Periods of linear development of the ENSO cycle and POP forecast experiments

Abstract

The results of the POP (principal oscillation pattern) analysis of the tropical Pacific wind stress data are presented. The wind stress data are smoothed and detrended in the same way as that used by Lamont's coupled ocean-atmosphere model to initialize El Nino forecasts. Thus, the present wind stress POP model serves as an indicator of prediction skill of the data alone, without the use of the coupled model. The POP results show that predictions of warm and cold events can be obtained at lead times of about two seasons, which is much shorter than the lead time of more than one year achieved by Lamont's coupled ocean-atmosphere model. It is shown that during the period of about two to three seasons before the peak of a warm/cold event, the ENSO system evolves in a linear, low-dimensional way. -from Author