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 ± 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.