FY 1986

Eastern Pacific Ocean circulation near the onset of the 1982–1983 El Niño

Mangum, L.J., S.P. Hayes, and J.M. Toole

J. Geophys. Res., 91(C7), 8428–8436, doi: 10.1029/JC091iC07p08428 (1986)

Over a 1-month period (October 5 to November 6, 1982) during the initial stages of the 1982–1983 El Niño, hydrographic and velocity profiling measurements were made in the eastern equatorial Pacific by two research vessels. Track lines approximated a square, centered near the Galápagos Islands with approximately meridional sections at 95°W and 85°W and nearly zonal sections at about 5°N and 5°S. Water mass characteristics and estimated currents on these sections are discussed. Sea surface temperature nearly everywhere was warmer than 25°C (an anomaly of 2°C to 3°C). The equatorial thermocline, represented by the 20°C isotherm, was depressed by nearly 50 m at 85°W and more than 100 m at 95°W relative to a historical mean profile. Across 95°W, estimated geostrophic (relative to 500 dbar) and directly measured near-equatorial velocity profiles indicated significant eastward surface flow. The South Equatorial Current south of the equator had disappeared. Estimated warm water transport (σ_t < 24.5 kg m^–3) indicated an influx into the region which was approximately that required to balance the observed low-frequency sea level change at the Galápagos Islands. Temperature and salinity properties as well as the transport estimates indicated that this warm water came predominantly from the west.