Stirring in the global surface ocean

Abstract

Global variations of stirring in the surface ocean are quantified using finite-time Lyapunov exponents (FTLEs) calculated from currents derived from satellite altimetry. It is shown that the stirring is highly non-uniform, and the probability distribution functions (PDFs) of the FTLEs are broad, asymmetric, and have long high-stretch tails. The characteristics of the PDFs vary with mesoscale activity and integration time: There are larger values and broader PDFs in regions of high strain rates and eddy kinetic energy (EKE), e.g., western boundary currents and the Antarctic Circumpolar Current, and for shorter integration times. The PDFs have a near-universal relationship with the mean strain of a region, and are reasonably well fit by Weibull distributions. The above variations in the stirring may help our understanding of the distribution and spatial heterogeneities of biogeochemical tracers, and raise the possibility of developing a parameterization of the stirring based on the, easily-calculated, EKE. Copyright 2008 by the American Geophysical Union.