1 The force acting on air due to pressure differences. Horizontal variations in pressure create a tendency for movement from higher to lower pressure: this is only one component of the forces acting on the actual wind, though, so air does not normally flow at right angles across the isobars. Other forces are associated with the rotation of the Earth underneath the moving wind, and with a centrifugal force where the path of the wind is curved. In practice the air moves nearly along the isobars above the friction layer. See also coriolis force; and geostrophic wind.
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.
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