ENSO Regulates The Interaction Of Interannual Climate Variability Among Tropical Ocean Basin

Tropical ocean basins provide a fertile ground for a wide range of coupled atmosphere-ocean phenomena across different timescales.The most energetic and most well-known among them is the El Ni(?)o-Southern Oscillation(ENSO)in the equatorial Pacific.It has been long established that ENSO has prominent imprints on the regional climate variability and climate modes farther afield.ENSO exhibits highly complicated temporal and spatial characteristics in the rapidly changing climate,and the prediction of ENSO is faced with serious challenges.Recently,several studies have further revealed that sea surface temperature(SST)anomalies in other ocean basins may also play a role in shaping ENSO evolution and that a better understanding of inter-basin interactions can be exploited advantageously to improve seasonal-to-interannual predictions.Yet these understandings of tropical trans-basin linkages as well as the previously identified precursory role on ENSO have not translated into an enhancement of operational ENSO predictability in recent decades.The key physical processes that determine the tropical inter-basin linkages remain unclear.This paper systematically investigates the interactions of climate variabilities among tropical ocean basins on interannual timescales.The main conclusions are summarized as follows:(1)ENSO and its spatiotemporal complexity characteristics have significant impacts on the tropical ocean-atmosphere system.ENSO itself exhibits highly complex spatiotemporal characteristics,including different spatial patterns and periodicity,which leads to complicated manifestations of the interaction between ENSO and the warm pool seasonal cycle.There are prominent differences in spatial pattern and periodicity between the combination mode emerging from the nonlinear interaction of the annual cycle with EP El Ni(?)o and that with CP El Ni(?)o.Besides,the combination mode associated with CP El Ni(?)o events exhibits large inter-event differences,which is mainly related to the zonal location of CP El Ni(?)o.(2)The observed character of the tropical Pacific and the North Tropical Atlantic(NTA)statistics are fully consistent with ENSO driving climate variations in the Atlantic rather than vice versa.On the one hand,local seasonal cycles of other tropical ocean basins play a key role in modulating ENSO’s teleconnection.Taking into account the modulation of the Atlantic seasonal cycle regarding its meridional migration,a robust year-round relationship can be established between ENSO and tropical Atlantic precipitation.On the other hand,based on statistical analyses of observational data,idealized pacemaker climate model experiments,and Coupled Model Intercomparison Project Phase6(CMIP6)climate model analyses,we demonstrate that the previously identified NTA precursor for ENSO based on its lead relationship over ENSO at around 8-month lead time remains spurious.The misinterpretations of causality emerge from the neglect of ENSO’s autocorrelation and the fact that the tropical climate modes as well as their atmospheric interaction are seasonally modulated.(3)ENSO pacing tightly orchestrates inter-basin tropical Pacific and Indian Ocean interactions via changes in fundamental ENSO properties.Based on observational analyses,theoretical demonstration,and CMIP6 climate model analyses,we show that ENSO periodicity and cycle regularity are the key factors that control the tropical inter-basin linkages between Pacific and Indian Ocean basins on interannual timescales.We further demonstrate that the uncertainty of the inter-basin linkages is largely a manifestation of ENSO cycle complexity.