This IMA Volume in Mathematics and its Applications NONLINEAR PHENOMENA IN ATMOSPHERIC AND OCEANIC SCIENCES is based on the proceedings of a workshop which was an integral part of the 1989-90 IMA program on "Dynamical Systems and their Applications". The aim of this workshop was to promote cross-fertilization of ideas between investigators who are using nonlinear dynamical systems and numerical simulations to study the earth's atmosphere and oceans. We thank George F. Carnevale, Shui-Nee Chow, Martin Golubitsky, Richard McGehee, Raymond Pierrehumbert and George R. Sell for organizing the meeting. We especially thank George F. Carnevale and Raymond Pierrehumbert for editing the proceedings. We also take this opportunity to thank those agencies whose financial support made the workshop possible: the Army Research Office, the Minnesota Supercom puter Institute, the National Science Foundation, and the Office of Naval Research. A vner Friedman Willard Miller, Jr. PREFACE When we took on this project, we did not realize we were organizing a workshop on two-dimensional fluid dynamics. The participants who were invited had been working on a broad range of mathematically challenging problems related to atmo spheric and oceanic phenomena, and they were given carte blanche to talk about their current interests. With few exceptions, the favored subject involved one or another aspect of fluid flow in two dimensions.