Amplitude vacillation in baroclinic flows

This chapter will introduce the phenomenology of vacillation in baroclinic flows based on experimental data, CFD and low-order numerical models. The processes leading to vacillation of a steady baroclinic wave will be discussed in terms of nonlinear interactions between different wave modes and between waves and the azimuthally or longitudinally averaged baroclinic flow. Complementing the review of the literature on amplitude vacillation, some new material will be presented to discuss the effect of the presence of lateral boundary layers in laboratory experiments and of the Prandtl number on feedback between the vacillating waves and the Ekman transport in the boundary layers. In the later sections, other forms of vacillation will be discussed and, finally, the role of vacillation in the transition to chaos and turbulence will be briefly addressed.