1. The force acting on air due to pressure differences. Horizontal variations in pressure create a tendency for movement from higher to lower pressure, but as air moves it experiences the Coriolis effect (CorF), deflecting it. When the PGF and CorF are in balance above the layer affected by friction with the surface, the air flows around the centre of low pressure, parallel to the isobars, forming the geostrophic wind. Near the surface, friction slows the moving air, reducing the magnitude of the CorF, and air flows at an angle across the isobars towards the centre of low pressure.

2. The force acting on a water mass due to pressure differences over distance. Horizontal variations in pressure create a tendency for movement from higher to lower pressure areas. See also geostrophic current.