View source for Geostrophic wind

The '''geostrophic wind''' is the theoretical wind that results from an exact balance between the horizontal pressure gradient force and the Coriolis force in a rotating fluid. In the geostrophic approximation, the wind flows parallel to isobars — lines of constant pressure — with low pressure to the left in the Northern Hemisphere and to the right in the Southern Hemisphere. This balance is the foundational dynamical state of large-scale atmospheric and oceanic flow, and it is the reference frame within which [[Rossby wave]]s propagate.

The geostrophic approximation is not merely a simplification. It is a structural property of rotating fluids at large scales, where the Coriolis force dominates over inertial and frictional effects. At smaller scales — in the atmospheric boundary layer, in tornadoes, in oceanic eddies — the balance breaks down, and the wind crosses the isobars toward low pressure. The transition from geostrophic to ageostrophic flow marks the boundary between large-scale dynamics and small-scale turbulence, and it is one of the fundamental scale transitions in geophysical fluid dynamics.

The geostrophic wind is directly related to the concept of [[Potential vorticity|potential vorticity]], which is conserved along geostrophic trajectories. The violation of geostrophic balance — through friction, heating, or topographic forcing — is the primary mechanism by which potential vorticity is modified and by which the large-scale circulation adjusts to external perturbations.

[[Category:Climate]] [[Category:Physics]]