Journal of Geophysical Research: Oceans

Observed surface oceanic and atmospheric variability in the tropical Pacific at seasonal and ENSO timescales: A tentative overview


  • Thierry Delcroix


Seasonal and El Niño-Southern Oscillation (ENSO)-related variations of sea surface temperature (SST) and salinity (SSS), 0/450-dbar dynamic height anomalies (η, an alias for sea level), zonal (τx) and meridional (τy) wind stress, wind stress curl (curl (τ)), and precipitation (P) are examined in the tropical Pacific during 1961–1995. In the equatorial band the El Niño (La Niña) events are chiefly concerned (1) in the east and center, with warmer (colder) than average SST and a η increase (decrease), and (2) in the west, with fresher (saltier) than average SSS, westerly (easterly) wind anomalies, above (below) average P limited to the east of about 150°E, and a η decrease (increase); Much smaller ENSO changes occur away from the equatorial band except in the convergence zones for SSS, P, arid τy changes and in two patches centered around 7°N and 7°S in the west for curl (τ). The ENSO-related η changes are schematically concerned with a zonal “seesaw” in phase with the Southern Oscillation Index (SOI) in the equatorial band and a meridional seesaw between the regions situated north and south of about 5°N, which lags by about 1 year behind the SOI. The double seesaws result in a longitudinal mean η rise (drop) within about 5°N–20°S up to the mature phase of El Niño (La Niña), and not just until its beginning, partly compensated by a longitudinal mean η drop (rise) within about 5°–20°N. Aside from its intrinsic substance, this paper offers a novel and concise observational basis for testing theoretical studies and model simulations.