  We apply a test for low-dimensional, deterministic dynamics to the Nino 3
time series for the El Nino Southern Oscillation (ENSO). The test is negative,
indicating that the dynamics is high-dimensional/stochastic. However,
application of stochastic forcing to a time-delay equation for equatorial-wave
dynamics can reproduce this stochastic dynamics and other important aspects of
ENSO. Without such stochastic forcing this model yields low-dimensional,
deterministic dynamics, hence these results emphasize the importance of the
stochastic nature of the atmosphere-ocean interaction in low-dimensional models
of ENSO.
