Temporal Changes in Ocean Eddy Transports
Detlef Stammer(1) , Carl Wunsch(2) , and Kyozo Ueyoshi(3)
University of Hamburg,
(2) Department of Earth, Atmospheric and Planetary Sci, Massachusetts Institute of Technology, 02139, United States
(3) Physical Oceanography Research Division, Scripps Institution of Oceanography, 92093, United States
New estimates from 11-years of altimetric data are made of the global
time-average variability kinetic energy and its decadal-scale variability. Making the approximation that the variability reflects primarily eddy motions, a time-mean, but spatially varying, eddy mixing coefficient is then estimated along with its changes over the last decade. With a record length more than twice as long as previously available, the time-mean variability kinetic energy, K_E, is statistically more reliable and smoother in its spatial pattern. Minimum values of K_E are present in the subpolar North Pacific and in the eastern South Pacific (both less than 100cm^2/s^2). In contrast to the North Pacific, the subpolar North Atlantic shows relatively enhanced K_E. Eddy kinetic energy and eddy mixing appears to have declined during the last decade over large parts of the western Pacific Ocean, in some regions by as much as 50% of the time-mean value. Increased eddy variability can be found in the Kuroshio and Gulf Stream regions, as well as in the Agulhas region, east of Australia, and at several locations along the Antarctic Circumpolar Current. Somewhat enhanced eddy variability and eddy mixing are also apparent in the eastern tropical Pacific. A numerical simulation of the ocean circulation at 1 degree spatial resolution over a 10 year period suggests that variations in eddy mixing of this order of magnitude measurably affect the deep temperature field in the vicinity of permanent frontal structures on a timescale of less than 4 years. The meridional overturning circulation also reacts on these time scales. If persistent over longer periods in the ocean, these effects would be important for climate simulations.