Langmuir circulation

In physical oceanography, Langmuir circulation consists of a series of shallow, slow, counter-rotating vortices at the ocean's surface aligned with the wind. These circulations are developed when wind blows steadily over the sea surface. Irving Langmuir discovered this phenomenon after observing windrows of seaweed in the Sargasso Sea in 1927.[1] Langmuir circulations circulate within the mixed layer; however, it is not yet so clear how strongly they can cause mixing at the base of the mixed layer. [2]

Langmuir Circulation
Langmuir circulation
Rodeo Lagoon From Trail
White streaks in this lagoon are due to the Langmuir circulation.
Lines of sargassum Sargasso Sea
These lines of sargassum can stretch for miles along the surface. The clumps of floating algae are often concentrated by the strong winds and wave action associated with the Gulf Stream.

Theory

The driving force of these circulations is an interaction of the mean flow with wave averaged flows of the surface waves. Stokes drift velocity of the waves stretches and tilts the vorticity of the flow near the surface. The production of vorticity in the upper ocean is balanced by downward (often turbulent) diffusion . For a flow driven by a wind characterized by friction velocity the ratio of vorticity diffusion and production defines the Langmuir number [2]

where the first definition is for a monochromatic wave field of amplitude , frequency , and wavenumber and the second uses a generic inverse length scale , and Stokes velocity scale . This is exemplified by the Craik–Leibovich equations[3] which are an approximation of the Lagrangian mean.[4][5] In the Boussinesq approximation the governing equations can be written

Langmuir Circulation at Newquay May 2019
Langmuir circulation lines during sunset at Porth Beach, Newquay.
Langmuir Circulation at Newquay May 2019
Langmuir circulation lines during sunset at Porth Beach, Newquay.

where is the fluid velocity, is planetary rotation, is the Stokes drift velocity of the surface wave field, is the pressure, is the acceleration due to gravity, is the density, is the reference density, is the viscosity, and is the diffusivity.

In the open ocean conditions where there may not be a dominant length scale controlling the scale of the Langmuir cells the concept of Langmuir Turbulence is advanced. [6]

Observations

The circulation has been observed to be between 0°–20° to the right of the wind in the northern hemisphere [7] and the helix forming bands of divergence and convergence at the surface. At the convergence zones, there are commonly concentrations of floating seaweed, foam and debris along these bands. Along these divergent zones, the ocean surface is typically clear of debris since diverging currents force material out of this zone and into adjacent converging zones. At the surface the circulation will set a current from the divergence zone to the convergence zone and the spacing between these zones are of the order of 1–300 m (3–1,000 ft). Below convergence zones narrow jets of downward flow form and the magnitude of the current will be comparable to the horizontal flow. The downward propagation will typically be in the order of meters or tenths of meters and will not penetrate the pycnocline. The upwelling is less intense and takes place over a wider band under the divergence zone. In wind speeds ranging from 2–12 m/s (6.6–39.4 ft/s) the maximum vertical velocity ranged from 2–10 cm/s (0.79–3.94 in/s) with a ratio of down-welling to wind velocities ranging from −0.0025 to −0.0085. [8]

References

  1. ^ Open University (2001), Ocean Circulation (2nd ed.), Butterworth-Heinemann, ISBN 9780750652780
  2. ^ a b Thorpe, S.A. (2004), "Langmuir circulation", Annual Review of Fluid Mechanics, 36: 55–79, Bibcode:2004AnRFM..36...55T, doi:10.1146/annurev.fluid.36.052203.071431
  3. ^ Craik, A.D.D.; Leibovich, S. (1976), "A Rational model for Langmuir circulations", Journal of Fluid Mechanics, 73 (3): 401–426, Bibcode:1976JFM....73..401C, doi:10.1017/S0022112076001420
  4. ^ Andrews, D.G.; McIntyre, M.E. (1978), "An exact theory of nonlinear waves on a Lagrangian-mean flow", Journal of Fluid Mechanics, 89 (4): 609–646, Bibcode:1978JFM....89..609A, doi:10.1017/S0022112078002773
  5. ^ Leibovich, S. (1980), "On wave-current interactions theories of Langmuir circulations", Journal of Fluid Mechanics, 99 (4): 715–724, Bibcode:1980JFM....99..715L, doi:10.1017/S0022112080000857
  6. ^ McWilliams, J.; Sullivan, P.; Moeng, C. (1997), "Langmuir turbulence in the ocean", Journal of Fluid Mechanics, 334 (1): 1–30, Bibcode:1997JFM...334....1M, doi:10.1017/S0022112096004375
  7. ^ Stewart, Robert H. (2002), Introduction To Physical Oceanography (Fall 2002 ed.)
  8. ^ Leibovich, S. (1983), "The form and dynamics of Langmuir circulations", Annual Review of Fluid Mechanics, 15: 391–427, Bibcode:1983AnRFM..15..391L, doi:10.1146/annurev.fl.15.010183.002135

External links

Bahama Banks

The Bahama Banks are the submerged carbonate platforms that make up much of the Bahama Archipelago. The term is usually applied in referring to either the Great Bahama Bank around Andros Island, or the Little Bahama Bank of Grand Bahama Island and Great Abaco, which are the largest of the platforms, and the Cay Sal Bank north of Cuba. The islands of these banks are politically part of the Bahamas. Other banks are the three banks of the Turks and Caicos Islands, namely the Caicos Bank of the Caicos Islands, the bank of the Turks Islands, and wholly submerged Mouchoir Bank. Further southeast are the equally wholly submerged Silver Bank and Navidad Bank north of the Dominican Republic.

Craik–Leibovich vortex force

In fluid dynamics, the Craik–Leibovich (CL) vortex force describes a forcing of the mean flow through wave–current interaction, specifically between the Stokes drift velocity and the mean-flow vorticity. The CL vortex force is used to explain the generation of Langmuir circulations by an instability mechanism. The CL vortex-force mechanism was derived and studied by Sidney Leibovich and Alex D.D. Craik in the 1970s and 80s, in their studies of Langmuir circulations (discovered by Irving Langmuir in the 1930s).

Critical depth

In biological oceanography, 'Critical Depth' is defined as a hypothesized surface mixing depth at which phytoplankton growth is precisely matched by losses of phytoplankton biomass within this depth interval. This concept is useful for understanding the initiation of phytoplankton blooms.

Front (oceanography)

In oceanography, a front is a boundary between two distinct water masses. The water masses are defined by moving in different directions, i.e. on one side of the front the water is generally moving in one way, and on the other side of the front, the water is moving in another. Depending on the directions of the water masses, a front may be defined as convergent or divergent. The water masses on either side of a front may also have different temperatures, salinities, or densities, along with differences in other oceanographic markers. While most fronts form and dissipate relatively quickly, some, such as the fronts caused by the antarctic circumpolar current, persist for long periods of time.

Index of physics articles (L)

The index of physics articles is split into multiple pages due to its size.

To navigate by individual letter use the table of contents below.

Irving Langmuir

Irving Langmuir (; January 31, 1881 – August 16, 1957) was an American chemist and physicist. He was awarded the Nobel Prize in Chemistry in 1932 for his work in surface chemistry.

Langmuir's most famous publication is the 1919 article "The Arrangement of Electrons in Atoms and Molecules" in which, building on Gilbert N. Lewis's cubical atom theory and Walther Kossel's chemical bonding theory, he outlined his "concentric theory of atomic structure". Langmuir became embroiled in a priority dispute with Lewis over this work; Langmuir's presentation skills were largely responsible for the popularization of the theory, although the credit for the theory itself belongs mostly to Lewis. While at General Electric from 1909 to 1950, Langmuir advanced several fields of physics and chemistry, invented the gas-filled incandescent lamp and the hydrogen welding technique. The Langmuir Laboratory for Atmospheric Research near Socorro, New Mexico, was named in his honor, as was the American Chemical Society journal for surface science called Langmuir.

Langmuir

Langmuir may refer to:

Langmuir (crater), an impact crater on the Moon's far side

Langmuir (journal), an academic journal on colloids, surfaces and interfaces, published by the American Chemical Society

Langmuir (unit), a unit of exposure of an adsorbate/gas to a substrate used in surface science to study adsorption

Langmuir Cove, a cove in the north end of Arrowsmith Peninsula, Graham Land, Antarctica

Langmuir Turbulence

In fluid dynamics, and oceanography, the term Langmuir Turbulence refers to a turbulent flow with coherent Langmuir circulation structures that exist and evolve over a range of spatial and temporal scales. These structures arise through an interaction between the ocean surface waves and the currents.

In the upper ocean Langmuir circulations are a special case where the turbulent structures exhibit a dominant cell size. In general it is expected that Langmuir turbulence is a global ocean phenomenon and not confined to gentle wind conditions or shallow water ways (as with most observations of Langmuir circulation).An important consequence of the Langmuir turbulence are deeply penetrating jets. These features occur between counter-rotating Langmuir circulations and can inject turbulent kinetic energy to depths well below the depth scale for the surface waves (Stokes drift depth scale). Langmuir turbulence could have an important impact on our understanding of climate. In particular, Langmuir turbulence could affect the global ocean's sea surface temperature as the deeply penetrating Langmuir jets modify the depth of the ocean mixed layer.

List of submarine volcanoes

A list of active and extinct submarine volcanoes and seamounts located under the world's oceans. There are estimated to be 40,000 to 55,000 seamounts in the global oceans. Almost all are not well-mapped and many may not have been identified at all. Most are unnamed and unexplored. This list is therefore confined to seamounts that are notable enough to have been named and/or explored.

List of things named after Irving Langmuir

Irving Langmuir (1881–1957), American chemist and physicist who made significant contributions to several widely varied areas of modern science, is the eponym of the topics listed below.

Mixed layer

The oceanic or limnological mixed layer is a layer in which active turbulence has homogenized some range of depths. The surface mixed layer is a layer where this turbulence is generated by winds, surface heat fluxes, or processes such as evaporation or sea ice formation which result in an increase in salinity. The atmospheric mixed layer is a zone having nearly constant potential temperature and specific humidity with height. The depth of the atmospheric mixed layer is known as the mixing height. Turbulence typically plays a role in the formation of fluid mixed layers.

Oceanic plateau

An oceanic or submarine plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides.There are 184 oceanic plateaus covering an area of 18,486,600 km2 (7,137,700 sq mi), or about 5.11% of the oceans. The South Pacific region around Australia and New Zealand contains the greatest number of oceanic plateaus (see map).

Oceanic plateaus produced by large igneous provinces are often associated with hotspots, mantle plumes, and volcanic islands — such as Iceland, Hawaii, Cape Verde, and Kerguelen. The three largest plateaus, the Caribbean, Ontong Java, and Mid-Pacific Mountains, are located on thermal swells. Other oceanic plateaus, however, are made of rifted continental crust, for example Falkland Plateau, Lord Howe Rise, and parts of Kerguelen, Seychelles, and Arctic ridges.

Plateaus formed by large igneous provinces were formed by the equivalent of continental flood basalts such as the Deccan Traps in India and the Snake River Plain in the United States.

In contrast to continental flood basalts, most igneous oceanic plateaus erupt through young and thin (6–7 km (3.7–4.3 mi)) mafic or ultra-mafic crust and are therefore uncontaminated by felsic crust and representative for their mantle sources.

These plateaus often rise 2–3 km (1.2–1.9 mi) above the surrounding ocean floor and are more buoyant than oceanic crust. They therefore tend to withstand subduction, more-so when thick and when reaching subduction zones shortly after their formations. As a consequence, they tend to "dock" to continental margins and be preserved as accreted terranes. Such terranes are often better preserved than the exposed parts of continental flood basalts and are therefore a better record of large-scale volcanic eruptions throughout Earth's history. This "docking" also means that oceanic plateaus are important contributors to the growth of continental crust. Their formations often had a dramatic impact on global climate, such as the most recent plateaus formed, the three, large, Cretaceous oceanic plateaus in the Pacific and Indian Ocean: Ontong Java, Kerguelen, and Caribbean.

Physical oceanography

Physical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters.

Physical oceanography is one of several sub-domains into which oceanography is divided. Others include biological, chemical and geological oceanography.

Physical oceanography may be subdivided into descriptive and dynamical physical oceanography.Descriptive physical oceanography seeks to research the ocean through observations and complex numerical models, which describe the fluid motions as precisely as possible.

Dynamical physical oceanography focuses primarily upon the processes that govern the motion of fluids with emphasis upon theoretical research and numerical models. These are part of the large field of Geophysical Fluid Dynamics (GFD) that is shared together with meteorology. GFD is a sub field of Fluid dynamics describing flows occurring on spatial and temporal scales that are greatly influenced by the Coriolis force.

Rodeo Lagoon

Rodeo Lagoon is a coastal lagoon located in the Marin Headlands division of the Golden Gate National Recreation Area, which is in southern Marin County, California. This brackish water body is separated from the Pacific Ocean by a sand bar that forms Rodeo Beach. Rodeo Lagoon stretches approximately 900 meters (3000 ft) by 250 meters (820 feet), and is about 2 meters (6.6 ft) deep at its maximum depth. It covers a surface area of about 15 ha (37 acres).

Secondary flow

In fluid dynamics, a secondary flow is a relatively minor flow superimposed on the primary flow, where the primary flow usually matches very closely the flow pattern predicted using simple analytical techniques that assume the fluid is inviscid. (An inviscid fluid is a theoretical fluid having zero viscosity.)

The primary flow of a fluid, particularly in the majority of the flow field remote from solid surfaces immersed in the fluid, is usually very similar to what would be predicted using the basic principles of physics, and assuming the fluid is inviscid. However, in real flow situations, there are regions in the flow field where the flow is significantly different in both speed and direction to what is predicted for an inviscid fluid using simple analytical techniques. The flow in these regions is the secondary flow. These regions are usually in the vicinity of the boundary of the fluid adjacent to solid surfaces where viscous forces are at work, such as in the boundary layer.

Tideline

A tideline refers to where two currents in the ocean converge. Driftwood, floating seaweed, foam, and other floating debris may accumulate, forming sinuous lines called tidelines (although they generally have nothing to do with the tide).

There are four mechanisms that can cause tidelines to form:

Where one body of water is sinking beneath or riding over top of the surface layer of another body of water (somewhat similar in mechanics to subduction of the earth plates at continental margins). These types of tidelines are often found where rivers enter the ocean.

Along the margins of back-eddies.

Convergence zones associated with internal gravity waves.

Along adjacent cells formed by wind currents.

Undersea mountain range

Undersea mountain ranges are mountain ranges that are mostly or entirely underwater, and specifically under the surface of an ocean. If originated from current tectonic forces, they are often referred to as a mid-ocean ridge. In contrast, if formed by past above-water volcanism, they are known as a seamount chain. The largest and best known undersea mountain range is a mid-ocean ridge, the Mid-Atlantic Ridge. It has been observed that, "similar to those on land, the undersea mountain ranges are the loci of frequent volcanic and earthquake activity".

Wave base

The wave base, in physical oceanography, is the maximum depth at which a water wave's passage causes significant water motion. For water depths deeper than the wave base, bottom sediments and the seafloor are no longer stirred by the wave motion above.

Windrow

A windrow is a row of cut (mown) hay or small grain crop. It is allowed to dry before being baled, combined, or rolled. For hay, the windrow is often formed by a hay rake, which rakes hay that has been cut by a mowing machine or by scythe into a row, or it may naturally form as the hay is mown. For small grain crops which are to be harvested, the windrow is formed by a swather which both cuts the crop and forms the windrow.

By analogy, the term may also be applied to a row of any other material such as snow, earth or materials for collection.

Snow windrows are created by snow plows when clearing roads of snow; where this blocks driveways the windrow may require removal. Snow windrowed to the centre of the street can be removed by a snow blower and truck. In preparing a pond or lake for ice cutting, the snow on top of the ice, which slows freezing, may be scraped off and windrowed.

Earth windrows may be formed by graders when grading earthworks or dirt roads

Leaf windrows may be required for municipal collection.

Fossil windrows are a grouping of fossils that have been deposited together as a result of turbulence or wave action in a marine or freshwater environment. Fossils of similar shape and size are commonly found grouped or sorted together as a result of separation based on weight and shape.

Seaweed windrows form on sea or lake surfaces because of cylindrical Langmuir circulation just under the surface caused by wind action.Windrow composting is a large scale vermicomposting system where garden and other biodegradable waste is shredded, mixed and windrowed for composting.

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