Roles of the Indo-Pacific subsurface Kelvin waves and volume transport in prolonging the triple-dip 2020-2023 La Niña

The rare triple-dip 2020-2023 La Nina event has resulted in a series of extreme climate events across the globe. Here, we reveal the role of tropical Indo-Pacific oceanic interactions in driving the first triple-dip La Nina of the twenty-first century. Specifically, we found that the eastern Indian Ocean subsurface warming anomalies were associated with the re-intensification of the subsequent La Nina event. The subsurface warming anomaly signals were propagated eastward by equatorial and coastal subsurface Kelvin waves from the eastern Indian Ocean to the western Pacific Ocean through the Indo-Pacific oceanic pathway, which contributes to the accumulation of heat content and deepens the thermocline in the western tropical Pacific. The westward Indonesian Throughflow (ITF) transported more heat during multi-year La Nina events from the western Pacific Ocean to the eastern Indian Ocean than during single-year events, resulting in the injection of more warm water into the eastern Indian Ocean. The combination of subsurface Kelvin wave propagation and increased ITF volume transport in the Indo-Pacific region acted to prolong the heat content in the western Pacific during the decay phase of La Nina, ultimately leading to the rare triple-dip 2020-2023 La Nina event.

Automated summary

This study reveals the role of tropical Indo-Pacific oceanic interactions in driving the first triple-dip La Nina event of the twenty-first century. The subsurface warming anomalies in the eastern Indian Ocean were associated with the re-intensification of the subsequent La Nina event. These anomalies were propagated eastward by equatorial and coastal subsurface Kelvin waves and contributed to the accumulation of heat content in the western Pacific Ocean. The westward Indonesian Throughflow transported more heat during multi-year La Nina events, resulting in the injection of warm water into the eastern Indian Ocean and prolonging the heat content in the western Pacific during the decay phase of La Nina.