Infragravity wave

Infragravity waves are surface gravity waves with frequencies lower than the wind waves – consisting of both wind sea and swell – thus corresponding with the part of the wave spectrum lower than the frequencies directly generated by forcing through the wind.

Infragravity waves are ocean surface gravity waves generated by ocean waves of shorter periods. The amplitude of infragravity waves is most relevant in shallow water, in particular along coastlines hit by high amplitude and long period wind waves and ocean swells. Wind waves and ocean swells are shorter, with typical dominant periods of 1 to 25 s. In contrast, the dominant period of infragravity waves is typically 80 to 300 s,[1] which is close to the typical periods of tsunamis, with which they share similar propagation properties including very fast celerities in deep water. This distinguishes infragravity waves from normal oceanic gravity waves, which are created by wind acting on the surface of the sea, and are slower than the generating wind.

Whatever the details of their generation mechanism, discussed below, infragravity waves are these subharmonics of the impinging gravity waves.[2]

Munk ICCE 1950 Fig1
Classification of the spectrum of ocean waves according to wave period.[3]

Technically infragravity waves are simply a subcategory of gravity waves and refer to all gravity waves with periods greater than 30 s. This could include phenomena such as tides and oceanic Rossby waves, but the common scientific usage is limited to gravity waves that are generated by groups of wind waves.

The term "infragravity wave" appears to have been coined by Walter Munk in 1950.[3][4]


Beacon - - 129502
Surf can be seen breaking as it crosses the sand bar offshore. Sandbars aid in generating infragravity waves and in turn are shaped by them.

Two main processes can explain the transfer of energy from the short wind waves to the long infragravity waves, and both are important in shallow water and for steep wind waves. The most common process is the subharmonic interaction of trains of wind waves which was first observed by Munk and Tucker and explained by Longuet-Higgins and Stewart.[5] Because wind waves are not monochromatic they form groups. The Stokes drift induced by these groupy waves transports more water where the waves are highest. The waves also push the water around in a way that can be interpreted as a force: the divergence of the radiation stresses. Combining mass and momentum conservation, Longuet-Higgins and Stewart give, with three different methods, the now well-known result. Namely, the mean sea level oscillates with a wavelength that is equal to the length of the group, with a low level where the wind waves are highest and a high level where these waves are lowest. This oscillation of the sea surface is proportional to the square of the short wave amplitude and becomes very large when the group speed approaches the speed of shallow water waves. The details of this process are modified when the bottom is sloping, which is generally the case near the shore, but the theory captures the important effect, observed in most conditions, that the high water of this 'surf beat' arrives with the waves of lowest amplitude.

Another process was proposed later by Graham Symonds and his collaborators.[6] To explain some cases in which this phase of long and short waves were not opposed, they proposed that the position of the breaker line in the surf, moving towards deep water when waves are higher, could act like a wave maker. It appears that this is probably a good explanation for infragravity wave generation on a reef.

In the case of coral reefs, the infragravity periods are established by resonances with the reef itself.[7][8]

Glacier-ice shelf interactions
Ice shelf processes.


Infragravity waves generated along the Pacific coast of North America have been observed to propagate transoceanically to Antarctica and there to impinge on the Ross Ice Shelf. Their frequencies more closely couple with the ice shelf natural frequencies and they produce a larger amplitude ice shelf movement than the normal ocean swell of gravity waves. Further, they are not damped by sea ice as normal ocean swell is. As a result, they flex floating ice shelves such as the Ross Ice Shelf; this flexure contributes significantly to the breakup on the ice shelf.[2][9]


  1. ^ Ardhuin, Fabrice; Arshad Rawat; Jerome Aucan (2014), "A numerical model for free infragravity waves: Definition and validation at regional and global scales", Ocean Modelling, 77, Elsevier, pp. 20–32
  2. ^ a b Bromirski, Peter D.; Olga V. Sergienko; Douglas R. MacAyeal (2010). "Transoceanic infragravity waves impacting Antarctic ice shelves". Geophysical Research Letters. 37 (L02502): n/a. Bibcode:2010GeoRL..37.2502B. doi:10.1029/2009GL041488.
  3. ^ a b Munk, Walter H. (1950), "Origin and generation of waves", Proceedings 1st International Conference on Coastal Engineering, Long Beach, California: ASCE, pp. 1–4, ISSN 2156-1028
  4. ^ Kinsman, Blair (1965). Wind Waves: Their Generation and Propagation on the Ocean Surface. Englewood Cliffs, N.J.: Prentice-Hall. pp. 22–23. OCLC 489729.
  5. ^ Longuet-Higgins, Michael; R.W. Stewart (1962), "Radiation stress and mass transport in gravity waves, with application to 'surf beats", Journal of Fluid Mechanics, 13, Cambridge University Press, pp. 481–504
  6. ^ Symonds, Graham; D. A. Huntley; A. J. Bowent (1982), "Two-dimensional surf beat: Long wavegeneration by a time-varying breakpoint", Journal of Geophysical Research, 87 (C1): 492–498, Bibcode:1982JGR....87..492S, CiteSeerX, doi:10.1029/JC087iC01p00492
  7. ^ Lugo-Fernández, A.; H. H. Roberts; W. J. Wiseman Jr.; B. L. Carter (December 1998). "Water level and currents of tidal and infragravity periods at Tague Reef, St. Croix (USVI)". Coral Reefs. 17 (4): 343–349. doi:10.1007/s003380050137.
  8. ^ Péquignet, A. C.; J. M. Becker; M. A. Merrifield; J. Aucan (2009). "Forcing of resonant modes on a fringing reef during tropical storm Man-Yi" (PDF). Geophys. Res. Lett. 36 (L03607): n/a. Bibcode:2009GeoRL..36.3607P. doi:10.1029/2008GL036259.
  9. ^ "Breaking waves: The coup de grace that shatters ice shelves is administered by ocean waves". The Economist. The Economist. February 18, 2010. Retrieved 2010-11-25.

External links

Media related to Gravity waves at Wikimedia Commons

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.

Carbonate platform

A carbonate platform is a sedimentary body which possesses topographic relief, and is composed of autochthonic calcareous deposits. Platform growth is mediated by sessile organisms whose skeletons build up the reef or by organisms (usually microbes) which induce carbonate precipitation through their metabolism. Therefore, carbonate platforms can not grow up everywhere: they are not present in places where limiting factors to the life of reef-building organisms exist. Such limiting factors are, among others: light, water temperature, transparency and pH-Value. For example, carbonate sedimentation along the Atlantic South American coasts takes place everywhere but at the mouth of the Amazon River, because of the intense turbidity of the water there. Spectacular examples of present-day carbonate platforms are the Bahama Banks under which the platform is roughly 8 km thick, the Yucatan Peninsula which is up to 2 km thick, the Florida platform, the platform on which the Great Barrier Reef is growing, and the Maldive atolls. All these carbonate platforms and their associated reefs are confined to tropical latitudes. Today's reefs are built mainly by scleractinian corals, but in the distant past other organisms, like archaeocyatha (during the Cambrian) or extinct cnidaria (tabulata and rugosa) were important reef builders.

Index of physics articles (I)

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.

Index of wave articles

This is a list of Wave topics.

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.

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.

Outline of oceanography

The following outline is provided as an overview of and introduction to Oceanography.

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.

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.

Wave setup

In fluid dynamics, wave setup is the increase in mean water level due to the presence of breaking waves. Similarly, wave setdown is a wave-induced decrease of the mean water level before the waves break (during the shoaling process). For short, the whole phenomenon is often denoted as wave setup, including both increase and decrease of mean elevation. This setup is primarily present in and near the coastal surf zone. Besides a spatial variation in the (mean) wave setup, also a variation in time may be present – known as surf beat – causing infragravity wave radiation.

Wave setup can be mathematically modeled by considering the variation in radiation stress (Longuet-Higgins & Stewart 1962). Radiation stress is the tensor of excess horizontal-momentum fluxes due to the presence of the waves.

Ocean zones
Sea level

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.