Temporal changes in eddy energy of the oceans

Insight into the sources of eddy energy in the ocean can be obtained by studying the degree and nature of its temporal changes. As a preliminary to a dynamical and modeling discussion, we provide a description of the changes in variability on the annual and interannual time scales as seen in the TOPEX/POSEIDON altimeter data and in current meter records with a focus on the North Atlantic and North Pacific Oceans. The patterns of change and corresponding ones in the wind stress are globally very variable and intricate, with few easy generalizations possible. Over most of the subtropical oceans and along major mean fronts, seasonal variations of the eddy energy are negligible. There are, however, regions that show a pronounced annual cycle in eddy energy, notably the northeastern Pacific, the northern and eastern North Atlantic, as well as the tropical oceans. In those locations a strong correlation of a time-varying altimetric eddy kinetic energy on annual and longer periods with wind stress forcing is found, and trends present in near-surface eddy kinetic energy can be related to drifts in meteorological wind stress fields (mean and storm tracks) over the four-year TOPEX/POSEIDON record. While the seasonal cycles in mooring data are found generally to agree with altimetry, the only statistically significant evidence for interannual trends in current meter data appears in the long duration eastern Atlantic site mooring near 33 degrees N, 22 degrees W. (C) 1999 Elsevier Science Ltd. All rights reserved.