Impact of the South and North Pacific Meridional Modes on the El Niño–Southern Oscillation: Observational Analysis and Comparison

Abstract

An interannual variability mode in the southeast Pacific with a physical interpretation similar to that of the Pacific meridional mode (PMM) in the North Pacific was recently identified. Both modes have been shown to influence the subsequent development of El Niño–Southern Oscillation (ENSO) events. This study investigates the relationship between ENSO and the two PMMs using observational and reanalysis data. The results show that the South Pacific meridional mode (SPMM) mainly favors the development of sea surface temperature anomalies (SSTAs) in the eastern equatorial Pacific, whereas the North Pacific meridional mode (NPMM) mainly favors the development of SSTAs in the central equatorial Pacific. Both of the meridional modes are considered to be analogous in terms of their physical interpretation and can be important predictors of ENSO when considering different flavors of ENSO. Neither the NPMM nor the SPMM can be precluded as accurate indicators when forecasting particular flavors of ENSO.

On the Differences Between the South Pacific Meridional and Quadrupole Modes

“…Our findings are generally consistent with those from previous studies that both the SPQ and SPMM modes could affect the subsequent development of ENSO events (Ding, Li, & Tseng, ; Min et al, ; You & Furtato, ; Zhang, Clement, & Di Nezio, ). However, our results emphasize that the SPQ, as a basin‐scale SST mode over the South Pacific, is more closely linked than the SPMM to ENSO.…”

“…The SPQ shares characteristics with the SPMM, with their related SSTAs overlapping over some regions of the South Pacific. Both the SPQ and SPMM mainly favor the development of SSTAs in the eastern equatorial Pacific (i.e., the eastern Pacific‐type ENSO) (Ding, Li, & Tseng, ; Min et al, ). However, given that the SPMM and SPQ represent a subtropical and extratropical mode of South Pacific climate variability, respectively, it is likely that there are major differences between their influences on ENSO.…”

The Relationship Between South Pacific Atmospheric Internal Variability and ENSO in the North American Multimodel Ensemble Phase‐II Models

“…Overall, unlike the short duration of the SPO′ NP , the SPO′ NP −related SSTA footprint has impacts well beyond the austral winter by thermodynamic and dynamic air-sea interactions. In CESM1, although the SPO′ NP JJA -associated off-equatorial wind anomalies vanish rapidly after JJA (Figures 4b and 4c), they alter the latent heat fluxes and thus leave an underlying SSTA footprint similar to the characteristic SSTA pattern of the SPMM Min et al, 2017;YF18;Larson et al, 2018). These SSTA subsequently propagate northwestward via the wind-evaporation-SST (WES) thermodynamic feedback (Xie and Philander, 1994).…”

“…On the other hand, emerging research studies have underscored the importance of South Pacific atmospheric and oceanic anomalies in the tropical Pacific climate variability across multiple timescales (van Loon & Shea, 1985;Luo et al, 2003;Okumura, 2013;Zhang et al, 2014;Ding et al, 2015;Imada et al, 2015;Min et al, 2015Min et al, , 2017You & Furtado, 2017. While the austral summer South Pacific SLP anomalies (SLPA) play a role in the onset of ENSO events (e.g., Ding et al, 2015;Min et al, 2017;YF18), relatively few studies have quantified the impacts of South Pacific SLPA during austral winter (i.e., June-August [JJA]) when ENSO is commonly underway (Imada et al, 2015;Meehl et al, 2017;YF17;Larson et al, 2018;Thomas et al, 2018). While Jin and Kirtman (2009) argued that the austral winter SLPA dipole mode between subtropical and high-latitude South Pacific is a Rossby wave response to the developing ENSO SSTA, YF17 proposed that significant internal variability in this mode makes it a skillful predictor for the flavor of the ensuing ENSO event (i.e., EP or CP).…”

Robust opposite‐changing tendency between the thermal advection damping by mean current and thermo‐dynamical damping of ENSO Feedback in a changing climate

“…In particular, it has still not been clearly identified whether an ENSO event will be enhanced or suppressed under a future warmer climate (Christensen et al, ). Future changes in the characteristics of ENSO could be related to how the tropical climate state will modify (An and Jin, ; An and Wang, ); the external impact on the tropical climate variability by the North Pacific Meridional Mode (Vimont et al, , ; Chang et al, ; Alexander et al, ; Yu and Kim, ; Vimont et al, ), the seasonal footprinting mechanism (Vimont et al, ), the South Pacific meridional mode (Zhang et al, ; Min et al, ; You and Furtado, ), and the inter‐basin interaction (Kug et al, ; Kug and Kang, ; Santoso et al, ; Wang et al, ; An and Kim, ); and how stochastic forcing (i.e., atmospheric noise) will change (e.g., Levine et al, ). Most of these ENSO‐modifying factors obviously influence ENSO characteristics through mutating the ENSO‐associated feedback processes.…”