On the spatial double peak of the 2023–2024 El Niño event

The 2023–2024 El Niño has raised widespread concern in scientific and public communities. Here, using latest observational reanalysis, we show that this event matured with two distinct spatial peaks of sea surface temperature anomaly in the equatorial central and eastern Pacific, respectively. Like other double-peaked El Niños, the central Pacific sea surface temperature peaked in winter due to zonal advective and thermocline feedbacks. However, the eastern counterpart matured asynchronously in autumn and then stopped growing. This peculiar behavior results primarily from a cooling zonal advection by the anomalous westward current in the eastern Pacific during the autumn of 2023, which is associated with the local wind-driven sea surface height meridional concavity. We further propose that the relatively stronger and more eastward-displaced autumn precipitation in the Pacific intertropical convergence zone in 2023, compared to other double-peaked El Niños, is the primary cause of this distinct wind and sea surface height pattern.