Sea state

Short description: The general condition of the free surface on a large body of water

NOAA ship Delaware II in foul weather on Georges Bank.

Sea State 5 and 8 range

In oceanography, 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 characterized by statistics, including the wave height, period, and spectrum. The sea state varies with time, as the wind and swell conditions change. The sea state can be assessed either by an experienced observer (like a trained mariner) or by using instruments like weather buoys, wave radar or remote sensing satellites.

In the case of buoy measurements, the statistics are determined for a time interval in which the sea state can be considered to be constant. This duration has to be much longer than the individual wave period, but shorter than the period in which the wind and swell conditions can be expected to vary significantly. Typically, records of one hundred to one thousand wave periods are used to determine the wave statistics.

The large number of variables involved in creating and describing the sea state cannot be quickly and easily summarized, so simpler scales are used to give an approximate but concise description of conditions for reporting in a ship's log or similar record.

## Contents

* 1 WMO sea state code
* 2 Sea states in marine engineering
* 3 See also
* 4 Citations
* 5 General and cited references

## WMO sea state code

Winter, North Atlantic – Water over deck and hatches, storm with huge waves (1958)

The World Meteorological Organization (WMO) sea state code largely adopts the 'wind sea' definition of the Douglas Sea Scale.

WMO Sea State Code | Wave height | Characteristics

|
|

0 | 0 metres (0 ft) | Calm (glassy)
1 | 0 to 0.1 metres (0.0 to 3.9 in) | Calm (rippled)
2 | 0.1 to 0.5 metres (3.9 in to 1 ft 7.7 in) | Smooth (wavelets)
3 | 0.5 to 1.25 metres (1 ft 8 in to 4 ft 1 in) | Slight
4 | 1.25 to 2.5 metres (4 ft 1 in to 8 ft 2 in) | Moderate
5 | 2.5 to 4 metres (8 ft 2 in to 13 ft 1 in) | Rough
6 | 4 to 6 metres (13 to 20 ft) | Very rough
7 | 6 to 9 metres (20 to 30 ft) | High
8 | 9 to 14 metres (30 to 46 ft) | Very high
9 | Over 14 metres (46 ft) | Phenomenal
Character of the sea swell  | 0\. None

|

Low | 1\. Short or average
2\. Long
Moderate | 3\. Short
4\. Average
5\. Long
High | 6\. Short
7\. Average
8\. Long
| 9\. Confused

The direction from which the swell is coming should be recorded.

## Sea states in marine engineering

In engineering applications, sea states are often characterized by the following two parameters:

* The significant wave height H1/3 — the mean wave height of the highest third of the waves.
* The mean wave period, T1.

In addition to the short-term wave statistics presented above, long-term sea state statistics are often given as a joint frequency table of the significant wave height and the mean wave period. From the long and short-term statistical distributions, it is possible to find the extreme values expected in the operating life of a ship. A ship designer can find the most extreme sea states (extreme values of H1/3 and T1) from the joint frequency table, and from the wave spectrum, the designer can find the most likely highest wave elevation in the most extreme sea states and predict the most likely highest loads on individual parts of the ship from the response amplitude operators of the ship. Surviving the once in 100 years or once in 1000 years sea state is a normal demand for design of ships and offshore structures.

## See also

* Beaufort scale
* Cross sea
* Douglas sea scale

## Citations

## General and cited references

* Bowditch, Nathaniel (1938), American Practical Navigator, H.O. publication No. 9 (revised ed.), United States Hydrographic Office, OCLC 31033357
* Faltinsen, O. M. (1990), Sea Loads on Ships and Offshore Structures, [Cambridge University Press], ISBN 0-521-45870-6

* v
* t
* e

Physical oceanography

Waves|

* Airy wave theory
* Ballantine scale
* Benjamin–Feir instability
* Boussinesq approximation
* Breaking wave
* Clapotis
* Cnoidal wave
* Cross sea
* Dispersion
* Edge wave
* Equatorial waves
* Fetch
* Gravity wave
* Green's law
* Infragravity wave
* Internal wave
* Iribarren number
* Kelvin wave
* Kinematic wave
* Longshore drift
* Luke's variational principle
* Mild-slope equation
* Radiation stress
* Rogue wave
* Rossby wave
* Rossby-gravity waves
* Sea state
* Seiche
* Significant wave height
* Soliton
* Stokes boundary layer
* Stokes drift
* Stokes wave
* Swell
* Trochoidal wave
* Tsunami
* megatsunami
* Undertow
* Ursell number
* Wave action
* Wave base
* Wave height
* Wave power
* Wave radar
* Wave setup
* Wave shoaling
* Wave turbulence
* Wave–current interaction
* Waves and shallow water
* one-dimensional Saint-Venant equations
* shallow water equations
* Wind wave
* model

Circulation|

* Atmospheric circulation
* Baroclinity
* Boundary current
* Coriolis force
* Coriolis–Stokes force
* Craik–Leibovich vortex force
* Downwelling
* Eddy
* Ekman layer
* Ekman spiral
* Ekman transport
* El Niño–Southern Oscillation
* General circulation model
* Geochemical Ocean Sections Study
* Geostrophic current
* Global Ocean Data Analysis Project
* Gulf Stream
* Halothermal circulation
* Humboldt Current
* Hydrothermal circulation
* Langmuir circulation
* Longshore drift
* Loop Current
* Modular Ocean Model
* Ocean dynamics
* Ocean gyre
* Princeton ocean model
* Rip current
* Subsurface currents
* Sverdrup balance
* Thermohaline circulation
* shutdown
* Upwelling
* Whirlpool
* World Ocean Circulation Experiment

Tides|

* Amphidromic point
* Earth tide
* Head of tide
* Internal tide
* Lunitidal interval
* Perigean spring tide
* Rip tide
* Rule of twelfths
* Slack water
* Tidal bore
* Tidal force
* Tidal power
* Tidal race
* Tidal range
* Tidal resonance
* Tide gauge
* Tideline
* Theory of tides

Landforms|

* Abyssal fan
* Abyssal plain
* Atoll
* Bathymetric chart
* Coastal geography
* Cold seep
* Continental margin
* Continental rise
* Continental shelf
* Contourite
* Guyot
* Hydrography
* Oceanic basin
* Oceanic plateau
* Oceanic trench
* Passive margin
* Seabed
* Seamount
* Submarine canyon
* Submarine volcano

Plate
tectonics|

* Convergent boundary
* Divergent boundary
* Fracture zone
* Hydrothermal vent
* Marine geology
* Mid-ocean ridge
* Mohorovičić discontinuity
* Vine–Matthews–Morley hypothesis
* Oceanic crust
* Outer trench swell
* Ridge push
* Seafloor spreading
* Slab pull
* Slab suction
* Slab window
* Subduction
* Transform fault
* Volcanic arc

Ocean zones|

* Benthic
* Deep ocean water
* Deep sea
* Littoral
* Mesopelagic
* Oceanic
* Pelagic
* Photic
* Surf
* Swash

Sea level|

* Deep-ocean Assessment and Reporting of Tsunamis
* Future sea level
* Global Sea Level Observing System
* North West Shelf Operational Oceanographic System
* Sea-level curve
* Sea level rise
* World Geodetic System

Acoustics|

* Deep scattering layer
* Hydroacoustics
* Ocean acoustic tomography
* Sofar bomb
* SOFAR channel
* Underwater acoustics

Satellites|

* Jason-1
* Jason-2 (Ocean Surface Topography Mission)
* Jason-3

Related|

* Argo
* Benthic lander
* Color of water
* DSV Alvin
* Marginal sea
* Marine energy
* Marine pollution
* Mooring
* National Oceanographic Data Center
* Ocean
* Ocean exploration
* Ocean observations
* Ocean reanalysis
* Ocean surface topography
* Ocean thermal energy conversion
* Oceanography
* Pelagic sediment
* Sea surface microlayer
* Sea surface temperature
* Seawater
* Science On a Sphere
* Thermocline
* Underwater glider
* Water column
* World Ocean Atlas

* Category
* Commons

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