# Quasigeostrophic

From AMS Glossary

## quasigeostrophic

A system or flow that evolves slowly in time compared to the rotation period of the earth, has a length scale of the deformation radius or larger, and undergoes only limited vertical excursions.

Formally, the quasigeostrophic system of equations is derived from an expansion of terms in powers of the Rossby number, which is presumed small.