Figure 1. 4-6 Month mean SST anomaly forecasts for the NINO 3 region. Solid line is observed (with three month running mean), diamonds are from the control (C_ERA) initial conditions and stars are from the assimilation (A_ERA) initial conditions; (a) individual ensemble members (b) ensemble mean.
Even though data assimilation has had a significant impact on the performance of the forecasts in most of the 1990's, it had a smaller impact on the 1997/98 El Nino period. The onset of the warming was well captured by the forecasts starting on 1 Oct'96.
