  A non-autonomous stochastic dynamical model approach is developed to describe
the seasonal to interannual variability of the El Ni\~no-Southern Oscillation
(ENSO). We determine the model coefficients by systematic statistical
estimations using partial observations involving only sea surface temperature
data. Our approach reproduces the observed seasonal phase locking and its
uncertainty, as well as the highly non-Gaussian statistics of ENSO. Finally, we
recover the intermittent time series of the hidden processes, including the
thermocline depth and the wind bursts.
