Geopotential Height

Geopotential height is the height of a pressure surface expressed through the geopotential Phi, the work done against gravity to raise unit mass to that level, Phi = integral of g dz. Dividing Phi by a standard gravity gives geopotential height in meters, which removes the variation of g with latitude and altitude. In the ocean the dynamic height (geopotential anomaly) between two pressure surfaces, computed from the hydrostatic balance and the density profile, gives the geostrophic velocity through the thermal-wind relation. It is the classic hydrographic method for mapping currents from temperature and salinity casts.