The main focus of this book is the study of large-scale circulation in the world's oceans. As a dynamical system, the circulation in the world's oceans is controlled by the combined effects of external forcing, including wind stress, heat flux through the sea surface and seafloor, surface freshwater flux, tidal force, and gravitational force. In addition, the Coriolis force should be included, because all our theories and models are formulated in a rotating framework. In this chapter, I first describe surface forcing and the distribution of physical properties. I then discuss the classification of different kinds of motion in the world's oceans, and briefly review the historical development of theories of oceanic general circulation.
Surface forcing for the world's oceans
The ocean is forced from the upper surface, including wind stress, and heat and freshwater fluxes. In addition, tidal forces affect the whole depth of the water column, and geothermal heat flux and bottom friction also contribute to the establishment and regulation of the motions in the ocean. However, the surface forces are the primary forces for the oceanic circulation, and these are the focus of this section.
Surface wind forcing
Wind stress is probably the most crucial force acting on the upper surface of the world's oceans. The common practice in physical oceanography is to treat the effect of wind as a surface stress imposed on the upper surface of the ocean.