Western boundary currents

The past decade has seen considerable progress toward clarifying the mean circulation of the World's oceans. At the same time we have come to realize that the specification of a mean circulation is difficult as there is energy at all time scales which are quantifiable and the spectrum is usually red. The western boundary currents (WBCs) of the oceans are the principal conduits for communication between the equatorial regions, where heat is added to the oceans and the polar regions where it is removed. Understanding how these current systems work is fundamental to understanding the earth's global climate engine. Several substantial observational programs focussed on WBCs have been undertaken in recent years especially within the North and South Atlantic. These include studies of the Brazil‐Malvinas Confluence and the South Atlantic Ventilation Experiment (SAVE) within the South Atlantic, the Western Tropical Atlantic Experiment (WESTRAX) in the tropics, and the Subtropical Atlantic Climate Study (STACS) and Synoptic Ocean Prediction experiment (SYNOP) in the subtropics. We shall concentrate in this review with a summary of the results from these programs but will also briefly cover new findings from other parts of the globe. Efforts connected with programs of the World Ocean Circulation Experiment in the Pacific and the South Atlantic (particularly the Deep Basin Experiment) are still underway and can be expected to make substantial contributions to the knowledge of WBCs in the future. The nature of this review also compells us to emphasize recent U.S. research but we will incorporate results from the international community, as well, especially in regions of the globe where the U.S. has done little. The reader may also wish to consult recent reviews by Ierley 1990 and Huang 1991, which discuss many issues relevant to WBCs in subtropical gyres.