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  • Author or Editor: L. J. Mangum x
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S. P. Hayes, J. M. Toole, and L. J. Mangum


An analysis of nine hydrographic sections collected in 1979–81 along 110°W in the equatorial Pacific Ocean is presented. Sections typically sampled the upper 500 m of the water column from 10°N to 3°S. Analysis concentrated on the repeated sections north of the equator. Examination of the variability of eastward transport indicates that the North Equatorial Countercurrent (NECC) and the Northern Subsurface Countercurrent (NSCC) cannot be distinguished solely on the basis of water-mass structure. However, using a potential density surface (σθ = 25.0) as a current boundary we find that on average the NSCC transports 13.7 × 106 m3 s−1 compared to only 8.3 × 106 m3 s−1 for the NECC. The NSCC flow is sufficiently stable so that meridional surface dynamic-height gradient remains a good index of zonal transport fluctuations. Variations in surface dynamic height observed in our data and in the EASTROPAC data indicate a seasonal cycle to the surface topography with large values for the equatorial and countercurrent depressions in boreal autumn and small values in spring. Broad meridional correlation scales for surface dynamic height were found; equatorial fluctuations were significantly positively correlated with variability at latitudes out to 5°N and significantly negatively correlated with variability at 9–10°N. The meridional and vertical structures or vertical displacement were reduced to two empirical orthogonal function (EOF) modes which contained 78% of the variance. These modes did not suggest simple dynamical interpretation in terms of first-vertical-mode linear waves.

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M. J. McPhaden, S. P. Hayus, L. J. Mangum, and J. M. Toole


We describe variability in the western Pacific Ocean during the 1986–87 El Niño/Southern Oscillation (ENSO) event, with emphasis on time series measurements of currents, temperature, sea level and winds near the equator at 165°E. Zonal winds were anomalously westerly from mid-1986 to late 1987 and were punctuated by 2–10 m s−1 episodes of westerlies lasting about 10 days to 2 months. Zonal current in the upper 100-m surface layer responded to these wind variations typically within a week, in some cases with speeds exceeding 100 cm s−1 to the east. Zonal current variations in the thermocline below 100 m were generally less coherent with the local wires than currents near the surface. They were also generally less variable, although the Equation Undercurrent disappeared for 3–4 weeks in October-November 1987 at a time when the normal eastward directed zonal pressure gradient force reversed along the equator. Periods of intense and prolonged eastward flow in the surface layer were associated with a decrease in sea level by 10–20 cm at the end of 1986 and in May-August, 1987. Similarly, significant westward flow near the surface and in the thermocline in September-November 1987 was accompanied by rising sea level and a westward migration from the date line of surface waters >30°C. These results suggest that wind-driven zonal currents at the equator were important in the evolution of the mass and heat balance of the western Pacific during the 1986–87 ENSO, Conversely, meridional wind stress and meridional velocity energy levels at periods longer than 100 days on the equator were 5–10 times weaker than in the zonal direction and less obviously related to the evolution of the 1986–87 ENSO.

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