Optimal growth of Central and East Pacific ENSO events

This is the authors' abstract. We don't add key points for this paper.

Central Pacific (CP)-type and Eastern Pacific (EP)-type El Niño and the Southern Oscillation (ENSO) events are investigated using linear inverse modeling. Optimal initial conditions and growth rates for CP or EP ENSO events are identified explicitly using a CP or EP ENSO norm. The dominant difference in initial conditions that lead to CP and EP ENSO events is the role of the second empirical orthogonal function of tropical sea surface temperature, which represents the Pacific Meridional Mode (PMM). Optimal initial conditions for CP-type ENSO events include warm SST anomalies in the central subtropical Pacific (a characteristic of the PMM) while optimal initial conditions for EP-type ENSO events are focused in the eastern equatorial Pacific and Southern Hemisphere subtropics along about 25°S. Thermocline anomalies differ in initial structures and in their influence on SST for CP and EP events. Results point to different roles of the PMM and thermocline variations in the evolution of CP and EP ENSO events.