FY 2023

Resolving the tropical Pacific/Atlantic interaction conundrum

Jiang, F., W. Zhang, F.-F. Jin, M.F. Stuecker, A. Timmermann, M.J. McPhaden, and J. Boucharel

Geophys. Res. Lett., 50(13), e2023GL103777, doi: 10.1029/2023GL103777, View open access article at AGU/Wiley (external link) (2023)

Understanding the interaction between the tropical Pacific and Atlantic Oceans has challenged the climate community for decades. Typically, boreal summer Atlantic Niño events are followed by vigorous Pacific events of opposite sign around two seasons later. However, incorporating the equatorial Atlantic information to variabilities internal to the Pacific lends no significant additional predictive skill for the subsequent El Niño-Southern Oscillation (ENSO). Here we resolve this conundrum in a physically consistent frame, in which the nascent onset of a Pacific event rapidly induces an opposite-signed summer equatorial Atlantic event and the lead correlation of Atlantic over Pacific is a statistical artifact of ENSO's autocorrelation. This Pacific-to-Atlantic impact is limited to a short window around late spring due to seasonally-amplified Atlantic atmosphere-ocean coupling. This new frame reconciles the discrepancies between the observed and multi-model simulated inter-basin relationship, providing a major advance in understanding seasonally-modulated inter-basin climate connections as well as their predictability.

Plain Language Summary. Previous studies interpreted the observed lead/lag relationship between Atlantic Niño/Niña and Pacific Niño/Niña sea surface temperature anomalies as evidence for a precursory role of the equatorial Atlantic on the development of El Niño–Southern Oscillation (ENSO) events. This study clearly demonstrates that this statistical relationship is not related to Atlantic-to-Pacific causality, but can rather be explained by seasonally modulated equatorial Atlantic's response to ENSO. We find that Pacific ENSO events drive equatorial Atlantic events rather than vice versa, and reconcile the apparent discrepancies between the observed and multi-model simulated tropical Pacific/Atlantic relationship.