Direct measurements of upper ocean currents and water properties across the tropical Pacific during the 1990s

Abstract

Meridional sections of upper ocean zonal currents, potential temperature, and salinity are estimated at ten longitudes from 143°E to 95°W using Conductivity–Temperature–Depth and Acoustic Doppler Current Profiler data from 172 synoptic sections taken in the tropical Pacific between 138°E and 86°W, mostly in the 1990s. Data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline, a mixed layer, water property extrema, and velocity extrema. Mean zonal currents, potential temperatures, and salinities are produced at each longitude. The seasonal cycles of these fields are also estimated, as well as a simple El Niño Southern Oscillation (ENSO) cycle. Zonal sections along the equator are also presented. Properties of the near-equatorial zonal currents, including transports, temperatures, and salinities, are estimated separately from the synoptic sections. The seasonal cycles of these quantities and their correlations with the Southern Oscillation Index are investigated. The work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data, allowing trans-Pacific estimates of near-equatorial current transports and properties, including those of the northern branch of the South Equatorial Current, the New Guinea Coastal Undercurrent, and the Equatorial Undercurrent.