The Role of Extratropical Pacific in Crossing ENSO Spring Predictability Barrier

This paper investigates the impacts of extratropical Pacific on El Nino-Southern Oscillation (ENSO) spring predictability barrier (SPB). Using an empirical dynamical model - Linear Inverse Model (LIM), we find that the dynamics of the northern and southern extratropical Pacific can significantly and equally weaken the Eastern Pacific (EP)-ENSO SPB, while the North Pacific is more important for weakening the Central Pacific (CP)-ENSO SPB. The evolution of the extratropical optimum initial structures illustrates the different roles of the northern and southern extratropical Pacific in crossing EP and CP ENSO SPBs and demonstrates the decisive role that the South Pacific initial condition plays in ENSO diversity. Additionally, the extratropical Pacific greatly influences the forecast skill of El Nino during SPB, while tropical dynamics may be more important for crossing the SPB of La Nina.