The Role of Extratropical Pacific in Crossing ENSO Spring Predictability Barrier

Abstract

This paper investigates the impacts of extratropical Pacific on El Niño‐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 Niño during SPB, while tropical dynamics may be more important for crossing the SPB of La Niña.

The Role of Tropical Atlantic in ENSO Predictability Barrier

“…Note that we only explicitly examine the impact of the tropical Atlantic in this paper, but other influences (e.g., extratropical Pacific) are not explicitly considered. Extratropical Pacific dynamics like the North and South Pacific Meridional Modes have been shown to greatly impact ENSO predictability and PB (Ren et al., 2019; Zhao et al., 2022). These influences can be expected to be implicitly included in the LIM, because the tropical Pacific region we used to construct the LIM is from 30˚S to 30˚N, and the SST PCs over this region are correlated with the extratropical Pacific PCs.…”

“…Therefore, in this study, we use the dominant PC time series of tropical Atlantic to represent the TNA mode and use the time series of PC2-PC3 to represent the EA mode. The approaches used to make predictions and to identify the "optimal" initial condition for anomaly growth using the LIM are very similar to those described in Zhao et al (2022). More details can be found in Text S4 in Supporting Information S1.…”

“…In this study, we follow Zhao et al. (2022) to investigate the roles that tropical Atlantic SST modes (TNA mode and EA mode) play in ENSO predictability and SPB.…”

“…Based on LIM, Zhao et al. (2022) explored the impact of the extratropical Pacific on ENSO predictability by decoupling the tropical Pacific and extratropical Pacific. In this study, we follow Zhao et al.…”

“…Also, since LIMs are derived from observations, they can realistically capture interactions between different components of the climate system. Based on LIM, Zhao et al (2022) explored the impact of the extratropical Pacific on ENSO predictability by decoupling the tropical Pacific and extratropical Pacific. In this study, we follow Zhao et al (2022) to investigate the roles that tropical Atlantic SST modes (TNA mode and EA mode) play in ENSO predictability and SPB.…”