Upper ocean thermohaline fields near 2°S, 156°E, during the Tropical Ocean‐Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment, November 1992 to February 1993

Zonal and meridional Seasoar sections centered at 1°50′S, 156°06′E were repeated >30 times in three 20-day periods between November 13, 1992, and February 15, 1993. Both sections were 130 km long, and sampling depth was 0–280 m, with a vertical resolution of ∼2 dbar (2×104 Pa) and a horizontal resolution of ∼3 km. The observed fields are complex and variable and are summarized graphically in several forms. Characteristics of the near-surface layer varied with the local winds which were variable and weak ( 10 m s−1) during much of the second, and moderate and westerly (4–10 m s−1) during most of the third. Near-surface temperatures were warmest (up to 30°C) during the first period and coldest (often <29°C) during the second. Thermal stratification in the near-surface layer was strong under weak winds and weak under strong and moderate winds. Except during and after heavy rainfall, salinity stratification in the near-surface layer was generally weak. Surface salinity generally decreased toward the north. The depth of the surface isopycnal layer was often but not always limited by salinity stratification; the surface isohaline layer was shallower than the top of the thermocline throughout. Strong lateral temperature and salinity gradients occurred on a few occasions. Increased wind stress was associated with lateral homogenization as well as vertical mixing. Structure and water properties of the thermocline also varied between cruises and within each cruise. The upper thermocline was shallowest in late January after prolonged easterly winds. Isotherms in the upper and midthermocline (20°–25°C) sloped generally upward to the north, while those in the lower thermocline (12°–14°C) sloped down to envelop the core of the Equatorial Undercurrent, which shoaled (from 225 to 160 m) and warmed (from 15°to 20°C) between the first and last survey periods. Mesoscale and fine-scale water mass features were usually recognizable in sections less than a few days apart and migrated eastward at about 0.3 m s−1. There is a remarkably high degree of nonstationarity in these thermohaline fields from the Warm Pool of the western Pacific Ocean.

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