Oceanography studies ocean waves and currents, which affect global climate. Significant wave height (Hsig) is the average height of one third of the highest waves during a given time. Hsig is used for graphing, forecasting, and ship design. Changes in global climate have led to a revision of Hsig data.
Oceanography is the scientific study of ocean waves and currents and is linked to meteorological meteorology by the effect of the oceans on global climate. Ships and other marine interests need information about ocean currents and waves for shipping lanes and to protect ports and marinas. Scientists have developed significant wave height as a way to show consistent information for graphing and forecasting. Significant wave height (Hsig) is the average height of one third of the highest waves during a given time, usually less than 30 minutes.
The height of a wave is defined as the difference between its crest and trough. A crest is the highest point on a wave and the trough is the lowest. Marine buoys can measure these differences with instruments, and trained observers can make visual estimates. Waves vary greatly in height and direction, particularly in bays or channels where the waves move in complex ways.
Research has shown that Hsig is related to sea surface displacement, a statistical average of the vertical motion of the surface over time. Scientists can measure the displacement of the surface with lasers or floating instruments and use the data to calculate the significant wave height. The calculated values agree well with the visual determinations of trained observers.
One value used for historical records is the significant peak wave height. This value is the highest measured wave height observed or measured during hurricanes or large storms. The data can be used to compare recorded storms and compare wave heights and subsequent storm damage, particularly along coasts or bays.
Ship builders must consider Hsig when designing new vessels. In the early 21st century, no significant wave heights greater than 36 feet (11 meters) were used in ship design, and extreme waves were considered to be 2.3 times the significant wave height. Ocean data showed that significant waves of 65 feet (20 meters) and larger were possible, with extreme or rogue waves well above. As new vessels continue to be built, height data and stresses resulting from extreme waves will need to be reviewed regularly.
Changes in global climate since the 20th century have led to a revision of Hsig data and how they change over time. Ocean levels could rise if global temperatures rise, resulting in higher tides and wave heights. Some scientists have predicted increased storm intensity due to warmer sea temperatures, resulting in new peak wave data. Marine and coastal mainland interests have continued to study these effects into the 21st century, seeking to determine what effects occur on people and buildings from changing weather conditions.
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