Publication: ENSO coupling to the equatorial Atlantic: analysis with an extended improved recharge oscillator model
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Introduction: Observational and modeling studies have examined the interactions between El Niño-Southern Oscillation (ENSO) and the equatorial Atlantic variability as incorporated into the classical charge-recharge oscillator model of ENSO. These studies included the role of the Atlantic in the predictability of ENSO but assumed stationarity in the relationships, i.e., that models’ coefficients do not change overtime. Arecentworkbytheauthors has challenged the stationarity assumption in the ENSO framework but without considering the equatorial Atlantic influence on ENSO. Methods: The present paper addresses the changing relationship between ENSO and the Atlantic El Niño using an extended version of the recharge oscillator model. The classical two-variable model of ENSO is extended by adding a linear coupling on the SST anomalies in the equatorial Atlantic. The model’s coefficients are computed for different periods. This calculation is done using two methods tofitthemodel tothe data: (1) the traditional method (ReOsc), and (2) a novel method (ReOsc+) based on fitting the Fisher’s Z transform of the auto and cross-correlation functions. Results: Weshowthat, duringthe 20th century, the characteristic dampingrate of the SST and thermocline depth anomalies in the Pacific have decreased in time by a factor of 2 and 3, respectively. Moreover, the damping time of the ENSO fluctuations has doubled from 10 to 20 months, and the oscillation period of ENSO has decreased from 60-70 months before the 1960s to 50 months afterward. These two changes have contributed to enhancing ENSO amplitude. The results also show that correlations between ENSO and the Atlantic SST strengthened after the 70s and the way in which the impact of the equatorial Atlantic is added to the internal ENSO variability. Conclusions: The remote effects of the equatorial Atlantic on ENSO must be considered in studies of ENSO dynamics and predictability during specific time-periods. Our results provide further insight into the evolution of the ENSO dynamics anditscoupling to the equatorial Atlantic, as well as an improved tool to study the coupling of climatic and ecological variables.
© 2023 Crespo-Miguel, Polo, Mechoso, Rodríguez-Fonseca and Cao-García. Weacknowledge Javier Jarillo and Lander R. Crespo for their help during the early stages of manuscript writing. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modeling, responsible for CMIP, and we thank the climate modeling groups for producing and making available their model output. This work was financially supported by 817578 TRIATLAS project of the Horizon 2020 Programme (EU) and RTI2018095802-B-I00 and PID2021-125806NB-I00 of Ministerio de Economía y Competitividad (Spain), Fondo Europeo de Desarrollo Regional (FEDER, EU), the European Union Seventh Framework Programme (EU-FP7/2007–2013) PREFACE (Grant Agreement No. 603521), the ERC STERCP project (grant 648982), the ARC Centre of Excellence in Climate Extremes (CE170100023) and the Spanish project (CGL201786415-R).