Progress in geophysical fluid dynamics

Abstract

Geophysical fluid dynamics deals with the motions and physics of the atmosphere, oceans and interior of the earth and other planets: the winds, the swirls, the currents that occur on myriads of scales from millimeter to climatological. Explanations of natural phenomena, basic processes and abstractions are sought. The rotation of the earth, the buoyancy of its fluids and the tendency towards large-scale turbulence characterize these flows. But geophysical fluid dynamics is importantly a part of modern fluid dynamics which is contributing to the development of nonlinear mechanics generally. Some general insights are emerging for nonlinear systems which must be regarded as partly deterministic and partly random or which are complex and aperiodic. Contributions from geophysical fluid dynamics come from its methodology, from the experience of examples, and from the perspective provided by its unique scale. Contributions have been made to turbulent, chaotic and coherently structured nonlinear process research. Turbulent vortices larger than man himself naturally invite detailed investigation and deterministic physical studies. Examples are storms in the atmosphere and large ring vortices spun off by the Gulf Stream current in mid-ocean. The statistics of these events determine critical aspects of the general circulations. Fluid dynamicists generally now know that it is often relevant or necessary to study local dynamical processes of typical eddies even though only the average properties of the flow are of interest; progress in understanding the turbulent boundary layer in pipes involves the study of millimeter-scale vortices. Weather-related studies were seminal to the construction of the new scientific field of chaos. Coherent vortices abound of which the Great Red Spot of Jupiter is a spectacular example. Geophysical fluid dynamicists have been among forefront researchers in exploiting the steadily increasing speed and capacity of modern computers. Supercomputers today are powerful enough to allow realistic simulations of turbulent and planetary flows. A school of scientists and philosophers regard such simulations of computational physics as representing the first major advance in scientific methodology in centuries; scientific enterprise is now tripartite, with simulation on a par with theory and experimentation. Data assimilation involves the continual blending of observational data with dynamical model output for the best overall representation of reality. The conceptual model of nature implied is novel. The named discipline of geophysical fluid dynamics is barely three decades old. Scientifically it is an interesting time in the history of human development on earth as aspects of the dynamics of our atmosphere and oceans become solved problems. Geophysical fluid dynamicists are ready to deal with interactive and whole-earth problems, and to continue to expand the horizons of their science via the opportunities provided by space exploration. Progress is occurring in understanding climate and climate change processes which involve dynamical coupling of the oceans and the atmosphere and which cause profound biological and economic effects. Applied geophysical fluid dynamics is essential for the potential success of the International Geosphere-Biosphere Program which seeks to unite earth scientists in the next decade in the pursuit of global change research dedicated to a more habitable planet. © 1989.