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

Seasonal and El Nino-Southern Oscillation (ENSO)-related variations of sea surface temperature (SST) and salinity (SSS), 0/450-dbar dynamic height, anomalies (eta, an alias for sea level), zonal (tau(x)) and meridional(tau(y)) wind stress, wind stress curl (curl (tau)), and precipitation (P) are examined in the tropical Pacific during 1961-1995. In the equatorial band the El Nino (La Nina) events are chiefly concerned (1) in the east and center, with warmer (colder) than average SST and a eta 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 degrees E; and a eta decrease (increase). Much smaller ENSO changes occur away from the equatorial band except in the convergence zones for SSS; P, and tau(y) changes and in two patches centered around 7 degrees N and 7 degrees S in the west for curl (tau). The ENSO-related eta 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 degrees N, which lags by about 1 year behind the SOI. The double seesaws result in a longitudinal mean eta rise (drop) within about 5 degrees N-20 degrees S up to the mature phase of El Nino (La Nina), and not just until its beginning, partly compensated by a longitudinal mean eta drop (rise) within about 5 degrees-20 degrees N. Aside from its intrinsic substance, this paper offers a novel and concise observational basis for testing theoretical studies and model simulations.