The height of a pressure surface above mean sea level, adjusted for gravity, used to represent atmospheric circulation and temperature structure.Geopotential height is a measure of the altitude of a constant-pressure surface in the atmosphere, expressed not in ordinary meters but in units that account for the variation of gravity with altitude and latitude. In essence, it tells you how high you would have to climb to reach a given pressure level, but adjusted so that the number directly reflects the potential energy of a unit mass at that height. Meteorologists use it as a fundamental tool to map the large-scale structure of the atmosphere, because on a constant-pressure surface, the geopotential height reveals the temperature distribution and the flow patterns of winds.
The concept was formalized in the early 20th century as meteorology adopted pressure-coordinate analysis. Vilhelm Bjerknes and his school in Norway pioneered the use of pressure surfaces for weather analysis around 1910, and the geopotential height became standard with the advent of upper-air soundings in the 1930s and 1940s.
The atmosphere is thinner at higher altitudes, so pressure decreases with height. A pressure surface, such as the 500 hPa level, is an imaginary surface where the pressure is the same everywhere. Geopotential height is the height of this surface above mean sea level, but corrected for the fact that gravity is slightly weaker at the equator and at high altitudes. The correction ensures that the height is proportional to the gravitational potential energy per unit mass. In practice, warmer air columns expand, pushing pressure surfaces upward, so high geopotential heights indicate warm air, while low heights indicate cold air. The gradient of geopotential height on a pressure surface is directly related to the wind speed through the geostrophic balance, making it a key diagnostic for weather systems.
Geopotential height maps are the primary charts used in weather forecasting to identify troughs, ridges, and jet streams, and they are also used to track the polar vortex and to study climate variability such as the North Atlantic Oscillation.
On the 500 hPa map, a difference of about 60 meters in geopotential height corresponds to a temperature difference of roughly 1 degree Celsius in the layer below, a rule of thumb forecasters use daily.
