Sea-surface height (SSH) is the height (or topography or relief) of the ocean's surface. On a daily basis, SSH is most obviously affected by the tidal forces 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.
See also Eddy (fluid dynamics).