  The Southern Oscillation (ENSO) is modelled with the help of a simple model
representing a classical damped oscillator forced by external forcing. Eastern
Pacific sea surface temperature (SST) and the mean equatorial Pacific
thermocline depth correspond to the roles of momentum and position. The
external forcing of the system is supplied by short-period meridional mass
fluctuations in the Pacific sector of the Southern Ocean due to the joint
effect of the atmospheric variability over the Antarctic Circumpolar Current
(ACC), bottom topography and coastlines, and also by the variability of
westerly winds in the tropics. Under such conditions the ENSO-like oscillations
arise as a result of propagation of signals due to both initial signals
appeared in the Southern Ocean and the tropical westerly wind anomaly, that
propagate then across the equatorial Pacific by means of fast wave processes.
The external forcings are the main factor in establishing the oscillation
pattern.
