Observations of the Equatorial Intermediate Current in the Western Pacific Ocean (165°E)

Abstract

Direct current measurements (0–600 m; re. 600 m) were carried out every six months from January 1984 to June 1986 in the western tropical Pacific Ocean (165°E) from 20°S to 10°N. The Equatorial Intermediate Current (EIC) occurred beneath the Equatorial Undercurrent (EUC) in the 300–500 m depth range between 20°S and 2°N. At 165°E, the mean (i.e., the average of six cruiser) EIC flow has a characteristic reversed-U shape centered at the equator. Its associated hydrological features are (i) the EIC transport water of salinity 34.6–34.9%; (ii) its upper and lower limits correspond to the 26.4 and 27.0 sigma-t surfaces; and (ifi) its velocity core is located in the 1 1 “-140C water. The average transport of the EIC is −7.0 ± 4.8 (10⁶ m³ s⁻¹ i.e., 35% of the mean EUC transport computed for the same cruises. Individual cruises exhibit little variability in the vertical (250–500 m) and meridional (2°S–2°N) EIC structure: The EIC velocity core during these cruises is thinnest at the equator and ranges in magnitude from −5 to −20 cm s⁻¹. A notable exception is the 3–8 July 1985 EIC measurements, which show a disappearance of the EIC velocity core at the equator (U = +20 cm s⁻¹). Our EIC observations show good agreement with EIC simulated from models forced by easterly winds.