The contribution of eddies to striations in absolute dynamic topography

Abstract

Distinct 4 year averages of absolute dynamic topography reveal striations in all ocean basins during 1993–2008. Striations are alternating mesoscale jet-like structures observed in time-averaged zonal geostrophic velocity, u¯. They are characterized by speeds O(1?cm?s–1) and are nominally separated by 200?km in the meridional direction. Similar patterns have been observed in sea level anomaly, mean dynamic topography, and Argo float measurements. Use of a tracked-eddy database in concert with a contour identification and eddy removal algorithm demonstrates that eddies are a dominant source of striations in u¯ in the South Pacific (20°S–50°S, 200°E–280°E). Eddies with lifetimes ? 4?weeks account for 46–57% of the variance in u¯ and correlation coefficients between total and eddy-only u¯ are 0.90–0.93. Attention is given to the ability of the algorithm to correctly identify eddies and suggests that a more appropriate bound on the variance due to eddies is ? 30–70%. This permits the existence of latent zonal jets and/or ?-plumes. Additional findings of the study include (1) a large number of eddies having a broad range of amplitudes and scales contribute most to the eddy-induced patterns and (2) the standard deviation of u¯ does not decay inversely with averaging period as proposed by a model of random eddies.

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