Quasi‐geostrophic flows

An exact balance between the horizontal pressure gradient term and the Coriolis term in the momentum defines a hypothetical velocity vector called the ‘geostrophic wind’. The magnitude of the ageostrophic wind is an order of magnitude smaller than the geostrophic wind. The direction of the ageostrophic wind indicates the direction in which fluid parcels are accelerating, which in turn has implications for the vertical motion field. The quasi-geostrophic equation set has been given in terms of the vorticity and thermodynamic equations. Quasi-geostrophic potential vorticity is not a straightforward approximation of Ertel's potential vorticity, but shows, they are related in certain parameter regimes.