Geophysical fluid dynamics

Abstract

Geophysical fluid dynamics deals with flows of air and water in the atmosphere and ocean. Here fluid velocities are subsonic, the medium is stratified, and the rotation rate of the earth is important. The latter two phenomena suppress vertical motions so horizontal velocities predominate, especially at large scales, even when the flow is turbulent. In fact, the length scales of the motion are often so large that the advective acceleration is small compared to the Coriolis acceleration (small Rossby number), and the fluid's horizontal velocity is perpendicular (not parallel) to the horizontal pressure gradient. Near surfaces where friction is important, the direction of the flow in a boundary layer depends on the distance from the surface. Coriolis effects also cause surface-wave motions to include particle deflections in both horizontal directions, and for surface waves to be trapped near vertical boundaries. Coriolis effects modify internal waves, too. At even larger scales where the curvature of the earth leads to nontrivial variations in the Coriolis frequency, Rossby waves spanning a significant range of latitude may be subject to barotropic and/or baroclinic instabilities.