A SIMPLE-MODEL FOR THE PACIFIC COLD-TONGUE AND ENSO

A conceptual model is constructed based upon the Bjerknes hypothesis o f tropical atmosphere-ocean interaction. It is shown that strong feedb acks among the trade winds, equatorial zonal sea surface temperature c ontrast, and upper-ocean heat content occur in the tropical Pacific ba sin. Coupled atmosphere-ocean dynamics produce both the strong Pacific cold-tongue climate state and the El Nino-Southern Oscillation (ENSO) phenomenon. The cold-tongue climate state is unstable and gives rise to the self-sustained ENSO, which can be understood as an equatorial o cean recharge oscillator The small basin size and the influence of a w ind system resulting from heating sources of its adjacent landmasses a re responsible for a weak and stable Atlantic cold-tongue state that c annot support ENSO-like interannual variability. The presence of weste rly wind associated with the Walker circulation ascending at the weste rn Pacific warm pool disables the dynamical coupling processes in the equatorial Indian Ocean. As a result, the equatorial Indian Ocean main tains a stable warm climate state. The conceptual coupled model reprod uces the basic features of the climate states of the tropical Pacific, Atlantic, and Indian Ocean basins and the dominant interannual climat e variability of the tropical climate system.