Nonlinear Processes in Oceanic and Atmospheric Flows


Stirring in the Global Surface Ocean from Altimetry

Author: Darryn W. Waugh, Department of Earth and Planetary Science, Johns Hopkins University. USA.

Names and affiliation of other authors:

Oral or poster: Oral presentation

Global variations in lateral stirring in the surface ocean are examined by calculating finite-time Lyapunov exponents (FTLEs) from surface geostrophic currents derived from satellite-altimeter measurements. These calculations show that stirring in the surface ocean is highly non-uniform, and vary on a wide range of scales. The probability distribution functions (PDFs) of the FTLEs are broad, asymmetric, and have long high-stretch tails. The mean FTLEs and widths of the PDFs vary with the level of mesoscale activity: There are large mean values and very broad distributions in regions of high strain rates and eddy kinetic energy (EKE), e.g., western boundary currents and the Antarctic circumpolar current, and weak mean values and narrower distributions in low strain and EKE regions, e.g. eastern subtropical oceans. The FTLEs also vary at smaller (~10 km) scales, with these variations are related to the characteristics of coherent vortex structures. There are low FTLES inside vortices and filaments of high FTLEs in strain-dominated regions surrounding these vortices.

*Satellite images from NASA and ESA

Nonlinear Processes in Oceanic and Atmospheric Flows. July 2-4, 2008. Castro Urdiales, Cantabria, Spain.