canary Current, the Benguela Current off Namimbia, and the Somali Current. Robert Stewart wrote in the “Introduction to Physical Oceanography”: Because steady winds blowing on the sea surface produce an Ekman layer that transports water at right angles to the wind direction, any spatial variability of the wind, or winds blowing along some coasts, can lead to upwelling. [Source: Robert Stewart, “Introduction to Physical Oceanography”, Texas A&M University, 2008]

Upwelling is important because: 1) it enhances biological productivity, which feeds fisheries; 2) cold upwelled water alters local weather. Weather onshore of regions of upwelling tend to have fog, low stratus clouds, a stable stratified atmosphere, little convection, and little rain. 3) Spatial variability of transports in the open ocean leads to upwelling and downwelling, which leads to redistribution of mass in the ocean, which leads to wind-driven geostrophic currents via Ekman pumping.

Water that rises to the surface as a result of upwelling is typically colder and is rich in nutrients. These nutrients “fertilize” surface waters, meaning that these surface waters often have high biological productivity. Therefore, good fishing grounds typically are found where upwelling is common.

To see how winds lead to coastal upwelling, consider north winds blowing parallel to the California Coast. The winds produce a mass transport away from the shore everywhere along the shore. The water pushed offshore can be replaced only by water from below the Ekman layer. This is upwelling. Because the upwelled water is cold, the upwelling leads to a region of cold water at the surface along the coast.

Upwelled water is colder than water normally found on the surface, and it is richer in nutrients. The nutrients fertilize phytoplankton in the mixed layer, which are eaten by zooplankton, which are eaten by small fish, which are eaten by larger fish and so on. As a result, upwelling regions are productive waters supporting the world’s major fisheries. The important regions are offshore of Peru, California, Somalia, Morocco, and Namibia.

Ekman transport and spatial variability of winds over distances of hundreds of kilometers and days leads to convergence and divergence of the transport and. A) Winds blowing toward the equator along west coasts of continents produces upwelling along the coast. This leads to cold, productive waters within about 100 kilometers of the shore. B) Upwelled water along west coasts of continents modifies the weather along the west coasts.

Monitoring Currents

To measure currents, you need three basic tools: 1) an observer, 2) a floating object or a drifter, and 3) a timing device. An observer stands on a ship, throws the drifter into the water, and then measures the time that it takes that object to move along the side of a ship. As technology improved over time, oceanographers began using mechanical current meters. A ship would deploy a meter and usually some sort of rotor would turn and measure the currents. This is still the basic process today; however there are more accurate and sophisticated instruments. [Source: NOAA]

Currents are observed at depths throughout the water column and are measured over a period of time. Today in the open ocean, a drifter is similar to a buoy in the water that may be equipped with global positioning system technology or satellite communications that would relay data and information. Drifters can also submerge for long periods of time to measure ocean currents at a particular depth. The drifter would then resurface occasionally to send a signal with its data and position to observers on the land.

In addition to buoys, there are other tools that are used to monitor currents. Acoustic Doppler Current Profiler (ADCP) is an instrument that measures the currents by emitting beams of sound, which reflect off of particles in the water and back to the ADCP. Commonly used to measure currents, it is normally deployed on the seafloor or attached to the bottom of a boat. It sends an acoustic signal into the water column and that sound bounces off particles in the water. The instrument can calculate the speed and direction of the current by knowing the frequency of the return signal, the distance it traveled, and the time it took for the signal to travel.

Many oceanographers also use radio antennas and high frequency Radio Detecting and Ranging systems (radar) to measure surface ocean currents. Similar to the Acoustic Doppler Current Profiler, these shore-based instruments use the Doppler effect to determine when currents are moving toward or away from the shore or to measure the velocity of a current. At NOAA, oceanographers use knots to measure current speed. The term knot is defined as one nautical mile per hour. One nautical mile is equal to 1.85 kilometers. One knot is also 51.44 centimeters per second.

After the ocean current measurements are collected, oceanographers download the data and then analyze it through a computer program. A statistical process called harmonic analysis determines the part of the current caused by the tides. This “tidal current” can then be predicted at that location for many years into the future. Other factors that influence the current, such as wind, cannot be forecast for more than a few days and are not included in the prediction.

NOAA’s Center for Operational Oceanographic Products and Services (CO-OPS) is primarily responsible for predicting and measuring water levels and currents and disseminating this information. CO-OPS collects, analyzes, and distributes such data to maintain safe maritime navigation and waterborne commerce. Tide and current data is available from CO-OPS Products and Services website. Among the things that are offered are: 1) Sea Levels, a global map depicting regional trends in sea level, with arrows representing the direction and magnitude of change; 2) Real-Time Current Data, collected by NOAA current meters around the U.S.; 3) Historic Current Data.; 4) Tidal Current Predictions, predictions for more than 2700 tidal current stations nationwide; 5) Storm QuickLook, real-time oceanographic and meteorological observations at locations affected by a tropical cyclone.

Why the Study of Currents Is Important

Current data is critical for supporting safe and efficient shipping and marine transportation. With predicted, real-time, and forecasted currents, people can safely dock and undock ships, maneuver them in confined waterways, and safely navigate through coastal waters. This helps to avoid ship collisions or delay the arrival of goods. In addition, current measurements are important for search and rescue operations, environmental disasters, and coastal engineering projects. [Source: NOAA]

When supporting search and rescue operations, understanding the speed and direction of the currents in an area helps to narrow down the rescue and recovery effort. Current prediction information can help scientists clean up after a hazardous oil spill by helping them understand the direction and movement of the oil. Engineers also use currents information to help build marine structures such as bridges or docks and piers. Current observations are also used to develop and evaluate coastal nowcast or forecast model products that are provided online.

An Operational Forecast System provides a nowcast and forecast (up to 48 hours) of water levels, currents, salinity, water temperatures, and winds for a given area. These systems are located in coastal waters and the Great Lakes in critical ports, harbors, and estuaries. NOAA periodically conducts current surveys in areas around the nation to ensure the accuracy of tidal current predictions. Commercial and recreational mariners depend on this information for safe navigation.

Image Sources: Wikimedia Commons; YouTube, NOAA

Text Sources: National Oceanic and Atmospheric Administration (NOAA) noaa.gov; “Introduction to Physical Oceanography” by Robert Stewart , Texas A&M University, 2008 uv.es/hegigui/Kasper ; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023