Importance of the vertical mixing process in the development of El Niño Modoki

The El Niño/Southern Oscillation (ENSO) stands out as the most prominent interannual climate mode, profoundly affecting global climate. This phenomenon exhibits remarkable diversity and is commonly classified into two groups based on the location of maximum sea surface temperature anomalies. One of the two flavors with the maximum anomalous warming in the central equatorial Pacific is called El Niño Modoki. It has been suggested that anomalous zonal advection primarily contributes to the development of the positive sea surface temperature anomalies. Using outputs from a realistic ocean model simulation, here I show for the first time that anomalous vertical mixing makes a dominant or comparable contribution to the anomalous zonal advection during the development of El Niño Modoki in four out of six simulated events. The present finding provides a significant advancement in the understanding of El Niño Modoki, potentially contributing to more reliable future projections of ENSO.