General Considerations and a Laboratory Example

Introduction

Both the atmosphere and ocean are rotating and stratified, and for large-scale motions (an attribute that needs careful definition), both are important in shaping the dynamics. Both the mean circulation, whose scales usually reflect the forcing, and the inevitable eddy fields that result from the instability of those motions are determined by the effects of rotation and stratification. In this chapter, I am going to examine some particular aspects of the buoyancy-driven motion of a rotating stratified fluid with an eye to oceanic phenomena, in particular the important question of the relationship between the vertical motion and the surface buoyancy forcing. This question is of particular importance in the discussion of the oceans' role in climate since a key issue in delineating that role is how and where the sinking of surface-cooled water takes place. It should not be surprising that the presence of rotation and, in particular, the variation of the local normal component of that rotation (the beta-effect) renders the association of forcing and sinking sometimes nonintuitive. In sections 2.2 and 2.3, we will examine the nature of the circulation in simple models with an eye to uncovering in easily understandable circumstances the underlying physics that determines the structure of the vertical motion. Of course, the nature of the horizontal motion is coupled to the vertical motion and will be discussed as well.