Waves exist due to the presence of a restoring force. In Part III, we investigated a variety of waves that occur in the atmosphere, oceans and Earth's mantle due to the action of:

If the fluid is rotating relative to an inertial frame of reference, the Coriolis force also acts as a restoring force and, as we shall see in this part, plays a crucial role in a number of types of waves. In fact, there is a bewildering array of waves because the Coriolis force comes in two flavors: f -plane and β-plane (see § 8.1.5) and can act alone or in conjunction with other effects, such as coastlines or bottom topography. In addition, the Coriolis force can modify the forms of some non-rotating waves, in effect creating new types of waves. So how can we make sense of all these? Let's begin our survey in Chapter 15 with an analysis of three “pure” rotating waves: geostrophic (f -plane), inertial and quasi-geostrophic (β-plane) waves.

Following this introduction, we will investigate the effect of the Coriolis force on several of the waves we previously studied. Rotation affects those waves that persist for a day or more, while shorter-period (higher frequency) waves are unaffected. Those waves having compressibility, elasticity or surface tension as the restoring force have high frequency and are unaffected by rotation. However, interfacial, stratified and (occasionally) deep-water waves have sufficiently low frequencies to be affected by rotation; these modified waves are considered in Chapter 16.