Optimal precursors of different types of ENSO events

Not all El Nino-Southern Oscillation (ENSO) events are the same. Their global impacts can differ substantially depending on whether the associated sea surface temperature (SST) anomalies are stronger in the central Pacific (CP) or the eastern Pacific (EP). The predictability of such differences is therefore of interest. In this study, the optimal two-season precursors of different ENSO types are investigated in a linear inverse modeling framework using observational SST and thermocline depth data for 1958-2007. It is shown that different SST precursor types alone do not favor the generation of different ENSO types. However, initial subsurface conditions characterized by a deeper thermocline in the eastern Pacific and a shallower thermocline in the central Pacific favor the generation of EP-type events, while a shallower thermocline in the east and a deeper thermocline in the central/western Pacific are conducive to CP-type events. The predictability of different ENSO types thus depends importantly on initial subsurface conditions.