Advances in observing and understanding the general circulation of the ocean have been made continuously through the past two centuries. A recent burst of activity in the Pacific has been due to an interest and ability to understand and model the El Niño phenomenon, primarily through the Tropical Ocean Global Atmosphere (TOGA) program, and due to the interest in larger scale phenomena such as heat transport and basics of the general circulation, through activities of the World Ocean Circulation Experiment (WOCE). These experiments have built on the extensive knowledge of the Pacific Ocean derived over the previous decades; a perusal of knowledge at this point shows it to be incomplete in both observations and theory and it is hoped that the greatly increased focus on climate issues, which very much include the ocean's general circulation and its variability, will go far to improve our understanding.
There have been equal or possibly greater advances in understanding the circulation of the Atlantic, and the observational base and theory of the circulation of the Indian and Arctic Oceans have been advanced substantially. Two other reports in this volume [ Fine, 1995; Hogg and Johns, 1995] survey general-circulation related issues in the Atlantic. A review of Indian Ocean circulation at this time would be premature given the expansion of WOCE programs to the Indian Ocean in the next year. Thus in order to limit the scope of this review, the principal focus is the Pacific Ocean, emphasizing the intermediate and deep circulation and long time scales of variability. Observations are reviewed as they relate to simple theories of the circulation.