SATELLITE ALTIMETRY, THE MARINE GEOID, AND THE OCEANIC GENERAL CIRCULATION

For technical reasons, the general circulation of the ocean has historically been treated as a steady, laminar flow field. The recent availability of extremely high-accuracy and high-precision satellite altimetry has provided a graphic demonstration that the ocean is actually a rapidly time-evolving turbulent flow field. To render the observations quantitatively useful for oceanographic purposes has required order of magnitude improvements in a number of fields, including orbit dynamics, gravity field estimation, and atmospheric variability. With five years of very high-quality data now available, the nature of oceanic variability on all space and time scales is emerging, including new findings about such diverse and important phenomena as mixing coefficients, the frequency/wavenumber spectrum, and turbulent cascades. Because the surface elevation is both a cause and consequence of motions deep within the water column, oceanographers soon will be able to provide general circulation numerical models tested against and then combined with the altimeter data. These will be complete three-dimensional time-evolving estimates of the ocean circulation, permitting greatly improved estimates of oceanic heat, carbon, and other property fluxes.