Abstract: A class of large scale geophysical fluid flows are modelled by the quasi-geostrophic equation.An averaging principle for quasi-geostrophic motion under rapidly oscil-lating(non-autonomous) forcing was obtained,both on finite but large time intervals and on the entire time axis.This includes comparison estimate,stability estimate,and convergence result between quasi-geostrophic motions and its averaged motions.Furthermore,the existence of almost periodic quasi-geostrophic motions and attractor convergence were also investigated.

Key words: averaging principle, quasi-geostrophic fluid flow, almost periodic motion, stable manifold and unstable manifold, rapidly oscillating forcing