What Controls the Evolution of Pacific Coastal Niño Events in the CESM Large Ensemble?

Abstract Coastal Niños, warm events in the far eastern tropical Pacific without corresponding strong anomalies in the central equatorial Pacific, strongly influence local rainfall and fisheries. However, individual events strongly differ from each other. They can develop into a basin‐wide El Niño (as in 2023) or stay confined to the South American coast (as in 2017). The large event‐to‐event variability in combination with the rarity of events in the observational record limits our understanding of Coastal Niños. The Community Earth System Model Large Ensemble Project (CESM‐LE) simulates Coastal Niños realistically, including their phase‐locking to boreal spring and variable evolution. Conditions in the subtropical Pacific, equatorial wave dynamics and western tropical Pacific wind anomalies are identified as factors important for the evolution of Coastal Niños in the CESM‐LE. Coastal Niños in turn increase the probability of a basin‐wide El Niño in the following months.