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The Ningaloo Nino refers to the evident interannual variability of sea surface temperature anomalies in the southeast Indian Ocean (SEIO), which can be caused by the Pacific La Nina. Through performing atmospheric general circulation model experiments, this study shows that the Ningaloo Nino can also actively impact on the tropical Pacific. The sea surface temperature anomalies associated with the Ningaloo Nino induces negative sea level pressure anomalies extending from the SEIO to the Maritime Continent, strengthens western Pacific trade winds, and thus cools the central tropical Pacific. In turn, the central Pacific cooling anomalies generate cyclonic wind anomalies over the SEIO, and the strengthened trades enhance the Indonesian throughflow, with both enhancing the Ningaloo Nino. As such, a positive feedback loop associated with an interbasin coupling mechanism is proposed, which acts to amplify the Ningaloo Nino and its subsequent impact on the tropical Pacific.

Plain Language Summary This study investigates the impact of the Ningaloo Nino, the dominant mode of interannual sea surface temperature variability of the southeast Indian Ocean, on the tropical Pacific using atmospheric general circulation model experiment and observational data sets. It is found that positive sea surface temperature anomalies in the southeast Indian Ocean associated with Ningaloo Nino enhance Pacific trade winds, favoring equatorial Pacific cooling. In turn, negative Pacific sea surface temperature anomalies can enhance the Ningaloo Nino. An interbasin coupling mechanism is thus proposed. The interbasin coupling mechanism and the prominent impact of the Ningaloo Nino on the tropical Pacific suggest an important modulation effect of the Ningaloo Nino on El Nino-Southern Oscillation. Hence, faithfully predicting Ningaloo Nino may be important for El Nino-Southern Oscillation forecast.