In
physical oceanographyPhysical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters....
,
significant wave height (
SWH), or
Hs or H
sig, is the average
wave heightIn fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighbouring trough. Wave height is a term used by mariners, as well as in coastal, ocean engineering and naval engineering....
(trough to
crestA crest is the point on a wave with the maximum value or upward displacement within a cycle. A trough is the opposite of a crest, so the minimum or lowest point in a cycle....
) of the one-third largest
wavesIn fluid dynamics, wind waves or, more precisely, wind-generated waves are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They usually result from the wind blowing over a vast enough stretch of fluid surface. Some waves...
. A well developed significant wave is approximately equal to
Hm0, defined as four times the
standard deviationIn probability theory and statistics, the standard deviation of a statistical population, a data set, or a probability distribution is the square root of its variance. Standard deviation is a widely used measure of the variability or dispersion, being algebraically more tractable though...
of the instantaneous displacement from the mean sea level. The
American Meteorological SocietyThe American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, the American Meteorological Society has a membership...
defines SWH as H
m0
.
The original definition resulted from work by the oceanographer Walter MunkWalter Heinrich Munk is an American physical oceanographer.-Biography:Born in Vienna, Austria, Munk was sent to a preparatory school in New York State in 1932. The family selected New York because they envisioned a career in finance for Munk in a New York bank with connections to the family...
during World War II.
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In
physical oceanographyPhysical oceanography is the study of physical conditions and physical processes within the ocean, especially the motions and physical properties of ocean waters....
,
significant wave height (
SWH), or
Hs or H
sig, is the average
wave heightIn fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighbouring trough. Wave height is a term used by mariners, as well as in coastal, ocean engineering and naval engineering....
(trough to
crestA crest is the point on a wave with the maximum value or upward displacement within a cycle. A trough is the opposite of a crest, so the minimum or lowest point in a cycle....
) of the one-third largest
wavesIn fluid dynamics, wind waves or, more precisely, wind-generated waves are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They usually result from the wind blowing over a vast enough stretch of fluid surface. Some waves...
. A well developed significant wave is approximately equal to
Hm0, defined as four times the
standard deviationIn probability theory and statistics, the standard deviation of a statistical population, a data set, or a probability distribution is the square root of its variance. Standard deviation is a widely used measure of the variability or dispersion, being algebraically more tractable though...
of the instantaneous displacement from the mean sea level. The
American Meteorological SocietyThe American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, the American Meteorological Society has a membership...
defines SWH as H
m0
.
The original definition resulted from work by the oceanographer Walter MunkWalter Heinrich Munk is an American physical oceanographer.-Biography:Born in Vienna, Austria, Munk was sent to a preparatory school in New York State in 1932. The family selected New York because they envisioned a career in finance for Munk in a New York bank with connections to the family...
during World War II. 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. 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 IMOThe International Maritime Organization , formerly known as the Inter-Governmental Maritime Consultative Organization , was established in Geneva in 1948, and came into force ten years later, meeting for the first time in 1959...
, the U.S. Code of Federal RegulationsThe Code of Federal Regulations is the codification of the general and permanent rules and regulations published in the Federal Register by the executive departments and agencies of the Federal Government of the United States...
, most classification societiesA classification society is a non-governmental organization in the shipping industry, often referred to as 'Class'. It establishes and maintains standards for the construction and classification of ships and offshore structures; supervises that construction is according to these standards; and...
, as well as many scientific papers. H
s
is a special case of Hn
.
Other statistical measures of the wave height are also widely used. The RMSIn mathematics, the root mean square , also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity. It is especially useful when variates are positive and negative, e.g., sinusoids....
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:
"… 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
In oceanography, a sea state is the general condition of the free surface on a large body of water—with respect to wind waves and swell—at a certain location and moment. A sea state is characterised by statistics, including the wave height, period, and power spectrum. The sea state varies with...
- Rogue wave: a wave of over twice the significant wave height
External links
Finnish Institute of Marine Research: Significant wave height