Sea surface height
Encyclopedia
Sea surface height is the height
(or topography
or relief
) of the ocean
's surface. On a daily basis, SSH is most obviously affected by the tidal force
s of the Moon
and the Sun
acting on the Earth
. Over longer timescales, SSH is influenced by ocean circulation. Typically, SSH anomalies resulting from these forces differ from the mean by less than ±1 m (3 ft) at the global scale. The slowest and largest variations are due to changes in the Earth
's gravitational field
(geoid
) due to the rearrangement of continents, formation of sea mounts and other redistribution of rock.
Since the Earth's gravitational field is relatively stable on decadal to centennial timescales, ocean circulation plays a more significant role in the observed variation of SSH. Across the seasonal cycle
changes in patterns of warming, cooling and surface wind
forcing affect circulation and influence SSH. Variations in SSH can be measured by satellite
altimetry
(e.g. TOPEX/Poseidon
) and used to calculate determine sea level rise and properties such as ocean heat storage.
Height
Height is the measurement of vertical distance, but has two meanings in common use. It can either indicate how "tall" something is, or how "high up" it is. For example "The height of the building is 50 m" or "The height of the airplane is 10,000 m"...
(or topography
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
or relief
Terrain
Terrain, or land relief, is the vertical and horizontal dimension of land surface. When relief is described underwater, the term bathymetry is used...
) of the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
's surface. On a daily basis, SSH is most obviously affected by the tidal force
Tidal force
The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force per unit mass exerted on one body by a second body is not constant across its diameter, the side nearest to the second being more attracted by it than the side...
s of the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
and the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
acting on the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Over longer timescales, SSH is influenced by ocean circulation. Typically, SSH anomalies resulting from these forces differ from the mean by less than ±1 m (3 ft) at the global scale. The slowest and largest variations are due to changes in the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
's gravitational field
Gravitational field
The gravitational field is a model used in physics to explain the existence of gravity. In its original concept, gravity was a force between point masses...
(geoid
Geoid
The geoid is that equipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest , and extended through the continents . According to C.F...
) due to the rearrangement of continents, formation of sea mounts and other redistribution of rock.
Since the Earth's gravitational field is relatively stable on decadal to centennial timescales, ocean circulation plays a more significant role in the observed variation of SSH. Across the seasonal cycle
Season
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...
changes in patterns of warming, cooling and surface wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
forcing affect circulation and influence SSH. Variations in SSH can be measured by satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
altimetry
Altimeter
An altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.-Pressure altimeter:...
(e.g. TOPEX/Poseidon
TOPEX/Poseidon
Launched in 1992, TOPEX/Poseidon was a joint satellite mission between NASA, the U.S. space agency, and CNES, the French space agency, to map ocean surface topography. The first major oceanographic research vessel to sail into space, TOPEX/Poseidon helped revolutionize oceanography by proving the...
) and used to calculate determine sea level rise and properties such as ocean heat storage.