Velocity Observations in the Equatorial Thermocline During Gate

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Velocity time series measured during GATE below the Equatorial Undercurrent are presented. The mean circulation at the equator was zonal over the two month sampling duration with slowly varying relative maxima below the Undercurrent core. A mean convergence upon the equator was observed at 1.5°N and 1.5 S. Large departures from the mean circulation occurred with polarizations and symmetries consistent with equatorially trapped wave kinematics. The most energetic oscillations had time scales around 36 days; the most orderly oscillations had time scales around 9 days; and the zonally most coherent oscillations were in the range of 3-5 days. Phase propagation was generally upward and westward with no clear evidence for vertical baroclinic modes. Dynamical consistencies are shown between the 9-day oscillations and the gravest symmetric meridional mode (n=2) inertia-gravity wave. We conclude that vertically propagating equatorially trapped waves exist in the Atlantic. They are energetic and may be related to the mean circulation.

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Velocity Observations in the Equatorial Thermocline During Gate, in G. Siedler, J. D. Woods & W. Düing (Eds.), Oceanography and Surface Layer Meteorology in the B/C Scale, GATE-2, Elsevier, p. 217-248