Significant wave height

Significant wave height

In physical oceanography, significant wave height, also known as SWH, or "H""s", is the average wave height (trough to crest) of the one-third largest waves. A well developed significant wave is approximately equal to "H""m0", defined as four times the standard deviation of the instantaneous displacement from the mean sea level. The American Meteorological Society "defines" SWH as "H""m0" [cite web | url = http://amsglossary.allenpress.com/glossary/search?p=1&query=significant+wave+height&submit=Search | title = Significant wave height | work = Glossary of Meteorology | accessdate = 2007-06-30 ] .

The original definition resulted from work by the oceanographer Walter Munk during World War II. [cite book | last = Denny | first = M.W. | year = 1988 | title = Biology and the Mechanics of Wave-swept Shores | publisher = Princeton University Press | location = Princeton, New Jersey | isbn = 0691084874 ] [cite book | last = Munk | first = W.H. | year = 1944 | title = Proposed uniform procedure for observing waves and interpreting instrument records | publisher = Wave Project at the Scripps Institute of Oceanography | location = La Jolla, California ] The significant wave height was intended to mathematically express the height estimated by a "trained observer". It is commonly used as a measure of the height of ocean waves.

A related notation, "H""n", where "n" is a percentage or a fraction, describes the wave height of the "n"th percent highest waves. [cite book | last = Sorenson | first = Robert M. | year = 1993 | title = Basic Wave Mechanics: For Coastal and Ocean Engineers | publisher = John Wiley & Sons | location = New York, NY | isbn = 0471551651 ] "H""n" is used to estimate the average maximum wave size ("H""0.99") and for certain other analysis. To eliminate any confusion with this "H""n" notation, the notation "H""1/3" is used by the IMO, the U.S. Code of Federal Regulations, most classification societies, as well as many scientific papers. "H""s" is a special case of H"n".

Other statistical measures of the wave height are also widely used. The RMS wave height, which is defined as square root of the average of the squares of all wave heights, is approximately equal to "H""s" divided by 1.4.

For example, according to the Irish Marine Institute: [cite web | url = http://www.marine.ie/home/aboutus/newsroom/news/ResultsofWeatherBuoyReadings.htm | title=Report on Weather Buoy Readings During December Storm — 6th to 11th December | publisher = Irish Marine Institute | accessdate = 2008-01-13 ] :"… at midnight on 9/12/2007 a record significant wave height was recorded of 17.2m at with a period of 14 seconds."

See also

* Sea state
* Rogue wave: A wave of over twice the significant wave height

References and notes

External links

[http://www.fimr.fi/en/palvelut/aallokko-ja-vedenkorkeus/merkitseva-aallonkorkeus.html Finnish Institute of Marine Research: Significant wave height]


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